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TLV62090 Start-up failing with no SS cap

WhiteHorse
Genius 4430 points
Other Parts Discussed in Thread: TLV62090

Is there any errata on the tlv62090? We have a customer that is having a problem when there is no SS capacitance the regulator won’t start at Vin = 5.0V.  They are also having a problem starting with 6800pf at 85C and Vin = 5.0V on some parts. 

Vin range is 3.3 to 5.5  the problem is Vin > 4V

Vout is 1.0V

The load current while running is .5A to 1A

The current should be the same + or – 10% due to temperature difference.  They don't see the problem when they added 10,000pf to the 6800pf SS cap.

See attached schematic.

4338.Schematic.pdf

 

  • 0
    TI__Guru**** 150770 points

    You are likely hitting the hiccup current limit that is active with a very low Vout.  Observing the inductor current occurring in pulses of 32 would confirm this.

    With your relatively large Cout, I would really recommend a SS cap.

  • 0 in reply to Chris Glaser
    Genius 4430 points

    We confirmed 32 pulses of inductor current so the TLV62090 is reaching the hiccup current trying to charge the load capacitence.  HOw can the customer calculate a soft start capacitance value that will not allow the 4.6A current limit to be reached during start up?

  • 0 in reply to WhiteHorse
    TI__Guru**** 150770 points

    The point is that it's not a 4.6A current limit during startup--it's 1/3 of that amount.  So, with your heavy load at startup, you easily reach it when no SS is used.

    You need to reduce the inrush current into the output caps by slowing the SS enough so that the load current plus the inrush current to charge the output caps is less than the startup current limit.  I would then add another 50% to the SS cap value to give margin to these values to account for component variation.