iMX28 charger appears to have too much voltage drop

[michaelkoelbl]

We're using the embedded iMX28 charger to charge a LiIon-battery. As it is a large battery we want to charge with 400 mA, drawing 600 mA from VDD5V as we need about 200 mA for the board itself (iMX28 + peripherials). Due to the voltage drop on the USB cable we have only 4.75V at the iMX28 (measured nearby the BGA ball). But with 4.75V - the specified minimum voltage in the iMX28 data sheet - the iMX only draws 400mA from VDD5V, delivering about 200 mA to the LiIon-battery, which had 4.0V at the measuring time. When I increase VDD5V so that I have 4.85V at the iMX28 VDD5V current increases up to 600 mA.

Has anyone an idea or had seen the same effect?

Thanks, Michael

[jamesbone]

How fast is configure the current flow ramp up? The rate at which the charging current can rampup to its maximum depends on the robustness of your power supply. If the charging current increases too rapidly, then the power rails may droop. Drooping could trip the brownout alarm and cause the system to shut down.

For your design  I think the charging current can ramp up at 75mA/s.

Have a great day,
Jaime

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