NRF52820 COMP issue

Question

Hello everyone! 
 I have some issue with the comparator module on the nrf52820 chip. 
 We need to compare one of external analog signal the 1.8V internal reference source. (But other variants – 1.2V / 2.4V don’t work either) 
 When I set 0 Volt on the measurement contact – the result of comparison is correct ( 0). 
 But as soon as I increase voltage, even on 0.1V - the result immediately becomes incorrect (1). 
 
 Moreover, I tried to use differential mode (just for an experiment). 
 In that mode comparison is performed relative to the reference signal on the external pin. 
 So, in that mode comparisons are performed perfect. 
 
 It seems for me there are some problems with internal reference source. 
 We develop the software for the nrf52820 mcu but at this moment we haven't received our boards and use the nrf52833 development kit for debug. 
 Could the problem be caused by that? 
 Also I thought that the problem might be with my board and tried to use others. But unfortunetely the result is the same. 
 
 Could you please help me with it? 
 Many thanks in advance! 
 
 All the best! 
 Ernst

Karl Ylvisaker · Answer

Hello again Ernst, 
 Ernst Smirnov said: Yes, I just checking the value of the result register after starting the NRF_COMP_TASK_SAMPLE task. 
 Is it incorrect? 
 No, this is fine. I was just wondering whether you were using the events as well. 
 Ernst Smirnov said: Sure! I start a debug session and put a break point to one of these lines. After that I adjust of a power source and so I can see comparison result has changed. Ernst Smirnov said: I see it on the debug session. If the voltage of the input is higher than 0V I get the first branch of the debug condition only. However, as soon as I decrease that to zero - I get the second branch immediately. 
 Thank you for clarifying, this makes it a lot clearer, and I now understand how you are using this for debugging with breakpoints only, and not as a way to monitor the value of 'a' - I just had to make sure. I see now that you do never set your TH registers - I'm sorry that I missed this the first time I looked through your code. You are currently not setting the TH register, which the VUP and VDOWN is derived from. Their default value is 0, which means your thresholds place at 1.8V/64 = 0.028 V. This could be why you are seeing the change immediately after manually increasing the voltage. If you want the reference level to be at exactly 1.8V with no hysteresis, please change them both to the value 63, so that the threshold is placed at 1.8V. You can set your TH register by using the nrf_comp_th_set function . Please try this, and let me know if it resolves your issue! :) 
 If this does not resolve your issue, could you possibly send me a stripped down version of the project, so I may test this on my end, and see if I am able to reproduce the issue? Best regards, Karl

NRF52820 COMP issue

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