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Original question:

BQ2970: Design review help needed, circuit not functioning

BQ2970: DOUT Low Voltage

Gabriel Shih
Prodigy 80 points
Part Number: BQ2970

Hi,

My circuit with BQ29700DSER is implemented as below, following your reference design. I found that the voltage on DOUT (pin 3) is very low. Therefore the MOSFET for discharge is not driven. I also measured V- (pin 6) and it is higher than Vocd.

I tried to pull down V- by connecting it to Vss. Then DOUT seems to become normal. I am very sure that there is no other load between J12 and GND.

What should I try next to solve this?

Thank you.

Gabriel

  • 0
    TI__Mastermind 42535 points

    Hi Gabriel,

    The protector AE's are out on vacation. You will have a reply here in a week.

  • 0 in reply to Batt
    Prodigy 80 points

    Hi,

    Some updates.

    I removed the connection between pin 4 and 6 after power up, and the voltages on pin 2, 3 (COUT, DOUT) were the same as they were before the removal.

    Then I replaced the connection with a 0.1uF capacitor. Sometimes it worked but sometimes it did not.

    Gabriel

  • 0 in reply to Gabriel Shih
    TI__Expert 7035 points

    Hi Gabriel,

    The behavior you are describing seems to be the correct response for the device. Refer to section 9.4.4 of the datasheet for a description of the device's behavior in discharge over current status. This section states that if the V- pin is equal to or higher than the discharge over current threshold (Vocd) for a time greater than the discharge over current detection delay (tocdd), the DOUT pin is pulled low to turn off the discharge FET to prevent further discharge of the battery. 

  • 0 in reply to Batt
    Prodigy 130 points

    Maybe,

        BQ2970 is not suitable for removable batteries. That is, you must connect battery and charge it at first. Then,  BQ2970 will be on-power and in-use. If you remove it's battery, it must-be re-charge again in-case-of powerup BQ2970 at first.   Sorry for my poor English.

  • 0 in reply to ju zhang56
    TI__Expert 7035 points

    Hi, 

    Yes, you are correct. The BQ2970 is not meant to be used with removable batteries.