We're implementing the AD5292 Digital Potentiometers in a daisy-chain configuration on our board and had to drop the SPI baudrate to 4MHz to make it marginally usable and 2MHz for reliable operation. The data is read fine for the first stage, but the SDO data pin (oscilloscope pics below) is the bottleneck for data in our system. So we have two questions:
1) It specifies on the datasheet that the maximum value is 50MHz but what is the actual value we should be expecting? (For reference)
2) We have a 2.2kohm pullup resistor as specified in the daisy-chain sample application but what is the lowest resistance we can use? In other words, what's the current tolerance of the SDO pin?
8MHz - Not usable
4MHz - Marginally usable
2MHz - Usable