LIS2DE12 Vdd and VddIO power path

[StefXinet]

Hello,

I'm developing an ultra-low-power circuit with LIS2DE12. I would like to have the accelerometer running with IRQ enabled, but serial communication shutted down.

I can't understand at whitch power path the INT1 and INT2 are connected (Vdd or VddIO).

Is it possible to have INT1 and INT2 output working if I power-up the LIS2DE12 only by Vdd?

Thanks.

[Eleon BORLINI]

Hi @StefXinet​ ,

I should have understood your point.

The Vdd is deputy for the measurement chain power on, while the Vdd_IO defines high and low voltages for the digital operation and communication. If you don't tie the Vdd_IO, the device could send the interrupt as well, but it is not a safe condition, since the voltage high level is not well defined, so there is a non zero probability of non-raising the interrupt. So, I would suggest you to tie all the voltage supplies, at least when the device operation starts.

Please consider, for completeness, the following statement of the datasheet, p. 19:

All the voltage and ground supplies must be present at the same time to have proper behavior of the IC (refer to Figure 5). It is possible to remove Vdd while maintaining Vdd_IO without blocking the communication bus, in this condition the measurement chain is powered off.

 

You could try this other approach, but the interrupt should never rise since the measurement chain is off.

-Eleon

[StefXinet]

Dear Eleon,

I need the measurement chain and the IRQ capability to be ON at the same time.

I'm sorry but I don't understand why it might be useful to have the communication ON while the measurement chain is OFF.

Apart from this, what I cannot find in the datasheet is that INT1 and INT2 are considered "communication PIN" therefore connected to VddIO or are considered in the low power measurement and function chain and are provided by Vdd.

If it were as you suggest, separate Vdd and VddIO could not be used and should always be linked together.

Thanks,

[Eleon BORLINI · Accepted solution]

Hi @StefXinet​ ,

I agree with you that keeping the measurement chain OFF is not useful in your specific case. It would be useful if for example one wants to reduce the current consumption in his application, by switching off the Vdd without troubles on the I2C or SPI lines.

By the way, INT1 and INT2 levels are managed by the Vdd_IO, so they need this supply voltage for a proper functionality, You may tie toghether the Vdd and Vdd_IO, or leaving the two paths separated, as you are more comfortable. Please note also that the Vdd_IO can be less (or equal) to the Vdd.

-Eleon