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?