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TPS7A10: Does Global UVLO enable active rail discharge ckt

Jeff Coletti
Expert 8675 points
Part Number: TPS7A10

Hi Support Team

Can you confirm that the GLOBAL UVLO will activate tactive discharge circuitry in the "p" version?

Customer wants this to trip if the voltage starts to fall.

Thanks

Jeff Coletti

  • 0
    TI__Expert 3995 points
    Hi Jeff,
    Active discharge pulldown MOSFET is powered off the device Vbias rail, so it depends on Vbias(UVLO) not on Vin(UVLO) when EN pin is tied to GND.
  • 0 in reply to Haidar Hamoo
    TI__Expert 8675 points

    Hi Haidar

    Not what I expected, just want to make sure I understand. In my customers system, we have the 1.1v LDO powered from a 1.2v buck, the bias is 3.3v. A battery powers both the buck, the 1.8v and a 3.3v buck boost. So if power fails the  3.3v will trip and all is good, I think.

    My other thought is that if the 1.2v goes out of regulation and causes the 1.1v to drop, will that cause the regulator to shut off?

    How is the input UVLO set up with custom voltage rails? and what would the limits be for a 1.1v LDO, is it the 675mv or do we add in a delta for the supply voltage? Example, suppose we have a 2.8v LDO, would not want an UVLO at 625mv.

    Also is the same true with the bias, or is that also fixed?. Believe we need 1.4v plus Vout(1.1vin my case) so a minimum of 2.5v. But if powered from the 3.3v, then there is significant  amount of drop before the regulator sees a UVLO to trip it? and if it is and absolute value in the data sheet then the regulator will be out of regulation!

    Thanks

    Jeff Coletti

  • 0 in reply to Jeff Coletti
    TI__Expert 3995 points
    Hi Jeff,
    My understanding is that the battery supplies a buck and a buck-boost to power the LDO Vin and Vbias rails respectively. Now if either Vin or Vbias rails hit their respective UVLO value specified in the datasheet, the device will turn off since Vin(UVLO) and Vbias(UVLO) are AND gated. Both UVLO values of Vin and Vbias are fixed regardless of LDO output.

    Now if Vin rail drops below 1.1V but > Vin(UVLO), the the LDO will be out of regulation and Vout will track Vin until Vin hits UVLO and device turns off. Similarly for Vbias rail if it dropped below 2.15V (Vout + 1.05V) (in your customer case 1.1V + 1.05V (max Vbias dropout) = 2.15V ) then the device will be out of regulation until Vbias hit UVLO and device turns off.

    Hopefully I have answered your question. Please feel free to post any followup or additional questions that you may still have.

    BR,
    Haidar