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TPS60400: Replace : LTC1983-5

user5163865
Genius 3980 points
Part Number: TPS60400
Other Parts Discussed in Thread: LM27761, LM27762, INA826, LM2776

Hi All,

Customers are evaluating LTC1983-5. Since Cout was pre-biased to 0.4 V, it was not able to start up normally.
They added Schottky diodes. Although this method works normally, it is still pre-biased to 0.3V. This is beyond the Abs Max Raitings.

 VOUT to GND (LTC1983-5)................... 0.2V to VOUT(= -5V) Max

ADI says it can not guarantee the safety of this circuit.

I thought TPS60400 was the best proposal. However, they need 100 mA Max output.

Does TI have a good suggestion?

I am planning to connect a Schottky diode to the LM2776x. But I could not judge this from the Abs Max Raitings.
The Schottky diode has a VF of 0.1V.

VIN to GND or GND to VOUT(LM27761) ................5.8 V Max

Does this method work well?
Or can the LM27762 with internal LDO avoid this problem?

*The load is INA826. Because positive power is first input, Cout is pre-biased.

Best regards
Hiroshi

  • 0
    TI__Guru**** 150770 points
    Hi Hiroshi-san,

    What Vin and Vout do they need?

    Yes, LM2776 or LM27761 can work with a diode on the output.
  • 0 in reply to Chris Glaser
    Genius 3980 points
    Hi Chris,

    Thank you for your reply.
    Ideally, VIN = 5 V, Vout = -5 V, but allow drop of 100~200mV at 60mA load.

    TPS60400 is 600mV drop at the same condition.
    At least it should have a smaller drop out voltage.

    Anyway, why is the absolute maximum rating of Vout positive voltage(5.8V max)?
    I think it means that -5.8V min to ??? V max.
    LTC1983-5 often latched up, so customers think that max value is important.

    Best regards,
    Hiroshi
  • 0 in reply to user5163865
    TI__Guru**** 150770 points
    Thanks for clarifying. The LT device has an output impedance of 8.5Ohm, so this would be a ~1V drop at 100 mA.

    LM2776 has a much lower output impedance and will thus give a higher voltage. You don't need the regulation provided by the LDO in LM27761, since your Vin is already too low to get -5.00Vout. Use the LM2776.

    LM2776 has no minimum abs max voltage, so this condition is safe for the device. You will need to order the EVM and test it to see if it starts properly with your specific load.
  • 0 in reply to Chris Glaser
    Genius 3980 points

    Chris-san

    Thank you for your clear answer and suggestion.

    I will try to replace LTC.

    Best regards

    Hiroshi