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ADC output fluctuation in LPC54608J512BD208 microcontroller

Question asked by Prasanna Naik on Jul 2, 2020
Latest reply on Aug 2, 2020 by Prasanna Naik

Hi,

I am using LPC54608J512BD208 microcontroller in an application.

The ADC accuracy is crucial as the product is used in a Power protection segment.

I am getting fluctuations in ADC output with constant DC input. The datasheet claims max error of 4.5LSB but i am getting more than 10 counts fluctuations as shown in the results below.

 

I have performed some experiments on the OM13092 development board to check the problem observed on LPC546 microcontroller. We have found fluctuations in the development board as well.
Details of connection/board configuration:
   1) Channels used ADC0_4 (J12/2),ADC0_5 (J12/4) & ADC0_6 (J12/6)
   2) Evaluation board: OM13092
   3) Power: Debug port J8 of OM13092
   4) Core clock: 100 MHz (External 12MHz crystal frequency stepped up through PLL)
   5) ADC clock: 1 MHz (Synchronous)
   6) ADC sample time number = 7 
   
   
Experiment 1: GND from P3 of OM13092 connected to ADC0_4, ADC0_5 & ADC0_6
ADC channel
                  ADC output
MinMax
ADC0_4010
ADC0_506
ADC0_605
Fluctuations of 10 count with GND input

 

Experiment 2: 1.65V DC generated through a Voltage divider circuit of 10K each fed to channel ADC0_4
                            3.3V(J10/12) of OM13092 and GND (J10/18) is used to dirve the voltage divider network.
ADC Channel
ADC Output
MinMax
ADC0_520412053
Fluctuation of 12 count with a fixed DC input.
I have also attached the code for your reference.
Please help in resolving the issue.
Two issues have been identified so far in LPC546 controller :
1) PE Micro debugger causes fluctuations in ADC output in custom board:
   I have used uart to verify the issue of PE Micro debugger.

Card 1:

 

 

Input Voltage(V)ADC Channel
With PE Micro
Without PE MIcro
MinMaxMinMax
1.65 V (DC)

 

ADC0_02014207520472051
ADC0_42020206420452054
ADC0_52032205820462051
ADC0_62016206020482056
ADC0_72021205620462052
ADC0_82018205120412048

Card 2:

 

 

 

Input Voltage(V)ADC Channel
With PE Micro
Without PE MIcro
MinMaxMinMax
1.65 V (DC)

 

ADC0_02010206620462052
ADC0_42035206120472054
ADC0_52031206220452051
ADC0_62025205920502056
ADC0_72019205620462052
ADC0_82037204920412048

 

2) Fluctuations in ADC output even on LPC546 board as explained earlier.
Kindly help in addressing these issues.
Thanks & best regards,
Prasanna

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