Electronic – How to deal with D+ and D- on the end of a device that will be charged only

battery-chargingcharginglithium ionusb

This is the opposite of the question posted here:

What is the ideal way to handle data pins D+ and D- on a USB power adapter to be compatible with fast charging on devices?

While that question is focused on how to design a charging port so that devices will be charged from it, I'm curious about designing an end device that I want to be charged with maximum current from all potential ports, if I don't need to use the data ports of the USB for anything else.

My device has a Li-Ion IC that self limits and can charge my Li-Ion battery up to 2A. How do I tell chargers to give as much current as they can? If I short D+ and D- on my board, I will appear as a dedicated charging port. Does that mean that wall outlets will give 1.5A or more if they can, and that laptop hubs or other sources may limit out at 500 mA? Is there any chance of a proprietary charger requiring something else other than D+ and D- being shorted in order to maximize charge current?

Edit:

I'm looking to make my own variant of this PCB from Adafruit. While the part is made to only supply up to 500 mA (despite the schematic labeling), I want to make a version that can charge a 4,000 mAh battery at 0.5C. I also want to remove the USB connection to the AtMega so it can't be reprogrammed.

So take the BQ2425 series for example. I know this is also a "power management" chip which also takes care of regulation in addition to battery charging. But there aren't any equivalent MCP73831 chips I could find that do simple battery charging, just with a higher current.

The point still stands though. If my USB is meant to sometimes pull 2A if the chip is charging, or much less if it's fully charged and maybe just powering the MCU, what do I so with the USB D+ and D- lines on my PCB? Already the two answers I've gotten don't agree, one says short them and one says leave them open.

Best Answer

In the answer you linked, the DP/DM termination is shown for the ‘host’ (downstream facing) port, be it a regular USB or a power-only port. This termination is how an endpoint can determine the host’s charging viability without having to enumerate as a USB device: the ’device’ (upstream facing) port senses the terminator and limits its current draw accordingly. The exact details of this are a bit of a mess - there’s the USB way, the Apple way, the Sony way, etc.

Fortunately, for a simple power connection you don’t have to do anything in the endpoint. Just leave the DP/DM pins open. The host’s current limiting will kick in if your device exceeds what the downstream-facing port can deliver.

More here: https://www.maximintegrated.com/en/design/technical-documents/tutorials/5/5801.html