S12G VDDF usage

[binli]

Hi:

I used S12G currently. Now want to use VDDF as a more accurate voltage reference. Below is my understanding:

1. First get the ADC result, stored it in IFR 0x0_4022/0x0_4023. It's a reference value which typical voltage is 2.82v.

Condition listed below from S12G datasheet.
Regulator supply voltage VDDR 5 V
I/O supply voltage VDDX 5 V
Analog supply voltage VDDA 5 V
ADC reference voltage VRH 5 V
ADC clock fADCCLK 2 MHz
ADC sample time tSMP 4 ADC clock cycles
Bus frequency fbus 24 MHz
Junction temperature Tj 150 and -40 °C
Code execution from RAM

2. In the code, just get the value and use calculation below:

Result=ConvertedADInput *(StoredReference • 5V/ConvertedReference 2n)

Am i right above? Thanks.

My questions are listed below:

1. Why in S12G we used VDDF as an accurate reference voltage? For other part, we have bandgap voltage as a reference.

2. How is the data format stored in 0x0_4022/0x0_4023?

[danielmartynek]

Hi,

The reference result of VDDF voltage, measured at that conditions you mentioned, is stored in Flash IFR and cannot be change. You should measure the voltage at conditions of your applications, store it somewhere and compare both results.

The VDDF is a constant voltage with a narrow distribution over temperature and external voltage supply, so it is similar to bandgap voltage. However, to ensure high accuracy of the VDDF, the Flash must not be programmed, erased, or read during the VDDF conversion.

The result at the IFR address is left justified. See Chapter 12.3.2.12.1 of the RM.

Regards,

Daniel

[binli]

Hi Danieal:

Got it, thanks.