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In some cases (about 1%) device doesn't function properly after power-up. external sleep / calibration doesn't help. there seem to be 2 error modes - 1. getting very high readings from all channels regardless of the analog inputs. 2. strange readings, there's some correlation to analog inputs (i.e ch1 affects ch3, etc..) but readings are wrong. do u have any ideas of what the problem might be? are there any "frequently done errors" ? could something happen during FPGA config were DIOs are unstable that put the device in such state? t
Check on power up that the power (Avdd and Dvdd) is applied and fully settled before signals at REF IN ,AIN, or the logic input pins are applied in order to avoid excessive current. Here are some ap-notes relating to the AD7859: 1) You cannot change channels and initiate a conversion on the new channel in the same write cycle. If you use the CONVST bit to initiate conversions, you need 1 write cycle to set the channel select bits and a second write to the control register to initiate a conversion on the newly selected channel. (If you do change the channel select bits and set the CONVST bit with the same write to the control register, the AD7859 will convert on the previously selected channel and only then change the input channel) 2)Finally, a datasheet omission that was noticed by another customer : Q) When using the AD7859 in byte-transfer mode, i.e. W/_B pin tied low, and using DB8/HBEN as low/high byte selecting pin, what is recommended for the unused DB9-DB15 pins ? Should they be left open, tied to GND or to Vcc ? A) These output pins should be tied to DVDD via 100 kΩ resistors when the AD7854/AD7854L is being interfaced to an 8-bit data bus.