SOT23, Rail-to-Rail, Fixed-Gain

GainAmps/Open-Loop Op Amps

12

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cause output phase reversal. A back-to-back SCR

structure at the input pins allows either input to safely

internal op-amp inputs are diode clamped to either

supply rail for the protection of sensitive input stage cir-

cuitry. Current through the clamp diodes is limited by a

5k

inverting input. An IN+ or IN- fault voltage as high as

±17V will cause less than 3.5mA of current to flow

through the input pin, protecting both the GainAmp and

the signal source from damage.

Applications Information

GainAmp fixed-gain amplifiers offer a precision, fixed

gain amplifier in a small package that can be used in a

variety of circuit board designs. GainAmp fixed-gain

amplifiers can be used in many op amp circuits that use

resistive negative feedback to set gain, and that do not

require other connections to the op-amp inverting input.

Both inverting and noninverting op-amp configurations

can be implemented easily using a GainAmp.

GainAmp Input Voltage Range

The MAX4174/MAX4175/MAX4274/MAX4275 combine

both an op amp and gain-setting feedback resistors on

the same chip. Because the inverting input pin is actu-

input voltage range is different from the noninverting

input voltage range. Just as with a discrete design,

care must be taken not to saturate the inputs/output of

the core op amp, to avoid signal distortions or clipping.

The inverting inputs (IN_-) of the MAX4174/MAX4175/

MAX4274/MAX4275 must be within the supply rails or

signal distortion may result. The GainAmp’s inverting

input structure includes diodes to both supplies, such

that driving the inverting input beyond the rails may

cause signal distortions (Figure 1). For applications that

require sensing voltages beyond the rails, use the

MAX4281/MAX4282/MAX4284 open-loop op amps

(Figure 4).

OUT

IN-

IN+

5k

BIAS RESISTORS (MAX4175/MAX4275 ONLY)

NOTE: INPUT STAGE PROTECTION INCLUDES

TWO 17V SCRs AND TWO DIODES AT THE INPUT STAGE.

MAX4174

MAX4175

MAX4274

MAX4275

17V

SCR

17V

SCR

Figure 3. Input Protection