LIS3DH current consumption

[bojan]

Posted on January 16, 2017 at 13:36

Hello guys,

I'm using LIS3DH accelerometer in my current design. I need it to detect the movement.

ODR is set to be 10Hz. According to

http://www.st.com/content/ccc/resource/technical/document/application_note/77/ed/e7/e1/28/5a/45/d6/CD00290pdf/files/CD00290pdf/jcr:content/translations/en.CD00290pdf

document (page 10), LIS3DH should consume about 4uA of the current in both Normal and Low power modes.

However, when I measure the current consumption, I get the value of about 78uA (@2.5V power supply). When I remove the accelerometer from the power rails and measure the current consumption of mcu in a sleep mode, I get the value of 3.2uA. This clearly implies that about 75uA of the current is consumed by the accelerometer.

The important thing to mention here is that I was supplying the mcu and accelerometer with 3.7V to 4.2V for some time. This is above the recommended supply range for LIS3DH (3.6V maximum). So, is it possible that this over-voltage permanently increased the current consumption? I have the desired functionality even when I supply the system with 3.7V to 4.2V.

Thank you very much for your time and effort.

Sincerely,

Bojan.

#lis3dh Note: this post was migrated and contained many threaded conversations, some content may be missing.

[Miroslav BATEK]

Posted on January 16, 2017 at 15:32

Hello Bojan,

the overvolatge can have an impact on the current consumption, but it is hard to predict how much the current would increase.

Some current can be also induced by internal pull-up resistors, but it would be probably more than 70uA.

Anyway can you please share you schematic, at least the sensor part, I can look at it.

[bojan]

Posted on January 16, 2017 at 17:00

Hello Miroslav,

Thanks for your prompt reply. Of course I can share the schematic with you.

As you can see, I have two external pull-ups for I2C. I used 10Mohms to additionally reduce leakage current and it I2C is working properly with them. Between MCU and the accelerometer, there is only I2C interface.

Is there anything you can suggest me? How could I disable internal pull-ups?

Thanks in advance,

Bojan.

[Miroslav BATEK]

Posted on January 16, 2017 at 17:11

There will be a current from SDO/SA0 pin to ground in your circuit, because you connected the pin to ground. According to datasheet the current should be higher than 70uA, but anyway try to disable the internal pull-ups in CTRL_REG0 register. Please check chapter 8.6 in the datasheet.

The pull-up for SDA/SCL are very high, you could have a problem with the communication. The recommended value for I2C pull-ups is 10kohms.

[Miroslav BATEK]

Posted on January 16, 2017 at 17:29

I'm sorry, the current from the internal pull-up is actually very close to what you measure. For the Vcc=2.5V the typical value of internal pull-up on SDA/SA0 pin is 30.4kohm. So the current should be 80uA. It is very close to you measurement. I believe that disabling the internal pull-up will solve your issue.

[bojan]

Posted on January 16, 2017 at 17:30

Hey Miroslav,

Thanks for the suggestions! In the case of I2C interface, SDO/SA0 pin is for defining LSB of the device address. It should be fixed to GND (I2C address 0x18) or VCC (I2C address 0x19). Do you think the current consumption will be decreased if I connect SDO/SA0 pin to VCC ?

http://www.st.com/content/ccc/resource/technical/document/datasheet/3c/ae/50/85/d6/b1/46/fe/CD00274221.pdf/files/CD00274221.pdf/jcr:content/translations/en.CD00274221.pdf

of the LIS3DH module. Chapter 8.6 describes of who_am_i register. I don't know what should I look there!? Furthermore, I can't see there is CTRL_REG0 in register map of LIS3DH. I wonder are we looking on the same datasheet. :)

Sincerely,

Bojan.

[Miroslav BATEK]

Posted on January 16, 2017 at 22:24

Yes, the current consumption will be decreased also if you connect the SDO/SA0 pin to Vcc. Inside the LIS3DH is pull-up resistor, so if you connect the pin to ground the current is flowing from Vcc trhough the pull-up resistor to ground, on the contrary if you connect the pin to Vcc there won't be any current as the voltage is the same on both side of the pull up.

I checked your link and the who_am_i register is described in chapter 8.5, CTRL_REG0 in chpater 8.6. Here is a screenshot, it is page 34.

The new version of the datasheet was published recently, so maybe that is the reason why you see different version. Please check it now.

[bojan]

Posted on January 16, 2017 at 22:47

Thank you very much, Miroslav, you are awesome! You've been of a great help to me!

I will try both to set SDO/SA0 to Vcc as well as to disable internal pull-up.

If I disable internal pull-up and keep SDO/SA0 to Gnd, I can expect to have lower current consumption, correct ?

Sincerely,

Bojan.

[Miroslav BATEK]

Posted on January 17, 2017 at 08:17

Yes, your assumption is correct.

[bojan]

Posted on January 17, 2017 at 08:20

Will try this today and will let you know !

:)