Thomas Kintzel

URGENT: Problems using ADC of MXRT1051

Discussion created by Thomas Kintzel on Nov 19, 2019
Latest reply on Nov 21, 2019 by Kerry Zhou

We are a bit under pressure to solve this problem, would be nice someone could help fast.


Wenn we measure with ADC the signals makes a jump than it reaches a certain level. 


First picture shows ADC result values (increments). The second is a measurement of the analoge input signal at the same time at the input of the operational amplifier (signal "SENSOR_1"). There is no jump to observe.


Signal "ADC1_CH00_SENSOR1" (=µC input) is not only defined by the voltage divider in the schematics. It seems that there is an additional e.g. 100 k pull down in the µC. And then it reaches a certain level, this internal resistor seems to be switched of. The signals jumps to its expected value. 


We think that this is a configuration error but we can't figure out. There is no option "No internal resistor". 1 pull down, a few pull up and "No Init". "No init" does not sound as a valid option and may cause in random results. (though I will test this next).


I'm using MCUXpresso IDE v11.0.0 [Build 2516] [2019-06-05]


Can you help me with that?

Thank you

Best regards



Signal with jump, wrong gain below a certain level



Signal measured with a reference system at the same time