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# DAC8571: question about definition of differential nonlinearity

Part Number: DAC8571
Other Parts Discussed in Thread: REF3425,

Hi team,

The max differential nonlinearity is 1 LSB in the datasheet. Customer tested that, with REF3425 reference,  the output is supposed to be 963.90mv with code=9000. But, it is actually 965mv which the code should be 9009. Customer think the nonlinearity is the 9bits which is much higher the 1 LSB differential nonlinearity in datasheet. I think the 9bits should include the offset error. Is it correct? What is the specific definition of differential nonlinearity in datasheet?

Thanks.

• Hi,

At any given code, error contributions can be due to the following factors.

1. Integral Non linearity

2.  Gain Error

3. Offset Error

4. DNL

We can calculate the effect of these factors using root sum square method and its called Total Unadjusted Error (TUE). For some devices it will be specified in datasheet itself as TUE or absolute accuracy. In DAC8571 case, its shown as 2.5mV.

You can calculate yourself these using the parameters explained above.

For DAC8571, INL ( typ) = +/-0.098%FSR = 64LSBs ( 0.098*2^16/100)

1LSB  = 2.5/65536 = 38.14uV

So INL = 38.4uV * 64LSB = 2.45mV

Gain error = 1mV (typ)

Offset Error = 0.3mV (typ)

So Total Undajusted Error (TUE) at any Code  = SQRT ( INL^2 + Offset Error^2 + Gain Error^2)

TUE = SQRT ((2.45mV)^2 + (0.3mV)^2 + (1mV^2)) = 2.669mV

So at any code you can expect a deviation of 2.669mV from the actual output. Note we didn't include DNL in this calculation, reason being DNL effect is captured in INL itself. So Looking at the DNL alone, you cannot estimate the error in DAC output. A DNL error specification of less than or equal to 1LSB guarantees a monotonic transfer function of the DAC.

Regards,

AK