Variation in A/D performance

[ButchT]

Part is CY8C27543-24

We are seeing some variations in ADC operation between parts in production that look to be bigger than expected, so I am Assuming the internal reference is at fault here.

Data sheet says this

What exactly does"trimmed for appropriate VDD mean" Using 5.0v here.....

Designer 5.4 chip editor shows this:

Which is a +/- 1.6 volt reference.. does not comply with data sheet?

If I read the DELSIG11 data sheet right it tells me I can expect a 3% error with this reference...Is this true, this equates to about a 64 tick difference, way too much..

So basic question is how good is this overall system and what can I count on? What kind of tick accuracy over temp range 0-70C

[SampathS_11 · Accepted solution]

Hello @ButchT ,

Q)What exactly does"trimmed for appropriate VDD mean

A)The trim values are programmed into the device at manufacturing to get the minimum error for the appropriate VDD values supported by the device. 

Q)Which is a +/- 1.6 volt reference.. does not comply with data sheet?

A)This is 1.6 times the bandgap voltage 2.08V ± 2.08V.

Q)So basic question is how good is this overall system and what can I count on? What kind of tick accuracy over temp range 0-70C

A) The bandgap has roughly 2% variation over  4.75 V to 5.25 V and –40 °C  <= TA  <= 85 °C, or 3.0 V to 3.6 V and –40 °C  <= TA  <= 85 °C. This will contribute to 3% variation in Delsig11. This error can be termed as "initial" error. Once this error is compensated by calibration (in user firmware), you can expect the error to reduce considerably. It will still be higher than the 0.3% error which is contributed by Delsig11 after eliminating the errors contributed by the bandgap. 

Best regards,

Sampath Selvaraj