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DRV8870: DRV8870 replacement for DRV8872

Part Number: DRV8870
Other Parts Discussed in Thread: DRV8872-Q1, DRV8872

Dear experts,

Due to supply shortage, customer is replacing DRV8872-Q1 by DRV8870 without changing any external circuit.. During debug DRV8870, there exist some issues and customer is focusing on PIN4 internal logic difference.

Referring to their schematic, do you have comments on the external configuration? 

Problem statement:

Under the same external circuit condition testing 8870. The abnormal driving problem is encountered during the process of raising the temperature from normal temperature to high(about 85 °C).
It can be seen from the test waveform that the waveforms of OUT1 and OUT2 are blocked under the condition of normal Vref of 5V, and the waveform interval time of 25us conforms to the internal overcurrent characteristics of the chip (actually, the input waveform of IN1 is 500ms pulse width). However, it can be seen from the actual current of CH4. There is no overcurrent.
CH1——out1,CH2——out2,CH3——PIN4(Vref),CH4——OUT1 current

  • Hi Zoe,

    What is the value of the ISEN resistor?

    The 25us OFF time points to the device being in current regulation mode. Overcurrent and current regulation are different. I just want to make that clear to the customer. Overcurrent protection is a safety feature that disables the H-bridge when the output current is above the OCP limit of 4.5A (typ) for longer than the deglitch time (1.5us).

    The odd thing is that the current is not increasing that much. Maybe decreasing the vertical scale will help to get a better reading of the current. Anyways, I asked for the ISEN reistor because the current regulation limit also depends on the resistance value. If the resistance is higher, the regulation limit will be lower.


    Pablo Armet

  • Thanks Pablo for quick response! Isense resistor is 100mohom

  • Thanks Zoe,

    At 100mohm, the itrip limit is well above what is shown on the oscilloscope waveforms. So something else is causing the device to go into current regulation.

    I want to remove the possibility that this device is damaged. Can you remove this driver from the PCB and solder in a new IC. Or try to see if this behavior is also present on another board with different IC.

  • Pablo,

    The most importance thing my customer would like your comments is the PIN4 external circuit. They multiplex the same external circuit and configuration compared with DRV8872. MCU default I/O signal internally goes pull up. Capacitance and resistance were shown in below diagram. Is there anything wrong? Would this may cause the device go into current regulation? Really appreciate your help here.

  • Do you think their PCB layout or schematic and other reasons that may also cause this issue?

  • Hi Zoe,

    You should not have two pull up resistors to 5V on the VREF pin. My recommendation is removing VREF from the MCU or setting the IO as a high impedance input.

    Please ask them to try the above and let me know if it fixes the issue.