INA2321 datasheet(12/18 Pages) TI

12 / 18 page

INA321

INA2321

SBOS168B − DECEMBER 2000 − REVISED JULY 2004

www.ti.com

OUTPUT BUFFERING

The INA321 is optimized for a load impedance of 10k

Ω or

greater. For higher output current the INA321 can be

buffered 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.

OPA340

OUT

+5V

0.1

µF

0.1

µF

INA321

OUT

V+

Shutdown

IN−

−

IN+

REF

Figure 4. Output Buffering Circuit. Able to drive

loads as low as 600

Ω.

SHUTDOWN MODE

The shutdown pin of the INA321 is nominally connected to

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

INA321 goes into sleep mode within nanoseconds. For

actual shutdown threshold, see typical performance curve

Shutdown Voltage vs Supply Voltage. Drawing less than

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 INA321 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 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 performance curve

Output Voltage Swing vs Output Current. The INA321’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.

ADS7818

ADS7822

12−Bits

+5V

INA321

OUT

V+

Shutdown

IN−

−

IN+

REF

S <100kHz

Figure 5. INA321 Directly Drives a

Capacitive-Input, A/D Converter

OFFSET TRIMMING

The INA321 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 VOUT is +1. An op-amp buffer is used to provide low

impedance at the REF terminal to preserve good

common-mode rejection.

OPA336

Adjustable

Voltage

INA321

OUT

V+

Shutdown

VIN−

−

IN+

REF(1)

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

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

Figure 6. Optional Offset Trimming Voltage

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