19-2318; Rev 0; 1/02
Precision Resistor Network for
Programmable Instrumentation Amplifiers
General Description
The MAX5426 is a precision resistor network optimized
for use with programmable instrumentation amplifiers.
The MAX5426 operates from dual ±5V to ±15V supplies
and consumes less than 40µA of supply current.
Designed to be used in the traditional three op amp
instrumentation amplifier topology, this device provides
noninverting gains of 1, 2, 4, and 8 that are accurate to
0.025% (A-grade), 0.09% (B-grade), or 0.5%
(C-grade) over the extended temperature range (-40°C
to +85°C). The MAX5426 is available in the 6.4mm
✕
5mm 14-pin TSSOP package.
o
Differential Gains: A
V
= 1, 2, 4, 8
o
Gain Accurate to 0.025%, 0.09%, or 0.5%
o
Dual Supply ±5V to ±15V Operation
o
Low 36µA Supply Current
o
Simple CMOS/TTL Logic Compatible 2-Wire
Parallel Interface
o
Space-Saving 14-Pin TSSOP Package
(6.4mm
✕
5mm)
o
OFFSET Pin Available to Offset the Output of the
Differential Amplifier
Features
MAX5426
Applications
General-Purpose Programmable Instrumentation
Amplifiers
Gain Control in RF Power Amplifiers
Precision Dual Attenuator
PART
MAX5426AEUD
MAX5426BEUD
MAX5426CEUD
Ordering Information
TEMP
RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
14 TSSOP
14 TSSOP
14 TSSOP
GAIN
0.025%
0.09%
0.5%
Pin Configuration and Functional Diagram appear at
end of data sheet.
Typical Operating Circuit
V
IN-
V
DD
FB1
OUT1
INDIF-
D0
D1
OUT
V
OUT
CM
MAX5426
OFFSET
V
SS
GND
FB2
OUT2
INDIF+
V
IN+
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
Precision Resistor Network for
Programmable Instrumentation Amplifiers
MAX5426
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND ............................................................-0.3V to +17V
V
SS
to GND.............................................................-17V to +0.3V
D0, D1 to GND ...........................................-0.3V to (V
DD
+ 0.2V)
D0, D1 to GND (V
DD
> +6V) .................................-0.3V to +6.0V
All Other Pins to GND ......................(V
SS
- 0.3V) to (V
DD
+ 0.2V)
Maximum Current Into V
DD
, V
SS
, D1, D0 .........................±50mA
Maximum Current from OUT1 to CM or OUT2 ..............±0.72mA
Maximum Current from OUT1 to INDIF- or OUT............±0.72mA
Maximum Current from OUT2 to INDIF+ or OFFSET.....±0.72mA
Continuous Power Dissipation (T
A
= +70°C)
14-Pin TSSOP (derate 9.1mW/°C above +70°C) ..........727mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
DD
= +15V, V
SS
= -15V, GND = 0, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Gain Range Accuracy (Notes 1, 2)
Capacitance at Analog Pins
C
ANALOG
Gain = 1
Differential CMRR (Notes 1, 2)
Gain = 2
Gain = 4
Gain = 8
DIGITAL INPUTS
Input High Voltage
Input Low Voltage
Input Leakage Current
EQUIVALENT RESISTANCES
Resistance Between OUT1 and
OUT2
Resistance Between OUT1 and
INDIF-
Resistance Between INDIF- and
OUT
Resistance Between OUT2 and
INDIF+
Resistance Between INDIF+ and
OFFSET
R
OUT1,
R
OUT2
R
OUT1,
R
INDIF-
R
INDIF-,
R
OUT
R
OUT2,
R
INDIF+
R
INDIF+,
R
OFFSET
Gain = 1
Resistance Between OUT1 and
FB1
R
OUT1,
R
FB1
Gain = 2
Gain = 4
Gain = 8
56
26
26
26
26
0
15
22
26
kΩ
kΩ
kΩ
kΩ
kΩ
kΩ
V
IH
V
IL
I
LKG
D1 = D0 = 0 or logic high
2.4
0.8
10
V
V
µA
SYMBOL
MAX5426A
MAX5426B
MAX5426C
CONDITIONS
MIN
TYP
0.004
0.025
0.080
5
79
85
91
97
dB
MAX
0.025
0.090
0.500
pF
%
UNITS
2
_______________________________________________________________________________________
Precision Resistor Network for
Programmable Instrumentation Amplifiers
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= +15V, V
SS
= -15V, GND = 0, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
Resistance Between FB1 and FB2
(Note 3)
SYMBOL
Gain = 2
R
FB1,
R
FB2
Gain = 4
Gain = 8
Gain = 1
Resistance Between OUT2 and
FB2
Input Impedance at FB1
Input Impedance at FB2
Input Impedance at OUT1
(Note 4)
R
OUT2,
R
FB2
Gain = 2
Gain = 4
Gain = 8
Z
FB1
Z
FB2
Gain = 1
Z
OUT1
Gain = 2
Gain = 4
Gain = 8
Gain = 1
Input Impedance at OUT2
(Note 4)
Z
OUT2
Gain = 2
Gain = 4
Gain = 8
Input Impedance at INDIF+
(Note 4)
Input Impedance at INDIF-
(Note 4)
Input Impedance at OUT (Note 4)
Input Impedance at OFFSET
(Note 4)
POWER REQUIREMENTS
Positive Power-Supply Voltage
Negative Power-Supply Voltage
Positive Supply Current
Negative Supply Current
TIMING REQUIREMENTS
Switching Time (Note 5)
t
SWITCHING
(Figure 3)
60
ns
V
DD
V
SS
I
DD
I
SS
D1 = D0 = 0
D1 = D0 = 5V
4.75
-15.75
10
36
0.01
80
10
15.75
-4.75
V
V
µA
µA
Z
INDIF+
Z
INDIF-
Z
OUT
Z
OFFSET
CONDITIONS
MIN
TYP
29
15
7
0
15
22
26
0
0
0
9.5
12
13
0
9.5
12
13
0
0
26
26
kΩ
kΩ
kΩ
kΩ
kΩ
kΩ
kΩ
kΩ
kΩ
kΩ
MAX
UNITS
MAX5426
Note 1:
Total error when configured as instrumentation amplifier. Assumes ideal op amps.
Note 2:
Each stage (input stage and output stage) is tested for accuracy separately and combined to give the total gain accuracy.
The input stage is tested as follows: OUT1 = 10V, OUT2 = 0. Output stage is tested as follows OUT1 = 10V, OUT2 = 0 and
OUT2 = 10V, OFFSET = 0.
Note 3:
Gain of 1 configuration is open circuit (infinite impedance).
Note 4:
Equivalent load at each pin is calculated according to instrumentation amplifier configuration and assumes ideal op amps.
Note 5:
See
Timing Diagram.
_______________________________________________________________________________________
3
Precision Resistor Network for
Programmable Instrumentation Amplifiers
MAX5426
Typical Operating Characteristics
(V
DD
= +15V, V
SS
= -15V, T
A
= +25°C, unless otherwise noted.)
MAX5426A GAIN ACCURACY
vs. TEMPERATURE
MAX5426 toc01
MAX5426A GAIN ACCURACY
vs. POSITIVE SUPPLY VOLTAGE
0.004
0.002
GAIN ACCURACY (%)
0
-0.002
-0.004
-0.006
-0.008
-0.010
-0.012
-0.014
GAIN 8
GAIN 4
GAIN 2
GAIN 1
MAX5426 toc02
MAX5426A GAIN ACCURACY
vs. NEGATIVE SUPPLY VOLTAGE
0.015
GAIN ACCURACY (%)
0.010
0.005
0
-0.005
-0.010
-0.015
-0.020
-15
GAIN 8
GAIN 2
GAIN 4
GAIN 1
MAX5426 toc03
0.020
0.015
GAIN ACCURACY (%)
0.010
0.005
0
-0.005
-0.010
-0.015
-0.020
-40 -25 -10
5
20
35
50
65
80
TEMPERATURE (°C)
GAIN 2
GAIN 8
GAIN 4
GAIN 1
0.006
0.020
4.75
6.75
8.75
10.75
12.75
14.75
-13
-11
-9
-7
-5
POSITIVE SUPPLY VOLTAGE (V)
NEGATIVE SUPPLY VOLTAGE (V)
MAX5426B GAIN ACCURACY
vs. TEMPERATURE
MAX5426 toc04
MAX5426B GAIN ACCURACY
vs. POSITIVE SUPPLY VOLTAGE
MAX5426 toc05
POSITIVE SUPPLY CURRENT
vs. TEMPERATURE
MAX5426 toc06
0.005
0
GAIN 1
GAIN ACCURACY (%)
-0.005
-0.010
-0.015
-0.020
-0.025
-0.030
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
GAIN 8
GAIN 4
GAIN 2
0.005
0
GAIN 1
GAIN ACCURACY (%)
-0.005
-0.010
-0.015
-0.020
-0.025
-0.030
4.75
6.75
8.75
10.75
12.75
GAIN 8
GAIN 4
GAIN 2
15
POSITIVE SUPPLY CURRENT (µA)
12
9
6
3
D1 = D0 = 0
14.75
0
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
POSITIVE SUPPLY VOLTAGE (V)
NEGATIVE SUPPLY CURRENT
vs. TEMPERATURE
MAX5426 toc07
POSITIVE SUPPLY CURRENT
vs. POSITIVE SUPPLY VOLTAGE
MAX5426 toc08
NEGATIVE SUPPLY CURRENT
vs. NEGATIVE SUPPLY VOLTAGE
MAX5426 toc09
35
POSITIVE SUPPLY CURRENT (µA)
30
25
20
15
10
D1 = D0 = 5V
5
0
NEGATIVE SUPPLY CURRENT (µA)
-0.2
-0.4
-0.6
-0.8
-1.0
D1 = D0 = 0
-1.2
0
NEGATIVE SUPPLY CURRENT (µA)
-2
-4
-6
-8
D1 = D0 = 0
-10
-40 -25 -10
5
20
35
50
65
80
TEMPERATURE (°C)
5
7
9
11
13
15
-15
-13
-11
-9
-7
-5
POSITIVE SUPPLY VOLTAGE (V)
NEGATIVE SUPPLY VOLTAGE (V)
4
_______________________________________________________________________________________
Precision Resistor Network for
Programmable Instrumentation Amplifiers
Pin Description
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13, 14
NAME
V
DD
GND
V
SS
FB2
OUT2
OFFSET
INDIF-
INDIF+
OUT
OUT1
FB1
CM
D0, D1
Ground
Negative Power Supply. Bypass V
SS
to GND with a 0.1µF capacitor.
First Stage Positive Input Terminal Resistor. Connect to the inverting terminal of the second input buffer
(see Figure 1).
First Stage Positive Output Terminal Resistor. Connect to the output terminal of the second input buffer.
Second Stage Offset Terminal. Connect to a DC voltage to offset the output of the differential amplifier.
Second Stage Negative Input Terminal Resistor. Connect to the inverting input terminal of the
differential op amp.
Second Stage Positive Input Terminal Resistor. Connect to the noninverting input terminal of the
differential op amp.
Second Stage Output Terminal, Final Output Terminal
First Stage Negative Output Terminal of Resistor. Connect to the output terminal of the first input buffer.
First Stage Negative Input Terminal of Resistor. Connect to the inverting input terminal of the first input
buffer.
Common-Mode Voltage. CM is the input common-mode voltage of the instrumentation amplifier.
Typically varies ±1% of input common-mode voltage.
Digital Inputs. See Table 1.
FUNCTION
Positive Power Supply. Bypass V
DD
to GND with a 0.1µF capacitor.
MAX5426
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).
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.
Table 1. Logic-Control Truth Table
DIGITAL INPUTS
D1
0
0
1
1
D0
0
1
0
1
GAIN
1
2
4
8
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.
_______________________________________________________________________________________
5
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