REV. D

–14–

AD8610/AD8620

supplies of

±5 V. Figures 24 and 25 compare the load current

versus output voltage of AD8610/AD8620 and OPA627.

LOAD CURRENT – A

10

0.1

0.00001

1

1

0.0001

0.001

0.01

0.1

Figure 24. AD8610 Dropout from

±13 V vs. Load Current

LOAD CURRENT – A

10

0.1

0.00001

1

1

0.0001

0.001

0.01

0.1

Figure 25. OPA627 Dropout from

±15 V vs. Load Current

Although operating conditions imposed on the AD8610 (

±13 V)

are less favorable than the OPA627 (

±15 V), it can be seen that the

AD8610 has much better drive capability (lower headroom to the

supply) for a given load current.

Operating with Supplies Greater than

±13 V

The AD8610 maximum operating voltage is specified at

±13 V.

When

±13 V is not readily available, an inexpensive LDO can

provide

±12 V from a nominal ±15 V supply.

Input Offset Voltage Adjustment

Offset of AD8610 is very small and normally does not require

additional offset adjustment. However, the offset adjust pins can

be used as shown in Figure 26 to further reduce the dc offset. By

using resistors in the range of 50 k

Ω, offset trim range is ±3.3 mV.

R1

2

3

7

5

4

6

1

AD8610

Figure 26. Offset Voltage Nulling Circuit

Programmable Gain Amplifier (PGA)

The combination of low noise, low input bias current, low input

offset voltage, and low temperature drift make the AD8610 a

perfect solution for programmable gain amplifiers. PGAs are often

used immediately after sensors to increase the dynamic range of

the measurement circuit. Historically, the large ON resistance of

created a large dc offset in PGAs. Recent and improved monolithic

switches and amplifiers completely remove these problems. A PGA

discrete circuit is shown in Figure 27. In Figure 27, when the 10 pA

bias current of the AD8610 is dropped across the (<5

Ω) R

the switch, it results in a negligible offset error.

When high precision resistors are used, as in the circuit of Figure 27,

the error introduced by the PGA is within the 1/2 LSB requirement

for a 16-bit system.

Y0

Y1

Y2

Y3

G

A

B

5

IN1

S1

D1

10k

10k

1k

–5V

+5V

IN2

S2

D2

IN3

S3

D3

IN4

S4

D4

ADG452

3

2

14

15

11

10

6

7

13

12

1

16

9

8

74HC139

4

GND

5

1k

100

11

5pF

100

G = 1

G = 10

G = 100

G = 1000

+5V

+5V

AD8610

U10

A0

A1

–5V

Figure 27. High Precision PGA

∆Ω

∆

∆

VI

R

Total Offset

Offset

V

Total Offset

Offset Trimmed

V

Total Offset

OS

B

ON

OS

OS

=×

=

×

=

=+

=+

=+

≅

25

10

510

5

pA

pV

()

(_

)

VpV

V

AD8610

AD8610

µµ

∆

Ω

VI

R

OS

B

ON

(C)

(

C)

(C)

pA

.

nV

@@

@

85

85

85

250

15

3 75

°=

°

×

°=

×=

3. Temperature coefficient of switch and AD8610/AD8620

∆∆

∆∆

∆∆

∆∆

VT total

V

T

V

T I

R

VT total

OS

OS

OS

B

ON

OS

/(

)

/

(

)

/

(

)

/(

)

.

V/ C

.

nV/ C

.V/ C

=+

×

=° +

° ≅°

AD8610

05

006

0 5

µµ