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BQ25756EVM: Hardware input current limit is not limiting input current to 8A

Spencer Waguespack
Prodigy 50 points
Part Number: BQ25756EVM

Tool/software:

Hi,

I have an BQ25756EVM. During bring up of the board I was able to pass more than 8A into the board while doing the procedure outlined in: "2.4.2 Equipment - Using a CV Load" from the user manual when I had the input power supply set to 10V. I measured an input current of 9.90A. Nothing on the board has been modified and the EN_ILIM_HIZ_PIN register is set to 1. When I increased the output current limit to 8A I was able to measure an input current of 20A. It seems like to me the currenting function is disabled however JP10 is installed. The Software current limit functions as expected.

  • +1
    TI__Mastermind 20530 points

    Hi Spencer,

    When you mean increase the output current limit to 8A do you mean that you increase the current limit on the power supply #1 in the user guide page 8 (2.4.1 Equipment Set Up) step 1 to 8A?

    Can you please check the input sense resistor value on your EVM board? Is it 2mohm or 5mohm? Assuming it is 2mOhm, the EVM has ILIM_HIZ resistor R66 = 2.49kohm. KILIM=50 A-kΩ, input current limit = KILIM/RILIM=20A. The default register setting is also 20A. This means the actual current limit in use is 20A.

  • 0 in reply to Jing Zou
    Prodigy 50 points

    Hi Jing,

    Yes, I increased the current limit from 8A to around 25A. When I had the current limit set to 8A the charger was browning out so I increased it. 

    I see the problem. The schematic and documentation make it seem like R2 is a 5mohm resistor However; The bom says it is a 2mOhm resistor and I measured it to be a 2mohm resistor.

  • 0 in reply to Spencer Waguespack
    TI__Mastermind 20530 points

    Hi Spencer,

    Apologize for the confusion on the sense resistor value. Yes, we had early release EVM with 2mohm sense resistor and had updated to 5mohm in the latest version to be compliant with our PD controller setting. We will update the user guide to clarify this. Thanks.

  • 0 in reply to Jing Zou
    Prodigy 50 points

    Hi Jing,

    I think there may be a lot of errors in that User Guide. I have been submitting document feedback when find them