I have done a PCB with a TPS63020 who delivers 3.3V under Vin=4.2V.
I measure a drop, off 100mV when the load takes 1.05 A. ( Vout = 3.3V , when Iout=50mA and Vout=3.2V, when Iout=1050 mA )
Measurements on the evaluation board shows a drop, off only 20mV.
You can see my schematic, board and component placement. Is there possible the problem come from the placement of the capacitors on Vout ?
you should track the voltage on FB pin, referrer to a GND as close as possible to the IC.
what you will see is that the FB voltage is basically flat Vs Output current (or at least, within the specifications stated into the datasheet).
the error (I guess) you are doing it to measure VOUT in a point that differs from the one in which you are drawing current: the voltage drop you are observing are nothing more that the copper pcb R times the Output current.
you should change you pcb moving the sensing point as close as possible to the Point Of Load: refer and compare your layout Vs the one of the EVM for clarification.
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