Hello,
I am starting with atmels xmega mcus. I did a small breakout pcb for the atxmega64a4u. I also included a voltage regulator for the 3V3, required by the mcu, with enough juice (1A) to power other peripherals while prototyping.
Unfortunately, I get an excessive voltage drop when connect a 3.2' tft.
The power supply configuration is:
USB 5V > shotky diode (1A rated, 0.4V drop) > NCP1117 linear regulator (1A rated, 1.2V drop max) > 10uH wire wound power inductor (1.4A rated) > 3V3
I followed atmel's AVR1012: XMEGA A Schematic Checklist for the breakout, hence the inductor.
when just blinking a led etc, I get a 3.3V on the rails, but when I connected the lcd pannel, the voltage drops to 2.8V
the backlight uses 80mA and the lcd panel uses 20mA, xmega has 200mA max current rating. all in all, the current consumption is less than 300mA. So I should be ok, running the board from USB 5V, 500mA supply. I even bypassed the diode, but it did not make any difference.
where is my mistake ? any ideas
thanks