JP2009273233A - Breakdown voltage protection circuit and control circuit for inverting charge pump using the same - Google Patents

Abstract

A power supply voltage supplied to a circuit element is reduced.
A protection circuit includes an input terminal, an output terminal, a control unit, a bypass switch, and a voltage clamp circuit. The bypass switch 14 is turned on / off based on the level of the control signal Sg generated by the control unit 10. The control unit 10 outputs a control signal Sg that becomes a high level when the power supply voltage Vcc exceeds a certain threshold value. The bypass switch 14 is turned on while the control signal Sg is at a low level, and outputs the power supply voltage Vcc to the output terminal 104 as it is. The bypass switch 14 is turned off when the control signal Sg becomes high level. While the bypass switch 14 is in the OFF state, the NPN bipolar transistor 18 outputs the clamped voltage to the output terminal 104.
[Selection] Figure 1

Description

  The present invention relates to a protection circuit that protects a circuit to be protected from overvoltage.

A maximum rated voltage (withstand voltage) that can be applied to each circuit element on the integrated circuit is determined. If a voltage exceeding the breakdown voltage is applied to a circuit element, the reliability of the element may be impaired. Normally, an integrated circuit is manufactured by a process corresponding to a power supply voltage in consideration of a withstand voltage.
JP 2002-76875 A JP 2002-343874 A

However, in a circuit that outputs a voltage having a sign opposite to that of the power supply voltage, such as an inverting charge pump, a potential difference between a positive potential node and a negative potential node exceeds the breakdown voltage of an element provided between the nodes. There may be places. In such a case, it is convenient if the potential difference can be controlled by some method.
Here, a regulator circuit may be used for the control. However, the output voltage of the regulator circuit may be lower than the input voltage. Therefore, in this case, there is a problem that the starting voltage of the circuit to be protected becomes high.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a protection circuit that protects a circuit to be protected from an overvoltage while keeping a starting voltage of the circuit to be protected low.

  One embodiment of the present invention relates to a protection circuit provided on a power supply voltage path of an integrated circuit. The protection circuit includes an input terminal to which a power supply voltage is input, an output terminal to which a circuit to be protected is connected, and a control unit that generates a control signal that takes a predetermined level when the power supply voltage is higher than a predetermined first reference voltage. And a bypass switch that is provided between the input terminal and the output terminal and is turned off when the control signal is at a predetermined level, and a voltage clamp that receives the power supply voltage and clamps it below a voltage corresponding to a predetermined second reference voltage A circuit.

  According to this aspect, when the power supply voltage is higher than the first reference voltage, the voltage clamped by the voltage clamp circuit is output to the protection target circuit, and when the power supply voltage is lower than the first reference voltage, the power supply voltage is the protection target. Output to the circuit. Therefore, the circuit to be protected can be protected from overvoltage, and the starting voltage of the circuit can be kept low.

  The voltage clamp circuit may include a first bipolar transistor having an emitter connected to the output terminal and a base applied with a voltage corresponding to the second reference voltage. In this case, the voltage clamp circuit can clamp to a voltage obtained by subtracting the forward voltage (Vf) between the base and emitter of the first bipolar transistor from the voltage corresponding to the second reference voltage.

  The first bipolar transistor may be an NPN type, and the voltage clamp circuit may further include a PNP type second bipolar transistor having an emitter connected to the base of the first bipolar transistor and a second reference voltage applied to the base. In this case, even if the forward voltage of the first and second bipolar transistors fluctuates with temperature, the change can be canceled and the output of the voltage clamp circuit can be stabilized with respect to temperature.

  Another aspect of the present invention is a control circuit that controls a switching element of an inverting charge pump. The control circuit includes the protection circuit, a gate clock generation circuit that generates a gate clock, and a level shift circuit that shifts the level of the gate clock and outputs it to the control terminal of the switch element. The level shift circuit shifts the high level of the gate clock to the voltage output by the protection circuit and outputs at least one end thereof to the control terminal of the switch element having a voltage equivalent to the output voltage of the inverting charge pump.

  The output voltage of the inverting charge pump is a negative voltage. Therefore, for example, a negative voltage is applied to one end of the switch element connected to the output side of the output capacitor. When the control signal of such a switch element becomes high level, a voltage given by the sum of the voltage corresponding to the high level and the absolute value of the negative voltage is applied between the gate and source. According to the above aspect, a control signal that does not exceed the gate-source breakdown voltage can be output to such a switch element.

  It should be noted that any combination of the above-described constituent elements, and those obtained by replacing the constituent elements and expressions of the present invention with each other between methods and apparatuses are also effective as an aspect of the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the protection circuit which protects the circuit from overvoltage can be provided, keeping the starting voltage of the circuit of protection object low.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and signals shown in the drawings are denoted by the same reference numerals, and repeated descriptions are appropriately omitted.

  FIG. 1 is a circuit diagram showing a configuration of a protection circuit 100 according to the embodiment. The protection circuit 100 includes an input terminal 102, an output terminal 104, a control unit 10, a bypass switch 14, and a voltage clamp circuit 12. A power supply voltage Vcc is input to the input terminal 102. An output voltage Vout is output from the output terminal 104. A circuit 106 to be protected is connected to the output terminal 104.

  The bypass switch 14 is turned on / off based on the level of the control signal Sg generated by the control unit 10. In the present embodiment, the bypass switch 14 is a P-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor), the drain is connected to the output terminal 104, and the source is connected to the input terminal 102. A control signal Sg generated by the control unit 10 is applied to the gate. When the control signal Sg is at the ground voltage level (low level), the bypass switch 14 is on. When the control signal Sg is at the power supply voltage Vcc level (high level), the bypass switch 14 is in an OFF state.

  The control unit 10 includes a first resistor R1, a second resistor R2, and a comparator 30. The first resistor R1 and the second resistor R2 are provided in series between the power supply voltage line and the ground voltage line, and divide the power supply voltage Vcc. A first connection node 32 between the first resistor R1 and the second resistor R2 is connected to a non-inverting input terminal of the comparator 30. The first reference voltage Vref <b> 1 is input to the inverting input terminal of the comparator 30. The comparator 30 compares the voltage input to the non-inverting input terminal and the voltage input to the inverting input terminal, and outputs the power supply voltage Vcc or the ground voltage to the gate of the bypass switch 14 as the control signal Sg. Composed. The comparator 30 may be configured to have hysteresis. This can be realized, for example, by applying a Schmitt trigger type feedback.

  For example, when there is no hysteresis, the first resistor R1 = 1.25 (kΩ), the second resistor R2 = 1.5 (kΩ), and the first reference voltage Vref1 = 1.5 (V), Vcc = Vref1 × { (1.25 + 1.5) /1.5} = 2.75 (V) is the threshold value Vt of the control unit 10. When power supply voltage Vcc is lower than threshold value Vt, control signal Sg from comparator 30 is at the ground voltage level. When power supply voltage Vcc is higher than threshold value Vt, control signal Sg from comparator 30 is at the level of power supply voltage Vcc.

  The voltage clamp circuit 12 includes a clamp voltage setting circuit 16, an NPN bipolar transistor 18, and a first constant current source 24. The collector of the NPN bipolar transistor 18 is connected to the input terminal 102. The emitter is connected to the output terminal 104. One end of the first constant current source 24 is connected to the second connection node 28 between the emitter and the output terminal 104, and the other end of the first constant current source 24 is grounded. The first constant current source 24 is set in a direction in which current flows from the second connection node 28 to the ground. The voltage generated by the clamp voltage setting circuit 16 is applied to the base of the NPN bipolar transistor 18. In particular, note that the NPN bipolar transistor 18 and the bypass switch 14 are connected in parallel.

  The clamp voltage setting circuit 16 includes a third resistor R 3, a PNP bipolar transistor 20, and a buffer 22. One end of the third resistor R3 is connected to the input terminal 102. The other end of the third resistor R3 and the emitter of the PNP bipolar transistor 20 are connected, and the base of the NPN bipolar transistor 18 is connected to the third connection node 26 thereof. The second reference voltage Vref <b> 2 is input to the base of the PNP bipolar transistor 20 through the buffer 22. The collector of the PNP bipolar transistor 20 is grounded.

The operation of the protection circuit 100 configured as described above will be described.
FIG. 2 is a graph showing changes in the power supply voltage Vcc and the output voltage Vout with respect to the power supply voltage Vcc. In the graph of FIG. 2, the power supply voltage Vcc is taken on the x axis, and the output voltage Vout and the power supply voltage Vcc are taken on the y axis. Of course, the power supply voltage Vcc is a straight line with a slope of 1. In FIG. 2, the power supply voltage Vcc is indicated by a broken line. The output voltage Vout is indicated by a solid line.

In order to simplify the description below, the case where the resistance and the reference voltage of the control unit 10 take the above values is considered. That is, the threshold value Vt of the control unit 10 is 2.75 (V). Consider a case where the NPN bipolar transistor 18 and the PNP bipolar transistor 20 are formed by pairing. That is, the forward voltage Vf1 of the NPN bipolar transistor 18 and the forward voltage Vf2 of the PNP bipolar transistor 20 are substantially the same, the temperature characteristics thereof are substantially the same, and the current amplification factor hfe is also substantially the same. Further, consider a case where the second reference voltage Vref2 is set to 2 (V).
The following description will be divided into cases depending on the magnitude relationship between the power supply voltage Vcc and the threshold value Vt.

Vcc <Vt:
The control signal Sg output from the control unit 10 is a ground voltage at a low level. Therefore, the ground voltage is applied to the gate of the P-channel MOSFET which is the bypass switch 14. In this case, the P-channel MOSFET is turned on, and the output voltage Vout and the power supply voltage Vcc are equal. Therefore, in FIG. 2, the output voltage Vout is drawn along the power supply voltage Vcc when Vcc <Vt.

Vcc ≧ Vt:
When the power supply voltage Vcc rises and exceeds the threshold value Vt, the level of the control signal Sg output from the control unit 10 is inverted to become the power supply voltage Vcc that is at a high level. Then, the power supply voltage Vcc is applied to the gate of the P-channel MOSFET which is the bypass switch 14. In this case, the P-channel MOSFET is turned off. Therefore, the emitter voltage VE1 of the NPN bipolar transistor 18 and the output voltage Vout are equal.

  From the circuit configuration of the voltage clamp circuit 12, VE1 = VE2−Vf1 is established using the emitter voltage VE2 of the PNP bipolar transistor 20. Also, VE2 = Vref2 + Vf2. Therefore, VE1 = Vref2 + Vf2-Vf1. Here, since Vf1≈Vf2, VE1≈Vref2. That is, the output voltage Vout is approximately equal to the second reference voltage Vref2. Since the second reference voltage Vref2 is 2 (V) regardless of the power supply voltage Vcc when the power supply voltage Vcc is sufficiently high, the output voltage Vout is also clamped to approximately 2 (V). Therefore, in FIG. 2, the output voltage Vout is drawn as a straight line parallel to the x-axis when Vcc ≧ Vt.

  However, when the power supply voltage Vcc is close to the second reference voltage Vref2, since a sufficient potential difference does not occur between the base emitters of the PNP bipolar transistor 20, the PNP bipolar transistor 20 is not turned on, and VE2 <Vref2 + Vf2. Therefore, VE1 <Vref2 and the output voltage Vout is lower than the second reference voltage Vref2. In the graph of FIG. 2, this state is indicated by dip DIP.

Thus, according to the protection circuit 100 according to the present embodiment, the output voltage Vout takes a value that does not depend on the power supply voltage Vcc when the power supply voltage Vcc is higher than the threshold value Vt. Therefore, it is possible to prevent an overvoltage from being applied to the circuit 106 to be protected and to expand the range of the operating voltage.
Further, since the output voltage Vout hardly fluctuates even if the power supply voltage Vcc fluctuates, stable power supply to the circuit to be protected is realized.

  Further, according to the protection circuit 100 according to the present embodiment, the output voltage Vout and the power supply voltage Vcc are equal in a range where the power supply voltage Vcc is lower than the threshold value Vt. Here, the power supply voltage Vcc is raised from 0 (V), and the power supply voltage Vcc when the circuit to be protected is started is called a start voltage, and this start voltage is examined. Consider a case where a power supply voltage is supplied through a known regulator circuit to a circuit to be protected that starts at a voltage lower than the threshold value Vt. In this case, since the output impedance of the regulator circuit is generally not negligible, the output voltage is lower than the power supply voltage when the load is heavy. That is, the voltage input to the circuit to be protected may be lower than the power supply voltage. On the other hand, when the power supply voltage is supplied through the protection circuit 100, since the input terminal 102 and the output terminal 104 are directly connected, the above-described output impedance problem is alleviated. Therefore, the starting voltage is lower in the latter case than in the former case. That is, according to the protection circuit 100 according to the present embodiment, the circuit to be protected can be activated using a lower power supply voltage Vcc, and the operating voltage range can be expanded to the low voltage side.

  Further, according to the protection circuit 100 according to the present embodiment, there is only one threshold value Vt for switching the output, and the power supply voltage Vcc is clamped on the high voltage side. On the other hand, consider a case where a power supply voltage is input to a circuit to be protected through a plurality of diodes connected in series as a comparative technique. In this comparative technique, it is assumed that the number of diodes through which the power supply current passes can be switched by a control signal. In this case, as the power supply voltage increases, the number of diodes through which the power supply current passes increases, but as the number of diodes increases, the power supply voltage input to the circuit to be protected becomes equal to the forward voltage of the diode. Jump in the direction of lowering. As a result, in the region where the power supply voltage Vcc is high, the voltage input to the circuit to be protected with respect to the power supply voltage Vcc shows a sawtooth change. On the other hand, in the protection circuit 100 according to the present embodiment, the output is clamped on the high voltage side. Therefore, a more stable output voltage can be supplied compared to the comparative technique, and noise due to switching can be reduced.

Moreover, according to the protection circuit 100 according to the embodiment, the circuit area can be reduced as compared with the case where a general regulator is used.
A general regulator includes an output transistor corresponding to the NPN-type bipolar transistor 18 and an operational amplifier that controls the potential of the control terminal of the output transistor by feedback. Therefore, in a general regulator, an operational amplifier requires a current capability corresponding to the size of the output transistor, and therefore its circuit area tends to increase.
On the other hand, according to the protection circuit 100 according to the present embodiment, the buffer 22 outputs a reference voltage to the base of the PNP bipolar transistor 20. The emitter of the PNP bipolar transistor 20 is connected to the base of the NPN bipolar transistor 18. In this configuration, when the power supply voltage Vcc is below the threshold value Vt, for supplying circuit to supply a current Iout to be protected (not shown), the buffer 22 is approximately the supply current Iout (1 / ^{hfe) 2} times What is necessary is just to supply an electric current. Therefore, the voltage clamp circuit 12 can be configured with a small and simple circuit as compared with the regulator, and can further reduce power consumption.

  Further, according to the protection circuit 100 according to the present embodiment, the forward voltage Vf1 in the NPN bipolar transistor 18 is compensated by the forward voltage Vf2 in the PNP bipolar transistor 20. Furthermore, the temperature change of both forward voltages is substantially the same. Therefore, in the range where the power supply voltage Vcc is higher than the threshold value Vt, it is possible to reduce the variation in offset of the output voltage Vout due to the variation in the value of the forward voltage, and to suppress the drift of the output voltage Vout due to the temperature change.

  The embodiment of the present invention is particularly preferably used for an LSI (Large Scale Integration) or the like in which an inverting charge pump and a circuit using positive and negative power supplies are integrated. Examples of circuits that use positive and negative power supplies include video amplifier circuits and audio amplifier circuits. In such an LSI, it is only necessary to supply only a positive power supply voltage from the outside by integrating it including an inverting charge pump. This eliminates the need to separately generate and supply the negative power supply voltage with another chip or the like.

Next, an application of the protection circuit 100 according to the embodiment will be described.
FIG. 3 is a block diagram showing an inverting charge pump 160 on which the protection circuit 100 of FIG. 1 is mounted. The inverting charge pump 160 includes a first power input terminal 206, a first ground terminal 208, a second power input terminal 212, a first capacitor connection terminal 214, a second ground terminal 216, and a second capacitor connection terminal. 218, a negative voltage output terminal 220, a control circuit 150, a first switch transistor Tr1, a second switch transistor Tr2, a third switch transistor Tr3, and a fourth switch transistor Tr4. For example, the first switch transistor Tr1 may be a P-channel MOSFET, and the second switch transistor Tr2, the third switch transistor Tr3, and the fourth switch transistor Tr4 may be N-channel MOSFETs. The gate-source breakdown voltage of a MOSFET is generally lower than the drain-source breakdown voltage. In the following, a case is considered where the gate-source breakdown voltage of the N-channel MOSFET is 5.5 (V).

  The first switch transistor Tr1 is provided between the second power input terminal 212 and the first capacitor connection terminal 214. The second switch transistor Tr2 is provided between the first capacitor connection terminal 214 and the second ground terminal 216. The third switch transistor Tr3 is provided between the second ground terminal 216 and the second capacitor connection terminal 218. The fourth switch transistor Tr4 is provided between the second capacitor connection terminal 218 and the negative voltage output terminal 220.

  The first power input terminal 206 is connected to the power supply line and supplies the power supply voltage Vcc to the inverting charge pump 160. The first ground terminal 208 is grounded and supplies a ground voltage to the inverting charge pump 160. The second power input terminal 212 is connected to the power line and is applied with the power voltage Vcc. The second ground terminal 216 is grounded. A flying capacitor Cf is connected between the first capacitor connection terminal 214 and the second capacitor connection terminal 218. An output capacitor Co is connected between the second ground terminal 216 and the negative voltage output terminal 220.

  The control circuit 150 includes the protection circuit 100 according to the embodiment, a reference voltage generation circuit 110, a reference clock generation circuit 120, a gate clock generation circuit 130, and a level shift circuit 140. The power supply voltage Vcc and the ground voltage are input to the protection circuit 100, the reference voltage generation circuit 110, and the reference clock generation circuit 120, respectively. The reference voltage generation circuit 110 generates one or a plurality of reference voltages and supplies them to the protection circuit 100. The reference voltage generation circuit 110 generates, for example, a band gap reference voltage.

  The reference clock generation circuit 120 generates a reference clock CLK and outputs it to the gate clock generation circuit 130. The gate clock generation circuit 130 includes a programmable frequency divider 34, a delay circuit 36, a NAND gate 38, a first NOR gate 40, an AND gate 42, and a second NOR gate 44. The programmable frequency divider 34 divides the reference clock CLK at a ratio that can be set from the outside, and outputs a reference gate clock GC.

  The delay circuit 36 includes a resistor and a capacitor, and delays the reference clock CLK by controlling the charging time of the capacitor with the resistor. Due to this delay, a dead time, that is, a period during which all the switch transistors are turned off, is set in the operation phase of the inverting charge pump 160.

The reference gate clock GC is input to one input terminal of each of the NAND gate 38, the first NOR gate 40, the AND gate 42, and the second NOR gate 44, and the delay gate clock GC via the delay circuit 36 is input to the other input terminal. 'Is entered.
The NAND gate 38 outputs the first gate clock V1 to the gate of the first switch transistor Tr1 through the level shift circuit 140. The first NOR gate 40 outputs the second gate clock V2 to the gate of the second switch transistor Tr2 through the level shift circuit 140. The AND gate 42 outputs the third gate clock V3 to the gate of the third switch transistor Tr3 through the level shift circuit 140. The second NOR gate 44 outputs the fourth gate clock V4 to the gate of the fourth switch transistor Tr4 through the level shift circuit 140.

  The level shift circuit 140 receives the power supply voltage Vcc and the output voltage Vout as the high level, and the ground voltage and the negative power supply voltage Vee as the low level. The level shift circuit 140 shifts the high level of the first gate clock V1 and the second gate clock V2 to the power supply voltage Vcc and the low level to the ground voltage. Further, the high level of the third gate clock V3 and the fourth gate clock V4 is shifted to the output voltage Vout, and the low level is shifted to the negative power supply voltage Vee.

  The level shift circuit 140 includes a first inverter 46, a second inverter 48, a third inverter 50, a fourth inverter 52, a fifth inverter 54, a sixth inverter 56, a seventh inverter 58, and an eighth inverter. And an inverter 60. The first inverter 46 and the second inverter 48 are provided in series on a signal line from the output terminal of the NAND gate 38 to the gate of the first switch transistor Tr1. The third inverter 50 and the fourth inverter 52 are provided in series on a signal line from the first NOR gate 40 to the gate of the second switch transistor Tr2. The power supply voltage Vcc is input to the high level side input terminals of the four inverters, and the ground voltage is input to the low level side input terminals.

The output of the AND gate 42 is input to the fifth inverter 54. The output of the second NOR gate 44 is input to the seventh inverter 58. The output voltage Vout is input to the high level side input terminals of the two inverters, and the ground voltage is input to the low level side input terminals.
The output of the fifth inverter 54 is input to the sixth inverter 56. The sixth inverter 56 outputs to the gate of the third switch transistor Tr3. The output of the seventh inverter 58 is input to the eighth inverter 60. The eighth inverter 60 outputs to the gate of the fourth switch transistor Tr4. The output voltage Vout is input to the high-level input terminal of the two inverters, and the negative power supply voltage Vee is input to the low-level input terminal.

Here, paying attention to the third switch transistor Tr3 and the fourth switch transistor Tr4, the source voltage of the inverting charge pump 160 during normal operation is the negative power supply voltage Vee. Further, due to the configuration of the level shift circuit 140, the maximum output voltage Vout is applied to the gate.
Therefore, the maximum gate-source voltage of the third switch transistor Tr3 and the fourth switch transistor Tr4 is Vout−Vee. Note that the negative power supply voltage Vee is a negative value.

The operation of the inverting charge pump 160 configured as described above will be described.
FIG. 4 is a time chart showing the clock waveform of each gate with respect to the reference clock in the inverting charge pump 160. Except for the delay time τ from the edge of the reference gate clock GC, the same level is applied to the two input terminals of the logic gate included in the gate clock generation circuit 130. Further, different levels are input to the two input terminals during the delay time τ from the edge of the reference gate clock GC.

In the first charging period φ1, the first switch transistor Tr1 and the third switch transistor Tr3 are turned on, and the second switch transistor Tr2 and the fourth switch transistor Tr4 are turned off. As a result, charges are stored in the flying capacitor Cf.
The fully closed period φ2 is the dead time described above. In FIG. 4, it is expressed as a period between both edges of the reference gate clock GC and the delay time τ. During this period, all switch transistors are turned off.
In the second charging period φ3, the first switch transistor Tr1 and the third switch transistor Tr3 are turned off, and the second switch transistor Tr2 and the fourth switch transistor Tr4 are turned on. As a result, negative charges are transferred from the flying capacitor Cf to the output capacitor Co, and a negative voltage is generated in the output capacitor Co.
During the operation of the inverting charge pump 160, the negative power supply voltage Vee is generated by repeating {φ1, φ2, φ3, φ2} as one cycle.

  Thus, according to the inverting charge pump 160 according to the application of the protection circuit 100 of FIG. 1, the level shift circuit 140 sets the high level of the gate clock to the gates of the third switch transistor Tr3 and the fourth switch transistor Tr4. The output voltage Vout controlled by the protection circuit 100 is shifted. As a result, an increase in the gate-source voltage of the third switch transistor Tr3 and the fourth switch transistor Tr4 accompanying an increase in the power supply voltage Vcc can be suppressed, and a wider operating voltage range is realized.

Next, an example of the LSI 200 that uses the inverting charge pump 160 will be described.
FIG. 5 is a block diagram showing a configuration of the LSI 200. The LSI 200 includes a third power input terminal 202, a third ground terminal 204, a negative voltage input terminal 210, an inverting charge pump 160, and a main circuit 170, and is integrated on a single semiconductor substrate. ing. The negative voltage output terminal 220 and the negative voltage input terminal 210 are connected.

  The main circuit 170 is a circuit that uses positive and negative power supplies, for example, a video amplifier circuit. The video amplifier circuit may include an LPF (Low Pass Filter) and a driver. The input video signal passes through the LPF, and after components having a predetermined frequency or higher are removed, the driver amplifies the signal by, for example, 6 dB and outputs it to the video equipment. Each of the LPF and the driver may use the negative power supply voltage Vee together with the power supply voltage Vcc.

  The main circuit 170 is supplied with the power supply voltage Vcc through the third power supply input terminal 202 and is supplied with the negative power supply voltage Vee through the negative voltage input terminal 210. The main circuit 170 is grounded via the third ground terminal 204. Hereinafter, a case where the operating voltage of the main circuit 170 is 2.85 (V) ≦ Vcc ≦ 3.45 (V) will be considered.

The operation of the LSI 200 configured as described above will be described.
FIG. 6 is a graph showing changes in the power supply voltage Vcc, the output voltage Vout, and the negative power supply voltage Vee with respect to the power supply voltage Vcc. In the graph of FIG. 6, the power supply voltage Vcc is taken on the x axis, and the output voltage Vout, the negative power supply voltage Vee, and the power supply voltage Vcc are taken on the y axis. Of course, the power supply voltage Vcc is a straight line with a slope of 1. In FIG. 6, the power supply voltage Vcc is indicated by a broken line. The negative power supply voltage Vee is generated by the inverting charge pump 160 and has a relationship of Vee = −Vcc. Therefore, the negative power supply voltage Vee in FIG. In FIG. 6, the negative power supply voltage Vee is indicated by a solid line. The output voltage Vout is indicated by a solid line in the first quadrant of the graph of FIG.

  In the operating voltage range ΔV of the main circuit 170, 2.85 (V) ≦ Vcc ≦ 3.45 (V), when the power supply voltage Vcc is Vcc = 3.45 (V), the third switch transistor Tr3 and the fourth switch transistor Tr3 The gate-source voltage (Vout−Vee) of the switch transistor Tr4 is maximized, and its value is Vc = 2 − (− 3.45) = 5.45 (V). This is lower than the gate-source breakdown voltage of 5.5 (V). In contrast to this, when there is no protection circuit 100, a voltage of Vcc-Vee is applied between the gate and source of the third switch transistor Tr3 and the fourth switch transistor Tr4. Within the operating voltage range ΔV, this is from Va = 2.85 − (− 2.85) = 5.7 (V) to Vb = 3.45 − (− 3.45) = 6.9 (V). This is a voltage in the range and exceeds the gate-source breakdown voltage of 5.5 (V).

  As described above, according to the LSI 200 equipped with the inverting charge pump 160 according to the application, when the power supply voltage Vcc is within the operating voltage range of the main circuit 170, the gate sources of the third switch transistor Tr3 and the fourth switch transistor Tr4. The inter-voltage does not exceed the breakdown voltage.

  The protection circuit 100 according to the embodiment has been described above. This embodiment is an exemplification, and it is understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements, and such modifications are also within the scope of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a protection circuit 100a according to a modification.
The voltage clamp circuit 70 includes a PNP bipolar transistor 64, an NPN bipolar transistor 62, a fourth resistor R 4, a second constant current source 68, and the buffer 22. The emitter of the PNP bipolar transistor 64 is connected to the output terminal 104. Its collector is grounded, and its base is connected in common with the emitter of the NPN bipolar transistor 62 and one end of the fourth resistor R4. The other end of the fourth resistor R4 is grounded. The power supply voltage Vcc is applied to the collector of the NPN bipolar transistor 62, and the output of the buffer 22 is applied to its base. One end of the second constant current source 68 is connected to the fourth connection node 66 between the emitter of the PNP-type bipolar transistor 64 and the output terminal 104, and the power supply voltage Vcc is applied to the other end.
According to this modification, the same effect as the circuit of FIG. 1 can be obtained.

  Although the case where Vcc> 0 has been described in the embodiment, the present invention is not limited to this. When the input power supply voltage is a negative voltage, for example, the bypass switch 14 may be an N-channel MOSFET, the type of the bipolar transistor may be switched, and the polarity of the terminal may be switched as appropriate.

  Although the present invention has been described based on the embodiments, the embodiments merely show the principle and application of the present invention, and the embodiments are defined in the claims. Needless to say, many modifications and arrangements can be made without departing from the spirit of the present invention.

It is a circuit diagram which shows the structure of the protection circuit which concerns on embodiment. 2 is a graph showing changes in power supply voltage and output voltage with respect to the power supply voltage in the protection circuit of FIG. 1. It is a block diagram which shows the inverting type charge pump carrying the protection circuit of FIG. It is a time chart which shows the clock waveform of each gate with respect to the reference clock in an inversion type charge pump. FIG. 4 is a block diagram showing a configuration of an LSI on which the inverting charge pump of FIG. 3 is mounted. 6 is a graph showing changes in power supply voltage, output voltage, and negative power supply voltage with respect to the power supply voltage in the LSI of FIG. It is a circuit diagram which shows the structure of the protection circuit which concerns on a modification.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Protection circuit, 102 Input terminal, 104 Output terminal, 130 Gate clock generation circuit, 160 Inversion type charge pump, 140 Level shift circuit, 150 Control circuit, 12 Voltage clamp circuit, 70 Voltage clamp circuit, 10 Control part, 14 Bypass switch Vcc power supply voltage, Vout output voltage, Vref1 first reference voltage, Vref2 second reference voltage, Sg control signal.

Claims (4)

A protection circuit provided on the power supply voltage path of the integrated circuit,
An input terminal to which power supply voltage is input;
An output terminal to which the circuit to be protected is connected;
A control unit that generates a control signal that takes a predetermined level when the power supply voltage is higher than a predetermined first reference voltage;
A bypass switch that is provided between the input terminal and the output terminal and is turned off when the control signal is at the predetermined level;
A protection circuit comprising: a voltage clamp circuit that receives the power supply voltage and clamps the power supply voltage below a voltage corresponding to a predetermined second reference voltage.   The protection circuit according to claim 1, wherein the voltage clamp circuit includes a first bipolar transistor having an emitter connected to the output terminal and a base to which a voltage corresponding to the second reference voltage is applied. The first bipolar transistor is an NPN type,
The voltage clamp circuit is:
3. The protection circuit according to claim 2, further comprising a PNP-type second bipolar transistor having an emitter connected to a base of the first bipolar transistor, and the second reference voltage being applied to the base. A control circuit for controlling a switching element of an inverting charge pump,
A protection circuit according to any one of claims 1 to 3;
A gate clock generation circuit for generating a gate clock;
A level shift circuit that shifts the level of the gate clock and outputs it to the control terminal of the switch element, and
The level shift circuit shifts the high level of the gate clock to a voltage output by the protection circuit, and at least one end of the level shift circuit has a voltage equivalent to the output voltage of the inverting charge pump. A control circuit characterized by output.

Images