I’m implementing MP2722 essentially directly in line with the datasheet application circuit and intend to use the connected batteries as a backup in the event of power loss.
The datasheet calls this “supplement mode” and says:
”If VSYS drops below VBATT, the BATTFET turns on to prevent VSYS from dropping further. In this scenario, the buck converter and the battery work together to provide power for the system.”
This is what I want, but I don’t see any timing specifications or waveform diagrams showing how exactly this takes place in the datasheet.
It looks like the changeover is dictated by “Vhdrm” which is the input vs. battery voltage headroom threshold:
What parameter should I be looking at to understand the timing of how this changeover takes place to supplement power to Vsys?
I don’t know anything about the timing but I use this supplement routinely now on a PCB that charges the 2S battery and provide supplement using MP2672 while the OPi SBC is running and also charges the battery when the OPi is off. One thing to watch out for is that in standalone mode, there is no way to disable the 20h charging safety timer, so after this time the supplemental power turns off. And I could not get I2C mode to work reliablly for the OPi off condition. There is a bug (I think) in the chip that causes the MP2672 to pull down on one of the I2C lines rendering any other device on the same bus unusable. There is another post about this here: MP2672 - I2C comms with power disconnected - #12 by todelbru
