Other Parts Discussed in Thread: ENERGYTRACE
Hi,
We have a sensor built around MSP430I2040. While trying to optimize its power consumption, I noticed that it draws on average 22uA when it is instructed to stay in LPM4.5.
It is quite a simple circuit as depicted below. MSP430I2040 wakes up to external interrupt on P2.1, stays in LPM4.5 if P2.1 remains low.
The following current trace is measured through the EnergyTrace++ tool that came with SimpleLInk Dev boards. All external parts that connect to positive power supply (VCC) has been removed, so only MSP430I2040, and RST pin through a pullup resistor is connected to VCC.
The overall current consumption being about 20uA indicates system does enter into LPM4.5, otherwise the current consumption will be > 70uA if in LPM4 as stated in datasheet. But the zoomed out current trace indicates frequent high current draw as much as 250uA.
I don't think this is an artifact of measurement, because we usually get good and expected results when measuring SimpleLink MCU based systems. I also don't think this is caused by some leak in the peripheral circuit or PCB itself, because in that case, there should be steady floor of current draw.
My suspicion is that somehow, probably because the voltage on P2.1 is not stable, therefore system may attempt to exit LPM4.5 but then immediately goes back into LPM4.5. What could be the other sources of current draw?
Thanks,
ZL