Hi @sming.1 ,
Let me try to give a look into your question, because this over current consumption is a little strange.
1. the power consumption gap is huge comparing the spec?
You mentioned the fact that, just after power on, i.e. after the Vdd (and VddIO) transition from 0V to 3.3V, the device consumes up to 700uA. I believe that there is a baseline overcurrent consumption, since the delta between the power down mode and the operating mode is pretty ok (1.3mA). This may be related to an hardware issue, since the device should be in power down and consume. Did you follow all the recommendation you can find in the "Default pin status" table, datasheet p.4? Can you please share the schematic of your application, at least as regards the IIS3DWB pin connections? You can find Application hints in datasheet p. 24 or in the STEVAL-MKI208V1K schematic. Please note also the sentence in the application note AN5444, p.6: "In order to avoid an unexpected increase in current consumption, the input pins which are not pulled-up/pulled-down must the polarized by the host".
2. why a SW_RESET can not be the same consumption with a just power on without any software init?
The Boot status and the sw reset flow are described in the AN5444, p.6. Reset flow is as follows:
1. Set the accelerometer in Power-down mode;
2. Set to 1 the SW_RESET bit of CTRL3_C to 1;
3. Monitor software reset status, two possibilities:
a. Wait 50 µs
b. Poll SW_RESET bit of CTRL3_C until it returns to 0.
The SW_RESET procedure can take 50 µs; since the status of reset is signaled by the status of the SW_RESET bit of the CTRL3_C register, you should check that, once the reset is completed, this bit is automatically set low.
3. how can achieve as low as possible power consumption ?
Once solved point 1 and point 2, the minimum power consumption basically depends on your application requirements. If you are bound to use 3.3V power supply, and you want to take advantage of the full dynamic range of the sensor (ODR = 26.667 kHz), you could use the wake-up / activity interrupts to leave the sensor in sleep mode when not used, and activate it when necessary, in order to reduce the overall average consumption. More details can be found in the AN5444, p.15.
-Eleon
