Q: What is the tolerance & accuracy for MAX5479?
A: MAX5479 has 25% tolearance. Typical End to End resistance is 100kohm with 75kohm min. & 125kohm max. This is chip to chip difference.
MAX5479 has 256 taps, so 1LSB=100kohm/256=390ohm approx (typ), its full scale error is -0.3LSB, which means 390*0.3=117ohm approx.
Q: Set one wiper resistance value in the chip, power on/off the system frequently. It can be found the wiper voltage is different as the setting in less opportunity, what is the possiblity for this phenomenon?
A： MAX5479 has volatile & nonvolatile register in the chip. The volatile register retains data as long as the device is powered. Removing power clears the volatile register. The nonvolatile register retains data even after power is removed.
In normal application, upon power-up, the power-on reset circuitry controls the transfer of data from the nonvolatile register to the volatile register, updating the wiper
position with the data stored in the nonvolatile memory register. This initialization period takes 10μs. If the chip had been power on/off frequently, and read the data too fast, the initialization may not be finalized yet. That means the data in nonvolatile register may not be recall to volatile register. Try to wait a longer time than 10us and then read the data again.
From hardware side, it requires a 0.1μF capacitor installed as close to the device as possible.