How the Power Profile Looks Like for the AT&T 35W PD Car Charger Supporting USB Power Delivery

The AT&T retail store is one of the many places to shop for different kinds of mobile/PC accessories and smart devices. From popular brands like Belkin, mophie and Samsung, AT&T also offers its own brand of products such as the AT&T 18W Type-C Wall Charger, AT&T 47W Dual Port Car Charger and AT&T 35W PD Car Charger.

The AT&T 35W PD Car Charger supports USB Power Delivery 2.0 technology for fast charging over the USB Type-C interface through the DC power outlet of your car. This car charger makes use of 15 watts (5 volts @ 3 amps), 27 watts (9 volts @ 3 amps) and 35 watts (15 volts @ 2.33 amps) power profiles to quickly charge tablets and smaller notebook computers like Apple's 11-inch iPad Pro (2018) and MacBook (Early 2016) and phones like the Apple  iPhone XS Max or Android phones such as Google's Pixel 3 XL and the Samsung Galaxy S10 Series.

Note if you need to charge your iPhone you need to use the Apple USB-C to Lightning Cable.

Like many AT&T chargers, the AT&T 35W PD Car Charger has been certified by both AT&T and USB-IF as seen from the USB certification logo on the box. This means that this car charger should have a high degree of compatibility to charge most other USB compliant devices.

It's a good thing that the AT&T 35W PD Car Charger comes with its own USB Type-C to Type-C cable accessory which you won't need to use your own cable with the charger.  

While the AT&T 35W PD Car Charger has only a single USB Type-C connector and in case you want to charge multiple devices, you may look for the  AT&T 47W Dual Port Car Charger which has both a Type-C and Type-A connector.

Using the USB Power Test App from Granite River Labs with the Granite River Labs USB Power Delivery Compliance C2 Tester, we performed the following tests for the AT&T 35W PD Car Charger to find out more on the charger's power capabilities.

The USB Power Test App first negotiates a power contract for every PDO supported by the AT&T charger, and increases the load gradually to find the threshold where over current protection (OCP) kicks in and voltage and current start to drop for safety reasons.

The USB Power Test App reports out all the PDO's supported by the AT&T charger and their OCP thresholds. We can see that for the 9V and 15V PDO's, the OCP thresholds above the maximum current levels are very high which should only be around 10-20% for best practices.

PDO	OCP (A)	%OCP
PDO#1 Fixed: 5V 3A	3.18	105.9%
PDO#2 Fixed: 9V 3A	5.48	182.6%
PDO#3 Fixed: 15V 2.33A	5.5	235.8%

The USB Power Test App from Granite River Labs also produces an I-V curve which graphically shows the relationship between voltage and current for each PDO. We can observe as the current increases beyond the OCP threshold, the voltage immediately shuts off.

Using the USB Power Delivery Compliance C2 Tester from Granite River Labs to run just a subset of the full USB Power Delivery compliance test suite for the AT&T 35W PD Car Charger, some compliance failures were observed even though the charger claims to be USB-IF certified so just be careful when using this charger.

USB-IF High Level Mapping Summary

Sl No	Test Category	Test Group Description	Test Result
1	PHY_PRIMARY_TX	BMC Physical Layer Transmitter	PASS
2	PHY_PRIMARY_RX	BMC Physical Layer Receiver	FAIL
3	PHY_PRIMARY_MISC	BMC Physical Layer Miscellaneous	PASS
4	PROT_PRIMARY	Protocol Specific Primary	FAIL
5	POWER_PRIMARY	Power Source/Sink Primary	PASS

Result Summary

Sl No	Test ID	Test Name	Test Result
1	TDA.2.1.1.1	TDA.2.1.1.1 BMC PHY TX EYE	PASS
2	TDA.2.1.1.2	TDA.2.1.1.2 BMC PHY TX BIT	PASS
3	TDA.2.1.2.2	TDA.2.1.2.2 BMC PHY RX INT REJ	FAIL
4	TDA.2.1.2.1	TDA.2.1.2.1 BMC PHY RX BUSIDL	PASS
5	TDA.2.1.3.1	TDA.2.1.3.1 BMC PHY TERM	PASS
7	TDA.2.2.1	TDA.2.2.1 BMC PROT SEQ GETCAPS	PASS
8	TDA.2.2.2.1	TDA.2.2.2.1 BMC PROT SEQ CHKCAP P PC	FAIL
9	TDA.2.2.2.2	TDA.2.2.2.2 BMC PROT SEQ CHKCAP NOMARK P PC	PASS
13	TDA.2.2.7	TDA.2.2.7 BMC PROT BIST NOT 5V SRC	PASS
15	TDA.2.2.9	TDA.2.2.9 BMC PROT GSC REC	FAIL
16	TDA.2.3.1.1	TDA.2.3.1.1 POW SRC LOAD P PC	PASS
17	TDA.2.3.2.1	TDA.2.3.2.1 POW SRC TRANS P PC	PASS

BMC Eye Diagram