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TPS65132: High current demand at startup

Natalia Parody
Prodigy 30 points

Part Number: TPS65132

I have this split-rail converter feeded with 3.3V, from a previous DC/DC converter (AAT1217ICA-3.3-T1). The TPS65132 It is loadad only with 1.6mA (resistive or linear) at both outputs. The whole system is feeded from an AAA battery. The layout is the same as recomended in the datasheet.

CASE 1: I turn on the system, and the TPS with all outputs disabled, and it's OK.

CASE 2: I turn on the system, and theTPS with outputs enabled and the inrush current is so high the previous converter cannot mantain the 3.3 and goes to a saturation state, the situation is permanent.

CASE 3: I turn on the TPS with the outputs disabled, and then enable POSitive, and after the NEGative, and sometimes, the error is the same.

The previous DC/DC is a AAT1217ICA-3.3-T1 (capable of an output current of 600mA)

The idea is to reduce this inrush current the TPS demands. The system works placing a high value capacitor (200uF), but not in the CASE 2. We want to avoid the use of this capacitor.

¿Can the TPS65132 operate with a 6.8uH or 10uH, or even more?

Thanks

  • 0
    TI__Expert 6330 points

    Hi Natalia,

    I have notified our expert regarding this topic. Please expect a response by 10/5/18.

    Thanks,
    Aaron

  • 0 in reply to Aaron Goodson
    Prodigy 30 points
    Hello Aron, thanks a lot, all those test correspond to a routine in which we want to operate with a near-empty AAA cell (up to 1V), and this can be the limiting factor here.
  • 0
    TI__Mastermind 18550 points

    Hello Natalia,

    How much capacitance do you have in your design for TPS65132 at the boost output REG, OUTP and OUTN? Is it 10uF or less as shown in the typical application circuits in the datasheet? If so, inrush current should not be that high.  Please see figures below from the datasheet that show inrush current to  be lower than 400mA so the pre-regulator should be able to handle it.

    As for maximum inductor value for boost, up to 10uH should work but if you use values higher than 4.7uH, please check loop stability margin to ensure that there enough phase/gain margin.

    Kind Regards,

    Liaqat

  • 0 in reply to Liaqat Khan
    Prodigy 30 points

    Thanks Liaqat,

    Yes, i have 10uF, we're playing with the EVM of the TPS65132W.

    The 300mA demand seems to be low, but after a DCDC converter powered from a AAA battery, the current the battery has to deliver is higher than the Amp for a brief time, and this is impossible in half of the lifetime of the battery.

    The problem is solved with enough capacitor between converters, to keep our lifetime of the battery the same, this capacitor has to be 470uF, but for us is not a viable solution.

    We'll change the topology to a pump charge to generate the -5V

    Thanks a lot for your response and time

    Best regards