S12ZVC Supply Voltage Measurement

[amit_dhand]

Hello,

I am calculating Supply Voltage (12 volts ) through the ADC0 internal channel by enabling BATS module (which connects the VSUP with ADC channel).
MC9S12ZVCRM V1.2 Page 326 say that input Analog signal are unipolar and must be within the potential range of  VSSA to VDDA.

So accordingly

Supply Voltage - 12,000 mVolts

VSSA - 0,00 volts
VDDA - 5,000 mVolts

Using 12 bit resolution of the ADC, it should give result correctly but that is not the case it is not giving correct answers.

Am I measuring the Supply voltage correctly or need to step down the voltage or something else?

Thank you

[RadekS · Accepted solution]

Hi Amit,

BATS already contain internal voltage divider. So, you must multiply measured value (in mV) by 9 for getting VSUP voltage.

According BATS Electrical Specifications in reference manual:

Pin Input Divider Ratio(2)

RatioVSUP = VSUP / VADC=9

Valid for 5.5V < VSUP < 29 V

2. VADC: Voltage accessible at the ADC input channel

Note: Accuracy of such measurement should be typically +/-2% (it is still without error of ADC conversion).

I hope it helps you.

Have a great day,
RadekS

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