256-Position I2C Compatible Digital Potentiometer
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© Semiconductor Components Industries, LLC, 2009 August, 2009 - Rev. 1 1 Publication Order Number: CAT5171/D CAT5171 256-Position I2C Compatible Digital Potentiometer The CAT5171 is a 256-position digitally programmable linear taper potentiometer ideally suited for replacing mechanical potentiometers and variable resistors. The wiper settings are controlled through an I2C-compatible digital interface. Upon power-up, the wiper assumes a midscale position and may be repositioned anytime after the power is stable. The device can be programmed to reset the wiper position to midscale or to go to a shutdown state during operation. An address input pin, AD0, allows the connection of two devices onto the same I2C bus. The CAT5171 operates from 2.7 V to 5.5 V, while consuming less than 2 A. This low operating current, combined with a small package footprint, makes the CAT5171 ideal for battery-powered portable applications. The CAT5171, designed as a pin for pin replacement for the AD5245, is offered in the 8-lead SOT23 package and operates over the -40°C to +85°C industrial temperature range. Features • 256-position • End-to-End Resistance: 50 k, 100 k • I2C Compatible Interface • Power-on Preset to Midscale • Single Supply 2.7 V to 5.5 V • Low Temperature Coefficient 100 ppm/°C • Low Power, IDD 2 A max • Wide Operating Temperature -40°C to +85°C • RoHS-compliant SOT-23 8-Lead (2.9 mm x 3 mm) Package Typical Applications • Potentiometer Replacement • Transducer Adjustment of Pressure, Temperature, Position, Chemical, and Optical Sensors • RF Amplifier Biasing • Gain Control and Offset Adjustment http://onsemi.com PIN CONNECTIONS SDA AD0 B A SCL GND VDD W 1 (Top View) See detailed ordering and shipping information in the package dimensions section on page 2 of this data sheet. ORDERING INFORMATION SOT23-8 TP, TB SUFFIX CASE 527AK AF = 50 k AG = 100 k Y = Production Year Y = (Last Digit) M = Production Month M = (1 - 9, A, B, C) AFYM MARKING DIAGRAM 1 AGYM 1

CAT5171 http://onsemi.com 2 Power On Midscale AD0 A B W SDA GND Figure 1. Functional Block Diagram VDD I2C Interface and Control SCL Table 1. ORDERING INFORMATION Part Number Resistance Temperature Range Package Shipping† CAT5171TBI-50GT3 50 k -40°C to 85°C SOT-23-8 (Pb-Free) 3000/Tape & Reel CAT5171TBI-00GT3 100 k 3000/Tape & Reel †For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. Table 2. PIN FUNCTION DESCRIPTION Pin No. Pin Name Description 1 W Resistor’s Wiper...

CAT5171 http://onsemi.com 3 Table 4. ELECTRICAL CHARACTERISTICS: 50 k and 100 k Versions VDD = 2.7 V to 5.5 V; VA = VDD; VB = 0 V; –40°C < TA < +85°C; unless otherwise noted. Parameter Test Conditions Symbol Min Typ (Note 2) Max Unit DC CHARACTERISTICS — RHEOSTAT MODE Resistor Differential Nonlinearity (Note 3) RWB, VA = no connection R-DNL -1 ±0.1 +1 LSB Resistor Integral Nonlinearity (Note 3) RWB, VA = no connection R-INL -2 ±0.4 +2 LSB Nominal Resistor Tolerance (Note 4) TA = 25°C RAB -20 +20 % Resistance Temperature Coefficient VAB = VDD, Wiper = no connection RAB/T 100 ppm/°C Wiper...

CAT5171 http://onsemi.com 4 Table 5. CAPACITANCE TA = 25°C, f = 1.0 MHz, VDD = 5 V Symbol Test Conditions Max Units CI/O (Note 10) Input/Output Capacitance (SDA, SCL) VI/O = 0V 8 pF Table 6. POWER UP TIMING (Notes 10 and 11) Symbol Parameter Max Units tPUR Power-up to Read Operation 1 ms tPUW Power-up to Write Operation 1 ms 10.This parameter is tested initially and after a design or process change that affects the parameter. 11. tPUR and t PUW are delays required from the time VCC is stable until the specified operation can be initiated. Table 7. DIGITAL POTENTIOMETER TIMING Symbol...

CAT5171 http://onsemi.com 7 Basic Operation The CAT5171 is a 256-position digitally controlled potentiometer. When power is first applied, the wiper assumes a mid-scale position. Once the power supply is stable, the wiper may be repositioned via the I2C compatible interface. Programming: Variable Resistor Rheostat Mode The resistance between terminals A and B, RAB, has a nominal value of 50 k or 100 k and has 256 contact points accessed by the wiper terminal, plus the B terminal contact. Data in the 8-bit Wiper register is decoded to select one of these 256 possible settings. The wiper’s...

CAT5171 http://onsemi.com 8 ESD Protection GND LOGIC Digital Input GND Potentiometer Figure 12. ESD Protection Networks W, A, B Terminal Voltage Operating Range The CAT5171 VDD and GND power supply define the limits for proper 3-terminal digital potentiometer operation. Signals or potentials applied to terminals A, B or the wiper must remain inside the span of VDD and GND. Signals which attempt to go outside these boundaries will be clamped by the internal forward biased diodes. W, A, B CAT5171 LOGIC GND Figure 13. VDD Power-up Sequence Because ESD protection diodes limit the voltage...

CAT5171 http://onsemi.com 9 I2C Bus Protocol The following defines the features of the I2C bus protocol: 1. Data transfer may be initiated only when the bus is not busy. 2. During a data transfer, the data line must remain stable whenever the clock line is high. Any changes in the data line while the clock is high will be interpreted as a START or STOP condition. The device controlling the transfer is a master, typically a processor or controller, and the device being controlled is the slave. The master will always initiate data transfers and provide the clock for both transmit and receive...

CAT5171 http://onsemi.com 10 START CONDITION SDA STOP CONDITION SCL Figure 16. Start/Stop Condition ACKNOWLEDGE 1 START SCL FROM MASTER 8 9 DATA OUTPUT FROM TRANSMITTER DATA OUTPUT FROM RECEIVER Figure 17. Acknowledge Condition

CAT5171 http://onsemi.com 11 INSTRUCTION AND REGISTER DESCRIPTION SLAVE ADDRESS BYTE The first byte sent to the CAT5171 from the master/processor is called the Slave Address Byte. The most significant six bits of the slave address are a device type identifier. For the CAT5171, these bits are fixed at 010110. The next bit, AD0, is the first bit of the internal slave address and must match the physical device address which is defined by the state of the AD0 input pin for the CAT5171 to successfully continue the command sequence. Only the device which slave address matches the incoming device...