How to calculate the ADC Clock?

[adrianocasimiro]

Hello, I'm trying use ADC at FRDM-K22F, it's working, but I didn't get success on calculate the ADC clock. I'm using http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/kinetis-cortex-m-mcus/adc... for calculate the ADC clock, but the result the calculator don't is equal at result of conversion.

I'm setting my ADC clock this way:

    adcUserConfig.resolution = kAdc16ResolutionBitOf16;

    adcUserConfig.highSpeedEnable = false;  

    adcUserConfig.clkSrc = kAdc16ClkSrcOfBusClk;

    adcUserConfig.lowPowerEnable = false;

    adcUserConfig.asyncClkEnable = false;

    adcUserConfig.longSampleTimeEnable = false;

    adcUserConfig.longSampleCycleMode = kAdc16LongSampleCycleOf24;

    adcUserConfig.clkDividerMode = kAdc16ClkDividerOf8;  

    ADC16_DRV_Init(ADC16_INSTANCE, &adcUserConfig);

What's the result of ADC clock for this example?

Thanks.

[xiangjun_rong]

Hi, Adriano,

Regarding your question about the ADC clock frequency, from hardware perspective, I suggest you should check the following register setting.

1)pls check the ADCx_CFG1[ADICLK], which selects the clock source of ADC.

For K22, I copied the part here:

2)there is divider set up in the ADCx_CFG[ADIV], I copy it here.

Clock Divide Select

Selects the divide ratio used by the ADC to generate the internal clock ADCK.

00 The divide ratio is 1 and the clock rate is input clock.

01 The divide ratio is 2 and the clock rate is (input clock)/2.

10 The divide ratio is 4 and the clock rate is (input clock)/4.

11 The divide ratio is 8 and the clock rate is (input clock)/8.

For your code, I think you select bus clock as ADC clock source with ADICLK bit=00 in binary, the divider is 8 with ADIV bits=11 in binary, the ADC clock frequency is (bus clock)/8. I do not know your bus clock frequency, it is dependent on the MCG mode, and SIM_CLKDIV1 register setting.

Hope it can help you.

B R

Xiangjun Rong

[adrianocasimiro]

Hi Xiangjun,

My bus clock is 60 MHz divided for 8, so, my ADC Clock is 7,5 MHz. Now, I want find the conversion time per sample, I have to use this formula  (ConversionTime = SFCAdder + AVGNUM x (BCT + LSTAdder + HSCAdder)) ?

Thank you very much.