How to use a digital potentiometer to eliminate voltage changes

How to use the digital potentiometer to eliminate the voltage change? The editor of okplazas.com found some technical posts shared by technical people from the Internet. If it is suitable for use, just follow it~

Both mechanical potentiometers and digital potentiometers have uncertain end-to-end tolerances. The end-to-end resistance error of digital potentiometers is typically 20% to 30%. When digital potentiometers are connected in series with other resistors to form a voltage divider network, this The deviation of the resistance value may cause some problems, causing the voltage variation to exceed the allowable error range.

This application note discusses a proportional circuit design method that converts resistance deviations into acceptable current changes, which can effectively eliminate voltage changes.

In the circuit given here, the voltage output depends on the ratio of the potentiometer, and the temperature coefficient can also be well controlled in the design. Proportional circuit design The immediate problem faced by this design is that a 3% error may cause the voltage to vary between 3V and 4.5V. Using the block diagram shown in Figure 1, basic calculations can be performed. The digital potentiometer is 50kΩ (25% tolerance), R1 is 16.5K (1%), and R2 is 100K (1%). The 25% tolerance of the potentiometer's end-to-end resistance is the largest source of error in the design. Now consider using different wiper resistances for the same calculation. If the potentiometer is 37.5kΩ, the top voltage is 4.46V, and the low end is 3.25V; if the potentiometer is 62.5kΩ, the top voltage is 4.54V and the low end voltage is 2.79V. In this circuit, due to the large end-to-end resistance deviation of the potentiometer, this basic structure cannot be used to solve the voltage change problem. Two voltage references are introduced into the circuit to control the error and temperature coefficient. The end-to-end absolute deviation of the digital potentiometer will change the loop current, but does not affect the voltage. The output voltage changes proportionally and only depends on the resistance ratio at the tap position of the potentiometer. Both references control the output voltage through feedback, and R2 (25K to 50K) determines the source current of the two references. The data sheet of MAXIM digital potentiometer will discuss the bypass capacitor, can increase the electric capacity according to the layout situation.