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# AD4115 output data don't match the formula

We have reproduced the whole evaluation bord circuirty, so the hw should be out of discussion.

We apply a differential voltage to the inputs of a given channel and read a value of 8755d0, instead of the value calculated with formula on page 24; Code = 2N – 1 × ((VIN × 0.1/VREF) + 1)

What suggst for this?

Other question is if gain and offset are always applied to the raw date read from the AD. If I apply the formula on page 32; Data = ((0.075 × VIN/VREF) × 223 – (Offset − 0x800000)) × (Gain/0x400000) + 0x800000 I get a different results, apart for the default gain of 0x5XXXX0, where I don't understand what the "XXXXX" value means, because if you use it for a multiplication the result can be influenced by the current value.

Parents
• Hi,

Can you clarify what is your register map configurations and also what is the actual analog input voltage value applied that results to 8755d0 results?

With regards to your second question. The ADC automatically applies the gain and offset corrections to the ADC conversions; therefore, the customer does not have to worry about these coefficients. From a customer perspective, the standard equation to convert codes to volts are used is the one listed on page 24 Code = 2^(N – 1) × ((VIN × 0.1/VREF) + 1). The default gain default register value may varied from part to part that is why the xxxx is a don't care as this value will change across different parts. So in order to know the default gain register value for a certain product you need to read it back so that you can relate it to the calibration equations.

Thanks,

Jellenie

• Hi Jelleie,

The voltage applied to the converter was 10V bipolar. But we discovered the problem: the input buffers were not enabled! We found out by reading the documentation carefully.

On page 18 it says:

the reference input buffers are disabled. The REF + and REF− pins
are selected as the reference source. Note that for this configuration,
the default channel does not work correctly because the
the input buffers must be enabled for a VINx input. "

It was enough to enable all the input buffers for everything to work fine.

We believe that the documentation must be drawn up with better clarity and appropriately highlighting the critical issues.

We hope this question will be of help to other readers

Angelo

• Hi Jelleie,

The voltage applied to the converter was 10V bipolar. But we discovered the problem: the input buffers were not enabled! We found out by reading the documentation carefully.

On page 18 it says:

the reference input buffers are disabled. The REF + and REF− pins
are selected as the reference source. Note that for this configuration,
the default channel does not work correctly because the
the input buffers must be enabled for a VINx input. "

It was enough to enable all the input buffers for everything to work fine.

We believe that the documentation must be drawn up with better clarity and appropriately highlighting the critical issues.