INA270

INA271

SBOS381 − FEBRUARY 2007

www.ti.com

10

0.48

0.48

0.40

0.36

0.32

0.28

0.24

0.20

0.16

0.12

0.08

0.04

0

0

2

4

6

8

10

12

14

16

18

20

22

V

24

INA271 V

(1)

V

CM2

V

CM1

V

CM3

V

CM4

V

from part to part of the V

maximum V

V

0

≤ V

NOTE: (1) INA271 V

Ideal

(INA271, Gain = 20)

SHUTDOWN

The INA270 and INA271 do not provide a shutdown pin;

however, because they consume a quiescent current less

than 1mA, they can be powered by either the output of logic

gates or by transistor switches to supply power. Driving the

gate low shuts down the INA270/INA271. Use a

totem-pole output buffer or gate that can provide sufficient

drive along with 0.1

µF bypass capacitor, preferably

ceramic with good high-frequency characteristics. This

gate should have a supply voltage of 3V or greater

because the INA270 and INA271 require a minimum

supply greater than 2.7V. In addition to eliminating

quiescent current, this gate also turns off the 10

µA bias

current present at each of the inputs. Note that the IN+ and

IN− inputs are able to withstand full common-mode voltage

under all powered and under-powered conditions. An

example shutdown circuit is shown in Figure 5.

RFI/EMI

Attention

to

good

layout

practices

is

always

recommended. Keep traces short and, when possible, use

a printed circuit board (PCB) ground plane with

surface-mount components placed as close to the device

pins as possible. Small ceramic capacitors placed directly

across amplifier inputs can reduce RFI/EMI sensitivity.

PCB layout should locate the amplifier as far away as

possible from RFI sources. Sources can include other

components in the same system as the amplifier itself,

such

as

inductors

(particularly

switched

inductors

handling a lot of current and at high frequencies). RFI can

generally be identified as a variation in offset voltage or dc

signal levels with changes in the interfering RF signal. If

the amplifier cannot be located away from sources of

radiation, shielding may be needed. Twisting wire input

leads makes them more resistant to RF fields. The

difference in input pin location of the INA270 and INA271

versus the INA193−INA198 may provide different EMI

performance.

0.1

µF

V+ > 3V

Load

−16V to +80V

S upply

N egative

an d

P ositive

Comm on−Mod e

Voltag e

I

L

A1

A2

S ingle−P ole F ilter

Capa citor

5k

Ω

5k

Ω

96kΩ

R

L

PR E OU T

BUF IN

GN D

OUT

IN

−

IN+

V +

IN A27 0, IN A271

74HC04

Figure 5. INA270−INA271 Example Shutdown Circuit