INA2128 datasheet(8/17 Pages) TI1

8 / 17 page

INA2128

SBOS035A

www.ti.com

APPLICATION INFORMATION

Figure 1 shows the basic connections required for operation

of the INA2128. Applications with noisy or high impedance

power supplies may require decoupling capacitors close to

the device pins as shown.

The output is referred to the output reference (Ref) terminals

(RefA and RefB) which are normally grounded. These must

be low-impedance connections to assure good common-

mode rejection. A resistance of 8

Ω in series with a Ref pin

will cause a typical device to degrade to approximately

80dB CMR (G = 1).

The INA2128 has separate output sense feedback connec-

tions, SenseA and SenseB. These must be connected to their

respective output terminals for proper operation. The output

sense connection can be used to sense the output voltage

directly at the load for best accuracy.

SETTING THE GAIN

Gain of the INA2128 is set by connecting a single external

resistor, RG, connected as shown:

Commonly-used gains and resistor values are shown in

Figure 1.

The 50k

Ω term in Equation 1 comes from the sum of the two

internal feedback resistors, A1 and A2. These on-chip metal

film resistors are laser-trimmed to accurate absolute values.

The accuracy and temperature coefficient of these resistors

are included in the gain accuracy and drift specifications of

the INA2128.

The stability and temperature drift of the external gain

setting resistor, RG, also affects gain. RG’s contribution to

gain accuracy and drift can be directly inferred from the gain

equation (1). Low resistor values required for high gain can

make wiring resistance important. Sockets add to the wiring

resistance which will contribute additional gain error in

gains of approximately 100 or greater.

DYNAMIC PERFORMANCE

The typical performance curve “Gain vs Frequency” shows

that despite its low quiescent current, the INA2128 achieves

wide bandwidth, even at high gain. This is due to its current-

feedback topology. Settling time also remains excellent at

high gain—see “Settling Time vs Gain.”

NOISE PERFORMANCE

The INA2128 provides very low noise in most applications.

Low frequency noise is approximately 0.2

µV

PP measured

from 0.1 to 10Hz (G

≥ 100). This provides dramatically

improved noise when compared to state-of-the-art chopper-

stabilized amplifiers.

= 1 +

50k

Ω

(1)

FIGURE 1. Basic Connections.

DESIRED

NEAREST 1% RG

GAIN

(

Ω)(Ω)

1NC

50.00k

49.9k

12.50k

12.4k

5.556k

5.62k

2.632k

2.61k

1.02k

100

505.1

511

200

251.3

249

500

100.2

100

1000

50.05

49.9

2000

25.01

24.9

5000

10.00

10000

5.001

4.99

NC: No Connection.

(11)

Sense

(10)

(12)

(13)

(14)

(16)

(15)

40k

Ω

40k

Ω

40k

Ω

40k

Ω

Pin numbers for

Channel B shown

in parentheses.

V+

V–

INA2128

G = 1 +

50k

Ω

–

Over-Voltage

Protection

25k

Ω

25k

Ω

Over-Voltage

Protection

Load

O = G • (VIN – VIN)

–

0.1

µF

0.1

µF

NOTE: If channel is unused,

connect inputs to ground, sense

to V

O, and leave Ref open-circuit.

–

Also drawn in simplified form:

INA2128

Ref

–

Ref

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