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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

SBAU200–June 2012 Performance Demonstration Kit for the ADS131E08

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