I’m using the MPM3515 configured exactly as in the data sheet. My resistor divider is 75K on top and 16K on bottom. Layout and schematic were reviewed by Monolithic FAE and all was deemed good. For some reason, the voltage at the FB pin is well outside the range stated in the data sheet. I was expecting to see roughly 807mV but instead I measure 860mV (the max is listed as 819mV).
The output voltage is right at 4.58V, which is what one would expect with the 75/16 divider. But there’s still the matter of the voltage at the FB pin. It’s almost as if the FB pin is sourcing current into the lower resistor, driving up the voltage from the expected 807mV to the higher 860mV.
Any ideas what could be causing this? The data sheet isn’t very wordy and it states that the range of VFB given (795mV to 819mV) is when VIN is 12V. Could it be as simple as 807mV is only normal at 12V input? My prior experience with regulators has been that the voltage at the FB pin is compared to an internal reference that is independent of supply voltage, so I’m going to guess that the voltage at the FB pin shouldn’t depend on the input voltage.