sparky:
Looks like a GM862 driver (3.8v?) and logic 5V? Want to share the specifics?
Right. It not only has to deal with the widely varying power requirements of the GSM862, it has to deal with the 5V side varying from 10 to 510 mA as the display backlight turns on and off.
With a 12V input, and 10 ohm loads on both outputs, it runs at about 75% efficiency, and gets fairly hot. It should be capable of somewhat better than that, although I have no idea even where to begin looking for the problem. In any case, it works much, much better than a linear power supply possibly could!
It’s for a commercial project, so I can’t really give any circuit details (although it’s pretty much taken straight from the datasheet).
Right. Note that this part is rated 1.4A max, to handle the GM862’s peaks I’ll need about 10,000uF of extra capacitance. Fortunately my application isn’t space-constrained…
The crazy power requirements are hardly specific to the GM862, they’re inherent in the GSM specs (1/8 transmit duty cycle at 200+Hz).
I received my 5 prototype PCB’s on Saturday morning. They look great and are just what I wanted. Now I need to build them up and see if I got it all rite! Great service, thanks Sarkfun.
When it is all checked I will do a production run in Blue with GP. Using Sparkfun for the prototypes makes the mistakes cheap. I will definately be using this service again.
