How does "smart" chargers for smartphones and tablets work

[aiq25]

Hi I was wondering if anyone provide some articles or sources where they explain how does the "smart" chargers for smartphones and tablets work. What I mean is I would like to understand what voltages the D+/D- lines on the USB have to be to get higher current output from the USB chargers.

I was always under the impression that a universal USB charger for devices "detects" the voltage on the D+/D- lines to determine if higher currents (1A, 2A, etc...) should be outputted. And the voltages on the D+/D- lines are set on the device (phones, tablets) and not on the charger.

[Towger]

AFAIK the data lines in the usb plug are shorted, so the device knows it can draw more current.

[ablacon64]

I have an HP Slate 7 2800 tablet and lost the AC adapter. The new adapter (not original) only worked after I shorted D+ and D-.

[sleemanj]

In brief:

Androidy stuff, the charger shorts the d pins.

Iphony stuff the charger provides a voltage on the d pins, the specifics of which determine the current capability.

In anycase, it is the charger that has the pins short or whatever, the shorting is the charger saying what ITs capablity is, the device looks at it to know how  uch it's charging circuit can draw.  Remember a usb charger is nothing more than a 5v power supply, the actual charging profile is managed by the device.

[Howardlong]

The Microchip USB3751 device will identify the various non-proprietary chargers for you (ie those in the USB spec). Take a look at Table 4-1 on page 14 of the datasheet here http://ww1.microchip.com/downloads/en/DeviceDoc/00001824A.pdf

USB battery charging is historically a complete mess due to glacial pace of standards bodies being out of sync with the pace of technology and market demands.

Edit: I just noticed they have an app note here http://ww1.microchip.com/downloads/en/AppNotes/en567019.pdf

[miguelvp]

You could get one of Franky's YZXstudio meter.

https://www.eevblog.com/forum/buysellwanted/franky's-sales-thread/msg690194/#msg690194

Not sure if it's the red one or the yellow one that has the feature to detect the voltages, I'm pretty sure is the red one, but the video review from Julian Ilett should explain more:



BTW Franky if you are reading this, what's up with the "Androd"? you should get the designer/maker of the device fix that. Then again, it might already be fixed on the firmware update you already mentioned.