I already have a case open CS0175983
I'm trying to understand why the SS does not appear to be working correctly.
Conditions:
VIN = 24V (ramps from 0-24V in 9ms)
VOUT = 15V
Css = 22nf (looking for a 10ms ramp from 0 to +15V in 10ms)
EN pin = floating
Cout = 60uF
When I apply +24V - Vout starts to ramp up to 15V but as it reaches +5V (in ~2ms) the output voltage just jumps to +15V without finishing the ramp. I have experimented with increasing Css to 200nf and while the Vout ramp is longer the result is the same... when Vout reaches 5V it then jumps directly to 15V. You can see these scope traces by looking at the case file# provided above. I took several scope traces of the EN pin, SS/TR pin and FB pin. I have run WEBENCH and TINA and they both behave as I would expect them to (with a monotonic ramp from 0 to 15V in the time I would have expected it to). I have also included in the case reports a copy of the circuit. Layout can also be provided if needed. I have several boards with this new part and they behave exactly the same. I had been using the TPS54335 which has performed very well but I needed to change because our input voltage requirement increased above the TPS54335 rating. I've been struggling with this issue for almost a week and need to resolve it or move to a different part. Please feel free to reach out and call 717-496-5400.
Thanks for your support
Bill