EL8170, EL8173

FN7490 Rev 8.00

Page 10 of 14

August 11, 2015

Description of Operation and

Applications Information

Product Description

The EL8170 and EL8173 are micropower instrumentation

amplifiers (in-amps) which deliver rail-to-rail input amplification and

EL8170 and EL8173 also deliver excellent DC and AC specifications

while consuming only 65µA typical supply current. The EL8170 and

EL8173 provides an independent pairs of feedback terminals to set

the gain and to adjust output level, these in-amps achieve high

common-mode rejection ratio regardless of the tolerance of the gain

setting resistors. The EL8173 is internally compensated for a

minimum closed loop gain of 10 or greater, well suited for moderate

to high gains. For higher gains, the EL8170 is internally

compensated for a minimum gain of 100.

Input Protection

All input and feedback terminals of the EL8170 and EL8173 have

internal ESD protection diodes to both positive and negative

supply rails, limiting the input voltage to within one diode drop

beyond the supply rails. The inverting inputs and FB- have ESD

diodes to the V-rail, and the non-inverting inputs and FB+

terminals have ESD diodes to the V+ rail. The EL8170 has

additional back-to-back diodes across the input terminals and

also across the feedback terminals. If overdriving the inputs is

necessary, the external input current must never exceed 5mA. On

the other hand, the EL8173 has no clamps to limit the

differential voltage on the input terminals allowing higher

differential input voltages at lower gain applications. It is

recommended however, that the input terminals of the EL8173

are not overdriven beyond 1V to avoid offset drift. An external

series resistor may be used as an external protection to limit

excessive external voltage and current from damaging the

inputs.

Input Stage and Input Voltage Range

The input terminals (IN+ and IN-) of the EL8170 and EL8173 are

single differential pair bipolar PNP devices aided by an Input

Range Enhancement Circuit to increase the headroom of

operation of the common-mode input voltage. The feedback

terminals (FB+ and FB-) also have a similar topology. As a result,

the input common-mode voltage range of both the EL8170 and

EL8173 is rail-to-rail. These in-amps are able to handle the input

voltages that are at or slightly beyond the supply and ground

voltage supply systems. There is no need to move the

common-mode input of the in-amps to achieve symmetrical input

voltage.

Pin Descriptions

EL8170

EL8173

PIN NAME

EQUIVALENT CIRCUIT

PIN FUNCTION

1

1

DNC

Do Not Connect; Internal connection - Must be left floating.

2

2

IN-

Circuit 1A, Circuit 1B

High impedance input terminals. The EL8170 input circuit is shown in Circuit 1A,

and the EL8173 input circuit is shown in Circuit 1B.

The EL8173: to avoid offset drift, it is recommended that the terminals are not

overdriven beyond 1V and the input current must never exceed 5mA.

3

3

IN+

Circuit 1A, Circuit 1B

4

4

V-

Circuit 3

Negative supply terminal.

5

5

FB-

Circuit 1A, Circuit 1B

High impedance feedback terminals. The EL8170 input circuit is shown in

Circuit 1A, and the EL8173 input circuit is shown in Circuit 1B.

The EL8173: to avoid offset drift, it is recommended that the terminals are not

overdriven beyond 1V and the input current must never exceed 5mA.

8

8

FB+

Circuit 1A, Circuit 1B

7

7

V+

Circuit 3

Positive supply terminal.

6

6

VOUT

Circuit 2

Output voltage.

IN-

V+

V-

V+

V-

OUT

CIRCUIT 2

CIRCUIT 1A

V+

V-

CAPACITIVELY

COUPLED

ESD CLAMP

CIRCUIT 3

V+

V-

CIRCUIT 1B

FB-

IN-

FB-

IN+

FB+

IN+

FB+