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A Quick Look at the AT&T 47W Dual Port Car Charger's Support of USB Power Delivery

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Pixel 3 XL

by Google Inc.

AT&T sells various mobile accessories from popular brands as well as its own brand of chargers like the AT&T 18W Type-C Wall Charger and AT&T 47W Dual Port Car Charger. While both chargers support USB Power Delivery 2.0 technology for fast charging over the USB Type-C interface, the AT&T 47W Dual Port Car Charger has two USB ports to offer a total of 47 watts based charging.  

The AT&T 47W Dual Port Car Charger supports 15 watts (5 volts @ 3 amps), 27 watts (9 volts @ 3 amps) and 35 watts (15 volts @ 2.33 amps) over its USB Type-C connector, allowing you 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 S9+ using USB Power Delivery through the DC power outlet of your car.

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

The AT&T 47W Dual Port Car Charger also provides a USB Type-A connector for 12 watts (5 volts @ 2.4 amps) legacy charging for USB peripherals.

Given that the AT&T 47W Dual Port Car Charger has been certified not only by AT&T but also USB-IF through the USB certification logo shown on the box meaning that the charger should have a high degree of compatibility to charge most other USB compliant devices.

The AT&T 47W Dual Port Car Charger conveniently allows you to charge two devices simultaneously in your car but in case you're looking for a single port ac wall charger good enough to charge your phone or tablet, you may also consider the AT&T 18W Type-C Wall Charger (click here for review).

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 47W Dual Port Car Charger.

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.

Port1 Plot

The USB Power Test App reports out all the PDO's supported by the AT&T charger and their OCP thresholds. OCP thresholds for the AT&T charger are set at about 24-135% above the maximum current levels for the fixed PDO's.

PDOOCP (A)
PDO#1 Fixed: 5V 3A3.73
PDO#2 Fixed: 9V 3A5.47
PDO#3 Fixed: 15V 2.33A5.47

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.

IV Curve

Since the AT&T 47W Dual Port Car Charger is a multi port charger, the USB Power Test App can be used to determine whether each output port of the charger is able to supply power independently. For every PDO supported by the AT&T charger, the USB Power Test App increases the load gradually for both the USB Type-C and Type-A ports to detect any power loss at the highest load limit for each port.

USB Type-C Port

Port1 Plot

USB Type-A Port

Port2 Plot

The USB Power Test App reports out the voltage, current and load limits for all the PDO's supported by the AT&T charger for each port.

Port1 PDOPort2 PDOPort1 (V)Port1 (A)Port1 Loading(%)Port2 (V)Port2 (A)Port2 Loading(%)
PDO#1 Fixed: 5V 3A 5.032.97100% (15W)   
PDO#1 Fixed: 5V 3APDO#1 Fixed: 5V 1.5A52.9899.59%5.161.51 
PDO#2 Fixed: 9V 3A 8.982.98100% (26.8W)   
PDO#2 Fixed: 9V 3APDO#1 Fixed: 5V 1.5A8.962.9799.66%5.161.5 
PDO#3 Fixed: 15V 2.33A 14.932.32100% (34.6W)   
PDO#3 Fixed: 15V 2.33APDO#1 Fixed: 5V 1.5A14.912.33100.49%5.141.5 
 PDO#1 Fixed: 5V 1.5A   5.11.5100% (7.7W)
PDO#1 Fixed: 5V 3APDO#1 Fixed: 5V 1.5A52.98 5.161.51101.42%
PDO#2 Fixed: 9V 3APDO#1 Fixed: 5V 1.5A8.962.97 5.161.5100.93%
PDO#3 Fixed: 15V 2.33APDO#1 Fixed: 5V 1.5A14.912.33 5.141.5100.67%

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 47W Dual Port Car Charger, some compliance failures were observed even though the charger claims it is 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

PASS

3

PHY_PRIMARY_MISC

BMC Physical Layer Miscellaneous

PASS

4

PROT_PRIMARY

Protocol Specific Primary

FAIL

5

POWER_PRIMARY

Power Source/Sink Primary

FAIL

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

PASS

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

11

TDA.2.2.7

TDA.2.2.7 BMC PROT BIST NOT 5V SRC

FAIL

13

TDA.2.2.9

TDA.2.2.9 BMC PROT GSC REC

FAIL

15

TDA.2.3.2.1

TDA.2.3.2.1 POW SRC TRANS P PC

FAIL

BMC Eye Diagram


Eye Diagram 

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