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TPS548D21: FSEL[2:1] and external SS and VSEL in AVSO mode

Toshihiro Watanabe
Genius 10235 points
Part Number: TPS548D21

Hello,

I am not clear what is difference if FSEL[2:1] changes. The datasheet says this change internal ramp ratio but I am not sure how to select this.

Mode2 can select external SS and Mode[1:0] can select the ramp time. I am not clear what value it is.

When AVSO is used, VSEL is set the center value. for example, 0.9V typ, we can set 0111 = 0.904. Is my understanding correct?

There are VSEL, FSEL, MODE but each settings are individual. We can select the mode individually what we want to do. Is my understanding correct?

Best regards,

Toshihiro Watanabe

  • 0
    TI__Guru**** 191445 points

    Watanabe-san,

    The preferred internal ramp ratio is a function of switching frequency, output voltage and duty cycle.  Table 7 in the datasheet summarizes preferred values based on those parameters.

    If MODE[2] = 0, then internal slow start is used.  The values are set by MODE[1] and MODE[0].  the options are 1 msec, 2 mscc, 4 msec and 8 msec.

    With AVSO, MODE[3] is set to 1.  In this case, the user will supply the external reference voltage.  The internal reference is not used.

    Yes the VSEL, FSEL and MODE are set individually.  They may affect each other such as the case of AVSO which does not use the internal reference so VSEL is ignored.