Datasheet

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4.2 Reference
5 Digital Interface
Digital Interface
The ADS7881/ADS7891EVM provides an onboard 2.5V reference circuit. The EVM also has the provision
for users to supply 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, therefore it is not necessary to
buffer externally. The reference buffer circuit on the EVM is used to generate the offset voltage for the
input amplifier, U2.
The EVM allows users to select from three reference sources. Set SJP1, SJP2, and SJP4 to select
on-board reference voltage (REF1004-2.5), ADC internal reference or a user supplied reference voltage
via P1 pin 20. See Table 2 for jumper settings. See Appendix B for full schematic.
Table 2. Solder Short Jumper Setting
Reference Pads
Description
Designator
1–2 2–3
SJP1 Apply on-board 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 on-board reference to U1, reference buffer Installed
Apply user supplied reference to U1, reference buffer Installed
SJP5 Apply DC offset to input signal Installed
(1)
N/A
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)
(1)
Factory set condition
The ADS7881/ADS7891EVM is designed for easy interfacing to multiple platforms. Samtec part numbers
SSW-110-22-F-D-VS-K , TSM-110-01-T-DV-P, SSW-116-22-S-D-VS , and TSM-116-01-T-D-V-P provide a
convenient dual row header/socket combination at P1, P2, P3, and J3. Please consult Samtec at
www.samtec.com or 1-800-SAMTEC-9 for a variety of mating connector options.
Connectors P1, P2 and P3 allows the user to plug the EVM into the 5-6k interface card to interface directly
with TMS320C5000 and TMS320C6000 series of DSP. See Table 3 for connector pin out.
Table 3. Pinout for Parallel Control Connector P2
Connector.Pin
(1)
Signal Description
P2.1 DC_CS Daughter card Board Select pin
P2.3
P2.5
P2.7 A0 Address line from processor
P2.9 A1 Address line from processor
P2.11 A2 Address line from processor
P2.13
P2.15
P2.17
(1)
All even numbered pins of P2 are tied to DGND.
ADS7881/ADS7891EVM 4 SLAU150 – December 2004