NRF51822 ADC

[zcmm]

Dear,all

SDK:8.1.0 s110

1. VDD use 2.6--3.6V，use VDD bandgap: (ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling << ADC_CONFIG_REFSEL_Pos)
   ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling << ADC_CONFIG_INPSEL_Pos , when adc measurement the voltage of 1.8V, the NRF_ADC->RESULT is 510;

2. VDD use 1.7-2.5V，use VDD bandgap: (ADC_CONFIG_REFSEL_SupplyOneHalfPrescaling<< ADC_CONFIG_REFSEL_Pos) ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling << ADC_CONFIG_INPSEL_Pos , when adc measurement the voltage of 1.8V, the NRF_ADC->RESULT is 336;

3. VDD use 1.7-2.5V，use VDD bandgap: (ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling << ADC_CONFIG_REFSEL_Pos)
   ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling << ADC_CONFIG_INPSEL_Pos
   , when adc measurement the voltage of 1.8V, the NRF_ADC->RESULT is 506;

QS1: why VDD use 1.7-2.5V,the NRF_ADC->RESULT is very inaccurate.But the bandgap use (ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling << ADC_CONFIG_REFSEL_Pos)
ADC_CONFIG_INPSEL_AnalogInputOneThirdPrescaling << ADC_CONFIG_INPSEL_Pos , the NRF_ADC->RESULT is right. (QS2: the PS said it can not allow use ADC_CONFIG_REFSEL_SupplyOneThirdPrescaling when VDD is in 1.7-2.5V,it is ture????)

[Jørn]

Hello zcmm

You mention bandgap in your question, but I see you have used the supply prescaler. I will assume you have NOT used the bandgap voltage (VBG) as reference, but prescaled versions of the supply voltage VDD. Please correct me if this is wrong.

As the product specification states VDD should be within 1.7-2.6 V when using 1/2 supply prescaler, and between 2.5-3.6 V when using 1/3 supply prescaler. If VDD is outside these ranges accuracy and performance cannot be guaranteed. This is the case in your final 1/3 prescaler set-up, and it is therefore not possible for me to comment on the results you get as the effects of operating outside the specified ranges is not documented.

The specific value for VDD you have, as well as any voltage scaling network you may have outside the ADC, can greatly affect the result you achieve. This makes it difficult for me to assess the results you have without knowing more about your system. How prescaling and voltage dividers affect ADC performance and results is described in the nRF51 series reference manual infocenter.nordicsemi.com/.../nRF51_RM_v3.0.1.pdf

I suggest you take a look at the ADC chapter in the reference manual, and ensure that you are operating within the specified voltage ranges, and have taken external circuits into consideration.

Best regards

Jørn Frøysa

[zcmm]

thanks,it is my question.
i have a other question.In addition to DTM bin, I can also use other routine test frequency,like beacon?