STM32F051 possible missconfig? makes Battery pin takes 100mA

[jgnoss]

Posted on March 05, 2013 at 15:57

Hi, I have a STM32F051C6 on a PCB that has a socket for a Battery, connected to VBat using a Schottky diode.

While development phase I don't fit the battery, just use a jumper wire and connect the Plus of the battery socket to same supply as the MCU. All the PCB uses 3.3V Supply, so I have 3V on VBat. My circuits are always connected to power source using an programmable Amp-meter with Amp limitation. At one instant (I was programming some Timers and ISR's) the Circuit tries to suck about 120mA, and the Amp-Meter instantly disconnected the entire circuit (because of preprogrammed 60mA max) I investigated the cause and found that the VBat Pin tries to get about 100mA. When I disconnect that Jumper wire to the battery socket, the entire circuit takes about 21mA and the MCU works normal. I have no idea what caused that change. Somebody please can give me an idea where to look for that. Thanks. #stm32f051-vbat

[waclawek.jan]

Posted on March 05, 2013 at 16:08

Short on pins PC13-PC15?

JW

[jgnoss]

Posted on March 05, 2013 at 16:46

Pin 13 is unconnected

14 and 15 is the crystall for RTC but no short between Pins and no short to VCC or GND

[jgnoss]

Posted on March 05, 2013 at 16:48

Sorry for the double post, there popped up a http error after first send, so I tried again.

[Tesla DeLorean]

Posted on March 05, 2013 at 18:21

Something has to be seriously amiss for the chip to pull 100mA, care to post a (partial) schematic of what you're doing with it?

Analogue supply connected?

[emalund]

Posted on March 05, 2013 at 19:35

If you have a pin connected/shorted to Vdd or gnd and set the other way, you can really suck power.

what is the consumption in reset? Erik

[jgnoss]

Posted on March 05, 2013 at 22:38

Analogue supply connected?

Yes, VDDA to VCC, VSSA to GND, (I don't use the ADC). I have de-soldered the STM from the PCB and powered up the PCB to be sure there is no error or short on another place on the PCB. Without STM the board pulls 9mA. I have all GPIO's in use, and all of them work well and do what they are programmed to do. As long as I keep the Power off on the Battery Socket, the entire circuit pulls 20mA to 29mA. My conclusion is, there is something on that RTC circuit where the VBat is connected to.  

[jgnoss]

Posted on March 05, 2013 at 23:20 In Reset the entire circuit pulls 15mA, out of reset 20mA to 29mA, depends on what of the extern circuitry is active. Powered off and Powered on (With no voltage on Plus of Battery socket) I get about 23kOhm from VBat Pin to GND. So, the consume of current seems to start when the VBat Pin see's some voltage. I'm afraid to connect some voltage to the Battery plus for more than a few ms and continue investigation. (I don't like to fry the chip)

[waclawek.jan]

Posted on March 06, 2013 at 08:13

Short between the battery holder's contact and some of the signals?

Improperly placed jumper wire? JW