AD660

REV. A

–7–

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 AD660

bipolar operation without any external components. Eliminat-

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

in the bipolar mode.

16-BIT LATCH

16-BIT DAC

CONTROL

LOGIC

+10V REF

16-BIT LATCH

20

24

22

21

5

11

12

16

15

14

13

17

18

19

23

AD660

10k

10.05k

10k

HBE

LBE

CS

SIN/

DB0

MSB/LSB/

DB1

DB7

S

OUT

SPAN/

BIP OFF

V

OUT

REF OUT

REF IN

LDAC

CLR

SER

DGND

–V

EE

+V

CC

+V

LL

1

2

3

4

OUTPUT

R2 50

AGND

UNI/BIP CLR/

Ω

Ω

R1 50

Figure 4a.

±10 V Bipolar Voltage Output

Gain offset and bipolar zero errors can be adjusted to zero us-

ing 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 required, set

the MSB ON, all other bits OFF, and readjust R2 for zero volts

output.

16-BIT LATCH

16-BIT DAC

CONTROL

LOGIC

+10V REF

16-BIT LATCH

20

24

22

21

5

11

12

16

15

14

13

17

18

19

23

AD660

10k

10.05k

10k

HBE

LBE

CS

SIN/

DB0

MSB/LSB/

DB1

DB7

S

OUT

SPAN/

BIP OFF

V

OUT

REF OUT

REF IN

LDAC

CLR

SER

DGND

–V

EE

+V

CC

+V

LL

1

2

3

4

OUTPUT

R2

100

Ω

AGND

R1

100

Ω

UNI/BIP CLR/

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

AD660. 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 AD660 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 AD660 is specified with the internal reference

driving the DAC and with the DAC alone (for use with a preci-

sion external reference ).

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

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

loads. The AD660 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.

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

allows 5 V, 8.192 V and 10.24 V ranges to be used. For ex-

ample, by using the AD586 5 V reference, outputs of 0 V to

+5 V unipolar or

±5 V bipolar can be realized. Using the

AD586 voltage reference makes it possible to operate the

AD660 with

±12 V supplies with 10% tolerances.