Hi, I’m considering the MP2722 for a DRP application, and it seems pretty much ideal for my purposes. However, I have a question about the power path in source mode, with two potential sources. Besides the battery, I’m also going to have an external power input that is unreliable, but notionally 5V. Note that this is not expected to be producing any power when in Sink mode.
I’d like to use this input to either supplement the USB source, or to charge the battery if no device is connected.
I expect that it would be possible to devise a circuit which connects it directly to IN when at voltage, and put the appropriate signals on D+ and D- for basic charging. However, it would seem more sane if this could be connected to Vsys. Is this possible?
Hello Nathaniel, welcome to the MPS Forums!
For your application, it seems better to connect the external power source to IN and let the MP2722 handle the switching between the battery and your external source since you wanted this external source to supplement the USB or charge the battery with no devices connected.
This would allow for more control over the charging process along with ensuring that your system is protected.
However, if you wanted to specifically supply Vsys directly with external power when no USB is connected, you will need to make sure that the external voltage is within the range Vsys operates at based off the specified range as outlined in the datasheet:
However connecting your external power supply directly to Vsys would bypass some of the intelligent power switching features of the IC, so I would still recommend deferring to connecting this external source to IN and let the MP2722 do the rest.
Hopefully this provided some insight.
Best,
Krishan
1 Like
Hi Krishan, thanks for you help on this. I think this works for both the possible operation sequences:
1:
USB device attached. MPS2722 goes to source mode.
Device is powered from battery.
External current added to VBUS, reducing current taken from battery.
2:
External voltage applied to VBUS.
MPS2722 goes to sink mode with an unknown device current limit of 500 mA.
Microcontroller sees that it is in sink mode (VIN_GD), and that the AC source is cycling. IIN_MODE programmed over I2C to 0.9 or 1.5A.
USB device is attached.
USB device pulls 500 mA current from VBUS.
This likely drops the supply to VIN_LIM, or in any event triggers one of the regulation loops, and interrupts the uC.
uC logic to discern between low speed/power condition and a device being attached.
MPS2722 is changed from sink to source by uC.
On this last operation, would this be a full reset of the 2722, or would simply disabling the charge and reconfiguring be sufficient?
I can verify the first operation based on the way the MP2722 . However, for your question regarding the second operation, disabling the charge and reconfiguring should be sufficient, but please test this before configuring as such. If not, a full reset may be necessary.
Best,
Krishan
1 Like
Hello all,
Sorry for jumping on this conversation, i am actually doing what Nathaniel is thinking about doing. i got a board, and i think i didn’t understand the rst, since i wanted to turn on and off the device added a small rocker (lighted) switch but when i turn it on i get nothing, checking voltages i get out my SYS, could you see where i am making a mistake?
Thank you,
Jeison
Hello arcos.jeison,
Since this post was solved, it seems this post nearly fell under the cracks:
Please see the associated typical application for the MP2722 with the attached BOM as a reference in comparison with this design:
If you are still working on this project, please reference this post and create a new one as a reply.
Best,
Krishan
