Low power mode MMA8451Q

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Low power mode MMA8451Q

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algisa
Contributor I

Hello,

I'm using MMA8451 and setting these registers: 0x0F <- 0x01 (High pass filter 1Hz); 0x2B <- 0x1B(Low power mode); 0x2A<-0xB1 (Sampling rate 6.25Hz), I am sending the data to registers in the order as it is written here. CA0 is directly connected to the ground. However the current is around 15mA. Can you advice me how  can I get those 6uAmps or so? Did I miss some other registers? I have made my own PCB and I used schematic as in MMA8451Q.pdf just instead of 4,7uF I use 6.8uF. I suppose that is not the reason for high current.
By the way I am reading data from accelerometer at around 20kHz.

Algis

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TomasVaverka
NXP TechSupport
NXP TechSupport

Hi Algis,

How are you measuring this current consumption? Are not there other devices drawing current as well?

Also be aware that the current consumption stated in the datasheet applies for VDD=2.5V and has been measured with an amperemeter between 2.5V voltage rail and VDD input only.

Regards,

Tomas

PS: If my answer helps to solve your question, please mark it as "Correct" or “Helpful”. Thank you.

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algisa
Contributor I

Hi Tomas,

I was measuring current on together connected VDDIO and VDD pins. Now I measured separately and VDD is just 6uA while VDDIO is 15mA. Can you give me some ideas how I could decrease the overall consumptions?

Regards,

Algis

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TomasVaverka
NXP TechSupport
NXP TechSupport

Hi Algis,

I have several recommendations to reduce the overall consumption:

1. Use interrupts instead of polling the data. This reduces I2C traffic and allows you to invoke the MCU’s low-power idle mode to reduce power consumption until the actual event (e.g. new data ready, change in orientation) occurrs.

2. Similarly, the embedded FIFO buffer allows the MCU to sleep longer while samples are being collected inside the sensor and further minimizes the traffic across the I2C bus if samples are read using I2C burst read mode. For more information on the FIFO buffer, please refer to our AN4073.

3. If you are not going to use low-power modes on your MCU and if you can accept lower bus speeds, then it makes sense to select higher-value pull-up resistors (e.g. 4.7k). This reduces current consumption as each logical low on the I2C bus creates a path to ground.

I hope it helps.

Regards,

Tomas

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