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BQ24725A: BQ24725A sense resistor and register setting

Fan WANG
Prodigy 140 points
Part Number: BQ24725A

Hi TI,

I am trying to use the BQ24725A in a lower cost battery charger design. Since our charging current is low(190mA), we used a relatively large sensing resister(0.15) at the output. Now it seems the output voltage(1.32V) is lower what we set(8.4V) through I2C, could you help to check?

 

BTW, I have jumped the pin CMSRC to VCC input(9V25), but I don’t know why I need to do that, because in the block diagram, this pin provides the base power for the voltage pumper of ACDRV.

 

Please check the schematic below:

The register setting is listed below:

 

0x12                0x0030 (option register)

0x14                0x0c00(charge current)

0x15                0x20c0(charge voltage)

0x3f                 0x1000(input current)

 

Thanks so much!

 

Best Regards,

  • 0
    Prodigy 140 points

    And I have tried to switch the sense resistor back to 10m. I can see some voltage output there. But it seems that the charge current I set through I2C is not accurate. Please check the voltage I measured across the load resistor(36ohm) at the output:

    charge voltage register setting: 0x20d0
    charge current register setting output voltage actual current
    0xc0 4.98V 138mA
    0x100 6.86V 190mA
    0x140 8.31V 231mA
    0x180 8.36V 232mA

    This is a bit confusing.

    Best Regards,