CN113381084B - Calibration circuit, battery protection chip and calibration method of calibration circuit - Google Patents

Abstract

The present application relates to a calibration circuit, a battery protection chip and a calibration method for the calibration circuit. The calibration circuit includes an adjustable resistance R _trim , a resistance voltage divider, a first routing switch, a second routing switch, an overvoltage comparator CP1 and an undervoltage comparator. The voltage comparator CP2 is provided, and the resistor voltage divider includes a resistor _RA , a resistor _RB , a resistor _RC , a resistor _RD and a resistor _RE which are connected in series in sequence. Overvoltage and overvoltage hysteresis taps are drawn out from the connection between the resistor _RA and the resistor _RB and the resistor _RB and the resistor _RC respectively and are electrically connected to the two input terminals of the first routing switch, and the output terminal of the first routing switch is electrically connected. Connect to the non-inverting input of the overvoltage comparator CP1. Undervoltage and undervoltage hysteresis taps are respectively drawn from the connection between the resistor _RC and the resistor _RD , and the resistor _RD and the resistor _RE are electrically connected to the two input terminals of the second routing switch, and the output terminal of the second routing switch. The non-inverting input terminal of the undervoltage comparator CP2 is electrically connected. Both the inverting input terminals of the overvoltage comparator CP1 and the undervoltage comparator CP2 are used to access the reference voltage. Significantly improved the overall performance of the circuit.

Description

Calibration circuit, battery protection chip and calibration method of calibration circuit

technical field

The invention belongs to the technical field of battery circuits, and particularly relates to a calibration circuit, a battery protection chip and a calibration method for the calibration circuit.

Background technique

Due to the natural characteristics of lithium batteries, they must be used with special protection chips to ensure safety, usable capacity and cycle life. Lithium battery protection chips generally provide multiple protections such as overvoltage, undervoltage, overcurrent, short circuit and overheating. Among them, the overvoltage protection has high absolute accuracy requirements. Even a deviation of +100mv is enough to shorten the battery life. , the battery overheats or even catches fire; the -100mv deviation will cause a significant loss of the battery's usable capacity.

Traditional integrated circuit technology cannot directly produce protection chips that meet the required overvoltage accuracy during mass production, and it is usually necessary to calibrate each protection chip individually. Since battery protection chips are generally cost-sensitive chips in large quantities, the time spent on calibration will directly affect the output and cost of the chip, and sometimes the calibration cost can account for a considerable proportion of the total chip cost. Therefore, a simple, fast, and effective calibration method is crucial for mass-produced battery protection chips. The traditional battery protection chip has two design schemes, such as double voltage divider and single voltage divider, which can support the calibration of the battery protection chip. However, in the process of realizing the present invention, the inventor found that the traditional battery protection chip still has the technical problem of insufficient comprehensive performance.

SUMMARY OF THE INVENTION

Based on this, it is necessary to provide a calibration circuit, a battery protection chip and a calibration method for the calibration circuit that can significantly improve the overall performance of the circuit, aiming at the technical problems existing in the above-mentioned conventional battery protection chips.

In order to achieve the above purpose, the embodiment of the present invention adopts the following technical solutions:

On the one hand, an embodiment of the present invention provides a calibration circuit, including an adjustable resistor R _trim , a resistor divider, a first routing switch, a second routing switch, an overvoltage comparator CP1 and an undervoltage comparator CP2, and the resistor The voltage divider includes a resistor _RA , a resistor _RB , a resistor _RC , a resistor _RD , and a resistor _RE in series in sequence;

One end of the adjustable resistor R _trim is used to electrically connect the positive electrode of the battery unit, the other end of the adjustable resistor _{R trim} is electrically connected to one end of the resistor RA, and the other end of the resistor _RE is used to electrically connect the negative electrode of the battery unit and the ground;

An overvoltage tap is drawn from the connection between the resistor _RA and the resistor _RB and is electrically connected to an input end of the first routing switch, and an overvoltage hysteresis tap is drawn from the connection between the resistor _RB and the resistor _RC and is electrically connected to the first selector switch. The other input end of the way switch, the output end of the first way selection switch is electrically connected to the non-inverting input end of the overvoltage comparator CP1;

The connection between the resistor R _C and the resistor R _D leads out an undervoltage tap and is electrically connected to an input end of the second routing switch, and the connection between the resistor R _D and the resistor _RE leads out an undervoltage hysteresis tap and is electrically connected to the second selector switch. The other input end of the route switch, the output end of the second route selection switch is electrically connected to the non-inverting input end of the undervoltage comparator CP2;

Both the inverting input terminals of the overvoltage comparator CP1 and the undervoltage comparator CP2 are used to access the reference voltage.

In one embodiment, the first routing switch is a two-to-one multiplexer Q ₁ , and the control signal input end of the two-to-one multiplexer Q ₁ is used to access an enable signal of overvoltage hysteresis;

The overvoltage hysteresis enable signal is used to instruct the two-to- _one multiplexer Q1 to turn on the overvoltage hysteresis tap to the overvoltage comparator CP1.

In one of the embodiments, the second routing switch is a two-to-one multiplexer Q ₂ , and the control signal input end of the two-to-one multiplexer Q ₂ is used to access an enable signal of undervoltage hysteresis;

The undervoltage hysteresis enable signal is used to instruct the two-to-one multiplexer _Q2 to turn on the undervoltage hysteresis tap to the undervoltage comparator CP2.

In one embodiment, the adjustable resistor R _trim includes 32 segment resistors connected in series.

In one embodiment, each segment resistance is a high-resistance polysilicon sheet resistance.

On the other hand, a battery protection chip is also provided, which includes a chip body and the above-mentioned calibration circuit.

In another aspect, a calibration method for a calibration circuit is also provided for calibrating the above-mentioned calibration circuit, and the above-mentioned method includes the following steps:

Determine the design parameters of the calibration circuit; design parameters include overvoltage tap divider ratio, undervoltage tap divider ratio, overvoltage hysteresis tap divider ratio, undervoltage hysteresis tap divider ratio, adjustable resistance ratio, and adjustable resistance segment number;

Measure the overvoltage protection threshold value of the calibration circuit before calibration;

Use the binary calibration code formula to calculate the calibration code according to the design parameters and the overvoltage protection threshold value; the calibration code is used to calibrate the above calibration circuit;

Using the method of fuse programming, the calibration code is written into the chip of the calibration circuit.

In one embodiment, the binary calibration code formula is:

Among them, V _{OV_target} represents the target value of the overvoltage protection threshold value after adjustment, V _{OV_raw} represents the overvoltage protection threshold value before calibration, and X _step represents the adjustment step size.

In one of the embodiments, the adjustable resistance ratio is determined by the following formula:

Among them, X _max represents the maximum resistance value of the adjustable resistor, _A represents the resistance value of the resistor RA, _B represents the resistance value of the resistor RB, V _{ref_max} represents the maximum value of the reference voltage, and V _{ref_min} represents the minimum value of the reference voltage;

The number of adjustable resistor segments is determined by the following formula:

Among them, X _step represents the adjustment step length, _A represents the resistance value of the resistor RA, V _{ref_max} represents the maximum value of the reference voltage, and P represents the adjustment precision.

In one embodiment, the valid area of the uncalibrated overvoltage protection threshold value is:

Among them, V _{ref_min} represents the minimum value of the reference voltage, A represents the resistance value of the resistor RA, _B represents the resistance value of the resistor _RB , V _{OV_raw} represents the overvoltage protection threshold value before calibration, and V _{OV_target} represents the overvoltage protection The target value after threshold adjustment.

A technical scheme in the above-mentioned technical scheme has the following advantages and beneficial effects:

The above-mentioned calibration circuit, battery protection chip and calibration method of the calibration circuit, by adopting an adjustable resistor R _trim , a resistor divider, a first routing switch, a second routing switch, an overvoltage comparator CP1 and an undervoltage comparison Compared with the traditional solution, the calibration circuit structure composed of CP2 saves a voltage divider, which saves half of the power consumption and area of the chip; it only needs to adjust an adjustable resistor R _trim to calibrate the overvoltage threshold at the same time and undervoltage threshold, the time spent in the trimming process will also be greatly reduced. In addition, the overvoltage comparator CP1 and the undervoltage comparator CP2 in this solution can use the same circuit design and can be reused; the reference voltage can also use a conventional design, it does not need to be designed to be adjustable, and the overvoltage/undervoltage The hysteresis can also be set separately without restraining each other, thereby greatly reducing the difficulty and complexity of circuit design, and achieving the purpose of significantly improving the comprehensive performance of the battery protection chip circuit.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present application or in the traditional technology, the following briefly introduces the accompanying drawings that are used in the description of the embodiments or the traditional technology. Obviously, the drawings in the following description are only the For some embodiments of the application, for those of ordinary skill in the art, other drawings can also be obtained according to these drawings without any creative effort.

1 is a schematic structural diagram of a traditional calibration circuit;

Fig. 2 is another kind of traditional calibration circuit structure schematic diagram;

3 is a schematic structural diagram of a calibration circuit in one embodiment;

4 is a schematic structural diagram of a calibration circuit in another embodiment;

5 is a simplified diagram of calculating the overvoltage divider ratio and the undervoltage divider ratio in one embodiment;

6 is a schematic diagram of the trimming principle in the present invention;

FIG. 7 is a schematic flowchart of a calibration method of a calibration circuit in one embodiment.

Detailed ways

In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are presented in the accompanying drawings. However, the application may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the technical field to which this application belongs. The terms used herein in the specification of the application are for the purpose of describing specific embodiments only, and are not intended to limit the application. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

It will be understood that the terms "first", "second", etc. used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, a first resistance may be referred to as a second resistance, and similarly, a second resistance may be referred to as a first resistance, without departing from the scope of this application. Both the first resistor and the second resistor are resistors, but they are not the same resistor. It should be noted that when an element is considered to be "connected" to another element, it may be directly connected to and integrated with the other element, or an intervening element may also be present, that is, it may also be indirectly connected to the other element .

It can be understood that the "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between them.

It can be understood that due to the different chemical compositions of battery cells and the optimization considerations and preferences of users in application, the protection threshold required by the battery protection chip is not fixed. For example, lithium manganate batteries usually require an overvoltage protection threshold of 4.2v and 2.75 Undervoltage protection threshold for v. In order to squeeze more battery capacity, the overvoltage protection will be set to 4.3v; in order to obtain a longer charging cycle life, part of the battery capacity will be sacrificed and the overvoltage value will be set to 4.1v. The lithium iron phosphate battery generally requires an overvoltage threshold of 3.8v and an undervoltage threshold of 2.0v. Although the high-end battery protection chip has built-in microcontroller MCU and memory, the user can arbitrarily change the threshold value and perform calibration by writing to the register. However, the scheme of purchasing factory-preset products in large quantities is more popular, which requires a relatively flexible architecture of the chip, and the above required settings can be completed by changing only one layer of metal to suit most batteries.

The calibration scheme needs to be matched with the corresponding circuit architecture. A more complex circuit architecture may make the calibration method simpler, more accurate and direct, but it will occupy more chip area and increase the die cost or power consumption. Using a circuit structure that is too simple, the calibration method may become complicated and time-consuming, the controllability and accuracy will become worse, and the parameters will affect and restrain each other, which increases the cost and complexity of the packaging and testing of the chip. Therefore, it is necessary to comprehensively consider the calibration. System circuit architecture and calibration methods to optimize and reduce cost.

In addition, because in applications such as electric vehicles and power tools, there may be strong interference in the voltage of the battery, and the battery protection chip generally has a hysteresis function. For example, after the overvoltage protection is triggered when the battery voltage reaches above 4.2v, the overvoltage protection will not be released when the battery voltage returns to just below 4.2v, and the overvoltage protection will not be released until the battery voltage is lower than 4.0v , the threshold difference of this 200mv (that is, 4.2v-4.0v=200mv) is called overvoltage protection hysteresis. Similarly, after the undervoltage protection is triggered when the battery voltage is lower than 2.75v, the undervoltage protection will not be released until the voltage rises above 2.95v. Solve the problem of over-voltage and under-voltage hysteresis function, by setting the two parts of the over-voltage and under-voltage circuits separately, so that they do not affect each other.

The following introduces the calibration circuit schemes of two traditional battery protection chips, and briefly analyzes the advantages and disadvantages of the two circuits:

Traditional scheme 1: As shown in Figure 1, this scheme uses two groups of voltage regulators, in which the overvoltage group consists of resistor R _trim _ _OV , resistor R _{hys_OV} , resistor R _{A_OV} and resistor R _{B_OV} in series in sequence, and the undervoltage group consists of Resistor R _{trim_UV} , resistor R _{hys_UV} , resistor R _{A_UV} and resistor R _{B_UV are} connected in series in sequence, resistor R _{trim_OV} and resistor R _{trim_UV} are adjustable resistors, resistor R _{hys_OV} , resistor R _{A_OV} , resistor R _{B_OV} , resistor R _{hys_UV} , resistor R _{A_UV} and Resistor _{RB_UV} is a fixed resistor. E ₀ represents a battery cell. Each set of voltage regulators has a tap to draw out electrical signals to the corresponding comparator CP for comparison. Both the overvoltage comparator CP1 and the undervoltage comparator CP2 use the same reference voltage V _REF . An adjustable resistor (ie, resistor R _{trim_OV} or resistor R _{trim_UV} ) is connected in series with each group to set and calibrate the overvoltage and undervoltage thresholds, respectively. It is realized by connecting or releasing a part of the resistance (ie resistance R _{hys_OV} or resistance R _{hys_UV} ). Since there are two sets of voltage regulators, this solution consumes more current and area, and needs to adjust two adjustable resistors; considering the matching characteristics of semiconductors, and the accuracy requirements of undervoltage are slightly lower than that of overvoltage, if Reasonable design, the above-mentioned separate adjustment design method is not necessary.

Conventional scheme 2: As shown in Figure 2, this scheme uses only one voltage divider (resistor _RA and resistor _RB in series), and the only tap is sent to both the overvoltage comparator CP1 and the undervoltage comparator CP2. E ₀ represents a battery cell. This scheme does not use different voltage divider ratios, but generates two different reference voltages through the reference voltage (i.e. reference voltage) generator REFS to compare the overvoltage and undervoltage respectively, and the hysteresis is also achieved by slightly changing the output of the voltage reference. . Compared with the above-mentioned traditional scheme 1, the voltage divider part can save half of the power consumption and area. However, the two comparators CP work under different common-mode voltages, and the comparators basically cannot use the same design, which will bring additional design and verification work, and the reference source that can independently output two reference voltages is designed There will be many limitations, such as the need for additional resistors and additional buffers, resulting in additional power consumption and stability problems, especially the power consumption benchmark commonly used in the prior art is not suitable for use in this solution.

Aiming at the technical problem of insufficient comprehensive performance of power consumption, area and circuit complexity in the traditional scheme, the present invention reduces power consumption and area, reduces the complexity of the circuit, simplifies the calibration process, and simultaneously has the advantages of the traditional scheme. The ability to re-customize the value of the threshold and hysteresis only by changing the position of the tap of the voltage divider, so that it can be very convenient and efficient to meet the needs and preferences of different batteries and different users. The overall performance is high.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings and specific embodiments.

As shown in FIG. 3 , in one embodiment, the present application provides a calibration circuit 100 , which includes an adjustable resistor R _trim , a resistor divider 12 , a first routing switch 14 , a second routing switch 16 , a Voltage comparator CP1 and undervoltage comparator CP2. The resistor divider includes a resistor _RA , a resistor _RB , a resistor _RC , a resistor _RD , and a resistor _RE in series in sequence. One end of the adjustable resistor R _trim is used to electrically connect the positive electrode of the battery unit _{E 0} , the other end of the adjustable resistor _{R trim} is electrically connected to one end of the resistor RA, and the other end of the resistor RE is used to electrically connect the negative electrode of the battery unit E ₀ with the ground end.

An overvoltage tap is drawn from the connection between the resistor _RA and the resistor _RB and is electrically connected to an input end of the first routing switch. An overvoltage hysteresis tap is drawn from the connection between the resistor _RB and the resistor _RC and is electrically connected to the other input end of the first routing switch. The output terminal of the first routing switch is electrically connected to the non-inverting input terminal of the overvoltage comparator CP1. An undervoltage tap is drawn from the connection between the resistor _RC and the resistor _RD and is electrically connected to an input end of the second routing switch. An undervoltage hysteresis tap is drawn from the connection between the resistor _{R D} and the resistor RE and is electrically connected to the other input end of the second routing switch. The output terminal of the second routing switch is electrically connected to the non-inverting input terminal of the undervoltage comparator CP2. Both the inverting input terminals of the overvoltage comparator CP1 and the undervoltage comparator CP2 are used to access the reference voltage.

It can be understood that, in this embodiment, the above-mentioned battery unit E ₀ may be various types of battery units E ₀ protected by the battery protection chip applied in the calibration circuit 100 in the art. Adjustable resistor R _trim can also be called trim resistor. In IC design in this field, the trim resistor that needs to be adjusted can usually be divided into several segments in series, and then some segments are short-circuited or released through fuses. way to change the size of the resistor step by step. The total resistance of the adjustable resistor R _trim can be selected according to the needs of different application scenarios, and the total resistance of the resistor divider 12 can be selected according to the needs of different application scenarios in the same way.

The first routing switch 14 and the second routing switch 16 may be the same routing switch or different routing switches, for example, but not limited to, the first routing switch 14 and the second routing switch 16 may both be The same multiple-choice multiplexer in this field, such as two-to-one multiplexer, four-to-one multiplexer, eight-to-one multiplexer, and sixteen-to-one multiplexer among various multiplexers any one; or, the first routing switch 14 can be any one of the various multiplexers in the art, and the second routing switch 16 can be any other one of the various multiplexers in the art A multiplexer other than the first routing switch 14 . In some embodiments, the first routing switch 14 and the second routing switch 16 may also be other selection switches that use electrical signals to control input switching.

Specifically, the resistor divider 12 shown in FIG. 3 is formed by connecting a resistor _RA , a resistor _RB , a resistor _RC , a resistor _RD and a resistor _RE in series. From the connection positions between the resistors in the resistor divider 12 in series, four taps are drawn out respectively. According to the order of the voltage divider ratio from high to low, they are: overvoltage tap, overvoltage hysteresis tap, undervoltage tap and undervoltage. Hysteresis taps, respectively, to support desired over/under voltage protection, (over/under voltage) hysteresis functions, etc.

In this application, a routing switch is used to realize the hysteresis function. The overvoltage tap and the overvoltage hysteresis tap are connected to an input end of the overvoltage comparator CP1 through the first routing switch 14. Similarly, the undervoltage tap and the undervoltage tap The hysteresis tap is connected to an input terminal of the undervoltage comparator CP2 through the second routing switch. The other input terminals of the overvoltage comparator CP1 and the undervoltage comparator CP2 are connected to a same reference voltage. By controlling the first routing switch 14 and the second routing switch 16 to select and turn on their hysteresis taps, the voltage division ratio is changed, and then the threshold value is changed, so that the hysteresis function can be realized.

The above calibration circuit adopts a calibration circuit structure composed of an adjustable resistor R _trim , a resistor divider, a first routing switch, a second routing switch, an overvoltage comparator CP1 and an undervoltage comparator CP2, which is different from the traditional one. Compared with the solution, a voltage divider is saved, which saves half of the power consumption and area of the chip; only by adjusting an adjustable resistor R _trim , the overvoltage threshold and undervoltage threshold can be calibrated at the same time, and the trimming process costs time will be greatly shortened. In addition, the overvoltage comparator CP1 and the undervoltage comparator CP2 in this scheme can use the same circuit design and can be reused; the reference voltage V _REF can also use a conventional design, it does not need to be designed to be adjustable, and the overvoltage/ The undervoltage hysteresis can also be set separately without restraining each other, which greatly reduces the difficulty and complexity of circuit design, and achieves the purpose of significantly improving the overall performance of the battery protection chip circuit.

As shown in FIG. 4 , in one embodiment, the first routing switch 14 is a two-to-one multiplexer Q ₁ . The control signal input end of the two-to-one multiplexer Q ₁ is used to access the enable signal of the overvoltage hysteresis. The overvoltage hysteresis enable signal is used to instruct the two-to- _one multiplexer Q1 to turn on the overvoltage hysteresis tap to the overvoltage comparator CP1.

It can be understood that in this embodiment, a two-to-one multiplexer Q ₁ can be used as the first routing switch 14 , and the two-to-one multiplexer Q ₁ is controlled by an enable signal of overvoltage hysteresis to realize overvoltage The tap and the overvoltage hysteresis tap are respectively connected to the non-inverting input of the overvoltage comparator CP1. The enable signal of the overvoltage hysteresis may be recorded as SEL_A, which may be provided by a corresponding enable pin on the battery protection chip where the calibration circuit 100 is located, or may be generated by an additionally set enable control signal source. By adopting the two-to- _one multiplexer Q1 to realize the switching of the required overvoltage protection/hysteresis function, the reliability is high and the cost is low, and the power consumption and area occupation of the chip will not be increased.

As shown in FIG. 4 , in one embodiment, the second routing switch 16 is a two-to-one multiplexer Q ₂ . The control signal input end of the two-to-one multiplexer Q ₂ is used to access the enable signal of undervoltage hysteresis. The undervoltage hysteresis enable signal is used to instruct the two-to-one multiplexer _Q2 to turn on the undervoltage hysteresis tap to the undervoltage comparator CP2.

It can be understood that in this embodiment, a two-to-one multiplexer Q ₂ can be used as the second routing switch 16 , and the two-to-one multiplexer Q ₂ is controlled by an enable signal of overvoltage hysteresis to realize undervoltage The tap and the undervoltage hysteresis tap are respectively connected to the non-inverting input of the undervoltage comparator CP2. The enable signal of undervoltage hysteresis may be recorded as SEL_B, which may be provided by a corresponding enable pin on the battery protection chip where the calibration circuit 100 is located, or may be generated by an additionally set enable control signal source. By adopting the two-to-one multiplexer _Q2 to realize the switching of the required undervoltage protection/hysteresis function, the reliability is high and the cost is low, and the power consumption and area occupation of the chip will not be increased.

Preferably, a two-to-one multiplexer Q ₁ can be used as the first routing switch 14 and a two-to-one multiplexer Q ₂ can be used as the second routing switch 16 to respectively realize the required function switching. Control, overvoltage/undervoltage hysteresis can be set separately without pinning each other, which can further reduce the difficulty and complexity of circuit design.

In one embodiment, the adjustable resistor R _trim includes 32 segment resistors connected in series. It can be understood that in IC design, the resistance to be adjusted is generally divided into several segments in series, and then the size of the resistance is changed step by step by short-circuiting or releasing some of the segments through a fuse. The design of the trim resistor should consider three aspects: first, it is hoped that the current consumed by the voltage divider is less than 0.5uA, which requires the resistance of the resistor to be large enough; second, it is necessary to consider meeting the accuracy requirements of trimming, which requires repairing The number of segments for adjusting the resistor is sufficient. Third, considering the area of the chip layout and the convenience of drawing, the area of the resistor (proportional to the resistance value) should not be too large, and the number of segments should not be too large. Preferably, since the segment of the trimming resistor needs to be divided into at least 28 parts, and at least a five-digit binary calibration code is required to correspond, the trimming resistor can be divided into 32 parts corresponding to the five-digit binary, that is, 32 The segment resistors are connected in series. By using the adjustable resistor R _trim with the above-mentioned number of segments, the calibration requirement can be efficiently met, and the overall performance of the chip can easily be optimized.

In one embodiment, each segment resistance is a high resistance polysilicon sheet resistance. It can be understood that, in this embodiment, a high-resistance polysilicon sheet resistance is provided in the IC manufacturing process, and the sheet resistance value is 3k ohm per square. In this way, the design requirement of the adjustable resistor R _trim can be better satisfied.

In order to more intuitively describe the calibration circuit 100 of the above embodiments of the present invention, the following specific design examples are given. It should be noted that the following examples are not the only limitations to the above-mentioned embodiments of the present invention, but are one of the illustrative specific design implementations:

For example: for a certain battery, the user wants to customize the battery protection chip, and the requirements are as follows: the target of the overvoltage protection threshold after adjustment is 4.2v, which is represented by V _{OV_target} in Table 1; the hysteresis of the overvoltage protection is 200mv, and the In Table 1, it is represented by V _{HYS_OV} ; the undervoltage protection threshold is 2.75v, and the hysteresis of undervoltage protection is +200mv. Similarly, they are represented by V _{UV_target} and V _{HYS_UV} respectively; after adjustment, the accuracy of overvoltage protection reaches ±25mv, In chip design, a common bandgap reference with a nominal output of 1.22v is used as the reference voltage V _ref . After a series of simulations and estimations, it is considered that the range of the reference voltage is 1.10-1.40v (ie V _{ref_min ˜V ref_max} ) considering all the variation of the reference voltage with process, voltage and temperature (PVT). Using Table 1, all five required ratios and design parameters such as the number of trim resistor segments can be derived. As shown in Figure 5, it is a simplified diagram of the overvoltage divider ratio and a simplified diagram of the undervoltage divider ratio, respectively.

Table 1 Determination of partial pressure ratio

Table 1 (continued)

The letters _A , B and B1 in the table represent the values of the corresponding resistors in Figure 5, X represents the trimming resistance value, _Xstep represents the trimming step size, and _{Vref_nominal} represents the nominal reference voltage value.

In IC design, the resistance to be adjusted is generally divided into several segments in series, and then some segments are short-circuited or released through fuses to change the size of the resistance step by step. The IC manufacturing process in this embodiment provides high-resistance polysilicon resistors with a sheet resistance value of 3k ohm per square. The design of the trimming resistor should consider three aspects: first, it is hoped that the current consumed by the voltage divider is less than 0.5uA, which requires the resistance of the resistor to be large enough; secondly, it is necessary to consider meeting the accuracy requirements of trimming, which requires trimming The number of segments of the resistor is sufficient. Third, considering the area of the layout and the convenience of drawing, the area of the resistor (proportional to the resistance value) should not be too large, and the number of segments should not be too large. After trade-offs and compromises, the total resistance of the resistor divider is determined to be 8.1M ohm, divided into 54 segments, each segment is 50um in length and 1um in width, and the minimum adjustable unit is 0.5 segments ( The two sections are connected in parallel), so in Table 1, for the sake of unity, 54 is used as the denominator.

Selecting H _OV = +1/54 for the positions of the overvoltage tap and overvoltage hysteresis tap means: move up one segment from the overvoltage protection (OV) tap; similarly, for the undervoltage tap and undervoltage hysteresis tap The location selection of H _UV = -2/54 means: move down two segments from the undervoltage protection (UV) tap. The segment of the trimming resistor X needs to be calculated separately, at least divided into 28 parts, and at least a five-digit binary calibration code is needed to correspond, so the trimming resistor X is divided into 32 parts corresponding to the five-digit binary.

So far, the design parameters of the resistance have been determined by the above chart and analysis, and the design is completed.

The principle of the method for obtaining the resistance ratio in Table 1 is explained and analyzed below. Here, the trim resistor represents an adjustable resistor R _trim that can only be adjusted in stages but not continuously: the method for determining the voltage divider ratio, as shown in Figure 4, firstly estimates the deviation range of the reference voltage, that is, when the reference voltage is in batches Maximum value (V _{ref_max} ) and minimum value (V _{ref_min} ) that may occur during production. When the trim resistors R _trim are all short-circuited, and the resistance value is X _min (generally set to zero), the voltage divider ratio is the largest, which corresponds to the case where the reference voltage reaches the upper limit of the deviation. Using the voltage divider ratio obtained in Table 1, when the trimming resistor X is zero and the reference error reaches the upper limit of the deviation, the threshold voltage is equal to the trimmed threshold target value (as in Equation 1).

When the trimming resistor X is fully released, the resistance value is the largest, which is equal to X _max , and the voltage division ratio is the smallest, which corresponds to the lower limit of the reference voltage deviation. Use Table 1 to set the voltage divider ratio to maximize the trimming resistance and when the reference error reaches the lower deviation limit. The threshold voltage is also equal to the trimmed target value (as in Equation 2).

Arrange the above formula to get:

At this time, the target value of trimming and the upper and lower limits of the deviation of the reference voltage are known, and two ratios can be obtained:

和

and

As long as the above ratio is met, the specific value can be specified according to the needs of circuit and layout design. In this embodiment, if the total resistance of the resistor divider is 6.4M ohm, and one of A, B and X _max is specified, then The other two can be determined accordingly. So far, the voltage divider ratio of OV has been determined:

The above conclusions are mainly calculated according to the principle of overvoltage threshold priority. The following proves that when the OV threshold is adjusted accurately, the UV threshold is also adjusted accurately: first divide the resistor B into two parts, B ₁ and B ₂ , and in the middle is the UV tap. After OV is calibrated, the trim resistor X is a specific constant, and when the cell voltage reaches the OV threshold, there is a reference voltage V _ref :

Then, when the threshold of the battery cell voltage to UV is reached, there is:

Combining the first two formulas, the following relationship can be obtained:

Therefore, to determine the voltage divider ratio of the UV tap, you only need to know the target values of overvoltage and undervoltage:

The process of determining the divider ratio of overvoltage hysteresis and undervoltage hysteresis is essentially the same as the process of determining the divider ratio of overvoltage and undervoltage, except that the hysteresis V _{OV_target} +V _{HYS_OV} and V are used. _{UV_target} +V _{HYS_UV} , respectively replacing V _{OV_target} and V _{UV_target} , which are essentially another slightly different threshold value. Since trimming the value of resistor X can have an effect on the hysteresis, here _{Vref_nominal} is used to replace _{Vref_max} and _{Vref_min} to get the smallest overall error:

An important conclusion can be drawn here: the step of trimming is not actually fixed, but is related to the reference voltage, as shown in Figure 6, the three segmented arrows in the figure indicate that with the calibration code (also called trimming) code) (taking the two-digit binary calibration code 00~11 as an example), the change of the overvoltage threshold or the undervoltage threshold, the upper arrow is the situation when the reference voltage is at the estimated maximum value, and the lower one is at the lowest value, the middle is when the reference voltage is a typical value. The trim step becomes longer when the reference voltage is higher. However, if the reference voltage reaches the upper limit of the estimation, the trimming step size can still meet the accuracy requirement, then all the cases where the reference voltage is within the estimation range can meet the accuracy requirement. In addition, if the following conditions are met: First, when the reference voltage is at the estimated highest value, when the calibration code is 00 (corresponding to X _max ), the actual threshold is equal to the adjustment target threshold (point P _A in the figure); second, the reference When the voltage is at the estimated minimum value, when the calibration code is 11 (corresponding to X _min ), the actual threshold is equal to the trim target threshold (point P _B in the figure). Then, all chips whose reference voltage is within the estimated range can be successfully trimmed.

In one embodiment, the present invention further provides a battery protection chip, including a chip body and the above-mentioned calibration circuit 100 . It can be understood that the chip body in this embodiment refers to the chip body of various battery protection chips to which the calibration circuit 100 can be applied in the art. For the specific explanation of the calibration circuit 100 in this embodiment, please refer to the above Corresponding explanations in the embodiments of each calibration circuit 100 should be understood in the same way, and will not be repeated here.

The above-mentioned battery protection chip, by applying the above-mentioned calibration circuit 100, can save the power consumption and area of the chip, greatly shorten the trimming time, greatly reduce the difficulty and complexity of the circuit design of the battery protection chip, and achieve a significant improvement in the circuit synthesis of the battery protection chip. performance purpose.

In one embodiment, as shown in FIG. 7 , the present invention further provides a method for calibrating a calibration circuit for calibrating the above-mentioned calibration circuit 100, and the above-mentioned method includes the following steps S12 to S18:

S12, determine the design parameters of the calibration circuit; the design parameters include the overvoltage tap divider ratio, the undervoltage tap divider ratio, the overvoltage hysteresis tap divider ratio, the undervoltage hysteresis tap divider ratio, the adjustable resistance ratio and the adjustable resistance number of segments;

S14, measure the overvoltage protection threshold value of the calibration circuit before calibration;

S16, use the binary calibration code formula to calculate the calibration code according to the design parameters and the overvoltage protection threshold value; the calibration code is used to calibrate the above-mentioned calibration circuit;

S18, using the method of fuse programming, write the calibration code into the chip of the calibration circuit.

It can be understood that each design parameter of the calibration circuit can be determined when the circuit design is completed. After the battery protection chip is produced, first measure the uncalibrated overvoltage protection threshold V _{OV_raw} , since the error of the resistor divider is negligible relative to the error of the reference voltage, the offset of the comparator can be equivalently converted Into the error of the voltage reference, the reference voltage V _ref can be inversely derived. Then, knowing that the comparator does not sink current, the current on resistor _RA is equal to the current on adjustable resistor R _trim . Therefore, for each step of increasing X (that is, the resistance value of the adjustable resistor R _trim ), the threshold will be increased accordingly

The method to get the calibrated resistance value by one measurement:

其中，N表示熔丝的根数(即熔丝的数量)。Now analyze how to guarantee the calibratable range and post-calibration accuracy. Calibration is accomplished by changing the value of the trim resistor X in stages. In this embodiment, five fuses are used, corresponding to five-digit binary calibration codes of 00000-11111. The number of segments of the trimming resistor X determines the accuracy that can be achieved after trimming, and the step size of trimming

Among them, N represents the number of fuses (ie, the number of fuses).

The trimming resistor X is divided into multiple parts. Each time the X resistor is released into the resistor divider, the threshold will increase by a step length X _step . To ensure the trimming accuracy is better than ±25mv, it is necessary to set X _step in the worst case. If it is less than 50mv, obviously, the worst case is V _ref =V _{ref_max} , so X is divided into at least 28 parts, then take five binary digits, and there are 32 parts in total.

In one embodiment, the generation formula of the binary calibration code (that is, the calibration code) is:

In one embodiment, the adjustable resistance ratio is determined by the following formula:

Among them, X _max represents the maximum resistance value of the adjustable resistor, _A represents the resistance value of the resistor RA, _B represents the resistance value of the resistor RB, V _{ref_max} represents the maximum value of the reference voltage, and V _{ref_min} represents the minimum value of the reference voltage;

The number of adjustable resistor segments is determined by the following formula:

Among them, X _step represents the adjustment step length, _A represents the resistance value of the resistor RA, V _{ref_max} represents the maximum value of the reference voltage, and P represents the adjustment precision.

In one embodiment, it is further necessary to define the valid area of the overvoltage protection threshold value V _{OV_raw} before calibration. If this area is exceeded, the required accuracy cannot be achieved through calibration, and the area is:

Among them, V _{ref_min} represents the minimum value of the reference voltage, A represents the resistance value of the resistor RA, _B represents the resistance value of the resistor _RB , V _{OV_raw} represents the overvoltage protection threshold value before calibration, and V _{OV_target} represents the overvoltage protection The target value after threshold adjustment. The calculation methods for all the design parameters in Table 1 are explained above.

After the design goals are given, the ratios of all resistors can be calculated. Under the condition that these ratios are met, the absolute value of the resistors is determined according to the requirements of the chip's power consumption, area and layout matching and convenience. After that, the chip design work That is done.

Test after a batch of chips is fabricated. For example, the overvoltage threshold of one of the chips is 3.89v before calibration. According to the calibration code generation method provided above in the present invention, the calibration code is 01110. Break the calibration fuse and write the calibration code into the chip. Then measure the overvoltage threshold again, which is expected to measure 4.197v. Then check the overvoltage hysteresis threshold, undervoltage threshold, and undervoltage hysteresis threshold. Confirm that the chip meets the design requirements after the calibration code is written, and the chip has been successfully calibrated so far.

In the calibration method of the above calibration circuit, the overvoltage threshold and the undervoltage threshold can be calibrated at the same time only by adjusting an adjustable resistor R _trim , and the time spent in the trimming process is also greatly shortened, which greatly improves the calibration efficiency.

In the description of this specification, description with reference to the terms "one of the embodiments", "one embodiment", etc. means that a particular feature, structure, material or feature described in connection with the embodiment or example is included in at least one implementation of the invention example or example. In this specification, schematic descriptions of the above terms do not necessarily refer to the same embodiment or example.

The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, all It is considered to be the range described in this specification.

The above examples only represent several embodiments of the present application, and the descriptions thereof are relatively specific and detailed, but should not be construed as a limitation on the scope of the invention patent. It should be noted that, for those skilled in the art, without departing from the concept of the present application, several modifications and improvements can be made, which all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the appended claims.

Claims (10)

1. A calibration circuit, characterized in that it comprises an adjustable resistor R _trim , a resistor divider, a first routing switch, a second routing switch, an overvoltage comparator CP1 and an undervoltage comparator CP2, and the resistor The voltage divider includes a resistor _RA , a resistor _RB , a resistor _RC , a resistor _RD , and a resistor _RE in series in sequence; One end of the adjustable resistor R _trim is used to electrically connect the positive electrode of the battery unit, the other end of the adjustable resistor R _trim is electrically connected to one end of the resistor R _A , and the other end of the resistor R _E is used to electrically connect the negative pole and the ground terminal of the battery unit; An overvoltage tap is drawn from the connection between the resistor _RA and the resistor _RB and is electrically connected to an input end of the first routing switch, and an overvoltage tap is drawn from the connection between the resistor _RB and the resistor _RC . a voltage hysteresis tap is electrically connected to the other input terminal of the first routing switch, and the output terminal of the first routing switch is electrically connected to the non-inverting input terminal of the overvoltage comparator CP1; An undervoltage tap is drawn from the connection between the resistor _RC and the resistor _RD and is electrically connected to an input end of the second routing switch, and an undervoltage tap is drawn from the connection between the resistor _RD and the resistor _RE . a voltage hysteresis tap and is electrically connected to the other input terminal of the second routing switch, and the output terminal of the second routing switch is electrically connected to the non-inverting input terminal of the undervoltage comparator CP2; Both the inverting input terminals of the overvoltage comparator CP1 and the undervoltage comparator CP2 are used to access the reference voltage. 2. The calibration circuit according to claim 1, wherein the first routing switch is a two-to-one multiplexer Q ₁ , and the control signal input end of the two-to-one multiplexer Q ₁ is used for Access the enable signal of overvoltage hysteresis; The enable signal of the overvoltage hysteresis is used to instruct the two-to- _one multiplexer Q1 to turn on the overvoltage hysteresis tap to the overvoltage comparator CP1. 3. The calibration circuit according to claim 1 or 2, wherein the second routing switch is a two-to-one multiplexer Q ₂ , and the control signal input end of the two-to-one multiplexer Q ₂ Enable signal for accessing undervoltage hysteresis; The enable signal of the undervoltage hysteresis is used to instruct the two-to-one multiplexer _Q2 to turn on the undervoltage hysteresis tap to the undervoltage comparator CP2. 4 . The calibration circuit according to claim 3 , wherein the adjustable resistor R _trim comprises 32 segment resistors connected in series. 5 . 5 . The calibration circuit according to claim 4 , wherein each of the segment resistances is a high-resistance polysilicon sheet resistance. 6 . 6 . A battery protection chip, comprising a chip body and the calibration circuit according to any one of claims 1 to 5 . 7 . 7. A calibration method for a calibration circuit, characterized in that, for calibrating the calibration circuit described in any one of claims 1 to 5, the method comprises the following steps: Determine the design parameters of the calibration circuit; the design parameters include the overvoltage tap divider ratio, the undervoltage tap divider ratio, the overvoltage hysteresis tap divider ratio, the undervoltage hysteresis tap divider ratio, the adjustable resistance ratio and the adjustable resistance ratio. Adjust the number of resistor segments; measuring the overvoltage protection threshold value of the calibration circuit before calibration; Using a binary calibration code formula to calculate a calibration code according to the design parameters and the overvoltage protection threshold; the calibration code is used to calibrate the calibration circuit; Using the method of fuse programming, the calibration code is written into the chip of the calibration circuit. 8. The calibration method of the calibration circuit according to claim 7, wherein the binary calibration code formula is:

Wherein, V _{OV_target} represents the target value of the overvoltage protection threshold value after adjustment, V _{OV_raw} represents the uncalibrated overvoltage protection threshold value, and X _step represents the adjustment step size. 9. The calibration method of the calibration circuit according to claim 7, wherein the adjustable resistance ratio is determined by the following formula:

Among them, X _max represents the maximum resistance value of the adjustable resistor, _A represents the resistance value of the resistor RA, _B represents the resistance value of the resistor RB, V _{ref_max} represents the maximum value of the reference voltage, and V _{ref_min} represents the minimum value of the reference voltage; The adjustable resistance segment number is determined by the following formula:

Among them, X _step represents the adjustment step length, _A represents the resistance value of the resistor RA, V _{ref_max} represents the maximum value of the reference voltage, and P represents the adjustment precision. 10. The method for calibrating a calibration circuit according to claim 9, wherein the valid area of the uncalibrated overvoltage protection threshold value is:

Among them, V _{ref_min} represents the minimum value of the reference voltage, A represents the resistance value of the resistor RA, _B represents the resistance value of the resistor _RB , V _{OV_raw} represents the uncalibrated overvoltage protection threshold value, and V _{OV_target} represents the overvoltage protection threshold. The target value after adjustment of the voltage protection threshold value.

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