SLAU150A December 2004 – October 2021 ADS7881 , ADS7891
The ADS78x1EVM provides an onboard 2.5-V reference circuit. The EVM also supplies a reference voltage via connecter P1 pin 20. This reference voltage can be filtered through amplifier U1. The converter itself has on-chip reference buffer, and therefore does not need to be buffered externally. The reference buffer circuit on the EVM is used to generate the offset voltage for the input amplifier, U2.
The EVM allows selection from three reference sources. Set SJP1, SJP2, and SJP4 to select either an onboard reference voltage (REF1004-2.5), ADC internal reference, or a user-supplied reference voltage via P1 pin 20. Table 1-3 lists jumper settings and Section 5 provides full schematics.
| Reference Designator |
Description | Pads | |
|---|---|---|---|
| 1–2 | 2–3 | ||
| SJP1 | Apply onboard reference directly to SJP2 pin 3 | Installed(1) | — |
| Apply buffered reference voltage to SJP2 pin 3 | — | Installed | |
| SJP2 | Apply internal reference to REFIN pin | Installed(1) | — |
| Apply external reference to REFIN pin | — | Installed | |
| SJP4 | Apply onboard reference to U1, reference buffer | Installed | — |
| Apply user-supplied reference to U1, reference buffer | — | Installed | |
| SJP5 | Apply DC offset to input signal | Installed(1) | — |
| SJP6 | Short to pin 4 of amplifier U1 to ground | Installed | — |
| Short to pin 4 of amplifier U1 to –VCC | — | Installed(1) | |
| SJP7 | Short to pin 4 of amplifier U2 to ground | Installed | — |
| Short to pin 4 of amplifier U2 to –VCC | — | Installed(1) | |