CN112736859A - Overcurrent diagnosis processing circuit and low-side drive circuit - Google Patents
Overcurrent diagnosis processing circuit and low-side drive circuit Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
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Abstract
The invention discloses an overcurrent diagnosis processing circuit and a low-side driving circuit, which utilize the cooperation of a current-limiting transistor and a transistor control circuit to adjust the current flowing through a low-side switch when the low-side driving circuit has overcurrent faults. Through the cooperation of the current-limiting transistor and the transistor control circuit, the low-side switch can be subjected to current-limiting protection when the low-side driving circuit has overcurrent faults. Because the MCU is not utilized in the fault diagnosis and processing process, and the switching speed of the current-limiting transistor is in nanosecond level, when an overcurrent fault occurs, the hardware response time of the overcurrent fault diagnosis and processing circuit is only microsecond level at the longest. The circuit has the advantages of no need of software to do any operation, quick response and low requirement on the power consumption of the circuit, thereby avoiding the damage to circuit devices and improving the safety.
Description
Technical Field
The invention relates to the field of circuits, in particular to an overcurrent diagnosis processing circuit and a low-side driving circuit.
Background
The low-side driving circuit is a circuit design for providing a long high level signal, a long low level signal or a pwm (pulse width modulation) signal to other controllers, please refer to fig. 1, and fig. 1 is a typical low-side driving circuit. Wherein U1 is a low side switch; r1 is a pull-down resistor that defaults to a low state prior to actuation; r2 is a current-limiting resistor, C1 is an input filter capacitor, and R2 and C1 form a filter circuit; r3 is a current-limiting voltage-dividing resistor, R4 is a pull-down voltage-dividing resistor, and R3 and R4 form a voltage-dividing diagnostic circuit; r5 is a current-limiting resistor, C2 is a filter capacitor of the diagnostic circuit, and R5 and C2 form a filter circuit; d1 is a bidirectional ESD (Electro-Static Discharge) diode, C3 is an ESD capacitor, and D1 and C3 are used for protecting the low-side switch from being damaged during ESD impact. In is a control input signal of the circuit, and is derived from an output of an MCU (micro controller Unit); the Diagout is a diagnosis output signal of the circuit, and the MCU judges whether a fault exists or not by sampling the voltage state of the Diagout; rloadThe pull-up resistor is connected with the Output of the controller, and the Output is an Output signal of the controller and provides a voltage state for the load end.
At present, fault diagnosis of low-side driving circuits mainly comprises SCB (short-circuit to power supply), SCG (short-circuit to ground) and OL (open circuit), and diagnosis requirements of different application conditions are different. When the low-side driving circuit is applied to Output a long high level signal and a long low level signal, if the low-side switch is turned off (Output is long and high), the MCU diagnoses whether the SCG and OL faults exist in the low-side driving circuit by sampling Diagout voltage; if the low-side switch is conducted (Output is long and low), the MCU diagnoses whether the low-side driving circuit has an SCB fault or not by sampling Diagout voltage analog values. When the low side driving circuit is applied to output the PWM signal, the MCU can diagnose whether the low side driving circuit has SCB, SCG, and OL by sampling the voltage state of Diagout during one sampling period. And the MCU diagnoses a corresponding fault by sampling the Diagout voltage state and performs corresponding post-processing. The diagnostic strategy of the low-side driving circuit is that the MCU samples the DiagOut voltage state through the AD port to determine whether a fault exists: for a low-side circuit which outputs signals with normal high and low levels, when a low-side switch is conducted, if no fault occurs, the MCU should sample a voltage value lower than a certain threshold, and if the Diagout voltage obtained by sampling of the MCU is higher than the threshold, the SCB fault of the low-side drive circuit can be judged; for a low-side driving circuit outputting a PWM signal, when the high and low levels change in a sampling period, the low-side driving circuit is judged to be in a normal condition, and if the Diagout voltage in the sampling period enables the I/O port of the MCU to be kept at a normal high level, the low-side driving circuit is judged to have an SCB fault.
Of the three types of failures, SCB (short to supply), SCG (short to ground), and OL (open), SCB is the most damaging to the controller when the low-side driver circuit is in the on state. The inventors found that the following problems exist when using the fault diagnosis circuit proposed in the prior art: if an SCB fault occurs, the diagnosis and processing time of the circuit needs several milliseconds or even several tens of milliseconds, and the short-circuit current during the fault can reach several tens of amperes, and a large current impact above the millisecond level has the following risks: burning low side switches, burning PCB traces, exceeding the turn-off time required for functional safety, and other safety risk issues. In summary, the failure diagnosis circuit proposed in the prior art has poor timeliness of failure confirmation and shutdown, and may damage circuit devices.
Therefore, it is necessary to provide a solution that can improve the failure confirmation and the shutdown timeliness.
It is noted that the information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Disclosure of Invention
The invention aims to provide an overcurrent diagnosis processing circuit and a low-side driving circuit, which are used for solving the problems that in the prior art, the timeliness of fault confirmation and turn-off is poor, and the risk of damaging circuit devices exists.
In order to solve the above technical problem, the present invention provides an over-current diagnosis processing circuit for an over-current diagnosis processing of a low-side driving circuit, the over-current diagnosis processing circuit comprising:
a current limiting transistor configured to adjust a magnitude of a current flowing through a low side switch in the low side driving circuit;
a transistor control circuit configured to implement a low-side drive function and adjust an operating state of the current-limiting transistor based on a current flowing through the low-side switch;
the working state of the current-limiting transistor comprises a conducting state and a switching-off state, and the current-limiting transistor is matched with the transistor control circuit to adjust the current flowing through the low-side switch when the low-side driving circuit has overcurrent faults.
Optionally, the current-limiting transistor adjusts the magnitude of the current flowing through the low-side switch by being turned on or off;
when the current flowing through the low-side switch is smaller than a set value, the current limiting transistor is in an off state, and when the low-side switch has an overcurrent fault, the current limiting transistor is in an on state to reduce the current flowing through the low-side switch.
Optionally, when the current flowing through the low-side switch is greater than a first threshold, the transistor control circuit adjusts the current-limiting transistor to be in a conducting state;
when the current flowing through the low-side switch is smaller than or equal to the first threshold value, the transistor control circuit adjusts the current-limiting transistor to be in an off state;
wherein the first threshold is a maximum current allowed to flow through the low side switch.
Optionally, the method further comprises:
the first filter circuit is configured to filter the output of the transistor control circuit and transmit the filtered output to the current limiting transistor.
Optionally, the transistor control circuit comprises a voltage dividing resistor and a sampling resistor;
one end of the divider resistor is connected with the low-side switch, the other end of the divider resistor and one end of the sampling resistor are connected to a first intersection point, and the other end of the sampling resistor is grounded;
the input end of the first filter circuit is connected with the first intersection point, the output end of the first filter circuit is connected with the control end of the current-limiting transistor, the first end of the current-limiting transistor is connected with the control end of the low-side switch, and the second end of the current-limiting transistor is grounded.
Optionally, the sampling resistor has a resistance value of R8, and the current-limiting transistor has a turn-on threshold voltage of VthThe first threshold is IthIn which Ith＝Vth/R8。
Optionally, when the low-side driver has an overcurrent fault, the current-limiting transistor is used for cooperating with the transistor control circuit to make the current flowing through the low-side switch be Ith。
Optionally, the first filter circuit includes a first filter capacitor and a first filter resistor;
one end of the first filter resistor is connected with the first intersection point, the other end of the first filter resistor and one end of the first filter capacitor are connected with the second intersection point, and the other end of the first filter capacitor is grounded;
the control end of the current-limiting transistor is connected with the second intersection point.
Optionally, the current limiting transistor is a bipolar transistor.
Based on the same inventive concept, the invention further provides a low-side driving circuit, which comprises the overcurrent diagnosis processing circuit described in any one of the above characteristic descriptions.
Compared with the prior art, the invention has the following beneficial effects:
1. the overcurrent diagnosis processing circuit provided by the invention utilizes the cooperation of the current-limiting transistor and the transistor control circuit to adjust the current flowing through the low-side switch when the low-side driving circuit has overcurrent faults. The transistor control circuit is used for adjusting the working state of the current limiting transistor based on the current flowing through the low-side switch, and the current limiting transistor is used for adjusting the current flowing through the low-side switch. Through the cooperation of the current-limiting transistor and the transistor control circuit, the low-side switch can be subjected to current-limiting protection when the low-side driving circuit has overcurrent faults. Because the MCU is not utilized in the fault diagnosis and processing process, and the switching speed of the current-limiting transistor is in nanosecond level, when an overcurrent fault occurs, the hardware response time of the overcurrent fault diagnosis and processing circuit is only microsecond level at the longest. The circuit has the advantages of no need of software to do any operation, quick response and low requirement on the power consumption of the circuit, thereby avoiding the damage to circuit devices and improving the safety.
2. When the low-side driving circuit has an overcurrent fault, the current limiting transistor is matched with the transistor control circuit to ensure that the current flowing through the low-side switch is constant to be the first threshold value, after the overcurrent fault disappears, the whole circuit continues to normally work without any software operation, so that the requirements on the power consumption of the current limiting resistor and the sampling resistor are very low, only a conventional small-packaged resistor is adopted, and the requirement on the type selection of the current capacity of the current limiting transistor can be reduced. The circuit can be an integrated chip with double channels, the circuit area of the whole module can be greatly reduced, and the hardware cost can be reduced.
The low-side driving circuit provided by the invention and the overcurrent diagnosis processing circuit belong to the same inventive concept, so that the low-side driving circuit has the same beneficial effects.
Drawings
FIG. 1 is a schematic diagram of a low-side driving circuit proposed in the prior art;
fig. 2 is a schematic diagram of a bottom side driving circuit with an overcurrent diagnosis processing circuit according to an embodiment of the present invention;
wherein, in fig. 1: u1-low side switch; r1-pull-down resistor, R2 is current-limiting resistor, C1-input filter capacitor, R3-current-limiting voltage-dividing resistor, R4-pull-down voltage-dividing resistor, R5-current-limiting resistor, C2-filter capacitor of diagnosis circuit, D1-bidirectional ESD (Electro-Static discharge) diode, C3-ESD capacitor, In-control input signal, Diagout-diagnosis output signal, R3-ESD capacitor, In-control input signal, diagnosis output signal, and diagnosis output signalloadPull-up resistor at load terminal, Output-Output signal of controller；
In fig. 2: r1-first resistor, R2-second resistor, R3-third resistor, R4-fourth resistor, R5-fifth resistor, R6-voltage-dividing resistor, R7-first filter resistor, C1-first capacitor, C2-second capacitor, C3-third capacitor, C4-first filter capacitor, D1-first diode, Q1-low-side switch, Q2-current-limiting transistor, R4-fourth resistor, R2-fourth resistor, R6-third resistor, Q4-low-side switch, R1-first diode, Q1-low-side switch, Q2-currentloadPull-up resistor, R8-sampling resistor, In-control input signal, DiagOut-diagnostic Output signal, Output-controller Output signal, 10-overcurrent diagnostic processing circuit, 100-transistor control circuit, 101-first filter circuit.
Detailed Description
The following describes in more detail embodiments of the present invention with reference to the schematic drawings. The advantages and features of the present invention will become more apparent from the following description. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
In the description of the present invention, it is to be understood that the terms "center", "upper", "lower", "left", "right", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present invention.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
Referring to fig. 2, an embodiment of the invention provides an over-current diagnosis processing circuit 10 for over-current diagnosis processing of a low-side driving circuit, where the over-current diagnosis processing circuit 10 includes: a current-limiting transistor Q2 and a transistor control circuit 100, wherein the current-limiting transistor Q2 is used for adjusting the current flowing through the low-side switch Q1 in the low-side driving circuit. The transistor control circuit 100 is used to implement a low-side driving function and adjust the operating state of the current-limiting transistor Q2 based on the current flowing through the low-side switch Q1. The operating state of the current-limiting transistor Q2 includes an on state and an off state, and the current-limiting transistor Q2 cooperates with the transistor control circuit 100 to adjust the current flowing through the low-side switch Q1 when the low-side driving circuit has an overcurrent fault.
Referring to fig. 2, when the low-side driving circuit normally works, the low-side switch Q1 is In an on state, when the low-side switch Q1 is turned on, because the load resistance on the path is large (generally 2k Ω), the current flowing through the low-side switch Q1 is small, at this time, the voltage on the transistor control circuit 100 is lower than the on voltage of the current-limiting transistor Q2, the current-limiting transistor Q2 keeps an off state, at this time, the current of the low-side switch Q1 is controlled by a control input signal In, and the low-side driving circuit keeps a normal working state; when the SCB fault occurs in the low side driver circuit, the conduction current flowing through the low side switch Q1 is large, and the voltage on the transistor control circuit 100 is higher than the turn-on voltage of the current-limiting transistor Q2, so that the current-limiting transistor Q2 is turned on. When the current-limiting transistor Q2 is turned on, the control terminal of the low-side switch Q1 is pulled low, the low-side switch Q1 is in an off state, and at this time, the voltage across the transistor control circuit 100 is reduced again, and the current-limiting transistor Q2 is turned off after the voltage is lower than the turn-on voltage of the current-limiting transistor Q2, so that the low-side switch Q1 is turned on again. This adjustment process repeats as long as the SCB failure is still present at this time, eventually reaching an equilibrium state. When the SCB fault disappears, the voltage on the transistor control circuit 100 is restored to be below the turn-on voltage of the current-limiting transistor Q2, so that the low-side switch Q1 is restored to a normal conduction state, and the low-side driving circuit can continue to operate normally. Because the switching speeds of the low-side switch Q1 and the current-limiting transistor Q2 in the circuit are both in nanosecond level, when an SCB fault occurs, the hardware response time of the over-current diagnosis processing circuit 10 is only in microsecond level at the longest, and the current flowing through the low-side switch Q1 is automatically limited during the SCB fault, when the SCB fault disappears, the low-side driving circuit can continue to work normally without any software operation, so that the power consumption requirement on devices in the circuit is very low, and the type selection requirement on the current capability of the low-side switch Q1 and the current-limiting transistor Q2 is also reduced. The low-side switch Q1 and the current-limiting transistor Q2 can be integrated on a dual-channel chip, so that the circuit area of the whole module can be greatly reduced, and the cost can be reduced.
The difference from the prior art is that the overcurrent diagnosis processing circuit 10 provided in the embodiment of the present invention utilizes the current-limiting transistor Q2 and the transistor control circuit 100 to cooperate to adjust the magnitude of the current flowing through the low-side switch Q1 when an overcurrent fault occurs in the low-side driving circuit. The transistor control circuit 100 is used to adjust the operating state of the current limiting transistor Q2 based on the current flowing through the low-side switch Q1, and the current limiting transistor Q2 is used to adjust the magnitude of the current flowing through the low-side switch Q1. Through the cooperation of the current-limiting transistor Q2 and the transistor control circuit 100, the low-side switch Q1 can be subjected to current-limiting protection when the low-side driving circuit has an overcurrent fault. Since the fault diagnosis and processing process does not utilize the MCU, and the switching speed of the current-limiting transistor Q2 is in the nanosecond level, when an overcurrent fault occurs, the hardware response time of the overcurrent fault diagnosis and processing circuit is only in the microsecond level at the longest. The circuit has the advantages of no need of software to do any operation, quick response and low requirement on the power consumption of the circuit, thereby avoiding the damage to circuit devices and improving the safety.
In the embodiment of the present invention, the current-limiting transistor Q2 is a bipolar transistor, and may be configured as an NPN transistor or a PNP transistor, and it is understood that the current-limiting transistor Q2 is a bipolar transistor, and has an on-threshold voltage at a base thereof, and when a voltage generated by a current flowing through the low-side switch Q1 across the resistor R8 is higher than an on-threshold voltage of the current-limiting transistor Q2, the current-limiting transistor Q2 starts to perform a current-limiting operation. For example, but not limited to, a triode or an MOS transistor or an igbt (insulated Gate Bipolar transistor) may also be selected, and other types of transistors may also be selected, which is not described in detail herein for the type of the current-limiting transistor Q2, and may be selected according to actual needs in specific applications. For convenience of explaining the technical solution of the present invention, in the embodiment of the present invention, the current-limiting transistors Q2 are all configured as bipolar transistors, and the implementation of other types of transistors is similar, which is not described herein again.
Further, the current-limiting transistor Q2 is turned on or off to adjust the current flowing through the low-side switch Q1. When the current flowing through the low-side switch Q1 is smaller than a set value, the current-limiting transistor Q2 is in an off state, and when the low-side switch Q1 has an overcurrent fault, the current-limiting transistor Q2 is in an on state to reduce the current flowing through the low-side switch Q1. Referring to fig. 2, since the current-limiting transistor Q2 and the low-side switch Q1 can be regarded as being connected in parallel in the circuit, when the current-limiting transistor Q2 is in a conducting state, the current-limiting transistor Q2 is equivalent to the current-limiting circuit of the low-side switch Q1, which can reduce the current flowing through the low-side switch Q1, and can effectively reduce the current flowing through the low-side switch Q1 to protect the low-side driving circuit when an overcurrent fault occurs.
Further, when the current flowing through the low-side switch Q1 is greater than a first threshold, the transistor control circuit 100 adjusts the current-limiting transistor Q2 to be in a conductive state. When the current through the low-side switch Q1 is less than or equal to the first threshold, the transistor control circuit 100 regulates the current-limiting transistor Q2 to be in an off state. Wherein the first threshold is a maximum current allowed to flow through the low-side switch Q1.
Optionally, with continued reference to fig. 2, the over-current diagnosis processing circuit 10 further includes a first filter circuit 101, where the first filter circuit 101 is configured to filter the output of the transistor control circuit 100 and transmit the filtered output to the current-limiting transistor Q2.
Specifically, the transistor control circuit 100 includes a voltage dividing resistor R6 and a sampling resistor R8. One end of the voltage-dividing resistor R6 is connected with the low-side switch Q1, the other end of the voltage-dividing resistor R6 is connected with one end of the sampling resistor R8 at a first intersection point, and the other end of the sampling resistor R8 is grounded. The input end of the first filter circuit 101 is connected to the first intersection, the output end of the first filter circuit 101 is connected to the control end of the current-limiting transistor Q2, the first end of the current-limiting transistor Q2 is connected to the control end of the low-side switch Q1, and the second end of the current-limiting transistor Q2 is grounded. It is understood that, when the current-limiting transistor Q2 is a bipolar transistor, the control terminal of the current-limiting transistor Q2 is a base of the bipolar transistor, and the first terminal and the second terminal of the current-limiting transistor Q2 are collectors and emitters of the bipolar transistor, and the specific connection method may be selected according to the actual type of the current-limiting transistor Q2, and is not limited herein.
It should be noted that the type of the first filter circuit 101 includes, but is not limited to, a filter circuit formed by a resistor and a capacitor, a filter circuit formed by a resistor and a inductor, and filtering is implemented by using only a capacitor, and the specific type of the first filter circuit 101 is not limited, and may be specifically selected according to actual needs. For convenience of explaining the technical solution of the present invention, in the embodiment of the present invention, the first filter circuit 101 is a filter circuit formed by using a resistor and a capacitor, please refer to fig. 2. Specifically, the first filter circuit 101 includes a first filter capacitor C4 and a first filter resistor R7. One end of the first filter resistor R7 is connected to the first intersection, the other end of the first filter resistor R7 is connected to the second intersection with one end of the first filter capacitor C4, and the other end of the first filter capacitor C4 is grounded. The control terminal of the current-limiting transistor Q2 is connected to the second intersection.
Further, the resistance value of the sampling resistor is R8, and the turn-on threshold voltage of the current-limiting transistor Q2 is VthThe first threshold is IthIn which Ith＝Vth/R8。
Preferably, when the low-side drive has an overcurrent faultThe current-limiting transistor Q2 cooperates with the transistor control circuit 100 to cause the current through the low-side switch Q1 to be Ith. When the low-side driving circuit has an overcurrent fault, the current limiting transistor Q2 is matched with the transistor control circuit 100, the current flowing through the low-side switch Q1 is guaranteed to be constant and is the first threshold, after the overcurrent fault disappears, the whole circuit continues to work normally without any software operation, so that the requirements on the power consumption of the current limiting resistor and the sampling resistor R8 are low, only a conventional small-packaged resistor is adopted, and the requirement on the type selection of the current capacity of the current limiting transistor Q2 is also reduced. The circuit can be an integrated chip with double channels, the circuit area of the whole module can be greatly reduced, and the hardware cost can be reduced.
When the low-side driver circuit normally works, the low-side switch Q1 is In an on state or an off state, when the low-side switch Q1 is In an on state, because the load resistance on the path is large (generally 2k), the on current of the low-side switch Q1 is small, the voltage on the sampling resistor R8 is lower than the on voltage of the current-limiting transistor Q2, the current-limiting transistor Q2 keeps In an off state, at this time, the low-side switch Q1 is controlled by the control input signal In, and the low-side driver circuit keeps In a normal working state. When the low-side driving circuit has an SCB fault, the on-state current of the low-side switch Q1 is large, the voltage formed on the sampling resistor R8 is higher than the turn-on voltage of the current-limiting transistor Q2, the current-limiting transistor Q2 is turned on, and the control end of the low-side switch Q1 is pulled down, the low-side switch Q1 is turned off, at this time, the voltage of the sampling resistor R8 is reduced again, the current-limiting transistor Q2 is turned off after the voltage is lower than the turn-on voltage of the current-limiting transistor Q2, the low-side switch Q1 is turned on again, and as long as the SCB fault of the low-side driving circuit still exists, the adjustment process is repeated until a balanced state is finally reached, and the value of the current flowing through the low-side switch Q1 is stable Vthand/R8. When the SCB fault disappears, the voltage on the sampling resistor R8 recovers below the turn-on voltage of the current-limiting transistor Q2, thereby causing the low-side switch Q1 to recover the normal conducting stateThe low-side driving circuit continues to work normally. The switching speed of the low-side switch Q1 and the current-limiting transistor Q2 in the circuit is nanosecond, the hardware response time of the over-current diagnosis processing circuit 10 when the SCB fault occurs is microsecond at the longest, and the current during the SCB fault can be automatically limited to be approximately equal to Vthand/R8. When the SCB fault of the low-side driving circuit disappears, the low-side driving circuit can continue to work normally without any software operation, so that the power consumption requirements on the voltage dividing resistor R6 and the sampling resistor R8 are very low, the low-side driving circuit is preferably implemented by a conventional small-package resistor, and the type selection requirements on the current capacity of the low-side switch Q1 and the current limiting transistor Q2 are also reduced. The circuit can be an integrated chip with double channels, the circuit area of the whole module can be greatly reduced, and the cost can be reduced.
Based on the same inventive concept, another embodiment of the present invention further provides a low-side driving circuit, which includes the over-current diagnosis processing circuit 10 described in any of the above features.
In order to facilitate understanding of the technical solution of the present invention, a more specific structure of the low-side driving circuit is provided below. The low-side driving circuit comprises a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a first capacitor C1, a second capacitor C2, a third capacitor C3, a first diode D1, a pull-up resistor RloadA low-side switch Q1 and the over-current diagnostic processing circuit 10. The diagnosis processing circuit comprises a sampling resistor R8, a voltage dividing resistor R6, a first filter resistor R7, a first filter capacitor C4 and a current limiting transistor Q2.
One end of the first resistor R1 is connected with one end of the second resistor R2 and is connected with a control input signal, and the other end of the first resistor R1 is grounded; the other end of the second resistor R2 is connected to one end of the first capacitor C1, and is connected to the control end of the low-side switch Q1 and the first end of the current-limiting transistor Q2, and the other end of the second capacitor C2 is grounded; a first terminal of the low-side switch Q1 is connected to one terminal of the third resistor R3, and a second terminal of the low-side switch Q1 is connected to one terminal of the voltage-dividing resistor R6(ii) a The other end of the third resistor R3 is connected with one end of the fourth resistor R4 and one end of the fifth resistor R5, and the other end of the fourth resistor R4 is grounded; the other end of the fifth resistor R5 is connected with one end of the second capacitor C2 and is used as an output end of a diagnosis output signal of the circuit, and the other end of the second capacitor C2 is grounded; one end of the third resistor R3 is further connected to one end of the third capacitor C3, the other end of the third capacitor C3 is grounded, one end of the third capacitor C3 is further connected to one end of the first diode D1, the other end of the first diode D1 is grounded, and one end of the first diode D1 is further connected to the pull-up resistor RloadAnd (4) connecting. The first resistor R1 is a pull-down resistor, and is in a pull-down state by default before driving; the second resistor R2 and the first capacitor C1 form a filter circuit; the third resistor R3 and the fourth resistor R4 form a voltage division diagnostic circuit; the fifth resistor R5 and the second capacitor C2 form a filter circuit; the first diode D1 and the third capacitor C3 are used to protect the low-side switch Q1 from damage during an ESD strike. In addition, In is a control input signal of the circuit and can be derived from the output of the MCU; the Diagout is a diagnosis output signal of the circuit, and the MCU judges whether a fault exists or not by sampling the voltage state of the Diagout; rloadPull-up resistor R for load sideloadAnd the Output is an Output signal of the controller and provides a voltage state for a load end. One end of the voltage-dividing resistor R6 is connected with the second end of the low-side switch Q1, the other end of the voltage-dividing resistor R6 is connected with one end of the sampling resistor R8 at a first intersection point, and the other end of the sampling resistor R8 is grounded. One end of the first filter resistor R7 is connected to the first intersection, the other end of the first filter resistor R7 is connected to the second intersection with one end of the first filter capacitor C4, and the other end of the first filter capacitor C4 is grounded. The control terminal of the current-limiting transistor Q2 is connected to the second intersection. A first terminal of the current-limiting transistor Q2 is connected to the control terminal of the low-side switch Q1, and a second terminal of the current-limiting transistor Q2 is grounded.
When the low-side driving circuit is in normal operation, the low-side driving circuit is in a standby stateThe low-side switch Q1 has two states of on or off, when the low-side switch Q1 is turned on, because the load resistance on the path is large (generally 2k), the on current of the low-side switch Q1 is small, the voltage on the sampling resistor R8 is lower than the turn-on voltage of the current-limiting transistor Q2, the current-limiting transistor Q2 keeps the off state, at this time, the low-side switch Q1 is controlled by the control input signal In, and the low-side driving circuit keeps the normal working state; when the output of the low-side driving circuit has an SCB fault, the on-state current of the low-side switch Q1 is large, the voltage formed on the sampling resistor R8 is higher than the on-state voltage of the current-limiting transistor Q2, the on-state of the current-limiting transistor Q2 pulls down the control end of the low-side switch Q1, the low-side switch Q1 is turned off, the voltage of the sampling resistor R8 is reduced again at this time, the current-limiting transistor Q2 is turned off after the on-state voltage of the current-limiting transistor Q2 is lower, the low-side switch Q1 is turned on again, the adjustment process is repeated as long as the SCB fault of the low-side driving circuit is still in place, the balance state is finally reached, and the value of the current flowing through the low-side switch Q1 is approximately Vthand/R8. When the SCB fault of the low-side driving circuit disappears, the voltage on the sampling resistor R8 is restored to be lower than the turn-on voltage of the current-limiting transistor Q2, so that the low-side switch Q1 is restored to a normal conducting state, and the low-side driving circuit continues to work normally.
In the low-side driving circuit, the low-side switch Q1 and the current-limiting transistor Q2 both adopt bipolar transistors, the switching speed of the bipolar transistors is nanosecond, the longest hardware response time of the low-side driving circuit is only microsecond when SCB faults occur, and the current can be automatically limited to be approximately equal to V during the SCB faultsththe/R8, after the SCB fault disappears, the low side driving circuit can continue to work normally without any operation of software, so the power consumption requirement for the divider resistor R6 and the sampling resistor R8 is very low, only a conventional small-package resistor is adopted, and the type selection requirement for the current capability of the low side switch Q1 and the current limiting transistor Q2 is also reduced. For the integrated chip which can use double channels for the part of the circuit, the whole module circuit area can be largeThe cost is also reduced. By adding the low-side driving circuit with the diagnosis processing circuit, the low-side driving circuit is subjected to shutdown processing in a millisecond level originally after SCB faults occur in an ON state or a PWM state and the circuit, the shutdown time is long, risks of damaging a controller are reduced, the improved circuit automatically performs current limiting protection ON the fault state, the power consumption of the current limiting state is low, a TCU (Transmission Control Unit) is not damaged, no software is needed to perform any operation, the response is fast, the power consumption requirement ON the circuit is low, the damage to the controller is avoided, and the safety is improved.
In the embodiment of the present invention, the low-side switch Q1 is configured as a bipolar transistor, the control of the low-side switch Q1 is a base of the bipolar transistor, and the first terminal and the second terminal of the low-side switch Q1 are a collector and an emitter of the bipolar transistor. It is understood that, in other embodiments, the low-side switch Q1 may be of other types, and the connection manner of the low-side switch Q1 of other types is similar to that of the low-side switch Q1, which is not described herein again, and may be specifically selected according to actual needs. It should be noted that, as can be seen from the above description, the low-side driving circuit includes a plurality of filter circuits, and the types of the filter circuits include, but are not limited to, a filter circuit formed by a resistor and a capacitor, and filtering is implemented only by a capacitor, and the specific types of the filter circuits are not limited, and can be selected according to actual needs.
In conclusion, the invention has the following beneficial effects:
1. the overcurrent diagnosis processing circuit provided by the invention utilizes the cooperation of the current-limiting transistor and the transistor control circuit to adjust the current flowing through the low-side switch when the low-side driving circuit has overcurrent faults. The transistor control circuit is used for adjusting the working state of the current limiting transistor based on the current flowing through the low-side switch, and the current limiting transistor is used for adjusting the current flowing through the low-side switch. Through the cooperation of the current-limiting transistor and the transistor control circuit, the low-side switch can be subjected to current-limiting protection when the low-side driving circuit has overcurrent faults. Because the MCU is not utilized in the fault diagnosis and processing process, and the switching speed of the current-limiting transistor is in nanosecond level, when an overcurrent fault occurs, the hardware response time of the overcurrent fault diagnosis and processing circuit is only microsecond level at the longest. The circuit has the advantages of no need of software to do any operation, quick response and low requirement on the power consumption of the circuit, thereby avoiding the damage to circuit devices and improving the safety.
2. When the low-side driving circuit has an overcurrent fault, the current limiting transistor is matched with the transistor control circuit to ensure that the current flowing through the low-side switch is constant to be the first threshold value, after the overcurrent fault disappears, the whole circuit continues to normally work without any software operation, so that the requirements on the power consumption of the current limiting resistor and the sampling resistor are very low, only a conventional small-packaged resistor is adopted, and the requirement on the type selection of the current capacity of the current limiting transistor can be reduced. The circuit can be an integrated chip with double channels, the circuit area of the whole module can be greatly reduced, and the hardware cost can be reduced.
The low-side driving circuit provided by the invention and the overcurrent diagnosis processing circuit belong to the same inventive concept, so that the low-side driving circuit has the same beneficial effects.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example" or "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. And the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments. Furthermore, various embodiments or examples described in this specification can be combined and combined by those skilled in the art.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention in any way, and the present invention includes, but is not limited to, the configurations listed in the above embodiments. Various modifications and alterations to the embodiments of the present invention will become apparent to those skilled in the art from the foregoing description of the embodiments. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. An overcurrent diagnostic processing circuit for use in overcurrent diagnostic processing of a low-side driver circuit, the overcurrent diagnostic processing circuit comprising:
a current limiting transistor configured to adjust a magnitude of a current flowing through a low side switch in the low side driving circuit;
a transistor control circuit configured to implement a low-side drive function and adjust an operating state of the current-limiting transistor based on a current flowing through the low-side switch;
the working state of the current-limiting transistor comprises a conducting state and a switching-off state, and the current-limiting transistor is matched with the transistor control circuit to adjust the current flowing through the low-side switch when the low-side driving circuit has overcurrent faults.
2. The overcurrent diagnostic processing circuit as set forth in claim 1, wherein said current limiting transistor adjusts the magnitude of current flowing through said low side switch by turning on or off;
when the current flowing through the low-side switch is smaller than a set value, the current-limiting transistor is in an off state; when the low-side switch has overcurrent fault, the current-limiting transistor is in a conducting state to reduce the current flowing through the low-side switch.
3. The over-current diagnostic processing circuit of claim 1, wherein the transistor control circuit adjusts the current-limiting transistor to be in a conductive state when the current through the low-side switch is greater than a first threshold;
when the current flowing through the low-side switch is smaller than or equal to the first threshold value, the transistor control circuit adjusts the current-limiting transistor to be in an off state;
wherein the first threshold is a maximum current allowed to flow through the low side switch.
4. The overcurrent diagnostic processing circuit as set forth in claim 1, further comprising:
the first filter circuit is configured to filter the output of the transistor control circuit and transmit the filtered output to the current limiting transistor.
5. The overcurrent diagnostic processing circuit as set forth in claim 4, wherein said transistor control circuit comprises a voltage dividing resistor and a sampling resistor;
one end of the divider resistor is connected with the low-side switch, the other end of the divider resistor and one end of the sampling resistor are connected to a first intersection point, and the other end of the sampling resistor is grounded;
the input end of the first filter circuit is connected with the first intersection point, the output end of the first filter circuit is connected with the control end of the current-limiting transistor, the first end of the current-limiting transistor is connected with the control end of the low-side switch, and the second end of the current-limiting transistor is grounded.
6. The over-current diagnostic processing circuit according to claim 5, wherein the sampling resistor has a resistance of R8, and the current limiting transistor has a turn-on threshold voltage of VthThe first threshold is IthIn which Ith＝Vth/R8。
7. The overcurrent diagnostic processing circuit as set forth in claim 6, wherein said current limiting transistor is adapted to cooperate with said transistor control circuit to cause a current I through said low side switch when an overcurrent fault occurs in said low side driveth。
8. The over-current diagnostic processing circuit according to claim 5, wherein said first filter circuit comprises a first filter capacitor and a first filter resistor;
one end of the first filter resistor is connected with the first intersection point, the other end of the first filter resistor and one end of the first filter capacitor are connected with the second intersection point, and the other end of the first filter capacitor is grounded;
the control end of the current-limiting transistor is connected with the second intersection point.
9. The over-current diagnostic processing circuit according to any of claims 1-8, wherein the current limiting transistor is a bipolar transistor.
10. A low side driver circuit comprising the overcurrent diagnostic processing circuit as set forth in any one of claims 1 to 8.
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| CN202011595337.3A CN112736859B (en) | 2020-12-29 | 2020-12-29 | Overcurrent diagnosis processing circuit and low-side driving circuit |
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