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BQ24892 - Settings for USB OTG

Ken Dillinger
Expert 1220 points

I have the BQ24892 EVM on my bench, and I am setting it up for OTG. The problem, is that I must be hitting some limit, because when I pull higher currents the OTG operation ceases. I have an SMU on VBAT set to 5A limit set at 3.3V, and another SMU on VBUS that sinks current during OTG operation. 

I believe I have the registers set up correctly:

Reg00: 0x3F - disable Hi-Z and ILIM pin, and IINLIM is set to 3.25A

Reg0A: 0x7F - default boost mode voltage, 2.45A boost current limit

I also disable the watchdog timer and thermistor protection:

Reg01: 0xFF

Reg07: 0x8D

I am able to start OTG operation and load VBUS, up until ~3A from VBAT. Then OTG ceases and the voltage I am measuring on VBUS is ~ -2V. Ouch.

The only things I can immediately think of is ripple current on the input? I know my SMU says ~3.05A, but that must be an average. Perhaps ripple current is still tripping the IIN LIM?

I will continue to RTFM in parallel.

Thanks!

-Ken

  • 0
    TI__Guru**** 166576 points
    What is the voltage at the BAT pin? If your cable from SMU to BAT pin is too resistive, the voltage at BAT may be drooping below the V(OTG_BAT) max of 2.9V, causing the charger to exit OTG mode. Regarding SMU current sink on VBUS, I suggest changing the voltage compliance that VBUS does not go more than 1V below ground at worst.