I have been reviewing the BMA400 datasheet for a very low power application. I'd like to keep it in low power mode most of the time. During that time, VDDIO will be 0 V, but VDD will be powered by a Lithium primary cell. Will the device continue to operate when I lower VDDIO to 0 V after configuring the device or enter reset until VDDIO is >1.2 V again?
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Thanks for your inquiry.
BMA400 needs both VDD and VDDIO to be in the operating range in order for it to work. If VDD is on and VDDIO = 0V, then BMA400 will stop operating. When VDDIO is back on again, BMA400 will have power on reset (POR) to enter sleep mode by default waiting for your initialization again.
Please be careful when you make VDDIO = 0V and keep VDD on. You need to make sure BMA400 digital IO pins such as CSB, SDX, SCX are 0V before you make VDDIO = 0V. Otherwise, BMA400 might be damaged.
Since BMA400 consumes 160nA in sleep mode, you can tie VDD and VDDIO together to keep it simple. It is recommended to add an LDO between your battery and BMA400 VDD/VDDIO to avoid power supply ripples that may cause POR. If you connect battery directly to BMA400 VDD/VDDIO, then in your firmware you may need to keep polling register 0x0D to see if POR is detected or not. If yes, then you need to reinitialize BMA400. Otherwise, BMA400 will be in sleep mode doing nothing.