TMS570LC4357: ADC Self-Test und Calibration

Hello Vitaliy,

HalCoGen generates ADC calibration sample code. In HL_adc.c, there are 2 functions: adcCalibration() and adcMidPointCalibration(). You can use either of them.

adcCalibration() computes the offset error using calibration mode.

adcMidPointCalibration(): computes the offset error using the mid point calibration mode.

Thank you for your fast reply!

I tried to store the value of the adcCalibration() with the following code:

#include "HL_adc.h"


int main(void)
{
adcData_t adc_calibration_data;
adcData_t *adc_calibration_data_ptr = &adc_calibration_data;
uint32 ADC_value_offset;

adcInit();

while(1)
{

adcCalibration(adcREG1);
adcStartConversion(adcREG1, 1U);
while(!adcIsConversionComplete(adcREG1, 1U));
adcGetData(adcREG1, 1U, adc_calibration_data_ptr);

ADC_value_offset = adc_calibration_data_ptr->value;

}

return 0;
}

The ADC_value_offset was 4294967144. If I subtract the ADC_value_offset from  2^32 = 4294967296, the result is 152. Is this the right procedure to calculate the offset?

Hello Vitaliy,

The adcCalibration() computes the offset and writes this value into ADCALR register in the 2's complement form. You don't need to compute the offset again in your code.

During normal operation (when calibration is disabled), the ADCALR register contents are automatically added to each digital output from the AD core before it is stored in the ADC results memory. The value you read back from ADC memory is the corrected value.

I assume you use 12-bit mode, the value you read from the DAC memory should be less than or equal to 0xFFF.

Hello Wang, 

I use now the adcMidPointCalibration(adcREG2);. I noticed that when I connect a pulldown resistor to PIN 7  - AD2IN, the ADC  mesure a value of 0,543 V (lower image). How is this possible where AD2IN is an Input Channel? There should not be any current flow while connected to the GND and there is no input (lower image) , when floating it would makes sense.

ADCALR Register has now a value of 0x00000004 when I use the adcCalibration(adcREG2);. While I am using the adcMidPointCalibration(adcREG2);, ADCALR has a value of 0x00000FF9. I build againd a voltage divider ( upper image) to proof the values of the adc. The incoming ADC voltage is now around 2,42V. I have  difference of around 56 mV. Where comes this from?

Best regards

Vitaliy

Hi Vitaliy,

some question that might help to solve your problem:

- Did you check the voltage level on ADC output pin when it is floating?

- Have you already tried another adc input pin in case that the input stage is damaged?

Regards

René

Hello René,

I haven't found the output pin, or do yo mean the input pins with output pins?

I checked all input pins of ADC1 and ADC2 with multimeter. I have mesured 0,035V - 0,049V between ADCIN and GND.

Of cource I have tried another ADC input but the result was the same.

best regards

Vitaliy

Hello Vitality,

I did several tests on RM57 and LC4357 launchpads, and the value I sampled using ADC1 is correct.

1. This is my sampled data

   Channel 0: I shorted AD1IN0 to GND directly (J3, pin 3 to pin2)

   Channel 1: floating

   Channel 6: Temp sensor

2. The offset of adcCalibration() is 0x0B

    The offset of adcMidPointCalibration() is 0x09

    They are very close to each other.

Hello René and QJ Wang,

I have noticed, like René have mentioned before, that the current for Csamp was to low due to the high resistors i have used in the voltage divider.

As I have increased the sample time of the Csamp, the values were just perfect! 

Newertheless I will use calibration although the errors are not very hight.

Thank you for advice and assistance!

Best regards

Vitaliy