currents in Deep power-down mode for LPC810

[lpcware]

Content originally posted in LPCWare by HaltPapa on Sat Mar 01 10:26:04 MST 2014
I have a problem for the currents in Deep power-down mode for a LPC810.

The datasheet of LPC81X stated that the typical Deep power-down mode current is  less than 1uA.
However, I tested is around 2mA.

I used PMU sample code in "LPC800 LPCXpresso Examples V1.03.zip".
http://www.lpcware.com/system/files/LPC800%20LPCXpresso%20Examples%20V1.03_1.zip
I added only one line below.

#define TEST_DEEPPOWERDOWN 1

I can enter __WFI() (I think it's Deep power-down mode) and can wake-up from it  using the WAKEUP pin.
When I was measureing the current, I used only Vdd, Vss and Reset pins. Reset pin was pulled up by R=10k. Other pins were open.

When Reset pin set to Low, the current drops to around 700uA. Does it mean that I'm not entering Deep power-down mode?

Thanks in advance for any help.

[lpcware]

Content originally posted in LPCWare by MarcVonWindscooting on Sun Apr 06 07:34:04 MST 2014

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Quote: HaltPapa

But I didn't pullup RESET pin consciously.

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Hi 'Papa',

don't take that too easy. My board shows increases leakage, because it has different flux residuals, different uC specimen (different internal leakages of the RESET GPIO output transistors I guess). I'm more lucky than you, because my board fails early - which is a blessing! Your design will fail in mass production - more of a curse :O

Measuring does not prove, it's working. Measuring can prove it's failing.
But to be fair, I should say, that I put my finger on every pin for testing (feeding of noise), to be sure. Using a linearly varying voltage (high impedance of course) in the range 0..Vdd would be better, but I'm lazy sometimes...

[lpcware]

Content originally posted in LPCWare by HaltPapa on Sun Apr 06 05:47:30 MST 2014
hi again,

I alredy checked the current of my circuit. It was <1uA at deep power-down mode.
(I don't know the exact value. The resolution of my multimeter is 1uA.)

But I didn't pullup RESET pin consciously.
Fortunately, I have assigned 1pin to SDA, and pulled-up externally for I2C. It's turned out all right.

Thank you for everything.

[lpcware]

Content originally posted in LPCWare by MarcVonWindscooting on Sat Apr 05 17:51:10 MST 2014

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Quote: HaltPapa

Please correct me if i'm wrong.
When we don't assign 1pin to RESET pin, we didn't need to pull-up 1pin for deep power-down mode. Is that right?

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Sorry, for disappointing you :(
GPIOs lose their driving capability (or pullup) in deep power down. So you end up in a floating reset pin, unfortunately. In my test circuit, that means around 10uA leakage versus 0.6uA in clean deep power down.

It seems to me, that 'normal' pins can be left floating without leakage penalty, but not WAKEUP and RESET.
The I2C pins are pulled up externally on my board, as mentioned somewhere in the UM, so I can't test for floating I2C pins. However, I like I2C that much, nearly every circuit I design has some I2C circuitry connected. Many of those devices provide very low power sleep modes  8-)

I do current measurements of power saving modes by using a 10k resistor (paralleled with a diode) in the power supply line. Using a high impedance (>>10k) multimeter allows measuring downto (and below) 1uA @ 10mV reading. High currents (a few mA!) are shorted by the diode and prevent range overflow of the multimeter. Thanks to the LPC800 wide voltage range, the diode drop at high current doesn't stop the LPC from working.
I suggest you use that for measuring yourself.  You don't want to be surprised with your final circuit, do you?

[lpcware]

Content originally posted in LPCWare by HaltPapa on Sat Apr 05 05:50:14 MST 2014
Thank you for your reply.

Please correct me if i'm wrong.
When we don't assign 1pin to RESET pin, we didn't need to pull-up 1pin for deep power-down mode. Is that right?

[lpcware]

Content originally posted in LPCWare by nxp_apps on Mon Mar 31 16:39:00 MST 2014
Hi,

Please keep in mind when not using self wake-up timer as a wake-up source, BOTH the WAKEUP pin and external reset pin needs to externally pulled out to get desired deep power-down current.

External reset pin has no functionality in deep power-down but it is required (as mentioned in the datasheet and user manual) that it must be externally pulled high while in deep power-down mode.

Thanks.

[lpcware]

Content originally posted in LPCWare by HaltPapa on Sun Mar 02 06:39:18 MST 2014
I get the point.

The RESET pin has no functionality in Deep power-down mode.
So I don't have to pull up the Reset pin.
But I must pull the WAKEUP pin HIGH externally.

Thank you for everything.

[lpcware]

Content originally posted in LPCWare by HaltPapa on Sat Mar 01 19:49:54 MST 2014
hi MarcVonWindscooting,

I just can't thank you enough for your quick response.
The current dropped less than 1uA when I pulled up some other pins.

But I still don't understand why. So I'll try the other sleep modes as you advised me.

Thank you again for everything you’ve done.

[lpcware]

Content originally posted in LPCWare by MarcVonWindscooting on Sat Mar 01 10:38:49 MST 2014
What you describe looks pretty normal to me.
First try deep-power down fails for everyone new to it.

Maybe you should go step-by-step and try the other modes before, like sleep and deep sleep, to get a bit of a 'feeling' for it.

Especially deep-power down won't work with floating pins. The input stages of a CMOS consume nearly no power if connected to one of the supply rails, but they definitely do for voltages between the rails.
However, with 2mA you're still far from the point, where you have to care about such issues of a few microamps to a few 100uA ;-)

Also have a look at postings in the LPC1100 forum. These controllers are similar and the experiences described there can be applied to the LPC800, too. I did and it helped me.
I'm about to release my lpc8 library, soon (this week-end). Part of it will be a very basic deep-power-down example. The lib is Linux-only, so not exactly what most people will appreciate.