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ADUC7034 Diagnostic current source

Question asked by amusin on Aug 7, 2012
Latest reply on Aug 9, 2012 by amusin

Hi!

 

The analog circuitry is very simple to clarify the issue.

Both IIN+ and IIN- pins are connected to GND.

ADC0CON = 0x8000; // (ADC enabled, Gain = 1).

ADCFLT=0x0000;

ADCMDE=0x1;

ADC's data are about 0. It's OK.

 

Then I switch on the IIN+ current source (50 uA).

ADC0CON = 0xA000;

I suppose that the ADC data will be the same (see above, IIN+ and IIN- pins are shorted).

In reality ADC data are 2380...2430 (I've got 2 PCBs).

 

ADC data are inversed (-2380) when the IIN- current source is switched on.

ADC0CON = 0xC000;

 

I read "Current ADC Diagnostics" chapter and tried other gains: 2, 4, and 8.

ADC data is scaled by corresponding factor.

 

My question - what is the strange 2400 data?

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