STM32L152 - Idd measure with voltmeter

[sicode]

Posted on June 25, 2013 at 09:07

Hi!

I try to test my firmware on STM32L152-Discovery. I'm creating low power application with ADC and SD card. Everything works perfectly, but now it's time for current reduction. When there is no need to do ADC conversion i'm putting MCU into STANDBY mode and seems to be OK. I'm looking at the schematics and i'm trying figure it out how to measure current during ADC converison, when MCU is awake. I think that i should measure it on SB2 (near JP1), with JP1 jumper set to ON. Now system is configured like below:- ADC in conitunous mode, 8bit resolution, sampling 10kHz without delay between.- DMA used for data transfer with HalfTransfer and Transfer Complete Interrupt enabled- SD card is enabled but there is no r/w on it.- systick running- all I/O except WAKEUP button are in AN mode without pullup- when there is no dma interrupt device is put to PWR_EnterSleepMode(PWR_Regulator_ON, PWR_SLEEPEntry_WFI)And for this configuration i got on voltmeter 0.380mV. Now there is general question: How to recalculate this value to current? Can I simply just replace 0.380mV at 3.8 mA? Or maybe 0.38mA? Maybe any one could tell, how much idd i should expect? #idd-voltmeter-adc-dma

[frankmeyer9]

Posted on June 25, 2013 at 12:03

And for this configuration i got on voltmeter 0.380mV.

I suggest to switch over to a current measurement range to measure currents. Using a voltmeter, i.e. a multimeter in voltmeter setting, is nonsensical here, and has certain side effects to your target ...

[sicode]

Posted on June 25, 2013 at 13:40

Thx for answer!

Of course current measure on multimeter is the best way to accomplish measure. But where i can connect amperometer on the board? I'm trying to use idd measure circut form ST32L152-Discovery board. I can't cut board  or desolder anything because it's not my hardware and i must resend it without any damage.

[Tesla DeLorean]

Posted on June 25, 2013 at 14:07

JP1 bridges the supply, you'd remove the jumper and measure the current flowing from pin 1 to pin 2

[frankmeyer9]

Posted on June 25, 2013 at 14:10

There is a Idd measurement jumper populated on the board, right between the MCU and the LCD.

Pull this jumper, and connect your ampmeter there. This is described in section 4.7 in the STM32L discovery user manual (DM00027954.PDF).

[sicode]

Posted on June 25, 2013 at 14:30

Thx all of you!

works perfectly. Do you think that current value about 4mA in this configuration is correct or i can reduce it?

[crt2]

Posted on June 26, 2013 at 11:44

I think you could go lower (below 1mA), but probably powering SD card takes some of current. Best current consumption I've achieved with GPIO_IN and GPIO_PuPd_DOWN, but basically all but floating is OK.

Maybe there is something on discovery board or you're disrupting with current measurement - I dont have discovery board for that below 1mA current, just uC on my own circuit.

[Tesla DeLorean]

Posted on June 26, 2013 at 13:37

GPIO_AN turns off ALL the digital circuitry on the pin, including the input buffer.