strange behavior with the ambient temperature and a switching regulator

Thread Starter


Joined Mar 19, 2016
Hello guys! i am wondering about the next issue:

I have used the next part of Monolithic Power to design the first stage of my power supply tree: MPQ4470A.

When I drive 24V to the input of the MPQ4470A, I get at its output 12V. However when the temperature increases, the output increases step by step until 24V. So when Ta=25 ºC è Vout = 12V. But when Ta=70ºC è Vout = 24V.

I have a PCB V1.0 where the sw regulator works fine. The only difference between my current PCB V2.0 and V1.0 is the output inductor L3. The PCB layout and the layer stackup is exactly the same. I have exchanged the inductors of V1.0 and V2.0 and PCB v1.0 works fine with both kind of inductors but V2.0 does not work fine with whichever inductor.

Finally I got a proper working of the sw regulator on PCB V2.0 making a short circuit L3. Then, the sw regulator works fine at whatever temperature. But I can’t figure out the reason of that behavior, and it is not a good solution because the output ripple is very large.

Does anyone figure out what is happening?