Hi Team,

I using FS32K146HAT0MLLT from NXP in my design.If you look at the hardware design guidelines of the microcontroller you can see the below image in page no 3.



Here VDDA is Analogue supply voltage and VREF is ADC Reference Supply high.

In my board I am using 5V supply to the microcontroller. This 5V is generated from a buck converter(15V-->5V).

My power supply schematic is given below.



The microcontroller power supply section is shown below.



My question: Is this a good idea to power ADC reference with a switcher like this.

Do we need to use any precession voltage reference.

Regards
Hiyo

 

It depends entirely on the output characteristics of the switching regulator. If you can, you should look for a specification of the output ripple under load. That and the frequency of the ripple may be too high for the ADC to notice. There are other strategies to provide a reference if you find you original strategy unworkable.

 

I always use a switched-mode to generate the 5V supply (which powers such things as CAN and RS485 drivers) then derive the 3.3V supply using a LP2951 linear regulator. It has good PSRR and produces an output voltage which is accurate enough to use for a A/D reference.
If the microcontroller uses 25mA then the additional power loss is 42mW. You would have to find a buck regulator that uses <8mA to break even. That is actually quite feasible, but is it worth the extra power for the application? That depends on the application.

 

As another example I run my K3S transceiver from an SMPS when doing very weak signal work on 6 meters. Never had a problem pulling weak signals out of the rug.

 

The accuracy of the A/D conversion depends upon the accuracy of Vrefh, so supply that volage according to your A/D conversion requirements.

 

You did not specify the nature of the A/D conversion you will be doing and there is a huge difference between a 6-bit flash converter and a 24-bit sigma-delta converter.