Open drain output circuit and chip

Abstract

This application provides an open-drain output circuit and chip. The open-drain output circuit includes a driving transistor, a first isolation transistor, a second isolation transistor, a control circuit, and an output port. Both the first and second isolation transistors include a body diode. The first isolation transistor conducts when the voltage at the output port is positive and greater than the forward voltage of the body diode in the first isolation transistor, allowing the pull-down current at the output port to flow to system ground through the first isolation transistor and the driving transistor. The second isolation transistor is controlled to conduct when the voltage at the output port is positive and lower than a preset threshold, allowing the pull-down current at the output port to flow to system ground through the second isolation transistor and the driving transistor. The forward voltage of the body diode in the first isolation transistor is less than the preset threshold. The minimum saturation voltage of the open-drain output circuit provided in this application meets the requirements of automotive-grade chips.

Description

Technical Field

[0001] This invention relates to the field of electronic circuits, and in particular to an open-drain output circuit and chip. Background Technology

[0002] As automotive-grade chips increasingly demand higher output signal swing, open-drain output circuits need to have lower saturation output voltages to support wider dynamic ranges. Traditional open-drain output circuits typically employ isolation high-voltage structures to handle potential positive or negative high voltages at the output. For example, when the output (OUT) is positively high-voltage, the driving transistor (such as a high-voltage MOSFET) of the open-drain output circuit directly bears the high voltage; when the output is negatively high-voltage, an isolation structure is needed to block the current path from the driving transistor to the OUT terminal to prevent large currents from burning out the circuit.

[0003] However, the isolation structure will correspondingly increase the minimum saturation voltage of the open-drain output circuit, thus failing to meet the requirements of automotive-grade chips for large output swing and extremely low saturation voltage. Summary of the Invention

[0004] This application provides an open-drain output circuit and chip to meet the requirements of automotive-grade chips for large output swing and extremely low saturation voltage.

[0005] In a first aspect, this application provides an open-drain output circuit, including a driving transistor, a first isolation transistor, a second isolation transistor, a control circuit, and an output port. Both the first and second isolation transistors include a body diode. The source of the driving transistor is connected to system ground, and the drain of the driving transistor is connected to a first terminal of the first isolation transistor and a first terminal of the second isolation transistor, respectively. The second terminals of the first and second isolation transistors are connected to the output port. The anodes of the body diodes of the first and second isolation transistors are both connected to the output port. The control terminal of the first isolation transistor is connected to system ground, and the control terminal of the second isolation transistor is connected to the output terminal of the control circuit. The input terminal of the circuit is connected to the output port; the first isolation transistor is configured to: conduct when the voltage at the output port is positive and greater than the forward voltage of the body diode in the first isolation transistor, so that the pull-down current of the output port flows to the system ground through the first isolation transistor and the driving transistor; and cut off when the voltage at the output port is less than the forward voltage of the body diode in the first isolation transistor; the control circuit is configured to: control the second isolation transistor to conduct when the voltage at the output port is positive and lower than a preset threshold, so that the pull-down current of the output port flows to the system ground through the second isolation transistor and the driving transistor; and control the second isolation transistor to cut off when the voltage at the output port is negative; wherein the forward voltage of the body diode in the first isolation transistor is less than the preset threshold.

[0006] In conjunction with the first aspect, in one possible implementation, the control circuit includes a voltage sampling module and a comparison module; the voltage sampling module is used to: acquire a sampling signal characterizing the voltage of the output port; the comparison module is used to: control the second isolation transistor to be turned on or off based on the voltage comparison result between the sampling signal and the preset threshold.

[0007] In conjunction with the first aspect, in one possible implementation, the voltage sampling module includes a detection circuit, and the comparison module includes a comparison circuit and a driving circuit; the comparison circuit is connected to both the detection circuit and the driving circuit; the detection circuit is used to: convert the sampled signal into a detection signal within a target level range; the comparison circuit is used to: output a control signal based on a voltage comparison result between the detection signal and the system ground, the control signal indicating whether the voltage at the output port is positive or negative; the driving circuit is used to: switch the operating mode based on the control signal, and generate a driving signal based on the acquired reference voltage, the driving signal being used to drive the second isolation transistor to turn on or off, the preset threshold being determined by the voltage of the driving signal and the on-state voltage of the second isolation transistor.

[0008] In conjunction with the first aspect, in one possible implementation, the detection circuit includes a first current mirror circuit, a first detection transistor, and a second detection transistor. The first current mirror circuit includes a first current branch and a second current branch. The first current branch is connected to a first terminal of the first detection transistor and the comparator circuit, respectively. The second current branch is connected to a first terminal of the second detection transistor and the comparator circuit, respectively. The control terminal of the first detection transistor is connected to the system ground, and the control terminal of the second detection transistor is connected to the output port. The second terminals of the first and second detection transistors are respectively connected to the system ground. The first current mirror circuit is used to: output a first bias current to the first detection transistor through the first current branch and output a second bias current to the second detection transistor through the second current branch, wherein the first bias current and the second bias current are the same. The first detection transistor and the second detection transistor form a differential input pair, which is used to: output a first detection signal and a second detection signal to the comparator circuit, wherein the first detection signal represents the control terminal voltage of the first detection transistor, and the second detection signal represents the control terminal voltage of the second detection transistor.

[0009] In conjunction with the first aspect, in one possible implementation, the detection circuit further includes a first protection circuit, which includes a first diode and a second diode; the anode of the first diode is connected to the control terminal of the second detection transistor, the cathode of the first diode is connected to the cathode of the second diode, and the anode of the second diode is connected to the system ground; the first protection circuit is used to protect the second detection transistor when the voltage at the output port is negative.

[0010] In conjunction with the first aspect, in one possible implementation, the comparison circuit includes a voltage comparator and a first switching circuit; the first input terminal of the voltage comparator is connected to the first terminal of the first detection transistor, the second input terminal of the voltage comparator is connected to the first terminal of the second detection transistor, the output terminal of the voltage comparator is connected to the control terminal of the first switching circuit, the first terminal of the first switching circuit is connected to the system ground, and the second terminal of the first switching circuit is connected to the driving circuit; the voltage comparator is used to: receive a first detection signal through the first input terminal, receive a second detection signal through the second input terminal, and output a first level signal when the second detection signal is greater than the first detection signal, the first level signal being used to control the first switching circuit to be off, and output a second level signal when the second detection signal is less than the first detection signal, the second level signal being used to control the first switching circuit to be on; the on / off state of the first switching circuit is related to the operating mode of the driving circuit.

[0011] In conjunction with the first aspect, in one possible implementation, the driving circuit includes a second current mirror circuit, a second switching circuit, a current-limiting resistor, and a voltage divider resistor network; the first terminal of the second current mirror circuit is connected to the first terminal of the second switching circuit and the reference voltage, the second terminal of the second current mirror circuit is connected to the second terminal of the second switching circuit and the first terminal of the current-limiting resistor, the third terminal of the second current mirror circuit is connected to the first terminal of the voltage divider resistor network, the second terminal of the current-limiting resistor is connected to the system ground, the control terminal of the second switching circuit is connected to the second terminal of the first switching circuit, and the second terminal of the voltage divider resistor network is connected to the control terminal of the second isolation transistor. The third terminal of the voltage divider network is connected to the control terminal of the second detection transistor, and the fourth terminal of the voltage divider resistor network is connected to the output port; the second current mirror circuit is used to output a stable bias current to the voltage divider resistor network, the amplitude of which is related to the resistance value of the current limiting resistor; the second switching circuit is used to control the opening or closing of the second current mirror circuit, the on / off state of the second switching circuit being related to the on / off state of the first switching circuit; the voltage divider resistor network is used to divide the reference voltage and the voltage of the output port based on the bias current, generate the driving signal based on the reference voltage after voltage division, and adjust the second detection signal based on the voltage of the output port after voltage division.

[0012] In conjunction with the first aspect, in one possible implementation, the driving circuit further includes a second protection circuit, which includes a third diode and a fourth diode; the anode of the third diode is connected to the reference voltage, the cathode of the third diode is connected to the cathode of the fourth diode and the power supply node, the anode of the fourth diode is connected to the output port, and the power supply node is connected to the first terminal of the second current mirror circuit and the first terminal of the second switching circuit; the second protection circuit is used to: clamp the voltage of the power supply node to the maximum value between the reference voltage and the voltage of the output port, so that the voltage divider resistor network divides the clamped voltage and protects the second isolation transistor.

[0013] In conjunction with the first aspect, in one possible implementation, the driving transistor is an NMOS transistor, the first isolation transistor is a PMOS transistor, and the second isolation transistor is an NMOS transistor.

[0014] Secondly, this application provides a chip that includes an open-drain output circuit as described in the first aspect or any possible implementation thereof.

[0015] In the technical solution provided in this application, the second isolation transistor is turned on when the first isolation transistor is turned off, so that the pull-down current of the output port flows to the system ground through the second isolation transistor and the drive transistor. This allows the minimum saturation voltage of the output port to be freed from the limitation of the conduction voltage of the body diode in the first isolation transistor, thus meeting the requirements of automotive-grade chips for large output swing and extremely low saturation voltage. The minimum saturation voltage refers to the minimum voltage output by the output port. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of an existing open-drain output circuit.

[0017] Figures 2 to 5 A schematic structural diagram of the open-drain output circuit provided in this application. Detailed Implementation

[0018] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] As automotive-grade chips increasingly demand higher output signal swing, open-drain output circuits need to have lower saturation output voltages to support wider dynamic ranges. Traditional open-drain output circuits typically employ isolation high-voltage structures to handle potential positive or negative high voltages at the output.

[0020] Figure 1 This is a schematic diagram of an existing open-drain output circuit. Figure 1 The open-drain output circuit shown has a diode D1 connected in series between the driver transistor MN1 and the output (OUT) port. Diode D1 is used to isolate the negative high voltage. The driver transistor MN1 can be a high-voltage MOSFET, and the isolation diode D1 is the body diode of the high-voltage MOSFET.

[0021] When the OUT terminal is at a positive high voltage, diode D1 conducts in the forward direction, and the positive high voltage is borne by the driving transistor MN1; when the OUT terminal is at a negative high voltage, diode D1 is reverse-biased and cut off, thereby isolating the current path from the driving transistor MN1 to the OUT terminal and reducing the probability of circuit burnout.

[0022] However, when this open-drain output circuit is operating, because diode D1 is always connected in series in the output path, the minimum saturation voltage of the open-drain output circuit is raised. In other words, the minimum saturation voltage of the open-drain output circuit is the sum of the diode's forward conduction voltage and the system ground potential (VSS in the figure). Therefore, this open-drain output circuit cannot meet the requirements of automotive-grade chips for large output swing and extremely low saturation voltage. The minimum saturation voltage refers to the minimum voltage output from the output port.

[0023] Therefore, this application provides an open-drain output circuit and chip, which can achieve an extremely low saturation voltage while ensuring that the open-drain output circuit can withstand negative high voltage, thereby meeting the requirements of automotive-grade chips.

[0024] The following is combined Figures 2 to 5 This application provides a detailed description of the technical solution provided.

[0025] Figure 2 A schematic structural diagram of an open-drain output circuit provided in this application. Figure 2 The open-drain output circuit 200 shown includes a driving transistor 210, a first isolation transistor 220, a second isolation transistor 230, a control circuit 240, and an output port 250. Both the first isolation transistor 220 and the second isolation transistor 230 include a body diode, which is not shown in the figure.

[0026] like Figure 2As shown, the source of the driving transistor 210 is connected to system ground, and the drain of the driving transistor 210 is connected to the first terminal of the first isolation transistor 220 and the first terminal of the second isolation transistor 230, respectively. The second terminals of the first isolation transistor 220 and the second isolation transistor 230 are connected to the output port 250, respectively. The anodes of the body diodes of the first isolation transistor 220 and the second isolation transistor 230 are both connected to the output port 250. The control terminal of the first isolation transistor 220 is connected to system ground, the control terminal of the second isolation transistor 230 is connected to the output terminal of the control circuit 240, and the input terminal of the control circuit 240 is connected to the output port 250.

[0027] The first isolation transistor 220 is configured to: turn on when the voltage at the output port 250 is positive and greater than the forward voltage of the body diode in the first isolation transistor 220, allowing the pull-down current at the output port 250 to flow to system ground through the first isolation transistor 220 and the drive transistor 210; or, in other words, allow the pull-down current from / flowing through the output port 250 to flow to system ground through the first isolation transistor 220 and the drive transistor 210. It is turned off when the voltage at the output port 250 is less than the forward voltage of the body diode in the first isolation transistor 220.

[0028] Specifically, the first isolation transistor 220 conducts when the voltage at the output port 250 is positive and greater than the forward voltage of the body diode in the first isolation transistor 220. This can be understood as the body diode in the first isolation transistor 220 conducting in the forward direction when the voltage at the output port 250 is positive and greater than the forward voltage of the body diode in the first isolation transistor 220. When the first isolation transistor 220 is off, this can be understood as the body diode in the first isolation transistor 220 being reverse-biased and off, thereby isolating the driving transistor 210 from the negative voltage when the output port 250 is negative, and protecting the driving transistor 210.

[0029] The control circuit 240 is used to: control the second isolation transistor 230 to conduct when the voltage at the output port 250 is positive and lower than a preset threshold, so that the pull-down current at the output port 250 flows to system ground through the second isolation transistor 230 and the drive transistor 210; and control the second isolation transistor 230 to turn off when the voltage at the output port 250 is negative. The forward voltage of the body diode in the first isolation transistor 220 is less than the preset threshold.

[0030] It should be noted that in this application, the driving transistor 210 is in the ON state and is used to withstand the high voltage from the output port 250. The working principle of the open-drain output circuit 200 is explained below.

[0031] When the voltage at the output port 250 is positive and greater than a preset threshold, only the first isolation transistor 220 is turned on. At this time, the pull-down current of the output port 250 flows to the system ground through the first isolation transistor 220 and the driving transistor 210.

[0032] When the voltage at the output port 250 is a positive voltage less than a preset threshold and greater than the conduction voltage of the body diode in the first isolation transistor 220, both the first isolation transistor 220 and the second isolation transistor 230 are turned on. At this time, the pull-down current of the output port 250 flows into the driving transistor 210 through the parallel first isolation transistor 220 and the second isolation transistor 230, and then flows to the system ground through the driving transistor 210.

[0033] When the voltage at output port 250 is positive and less than the forward voltage of the body diode in the first isolation transistor 220, only the second isolation transistor 230 is turned on. At this time, the pull-down current of output port 250 flows to system ground through the second isolation transistor 230 and the driving transistor 210. It should be noted that when the voltage at output port 250 is positive and less than the forward voltage of the body diode in the first isolation transistor 220, the first isolation transistor 220 is turned off. If the second isolation transistor 230 is not set, the minimum saturation voltage of output port 250 will be pulled high due to the forward conduction voltage of the body diode of the first isolation transistor 220. After setting the second isolation transistor 230, the pull-down current of output port 250 can flow to system ground through the second isolation transistor 230 and the driving transistor 210, so that the minimum saturation voltage of output port 250 can continue to decrease and approach the potential of system ground, thereby meeting the requirements of automotive-grade chips for large output swing and extremely low saturation voltage.

[0034] When the voltage at the output port 250 is negative, since the anodes of the body diodes of the first isolation transistor 220 and the second isolation transistor 230 are connected to the output port 250, the body diodes in the first isolation transistor 220 and the second isolation transistor 230 are both in a reverse cutoff state. This allows the first isolation transistor 220 and the second isolation transistor 230 to isolate the driving transistor 210 from the negative voltage at the output port 250, thereby protecting the driving transistor 210.

[0035] Optionally, the driving transistor 210 is an NMOS transistor, the first isolation transistor 220 is a PMOS transistor, and the second isolation transistor 230 is an NMOS transistor, such as... Figure 2 As shown.

[0036] It should be noted that the control terminal of the first isolation transistor 220 can also be connected to other voltages, as long as the conduction control of the first isolation transistor 220 can be achieved. This application does not limit this.

[0037] In one possible implementation, the control circuit 240 includes a voltage sampling module and a comparison module.

[0038] The voltage sampling module is used to acquire a sampled signal representing the voltage at output port 250.

[0039] The comparison module is used to control the second isolation transistor 230 to turn on or off based on the voltage comparison result between the sampled signal and a preset threshold.

[0040] In this implementation, the control circuit 240 can sample the voltage at the output port 250 and control the second isolation transistor 230 to turn on or off based on the voltage comparison result between the sampled signal and a preset threshold. For example, when the sampled signal is greater than the preset threshold, the second isolation transistor 230 is turned off. When the sampled signal is positive and less than the preset threshold, the second isolation transistor 230 is turned on.

[0041] Optionally, the voltage sampling module includes a detection circuit, and the comparison module includes a comparison circuit and a drive circuit. The comparison circuit is connected to both the detection circuit and the drive circuit.

[0042] The detection circuit is used to convert the sampled signal into a detection signal within a target level range. This target level range can be determined by the operating level range of the comparator circuit.

[0043] The comparator circuit is used to output a control signal based on the comparison result between the detected signal and the voltage of the system ground.

[0044] The driving circuit is used to: acquire control signals and reference voltages, switch operating modes based on the control signals, and generate driving signals based on the reference voltages. These driving signals are used to turn the second isolation transistor 230 on or off. A preset threshold can be determined by the voltage of the driving signal and the on-state voltage of the second isolation transistor 230. Optionally, the control signal is also used to indicate whether the voltage at the output port 250 is positive or negative.

[0045] For example, when the second isolation transistor 230 is an NMOS transistor, the conduction condition should be: the voltage difference Vgs between the gate and source of the second isolation transistor 230 is greater than the conduction voltage Vth. The gate of the second isolation transistor 230 can be connected to a drive signal generated by a reference voltage, and the source of the second isolation transistor 230 can be connected to a sampling signal. Then, when the voltage at the output port 250 is positive and the sampling signal is less than the difference between the drive signal voltage and the conduction voltage, the second isolation transistor 230 is controlled to conduct; when the voltage at the output port 250 is positive and the sampling signal is greater than the difference between the drive signal voltage and the conduction voltage, the second isolation transistor 230 is controlled to turn off; when the voltage at the output port 250 is negative, the second isolation transistor 230 is controlled to turn off. In this example, the preset threshold is the difference between the reference voltage and the conduction voltage of the second isolation transistor 230. It should be understood that when the information indicated by the control signal is different, the driving circuit adopts different operating modes, thereby outputting different drive signals to control the second isolation transistor 230.

[0046] Figure 3 A schematic structural diagram of another open-drain output circuit provided in this application. Figure 3 In the control circuit 240 shown, the detection circuit includes a first current mirror circuit 241, a first detection transistor 242, and a second detection transistor 243. The comparison circuit includes a voltage comparator 244 and a first switching circuit 245. The drive circuit includes a second current mirror circuit 246, a second switching circuit 247, a current-limiting resistor 248, and a voltage divider resistor network 249.

[0047] The first current mirror circuit 241 includes a first current branch and a second current branch. The first current branch is connected to the first terminal of the first detection transistor 242 and the first input terminal of the voltage comparator 244, respectively. The second current branch is connected to the first terminal of the second detection transistor 243 and the second input terminal of the voltage comparator 244, respectively. The control terminal of the first detection transistor 242 is connected to system ground, and the control terminal of the second detection transistor 243 is connected to the output port 250 through a voltage divider resistor network 249. The second terminals of the first detection transistor 242 and the second detection transistor 243 are connected to system ground, respectively. The output terminal of the voltage comparator 244 is connected to the control terminal of the first switching circuit 245, and the first terminal of the first switching circuit 245 is connected to system ground. The second terminal of circuit 245 is connected to the control terminal of the second switching circuit 247 in the drive circuit. The first terminal of the second current mirror circuit 246 is connected to the first terminal of the second switching circuit 247 and the reference voltage (VCC1 in the figure). The second terminal of the second current mirror circuit 246 is connected to the second terminal of the second switching circuit 247 and the first terminal of the current limiting resistor 248. The third terminal of the second current mirror circuit 246 is connected to the first terminal of the voltage divider resistor network 249. The second terminal of the current limiting resistor 248 is connected to the system ground. The second terminal of the voltage divider resistor network 249 is connected to the control terminal of the second isolation transistor 230. The third terminal of the voltage divider resistor network 249 is connected to the control terminal of the second detection transistor 243. The fourth terminal of the voltage divider resistor network 249 is connected to the output port 250.

[0048] The first current mirror circuit 241 is used to: output a first bias current to the first detection transistor 242 through the first current branch, and output a second bias current to the second detection transistor 243 through the second current branch, wherein the first bias current and the second bias current are the same.

[0049] The first detection transistor 242 and the second detection transistor 243 form a differential input pair, which is used to output a first detection signal and a second detection signal to the voltage comparator 244. The first detection signal represents the control terminal voltage of the first detection transistor 242, and the second detection signal represents the control terminal voltage of the second detection transistor 243.

[0050] like Figure 3 As shown, the first current mirror circuit 241 includes switching transistors MP10, MP11, and MP12. The first detection transistor 242 is as follows... Figure 3 The switching transistor MP1 is used in the middle. The second detection transistor 243 is as follows: Figure 3 The switching transistor MP2 in the middle.

[0051] The sources of switching transistors MP10, MP11, and MP12 are connected to the reference voltage VCC1. The gates of switching transistors MP10, MP11, and MP12 are connected together. The drain of switching transistor MP10 is connected to the reference current source Ibias. The drain of switching transistor MP11 is shorted to the gate of switching transistor MP11, and the drain of switching transistor MP12 is shorted to the gate of switching transistor MP12.

[0052] The switching transistor MP10 is used to: convert the reference current source Ibias into the reference current inside the first current mirror circuit 241, and isolate the reference current source Ibias from the subsequent signal paths (such as switching transistors MP1 and MP2) to improve signal stability.

[0053] The switching transistor MP11 serves as the first current branch, used to transmit the first bias current to the switching transistor MP1. The first bias current is the drain-source current of the switching transistor MP11.

[0054] The switching transistor MP12 serves as the second current branch, used to transmit the second bias current to the switching transistor MP2. The second bias current is the drain-source current of the switching transistor MP12.

[0055] Optionally, by making the width-to-length ratio of switching transistor MP11 to switching transistor MP12 1:1, the first bias current and the second bias current are the same, thereby placing switching transistors MP1 and MP2 under the same circuit conditions and reducing subsequent interference to the comparator circuit.

[0056] The voltage comparator 244 is used to: receive a first detection signal through a first input terminal, receive a second detection signal through a second input terminal, and output a first level signal when the second detection signal is greater than the first detection signal, the first level signal being used to control the first switching circuit 245 to turn off; and output a second level signal when the second detection signal is less than the first detection signal, the second level signal being used to control the first switching circuit 245 to turn on. Figure 3 As shown, the first level is low and the second level is high.

[0057] The on / off state of the first switching circuit 245 is related to the operating mode of the drive circuit. For example, by switching the on / off state of the first switching circuit 245, the on / off state of the second switching circuit 247 can be switched, thereby further switching the on or off state of the second current mirror circuit 246.

[0058] Voltage comparator 244, etc. Figure 3 The comparator CMP1 is used in the circuit. Voltage comparator 244 operates at a reference voltage VCC1 and controls the switching on / off state of the first switching circuit 245 by comparing the gate voltages of switching transistors MP1 and MP2. The first switching circuit 245 is as follows: Figure 3 The switching transistor MN3 in the circuit. It should be noted that... Figure 3 The source of switching transistor MP1 is connected to the output of the first current mirror circuit 241 and the first input of voltage comparator 244, respectively. The source of switching transistor MP2 is connected to the output of the first current mirror circuit 241 and the second input of voltage comparator 244, respectively. The drains of switching transistors MP1 and MP2 are both connected to system ground. The gate of switching transistor MP1 is grounded through a resistor, and the gate of switching transistor MP2 is indirectly connected to output port 250. When the first bias current and the second bias current are the same, and switching transistors MP1 and MP2 are matched and operating in the saturation region, the difference between the drain-source voltage of switching transistor MP1 and the drain-source voltage of switching transistor MP2 is the same as the difference between their gate voltages. Therefore, voltage comparator 244 can be considered as being used to compare the gate voltages of switching transistors MP1 and MP2, thereby determining whether the voltage at output port 250 is positive or negative, and controlling the on / off state of the first switching circuit 245.

[0059] The second current mirror circuit 246 is used to output a stable bias current to the voltage divider resistor network 249. The second current mirror circuit 246 is as follows: Figure 3 The switching transistors MP5 and MP6 are used in the circuit. The magnitude of the bias current is related to the resistance value of the current-limiting resistor 248. The current-limiting resistor 248 is as follows... Figure 3 The resistor R1 in the middle.

[0060] The second switching circuit 247 is used to control the opening or closing of the second current mirror circuit 246. The on / off state of the second switching circuit 247 is related to the on / off state of the first switching circuit 245. For example, when the first switching circuit 245 is off, the second switching circuit 247 is off, and the second current mirror circuit 246 is on; when the first switching circuit 245 is on, the second switching circuit 247 is on. The second switching circuit 247 is as follows... Figure 3 The switching transistor MP4 in the circuit is turned off, and the second current mirror circuit 246 is turned off.

[0061] The voltage divider resistor network 249 is used to: divide the reference voltage and the voltage at the output port 250 based on the bias current, generate a drive signal based on the divided reference voltage, and adjust the second detection signal based on the divided voltage at the output port 250. The voltage divider resistor network 249 is as follows: Figure 3 The resistors are R2, R3, and R4. The resistance of R3 should be much greater than the resistance of R2.

[0062] The following is about Figure 3 The working principle of the open-drain output circuit shown will be explained.

[0063] When the voltage at output port 250 is positive and greater than the reference voltage VCC1, since the gate voltage of switch MP2 is higher than that of switch MP1, comparator CMP1 outputs a low level, causing switches MN3 and MN4 to turn off, and the second current mirror circuit 246 composed of switches MP5 and MP6 to turn on. The gate voltage of switch MN7 is a voltage divider of the reference voltage VCC1. Since resistor R3 is much larger than resistor R2, the gate voltage of switch MN7 is approximately the reference voltage VCC1. The VGS voltage of switch MN7 is approximately the difference between the reference voltage and the voltage at output port 250. This difference is less than the turn-on voltage of switch MN7, so the channel of switch MN7 is turned off. At the same time, switch MP9 is in the on state, and the body diode of switch MP9 is turned on. At this time, the pull-down current of output port 250 flows to system ground through switch MP9 and drive transistor MN8.

[0064] When the voltage at output port 250 gradually decreases and becomes less than the reference voltage VCC1, and the VGS voltage of switch MN7 is greater than the turn-on voltage of switch MN7, the channel of switch MN7 opens. At this time, since switch MP9 is also in the turn-on state and its body diode is turned on, the pull-down current of output port 250 flows to drive transistor MN8 through switch MP9 and switch MN7, and then to system ground.

[0065] When the voltage at output port 250 continues to decrease until it falls below the forward voltage of the body diode in switching transistor MP9, switching transistor MP9 turns off. At this time, because the channel of switching transistor MN7 is open, the pull-down current of output port 250 flows to system ground through switching transistor MN7 and driving transistor MN8. Due to the presence of switching transistor MN7, the voltage at output port 250 can continue to decrease, thus allowing the minimum saturation voltage of output port 250 to be freed from the limitation of the forward voltage of the body diode in switching transistor MP9.

[0066] When the voltage at output port 250 drops to a negative level, since the gate voltage of switch MP2 is lower than that of switch MP1, comparator CMP1 outputs a high level, turning on switch MN3 and switch MP4, while turning off the second current mirror circuit 246 formed by switches MP5 and MP6. At this time, the channel of switch MN7 is closed and its body diode is reverse-biased. Simultaneously, the body diode in switch MP9 is in a reverse-biased state, therefore no negative current flows from output port 250 to drive transistor MN8, thus achieving the negative voltage isolation function.

[0067] In the technical solution provided in this application, by setting a first isolation transistor and a second isolation transistor, the open-drain output circuit can be guaranteed to withstand negative high voltage while achieving extremely low saturation voltage, thereby meeting the requirements of automotive-grade chips.

[0068] Figure 3 In the open-drain output circuit shown, when the voltage at output port 250 continuously decreases to a negative high voltage, the maximum value of VGS of switching transistor MP2 is the difference between the voltage at output port 250 and the reference voltage VCC1. Therefore, the VGS withstand voltage requirement for switching transistor MP2 is relatively high, which in turn places higher demands on the withstand voltage process of switching transistor MP2. If the VGS withstand voltage level of switching transistor MP2 is low, it may cause damage to switching transistor MP2.

[0069] Furthermore, when the voltage at output port 250 is a positive high voltage, the VGS voltage of switching transistor MN7 is approximately the difference between the reference voltage and the voltage at output port 250. It can be seen that the maximum withstand voltage that output port 250 can withstand is limited by the VGS withstand voltage of switching transistor MN7, thus imposing requirements on the VGS withstand voltage of switching transistor MN7. If the VGS withstand voltage level of switching transistor MN7 is low, it may cause damage to switching transistor MN7.

[0070] Therefore, this application reduces the voltage difference between the gate and source of the switching transistor MP2, and the voltage difference between the gate and drain, by adding a first protection circuit, thereby protecting the switching transistor MP2 and reducing the VGS withstand voltage requirement for the switching transistor MP2. Figure 3 As shown, the first protection circuit includes a first diode D1 and a second diode D2. The anode of the first diode D1 is connected to the gate of the switching transistor MP2, the cathode of the first diode D1 is connected to the cathode of the second diode D2, and the anode of the second diode D2 is connected to system ground.

[0071] It should be noted that, Figure 3 Resistor R5 is used to limit the current flowing into the drain of switch MN3 when switch MN3 is turned on, thereby protecting switch MN3. Resistor R6 is used to limit the current flowing into switch MP2, first diode D1, and second diode D2, thereby protecting switch MP2, first diode D1, and second diode D2.

[0072] To reduce the withstand voltage requirement of the switching transistor MN7, or to increase the maximum withstand voltage of the output port 250, a second protection circuit can be added to the open-drain output circuit. This second protection circuit includes a third diode D3 and a fourth diode D4, such as... Figure 4 As shown. The anode of the third diode D3 is connected to the reference voltage, the cathode of the third diode D3 is connected to both the cathode of the fourth diode D4 and the power supply node, and the anode of the fourth diode D4 is connected to the output port 250. The power supply node is connected to the first terminal of the second current mirror circuit 246 and the first terminal of the second switching circuit 247, respectively. The power supply node is as follows... Figure 4 The X node in the [theory / system].

[0073] like Figure 4 As shown, the third diode D3 and the fourth diode D4 are used to clamp the voltage Vx of the power supply node to the maximum value between the reference voltage and the voltage at the output port 250, causing the voltage divider network 249 to divide the clamped voltage, thereby protecting the second isolation transistor 230. It should be understood that the voltage Vx of the power supply node is the maximum value between the reference voltage and the voltage at the output port 250.

[0074] and Figure 3 Compared to the open-drain output circuit shown, Figure 4 In the open-drain output circuit, the gate voltage of the switching transistor MN7 is a voltage divider of Vx.

[0075] For example, when the voltage at output port 250 is positive and greater than the reference voltage VCC1, comparator CMP1 outputs a low level, switching transistors MN3 and MN4 are turned off, and the second current mirror circuit 246 is turned on. The gate voltage of switching transistor MN7 is a voltage divider of Vx. Since resistor R3 is much larger than resistor R2, the gate voltage of switching transistor MN7 is approximately Vx. The VGS voltage of switching transistor MN7 is approximately the difference between Vx and the voltage at output port 250. This difference is less than the turn-on voltage of switching transistor MN7, so the channel of switching transistor MN7 is turned off. Simultaneously, since switching transistor MP9 is in the on state and its body diode is conducting, the pull-down current at output port 250 flows to system ground through switching transistor MP9 and drive transistor MN8. Here, Vx is the difference between the voltage at output port 250 and the forward conduction voltage of the third diode D3 / fourth diode D4.

[0076] When the voltage at output port 250 gradually decreases and falls below the reference voltage VCC1, Vx is the difference between the reference voltage VCC1 and the forward conduction voltage of the third diode D3 / fourth diode D4. When the VGS voltage of switch MN7 is greater than the conduction voltage of switch MN7, the channel of switch MN7 opens. At this time, since switch MP9 is also in the conducting state and its body diode is conducting, the pull-down current of output port 250 flows to the driver transistor MN8 through switch MP9 and switch MN7, and then to system ground through driver transistor MN8.

[0077] When the voltage at output port 250 continues to decrease until it falls below the forward voltage of the body diode in switching transistor MP9, switching transistor MP9 turns off. Vx is the difference between the reference voltage VCC1 and the forward voltage of the third diode D3 / fourth diode D4. At this time, since the channel of switching transistor MN7 is open, the pull-down current of output port 250 flows to system ground through switching transistor MN7 and driving transistor MN8.

[0078] When the voltage at output port 250 drops to a negative level, comparator CMP1 outputs a high level, switching transistors MN3 and MP4 turn on, and the second current mirror circuit 246 turns off. At this time, the gate and source of switching transistor MN7 are short-circuited through resistor R2, the channel of switching transistor MN7 is closed, and the body diode is reverse-biased and cut off. Simultaneously, the body diode in switching transistor MP9 is in a reverse-biased cutoff state, therefore no negative current flows from output port 250 to the driving transistor MN8, thus achieving the function of isolating the negative voltage.

[0079] In addition, since the anode of the fourth diode D4 is connected to the output port 250, there will be no current flowing from Vx to the output port 250. At this time, Vx is the difference between the reference voltage VCC1 and the forward conduction voltage of the third diode D3 / fourth diode D4.

[0080] In this application, when a high voltage appears at the output port, the VGS voltage of the switching transistor MN7 is limited by a second protection circuit, and when the voltage at the output port is a negative high voltage, the gate and source of the switching transistor MN7 are short-circuited through a resistor, thereby reducing the withstand voltage requirement of VGS in the switching transistor MN7 and thus adapting to more processes.

[0081] It should be noted that, Figure 4 The resistor R5 is also used to limit the current flowing into the third diode D3, thereby protecting the third diode D3.

[0082] In one possible implementation, the drive circuit can also be connected to another independent power supply VCC2 to decouple the drive circuit from the reference voltage VCC1, such as... Figure 5 As shown. This implementation allows VCC1 to operate at a low voltage, while VCC2 can operate at a higher voltage, thus increasing the maximum withstand voltage of the output port to the sum of VCC2 and the output port voltage. Figure 4 compared to, Figure 5 The open-drain output circuit shown can improve the voltage withstand capability of the output circuit while saving space, thereby reducing the implementation cost.

[0083] This application also provides a chip that includes the open-drain output circuit as described in the foregoing embodiments.

[0084] The term "multiple" in this document refers to two or more. The character " / " generally indicates an "or" relationship between related objects; in formulas, " / " indicates a "division" relationship. Furthermore, it should be understood that in the description of this application, terms such as "first" and "second" are used only for descriptive purposes and should not be construed as indicating or implying relative importance or order. Connections in this application can be understood as electrical connections, and can be direct or indirect connections.

[0085] It is understood that, in the embodiments of this application, the order of the above-mentioned process numbers does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0086] It should be emphasized that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. An open-drain output circuit, comprising a driving transistor, characterized in that, Also includes: The system comprises a first isolation transistor, a second isolation transistor, a control circuit, and an output port, wherein both the first isolation transistor and the second isolation transistor include a body diode. The source of the driving transistor is connected to system ground, the drain of the driving transistor is connected to the first terminal of the first isolation transistor and the first terminal of the second isolation transistor, the second terminal of the first isolation transistor and the second terminal of the second isolation transistor are connected to the output port, the anode of the body diode of the first isolation transistor and the anode of the body diode of the second isolation transistor are both connected to the output port, the control terminal of the first isolation transistor is connected to system ground, the control terminal of the second isolation transistor is connected to the output terminal of the control circuit, and the input terminal of the control circuit is connected to the output port. The first isolation transistor is configured to: turn on when the voltage at the output port is positive and greater than the forward voltage of the body diode in the first isolation transistor, so that the pull-down current at the output port flows to the system ground through the first isolation transistor and the driving transistor; and turn off when the voltage at the output port is less than the forward voltage of the body diode in the first isolation transistor. The control circuit is used to: control the second isolation transistor to turn on when the voltage at the output port is positive and lower than a preset threshold, so that the pull-down current at the output port flows to the system ground through the second isolation transistor and the driving transistor; and control the second isolation transistor to turn off when the voltage at the output port is negative. Wherein, the forward voltage of the body diode in the first isolation transistor is less than the preset threshold.

2. The open-drain output circuit according to claim 1, characterized in that, The control circuit includes a voltage sampling module and a comparison module; The voltage sampling module is used to: acquire a sampling signal characterizing the voltage of the output port; The comparison module is used to control the second isolation transistor to turn on or off based on the voltage comparison result between the sampled signal and the preset threshold.

3. The open-drain output circuit according to claim 2, characterized in that, The voltage sampling module includes a detection circuit, and the comparison module includes a comparison circuit and a driving circuit. The comparison circuit is connected to both the detection circuit and the driving circuit. The detection circuit is used to: convert the sampled signal into a detection signal within the target level range; The comparison circuit is used to: output a control signal based on the comparison result between the detection signal and the voltage of the system ground; The driving circuit is used to: switch the operating mode based on the control signal, and generate a driving signal based on the acquired reference voltage. The driving signal is used to drive the second isolation transistor to turn on or off. The preset threshold is determined by the voltage of the driving signal and the on-state voltage of the second isolation transistor.

4. The open-drain output circuit according to claim 3, characterized in that, The detection circuit includes a first current mirror circuit, a first detection transistor, and a second detection transistor; The first current mirror circuit includes a first current branch and a second current branch. The first current branch is connected to the first terminal of the first detection transistor and the comparator circuit, respectively. The second current branch is connected to the first terminal of the second detection transistor and the comparator circuit, respectively. The control terminal of the first detection transistor is connected to the system ground. The control terminal of the second detection transistor is connected to the output port. The second terminals of the first detection transistor and the second detection transistor are connected to the system ground, respectively. The first current mirror circuit is used to: output a first bias current to the first detection transistor through the first current branch, and output a second bias current to the second detection transistor through the second current branch, wherein the first bias current and the second bias current are the same; The first detection transistor and the second detection transistor form a differential input pair, which is used to output a first detection signal and a second detection signal to the comparator circuit. The first detection signal represents the control terminal voltage of the first detection transistor, and the second detection signal represents the control terminal voltage of the second detection transistor.

5. The open-drain output circuit according to claim 4, characterized in that, The detection circuit further includes a first protection circuit, which includes a first diode and a second diode. The anode of the first diode is connected to the control terminal of the second detection transistor, the cathode of the first diode is connected to the cathode of the second diode, and the anode of the second diode is connected to the system ground. The first protection circuit is used to protect the second detection transistor when the voltage at the output port is negative.

6. The open-drain output circuit according to claim 5, characterized in that, The comparison circuit includes a voltage comparator and a first switching circuit; The first input terminal of the voltage comparator is connected to the first terminal of the first detection transistor, the second input terminal of the voltage comparator is connected to the first terminal of the second detection transistor, the output terminal of the voltage comparator is connected to the control terminal of the first switching circuit, the first terminal of the first switching circuit is connected to the system ground, and the second terminal of the first switching circuit is connected to the driving circuit. The voltage comparator is configured to: receive a first detection signal through a first input terminal, receive a second detection signal through a second input terminal, and output a first level signal when the second detection signal is greater than the first detection signal, wherein the first level signal is used to control the first switching circuit to be turned off; and output a second level signal when the second detection signal is less than the first detection signal, wherein the second level signal is used to control the first switching circuit to be turned on. The on / off state of the first switching circuit is related to the operating mode of the driving circuit.

7. The open-drain output circuit according to claim 6, characterized in that, The driving circuit includes a second current mirror circuit, a second switching circuit, a current-limiting resistor, and a voltage divider resistor network. The first terminal of the second current mirror circuit is connected to the first terminal of the second switching circuit and the reference voltage, the second terminal of the second current mirror circuit is connected to the second terminal of the second switching circuit and the first terminal of the current limiting resistor, the third terminal of the second current mirror circuit is connected to the first terminal of the voltage divider resistor network, the second terminal of the current limiting resistor is connected to the system ground, the control terminal of the second switching circuit is connected to the second terminal of the first switching circuit, the second terminal of the voltage divider resistor network is connected to the control terminal of the second isolation transistor, the third terminal of the voltage divider resistor network is connected to the control terminal of the second detection transistor, and the fourth terminal of the voltage divider resistor network is connected to the output port. The second current mirror circuit is used to: output a stable bias current to the voltage divider resistor network, the magnitude of which is related to the resistance value of the current limiting resistor; The second switching circuit is used to control the opening or closing of the second current mirror circuit, and the on / off state of the second switching circuit is related to the on / off state of the first switching circuit. The voltage divider resistor network is used to: divide the reference voltage and the voltage of the output port based on the bias current, generate the drive signal based on the reference voltage after voltage division, and adjust the second detection signal based on the voltage of the output port after voltage division.

8. The open-drain output circuit according to claim 7, characterized in that, The driving circuit also includes a second protection circuit, which includes a third diode and a fourth diode. The anode of the third diode is connected to the reference voltage, the cathode of the third diode is connected to the cathode of the fourth diode and the power supply node, the anode of the fourth diode is connected to the output port, and the power supply node is connected to the first terminal of the second current mirror circuit and the first terminal of the second switching circuit. The second protection circuit is used to clamp the voltage of the power supply node to the maximum value between the reference voltage and the voltage of the output port, so that the voltage divider resistor network divides the clamped voltage.

9. The open-drain output circuit according to claim 1, characterized in that, The driving transistor is an NMOS transistor, the first isolation transistor is a PMOS transistor, and the second isolation transistor is an NMOS transistor.

10. A chip, characterized in that, It includes an open-drain output circuit as described in any one of claims 1 to 9.

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