AD9231 datasheet(22/36 Pages) AD

22 / 36 page

AD9231

Rev. 0 | Page 22 of 36

VOLTAGE REFERENCE

A stable and accurate 1.0 V voltage reference is built into the

AD9231. The VREF can be configured using either the internal

1.0 V reference or an externally applied 1.0 V reference voltage.

The various reference modes are summarized in the sections

that follow. The Reference Decoupling section describes the

best practices PCB layout of the reference.

Internal Reference Connection

A comparator within the AD9231 detects the potential at the

SENSE pin and configures the reference into two possible modes,

which are summarized in Table 10. If SENSE is grounded, the

reference amplifier switch is connected to the internal resistor

divider (see Figure 46), setting VREF to 1.0 V.

VREF

SENSE

0.5V

ADC

SELECT

LOGIC

0.1µF

1.0µF

VIN–A/VIN–B

VIN+A/VIN+B

ADC

CORE

Figure 46. Internal Reference Configuration

If the internal reference of the AD9231 is used to drive multiple

converters to improve gain matching, the loading of the reference

by the other converters must be considered. Figure 47 shows

how the internal reference voltage is affected by loading.

–3.0

LOAD CURRENT (mA)

–0.5

–1.0

–1.5

–2.0

–2.5

0.2

0.4

0.6

0.8

1.0

1.4

1.6

1.8

1.2

INTERNAL VREF = 0.993V

Figure 47. VREF Accuracy vs. Load Current

Table 10. Reference Configuration Summary

Selected Mode

SENSE Voltage (V)

Resulting VREF (V)

Resulting Differential Span (V p-p)

Fixed Internal Reference

AGND to 0.2

1.0 internal

2.0

Fixed External Reference

AVDD

1.0 applied to external VREF pin

2.0

AD9231 Datasheet(PDF) 22 Page - Analog Devices

AD9231 Datasheet(HTML) 22 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Datasheet Download

Link URL