Question
Inquiry Description:Hi,
In your datasheet of the AD8426, it is written for a G>1 a gain drift of-100ppm for the full temperature range.This is huge.
Could you please provide me more information about this gain drift?I set my gain around 5 and my temperature range is about [-40°C/70°C]. Can Itake a lower drift value?
Thank you for your support.Regards.
Answer
The temperature drift of the internal resistor film (which is what dominates the gain drift) is closer to -70ppm/C. Therefore, a gain drift of-100ppm/C can be guaranteed for gains greater than unity. Because the gain is set by the external resistor RG and the internal resistors RF, youhave to take account for the external resistor drift. The number provided on the data sheet is assuming that the external resistor doesn’t drift.Considering the gain equation 1+2RF/RG, at low gain the drift is less than the drift of the internal resistors. For example, at gain of 2 the gaindrift is actually only half because half of the output signal depends on the 2RF/RG term. However, at gain of 10, 90% of the output signal depends onthe resistor ratio, so the drift is pretty much that of the resistors. At gain of 5, is not much better, so I would simply stick to -100ppm/C to besafe.