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TPS40345: VREF/SS Pin not operating as expected

Tyler Mills
Prodigy 40 points
Part Number: TPS40345

Tool/software:

Hello,

In my design , I use the TPS40345DRCR to output power on a rail. I need to adjust (lower) VREF at times to adjust the output set point:

https://www.ti.com/lit/ds/symlink/tps40345.pdf?ts=1717945785633&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS40345%252Fpart-details%252FTPS40345DRCR

Based on the datasheet, when the SS pin is below the 600mV internal reference, the internal op amp uses the SS pin's voltage as the reference (bottom of page 10):

There is an 800mV offset, so 1.4V on the SS pin is equal to 1.4-800 = 600mV being compared to the reference. So, (slowly) pulling this pin below 1.4V, I would expect the reference voltage (and thus the output) to be reduced after the converter has reached steady state. 

However after letting the converter reach steady state, and then beginning to pull this pin below 1.4V, nothing happens. The converter keeps operating as if the original reference is still being utilized. I have pulled this pin below 1V to no effect. I can still turn off the device by pulling it low. What am I missing?

Thanks

Jesse