This question is for the SPX-16740 Qwiic Power Switch.
I am getting 74 microamps quiescent current draw from this board with the Input LED Jumper cut instead of the 0.2 microamps described in the product page. To be clear, this is for just the Qwiic Power Switch board, not my whole system. This number is very similar to what another person commented on the product page.
Is there a minor design flaw or do I need to do something to bring the current draw down further? I tried setting the GPIOs low, but that had no effect. The isolation is working because my measurement are the same whether there is another board attached to the Qwiic Power Switch’s output.
74 microamps is pretty good and the product is otherwise great and easy to use; however, 0.2 microamps would allow for much much longer battery use.
The 0.2uA is the standby current for the PCA9536 port expander (taken straight from the datasheet). But there are other things on the board which draw power:
The PCA9306 I2C isolator will draw current - but the datasheet doesn’t say how much. It only quotes the recommended pass switch current and maximum continuous channel current, not the typical current draw (with outputs disabled).
The 74HC1G04 inverter is continuously powered and it too will draw current.
There may be some leakage into the PCA9306’s VREF2 pin (via the 200K resistor).
So, I agree, 74uA is pretty good - all things considered!
If I were re-designing the board now I would probably use a dedicated high-side power switch and look around for lower current options for the port expander and isolator… But, as you know, hindsight is always perfect…
Also a tangential suggestion, figuring out mosfets and transistors is quite tricky for people just getting into this stuff. Especially with the complexities of multiple transistors when the load requires higher voltage than the logic. A Qwiic load switch would be a really neat product especially if quiescent current was low. Below are some breakout examples, but not Qwiic. TI seems to have some load switches that can do high power.
