INA331, INA2331

SBOS215B

11

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SHUTDOWN MODE

The shutdown pin of the INA331 is nominally connected to V+.

When the pin is pulled below 0.8V on a 5V supply, the INA331

goes into sleep mode within nanoseconds. For actual shut-

down threshold, see typical characteristic “Shutdown Voltage

vs Supply Voltage”. Drawing less than 2

µA of current, and

returning from sleep mode in microseconds, the shutdown

feature is useful for portable applications. Once in ‘sleep-

mode’ the amplifier has high output impedance, making the

INA331 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.

For resistive loads greater than 10k

Ω, the output voltage can

swing to within 25 millivolts of the supply rail while maintain-

ing low gain error. For heavier loads and over temperature,

see the typical characteristic “Output Voltage Swing vs

Output Current.” The INA331’s low output impedance at high

frequencies makes it suitable for directly driving Capacitive-

Input A/D converters, as shown in Figure 4.

FIGURE 4. INA331 Directly Drives Capacitive-Input, High-

Speed A/D Converter.

OUTPUT BUFFERING

The INA331 is optimized for a load impedance of 10k

Ω or

greater. For higher output current the INA331 can be buff-

ered using the OPA340, as shown in Figure 5. 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

The INA331 is laser trimmed for low offset voltage. 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

impedance at the REF terminal to preserve good common-

mode rejection.

FIGURE 7. Sample Output Buffering Circuit.

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

are inherently current-limited to less than 10mA, therefore, a

limiting resistor is not required.

ADS7818

or

ADS7822

12-Bits

+5V

INA331

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V–

V

REF

f

OPA340

V

OUT

+5V

0.1

µF

0.1

µF

INA331

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V–

V

REF

FIGURE 5. Output Buffering Circuit. Able to drive loads as

low as 600

Ω.

FIGURE 6. Optional Offset Trimming Voltage.

OPA336

Adjustable

Voltage

INA331

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V–

V

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

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

R

LIM

R

LIM

I

OVERLOAD

10mA max

INA331

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V–

V

REF