Voltage-Reference Temperature Drift
Temperature coefficient (tempco) is the specification that defines how a voltage reference’s output voltage will drift over a given temperature.
The first plot shows data for the MAX6033 and the second plot is data for the MAX6005. It is immediately apparent that the devices have significantly different shaped characteristics. The MAX6033A is specified as a 7ppm (max) reference, while the MAX6005 is specified as a 100ppm (max) reference. What does this really mean for a design? It certainly does not mean that if we increase the temperature of a part by 1°C, we will change the output voltage by the tempco. To understand what is happening, you must remember that Maxim specifies its series voltage references using the “box” method. This method makes it easy to compare a whole family of voltage references, and is the industry-standard method.
The MAX6033A serves as a good example of how the box method works. This device is specified as a 7ppm (max) reference over a temperature range of -40°C to +85°C. It’s also worth noting that the MAX6033 is also specified over the wider -40°C to +125°C, which is why Figure 1 goes all the way to +125°C. To calculate how accurate it will be over the specified temperature range, simply multiply the tempco by the device’s specified temperature range. The MAX6033A is 7ppm/°C x 125°C = 875ppm. This value is always positive and negative. So over the device’s specified temperature range, we can guarantee that the reference will drift by less than ±875ppm of the initial value.