AD6688 datasheet(29/138 Pages) AD

29 / 138 page

Data Sheet

AD6688

Rev. 0 | Page 29 of 138

VOLTAGE REFERENCE

A stable and accurate 0.5 V voltage reference is built into the

AD6688. This internal 0.5 V reference sets the full-scale input

range of the ADC. The full-scale input range can be adjusted via

the ADC input full-scale control register (Register 0x1910). For

more information on adjusting the input swing, see Table 46.

Figure 51 shows the block diagram of the internal 0.5 V reference

controls.

The SPI Register 0x18A6 enables the user to either use this

internal 0.5 V reference or to provide an external 0.5 V

reference. When using an external voltage reference, provide a

0.5 V reference. The full-scale adjustment is made using the SPI,

irrespective of the reference voltage. For more information on

adjusting the full-scale level of the AD6688, refer to the

Memory Map section.

The SPI writes required to use the external voltage reference, in

order, are as follows:

1. Set Register 0x18E3 to 0x00 to turn off the VCM export.

2. Set Register 0x18E6 to 0x00 to turn off the temperature

diode export.

3. Set Register 0x18A6 to 0x01 to turn on the external voltage

reference.

The use of an external reference may be necessary in some

applications to enhance the gain accuracy of the ADC or to

improve thermal drift characteristics. Figure 50 shows the

typical drift characteristics of the internal 0.5 V reference.

0.5060

0.5055

0.5050

0.5045

0.5040

0.5035

0.5030

–10

110

130

JUNCTION TEMPERATURE (°C)

Figure 50. Typical VREF Drift

The external reference must be a stable 0.5 V reference. The

ADR130 is a good option for providing the 0.5 V reference.

Figure 52 shows how the ADR130 can be used to provide the

external 0.5 V reference to the AD6688. The grayed out areas

show unused blocks within the AD6688 while using the

ADR130 to provide the external reference.

VREF

CONTROL SPI

(0x18A6)

INTERNAL

0.5V

REFERENCE

GENERATOR

ADC

CORE

INPUT FULL-SCALE

CONTROL

SPI REGISTER

(0x1910)

VFS

ADJUST

VREF

VIN+A/VIN+B

VIN–A/VIN–B

Figure 51. Internal Reference Configuration and Controls

VREF

VREF PIN AND VFS

CONTROL

INTERNAL

0.5V

REFERENCE

GENERATOR

VFS

ADJUST

ADR130

GND SET

VIN VOUT

INPUT

ADC

0.1µF

Figure 52. External Reference Using ADR130

AD6688 Folha de dados(PDF) 29 Page - Analog Devices

AD6688 Folha de dados(HTML) 29 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 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Folha de dados Download

Ligação URL