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BQ25121: Writing a value but reading a different one.

Dima S
Prodigy 220 points
Part Number: BQ25121

I want to get a LDO voltage of 3.3V.

I am Writing to Register : 0x07h , Load Switch and LDO Control Register the value: 0xE4

But when i read it i get the value : 0xFC

when i looked in Bq battery management Studio, 0xFC writes "Load Switch" ? what does it mean? and why don't i read exactly what i wrote?

Thanks!

  • 0
    TI__Genius 12485 points
    Dima,

    Are you having VIN present when you do so? If not, is /CD pin high? Also make sure other register writes and reads are okay for checking.

    On the LS/LDO, make sure watchdog is not overwriting these values within 50s. Your code of 0xE4 is correct. You have to toggle the enable/ disable bit for the voltage to update.

    thanks,
    gautham
  • 0 in reply to Gautham
    Prodigy 220 points
    After checking the device:
    VIN is present, the device is connected to an external power source and BQ_POWER_GOOD pin is LOW.
    CD pin is LOW.
    All other registers are read and they hold the correct values that were written.
    I write the LDO register and read it immediately (on device boot) , 50 sec does not pass between write and read.
  • 0 in reply to Gautham
    Prodigy 220 points
    i tried writing 0x64 and them writing 0xe4 ( regarding toggle enable bit) it didnt help.
  • 0 in reply to Dima S
    TI__Genius 12485 points
    Dima,

    where is VINLS connected to? PMID? Is 0xE4 the only setting you are having issues with? What if you write another LDO voltage? is LSCTRL left floating (internally pulled down)