USB Tester Legacy Charger

[dattatreyaroy]

Hello,

I recently used the USB tester to test a USB charger. Upon connecting the device under test / charger to the testing device, the tester identified the charger as a legacy charger (5V, 500mA - attached screenshot). So is this charger a SDP (standard downstream port), CDP (charging downstream port) or a DCP (dedicated charging port)?

BR,
Dattatreya

[David (PassMark)]

SDP and CDP both allow data transfers (like the USB ports on a computer). So a phone charger can't be either of these.

DCP is for charging only. Usually DCP devices support between 500mA and 1.5A (up to 7.5W) of power at 5V.

But very old chargers might only support 500mA. Which is a tiny 2.5W. For comparison, some new high end chargers now run at excess of 100W.

There was also very very very old USB ports that did only 100mA.

So I don't think your charger is meets the requirements for any of those options. It is a legacy device, maybe made before the DCP standard was defined?

[dattatreyaroy]

Okay, yes it definitely is one of either DCP or a legacy charger.

Interestingly I just switched the cable and used a thicker USB-A to USB-C cable (provided in the package), and now it detects the charger as follows - "BC-DCP Voltage: 5.00V Max Current: 1500mA" (attached screenshot)

What can we conclude now? What is a BC-DCP charger?

[David (PassMark)]

USB cables are a bit complex now with Type-C and the evolution over time.

So some cables have a pull up resistor on the CC lines that indicate that the cable can carry more current. Some also have chips in the cable (E-Marked cables).

In addition to this the ports on the charger might also have the USB2 data lines shorted with ~200Ω between data lines. If you have a cable that doesn't contain the data lines (a cheap charging only, no data, cable) then this short can not be detected and it becomes a legacy device.