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BQ25895: Standalone charging, current negotiation, etc.?

Gregory Duperon
Expert 7420 points
Part Number: BQ25895
Other Parts Discussed in Thread: TUSB320LAI

I have a few questions regarding the BQ25895:

1)      Does the BQ25895 retain the programmed settings after a power cycle and the host processor is not present? Device is turned off, but the battery needs charged.

2)      How does the BQ25895 negotiate current without the use of the CC signals? Everything I read indicates that the CC signals are required for the higher currents.  I suspect that D+/D- will only negotiate to 500mA. I need 3A.

3)      Can the BQ25895 be on the D+/D- signals along with the processor that is receiving the data? Will that create signal contention?  Do I need to use a switch instead?  Recommendations?

  • 0
    TI__Guru**** 165766 points
    Hello Gregory,

    Great questions!

    Regarding 1, if powered is removed from both VBUS and BAT OR with either VBUS or BAT or both applied and the watchdog timer expires, the registers reset to default values. The watchdog timer can be disabled via I2C.

    Regarding 2, BQ25895 is not standalone USB type C compatible. It is compatible with USB BC1.2 plus some other HVDCP adapters, performing negotiation over the D+/D- lines. If the D+/D- lines are shorted and the ILIM resistor is set for maximum input current, then the charger input current is 3.25A max. For full USB type C power source compatiblity, you would need another IC, like TUSB320LAI and host software.

    Regarding 3, the BQ25895 only automatically communicates via D+/D- lines during the first 2 seconds following VBUS powerup. After that, they go high Z. There is also I2C to force communication. Many customers simply prevent communication via D+/D- lines until after 2 seconds. Some customers are using a switch similar to that on the BQ25895EVM.

    Best regards,
    Jeff