Random value obtained in ADC output on ICE AM335x

Pankesh Yadav

Other Parts Discussed in Thread: SYSBIOS

Sir,

I have build and run successfully ADC project in CCS v6.1.2 sysbios 2.1.1.2 ,but it indicates random value even if nothing is connected to its port.

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

When nothing is connected the ADC inputs are floating. Note that you must not connect any voltages higher than +1.8V to the ADC inputs, as this will damage the device.

0 Pankesh Yadav over 9 years ago in reply to Biser Gatchev-XID

Prodigy 130 points

In the begining I tried with potentiometer and it gave constant output ,even if nothing was connected. Then I changed the voltage resolution value ,after that it started to give random value. So I changed the voltage resolution value to the default one.
Can you please tell how to verify that board has been damaged.

Regards
Pankesh

0 Biser Gatchev-XID over 9 years ago in reply to Pankesh Yadav

TI__Guru**** 393215 points

With a potentiometer you have always a defined input. As for checking the ADC, you can do this with a known voltage source in the range from 0V to +1.8V.

0 Pankesh Yadav over 9 years ago in reply to Biser Gatchev-XID

Prodigy 130 points

Hi Biser
Thanks for your response I will try to check the ADC with these known voltage source. Ours all others sample project are working properly on board ,and ADC alone is malfunctioning on it.So does it still indicate that board has been damaged.

Regards
Pankesh

0 Biser Gatchev-XID over 9 years ago in reply to Pankesh Yadav

TI__Guru**** 393215 points

If you applied voltages higher than +1.8V to the ADC inputs they are probably damaged.

0 Pankesh Yadav over 9 years ago in reply to Biser Gatchev-XID

Prodigy 130 points

Hi Biser,

In starting when we applied voltages higher than +1.8V to ADC input, then it saturates at max of 1797mV and we tried that many times,but it continued working fine. Recently when we changed voltage resolution ,then it started to malfunction .

So is there any problem associated with change in voltage resolution of ADC.

Regards,
Pankesh

0 peaves over 9 years ago in reply to Pankesh Yadav

TI__Guru 63065 points

What do you mean when saying you changed voltage resolution? Did you change the voltage applied to VREFN and VREFP?

Regards,
Paul

0 Pankesh Yadav over 9 years ago in reply to peaves

Prodigy 130 points

Hi,
I dint change VREFN and VREFP. I just changed a constant named voltage resolution equal to 439, since I dint know that only 1.8V could be given to analog input so I changed it for 5V. Does this effects the ADC working? Because before I changed it, everything was working fine. Now even after changing it to 439, it continues to show the same random values.

Regards
Pankesh

0 peaves over 9 years ago in reply to Pankesh Yadav

TI__Guru 63065 points

I’m not able to help you with the effect of software variables, but can assure you the only way to change the actual resolution of the ADC is by changing the voltage applied to VREFP and VREFN. The ADC measures the voltage applied to the input relative to the voltage applied to VREFP minus the voltage applied to VREFN. If you applied 5 volts to the ADC input, there is a very good chance you permanently damaged the device. The maximum input voltage for the ADC has no relationship to a software variable.

Regards,
Paul

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Random value obtained in ADC output on ICE AM335x