Hi,
I'm using a LMR16006 simple switcher and I'm using the !Shutdown input to get an undervoltage lockout.
Im using a voltage divider with 330k and 22k. This results in a Vstart = 19.7V and Vstop = 18.7V. Vhysteresis is about 1V.
When I tested the circuit I found that the switcher doesn't stay shutdown. It comes back up only to shutdown again after a couple of milliseconds.
See attached scope (Ch1 = open; Ch2 = LMR16006 output voltage; Ch3 = Input voltage; Ch4 = voltage at !shutdown pin of simple switcher)
First I thought that this is probably due to the noise on the shutdown pin. But at t = 0 (where it seems that the shutdown is triggered) the voltage at the shutdown pin should drop by about 66mV (3µA * 22k || 330k) but it doesn't. Which makes me think that the shutdown logic may not be responsible for the first dip in the output voltage. But what is?
Thanks in advance!
Regards,
Konstantin