Digital Interface - Texas Instruments ADS8481EVM User Manual

Digital Interface

Reference
Designator
SJP1 Select onboard reference
Select user-supplied reference
SJP2 Short voltage node +DC to U6 pin 3
SJP3 Set U6 operational amplifier minus rail supply to ground
Set U6 operational amplifier minus rail supply to –VCC
SJP4 Set U7 operational amplifier minus rail supply to ground
Set U7 operational amplifier minus rail supply to –VCC
SJP6 Set REFIN pin of ADS8481 to on-chip (internal) reference voltage.
Set REFIN pin of ADS8481 to reference selected by SJP1.
SJP7 Short voltage node –DC to U6 pin 2 via R35.
SJP8 Short voltage node +DC to U7 pin 3.
SJP9 Short –IN pin of U5 to ground at C45.
(1)
Indicates factory-installed option.
3.2 Reference
The ADS8481 can operate with an external reference voltage in the range of 3 V up to 4.2 V. It generates
an on-chip 4.096-V reference voltage. The ADS8481EVM allows the user to select the external reference
voltage from three sources. The first option is to use the internally generated 4.096 V from the ADC. The
other two options are to select from the 3-V onboard reference (U1) or a user-supplied voltage applied at
pin 20 of P1. See Table 2
The reference voltage provides the scale factor for the conversion result. The input voltage is measured
against the reference voltage. It is therefore imperative that the reference voltage be clean, low noise, and
well-decoupled.
The default configuration is to use the internal on-chip reference.
4 Digital Interface
The ADS8481EVM is designed for easy interfacing to multiple platforms. The digital interface input and
output signals of the converter are on connectors P2, P3, and J6. These are 0.1-inch center plug and
socket connectors, allowing the user to plug the ADS8481EVM onto the various motherboard interface
boards from Texas Instruments, or ribbon cable onto the user development board. The following tables list
the connector pinouts.
Description
Daughtercard Chip Select
Reserved
Reserved
Address line 0
Address line 1
Address line 2
Reserved
Reserved
Convert Start
Interrupt pin
4 ADS8481EVM
Table 2. Analog Circuitry Jumper
Description
for solder jumper options for selecting from the various reference sources.
Table 3. Pinout for Parallel Control Connector P3
Signal Name Connector Pin No.
DC_CS P3.1
N/A P3.3
N/A P3.5
A0 P3.7
A1 P3.9
A2 P3.11
N/A P3.13
N/A P3.15
DC_CONVST P3.17
INTC P3.19
Installed
Not Installed
Installed
Installed
Not installed
Installed
Not installed
Installed
Not installed
Installed
Installed
Installed
Signal Name
P3.2 +
P3.4 GND
P3.6 GND
P3.8 GND
P3.10 GND
P3.12 GND
P3.14 GND
P3.16 GND
P3.18 GND
P3.20 GND
SLAU182A – June 2006 – Revised September 2006
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Jumper Position
1-2 2-3
(1)
Not Installed
Installed
(1)
N/A
Not installed
(1)
Installed
Not installed
(1)
Installed
(1)
Not installed
Installed
N/A
N/A
(1)
N/A
Description
Non-inverting input channel
Ground
Ground
Ground
Ground
Ground
Ground
Ground
Ground
Ground