ADC external reference usage on MKL33

[elliotwhite]

In order to reduce power usage I need to turn off the analog part of the circuit, If I have understood the data sheets

for the MKL33P80  correctly the following (outline) diagram should work (I hope).

I assume that the VREFs when configured correctly are effectively connected to the ends of the resistor chain in the SAR, and that when disabled (BJT off) it is ok to have VREFN float upto VDDA.

Any assistance would be greatly appreciated

[bobpaddock]

Use a PNP to switch on the high side.

Having the A/D biased above 'ground' by the transistor drop will causes offsets.

It is still best to connect the VAdd/VAss lines to non-switched power.

We can not know what goes on inside the chip and the unpowered section could actually increase current consumption from unbiased internal impedance's.

[jorge_a_vazquez]

Hi elliot white

VDDA and VSSA pins should be always connected, even if you are not planning to use analog modules of your MCU. But in Vref, If you are not planning to use any analog circuit of the KL33 (they are off), then there shouldn't be problem if you left this pin floating, but if you try to use ADC for example, with this pin floating, it will cause you problems.

Hope this helps.

Best Regards

Jorge Alcala