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TPS62163: Dropout Voltage

Part Number: TPS62163
Other Parts Discussed in Thread: TPS62162

I cannot find the drop-out voltage in the spec.  It says that it'll run up to 100%, which implies a very low dropout voltage, approaching 0.  I need a 5V supply with a Vin down to 5.5V.  I would think this part can do it easily, but when I tried the WeBench tool it said there was no solution for 5.5Vin/5Vout for this part.  Thanks for help on this question.

  • Steve,

    The high side FET RDSon may possibly be as high as 600 ohm.  That would result in a 600 mV drop at 100% duty cycle.  That is why Webench did not find TP621163.  Can you tell me your requirements?  Then I can suggest an alternative.

  • Thanks for this info, John.  My application is a battery powered device with a Li-Ion pack that's nominal at 7.2V, but doesn't shut off until 5.5V.  So I want the switcher to operate down to 5.5V, although in practice that won't happen often.  The switcher output is 5V for a USB-powered internal device that draws 450mA.  I don't think I'll actually need more than .5A, but like to have a minimum 1A switcher supplying it for margin.  Given this voltage and current headroom, I think this part will work (since USB can go as low as 4.4V at the device).  I finally did find the spec on the headroom required by this device, .9V, which is likely the .6V plus margin.  If I only need .5A, then it would be a 300mV drop, when I have 500mV available.  I like this part because it's small, simple, synchronous/efficient, I've never used it before (so want to try it to see if it becomes a go-to part going forward), and it's also already in our library.  But I'm open to other parts if they have an advantage over this one, so your feedback is appreciated.  I also need a 3.3V supply, which my current plan is to use another of the same part.  I could use an LDO from the 5V, but being a battery powered I'd rather do for the efficiency.

    - SteveP

  • Steve,

    The worst case RDSon occurs when the input voltage is lower, so with 5.5 V input, you should stay above 5 V output up to about 800 mA output.  For a different device, the trade off would be to use a higher current rated device that will have a lower RDSon.  I think you should be fine with TPS62163 and TPS62162 for you 3.3 V output.

  • Thanks John.  Quick question, do the fixed voltage parts behave identically to the adjustable parts in regards to the drop-out voltage?  If so, I'll go adjustable so I can use the same part twice, reducing the BPM cost (and not having to create two new parts in our library).

    - SteveP