Data Sheet

MAX74840

analog.com

Rev. 0

12 of 17

THEORY OF OPERATION

Figure 25. Simplified Circuit Diagram

Input Characteristics

The MAX74840 input stage consists of N-channel JFETs that provide low offset, low noise, and high impedance. The

minimum input common-mode voltage extends from −0.2mV below V− to 1V less than V+. Driving the input closer to

the positive rail causes loss of amplifier bandwidth and increased common-mode voltage error. Figure 26 shows the

rounding of the output due to the loss of bandwidth. The input and output are superimposed.

Figure 26. Bandwidth Limiting due to Headroom Requirements

Input Overvoltage Protection

The MAX74840 has internal protective circuitry that allows voltages as high as 0.2V beyond the supplies applied at

the input of either terminal without causing damage. Use a current-limiting resistor in series with the input of the

MAX74840 if the input voltage exceeds 0.2V beyond the supply rails of the amplifiers. If the overvoltage condition

persists for more than a few seconds, damage to the amplifiers can result.

SLEW

ENHANCEMENT

CIRCUIT

ED1

+IN x

V+

OUT x

V–

–IN x

ED2

R1

R3

R4

R8

R9

R10

R7

Q1

Q3

C1

Q2

Q4

Q5

RR

OUTPUT

STAGE

VBIAS

R5

R6

IN

OUT1

OUT2

J2

J1

R2

ED3

ED4

ED5

ED6

IMAGIC

CURRENT

CURRENT MIRROR

CH1 1.00V CH2 1.00V

M2.00µs

A CH1

3.00V

1