A control circuit and control method for compensating for CAN port leakage

Abstract

The application discloses a control circuit for compensating CAN port leakage, comprising a CAN driving circuit and a CAN port network, and further comprising a compensation circuit connected to the cathode of a diode in the CAN driving circuit, wherein the compensation circuit injects a compensation current when detecting that the cathode voltage of the diode is lower than a common-mode voltage, and disconnects the compensation current when the cathode voltage of the diode is higher than the common-mode voltage. The application compensates for the problem that the reverse recovery current of the diode causes a differential voltage between CANH and CANL when switching from dominant to recessive, thereby affecting the bit width symmetry of the CAN bus, and compensates for the problem that the leakage of the parasitic PNP transistor causes a common-mode level mutation when switching from dominant to recessive, thereby causing electromagnetic interference of the CAN transceiver.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of CAN transceivers, and more particularly relates to a control circuit and a control method for compensating for CAN port leakage. BACKGROUND

[0002] As shown in the structural schematic diagram of the prior art CAN transceiver: composed of a CAN drive circuit and a CAN port network. Figure 1 According to ISO11898-2-2024, the CAN port network is composed of two differential load resistors RL, a differential load capacitor C2 and a split termination capacitor C1. The CAN drive circuit is composed of an explicit drive circuit, an implicit drive circuit and an anti-backflow circuit. Among them, the explicit drive circuit is composed of a bias current Ibias, four switches S1-S4, current leaks PM1 and PM2, and current mirrors NM1 and NM2.

[0003] According to ISO11898-2-2024, the implicit drive circuit is composed of a fixed bias power supply Vbus_Bias and two differential input resistors Rdiff.

[0004] The anti-backflow circuit is composed of diode D1 and PM3, and diode D2 and NM3 also compose an anti-backflow circuit, and the function of the anti-backflow circuit is to completely isolate the CAN port voltage from the internal VCC and GND of the chip, avoiding leakage and causing system abnormalities.

[0005] The specific working principle is as follows:

[0006] When the switches S1 and S2 are closed and the switches S3 and S4 are opened, PM1 and PM2 form a current leak, and NM1 and NM2 form a current mirror, which mirrors the bias current Ibias to the CAN bus. According to ISO11898-2-2024, the typical value of the differential load resistor RL is 60Ω, and the typical value of the differential input resistor Rdiff is 35KΩ, so the differential voltage of the CAN bus CANH-CANL=Ibias×(RL / / 2Rdiff)≈Ibias×RL, at this time, the CAN is in an explicit state.

[0007] When the switches S1 and S2 are opened and the switches S3 and S4 are closed, PM1 and PM2 will not form a current leak, and NM1 and NM2 will not form a current mirror, PM2 and NM2 will be turned off, and the bias voltage Vbus_Bias will pull the CAN bus port CANH and CANL to Vbus_Bias through the differential input resistor Rdiff, so the differential voltage of the CAN bus CANH-CANL=Vbus_Bias-Vbus_Bias=0, at this time, the CAN is in an implicit state.

[0008] ​

[0009] Reference Figure 1 The existing CAN transceiver structure diagram shows that when the CAN bus is switched from the dominant state to the recessive state, the diode is switched from the conduction state to the cut-off state, and because the diodes all have reverse recovery time, current still flows through the diode into the CAN port load resistor RL in the reverse recovery time, a differential voltage generated is incorrectly identified as the CAN dominant state, thereby affecting the CAN bus bit width symmetry.

[0010] Meanwhile, in order to meet the cost reduction and efficiency improvement, the BCD process is often used to replace the SOI process in the actual circuit design process.

[0011] Reference Figure 2 As shown in the cross-sectional view of the diode with a parasitic parameter, the diode will parasitically form a triode PNP, the anode of the diode constitutes the emitter of the parasitic triode, the cathode of the diode constitutes the base of the parasitic triode, and the substrate of the wafer is fixed to the ground to constitute the collector of the parasitic triode; in the conduction stage of the diode, the parasitic triode will also be turned on to produce leakage.

[0012] Reference Figure 3 As shown in the CAN port structure diagram with a parasitic triode, when the CAN bus is switched from the dominant state to the recessive state, the diode D1 extracts current I1 from the node parasitic capacitor C3 in the reverse recovery time, part of the current I1a is discharged to the ground through the parasitic triode Q1; the other part of the current I1b flows through the diode D1 and is injected into the CAN port; similarly, the diode D2 extracts current from the bias power supply Vbus provided on the CAN port in the reverse recovery time, part of the current I2a is discharged to the ground through the parasitic triode Q2; the other part of the current I2b flows through the node parasitic capacitor C4; because the node parasitic capacitor C3 of the anode of the diode D1 is much smaller than the CAN port network capacitors C1 and C2, and most of the current I1a is discharged to the ground through the parasitic triode, only a small amount of current I1b flows into the CAN port, in short, the CAN port is charged less; while the diode D2 extracts all the current I2 from the CAN port in the reverse recovery time, in short, the CAN port is discharged more;

[0013] Reference Figure 4 As shown in the CANH and CANL port voltage change diagram in the recessive switching process, when the dominant state is switched to the recessive state, the reverse current of the diode causes the differential voltage of CANH and CANL, which affects the CAN bus bit width symmetry; at the same time, the leakage of the parasitic triode causes the discharge to be greater than the charge, the overall pull-down of the CAN port network common-mode voltage causes the common-mode level to jump, thereby causing the CAN transceiver electromagnetic interference problem. SUMMARY

[0014] To solve the problem that when the dominant state is switched to the recessive state, the compensation diode reverse recovery current causes the differential voltage of CANH and CANL, thereby affecting the CAN bus bit width symmetry, and when the dominant state is switched to the recessive state, the compensation parasitic transistor PNP leakage causes the common mode level mutation, thereby causing the CAN transceiver electromagnetic interference, the application provides a control circuit and a control method for compensating CAN port leakage, when the CAN bus is switched from the dominant state to the recessive state, a compensation circuit is introduced, a compensation current IC is injected by detecting that the diode cathode voltage is lower than the common mode voltage Vbus_Bias, and the problems caused by the diode reverse recovery current and the parasitic transistor leakage in the prior art are solved.

[0015] According to an aspect of the application, a control circuit for compensating CAN port leakage is provided, which comprises a CAN drive circuit and a CAN port network, and further comprises a compensation circuit connected to the cathode of a diode in the CAN drive circuit, the compensation circuit injects a compensation current when detecting that the diode cathode voltage is lower than the common mode voltage, and disconnects the compensation current when the diode cathode voltage is higher than the common mode voltage.

[0016] As a further technical solution, the compensation circuit comprises a negative feedback loop and a voltage detection branch, the negative feedback loop maps the reference voltage to the first resistor, and then copies the current flowing through the first resistor to all current leakage branches through the current leakage, and the voltage detection branch is used to detect the cathode voltage of the diode.

[0017] As a further technical solution, the compensation circuit comprises two compensation branches connected to the cathodes of diodes D1 and D2, and when detecting that the cathode voltages VB1 and VB2 of diodes D1 and D2 are lower than the common mode voltage, the switch is closed to inject a compensation current.

[0018] As a further technical solution, in the negative feedback loop, the positive end of the operational amplifier is connected to the reference voltage, the output end is connected to the gate end of NMOS tube NM1, the drain end of NMOS tube NM1 is connected to the drain end and the gate end of PMOS tube PM11, respectively, the negative end of the operational amplifier and the source end of NMOS tube NM1 are connected to the first resistor, and PMOS tube PM11, PMOS tube PM12, PMOS tube PM13 and PMOS tube PM14 together constitute the current leakage.

[0019] As a further technical solution, the voltage detection branch is composed of a current mirror, an anti-backflow diode and a second resistor, the current mirror is composed of NMOS tube NM12, NMOS tube NM13 and NMOS tube NM14, the source end of each NMOS tube is connected to the anode of the anti-backflow diode, the cathode of the anti-backflow diode is connected to the second resistor, and the second resistor is connected to the first resistor at the ground.

[0020] As a further technical solution, in the detection When the voltage of VB1 is lower than the common-mode voltage Vbus_Bias, NMOS NM13 is turned on, the branch circuit injects VB1 through NMOS NM13 and the anti-inrush diode D12, and the voltage of VB1 is raised. When the voltage of VB1 is higher than the common-mode voltage Vbus_Bias, NMOS NM13 is turned off, the branch circuit is disconnected, and the voltage of VB1 is lowered.

[0021] As a further technical solution, when the voltage of VB2 is lower than the common-mode voltage Vbus_Bias, NMOS NM14 is turned on, the branch circuit injects VB2 through NMOS NM14 and the anti-inrush diode D13, and the voltage of VB2 is raised. When the voltage of VB2 is higher than the common-mode voltage Vbus_Bias, NMOS NM14 is turned off, the branch circuit is disconnected, and the voltage of VB2 is lowered.

[0022] According to an aspect of the present application, a control method for compensating for CAN port leakage is provided, and the control circuit for compensating for CAN port leakage is used to introduce a compensation circuit when the CAN bus is switched from a dominant state to a recessive state, the compensation circuit is used to detect the cathode voltage of a diode, and when the cathode voltage of the diode is lower than the common-mode voltage, a compensation current is injected, and when the cathode voltage of the diode is higher than the common-mode voltage, the compensation current is disconnected.

[0023] According to an aspect of the present application, a CAN transceiver is provided, which is configured with the control circuit for compensating for CAN port leakage.

[0024] Compared with the prior art, the present application has the following advantages:

[0025] 1. When the CAN bus is switched from a dominant state to a recessive state, the present application introduces a compensation circuit, detects the cathode voltage of a diode, and injects a compensation current IC when the cathode voltage of the diode is lower than the common-mode voltage Vbus_Bias, thereby compensating for the differential voltage of CANH and CANL caused by the reverse recovery current of the diode, and thereby affecting the bit width symmetry of the CAN bus.

[0026] 2. When the CAN bus is switched from a dominant state to a recessive state, the present application introduces a compensation circuit, detects the cathode voltage of a diode, and injects a compensation current IC when the cathode voltage of the diode is lower than the common-mode voltage Vbus_Bias, thereby compensating for the common-mode level mutation caused by the leakage of the parasitic transistor PNP, and thereby causing the electromagnetic interference problem of the CAN transceiver. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings used in the embodiments or prior art description will be briefly described below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0028] ​Figure 1 Figure for prior art structure example.

[0029] Figure 2 Figure for diode profile with parasitic triode parameters.

[0030] Figure 3 Figure for CAN port structure schematic with parasitic triode.

[0031] Figure 4 Figure for CAN port voltage change schematic during show and hide switching process.

[0032] Figure 5 Figure for circuit structure schematic provided by the embodiment of the present application.

[0033] Figure 6 Figure for circuit implementation schematic provided by the embodiment of the present application.

[0034] Figure 7 Figure for CAN port voltage optimization schematic after compensation of the embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the embodiment of the present application clearer, the technical scheme in the embodiment of the present application will be described clearly and completely below in combination with the drawings in the embodiment of the present application. Obviously, the described embodiment is a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the present application. In addition, the technical features in each embodiment or single embodiment provided by the present application can be combined with each other at will to form new technical scheme, and the combination is not restricted by the order of steps and / or structure composition mode, but should be based on the realization by those skilled in the art. When the combination of technical scheme appears contradictory or cannot be realized, it should be considered that the combination of technical scheme does not exist, and is not within the protection scope required by the present application.

[0036] The embodiment of the present application provides a control circuit for compensating CAN port leakage, which comprises a CAN driving circuit and a CAN port network, and further comprises a compensation circuit connected to the cathode of a diode in the CAN driving circuit. The compensation circuit injects a compensation current when detecting that the cathode voltage of the diode is lower than a common mode voltage, and disconnects the compensation current when the cathode voltage of the diode is higher than the common mode voltage.

[0037] Figure 5 Figure for structure schematic for compensating CAN port leakage, compared with Figure 3The compensation circuit is added, which determines whether the switches S5 and S6 are closed or opened by detecting the voltage state of VB1 and VB2. When the switches S5 and S6 are closed, the currents Ic1 and Ic2 are injected into the cathodes of the diodes D1 and D2 respectively, and the voltages of VB1 and VB2 are quickly pulled up respectively, so that the diodes and the triodes quickly turn into the off state to eliminate the leakage effect. When the CAN port voltage reaches the preset value Vbias_Bus of the recessive driving voltage, the switches S5 and S6 are opened to eliminate the influence of the compensation circuit on the CAN port network.

[0038] The specific working principle is as follows:

[0039] When the CAN bus is switched from the dominant to the recessive, due to the reverse recovery current of the diode and the parasitic leakage of the triode, the CAN bus port voltage is pulled down, and the cathode voltage VB1 of the diode D1 is also pulled down synchronously. The compensation circuit detects that the cathode voltage VB1 of the diode D1 is pulled down, closes the switch S5, and injects the compensation current Ic1 into the cathode end of the diode D1 to quickly pull up the voltage VB1, so that the diode D1 and the triode Q1 quickly turn into the off state to eliminate the leakage. When the CAN port voltage reaches the preset value Vbias_Bus of the recessive driving voltage, the switch S5 is opened to eliminate the influence of the compensation circuit on the CAN port network.

[0040] Similarly, when the compensation circuit detects that the cathode voltage VB2 of the diode D2 is lower than Vbias_Bus, the switch S6 is closed, and the compensation current Ic2 is injected into the cathode end of the diode D2 to quickly pull up the voltage VB2, so that the diode D2 and the triode Q2 quickly turn into the off state to eliminate the leakage. When the cathode voltage VB2 of the diode reaches the preset value Vbias_Bus of the recessive driving voltage, the switch S6 is opened to eliminate the influence of the compensation circuit on the CAN port network.

[0041] In Figure 6 , the positive terminal of the operational amplifier OP is connected to the reference voltage VREF, the output terminal of the operational amplifier OP is connected to the gate terminal of NM1, the drain terminal of NM1 is connected to the drain terminal and gate terminal of PM11 respectively, and the negative terminal of the operational amplifier OP and the source terminal of NM1 are connected to the resistor R1. Here, a negative feedback loop is formed, and the reference voltage VREF is mapped to the resistor R1 by using the virtual short principle of the operational amplifier, i.e. .

[0042] The PM11~PM14 form a current mirror to copy the current I flowing through the resistor R1 to all current mirror branches. The current I flowing through each branch will flow through the current mirror composed of NM12~NM14. As long as the sizes of NM12~NM14 are consistent, it can be known from the MOS tube current formula that I, Kn, , VTH is same, deduce NM12~NM14 VGS is same.

[0043] Note: I represents the circuit size of each branch; Kn represents the device parameters related to the process; W represents the width of the device; L represents the length of the device; VGS represents the gate-source voltage of the device; VTH represents the threshold voltage of the device; VD represents the on-voltage drop of the diode.

[0044] VB1 and VB2 voltage detection circuit is composed of NM12~NM14 current mirror, anti-inrush diode D11~D13 and resistor R2.

[0045] From Kirchhoff's voltage law KVL, VGS+VD+I×R2=VGS+VD+VB1= VGS+VD+VB2,

[0046] The formula is simplified to .

[0047] From the formula , it can be seen that by adjusting value, the clamping voltage of VB1 and VB2 can be obtained, that is, adjusting the cathode voltage of diodes D1 and D2 in the prior art.

[0048] Specific implementation principle:

[0049] When detecting , NM13 is turned on, branch circuit I flows through NM13 and D12 to inject VB1, and VB1 voltage rises; when detecting , NM13 is turned off, branch circuit I is disconnected, and will not flow through NM13 and D12 to inject VB1, VB1 voltage drops; finally, VB1 will be clamped at . Similarly, VB2 will be clamped at .

[0050] Reference Figure 6 circuit diagram is applied to Figure 5 structure schematic diagram, VB1 and VB2 are connected to the cathode of diodes D1 and D2 in Figure 5 , because the cathode of diode D1 is connected to CANH after passing through MOS PM3, and the on-voltage drop of MOS PM3 is ignored, that is, VB1 voltage is equal to CANH voltage, set , to ensure that when the CAN bus is explicitly cut to implicit, it is maintained at common mode voltage ; similarly, set When the CAN bus is switched from dominant to recessive, the diode D2 anode voltage is less than or equal to VB2, that is, the base voltage of the transistor Q2 is greater than the emitter voltage, so the diode D2 and the transistor quickly turn off to eliminate the influence of the leakage current.

[0051] Reference Figure 7 As shown in the schematic diagram of the compensated CAN port voltage optimization of the application, after the leakage current is eliminated when the CAN bus is switched from dominant to recessive, the bias power supply Vbias_Bus of the recessive driving circuit adjusts the CAN port voltage to Vbias_Bus through the differential input resistor Rdiff.

[0052] Based on the same inventive concept as the foregoing embodiments, the application also provides a control method for compensating CAN port leakage current, which is implemented by using the control circuit for compensating CAN port leakage current, introduces a compensation circuit when the CAN bus is switched from dominant to recessive, and the compensation circuit is used for detecting the diode cathode voltage and injecting a compensation current when the diode cathode voltage is lower than the common-mode voltage, and disconnecting the compensation current when the diode cathode voltage is higher than the common-mode voltage.

[0053] Based on the same inventive concept as the foregoing embodiments, the application also provides a CAN transceiver configured with the control circuit for compensating CAN port leakage current.

[0054] In summary of the foregoing embodiments, the key technical features of the application are that a compensation circuit is introduced when the CAN bus is switched from dominant to recessive, a compensation current IC is injected by detecting the diode cathode voltage lower than the common-mode voltage Vbus_Bias, and the problems of the reverse recovery current of the diode and the leakage current of the parasitic transistor in the prior art are solved.

[0055] ① When the diode cathode voltage is detected to be lower than the common-mode voltage Vbus_Bias, a compensation current IC is injected.

[0056] ② When the diode cathode voltage is detected to be higher than the common-mode voltage Vbus_Bias, the compensation current IC is disconnected, and the common-mode voltage is maintained at Vbus_Bias in the recessive stage.

[0057] The terms "include" and "have" and any variations thereof in the specification and claims of the application and the above-described drawings are intended to cover the non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not have to be limited to the steps or units clearly listed, but can include other steps or units not clearly listed or inherent to the process, method, product or device.

[0058] It should be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the embodiments of the present application.

Claims

1. A control circuit for compensating for CAN port leakage, comprising a CAN driver circuit and a CAN port network, characterized in that, The compensation circuit comprises two compensation branches connected to cathodes of diodes D1 and D2 in the CAN driving circuit respectively; the diodes D1 and D2 are used for preventing reverse flow, wherein an anode of D1 is coupled to a power supply VCC port, a cathode is coupled to a CAN bus port CANH, an anode of D2 is connected to a CAN bus port CANL, and a cathode is coupled to a ground terminal; when cathode voltages VB1 and VB2 of the diodes D1 and D2 are detected to be lower than a common mode voltage, a switch is closed to inject a compensation current, and when the cathode voltages VB1 and VB2 are higher than the common mode voltage, the compensation current is disconnected; The compensation branch comprises a negative feedback loop and a voltage detection branch; the negative feedback loop maps a reference voltage to a first resistor, and then copies a current flowing through the first resistor to all current leakage branches via a current leakage; the voltage detection branch is used for detecting a cathode voltage of the diode; In the negative feedback loop, a positive terminal of an operational amplifier is connected to a reference voltage, an output terminal is connected to a gate terminal of an NMOS transistor NM11, a drain terminal of the NMOS transistor NM11 is connected to a drain terminal and a gate terminal of a PMOS transistor PM11, a negative terminal of the operational amplifier and a source terminal of the NMOS transistor NM11 are connected to the first resistor, and the PMOS transistor PM11, a PMOS transistor PM12, a PMOS transistor PM13 and a PMOS transistor PM14 together constitute a current leakage; wherein the drain terminal and the gate terminal of the PMOS transistor PM11 are connected, and the gate terminal of the PMOS transistor PM12 and the drain terminal of the NMOS transistor NM11 are connected; the drain terminal and the gate terminal of the NMOS transistor NM12 are connected to the drain terminal of the PMOS transistor PM12, the gate terminal is connected to the gate terminal of the PMOS transistor PM11, the drain terminal of the PMOS transistor PM13 and the drain terminal of the NMOS transistor NM11; the drain terminal of the PMOS transistor PM13 is connected to the drain terminal of the NMOS transistor NM13, and the gate terminal is connected to the gate terminals of the PMOS transistor PM12 and the PMOS transistor PM14; the drain terminal of the PMOS transistor PM14 is connected to the drain terminal of the NMOS transistor NM14; the source terminals of the PMOS transistors PM11 to PM14 are connected to power supplies respectively; The voltage detection branch comprises a current mirror, a reverse flow prevention diode and a second resistor; the current mirror comprises the NMOS transistor NM12, the NMOS transistor NM13 and the NMOS transistor NM14; the drain terminal of the NMOS transistor NM12 is connected to the gate terminal and the drain terminal of the PMOS transistor PM12, the gate terminal is further connected to the gate terminal of the NMOS transistor NM13, and the source terminal is connected to the anode of the reverse flow prevention diode D11; the cathode of the reverse flow prevention diode D11 is connected to one end of the second resistor, and the other end of the second resistor is grounded; the drain terminal of the NMOS transistor NM13 is connected to the drain terminal of the PMOS transistor PM13, the source terminal is connected to the anode of the reverse flow prevention diode D12, and the cathode of the reverse flow prevention diode D12 is connected to VB1; the drain terminal of the NMOS transistor NM14 is connected to the drain terminal of the PM14, the gate terminal is connected to the gate terminal of the NMOS transistor NM13, the source terminal is connected to the anode of the reverse flow prevention diode D13, and the cathode of the reverse flow prevention diode D13 is connected to VB2.

2. The control circuit for compensating CAN port leakage according to claim 1, wherein, When detecting , NMOS NM13 is turned on, and the branch circuit injects VB1 through NMOS NM13 and anti-inrush diode D12, and the voltage of VB1 rises; when detecting , NMOS NM13 is turned off, the branch circuit is disconnected, and the voltage of VB1 drops.

3. The control circuit for compensating CAN port leakage according to claim 1, wherein, When detecting , NMOS NM14 is turned on, and the branch circuit injects VB2 through NMOS NM14 and anti-inrush diode D13, and the voltage of VB2 rises; when detecting , NMOS NM14 is turned off, the branch circuit is disconnected, and the voltage of VB2 drops.

4. A control method for compensating CAN port leakage, implemented by using the control circuit for compensating CAN port leakage according to any one of claims 1-3, characterized in that, A compensation circuit is introduced when the CAN bus is switched from dominant to recessive, said compensation circuit is used to detect the diode cathode voltage and inject a compensation current when the diode cathode voltage is detected to be below the common mode voltage and to disconnect the compensation current when the diode cathode voltage is detected to be above the common mode voltage.

5. A CAN transceiver, characterized by The control circuit for compensating the CAN port leakage according to any one of claims 1-3 is configured.

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