Currently USB screen are using two version of power supply chip, one is SY7200AABC, another is PT4103.
I thought they should be same function and work in same way…but I am wrong. PT4103 backlight is not as bright as SY7200AABC.
There is something wrong about PT4103…I set its current to 40mA, but the voltage on backlight is only 11.3V~11.5V, far from the required voltage 12.8V(3.2V x 4), but SY7200AABC works well, it is able to reach 12.5V.
First I think it is my design problem, maybe my resistors and inductors are wrong, but I tried modify the feedback resistor from 2ohm to 10ohm and change the inductor from 10uH~47uH, still no acceptable result. I find even I setup feedback resistor to 2ohm, the voltage is still lower than 11.5V.
I have no idea why PowTech’s PT4103 does not work, it should be a widely used chip but it is not as stable as SY7200AABC. Later version screen driver board I will use SY7200AABC.