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BQ77904: The UV fault and OC fault can not recover by Load Removal

dewen gong
Prodigy 30 points
Part Number: BQ77904

Hi Sir/Madam:

        There was a problem in my design when I used BQ7790400PWR,When undervoltage protection and overcurrent protection start, it can not be recovered by Load Removal.The following is my circuit diagram, please help me to confirm what is the problem, thank you.

       I've changed R9 to 3.3M and still can't work by Load Removal .

  • 0
    TI__Guru 54715 points
    Hi Dewen,
    Be sure your system has released the BATTERY- voltage and check the voltage at the LD pin. The LD pin must go below the VLDT level for recovery. Be sure to use a high impedance meter when measuring to avoid loading the circuit.
  • 0 in reply to WM5295
    Prodigy 30 points
    Hi WM5295
    I check the voltage at the LD pin according to your guidance.The voltage of the LD pin is about 2.335 Volts.
  • 0 in reply to dewen gong
    TI__Guru 54715 points
    Hi Dewen,
    2.335V is above the VLDT threshold so the part is not seeing load removal. Check the expected voltage from the voltage divider with the internal pull down resistor shown in the data sheet.
    It sounds like either the load is not completely removed, or some component is not as expected, or the bq77904 LD input may be damaged and have the wrong resistance, you will need to determine which or something else.
  • 0 in reply to WM5295
    Prodigy 30 points
    Hi WM5295,
    I check the datasheet"the load, RLD and RLD_INT create a resister divider".the RLD_INT is 250K,so i change the RLD to 1.7M, it can be recovered by Load Removal when overcurrent protection start.I test my system using a 3ohm resistor for OCD1 test.Will it cause other problems because I increase the RLD value?
  • 0 in reply to dewen gong
    TI__Guru 54715 points
    Hi Dewen,
    I do not expect the larger resistor to cause problems, but be sure to check the voltage divider under all system conditions you care about. Casually those might be OCD fault with residual load after system shutdown, OCD fault and open circuit, UV with residual load and UV with open circuit, but consider your system specifics.