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19-1848; Rev 0; 10/00
256-Tap SOT-PoT, Low-Drift Digital Potentiometers in SOT23
General Description
The MAX5400/MAX5401 digital potentiometers offer 256-tap SOT-PoTTM digitally controlled variable resistors in tiny 8-pin SOT23 packages. Each device functions as a mechanical potentiometer, consisting of a fixed resistor string with a digitally controlled wiper contact. They operate from +2.7V to +5.5V single-supply voltages and use an ultra-low supply current of 0.1A. These devices also provide glitchless switching between resistor taps, as well as a convenient poweron reset 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 MAX5400/MAX5401 serve 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 50ppm/C allows these parts to be used as variable resistors in applications such as low-tempco adjustable gain and other circuit configurations. Two resistance values are available: 50k (MAX5400) and 100k (MAX5401). Each device is guaranteed over the extended industrial temperature range (-40C to +85C). o Miniature 8-Pin SOT23 (3mm x 3mm) o 256 Tap Positions o Ultra-Low 0.1A Supply Current o Single-Supply Operation: +2.7V to +5.5V o Low Ratiometric Temperature Coefficient: 5ppm/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 50k/100k Resistor Values
Features
MAX5400/MAX5401
Ordering Information
PART MAX5400EKA-T MAX5401EKA-T TEMP. RANGE -40C to +85C -40C to +85C PINPACKAGE 8-SOT23 8-SOT23 R (k) 50 100
________________________Applications
Mechanical Potentiometer Replacement Low-Drift PGAs Adjustable Voltage References
SOT-PoT is a trademark of Maxim Integrated Products. SPI is a trademark of Motorola, Inc. Pin Configuration appears at end of data sheet.
Functional Diagram
VDD H 8 8-BIT SHIFT REGISTER 8-BIT LATCH 8
DECODER
W
DIN
L
MAX5400/MAX5401
SCLK CS CLOCK LOGIC POR
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 SOT-PoT, Low-Drift Digital Potentiometers in SOT23 MAX5400/MAX5401
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 + 0.3V) Maximum Continuous Current into Pins H, L, and W ...........................................................1mA Continuous Power Dissipation (TA = +70C) 8-Pin SOT23 (derate 8.7mW/C above +70C)...........697mW 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 TA = +25C, unless otherwise noted. Parameters are measured at TA = +25C. Values over full temperature range are guaranteed by design.)
PARAMETER Resolution Integral Nonlinearity (Notes 1, 2) Differential Nonlinearity (Notes 1, 2) End-to-End Resistor Tempco Ratiometric Resistor Tempco Full-Scale Ratio Error Zero-Scale Ratio Error POWER SUPPLIES Supply Voltage Supply Current VDD IDD CS = SCLK = DIN = VDD VDD = 5V VDD = 2.7V 8 VCC = 5V INL VCC = 3V VCC = 5V VCC = 3V 250 25 MAX5401 MAX5400 75 37.5 100 50 125 62.5 MAX5400 MAX5401 1 1.5 1 1/2 1/2 800 LSB LSB 2.7 0.7 0.1 5.5 5 V A A Bits MAX5400 MAX5401 MAX5400 MAX5401 SYMBOL N INL DNL TCR 50 5 -0.8 -0.4 +0.8 +0.4 CONDITIONS MIN 8 1/2 1/2 TYP MAX UNITS Bits LSB LSB ppm/C ppm/C LSB LSB
DC PERFORMANCE (Voltage Divider Mode)
DC PERFORMANCE (Variable Resistor Mode) Resolution Integral Nonlinearity (Notes 1, 3) Differential Nonlinearity (Notes 1, 3) Wiper Resistance (Note 4) Wiper Capacitance End-to-End Resistance N
DNL
DC PERFORMANCE (Resistor Characteristics) RW CW RHL pF k
2
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256-Tap SOT-PoT, Low-Drift Digital Potentiometers in SOT23
ELECTRICAL CHARACTERISTICS (continued)
(VDD = +5V, VH = VDD, VL = 0, TA = TMIN to TMAX. Typical values are at TA = +25C, unless otherwise noted. Parameters are measured at TA = +25C. Values over full temperature range are guaranteed by design.)
PARAMETER DIGITAL INPUTS Input High Voltage Input Low Voltage Input High Voltage Input Low Voltage Input Leakage Current Input Capacitance TIMING CHARACTERISTICS (Voltage Divider Mode) MAX5400 (to 50% of final value, from code 0 to code 128) MAX5401 (to 50% of final value, from code 0 to code 128) 100 40 40 40 0 40 0 10 40 100 300 ns 600 5.0 VIH VIL VIH VIL VCC = 5V VCC = 5V VCC = 3V VCC = 3V 0.7 VDD 0.3 VDD 1.0 0.7 VDD 0.3 VDD V V V V A pF SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX5400/MAX5401
Wiper Settling Time
tIL
TIMING CHARACTERISTICS (Digital) (Note 5) SCLK Clock Period SCLK Pulse Width High 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 tCP tCH tCL tCSS tCSH tDS tDH tCS0 tCS1 tCSW ns ns ns ns ns ns ns ns ns ns
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 80A for the 50k configuration and 40A for the 100k configuration. Note 4: The wiper resistance is measured assuming the source currents given in Note 2. Note 5: Digital timing is guaranteed by design.
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256-Tap SOT-PoT, Low-Drift Digital Potentiometers in SOT23 MAX5400/MAX5401
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
END-TO-END RESISTANCE % CHANGE vs. TEMPERATURE
MAX5400toc02 MAX5400 toc01
WIPER RESISTANCE vs. VOLTAGE
600 500 WIPER RESISTANCE () 400 300 VDD = +5V 200 100 0 0 1 2 3 4 5 WIPER VOLTAGE (V) VDD = +3V 0.05 END-TO-END RESISTANCE % CHANGE 0.03 0.01 -0.01 -0.03 -0.05 -0.07 -0.09 -0.11
W-to-L RESISTANCE vs. INPUT CODE (100k)
90 W-TO-L RESISTANCE (k) 80 70 60 50 40 30 20 10 0 VDD = 2.7V to 5.5V
MAX5400 Toc03
100
100k
50k
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C)
0
32
64
96
128 160 192 224 256
INPUT CODE-DECIMAL
W-to-L RESISTANCE vs. INPUT CODE (50k)
MAX5400 Toc04
VARIABLE RESISTOR DNL vs. INPUT CODE (50k)
MAX5400 Toc05
VARIABLE RESISTOR INL vs. INPUT CODE (50k)
0.15 0.10 0.05 (LSB) 0 -0.05 -0.10 -0.15 -0.20
MAX5400 Toc06
50 45 W-TO-L RESISTANCE (k) 40 35 VDD = 2.7V to 5.5V
0.020 0.015 0.010 0.005 (LSB) 0 -0.005 -0.010 -0.015 -0.020
0.20
30 25 20 15 10 5 0 0 32 64 96 128 160 192 224 256 INPUT CODE-DECIMAL
0
32
64
96
128 160 192 224 256
0
32
64
96
128 160 192 224 256
INPUT CODE-DECIMAL
INPUT CODE-DECIMAL
VARIABLE RESISTOR DNL vs. INPUT CODE (100k)
MAX5400 Toc07
VARIABLE RESISTOR INL vs. INPUT CODE (100k)
0.15 0.10 0.05 (LSB) 0 -0.05 -0.10 -0.15 -0.20 0 0 32 64 96 128 160 192 224 256
MAX5400 Toc08
SUPPLY CURRENT vs. TEMPERATURE
MAX5400toc09
0.020 0.015 0.010 0.005 (LSB) 0 -0.005 -0.010 -0.015 -1.020 0 32 64 96
0.20
1.0 VDD = +5V
0.8 SUPPLY CURRENT (A)
0.6
0.4
0.2
VDD = +3V
128 160 192 224 256
-40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (C)
INPUT CODE-DECIMAL
INPUT CODE-DECIMAL
4
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256-Tap SOT-PoT, Low-Drift Digital Potentiometers in SOT23
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
TAP-to-TAP SWITCHING TRANSIENT (FROM CODE 127 toc CODE 128)
MAX5400 Toc10
MAX5400/MAX5401
SUPPLY CURRENT vs. INPUT LOGIC VOLTAGE
10mV/div SUPPLY CURRENT (mA)
MAX5400 Toc11
10
VW-L 2.5V
1 VDD = +5V 0.1
5V/div CS 0
0.01 VDD = +3V 0.001
0.0001 0 1 2 3 4 5 DIGITAL INPUT VOLTAGE (V)
VOLTAGE DIVIDER DNL vs. INPUT CODE (50k)
MAX5400 Toc12
VOLTAGE DIVIDER INL vs. INPUT CODE (50k)
VDD = +2.7V to +5.5V 0.15 0.10 0.05 (LSB) 0 -0.05 -0.10 -0.15 -0.20
MAX5400 Toc13
0.10 0.08 0.06 0.04 0.02 (LSB) 0 -0.02 -0.04 -0.06 -0.08 -0.10 0 32 64 96
0.20
128 160 192 224 256
0
32
64
96
128 160 192 224 256
INPUT CODE-DECIMAL
INPUT CODE-DECIMAL
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 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 SOT-PoT, Low-Drift Digital Potentiometers in SOT23 MAX5400/MAX5401
POT REGISTER LOADED
CS
SCLK 1ST CLOCK PULSE 8TH CLOCK PULSE
DIN
D7
D6
D5
D4
D3
D2
D1
D0
MSB TIME
LSB
Figure 2. Serial Interface Timing Diagram
CS tCSO SCLK tCSS tCH tCL tCP tCSH tCS1
tCSW
tDS tDH DIN
Figure 3. Detailed Serial Interface Timing Diagram
Detailed Description
The MAX5400/MAX5401 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 MAX5400/MAX5401 uses a 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. The MSB is shifted in first as shown in Figure 4. 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 50k/255 or 196.1 for the MAX5400 and 100k/255 or 392.2 for the MAX5401. The MAX5400/MAX5401 feature power-on reset (POR) circuitry that sets the wiper to the midscale position at power-up by loading a binary value of 128 into the 8-bit latch. The MAX5400/MAX5401 can be used as a variable resistor by connecting pin W to either pin H or pin L.
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256-Tap SOT-PoT, Low-Drift Digital Potentiometers in SOT23 MAX5400/MAX5401
DATA WORD B0 (D7) (MSB) FIRST BIT IN B1 (D6) B2 (D5) B3 (D4) B4 (D3) B5 (D2) B6 (D1) B7 (D0) (LSB) LAST BIT IN
Figure 4. Serial Data Format
Applications Information
The MAX5400/MAX5401 are intended for a variety of circuits that require accurate, fine-tuning adjustable resistance, such as adjustable voltage or adjustable gain circuit configurations. The MAX5400/MAX5401 are primarily used in either a potentiometer divider or a variable resistor configuration.
resistor configuration so that the gain of the circuit can be digitally controlled.
Adjustable Voltage Reference
In Figure 7, the MAX5400/MAX5401 are shown with the MAX6160 to make an adjustable voltage reference. In this circuit, the H pin of the MAX5400/MAX5401 is connected to the OUT pin of the MAX6160, the L pin of the MAX5400/MAX5401 is connected to GND, and the W pin of the MAX5400/MAX5401 is connected to the ADJ pin of the MAX6160. The MAX5400/MAX5401 allow precise tuning of the voltage reference output. A low 5ppm/C ratiometric tempco allows a very stable adjustable voltage over temperature.
Adjustable Current-to-Voltage Converter
Figure 5 shows the MAX5400/MAX5401 being used with a MAX4250 low-noise op amp to fine tune a current-to-voltage converter. Pins H and W of the MAX5400/MAX5401 are connected to the node between R3 and R2 and pin L is connected to ground.
Adjustable Gain Amplifier
The MAX5400/MAX5401 are used again with the MAX4250 to make a digitally adjustable gain circuit as shown in Figure 6. The normal feedback resistor is replaced with the MAX5400/MAX5401 in a variable
+5V R3 VS +5V R1 R2 VO
VO
MAX4250
R2 MAX4250
R1
VO / IS = R3(1 + R2 / R1)+ R2 VO / VS = 1 + R2 / R1
Figure 5. I to V Converter
Figure 6. Noninverting Amplifier
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256-Tap SOT-PoT, Low-Drift Digital Potentiometers in SOT23 MAX5400/MAX5401
+5V VIN VO REF OUT H W
Chip Information
TRANSISTOR COUNT: 3769 TECHNOLOGY: BiCMOS
MAX6160
ADJ GND
L
VO = 1.23V x 100k FOR MAX5401 R2(k) VO = 1.23V x 50k FOR MAX5400 R2(k)
Figure 7. Adjustable Voltage Reference
Pin Configuration
TOP VIEW
L1 GND 2 CS 3
8 7
H W VDD SCLK
MAX5400/ MAX5401
6 5
DIN 4
SOT23
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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