Hello,
We are developing 16ch USB charger using TPS2513 controller and TPS2561 switch.
In addition to basic function customers wish is to have also LED indication of port status like "Ready"/"Charge"/"Error". To fulfil this we added simple low side current sense resistor 50mOhm and LM324 opamp with 15mV negative reference.
While 2ch prototype worked well we are experiencing now on 16ch prototype big troubles due to unstable GND which can shift up under load for a few ten mV, measured also more than 100mV (20mV @ 250mA load; 80mV @ 1A load; 160mV @ 2A load; all with reference to PS ground) and indication doesn't work well any longer.
Since we are not very experienced I would like to ask is this GND issue something to expect or maybe, for example, inappropriate PCB layout could lead to such consequence.
Thanks in advance,
Stane
