Hi,
We use LTC3890 on our PCB to convert a 18V battery input to 12V. We follow the schematics of evaluation board DC2236A-B (12V 25A output). It was working fine in our hand-soldering prototype board. But after ordering 20 of the assembled boards from a factory, we are seeing inconsistent ringing behavior during start-up for different boards.
Expected behavior
When the board is working correctly, it should convert 18V battery input to 12V. We should be able to draw current from it. We shouldn't hear any ringing sound. The video below shows this behavior with a load tester.
Observed behavior 1: short ringing and then stabilized
In this case, when we turn on the power, there will be a short ringing sound and the output voltage will be around 10.8V. Then it gradually increases to 12V and the ringing sound goes away.
Observed behavior 2: long ringing then stabilized
In this case, the ringing sound is longer, but still stabilized afterwards.
Observed behavior 3: keep ringing and never stabilized
In this case, it just keeps ringing and outputs 10.5V. Once we try to draw current from the converter, it drops down to almost 0V.
Instead of being 0.8V, the feedback voltage will be around 0.72V.
Inconsistency
The most frustrating part is the inconsistency of the issue
- Some boards works as expected even after 50 times turning on and off.
- Some boards works the first couple times then starts having brief ringing. Then becomes not working with continuous ringing.
- Some boards will start working after I reflow the same LTC3890 IC.
- Some boards will start working after I swap out to another LTC3890 IC.
- Some boards will start working somehow after I add some flux around the IC.
