AD7804 Просмотр технического описания (PDF) - Analog Devices

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производитель

AD7804

+3.3 V to +5 V Quad/Octal 10-Bit DACs

Analog Devices 

Table IX. Offset Binary Code Table for Sub DAC

Digital Input

MSB . . . LSB

11111111

11111110

10000001

10000000

01111111

00000001

00000000

Analog Output

VBIAS/16 × 127/256

VBIAS/16 × 126/256

VBIAS/16 × 1/256

0

–VBIAS/16 × 1/256

–VBIAS/16 × 127/256

–VBIAS/32

127

128

؋

VBIAS

32

AD7804/AD7805/AD7808/AD7809

+3.3V/+5V

10␮F

0.1␮F

0.1␮F

0.01␮F

0.01␮F

SERIAL

INTERFACE

DVDD

AVDD DVDD

COMP

REFIN

AD7804/

AD7808

FSIN

REFOUT

SDIN

CLKIN

VOUTA

VOUTB

CLR

LDAC

DGND

VOUTC

VOUTD

AGND

6.8k⍀

AD589

0

VBIAS

32

DAC INPUT CODE 00 01

7F 80 81

FE FF

Figure 26. Sub DAC Output Voltage vs. DAC Input Codes

(HEX) for Offset Binary Coding

Configuring the AD7804/AD7808 for Offset Binary Coding

Figure 27 shows a typical configuration for the AD7804/AD7808.

This circuit can be used for both 3.3 V or 5 V operation and

uses an external AD589 as the reference for the part and serial

interfacing with offset binary coding is used. The MX1 and

MX0 bits in the system control register have to be set to enable

selection of the AD589 as the reference. The following are the

steps required to operate the DACs in this part. Figures 4 to 7

show the contents of the registers on the AD7804/AD7808.

Figure 27. Typical Configuration for AD7804/AD7808

Using an AD589 1.23 V Reference for the AD7804/AD7808

System Control Register Serial Write:

Write 0060 Hex Mode bits select system control register

and configure system for offset binary

coding and normal operation.

Channel Control Register Serial Write:

Write 4210 Hex Mode bits select channel control register,

channel A is configured for operation with

external reference.

Main DAC Data Register Serial Write:

Write 23FF Hex This 16-bit write selects writing to channel

A and writes full scale to the Main DAC.

Sub DAC Data Register Serial Write:

Write A3FF Hex This 16-bit write selects writing to channel

A Sub DAC and writes full scale to the

Sub DAC.

Table VIII and Figure 25 show the analog outputs available for

the above configuration when writing to the Main DAC only

while Table IX and Figure 26 show the contributions from the

Sub DAC to the overall transfer function. The total output for a

single channel when using offset binary coding is the sum of that

from the Main DAC and the Sub DAC.

VOUT = VOUT' + VOUT"

= VBIAS + 1.875 × VBIAS × ((NA-512)/1024) + VBIAS/16

= × [(NB-128)/256]

= VBIAS × (1 + 1.875 × ((NA-512)/1024) + (NB-128)/

4096)

where NA ranges from 0 to +1023 and NB ranges from 0 to

+255. Figure 28 shows a pictorial view of the transfer function

for any DAC channel.

REV. A

–19–

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