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TPS54620 - Minimum Vin to Output 4.25V

John Porter1
Intellectual 345 points
Other Parts Discussed in Thread: TPS54620, TPS62130, TPS62180

My customer needs to generate a 4.25V output , and would like to know how low the input could be to support a 4.25V output in a buck only regulator?

Requirements:

Vin @  4- 9 volts  (4.5V input may be low enough,  would like to go all the way to 4 volts but if its not practical, I will push for 4.5 to 4.75V input)

Vout @ 4.25V

Iout @ 4amps max

Integrated would be preferred (hence the TPS54620), but I am willing to use external fets if needed.

  • 0
    TI__Guru*** 142710 points

    We just released TPS62180, which has a true 100% duty cycle mode.  Otherwise, TPS62130 gives 3A with 100% duty cycle support.

  • 0 in reply to Chris Glaser
    Intellectual 345 points

    Chris,

    Thanks for the response. I passed the suggestions along to the customer. They would still like to know what the minimum input voltage that is required for the TPS54620 to output 4.25V output?

    Thanks,

    John

  • 0 in reply to John Porter1
    TI__Guru**** 191445 points

    TPS54620 can operate at near 100% duty cycle.  The limitation is the BOOT cap charge.  When the BOOT voltage falls below the BOOT UVLO, the high side turns off and the low side turns on to recharge the BOOT cap.  The other limitation on headroom is the drop across the FETs, which depend on the actual RDS on and load current.  The output voltage is the time average of the switch node voltage. It is pretty easy to get the rough number from the first order approximation (assume typical RDS on and SW waveform a simple pulse train) but gets more complicated if you want to add temperature compensation, dead time, switch rise and fall times, inductor losses, etc.

    So for the easy case, assuming the BOOT charge is between 3 and 6 V and RDSon is 50 mohm max, and Iout = 6 A, then Vin min = 4.25 + 0.05*6 = 4.55 V

  • 0 in reply to JohnTucker
    Intellectual 345 points

    John,

    Thanks for the quick response. This is exactly what the customer was looking for.

    John