Hi all,
I am using ADC AD7643 with an external reference of 2.5V and testing its 18-bit parallel mode. I calculate the voltage from the ADC digital output bits and compare it with the actual differential input between pin 43 and 39. There is significance difference between the two voltage. Yet the difference diminish at higher input voltage. What could be the problem?
| Differential Input (mV) | Voltage calculated from ADC output (mV) |
| 493 | 42.5 |
| 526 | 91 |
| 571 | 208 |
| 624 | 315 |
| 672 | 402 |
| 738 | 519 |
| 900 | 782 |
| 997 | 918 |
| 1114 | 1073 |
| 1215 | 1197 |
| 1325 | 1314 |
| 1406 | 1392 |
| 1509 | 1507 |
| 1593 | 1601 |
| 1708 | 1702 |
| 1807 | 1867 |
| 1898 | 1912 |
| 2007 | 1995 |
