How to minimize current draw when off?

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I have a battery powered circuit using an atmega and I've been considering the best way to conserve power when everything is idle. I could put everything to sleep and the atmega in power down mode, but current draw will still be ~5mA.

The majority of the current is consumed by the LDO. I could use a switching regulator instead of and LDO and save ~3mA, but switching regulators require quite a few more external components and I don't want to increase my BOM by that much.

What I'd like to do is put the LDO in sleep mode when the atmega powers down. I have a button tied to INT0 for a wakeup signal, the button has to be tied to ground with a pull up resistor. I was thinking about using a single inverter and an RC circuit to control switching the LDO on. The switch output would be tied to the inverter and when pressed would generate a voltage which would in turn charge the RC circuit giving the atmega enough time to boot up.

Has anyone handled this in the past? Any recommendations?

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You might find something useful in this thread.

https://www.avrfreaks.net/index.p...

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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There are LDOs that have a substantially lower quiescent current. The lp2950 is one classic example, but there are many of them from the usual vendors: ti/national, linear, st micro, on semi, micrel, microchip, and others.

- S

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If you shut the LDO off, you have the old "chicken and egg" problem when you try to turn it back on. You cannot turn it on via the micro because the micro has no power.

You would be best off forgetting about sleep, and just turn the LDO off. To turn things on, enable the LDO. Let the micro turn on and boot up when the power comes on. Or, just turn the power to the LDO on and off with a series switch so that there is no LDO standby power issue, at all.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Thanks for all the help guys, I decided to just give the MCU its own power supply. The power supply being used has a quiescent current of 40uA, which is acceptable.

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The MCP1702 LDO has only 2 uA.

Warning: Grumpy Old Chuff. Reading this post may severely damage your mental health.

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Maybe use oldskool methods, like here?
http://www.eevblog.com/2012/03/3...

The Dark Boxes are coming.

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My mega48 and MCP1702 in sleep mode has total drain<2uA
With NRF905 it's still <5uA @3v3

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A (block)schematic diagram of your product might help, be sure you know exactly were power is used. What chips do you use besides your uP ? I recently found out that in a product of mine, the external ADC was consuming the most power of all - when NOT IN USE. Is there a way to lower you battery voltage so you dont need a regulator ?

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Checkout the technique used in this project:

http://kripton2035.free.fr/Semiconductor%20testers/semiconductor-ma.html

Don

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@donblake... How is that relevant to low power AVR operation ? For a start, I suggest the use of sleep mode and PCI to turn on/off an AVR... A couple of uA for sleep current is tolerable for most applications.

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chartman wrote:
@donblake... How is that relevant to low power AVR operation ? For a start, I suggest the use of sleep mode and PCI to turn on/off an AVR... A couple of uA for sleep current is tolerable for most applications.
It's not. I believe the OP was asking about conserving power when the AVR was powered off. Putting the AVR in sleep mode isn't going to help LCD current draw. This technique IS relative to that - push a button to power on the AVR. The AVR then holds power on as long as needed and then powers itself and the entire remaining circuitry off. Very low power draw when off.

Edit: even with the AVR in sleep mode and the LCD powered-off, the LDO regulator is going to draw enough current to drain the battery. The technique used in the project I referenced might be a good solution.

Edit: I thought I saw a reference to an LCD in the original post. My error. Maybe a 3V battery and sleep mode is the answer.

Don

Last Edited: Mon. Apr 23, 2012 - 12:02 AM
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What MCU and WHY have a regulator since it's battery powered ?

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Because the OP uses a 9V battery ????

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chartman wrote:
Because the OP uses a 9V battery ????
Or maybe it's a 6V one, we don't know . Maybe it's a battery that doesn't even need a regulator, but OP might think it does . There have been these kinds of posts in the past .

Anyway, a battery value that doesn't need a regulator would be best/easiest .

1) Studio 4.18 build 716 (SP3)
2) WinAvr 20100110
3) PN, all on Doze XP... For Now
A) Avr Dragon ver. 1
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