TPS7A94: Fast start up control

Part Number: TPS7A94

The datasheet for the TPS7A94 reports that the fast charge up (here called soft-start) supplies extra current to ramp up the reference until the reference reaches 93% of the intended Vout value.  However, there does not seem to be a clear way for internal logic to be aware of that voltage value.  For example, there is not a voltage divider on the output that provides it to a comparator on the die as is done in the similar LT304X line, where it is part of combined power good and fast start up control.  Here the output divider for Power Good has been combined with current limit programming instead of fast charge control. 

Is there anything the user needs to do to set up the threshold of output voltage at which the 2mA fast start up current turns off? 

  • Hi Farron,

    That's a typo in the datasheet and we have it logged as something to correct for our next datasheet revision.  The FB_PG resistor dividers set the threshold for the changeover voltage from fast charge to steady state operation.  You can find the rest of the information in the datasheet but to make it easy, the internal voltage being compared is 0.2V.  Set your FB_PG resistors to sense Vout and compare it to 0.2V.  If your Vout is 1V and you want 93%, then the FB_PG voltage will read 0.2V when Vout = 0.93V.  Etc.

    Thanks,

    Stephen

  • Thanks Stephen, that would seem to close the issue.