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TPS54020 in a 100% duty cycle application

David Ellis
Prodigy 185 points
Part Number: TPS54020

section 8.3.12 of the TPS54020 mentions:

"100% duty cycle operation can be achieved as long as (VIN – PVIN) > 4V."

Q1) what is the current needed to supply the Vin control circuitry?

Q2) If another boost regulator is used to provide VIN separate from PVIN, can the TPS54020 be used for ths application requirement:

 

  •  need to step down from 12V and need to be able to have Vout = Vin (understand not possible due to RDS on and inductor resistance) but would like to have 100% duty cycle capable. 

  • Nominal Vin is 12V +/- 10%.    Vout = Vin and digitally controlled down to anything lower (will use a digital POT as the feedback element).

    • Regulation tolerance is not that important but would prefer a higher freq. of operation to keep inductor size reasonable. 

 Vin =  4V min  to 17V max 

Vout = ~ Vin …..100% duty cycle capable

Iout =  5A

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  • 0
    TI__Guru**** 191445 points

    David,

    The internal control circuitry uses about 1 mA.  There is also the BOOT charge current, which is application dependent, Probably in the range of 10 mA during each recharge cycle,  I think you have another thread n this topic.  Are you sure you would not rather use a buck-boost controller?  Will you ever require an output voltage greater than 12 V?  For Vin = 17 V when PVIN is greater than 13 V, you can no longer operate in 100 % duty cycle.  The other thing I need to mention is that for current mode control, the term Vout / Vref enters into the small signal transfer function (unlike voltage mode control).  So you have to be very conservative with your loop compensation to operate over a wide range of output voltages.

  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points
    David,

    Do you need any further assistance?