We used the USB Power Test App from Granite River Labs with the Granite River Labs USB Power Delivery Compliance C2 Tester to generate the following test results for the Essential Fast Charger.
The USB Power Test App first negotiates a power contract for every PDO supported by the Essential Fast 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 also reports out all the PDO's supported by the Essential charger and their OCP thresholds. We can see that this charger actually supports four PDO's for charging: 15 watts (5 volts @ 3 amps), 18 watts (6 volts @ 3 amps), 21 watts (7 volts @ 3 amps), and 27 watts (9 volts @ 3 amps). The USB-IF specification does not require that the Essential PH-1 phone support 6 and 7 volts but we observe in a later post that the phone actually uses all these four voltage levels when charging from the Essential Fast Charger.
OCP thresholds for the Essential charger are set at about 10% above the maximum current levels for the fixed PDO's.
|PDO#1 Fixed: 5V 3A||3.35|
|PDO#2 Fixed: 6V 3A||3.34|
|PDO#3 Fixed: 7V 3A||3.33|
|PDO#4 Fixed: 9V 3A||3.32|
The USB Power Test App takes this data to produce an I-V curve which graphically shows the relationship between voltage and current for each PDO. We can observe current fold-back behavior for the 1st, 3rd and 4th PDO's where as the current increases beyond the OCP threshold, the voltage starts to drop down rather than immediately shutting off. The 2nd PDO behaves differently than the other PDO's where the voltage just shuts off once the current goes over the OCP threshold.
The USB Power Test App can also use the Granite River Labs USB Power Delivery Compliance C2 Tester integrated with the GW Instek APS-7100 programmable AC power supply to compare the charger's power output vs power input so that power efficiency can be measured and compared to regulatory limits from United States of Energy (DOE) Level VI or European Union's CoC Tier 2 requirements. We can repeat the power efficiency tests for different PDO's, current load conditions, and different AC input ranges, allowing us to get a complete picture of power efficiency ranges across all different usage scenarios.
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, most of the tests performed for the Essential Fast Charger were observed to pass compliance except for one compliance failure as seen below.
BMC Eye Diagram
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