I have been working on a little project with an AVR32 and TFT lately, and I have just completed a draft of the power supply unit... This is intended to run off a 7.4v 3200mAH 1C 2S lipo pack, I have not included the charger or protection circuitry here because well, I can't give it all away... ;)
This takes the lipo pack 7.4v and generates the following supplies:
- 1.8v 600mA max for avr32 core
- 3.3v 600mA max for most of the ics on board
- 5v 1.2A max for TFT module AVDD, also cascading 3.3v and 1.8v (should not draw more than 900mA together, to test...)
- 20v 800mA for 6x leds TFT backlight
This is all done through high efficiency buck and boost converters. Because of board needing a sequenced startup, I included a Tiny25V to control the power up, power down and reset sequence. The program for it is done and simply creates proper power sequencing for the hardware, as well as pauses on reset and shutdown for linux to terminate properly, via the converters' enable pins, and a power N-channel MOSFET on 5v to the board. The gate voltage is elevated to 6v from 5v avr output through the lm321 opamp, to satisfy the Si1050X's gate saturation treshold. The Tiny25V is always in deep sleep and woken up from int0 low level, the pushbutton... If the unit is already running, a momentary push on delays 10 seconds (while the avr32 receives the pushbutton signal and shutsdown, unmount flashes, etc..), then issues a board reset. Holding the pushbutton for a while (4 secs) delays 10 secs, and then sequences the power down. If the unit is off, a momentary press sequences the power up.
I would like your comments, suggestions, and corrections on this before I get a couple of boards done... Most of the chips are very small QFN or SOT23, so a board is crucial, and costs quite a bit for a prototype... :)
This has not been yet tested, and is open for improvements.