topic Re: S32K144 ADC Accuracy Problem in S32K

S32K144 ADC Accuracy Problem

ldj979 — Mon, 11 Oct 2021 17:07:07 GMT

Dear Team,

I am having an accuracy problem reading the voltage value using the adc of the s32k144, so I have a question.

I used an op amp on the front to read a voltage of around 240.31mV.

Two points were measured with a multimeter.

1. When I measured pin 1 of the opamp side, I read 240.31mV voltage.

2. When I measured ADC0 13 on pin 45 of s32k144 MCU, I read 240.31mV voltage.

I read the ADC value using S32DS SDK, but the value is incorrect.

I am attaching a code and picture of setup.

What's wrong?

#############################################################

/* Including necessary module. Cpu.h contains other modules needed for compiling.*/
#include "Cpu.h"

volatile int exit_code = 0;

/* User includes (#include below this line is not maintained by Processor Expert) */
#include "stdint.h"

#define ADC_INSTANCE 0UL
#define ADC_CHN 13U
#define ADC_VREFH 5.0f
#define ADC_VREFL 0.0f

int main(void)
{
/* Write your local variable definition here */

uint16_t adcRawValue;
uint16_t adcMax;
float adcValue = 0.0f;

adcMax = (uint16_t) (1 << 12);

/* Write your code here */
/* For example: for(;;) { } */

CLOCK_SYS_Init(g_clockManConfigsArr, CLOCK_MANAGER_CONFIG_CNT,
g_clockManCallbacksArr, CLOCK_MANAGER_CALLBACK_CNT);

CLOCK_SYS_UpdateConfiguration(0U, CLOCK_MANAGER_POLICY_AGREEMENT);

PINS_DRV_Init(NUM_OF_CONFIGURED_PINS, g_pin_mux_InitConfigArr);

DEV_ASSERT(PackV_ADC_ConvConfig0.channel == ADC_CHN);

ADC_DRV_ConfigConverter(ADC_INSTANCE, &PackV_ADC_ConvConfig0);
ADC_DRV_AutoCalibration(ADC_INSTANCE);

while(1)
{

/* Configure ADC channel and software trigger a conversion */
ADC_DRV_ConfigChan(ADC_INSTANCE, 0U, &PackV_ADC_ChnConfig0);
/* Wait for the conversion to be done */
ADC_DRV_WaitConvDone(ADC_INSTANCE);

/* Store the channel result into a local variable */
ADC_DRV_GetChanResult(ADC_INSTANCE, 0U, &adcRawValue);

/* Process the result to get the value in volts */
adcValue = ((float) adcRawValue / adcMax) * (ADC_VREFH - ADC_VREFL);

OSIF_TimeDelay(1000);

}

/*** Don't write any code pass this line, or it will be deleted during code generation. ***/
/*** RTOS startup code. Macro PEX_RTOS_START is defined by the RTOS component. DON'T MODIFY THIS CODE!!! ***/
#ifdef PEX_RTOS_START
PEX_RTOS_START(); /* Startup of the selected RTOS. Macro is defined by the RTOS component. */
#endif
/*** End of RTOS startup code. ***/
/*** Processor Expert end of main routine. DON'T MODIFY THIS CODE!!! ***/
for(;;) {
if(exit_code != 0) {
break;
}
}
return exit_code;
/*** Processor Expert end of main routine. DON'T WRITE CODE BELOW!!! ***/
} /*** End of main routine. DO NOT MODIFY THIS TEXT!!! ***/

######################################################################

error print

Regards,

DJ LEE

Re: S32K144 ADC Accuracy Problem

ldj979 — Mon, 11 Oct 2021 17:10:02 GMT

The schematic diagram of the front part is also attached.

Re: S32K144 ADC Accuracy Problem

Robin_Shen — Tue, 12 Oct 2021 03:58:58 GMT

Hi ldj979, Please check the voltage of VREFH. Make sure the value match the #define ADC_VREFH 5.0f. I did not find any obvious errors in your configuration. Have you try to measure another voltage signal? (RAD<5kΩ) Is the ADC conversion result still inaccurate?

Best Regards,
Robin
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Re: S32K144 ADC Accuracy Problem

ldj979 — Wed, 20 Oct 2021 12:36:34 GMT

Dear Robin,

Is RC filter necessary in front of the ADC pin of the s32k144?

Regards,

DJ LEE

Re: S32K144 ADC Accuracy Problem

ldj979 — Wed, 20 Oct 2021 12:37:28 GMT

Also, VREFH is stable.

Re: S32K144 ADC Accuracy Problem

Robin_Shen — Fri, 22 Oct 2021 09:04:37 GMT

Whether RC filter is needed depends on whether there are glitches in the signal to be sampled.
In addition, please tell me whether the result of ADC sampling on-board POT R13 is accurate.
VREFH is stable. Did you measure the voltage and ensure it was 5V?

Re: S32K144 ADC Accuracy Problem

ldj979 — Tue, 28 Dec 2021 01:56:38 GMT

I solved it by attaching a pull-up resistor on the front end. Thank you for answer