CC430F5137 ADC pin - current consumption in LPM3

Daniel Berenguer

Other Parts Discussed in Thread: CC430F5137

We have a board based on the CC430F5137 MCU. This board has P2.0 (ADC channel 0) connected to a 1.5V battery in order to measure the voltage of the battery. Periodically, our board enters LPM by running the following code:

  // Stop WDT
  disableWatchDog();

  // Keep current port selections
  portSelection[0] = P1SEL;
  portSelection[1] = P2SEL;
  portSelection[2] = P3SEL;

  // Configure port 1 pins as binary outputs tied to GND
  P1SEL = 0;
  P1DIR |= 0xFF;
  P1OUT = 0;

  // Enter lowest power VCore level and MCLK = 1 MHz
  _SET_VCORE_1MHZ(0);

  // Turn off SVSH, SVSM
  PMMCTL0_H = 0xA5;
  SVSMHCTL = 0;
  SVSMLCTL = 0;
  PMMCTL0_H = 0x00;

  // Enter LPM3 with interrupts
  __bis_SR_register(LPM3_bits + GIE);

The above code works perfect without P2.0 connected to the battery, making the board consume less than 2 uA. However, with P2.0 (ADC 0) connected to 1.5V the current consumption rises up to 21 mA or so. Setting this pin as an output during LPM is not a solution, given that there will always be a voltage difference between battery and the pin voltage so there will always be a current flow between pin and battery.

I'm not sure why this is happening. Maybe turning SVSH/SVSM off is causing P2.0 to lose its configuration as an analog input?

Thanks guys for your ideas.

over 9 years ago

0 Clemens Ladisch over 9 years ago

Guru 243770 points

Did you set P2MAP0? Did you check that this setting worked?

0 Daniel Berenguer over 9 years ago in reply to Clemens Ladisch

Expert 2185 points

I didn't check P2MAP0 until I read your reply. P2MAP0 seems to remain stalled on PM_CBOUT1/PM_TA1CLK even if I I set P2MAP0 to PM_ANALOG before reading the register. This is independent of entering into LPM or not. However, ADC readings can be done from that pin without problems.

0 Clemens Ladisch over 9 years ago in reply to Daniel Berenguer

Guru 243770 points

You did not mention that you enabled write access with PMAPKEYID, so I guess you didn't.

Read the entire section 9.2.1 of the User's Guide.

0 Daniel Berenguer over 9 years ago in reply to Clemens Ladisch

Expert 2185 points

You found it Clemens!

For some reason I was doing analog conversions without having previously mapped the pin to the PM_ANALOG function. The MCU was still capable to do the ADC's and return the correct values but internally the TA1 clock seemed to be taking current from the pin.

Thanks a lot!!

0 Jens-Michael Gross over 9 years ago in reply to Daniel Berenguer

Guru 227245 points

PM_ANALOG actually means PM_NONE, as it maps no _digital_ function to the pin. Analog is always connected (if you look at the port pin schematics in the datasheet, you'll see).
It is also not necessary to set PxSEL.y for analog operation, as long as PxDIR.x is clear (I/O set to input, no pull-up)
However, if the input signal is in the range of the input trigger level, then additional current flows in the input logic. This will be avoided if PM_NONE is selected AND PxSEL.y is set.

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CC430F5137 ADC pin - current consumption in LPM3