SparkFun Forums

[cesium]

I've reduced the LPC2148 current consumption during power down to 330 uA.
I got to this level by:
- Making sure my IO pins were not sinking current through their pullups.
- Eliminating all floating inputs.
- Turning off unused peripherals.
- Pulling the USB pins D+ and D- to ground with 100k Ohms each.

Does anyone know how to get below this current level? I'd like
to reach the data sheet spec or even the level described in some of
the NXP app notes. 100uA would be sweet. Any ideas?

Cheers,
David

[cesium]

So, I've been trying all sorts of things with no significant reduction in
current consumption during power down.

Then I thought about the results that have been reported using a Keil eval board.
The context of the app note was reducing the power down current for a USB device.
There has been some discussion about USB configuration (or the lack thereof) interfering
with the power down process.

I know that I am achieving power down, but I have basically ignored USB configuration.

I think I'll implement the USB related inits and see what happens.

Regards,
David

[cesium]

Yup. That did it. LPC2148 power down current is under 100 uA.

FWIW, you know what I hate? Engineering by consensus.

All this guess work was entirely avoidable.

The solution: Useful docs from NXP.

And don't DARE mention that awful document AN10493.

David

[exuvo]

I do not really understand what you did in the last step, could you please elaborate. Does the USB peripheral not enter power down unless initialized first?
If my unused USB peripheral is wasting power i am interested in reducing that.

[cesium]

It appears that not configuring the USB peripheral leads to
excess power usage during power down.

First, I need to update my guidelines. I achieved low current
draw from the LPC2148 during power down by:

Code: Select all

- Making sure my IO pins were not sinking current through their pullups.
- Eliminating all floating inputs.
- Turning off unused peripherals.
- Pulling the USB pin D+ to VCC with 1.5k Ohms.
- Pulling the USB pin D- to ground with 100k Ohms.
- Initializing the USB peripheral:
     - Configure PLL1 to supply 48MHz, and wait for it to lock.
     - Connect PLL1 to the USB peripheral.
     - Wait for USBIntSt:usb_need_clk to go low.
     - Disable the USB peripheral in PCONP.

I've re-drawn my boards to include these changes and I'll investigate more on the new revision.

Cheers,
David

[cesium]

OK, I've got the new board up and running and the measured
LPC2148 power down current is 40uA.

Yep, that's 40 microamps.

David