AD822ARMZ datasheet(20/24 Pages) AD

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AD822

Rev. I | Page 20 of 24

SINGLE-SUPPLY PROGRAMMABLE GAIN

INSTRUMENTATION AMPLIFIER

The AD822 can be configured as a single-supply instrumenta-

tion amplifier that is able to operate from single supplies down

to 3 V or dual supplies up to ±15 V. Using only one AD822 rather

than three separate op amps, this circuit is cost and power efficient.

The 2 pA bias currents of the AD822 FET inputs minimize

offset errors caused by high unbalanced source impedances.

An array of precision thin film resistors sets the in-amp gain to

be either 10 or 100. These resistors are laser trimmed to ratio

match to 0.01% and have a maximum differential TC of 5 ppm/°C.

Table 6. In-Amp Performance

Parameters

VS = 3 V, 0 V

VS = ±5 V

CMRR

74 dB

80 dB

Common-Mode Voltage Range

−0.2 V to +2 V

−5.2 V to +4 V

3 dB BW

G = 10

180 kHz

G = 100

18 kHz

tSETTLING

2 V Step

2 μs

5 V Step

5 μs

Noise @ f = 1 kHz

G = 10

270 nV/√Hz

G = 100

2.2 μV/√Hz

ISUPPLY (Total)

1.10 mA

1.15 mA

100

....

.... .... . ..

... .... . ... . ... . ...

....

.... .... . . .. .... .... .... .... . ...

5µs

Figure 48. Pulse Response of In-Amp to a 500 mV p-p Input Signal;

VS = 5 V, 0 V; Gain = 0

G = 100

G = 10

OHMTEK

PART # 1043

Ω

90k

Ω

90k

Ω

VREF

V+

0.1µF

1/2

AD822

1/2

AD822

VOUT

VIN1

VIN2

Ω

(G = 10) VOUT = (VIN1 – VIN2)+VREF

R4 + R5

()

(G = 100) VOUT = (VIN1 – VIN2)+VREF

R5 + R6

()

Figure 49. A Single-Supply Programmable Instrumentation Amplifier

LOW DROPOUT BIPOLAR BRIDGE DRIVER

The AD822 can be used for driving a 350 Ω Wheatstone bridge.

Figure 50 shows one-half of the AD822 being used to buffer the

AD589, a 1.235 V low power reference. The output of 4.5 V can

be used to drive an analog-to-digital converter (ADC) front end.

The other half of the AD822 is configured as a unity-gain inverter

and generates the other bridge input of −4.5 V. Resistor R1 and

Resistor R2 provide a constant current for bridge excitation. The

AD620 low power instrumentation amplifier is used to condition

the differential output voltage of the bridge. The gain of the AD620

is programmed using an external resistor RG and determined by







+1.235V

49.9k

Ω

25.4k

Ω 1%

10k

Ω 1%

350

Ω

350

Ω

350

Ω

350

Ω

AD589

10k

Ω 1%

10k

Ω 1%

Ω

–4.5V

GND

+5V

–5V

1/2

AD822

–

1/2

AD822

V+

+VS

–VS

VREF

V+

V–

AD620

–

0.1

μF

0.1

μF

TO A/D CONVERTER

REFERENCE INPUT

Figure 50. Low Dropout Bipolar Bridge Driver

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