TPS548D22: SS=4ms Waveform

Yone-san,

It appears that is normal variation.  See the following waveform from the users guide.  It shows just less than 1.2 msec (400 msec/minor division):

Compare this to another EVM I measured today in the lab.  It shows 1.02894 msec:

Yone-san,

See the datasheet section 7.5.1.3.1.  4 msec SS time requires 9 x 0.95 = 8.55 msec delay from VDD_UVLO and EN_UVLO.  Please increase the delay and remeasure.

Yone-san,

Tss is generally measured as the ramp time of the internal reference from the initial zero voltage to the final regulation voltage.  There is typically a small amount of loop-delay between when the reference voltage starts to rise and when the output voltage starts to rise, to the exact rise time of the output voltage is typically slightly shorter than the programmed Tss time.