Hello,
I am using a LM2599 to buck my voltage from 7.4V to 5V. The regulator functions correctly in normal operation, but it doesnt work in shutdown (SHDN driven low).
Briefly, my setup is a 0.1uF capacitor between SHDN/SS and GND, and a switch that can drive it low. I included a diode between the LM2599 and the switch, but because the datasheet lists 0-1.3V as the shutdown range this seemed fine. When I flick the switch, the voltage on SHDN/SS correctly goes to 300mV (the forward drop of the diode) but the output doesnt go to 0V. Instead, it hovers around 0.8V.
Perhaps most strangely, I have implemented this same design on another board (EAGLE's 'cut' command) and it works fine - output voltage goes to 0V when SHDN goes to 300mV.
Any ideas as to what I am doing wrong? Thank you
Sam