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I'm working on a design that uses a custom USB charging cable that can be inserted into the device with either polarity. The +5V is rectified using a BAS3007A Low VF Schottky Diode Array. This is then fed into an MCP73831 charge controller.

The issue I'm facing is that, due to the diode drop across the rectifier, the charge controller terminates charging before the battery is completely charged.

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During charging I am measuring +4.36V on the output of the BAS3007A (net label: USB). Just before the controller switches to constant voltage charging, the current consumption drops to ~10mA with the status pin of the MCP73831 toggling on/off at about 1kHz.

If I apply a voltage of >4.5V after the rectifier, the same battery will resume drawing 200mA and the status pin will stay low until the charge sequence terminates as expected.

I believe it is because of this statement from the MCP73831 datasheet shown here:

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Any thoughts on how to fix this? Any other charge controllers to recommend that will function with this low of an input voltage? Should I consider boosting the rectified voltage back up to +5V?

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I was able to solve this by using an H-Bridge wired as an active rectifier. By using the recommendation here as inspiration, I bought a MOSFET Array 2 N and 2 P-Channel H-Bridge (DMHC3025) and wired it up as shown in the image below. This removed the voltage drop across the diode bridge and fix the inconsistent performance of my charging circuit.

enter image description here

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You have to add a step-up converter that will boost the 3.36V up to 5V. You need 5V to charge li-ion up to 4.2V

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  • \$\begingroup\$ Sorry, I had a typo there. I'm measuring 4.36V which should be enough to charge a li-ion up to 4.2V \$\endgroup\$ Sep 29 '20 at 12:25

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