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Bandgap reading accuracy (bandgap is enabled in PMC)

Question asked by Ryan Parasram on Nov 12, 2014
Latest reply on Dec 5, 2014 by Ryan Parasram

Hi,

 

I am using a S9KEAZN64AMLC controller with a 5.3V power supply. I have a scope on the power supply and see that it is stable.

 

I have the PIT triggering ADC conversions at 500us.

The ADC is configured to take 4 12 bit readings with 16 bit right justified results.

The ADC is configured as

- Discontinuous mode OFF, Low power mode OFF, ADC clock 1Mhz, Conversion time 40us, Sample time 23.5 clock periods.

- When I read the bandgap and dump the results to a serial port, I see the 8 LSB's changing, corresponding to about 1.11 to 1.21V

- The CPU is clocked at 8Mhz (both Core and Bus)

 

I was hoping that the values will have good precision and maintain at least 4LSB's.

Could you tell me what I am doing wrongly and what I may try?

 

Thanks,

Ryan

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