AD7669AR datasheet(15/20 Pages) AD

15 / 20 page

AD7569/AD7669

–15–

REV. B

an RD pulse for the AD7569/AD7669. This RD pulse accesses

data from the ADC and places the conversion result into a regis-

ter on the 74646. The rising edge of this pulse generates an in-

terrupt request to the processor. The conversion result is read

from the 74646 register by performing an I/O read to the

decoded address of the 74646. Writing data to the relevant

AD7569/AD7669 DAC involves an I/O write to the 74646,

which transfers the data to the data inputs of the AD7569/

AD7669. Data is latched into the selected DAC register on the

rising edge of IOW.

APPLYING THE AD7569/AD7669 DAC

An internal gain/offset network on the AD7569/AD7669 allows

several output voltage ranges. The part can produce unipolar

output ranges of 0 V to +1.25 V or 0 V to +2.5 V and bipolar

output ranges of –1.25 V to +1.25 V or –2.5 V to +2.5 V. Con-

nections for these various output ranges are outlined below.

UNIPOLAR (0 V to +1.25 V) CONFIGURATION

The first of the configurations provides an output voltage range

of 0 V to +1.25 V. This is achieved by tying the VSS and

RANGE inputs to AGNDDAC(= 0 V). Figure 21 shows the con-

figuration of the AD7569 to achieve this output range. A similar

configuration of the AD7669 gives the same output range. The

table for output voltage versus the digital code in the DAC regis-

ter is shown in Table IV.

Figure 21. AD7569 Unipolar (0 V to +1.25 V) Operation

Table IV. Unipolar (0 V to +1.25 V) Code Table

DAC Register Contents

MSB

LSB

Analog Output, VOUT

1111

+VREF

255

256









1000

0001

+VREF

129

256









1000

0000

+VREF

128

256









= +VREF/2

0111

1111

+VREF

127

256









0000

0001

+VREF

256









0000

0 V

NOTE: 1 LSB = (VREF) (2

–8) = V

REF (1/256); VREF = +1.25 V Nominal

UNIPOLAR (0 V to +2.5 V) CONFIGURATION

The 0 V to +2.5 V output voltage range is achieved by tying VSS

to AGNDDAC(= 0 V) and the RANGE input to VDD. The table

for output voltage versus digital code is as in Table IV with

2.VREF replacing VREF. Note that for this range

1 LSB

= 2.V

REF (2

−8 ) = V

REF

128

BIPOLAR (–1.25 V to +1.25 V) CONFIGURATION

The first of the bipolar configurations is achieved by tying the

RANGE input to AGNDDAC(= 0 V) and VSS to –5 V. The VSS

voltage level at which the AD7569/AD7669 changes to bipolar

operation is approximately –1 V. When the part is configured

for bipolar outputs, the input coding becomes twos comple-

ment. The table for output voltage versus the digital code in the

DAC register is shown in Table V. Note as with the unipolar

configuration, a digital input code of all 0s produces an output

of 0 V. It should be noted, however, that a low pulse on the

RESET

line for the bipolar ranges sets the output voltage to

negative full scale.

Table V. Bipolar (–1.25 V to +1.25 V) Code Table

DAC Register Contents

MSB

LSB

Analog Output, VOUT

0111

1111

+VREF

127

128









0000

0001

+VREF

128









0000

0 V

1111

–VREF

128









1000

0001

–VREF

127

128









1000

0000

–VREF

128









= –VREF

NOTE: 1 LSB = (VREF)(2

–7) = V

REF (1/128)

BIPOLAR (–2.5 V to +2.5 V) CONFIGURATION

The –2.5 V to +2.5 V bipolar output range is achieved by tying

the RANGE input to VDD and the VSS input to –5 V. Once

again, the input coding is 2s complement. The table for output

voltage versus digital code is as in Table V with 2.VREF replacing

VREF. Note that for this range

1 LSB

= 4.V

REF (2

−8 ) = V

REF

AD7669AR Datasheet(PDF) 15 Page - Analog Devices

AD7669AR Datasheet(HTML) 15 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

Datasheet Download

Link URL