MAX5426CEUD+T Datasheet MAX5426AEUD+T, MAX5426BEUD+T, MAX5426CEUD+T | P4-P6

MAX5426

Precision Resistor Network for

Programmable Instrumentation Amplifiers

4 _______________________________________________________________________________________

Typical Operating Characteristics

= +15V, V

= -15V, T

= +25°C, unless otherwise noted.)

MAX5426A GAIN ACCURACY

vs. TEMPERATURE

MAX5426 toc01

TEMPERATURE (°C)

GAIN ACCURACY (%)

8065-25 -10 5 3520 50

-0.015

-0.010

-0.005

0.005

0.010

0.015

0.020

-0.020

-40

GAIN 4

GAIN 1

GAIN 2

GAIN 8

MAX5426A GAIN ACCURACY

vs. POSITIVE SUPPLY VOLTAGE

MAX5426 toc02

POSITIVE SUPPLY VOLTAGE (V)

GAIN ACCURACY (%)

14.7512.7510.758.756.75

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.002

0.004

0.006

-0.014

4.75

GAIN 1

GAIN 4

GAIN 2

GAIN 8

MAX5426A GAIN ACCURACY

vs. NEGATIVE SUPPLY VOLTAGE

MAX5426 toc03

NEGATIVE SUPPLY VOLTAGE (V)

GAIN ACCURACY (%)

-5-7-13 -11 -9

-0.015

-0.010

-0.005

0.005

0.010

0.015

0.020

-0.020

-15

GAIN 1

GAIN 4

GAIN 8

GAIN 2

MAX5426B GAIN ACCURACY

vs. TEMPERATURE

MAX5426 toc04

TEMPERATURE (°C)

GAIN ACCURACY (%)

806040200-20

-0.025

-0.020

-0.015

-0.010

-0.005

0.005

-0.030

-40

GAIN 1

GAIN 2

GAIN 4

GAIN 8

MAX5426B GAIN ACCURACY

vs. POSITIVE SUPPLY VOLTAGE

MAX5426 toc05

POSITIVE SUPPLY VOLTAGE (V)

GAIN ACCURACY (%)

14.7512.7510.758.756.75

-0.025

-0.020

-0.015

-0.010

-0.005

0.005

-0.030

4.75

GAIN 1

GAIN 4

GAIN 2

GAIN 8

-40 0-20 20 40 60 80

POSITIVE SUPPLY CURRENT

vs. TEMPERATURE

MAX5426 toc06

TEMPERATURE (°C)

POSITIVE SUPPLY CURRENT (µA)

D1 = D0 = 0

-10

-8

-6

-4

-2

-40 -10-25 5 2035506580

NEGATIVE SUPPLY CURRENT

vs. TEMPERATURE

MAX5426 toc07

TEMPERATURE (°C)

NEGATIVE SUPPLY CURRENT (µA)

D1 = D0 = 0

515

POSITIVE SUPPLY CURRENT

vs. POSITIVE SUPPLY VOLTAGE

MAX5426 toc08

POSITIVE SUPPLY VOLTAGE (V)

POSITIVE SUPPLY CURRENT (µA)

971113

D1 = D0 = 5V

-1.2

-0.8

-1.0

-0.4

-0.6

-0.2

-15 -5

NEGATIVE SUPPLY CURRENT

vs. NEGATIVE SUPPLY VOLTAGE

MAX5426 toc09

NEGATIVE SUPPLY VOLTAGE (V)

NEGATIVE SUPPLY CURRENT (µA)

-11-13 -9 -7

D1 = D0 = 0

MAX5426

Precision Resistor Network for

Programmable Instrumentation Amplifiers

_______________________________________________________________________________________ 5

Detailed Description

The MAX5426 is a precision resistor network with low

temperature drift and high accuracy that performs the

same function as a precision resistor array and CMOS

switches. Operationally, this device consists of fixed

resistors and digitally controlled variable resistors that

provide differential gains of 1, 2, 4, and 8 (see

Functional Diagram). The MAX5426 provides gains

accurate to 0.025% (MAX5426A), 0.09% (MAX5426B)

or 0.5% (MAX5426C).

The MAX5426 is ideal for programmable instrumenta-

tion amplifiers. An offset pin is available to apply a DC

offset voltage to the output of the differential amplifier.

Pin CM is the common-mode input voltage and can be

buffered and connected to the common-mode input of

the instrumentation amplifier (usually the shield of the

input cable to reduce the effects of cable capacitance

and leakage).

Digital Interface Operation

The MAX5426 features a simple two-bit parallel pro-

gramming interface. D1 and D0 program the gain set-

ting according to the Logic-Control Truth Table (see

Table 1). The digital interface is CMOS/TTL logic com-

patible.

Timing Diagram

Figure 3 shows the timing diagram of MAX5426 for two

cases. In case 1, the differential input changes are at

OUT1 and OUT2, while the voltage settling is observed

at FB1 and FB2. The settling time (t

SETTLE

) is defined

as the time for the output voltage (from the change in

the input) to reach (and stay) within 0.02% of its final

value.

In case 2, the differential inputs (OUT1 and OUT2) are

at constant voltages, while D1 and D0 are varied (for

example from 01 to 10) to make a change in the gain.

No op amps are used in these cases.

Pin Description

PIN NAME FUNCTION

Positive Power Supply. Bypass V

to GND with a 0.1µF capacitor.

2 GND Ground

Negative Power Supply. Bypass V

to GND with a 0.1µF capacitor.

4 FB2

First Stage Positive Input Terminal Resistor. Connect to the inverting terminal of the second input buffer

(see Figure 1).

5 OUT2 First Stage Positive Output Terminal Resistor. Connect to the output terminal of the second input buffer.

6 OFFSET Second Stage Offset Terminal. Connect to a DC voltage to offset the output of the differential amplifier.

7 INDIF-

Second Stage Negative Input Terminal Resistor. Connect to the inverting input terminal of the

differential op amp.

8 INDIF+

Second Stage Positive Input Terminal Resistor. Connect to the noninverting input terminal of the

differential op amp.

9 OUT Second Stage Output Terminal, Final Output Terminal

10 OUT1 First Stage Negative Output Terminal of Resistor. Connect to the output terminal of the first input buffer.

11 FB1

First Stage Negative Input Terminal of Resistor. Connect to the inverting input terminal of the first input

buffer.

12 CM

Common-Mode Voltage. CM is the input common-mode voltage of the instrumentation amplifier.

Typically varies ±1% of input common-mode voltage.

13, 14 D0, D1 Digital Inputs. See Table 1.

DIGITAL INPUTS

D1 D0 GAIN

00 1

01 2

10 4

11 8

Table 1. Logic-Control Truth Table

MAX5426

Precision Resistor Network for

Programmable Instrumentation Amplifiers

6 _______________________________________________________________________________________

Applications Information

The MAX5426 is ideal for programmable instrumentation

amplifier applications. The typical application circuit of

Figure 1 uses the MAX5426 in classical instrumentation

amplifier configurations. Two digital inputs set the gain to

1, 2, 4, or 8.

Op Amp Selection Guidelines

Selection of an op amp for instrumentation amplifier cir-

cuits depends on the accuracy requirements of the

specific application. General guidelines are to choose

an op amp with sufficient open-loop gain, low input-off-

set voltage, and a high common-mode rejection ratio.

High open-loop gain is needed to increase the gain

accuracy, while low input-offset voltage and low input-

offset current help meet gain and offset requirements.

Other parameters such as low input capacitance, low

input bias current, high input common-mode range,

and low noise often need to be considered for a wide

input voltage range stability and AC considerations.

The MAX427 is an excellent choice to use with the

MAX5426.

Stereo Audio-Taper Attenuator

Figure 2 shows the application of the MAX5426 as a dual

attenuator that can be used in stereo audio systems.

Power Supplies and Bypassing

The MAX5426 operates from dual ±5V to ±15V sup-

plies. In many applications the MAX5426 does not

require bypassing. If power-supply noise is excessive,

bypass V

and V

with 0.1µF ceramic capacitors to

GND.

Layout Concerns

For best performance, reduce parasitic board capaci-

tance by minimizing the circuit board trace from ampli-

fier outputs to inverting inputs. Also choose op amps

with low input capacitance.

FB2

INDIF-

OUT2

INDIF+

OUT

OFFSET

IN-

IN+

GND

FB1 OUT1

OUT

MAX5426

MAX427

Figure 1. Programmable Instrumentation Amplifier Using MAX5426

P1-P3 P4-P6 P7-P9

MAX5426CEUD+T

Mfr. #:

Buy MAX5426CEUD+T

Manufacturer:

Maxim Integrated

Description:

Instrumentation Amplifiers Prec Resistor Net for Prog Inst Amp

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MAX5426CEUD+T

MAX5426CEUD+T

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