We use a AD5258 digital pot to adjust the gain of an non-inverting amplifier (see schematic). In a small number of units in the field, which originally passed factory test and calibration, now have the pot at 0 Ohms. Sometimes power cycling the product will correct the problem, but sometimes it will not. Resending the pot setting to the unit does not fix the problem. Unfortunately, we haven not taken any particular care to manage the power up sequence, and it could be that pot leads A, B, W see some voltage before the supply voltages come up. Is the zero Ohms state an expected fault if the power is not sequenced properly? Is there an application note or sample circuits that suggests proper power up of these type of components?
I moved this question about the AD5258 to the Precision DACs Community. Someone here should be able to assist you.
EngineerZone Support Community Manager
The minimum measurable impedance in a digipot is the wiper resistance.
If the measured resistance is 0ohms means that the part is broken or the ESD protection has been turned on.
Could you verify the voltage supplies?
I did not actually measure the resistance. I simply observe that the gain in the amplifier is the highest it can be and it does not change when the pot is changed. So I should have said the pot is at it's minimum resistance, not zero. Both voltages applied were 5.0 V when the problem occurred.
Could you check if the digipot ack the commands when the faulty state is detected?
Could you provide a plot including the inverting, non-inverting and output voltages in the opamp?
If any voltage goes below GND, the internal protection diodes will drive the current to GND.
Maybe your opamp cannot recover from that?