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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 40A 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 (-40C to +85C). The MAX5426 is available in the 6.4mm 5mm 14-pin TSSOP package. o Differential Gains: AV = 1, 2, 4, 8 o Gain Accurate to 0.025%, 0.09%, or 0.5% o Dual Supply 5V to 15V Operation o Low 36A 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 -40C to +85C -40C to +85C -40C to +85C PINPACKAGE 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
VIN-
VDD
FB1
OUT1
INDIF-
D0 D1
OUT
VOUT CM MAX5426
OFFSET
VSS
GND
FB2
OUT2
INDIF+
VIN+
________________________________________________________________ Maxim Integrated Products
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Precision Resistor Network for Programmable Instrumentation Amplifiers MAX5426
ABSOLUTE MAXIMUM RATINGS
VDD to GND ............................................................-0.3V to +17V VSS to GND.............................................................-17V to +0.3V D0, D1 to GND ...........................................-0.3V to (VDD + 0.2V) D0, D1 to GND (VDD > +6V) .................................-0.3V to +6.0V All Other Pins to GND ......................(VSS - 0.3V) to (VDD + 0.2V) Maximum Current Into VDD, VSS, 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 (TA = +70C) 14-Pin TSSOP (derate 9.1mW/C above +70C) ..........727mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-60C to +150C
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
(VDD = +15V, VSS = -15V, GND = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Gain Range Accuracy (Notes 1, 2) Capacitance at Analog Pins CANALOG 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 INDIFResistance Between INDIF- and OUT Resistance Between OUT2 and INDIF+ Resistance Between INDIF+ and OFFSET ROUT1, ROUT2 ROUT1, RINDIFRINDIF-, ROUT ROUT2, RINDIF+ RINDIF+, ROFFSET Gain = 1 Resistance Between OUT1 and FB1 ROUT1, RFB1 Gain = 2 Gain = 4 Gain = 8 56 26 26 26 26 0 15 22 26 k k k k k k VIH VIL ILKG D1 = D0 = 0 or logic high 2.4 0.8 10 V V A 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
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Precision Resistor Network for Programmable Instrumentation Amplifiers
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +15V, VSS = -15V, GND = 0, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Resistance Between FB1 and FB2 (Note 3) SYMBOL Gain = 2 RFB1, RFB2 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) ROUT2, RFB2 Gain = 2 Gain = 4 Gain = 8 ZFB1 ZFB2 Gain = 1 ZOUT1 Gain = 2 Gain = 4 Gain = 8 Gain = 1 Input Impedance at OUT2 (Note 4) ZOUT2 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) tSWITCHING (Figure 3) 60 ns VDD VSS IDD ISS D1 = D0 = 0 D1 = D0 = 5V 4.75 -15.75 10 36 0.01 80 10 15.75 -4.75 V V A A ZINDIF+ ZINDIFZOUT ZOFFSET 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 k k k k k k k k k k 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.
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Precision Resistor Network for Programmable Instrumentation Amplifiers MAX5426
Typical Operating Characteristics
(VDD = +15V, VSS = -15V, TA = +25C, 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 (A)
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 (A) 30 25 20 15 10 D1 = D0 = 5V 5
0 NEGATIVE SUPPLY CURRENT (A) -0.2 -0.4 -0.6 -0.8 -1.0 D1 = D0 = 0 -1.2
0 NEGATIVE SUPPLY CURRENT (A) -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)
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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 VDD GND VSS FB2 OUT2 OFFSET INDIFINDIF+ OUT OUT1 FB1 CM D0, D1 Ground Negative Power Supply. Bypass VSS to GND with a 0.1F 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 VDD to GND with a 0.1F 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 instrumentation 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 (tSETTLE) 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 programming interface. D1 and D0 program the gain setting according to the Logic-Control Truth Table (see Table 1). The digital interface is CMOS/TTL logic compatible.
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Precision Resistor Network for Programmable Instrumentation Amplifiers MAX5426
VINMAX427
VDD
FB1
OUT1
INDIF-
D0 D1
OUT
VOUT CM MAX5426 MAX427 OFFSET
VSS
GND
FB2
OUT2
INDIF+
VIN+ MAX427
Figure 1. Programmable Instrumentation Amplifier Using MAX5426
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.
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 supplies. In many applications the MAX5426 does not require bypassing. If power-supply noise is excessive, bypass VDD and VSS with 0.1F ceramic capacitors to GND.
Op Amp Selection Guidelines
Selection of an op amp for instrumentation amplifier circuits depends on the accuracy requirements of the specific application. General guidelines are to choose an op amp with sufficient open-loop gain, low input-offset 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 inputoffset 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.
Layout Concerns
For best performance, reduce parasitic board capacitance by minimizing the circuit board trace from amplifier outputs to inverting inputs. Also choose op amps with low input capacitance.
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Precision Resistor Network for Programmable Instrumentation Amplifiers MAX5426
TO RIGHT CHANNEL AMPLIFIER RIGHT CHANNEL OUT1 INDIF-
FB1 VDD
OUT
CM
D1 D0 VSS OFFSET
GND
FB2
OUT2
INDIF+ LEFT CHANNEL
TO LEFT CHANNEL AMPLIFIER
Figure 2. Stereo Audio-Taper Attenuator
OUT1 tSETTLE
OUT1
tSWITCHING
tSETTLE
FB1
FB1
FB2
FB2
OUT2
OUT2
D1, D0 CASE 1: DIFFERENTIAL INPUT IS CHANGED, WHILE D1, D0 IS FIXED. NOTE: SEE TIMING DIAGRAM SECTION
D1, D0 CASE 2: DIFFERENTIAL INPUT IS FIXED, WHILE D1, D0 IS CHANGED FROM 00 TO 01.
Figure 3. Timing Diagram _______________________________________________________________________________________ 7
Precision Resistor Network for Programmable Instrumentation Amplifiers MAX5426
Functional Diagram
VDD FB1 OUT1 INDIF-
D1 D0
OUT
CM
MAX5426
OFFSET GND
VSS
FB2
OUT2
INDIF+
Pin Configuration
TOP VIEW
VDD 1 GND VSS 2 3 14 D1 13 D0 12 CM
Chip Information
TRANSISTOR COUNT: 126 PROCESS TECHNOLOGY: BICMOS
FB2 4 OUT2 5 OFFSET 6 INDIF- 7
MAX5426
11 FB1 10 OUT1 9 8 OUT INDIF+
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Precision Resistor Network for Programmable Instrumentation Amplifiers
Package Information
TSSOP,NO PADS.EPS
MAX5426
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________ 9 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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