topic Re: QG8 internal pullup = 150uA??? in 8-bit Microcontrollers

QG8 internal pullup = 150uA???

UtopiaTim — Thu, 04 Dec 2008 09:35:53 GMT

Hi Folks,

I must be missing something - I'm working on reducing current consumption on a

battery device, and it's drawing about 150 uA more than it should in STOP3 mode.

I narrowed it down to when I select an internal pullup with PTAPE. If no pullup is

selected, the current is basically nothing. With it, it is 150uA. It is PTA1, and I'm

using it as a keyboard interrupt.

If I put an external pullup on it (for a switch), the circuit works fine, and there

is no extra current.

Ideas?

Thanks,

Tim

Re: QG8 internal pullup = 150uA???

Lundin — Thu, 04 Dec 2008 17:52:48 GMT

150uA seems resonable to me. 3.3V / 150u = 22kOhm.

I might have misunderstood the problem, but how exactly do you expect a pull-up to work with 0A current through it?

Re: QG8 internal pullup = 150uA???

peg — Thu, 04 Dec 2008 20:39:14 GMT

Ah, I presume he meant with the switch open.
With it closed you should see something like this (probably a fair bit less)
A pullup will work with virtually no current when it is pulling up a CMOS input gate.
A Utopian one

Re: QG8 internal pullup = 150uA???

UtopiaTim — Thu, 04 Dec 2008 22:38:55 GMT

Cute!

Yes, it's with the switch open.

I'm not worried about the current when the switch is closed (it's minimal

compared to what the rest of the circuit is drawing).

Guess I'll put a pullup on the board, & if I figure it out before production,

it'll just be a no populate.

Thanks,

Tim

Re: QG8 internal pullup = 150uA???

admin — Sat, 06 Dec 2008 04:14:22 GMT

You wouldn't happen to have the KBEDG1 bit set, do you? If set this would make the internal resistor a pulldown rather than a pullup. Not having seen your circuit I don't know if this is relevant or not.

Re: QG8 internal pullup = 150uA???

UtopiaTim — Sat, 06 Dec 2008 05:02:40 GMT

Hi Wingsy,

Checked, and the bit is clear - set for falling edge.

Tim