Power saving / reduce idle current for SD card

Other Hardware General Electronics
1

Hello,
a battery driven data logger stores the data on an SD card. The access to the card occurs only once every few minutes, but even in idle the card consumes quite a few milliamps.

So I was wondering, if there is a way to "unplug" the card during those idle times using some logic level MOSFETs.
My initial thought was to use one of those on the Vcc of the card module. But on a second thought: If there is some other communication on the SPI going on, is there the potential for damaging the card? Because in that case V(MISO) / V(CLK) / V(MOSI) could all be greater than Vcc of the card which would be 0.

So I guess the general question would be: How to "unplug" a load that also has some bus communication lines?

2

You need to remove the signals before you remove the power. This can be done by making the data pins into inputs before the power is removed.

3

@Grumpy_Mike
If there is only one module on the bus, you are right of course.

But if there were multiple clients connected on the SPI / I2C / CAN, how could I turn one of those devices off without shutting the entire communication down?
At the moment I can only think of a level shifter whose client side Vcc is connected to the switchable Vcc of the module.

4

You would use analogue switches to isolate the sections of the bus you want to shut down.

5

Oh boy, that was just too obvious :wink:

Thanks!