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BQ25171-Q1: Leakage from VOUT to VIN during off-state

R_Lo_88
Prodigy 10 points
Part Number: BQ25171-Q1

Tool/software:

Hello, 

We are using the BQ25171 to charge a single cell Li-ion battery when our system is connected to an external power source. We have also implemented a power path design similar to what is shown on page 29 of the datasheet. After experiencing a number of failures related to the charger circuit, we noticed that VIN = VBat - 0.7V during the off state. This is also causing functionality issues with our power path because VGS on the P-channel MOSFET is too low to reliably turn on. As a result, the system load power flows through the P-MOS body diode, resulting in a problematic voltage drop when the battery is not fully charged. We presume that due to /CE being 0V when power is off, one of the back-to-back switches in the BQ25171 is on, allowing current to flow through the body diode of the other internal switch and appear at VIN. 

I have not been able to find information explaining how the device operates when VIN is not actively powered and /CE is low. Can someone confirm that this is what we are experiencing? Does /CE need to be pulled high at all times, even when power is turned off, to prevent leakage from the battery into VIN?

Thanks!

  • 0
    TI__Guru* 75806 points

    Hello

    We are checking on this Question and will have an update Monday.

    Looked at this in the lab and do not see voltage on the input when battery voltage is applied.  

    Can you send your schematic for review?

  • 0 in reply to Bill Johns
    TI__Guru* 75806 points

    Hello

    I have done some additional checking on this question and the two mosfets will be off in the 0V in condition, will not have leakage from Output to Input.  Battery leakage is typically only 350nA out of battery and this does not go to input. 

    With the VIN = VBat - 0.7V the BQ25171 will be in SLEEP, this is a low power shutdown mode with both mosfets off.

    Is it possible there is a path between SYSTEM and Vin?

  • 0 in reply to Bill Johns
    Prodigy 10 points

    Hi Bill, appreciate the response! There is a small amount of reverse current from SYS/battery to VIN through the schottky diode in the power path. Aside from that, nothing else should be creating a path. I am swapping out those schottky diodes for a part number with lower reverse current and will see if it makes a difference. I can share schematics but would have to do that through a non-public channel. 

    Thanks!

  • 0 in reply to R_Lo_88
    TI__Guru* 75806 points

    The forum has a Private Message feature, will contact you and we can set up a conversation there.