• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 630 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Why does the TPS63001 latch up when supplied with lower current?

Marko S
Intellectual 670 points
Other Parts Discussed in Thread: TPS63001, TPS63051

If I supply the TPS63001  with current limited current it will latch up and start drawing high current. Why is that?

First we thought we got bad circuit boards witch short circuits. But when we increased the current limit they started to work ok.

  • 0
    Prodigy 130 points

    No answer to Marko's post for over a year, perhaps it was not detailed enough. We have the same problem and it is a real problem.

    Our system has two alternate sources of power, one is a single cell lithium ion and that works fine. The other is a NiMH stack at nominally 7.2v with a 68 ohm resistor in series. There is no way to change either the voltage or the series resistor, we are interfacing to a legacy device.

    I implemented a 5v pre-regulator to avoid going above the absolute maximum input voltage ratings but the combination will not start. The output goes up to about 2v and just hangs there. The regulator is drawing about 38 ma which drags down the input voltage too far. Once it is running it is fine (if you turn it on then off then on right away it will start up and run). It just cannot start cold with a high impedance source.


    I tried 100uF bulk capacitor on the NiMH battery to try to swamp out the startup current pulse but it still locks up.

    Any way to get this device to start with a high impedance source?

  • 0 in reply to Bruce Ploetz
    TI__Expert 7110 points
    The challenge here is the high impedance in the input path. The device draws a higher current at start-up to pre-charge it's output. If you check the waveforms, I am pretty sure that the device is periodically in following loop: starting up -> VIN collapses -> shutting down -> VIN recovers -> starting up -> ....
    Have you tried to add bulk capacitance after the impedance?

    Maybe using TPS63051 is an option for you as it features a soft-start function.
  • 0 in reply to Florian Feckl
    Prodigy 130 points

    Thanks, Florian, I think your post should be marked as the answer to the original poster. In the data sheet there are graphs that clearly show the startup current required to operate this part. It is not obvious from the text description and specifications but if you read the graphs you can see the problem. For most users this will never be an issue as they are supplying from a low impedance source, like a battery or rectified power supply.


    For reference, if anyone else runs into this problem, I finally solved it by using an LDO to regulate the high impedance power source. The LDO and the TPS63001 can both tolerate being paralleled, so I just connected the outputs directly together and used the enable inputs to control them. This also removed a sharing diode that was wasting power before the regulator. That way the TPS63001 only operates with the battery when it is available and the high impedance power source only has to power an LDO which imposes a very soft startup load.