INA322EASLASH2K5.B datasheet(11/18 Pages) TI2

11 / 18 page

INA322

SBOS174B

SHUTDOWN MODE

The shutdown pin of the INA322 is nominally connected to

V+. When the pin is pulled below 0.8V on a 5V supply, the

INA322 goes into sleep mode within nanoseconds.

For actual shutdown threshold, see typical characteristic curve

“Shutdown Voltage vs Supply Voltage”. Drawing less than

µA of current, and returning from sleep mode in microsec-

onds, the shutdown feature is useful for portable applications.

Once in ‘sleep-mode’ the amplifier has high output imped-

ance, making the INA322 suitable for multiplexing.

RAIL-TO-RAIL OUTPUT

A class AB output stage with common-source transistors is

used to achieve rail-to-rail output for gains of 10 or greater.

When the amplifier is in G = 5 the output will not swing to

positive rail. For resistive loads greater than 25k

Ω, the

output voltage can swing to within a few millivolts of the

supply rail while maintaining low gain error. For heavier

loads and over temperature, see the typical characteristic

curve “Output Voltage Swing vs Output Current.” The

INA322’s low output impedance at high frequencies makes

it suitable for directly driving Capacitive Digital-to-Analog

(CDAC) input A/D converters, as shown in Figure 5.

OUTPUT BUFFERING

The INA322 is optimized for a load impedance of 10k

Ω or

greater. For higher output current the INA322 can be buff-

ered using the OPA340, as shown in Figure 4. The OPA340

can swing within 50mV of the supply rail, driving a 600

Ω

load. The OPA340 is available in the tiny MSOP-8 package.

OFFSET TRIMMING

In the event that external offset adjustment is required, the

offset can be adjusted by applying a correction voltage to the

reference terminal. Figure 6 shows an optional circuit for

trimming offset voltage. The voltage applied to the REF

terminal is added to the output signal. The gain from REF to

VOUT is +1. An op-amp buffer is used to provide low

impedance at the REF terminal to preserve good common-

mode rejection.

FIGURE 4. Output Buffering Circuit. Able to drive loads

as low as 600

Ω.

INPUT PROTECTION

Device inputs are protected by ESD diodes that will conduct

if the input voltages exceed the power supplies by more than

500mV. Momentary voltages greater than 500mV beyond

the power supply can be tolerated if the current through the

input pins is limited to 10mA. This is easily accomplished

with input resistor RLIM, as shown in Figure 7. Many input

signals are inherently current-limited to less than 10mA,

therefore, a limiting resistor is not required.

FIGURE 6. Optional Offset Trimming Voltage.

FIGURE 5. INA322 Directly Drives a Capacitive-Input,

A/D Converter.

FIGURE 7. Input Protection.

OPA340

OUT

+5V

0.1

µF

0.1

µF

INA322

OUT

V+

Shutdown

IN–

IN+

REF

ADS7818

ADS7822

12-Bits

+5V

INA322

OUT

V+

Shutdown

IN–

V–

IN+

REF

S < 100kHz

OPA336

Adjustable

Voltage

INA322

OUT

V+

Shutdown

IN–

V–

IN+

REF(1)

NOTE: (1) REF should be adjusted for the desired output level.

The value of REF affects the common-mode input range.

LIM

OVERLOAD

10mA max

INA322

OUT

V+

Shutdown

IN–

V–

IN+

REF

INA322EA/2K5.B Datasheet(PDF) 11 Page - Texas Instruments

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