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Looking for a simple switcher without cycle by cycle current limitation feature

christopher2
Intellectual 515 points
Other Parts Discussed in Thread: TL494, TPS544B25, TPS56121, TPS53353, TPS53355

I have a problem with interaction between the DC/DC converter and its protecting IC TPS25944 which is before the DC/DC.

The protector TPS25944 has current limit set to 0,7A and  if dc dc converter is overloaded and shorted it starts to limit current cycle by cycle. This makes a problem for the TPS25944 to be proper trigerred and switched off when system starts with the overload already at the output what can happens. The current spikes are smaller than single shot Itrip value and they are to short, for the internal 4ms timer, which is switching off the TPS if overload is higher than 0.7A and longer than 4ms.

So the solution could be find a simple switcher which has no cycle by cycle current limitation. the general idea to protect the dc/dc on its input is to safe battery which supplies the circuit. I know the nominal output current on the 3.3 output, I can recalculate its for the input current, and if something happens DC/Dc is switched off. What is also behind this solution is also this, that the battery is protected also in case of internal failure or short in the dc/dc, internal diode or internal low high side short.

So I am looking for a simple switcher:

9-12V input, 3.3 V output 2-3A. With thermal pad and no cycle by cycle current limit. Just simple PWM modulator with voltage control loop ( internal current loop can be for better stability), can be with internal diode and with internal FET and also internal low side FET, instead of the diode.

The post with my problem was also described here:

e2e.ti.com/.../2417600

  • 0
    TI__Guru**** 191445 points
    Christopher,

    I don't think we would have any integrated parts without current limit. You could look at a really old controller such as TL494:
    www.ti.com/.../TL494
    You could also consider a device like TPS544B25 with PMBus control. With PMBus you have a lot of options about how the device responds to over current events. The down side for you is implementing PMBus control and the fact that it is rated for 20 A load current.
    You could consider a non-PMBus control with a very high adjustable current limt. Set the OCP level to a very high value such as 30 A. That way your input protection would trigger way before. if this would work for you, look at TPS56121 or TPS53353.

    Let me know if any of these suggestions would work.
  • 0 in reply to JohnTucker
    Intellectual 515 points

    Hi, Thanks for the suggestions. I am considering these without PMBus. TL494 looks quite good as well but external the FET is needed in this case. What is also important is a low Iq, so What i see only TPS53353 would fit or 355.

  • 0 in reply to christopher2
    TI__Guru**** 191445 points
    Christopher,

    Yes, TPS53353 (20 A) or TPS53355 (30 A) would be potential solutions. They are very much overkill , but you won't have to worry about current limit occurring prior to your protector tripping.