my company is designing a high volume automated test system for a customer that is using an MPQ4484 charger on it’s design.
We build a PCB that can load the VBUS supplied and measure the current, and we have probes to measure the Dp Dn lines too.
The data lines are connected with a 150 Ohm resistor on the device.
We noticed that sometimes the MCP4484 is giving out 2.7 volts on Dp/n to gnd, sometimes 0.5v.
The measure is taken with no load on VBUS and no pullup/down resitor on Dp/Dn.
My guess is that we are confusing the autodecttion scheme described in the datasheet as below:
The MPQ4484 integrates a USB-dedicated
charging port auto-detect function. This function
recognizes most mainstream portable devices
and supports the following charging schemes:
–> USB battery charging specification BC1.2/
Chinese Telecommunications Industry
Standard YD/T 1591-2009
–> Apple divider mode
–> 1.2V/1.2V mode
–> USB Type-C 5V @ 3A DFP mode
The auto-detect function is a state machine that
supports all of the DCP charging schemes
above. Connect DP and DM with 150Ω resistor
for DCP mode.
So my questions are the following, is there a way to trick the autodetection to go always in the same direction (eg Apple divider mode)? How does this autodetecton work?