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BQ25710: OTG_RANGE_LOW

Konstantin Avdashchenko
Prodigy 225 points
Part Number: BQ25710

What is the purpose of the OTG_RANGE_LOW bit? It seems that the possible range in the OTGVoltage Register is 0v-32.76v. In which case there is no need for the 1.28v offset or the switch to enable a lower range to target 3v. Also, with the 1.28v offset, and OTG min voltage of 3v can be defined whether the low range is set or not.

Am I missing something here? Also, is it fair to say that the strange almost powers of 2 in the datasheet OTGVoltage Register are typo's, and powers of 2 were intended? Or are those values from testing the chips?

Thank you,

Konstantin 

  • 0
    TI__Mastermind 24075 points

    Hi Konstantin,

      OTG_RANGE_LOW sets the offset for the register to configure OTG voltage. The OTGVoltage register is capped by the number of bits used for different OTG configurations, and the resolution between each bit corresponds to 8mV.

    There is no use for the charger to be able to operate in OTG mode to reverse boost from the battery to VBUS to output 0V, as there is a minimum battery threshold for OTG to be active (Vvbat_otgen, Vvbat_otgenz)

  • 0 in reply to Kedar Manishankar
    Prodigy 225 points

    Hi Kedar,

    Thank you for clarifying the 8mv step size. The datasheet says some strange numbers on page 61 of slusd20.pdf.

    Still though, the datasheet shows that we have 12bits of resolution, which at 8mv would correspond to a range of 32.768V. 

    Alright, I think I see it now. Easier to manufacture this way. The OTG V setting is capped logically by which bits are set and the range of allowed options to accept updates. As such, adding an extra bit allows you to put an offset and pull back the voltage range by 1.28v. This explains the 4.28v becoming 3v, and 20.8v becoming 19.52v.

    I understand that the DAC can only regulate between 3v and 20.8v, but the 12 bit selection range can cover this entire range.

    Does the OTG range low bit prevent setting the DAC output below 4.28v if not set? And if so, is it meant as a logical safety switch to prevent lower than 5v operation on a usb line? Also, if that is the case, why the offset and the high voltage range cap of 19.52v when set (page 42)?

    Thank you,

    Konstantin