Hello,
We’ve got a MPM3810GQB-33-Z running from a 5V input powering a number of PCBs in a stack. It runs happily until we plug in the last board in the stack - with the extra board added the load on the 3V3 rail on startup looks like this.
If I overdrive the output of the MPM3810 with an external PSU at 3V3 and then remove it it regulates fine and stays working. Tweaking up he external bench PSU the current being draw from the MPM3810 by the stack is 0.56A in the running state.
Is there any way to increase the soft-start time / do something with the OUT_S pin that might help get the MPM3810 get starting up?
Kind regards,
Dave
Hi Dave,
This part has built in soft start, so I don’t believe it can be changed. This could be from inrush current. Would you mind clarifying a few questions below?
What is the output current being drawn from these loads?
Would you mind clarifying what the waveform is measuring?
Do you have a schematic you can share?
Best Regards,
Yu
Hi Yu,
The waveform above is the voltage at the VOUT output of the MPM3810GQB-33-Z
The converter is delivering 0.56A to the 3V3 output when the MPM3810GQB-33-Z has been started-up by applying an external power supply briefly to its output.
Our circuit is here: the 10uF caps are 25V X5R
Kind regards,
Dave
Hi Dave,
Would you mind elaborating on what is downstream? Are there input caps at the load side?
Best Regards,
Yu
One potential issue with downstream converters is they can draw far higher than operating currents at low input voltages. So for instance a 3.3V 1A supply operating form 9.9V only takes 0.33A off the supply but if it has no undervolatge lockout will load that 9.9V supply at 1A as the 9,9V supply comes up to 3.3V. A 3X overload vs the normal operating condition.
You can get around this by using the PG of the upstream converter to old off the downstream converters, or by using a voltage divider to the EN pin to hold off the downstream converter until the upstream converter is a nearly its final voltage.
