Based on XC164CS and BTS7741G central door lock control design
Today, more and more cars use electronic door control system, central door lock door control system is an important component. In this paper, door control module design project in practice, highlighting the central lock part of the hardware and software design, the smart-power chip BTS7741G work characteristics and fault detection characteristics are analyzed, and experimental results are given.
The overall design of the door control module
Auto Door Control systems With the development of semiconductor technology development, due to the traditional relay, fuse control exists in all kinds of abuses, there is an urgent need to introduce a new control approach to improving the status of the door control, this design is based on a 16-bit embedded system, the vehicle door control system solutions.
Figure 1 System block diagram
Shown in Figure 1, door control module mainly consists of the following components: power supply circuit, power windows driver circuit, rear-view mirror driving circuit, heater drive circuit, central door lock driver circuit, lamp driver circuit, CAN General line interface circuit, RS232 interface circuit and the key interface circuit. XC164CS microcontroller used to control all the power devices switching action, while the system state from time to time monitor the provision of appropriate feedback signal, and periodically displays diagnostic information, and through-vehicle networks (eg CAN) to achieve information exchange. Result of the selection of power devices has provided a complete protection, this design avoids the use of excessive power components and to reduce the module size, and improve the electromagnetic compatibility of the module.
Central Lock Control Hardware Design
The choice of a smart power chip
The existing central door lock relay-driven approach to use more. However, the relay driver has many drawbacks: power relay excitation coil drive current larger, higher power consumption and the need to interface circuit complex; relays used to control the volume increase, weight increase; relay switching frequency is relatively low the contacts easy to shake, it is difficult to meet the vehicles charged cases, the mechanical vibrations travel requirements. In addition, the relay contacts will affect the life of jitter, and EMI serious, difficult to effectively achieve the right headlight overheating, overvoltage, short circuit fault diagnosis and protection, need to fuse with the use, in order to prevent overcurrent. But the fuse once the action (ie, fuse), the circuit will be completely cut off, the need to manually replace the fuse.
Smart Power ICs for automotive electronics BTS7741G demanding application environments. Its two high-side switch and two low-side switch with undervoltage protection, short circuit protection to ground on the power supply short-circuit protection, thermal shutdown, restart after cooling a variety of intelligent protection functions, while two high-side switch also includes a circuit fault diagnosis, through the fault feedback pin ST can be diagnosed open-circuit fault, short circuit fault and other fault condition, suitable for central door lock control.
BTS7741G includes four MOS pipe, two high-side switch and two low-side switch that can flexibly configure the output mode, as a H-bridge or switch can be used as a separate. High-side switch on-resistance of 110mΩ, low-side switch on-resistance of 100mΩ, working voltage up to 40V.
2 Central Door Lock Control and Drive Circuit Design
BTS7741G with the micro-controller circuit shown in Figure 2. BTS7741G used as a H-bridge, drive or reverse the central lock is transferred. -Driven process to rely on time to control the motor to run a certain time (The design value of 0.25s) produce a certain displacement to achieve lock or unlock. Motor run time in the program variable. No active braking process, through the realization of the possession of freewheeling motor braking. Central door lock switch between the two movements at least 0.5s time interval, to ensure reliable turn-off MOS tube.
Figure 2 BTS7741G and micro-controller circuit
After power-locks status is unknown, so the micro-controller, the first closed door. Central door lock does not use the motor drive mode PWM regulator. SH2 external 1kΩ pull-up resistor from the +12 V power supply, can be realized in the off-state open-circuit fault detection.
BTS7741G-to-ground short-circuit experiment
Although the BTS7741G of two high-side switch and two low-side switches have a complete short-circuit protection, but the failure only feedback from the feedback pin ST has two high-side switch short-circuit fault condition. Therefore, this design the high-side switch for BTS7741G done a right to short-circuit experiment. After the experiment was divided into the first short-circuit power and the first after the short-circuit power on two cases.
BTS7741G-to-ground short-circuit test conditions +12.45 V battery voltage, +5 V power supply, 1.5m short-circuit conductor (R = 0.12Ω). Shown in Figure 3, which VST for the ST pin-to-ground voltage, VIN is the IH1 pin-to-ground voltage, VOUT is the OUT pin-to-ground voltage, IL-to-ground fault that occurs when the short-circuit flows through BTS7741G current.
After a first short-circuit power to ground short-circuit under the conditions of experiment
Figure 3 BTS7741G power after the first short-circuit short-circuit test waveform the first half of
Figure 4 BTS7741G power after the first short-circuit short-circuit experiment half of the waveform
Figure 5 BTS7741G first power short-circuit short-circuit test waveforms after the first half of
Figure 6 BTS7741G power after the first short-circuit short-circuit experiment half of the waveform
Shown in Figure 3, in the switch is pressed, the moment, due to its mechanical switch structure has led to a large number of burr; instantaneous surge current of 10A (25 ℃, BTS7741G typical short-circuit current peak value is 10A); the output voltage VOUT has been is low; ST short-circuit fault diagnosis pins are pulled down after about 1.4ms, which means BTS7741G diagnosed a fault at this time. Since then, BTS7741G will be periodically off the internal MOS pipe, so short-circuit current IL has been periodically clamp for 0A, effectively inhibited the short-circuit current caused by chips continue to heat, thereby protecting chip will not short-circuit damage; ST pin With the short-circuit current level will also be changes in the cyclical pulled to low. As shown in Figure 4, when the chips completely cooled, BTS7741G can re-start, to continue to work properly.
After the first two power-ground short-circuit under the conditions of short-circuit experiment
Figure 5 shows, the switch is pressed, the moment, and instantly the surge current is 25A, is much higher than 25 ℃, short-circuit current peak BTS7741G typical 10A. However, this surge current is 25A lasted less than 30μs time immediately reduced to 10A, so the chip is not damaged; the output voltage VOUT at the moment are pulled down as low short-circuit; ST pin in the short-circuit fault diagnosis after the occurrence of 1.6ms or so have been pulled down, which means BTS7741G diagnosed a fault at this time. Since then, BTS7741G will be periodically off the internal MOS pipe, similar to the first short-circuit short-circuit power after the experiment, short-circuit current IL has been periodically clamp for 0A, ST pin levels are as cyclical changes in short-circuit current The pulled to low. As shown in Figure 6, when the short-circuit phenomenon disappeared, BTS7741G can re-start, the output voltage VOUT is high, the chip has not been any impact on short-circuit conditions, to continue normal work, it shows that BTS7741G perfect short-circuit protection.
Lock part of the software design
Locks the software algorithm is appropriate to control the state of the appropriate arm of the bridge, or turn off. In the door to open or close a bridge when you need to arm up and down the conduction, in the open or turn-off after the need for continued flow, then the only off the bridge arm, and let the bridge arm can turn for some time. The specific control algorithm can refer to the lock as shown in Figure 7, the state flow diagram.
Figure 7 door lock control state flow diagram
Table 1 shows the working status of several locks.
Conversion between the various working conditions is not triggered by the control commands ubCmdLatch activated. From LATCH_CLOSED to LATCH_OPENING and from LATCH_OPENED to LATCH_CLOSING the two conversion is triggered by the ubCmdLatch, and its meaning lies in order to be open or closed, the door began to change from a static state to a state of movement, that is, locks from the stationary state began to open the closed, or opened to begin closing. In PASSAT B5 is used in electric power door locks, door locks open or close the lock bolt is driven by a motor before and after the move to achieve. The internal BTS7741G is a simple H-bridge circuit, it is through programmed H-bridge at the right time to open the bridge up and down the right arm, to control electric locks positive inversion purposes. The LATCH_OPENING and LATCH_CLOSING these two states on the preparation of a pair of upper and lower control arms control the bridge turn command. In the state LATCH_CLOSED and LATCH_OPENED, four tubes do not turn.
The remaining conversion between the various states are not triggered by the control commands, and some through from time to time, others by the error detection. Fault detection by monitoring the ST pin output level to achieve. In normal state, ST pin output high; the event of failure, ST pin output is low. The specific status of switches can be clearly shown in Figure 7. For example, from the state LATCH_OPENING to LATCH_OPEN_FREE is time to lock open time (LATCH_OPENING_TIME) end, and if detected, open-circuit fault or overload failure, door locks will always remain at LATCH_CLOSED or LATCH_OPENED state.
Through the work of smart power chip BTS7741G properties and characteristics of fault detection and analysis, given the security of the chip has been positive, ensuring the accuracy and reliability of this design.
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