LIS3DH power consumption too high

emariatos · ‎2012-07-31

Posted on July 31, 2012 at 20:12

We use LIS3DH at 10Hz, with FIFO, low power mode, I2C for communication. We measure current at we get:

- at 3.6V supply, 160uA

- at 3.0V supply, 100uA

- at 2.3V supply 60uA

The datasheet claims 6uA, what might we be doing wrong?

#lis3dh

dannym · ‎2012-08-01

Posted on August 01, 2012 at 23:54

Have you ruled out leakage on the input capacitors, and through the board? If soldering flux remains on the board, this can cause board leakage plausibly similar to this magnitude.

Have you measured current at power-down mode? If the power-down current is within spec, you can exclude capacitor or board leakage as the cause.

I hope this is not a silly question, but did your measured current exclude the current drawn by the I2C pullup resistors? This would not be part of the specified current.

emariatos · ‎2012-08-06

Posted on August 06, 2012 at 19:52

Thanks for your suggestions. I measured all points and I see no leakage. I also believe it is not the pull-up resistors (although I was not aware their current was excluded from the spec). I will try with higher value of resistors, if it is the I2C the consumtion will go down, right?

dannym · ‎2012-08-09

Posted on August 09, 2012 at 22:51

The I2C resistors are external. The open-collector pulldowns that I2C devices use will not increase the device's current into Vdd itself, but if you measure the entire current for the board including the I2C pullup resistors (or the ground current through the LIS3DH), you will see some additional current. Note that the current will also be pulled down externally by the I2C master, but the resistors may be located with the slave and you might have positioned the current meter to read that. However, this is unusual, usually you place the resistors by the master, but that may just be me.

If they're 2.2k pullups on a 3.3v system, and each spends 5% of the time pulled down, that would be 150uA of average current through them.

When there is no communication, the I2C bus is never pulled down. Slaves such as the LIS3DH never initiate a transfer. So if you use the master to configure the device, put it in continuous conversion low-power mode, and stop polling the registers, there will be no I2C current yet the LIS3DH will continue to construct samples in continuous mode even if the registers are never read back, so you have operating current to measure.

mitkot · ‎2012-10-09

Posted on October 09, 2012 at 19:22

Have you found why you have that high consumption?

I have more or less the same problem - examined it in a bit more detail:

At 3.4V it consumes c.a. 145ÂµA and at 2V it consumes c.a. 45ÂµA all this in power down

mode.

The current is drawn by Vdd_IO as I find:

When I disconnect the power to the chip Vdd, Vdd_IO & SC (by jumper) and cut the I2C lines my whole board goes within specs (5ÂµA). Hence the PCB is fine.

If I connect only Vdd the circuit is still within specs. But if only Vdd_IO is connected or together with Vdd and SC then the above mentioned consumption is measured by multimeter (Agilent 34411A).

The datasheed proposes supplying only Vdd_IO as an option to keep the bus not blocked but disconnect the measurement engine.

When all power is supplied I can read the CTRL_REG1 default value of 0x07 and successfully set it to 0x00

Should the SC be kept low? The datasheet only says that it needs to be high for I2C.

I can reproduce this on 4-5 boards. Does ST have any comment, please? .....

serra · ‎2012-11-22

Posted on November 22, 2012 at 09:57

Hello,

I had the same problem: 138 ÂµA @3.3V in I2C configuration.

Try to put the SDO/SA0 (pin 7) at 3,3V instead of GND and the power comsuption will go down at 0.6 ÂµA.

I think there is an internal pull-up on this pin.

After this operation the address of I2C is different then change your firmware.

fernando2 · ‎2014-02-06

Posted on February 06, 2014 at 16:56

Hello,

I'm facing the same problem with the LIS3DH power consumption in a custom design. I would like to know if the solution to attach the Pin7 to VCC is working for everybody with this problem.

I would appreciate your help with this as nobody from ST is resolving me this question.

Thank you in advance. Cheers.

pcborenstein · ‎2014-02-12

Posted on February 12, 2014 at 22:14

I have the same problem in SPI mode. I am seeing 160uA in low power mode with Vcc = 3V

Nickname3819_O · ‎2015-03-20

Posted on March 20, 2015 at 09:09

Hi,

the problem is most probably in SA0 pin connection. There is an internal pull up with value of ~30kohms so in case you ground it, you can see this higher consumption.

We suggest to connect SA0 to Vcc, then you should see power consumption in uA range.

Rgds

St customer support

paulo2 · ‎2015-10-02

Posted on October 02, 2015 at 14:50

We have the same issue with LIS3DH. If ST support does know this problem regarding SA0 internal pull up, why they don't promote a errata or datasheet revision?????