I have recently designed and assembled a circuit for a Quectel M95 unit to be controlled by Usart from an Atmel micro-controller. I have a problem with the power supply of the M95, I followed the reference circuit provided in their datasheet, only thing I changed was the voltage divider circuit near the regulator to get 4.5V rather then 4.16, still within the M95 limits. Whenever I turn it on it starts to smoke and short exactly on the Vbat pins, I have been looking at it for a couple of days now trying to figure out what I missed.
Maybe some fresh eyes will notice something I missed.
I have uploaded my circuit below.
Thanks
Best Answer
Looking at it won't help a whole lot, beyond seeing which bit smokes.
Time to start debugging.
Measure resistance between Vbatt and ground.
If short circuits, pull the PSU chip off and see if it's still shorted. If you have a spare bare PCB, check that for shorts too, in case there's a layout problem.
Measure current.
If current is exactly what you calculated, look at your heatsinking arrangements.
If current is greater than you calculated, isolate everything after the PSU chip and see if that's OK. Add bits back in one by one until current shoots up, then fix that. That's what razor blades, Dremels and soldering irons are for.
When you find a part that consumes too much, check the soldering - and orientation - carefully. Wouldn't be the first time someone soldered a chip on backwards.