Texas Instruments ADS131E08, User Manual, Page: 13 / 47

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ADS131E08EVM Daughter-Card Hardware Overview
3.2 Clock
The ADS131E08 has an on-chip oscillator circuit that generates a 2.048-MHz clock (nominal). This clock
can vary by ±5% over temperature. For applications that require higher accuracy, the ADS131E08 can
also accept an external clock signal. The ADS131E08 provides an option to test both internal and external
clock configurations. It also provides an option to generate the external clock from either the onboard
oscillator or from an external clock source.
The onboard oscillator is powered by the DVDD supply of the ADS131E08. Care must be taken to ensure
that the external oscillator can operate either with +1.8 V or +3.3 V, depending on the DVDD supply
configuration.
Table 4 shows the jumper settings for the three options for the ADS131E08 clocks.
Table 4. CLK Jumper Options
ADS131E08 Clock Internal Clock External OSC Clock External Clock
JP5 Not installed 2-3 1-2
JP6 Don't care 1-2 (disable) Don't care
J4 - pin 10 Don't care Don't care Clock source
A 2.048-MHz oscillator available for the +3.3-V DVDD supply is the FXO-HC735-2.048MHz. For a +1.8-V
DVDD supply, use the SiT8002AC-34-18E-2.048. The EVM is shipped with the external oscillator enabled.
3.3 Reference
The ADS131E08 has an on-chip internal reference circuit that provides reference voltages to the device.
Alternatively, the internal reference can be powered down and VREFP can be applied externally. This
configuration is achieved with the external reference generators (U2 and U3) and driver buffer. These
components (U2, U3, and U4) must be installed by the user; they are not installed at the factory. The
external reference voltage can be set to either 4.096 V or 2.5 V, depending on the analog supply voltage.
Measure TP3 to make sure the external reference is correct and stable. The settings for the external
reference is described in
Table 5 . This table assumes REF5025 is installed at U2 and REF5040 at U3. A
low-noise amplifier like the OPA350 can be installed at U4.
Table 5. External Reference Jumper Options
Internal Reference External Reference
ADS131E08 Reference VREF = 2.5 V VREF = 4.096 V VREF = 2.5 V
JP12 Don't care 2-3 1-2
JP2 Not installed Installed Installed
3.3.1 Accessing ADS131E08 Analog Supplies
Some ADS131E08 output signals are provided as test points for probing purposes using J4 (not installed
on the board).
Table 6 lists the various test signals with the corresponding test points.
Table 6. Auxiliary Connector Test Signals and Test Points
Signal J4 Pin Number Signal
Not connected 1 2 GPIO1
Not connected 3 4 GPIO2
PWDN 5 6 GPIO3
Dasiy in 7 8 GPIO4
AGND 9 10 Not connected
13 SBAU200 – June 2012 Performance Demonstration Kit for the ADS131E08
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