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AD669BR

Monolithic 16-Bit DACPORT

Analog Devices

AD669BR Datasheet PDF : 12 Pages

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AD669

If it is desired to adjust the gain and offset errors to zero, this

can be accomplished using the circuit shown in Figure 3b. The

adjustment procedure is as follows:

STEP1 . . . ZERO ADJUST

Turn all bits OFF and adjust zero trimmer, R4, until the output

reads 0.000000 volts (1 LSB = 153 µV).

STEP 2 . . . GAIN ADJUST

Turn all bits ON and adjust gain trimmer, R1, until the output

is 9.999847 volts. (Full scale is adjusted to 1 LSB less than the

nominal full scale of 10.000000 volts).

(MSB)

DB15

(LSB)

DB0

CS 6

L1 5

LDAC 23

16-BIT LATCH

100⍀

10k⍀

16-BIT DAC

10V REF

AD669

10k⍀

10.05k⍀

16k⍀

50⍀

+15V

10k⍀

–15V

AMP

OUTPUT

GND

–VEE +VCC

+VLL

Figure 3b. 0 V to +10 V Unipolar Voltage Output with

Gain and Offset Adjustment

BIPOLAR CONFIGURATION

The circuit shown in Figure 4a will provide a bipolar output

voltage from –10.000000 V to +9.999694 V with positive full

scale occurring with all bits ON. As in the unipolar mode, resis-

tors R1 and R2 may be eliminated altogether to provide AD669

bipolar operation without any external components. Eliminating

these resistors will increase the gain error by 0.50% of FSR in

the bipolar mode.

(MSB)

DB15

50⍀

(LSB)

DB0

CS 6

L1 5

LDAC 23

16-BIT LATCH

10k⍀

10.05k⍀

10k⍀

50⍀

16-BIT DAC

AMP

OUTPUT

10V REF

AD669

GND

–VEE +VCC +VLL

Figure 4a. ±10 V Bipolar Voltage Output

Gain offset and bipolar zero errors can be adjusted to zero using

the circuit shown in Figure 4b as follows:

STEP I . . . OFFSET ADJUST

Turn OFF all bits. Adjust trimmer R2 to give –10.000000 volts

output.

STEP II . . . GAIN ADJUST

Turn all bits ON and adjust R1 to give a reading of +9.999694

volts.

STEP III . . . BIPOLAR ZERO ADJUST

(Optional) In applications where an accurate zero output is re-

quired, set the MSB ON, all other bits OFF, and readjust R2

for zero volts output.

(MSB)

DB15

100⍀

(LSB)

DB0

CS 6

L1 5

16-BIT LATCH

LDAC 23

16-BIT LATCH

10k⍀

16-BIT DAC

100⍀

10V REF

AD669

10k⍀

10.05k⍀

AMP

OUTPUT

GND

–VEE +VCC +VLL

Figure 4b. ±10 V Bipolar Voltage Output with Gain and

Offset Adjustment

It should be noted that using external resistors will introduce a

small temperature drift component beyond that inherent in the

AD669. The internal resistors are trimmed to ratio-match and

temperature-track other resistors on chip, even though their ab-

solute tolerances are ± 20% and absolute temperature coeffi-

cients are approximately –50 ppm/°C. In the case that external

resistors are used, the temperature coefficient mismatch be-

tween internal and external resistors, multiplied by the sensitiv-

ity of the circuit to variations in the external resistor value, will

be the resultant additional temperature drift.

INTERNAL/EXTERNAL REFERENCE USE

The AD669 has an internal low noise buried Zener diode refer-

ence which is trimmed for absolute accuracy and temperature

coefficient. This reference is buffered and optimized for use in a

high speed DAC and will give long-term stability equal or supe-

rior to the best discrete Zener diode references. The perfor-

mance of the AD669 is specified with the internal reference

driving the DAC since all trimming and testing (especially for

gain and bipolar offset) is done in this configuration.

The internal reference has sufficient buffering to drive external

circuitry in addition to the reference currents required for the

DAC (typically 1 mA to REF IN and 1 mA to BIPOLAR OFF-

SET). A minimum of 2 mA is available for driving external

loads. The AD669 reference output should be buffered with an

external op amp if it is required to supply more than 4 mA total

current. The reference is tested and guaranteed to ± 0.2% max

error. The temperature coefficient is comparable to that of the

gain TC for a particular grade.

If an external reference is used (10.000 V, for example), addi-

tional trim range should be provided, since the internal refer-

ence has a tolerance of ± 20 mV, and the AD669 gain and

bipolar offset are both trimmed with the internal reference. The

optional gain and offset trim resistors in Figures 5 and 6 provide

enough adjustment range to null these errors.

It is also possible to use external references other than 10 volts

with slightly degraded linearity specifications. The recom-

mended range of reference voltages is +5 V to +10.24 V, which

–6–

REV. A

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