I am considering to use AD8429 instrumentation amplifier over a wider temperature range, and for high accuracy application. Unfortunately, the gain error vs. temperature specification is not documented in very detail in the data sheet. It says that at >1 Gain, the error is -100 ppm max. Is the case regardless to gain value (as long as it is above 1)? I will be using a gain between 10 to 100, and I wonder if I keep the gain within some range, can I achieve a better temperature stability <25ppm/°C?

In this context, I also wonder what are typical values for the temperature dependency of gain (set at 10 to 100), and what is the statistical variance in this?

Many thanks in advance for any additional support,

Hi Pekka,

Thanks for considering ADI products on your applications.

You are right that there is a value in-between but it only matters at those gains > 1 but less than about 10 V/V.

The G=1 drift is mainly just the relative drift of the subtractor resistors. The G>1 drift includes the drift of the RF resistors . This is clearly shown on the gain equation: G=1+ 2RF/RG. When RG is open and G =1, the 2RF/RG term is equal to zero so the RF drift doesn't affect the gain. But when the RG is small, the 2RF/RG term is much greater than 1, so the 2RF drift (-100ppm/°C) and the RG drift contribute more.

You can actually use the gain equation to calculate the real worst-case drift versus gain, but this is only valuable at low gains. The total drift calculated this way:

Gdrift_total = G1drift/Gain + (G>1drift + RGdrift)*(Gain -1)/GainFor the AD8429, if we had a perfect RG and a gain of 10, the worst case drift (ppm/°C) would be:

-90.5 ppm/°C (worst case)Here you can see that it doesn’t make a big difference for gain of 10 or above.

The max -100ppm/°C is a guarantee given by the thin-film process that we use for the RF resistors.

I hope this helps.

Best regards,

Emman