Instability in RT1170 inputs

ibravo — Fri, 10 Jan 2025 10:56:02 GMT

I am working with the ADC of the i.MXRT 1170.

To do my test I am using the Fully-Differencial Amplifier circuit shown in Figure_1. In this configuration, I get 1.6V in both outputs positive and negative (the input is shortcircuited and connected to GND). If I do not connect anything else to this circuit the output is pretty stable (20.9mV of noise p-p): Figure_2 shows the noise in the output. This noise has been measured with a 200MHz Bandwith oscilloscope.

Then, I have connected te output of this circuit to the balls L13 and M15 of the i.MX RT1170. First I have configured this pins as analog inputs with the keeper option selected. At the moment I connect the outputs of the amplifier circuit to the processor the signal begins to oscililate. Figure_3 shows the signal measured at that moment in a test-point near the pin L13 of the processor.

I have tried with other pins, and other configurations (digital input, analog input, with pull-up, with pull-down, with keeper). I get the same result with all configurations: the signal begins to oscilate at the moment I connect it to the processor and it is stable when I disconect the processor.

I would appreciate a lot If someone could shed light in this issue.

Re: Instability in RT1170 inputs

Habib_MS — Fri, 10 Jan 2025 22:14:07 GMT

Hello @ibravo,
I understand that you are currently using an EVK. In order to support you better, can you provide me the specific EVK where you are testing?
Also, I understand that you are using a test point as a reference, in order to try a pinpoint if this causes the issue, can you use a GND pin instead a test point?
BR
Habib

topic Instability in RT1170 inputs in i.MX RT Crossover MCUs

Instability in RT1170 inputs

Re: Instability in RT1170 inputs