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AD588KQ

High Precision Voltage Reference

Analog Devices 

AD588

Table I. AD588 Connections

Range

Connect

Pin 10 Unbuffered1 Output on Pins

Buffered

Output

To Pin: –10 V –5 V 0 V +5 V +10 V Connections

Buffered Output on Pins

–10 V –5 V 0 V +5 V +10 V

+10 V

8

–

–

8

11 6

11–13 & 14–15 –

–

– 15 –

6–4 & 3–1

–

–

––

1

–5 V or +5 V 11

–

18

11

6–

8–13 & 14–15 –

6–4 & 3–1

–

15

––

–

–

–1

–10 V

6

8

11

6

––

8–13 & 14–15 –

15

––

–

11–4 & 3–1 1

–

––

–

+5 V

–5 V

–

–

–

6–

6–4 & 3–1

–

11

–

8

–

––

8–13 & 14–15 –

1“Unbuffered” outputs should not be loaded.

–

–1

–

15

––

–

accuracies of 12–16 bits. However, in applications where an

even greater level of accuracy is required, additional calibration

may be called for. Provision for trimming has been made

through the use of the GAIN ADJUST and BALANCE AD-

JUST pins (Pins 5 and 12 respectively).

The AD588 provides a precision 10 V span with a center tap

(VCT) which is used with the buffer and ground sense amplifiers

to achieve the voltage output configurations in Table I. GAIN

ADJUST and BALANCE ADJUST can be used in any of these

configurations to trim the magnitude of the span voltage and the

position of the center tap within the span. The GAIN ADJUST

should be performed first. Although the trims are not interactive

within the device, the GAIN trim will move the BALANCE trim

point as it changes the magnitude of the span.

Figure 2b shows GAIN and BALANCE trims in a +5 V and

–5 V tracking configuration. A 100 kΩ 20-turn potentiometer is

used for each trim. The potentiometer for GAIN trim is con-

nected between Pins 6 (VHIGH) and 8 (VLOW) with the wiper

connected to Pin 5 (GAIN ADJ). The potentiometer is adjusted

to produce exactly 10 V between Pins 1 and 15, the amplifier

outputs. The BALANCE potentiometer, also connected be-

tween Pins 6 and 8 with the wiper to Pin 12 (BAL ADJ), is then

adjusted to center the span from +5 V to –5 V.

Trimming in other configurations works in exactly the same

manner. When producing +10 V and +5 V, GAIN ADJ is used

to trim +10 V and BAL ADJ is used to trim +5 V. In the –10 V

and –5 V configuration, GAIN ADJ is again used to trim the

magnitude of the span, –10 V, while BAL ADJ is used to trim

the center tap, –5 V.

In single output configurations, GAIN ADJ is used to trim out-

puts utilizing the full span (+10 V or –10 V) while BAL ADJ is

used to trim outputs using half the span (+5 V or –5 V).

Input impedance on both the GAIN ADJUST and BALANCE

ADJUST pins is approximately 150 kΩ. The GAIN ADJUST

trim network effectively attenuates the 10 V across the trim

potentiometer by a factor of about 1500 to provide a trim range

of –3.5 mV to +7.5 mV with a resolution of approximately

550 µV/turn (20 turn potentiometer). The BALANCE ADJUST

trim network attenuates the trim voltage by a factor of about

1400, providing a trim range of ± 4.5 mV with resolution of

450 µV/turn.

Figure 2a. +10 V Output

Figure 2b. +5 V and –5 V Outputs

REV. B

–4–

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