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TRANSIENT PROTECTION

OUTPUT VOLTAGE RANGE

a)Single-PoleFilter

b)Second-Order,Sallen-KeyFilter

A1

A2

Single-PoleFilter

Capacitor

+2.7Vto+18V

5kW

5kW

96kW

R

L

PREOUT

BUFIN

GND

Output

IN-

IN+

V+

Load

Supply

R

S

INA270

A1

A2

Second-Order,Sallen-KeyFilterConnection

+2.7Vto+18V

C

FILT

C

FILT

5kW

5kW

96kW

R

L

PREOUT

BUFIN

GND

Output

IN-

IN+

V+

Load

Supply

R

S

R

S

INA270

INA270

INA271

SBOS381A – FEBRUARY 2007 – REVISED APRIL 2007

Despite

the

use

of

internal

zener-type

ESD

protection, the INA270 and INA271 are not suited to

The –16V to +80V common-mode range of the

using external resistors in series with the inputs since

INA270

and

INA271

is

ideal

for

withstanding

the internal gain resistors can vary up to

±30%, but

automotive fault conditions ranging from 12V battery

are tightly matched (if gain accuracy is not important,

reversal up to +80V transients, since no additional

then resistors can be added in series with the

protective components are needed up to those

INA270 and INA271 inputs with two equal resistors

levels. In the event that the INA270 and INA271 are

on each input).

exposed to transients on the inputs in excess of their

ratings,

external

transient

absorption

with

semiconductor

transient

absorbers

(zeners

or

Transzorbs) will be necessary.

The output of the INA270 and INA271 is accurate

within the output voltage swing range set by the

Use of MOVs or VDRs is not recommended except

power-supply pin, V+.

when they are used in addition to a semiconductor

transient absorber. Select the transient absorber

The INA270 and INA271 readily enable the inclusion

such that it will never allow the INA270 and INA271

of filtering between the preamp output and buffer

to be exposed to transients greater than 80V (that is,

input. Single-pole filtering can be accomplished with

allow for transient absorber tolerance, as well as

a single capacitor because of the 96k

Ω output

additional voltage because of transient absorber

impedance at PRE OUT on pin 3, as shown in

dynamic impedance).

Figure 16a.

The INA270 and INA271 readily lend themselves to

second-order Sallen-Key configurations, as shown in

Figure 16b. When designing these configurations

consider that the PRE OUT 96k

Ω output impedance

exhibits an initial variation of

±30% with the addition

of a –2200ppm/

°C temperature coefficient.

Figure 16. The INA270–INA271 can be easily connected for first- or second-order filtering. Remember to

use the appropriate buffer gain (INA270 = 1.4, INA271 = 2) when designing Sallen-Key configurations.

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