Datasheet

Voltage Reference

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4.1 Power Options

J10 is arranged as five rows, each of which can be shorted. Table 4 lists the power option details for J10.

For normal operation, J10.1-2, J10.3-4, and J10.5-6 must be connected (direct or through an ammeter),

and either (or both) of J10.7-8 and J10.9-10 must be connected; otherwise, the board does not function.

Table 4. J4 Configuration: Power Options

Row Name Function

1-2 ADC AVDD AVDD supply current measurement point for the ADC. Must

be connected for operation.

3-4 ADC AVSS AVSS supply current measurement point for the ADC. Must

be connected for operation.

5-6 ADC DVDD DVDD supply current measurement point for the ADC. Must

be connected for operation.

7-8 DGND Connects DGND to board ground.

9-10 AGND Connects AGND to board ground.

5 Voltage Reference

The ADS1247 device has the option of selecting between two different references: REF0, and the internal

reference, through registers in the ADS1247 chip. The EVM provides a 2.048V reference for REF0 from

U1, filtered and buffered through U2. This 2.048V may be used to drive the REF0P input, or REF0P can

be connected to the external reference input on J8 through switch S1. REF0P should not be connected to

AVDD through switch S1 because this connection will violate the specification for the maximum reference

input. Figure 1 shows switch S1 as it appears on the EVM. The low side of the reference (REF0N) is tied

to AVSS. The different reference options under different supply conditions are outlined in Table 5.

Figure 1. Reference Select Switch S1

Table 5. REF1 Reference Voltage Options

REF0

Reference

AVDD AVSS J1 Setting S1 Position

(1)

REF0P REF0N Voltage

5V 0V 1-2 BUFF 2.048V 0V 2.048V

5V 0V 2-3 BUFF 0V 0V Invalid selection

5V 0V — Center REF+ (J8.20) 0V Up to AVDD – 1

2.5V –2.5V 1-2 BUFF –0.452V –2.5V 2.048V

2.5V –2.5V 2-3 BUFF 0V –2.5V 2.5V

2.5V –2.5V — Center REF+ (J8.20) –2.5V Up to AVDD –

AVSS – 1

(1)

Switch S1 should not be set to AVDD.

The internal reference voltage can be measured between testpoints TP3 (Int REF) and TP5 (REFCOM).

ADS1147EVM, ADS1247EVM, ADS1147EVM-PDK, ADS1247EVM-PDK SBAU148B– June 2009– Revised May 2011

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