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19-1896; Rev 0; 1/01
256-Tap, PoT, Low-Drift, Digital Potentiometer
General Description
The MAX5402 PoTTM digital potentiometer is a 256-tap variable resistor with 10k total resistance in a tiny 8pin MAX package. This device functions as a mechanical potentiometer, consisting of a fixed resistor string with a digitally controlled wiper contact. It operates from +2.7V to +5.5V single-supply voltages and uses an ultra-low 0.1A supply current. This device also provides glitchless switching between resistor taps, as well as a convenient power-on reset (POR) that sets the wiper to the midscale position at power-up. A low 5ppm/C ratiometric temperature coefficient makes it ideal for applications requiring low drift. The MAX5402 serves well in applications requiring digitally controlled resistors, including adjustable voltage references and programmable gain amplifiers (PGAs). A nominal end-to-end resistor temperature coefficient of 35ppm/C makes this part suitable for use as a variable resistor in applications such as low-tempco adjustable gain and other circuit configurations. This device is guaranteed over the extended industrial temperature range (-40C to +85C). o Ultra-Low 100nA Supply Current o +2.7V to +5.5V Single-Supply Operation o 256 Tap Positions o Low Ratiometric Temperature Coefficient 5ppm/C o Low End-to-End Resistor Temperature Coefficient 35ppm/C o Power-On Reset: Wiper Goes to Midscale (Position 128) o Glitchless Switching Between the Resistor Taps o 3-Wire SPITM-Interface Compatible o 10k Resistor Value
Features
o Small Footprint, 8-Pin MAX Package
MAX5402
________________________Applications
Mechanical Potentiometer Replacement Low-Drift PGAs Adjustable Voltage References
PART MAX5402EUA
Ordering Information
TEMP. RANGE -40C to +85C PINPACKAGE 8 MAX R (k) 10
PoT is a trademark of Maxim Integrated Products. SPI is a trademark of Motorola, Inc.
Functional Diagram
VDD
Pin Configuration
TOP VIEW
H R 8 8-BIT SHIFT REGISTER R 8-BIT LATCH 8 256 DECODE W L
L GND CS
1 2
8 7
H W VDD SCLK
DIN
MAX5402
3 6 5 DIN 4
MAX5402
SCLK CS CLOCK LOGIC POR
MAX
GND
________________________________________________________________ Maxim Integrated Products
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For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
256-Tap, PoT, Low-Drift, Digital Potentiometer MAX5402
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..............................................................-0.3V to +6V DIN, SCLK, CS to GND ............................................-0.3V to +6V H, L, W to GND .............................................-0.3V to (VDD + 0.3) Maximum Continuous Current into Pins H, L, and W ...........1mA Continuous Power Dissipation (TA = +70C) 8-Pin MAX (derate 4.1mW/C above +70C) ............330mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = +5V, VH = VDD, VL = 0, TA = TMIN to TMAX. Typical values are at VDD = +5V, TA = +25C, unless otherwise noted.)
PARAMETER Resolution Integral Nonlinearity (Notes 1, 2) Differential Nonlinearity (Notes 1, 2) End-to-End Resistor Tempco Ratiometric Resistor Tempco Full-Scale Error Zero-Scale Error DC PERFORMANCE (Variable-Resistor Mode) Resolution Integral Nonlinearity (Notes 1, 3) Differential Nonlinearity (Notes 1, 3) N INL DNL VDD = +5V VDD = +3V VDD = +5V VDD = +3V VDD = +5V VDD = +3V 46 7.5 0.7 VDD 0.3 VDD 1.0 5 tS tCP tCH To 50% of final value from code 0 to code 128 100 40 100 10 12.5 275 550 8 1 3 1/2 1/2 Bits LSB LSB LSB LSB SYMBOL N INL DNL TCR 35 5 -6 +6 CONDITIONS MIN 8 1/2 1 TYP MAX UNITS Bits LSB LSB ppm/C ppm/C LSB LSB
DC PERFORMANCE (Voltage-Divider Mode)
DC PERFORMANCE (Resistor Characteristics) Wiper Resistance (Note 4) Wiper Capacitance End-to-End Resistance DIGITAL INPUTS Input High Voltage Input Low Voltage Input Leakage Current Input Capacitance TIMING CHARACTERISTICS (ANALOG) Wiper-Settling Time SCLK Clock Period SCLK Pulse Width High ns ns ns TIMING CHARACTERISTICS (DIGITAL) (Note 5) (Figure 2) VIH VIL V V A pF RW CW RHL pF k
2
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256-Tap, PoT, Low-Drift, Digital Potentiometer
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +5V, VH = VDD, VL = 0, TA = TMIN to TMAX. Typical values are at VDD = +5V, TA = +25C, unless otherwise noted.)
PARAMETER SCLK Pulse Width Low CS Fall to SCLK Rise Setup Time SCLK Rise to CS Rise Hold Time DIN Setup Time DIN Hold Time SCLK Rise to CS Fall Delay CS Rise to SCLK Rise Hold CS Pulse Width High POWER SUPPLIES Supply Voltage Supply Current VDD IDD CS = SCLK = DIN = VDD VDD = +5V VDD = +2.7V 2.7 0.8 0.1 5.5 5 V A A SYMBOL tCL tCSS tCSH tDS tDH tCS0 tCS1 tCSW CONDITIONS MIN 40 40 0 40 0 10 40 100 TYP MAX UNITS ns ns ns ns ns ns ns ns
MAX5402
Note 1: Linearity is defined in terms of the H-to-L code-dependent resistance. Note 2: The DNL and INL are measured with the potentiometer configured as a voltage-divider with H = VDD and L = 0. The wiper terminal is unloaded and measured with an ideal voltmeter. Note 3: The DNL and INL are measured with the potentiometer configured as a variable resistor. H is unconnected and L = 0. The wiper terminal is driven with a source current of 200A at VDD = +3V and 400A at VDD = +5V. Note 4: The wiper resistance is the worst value measured, injecting a current, IW = VDD/RHL into terminal W. Note 5: Digital timing is guaranteed by design.
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256-Tap, PoT, Low-Drift, Digital Potentiometer MAX5402
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.) WIPER RESISTANCE vs. WIPER VOLTAGE
MAX5402 Toc01
END-TO-END RESISTANCE % CHANGE vs. TEMPERATURE
END-TO-END RESISTANCE % CHANGE
MAX5402 Toc02
300 275 WIPER RESISTANCE () 250 225 200 175 150 125 100 0 1 2 3 4 5 WIPER VOLTAGE (V) VDD = +5V VDD = +3V
0.10 0.05 0.00
-0.05 -0.10 -0.15 -0.20 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 TEMPERATURE (C)
RESISTANCE vs. INPUT CODE
MAX5402 Toc03
VARIABLE RESISTOR DNL vs. INPUT CODE
0.20 0.15 RDNL (LSB) 0.10 0.05 0.00
MAX5402 Toc04
10 9 W-TO-L RESISTANCE (k) 8 7 6 5 4 3 2 1 0 0 32 64 96
0.25
-0.05 -0.10 -0.15 -0.20 128 160 192 224 256 0 32 64 96 128 160 192 224 256 INPUT CODE (DECIMAL) INPUT CODE (DECIMAL)
VARIABLE RESISTOR INL vs. INPUT CODE
MAX5402 Toc05
VOLTAGE-DIVIDER DNL vs. INPUT CODE
0.06 0.04 DNL (LSB) 0.02 0.00 -0.02 -0.04 -0.06 -0.08 0 32 64 96 128 160 192 224 256
MAX5402 Toc06
0.3 0.2 0.1 RINL (LSB) 0.0 -0.1 -0.2 -0.3 -0.4 0 32 64 96
0.08
128 160 192 224 256
INPUT CODE (DECIMAL)
INPUT CODE (DECIMAL)
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256-Tap, PoT, Low-Drift, Digital Potentiometer
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.) VOLTAGE-DIVIDER INL vs. INPUT CODE
MAX5402 Toc07
MAX5402
SUPPLY CURRENT vs. TEMPERATURE
MAX5402 Toc08
0.20 0.15 0.10 INL (LSB) 0.05 0.00 -0.05 -0.10 -0.15 -0.20 0 32 64 96
1.2 1.0 SUPPLY CURRENT (A) VDD = +5V 0.8 0.6 0.4 0.2 VDD = +3V 0.0
128 160 192 224 256
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C)
INPUT CODE (DECIMAL)
TAP-TO-TAP SWITCHING TRANSIENT
MAX5402 toc09
INPUT LOGIC VOLTAGE
MAX5402 Toc10
10 +2.51V 1
VW-L
+2.49V
SUPPLY CURRENT (mA)
0.1 VDD = +5V
+5V CS 0
0.01
0.001 VDD = +3V 0.0001
200ns/div (CODE 127 TO 128)
0
1
2
3
4
5
DIGITAL INPUT VOLTAGE (V)
Pin Description
PIN 1 2 3 4 5 6 7 8 NAME L GND CS DIN SCLK VDD W H Low Terminal of Resistor Ground Chip Select Input Serial Data Input Serial Clock Input Power Supply. Bypass with a 0.1F capacitor to GND. Wiper Terminal High Terminal of Resistor FUNCTION
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256-Tap, PoT, Low-Drift, Digital Potentiometer MAX5402
POT REGISTER LOADED
CS
SCLK 1ST CLOCK PULSE 8TH CLOCK PULSE
DIN
D7
D6
D5
D4
D3
D2
D1
D0
MSB TIME
LSB
Figure 1. Serial Interface Timing Diagram
CS tCSO SCLK tCSS tCL tCH tCP tCSH tCS1
tCSW
tDS tDH DIN
Figure 2. Detailed Serial Interface Timing Diagram
Detailed Description
The MAX5402 consists of 255 fixed resistors in series between pins H and L. The potentiometer wiper (pin W) can be programmed to access any one of the 256 different tap points on the resistor string. The MAX5402 has an SPI-compatible 3-wire serial data interface to control the wiper tap position. This write-only interface contains three inputs: Chip Select (CS), Data In (DIN), and Data Clock (SCLK). When CS is taken low, data from the DIN pin is synchronously loaded into the 8-bit serial shift register on the rising edge of each SCLK pulse (Figure 1). The MSB is shifted in first, as shown in Figure 3. Note that if CS is not kept low during the entire data stream, the data will be corrupted and the device
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will need to be reloaded. After all 8 data bits have been loaded into the shift register, they are latched into the decoder once CS is taken high. The decoder switches the potentiometer wiper to the tap position that corresponds to the 8-bit input data. Each resistor cell is 10k/255 or 39.2 for the MAX5402. The MAX5402 features POR circuitry. This sets the wiper to the midscale position at power-up by loading a binary value of 128 into the 8-bit latch. The MAX5402 can be used as a variable resistor by connecting pin W to either pin H or L.
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256-Tap, PoT, Low-Drift, Digital Potentiometer MAX5402
Data Word B0 (D7) B1 (D6) B2 (D5) B3 (D4) B4 (D3) B5 (D2) B6 (D1) B7 (D0)
(MSB) First Bit In
Figure 3. Serial Data Format
(LSB) Last Bit In
Applications Information
The MAX5402 is intended for a variety of circuits where accurate, fine-tuned adjustable resistance is required, such as in adjustable voltage or adjustable gain circuit configurations. The MAX5402 is used in either a potentiometer divider or a variable resistor configuration.
R3 H +5V W L
MAX4250 MAX5402
R1
R2
Adjustable Current to Voltage Converter
Figure 4 shows the MAX5402 used with a MAX4250 low-noise op amp to precisely tune a current-to-voltage converter. Pins H and W of the MAX5402 are connected to the node between R3 and R2, and pin L is connected to ground.
VO
Adjustable Gain Amplifier
The MAX5402 is used again with the MAX4250 to make a digitally adjustable gain circuit as shown in Figure 5. The normal feedback resistor is replaced with the MAX5402 in a variable resistor configuration, so that the gain of the circuit can be digitally controlled.
VO / IS = R3(1 + R2 / R1) + R2
Figure 4. I to V Converter
Adjustable Voltage Reference
In Figure 6, the MAX5402 is shown with the MAX6160 to make an adjustable voltage reference. In this circuit, the H pin of the MAX5402 is connected to the OUT pin of the MAX6160, the L pin of the MAX5402 is connected to GND, and the W pin of the MAX5402 is connected to the ADJ pin of the MAX6160. The MAX5402 allows precise tuning of the voltage reference output. A low 5ppm/C ratiometric tempco allows a very stable adjustable voltage overtemperature.
VS
+5V
MAX4250
VO
L
R2
H
MAX5402
R1
W
VO / VS = 1 + R2 / R1
Figure 5. Noninverting Amplifier
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256-Tap, PoT, Low-Drift, Digital Potentiometer MAX5402
Chip Information
+5V VIN VO REF OUT
MAX6160
TRANSISTOR COUNT: 3475 PROCESS: BiCMOS
H W
ADJ GND
MAX5402
L
VO =
1.23V 255 C
WHERE C IS THE DECIMAL EQUIVALENT WRITTEN CODE.
Figure 6. Adjustable Voltage Reference
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256-Tap, PoT, Low-Drift, Digital Potentiometer
Package Information
8LUMAXD.EPS
MAX5402
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) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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