How to put MCP3008 into sleep mode

Question

I am using an MCP3008 ADC connected to a Seeed Studio Xiao nRF52840.
I am using the adafruit library #include <Adafruit_MCP3008.h>
It operates as expected, but after taking readings I would like the MCP to 'turn off' or enter into sleep mode.

Before I call the function adc.begin(pin_adcCS); the current draw of the circuit is 150uA, once the MCP turns on, it draws about 1mA.

In the datasheet, it says you can set the CS pin high in order to set the MCP into "low-power" mode. However, I don't observe a change in current consumption.

I am attempting to put it into low-power mode by calling:

adc.begin(pin_adcCS); //turn on adc
doorVal = adc.readADC(1); //take reading
pinMode(pin_adcCS, OUTPUT); //change CS pinmode
digitalWrite(pin_adcCS, HIGH);//write to the MCP
delay(100);
pinMode(pin_adcCS, INPUT);//Change back to INPUT to reduce current consumption

I tried to keep the pin high for longer and see if the current dropped, but there was no change, it appears to have no effect.

Any ideas about what I could be missing here?

Answer 1

Normally the CS pin is high between SPI bus transactions, because that's the purpose for being able to select between multiple chips on SPI bus.

The chip even needs CS to go high to complete a SPI transaction.

So since the driver likely leaves the SPI already high, the ADC is already in powerdown mode, so it does not change anything if you manually try to set CS pin as input or high.

Answer 2

Turns out you need to call SPI.end() and also set pinMode(MCP3008_CS_PIN, INPUT_PULLUP); as it does continue to draw current when set as output and HIGH. This will put the MCP3008 into low-power mode. I also imported arduino SPI.h (which I was before too).