AD5222: Residual audio signal

Question I would like to use the AD5222BR10 part as a volume controller. It works fine, but if I step down the counter to zero, the sound doesn`t fade entirely. ( There is a measurable signal. ) The supply is +/- 2.5 Volt. Please help me, or explain why the part works such mode. Answer Figure 33 shows that there is a switch which directly connects terminals W and B and all switches connecting W to A are open when pot is set to 00h. So if you connect the signal input to A, the signal output to W and GND to B theoretically there should be no signal when code is 00h. If you connect the signal input to B and grnd to A then there will be some remaining signal at 7Fh because W is never directly connected to A - see the resistor at the top of the string in figure 33. The reason for seeing some signal when code is set to 00h is that the switches have some parasitic capacitance allowing AC signals to propagate from the input to the output. The isolation is not perfect and with sensitive measurements it will be possible to detect some residual signal, particularly at higher frequencies. You might also try measuring the signal that appears at the B terminal - system level issues (too much impedance in the ground plane, capacitive coupling between traces etc) mean that there are other paths for the signal to propagate. You could add an additional switch with good isolation properties in series with the Digipot.

AD5222: Absolute maximum ratings, latchup, zero code resistance and distortion

Question 1.In DS of AD5222 absolute max rating of Va,Vb,Vw to GND equals 0V,Vdd. Is it correct? I think it should be equals Vss,Vdd. 2.Must I cut off input voltage of pins Va,Vb,Vw before switching power off? If I understand correctly, pins Va,Vb,Vw and digital inputs of AD5222 should be powered after Vdd,Vss because otherwise the internal protection diodes may be damaged. But I can to power these input pins via external serial resistors. What values of input voltage or current via input terminals of AD5222 are really dangerous in that case? If latch up can occur when the prescribed power-up sequence is not followed, can I preserve from such by connection to Vdd,Vss pins external serial resistors? 3.What is B-W resistanse and max B-W current if counters code equal zero? 4.What is Total Harmonic Distortion vs. code (i.e. resistanse value)? Answer 1. Yes you are correct. In the specification page of the datasheet, V_a,b,w can go from Vss to Vdd. 2. If there is a risk that input voltages may be present at AD5222 without the power supplies being present, you need to take some measures to limit the current that can flow in the ESD protection diodes - by placing series resistors at R, W and B. We recommend choosing resistor values to keep the current below 5mA in these protection diodes. The FAQs mention the danger of the latchup if the power sequencing is not respected. By limiting the current to low values you prevent any latchup phenomenon from taking place. 3. The B-W resistance at zero code is simply the wiper resistance (45 Ohms typ, 100 Ohms max). The current should be limited to 20mA max to avoid damaging the device. 4. The THD should remain essentially constant with code. The point is that the only source for non-linearity is the variation of Ron of the analog swtich connecting the W terminal to the resistor string (see figure 16 Incremental Wiper Contact Resistance vs. VDD/VSS). There is only ever one switch connecting the resistor string to the W terminal so the source of non-linearity is always the same independent of code.

Difference between Volatile and Non-VOlatile Digipots

Question Is there a difference between volatile and non-volatile Digipots? Answer ADI’s wide portfolio supports four different options of integrated memory, allowing the user the flexibility to select the ideal digiPOT for the endapplication. Internal memory allows the user to set the wiper’s power-on reset (POR) position to a user programmed value. The wiper position can bereprogrammed multiple times but always returns to the programmed position on power-up. This function is ideal for calibration or for applicationsthat require a fast power-on time.• Volatile memory only: digiPOT typically powers up to midscale.• One-time programmable (OTP): allows user to program the wiper power-up position once—ideal for factory calibration.• Multitime programmable (MTP): ADI has product offerings that support 2×, 20×, or 50× programmable wiper memory.• EEPROM: ADI’s integrated EEPROM offers endurance up to 1M programming cycles and data retention of 50 years at 125°C.