Digitally Controlled Potentiometer

APPLICATION NOTE AVAILABLE AN42 • AN44–48 • AN50 • AN52 • AN53 • AN71 • AN92 Terminal Voltage ±5V, 100 Taps, Log Taper X9C303 Digitally Controlled Potentiometer (XDCP™) FEATURES • Solid-state potentiometer • Three-wire serial interface • 100 wiper tap points —Wiper position stored in nonvolatile memory and recalled on power-up • 99 resistive elements, log taper —Temperature compensated —End to end resistance, ±15% —Terminal voltages, ±5V • Low power CMOS —VCC = 5V —Active current, 3mA max. —Standby current, 750µA max. • High reliability —Endurance, 100,000 data changes per bit —Register data retention, 100 years • X9C303, 32 kΩ • Packages —8-lead TSSOP www.DataSheet4U.com —8-lead SOIC —8-pin DIP DESCRIPTION The Xicor X9C303 is a digitally controlled potentiometer (XDCP). The device consists of a resistor array, wiper switches, a control section, and nonvolatile memory. The wiper position is controlled by a threewire interface. The resistor array is composed of 99 resistive elements. Between each element and at either end are tap points accessible to the wiper terminal. The position of the wiper element is controlled by the CS, U/D, and INC inputs. The position of the wiper can be stored in nonvolatile memory and then be recalled upon a subsequent power-up operation. The device can be used as a three-terminal potentiometer or as a two-terminal variable resistor in a wide variety of applications ranging from control, to signal processing, to parameter adjustment. Digitallycontrolled potentiometers provide three powerful application advantages; (1) the variability and reliability of a solid-state potentiometer, (2) the flexibility of computer-based digital controls, and (3) the use of nonvolatile memory for potentiometer settings retention. BLOCK DIAGRAM U/D INC CS 7-Bit Up/Down Counter 99 98 97 7-Bit Nonvolatile Memory 96 One of OneHundred Decoder 2 Store and Recall Control Circuitry 1 0 RL/VL RW/VW XDCP™ is a trademark of Xicor, Inc. REV 1.1 4/27/01 RH/VH Transfer Gates Resistor Array VCC VSS www.xicor.com Characteristics subject to change without notice. 1 of 10 X9C303 PIN DESCRIPTIONS VH and VL The high (VH) and low (VL) terminals of the device are equivalent to the fixed terminals of a mechanical potentiometer. The minimum voltage is –5V and the maximum is +5V. It should be noted that the terminology of VL and VH references the relative position of the terminal in relation to wiper movement direction selected by the U/D input and not the voltage potential on the terminal. VW VW is the wiper terminal, equivalent to the movable terminal of a mechanical potentiometer. The position of the wiper within the array is determined by the control inputs. The wiper terminal series resistance is typically 40Ω. Up/Down (U/D) The U/D input controls the direction of the wiper movement and whether the counter is incriminated or decremented. Increment (INC) The INC input is negative-edge triggered. Toggling INC will move the wiper and either increment or decrement the counter in the direction indicated by the logic level on the U/D input. Chip Select (CS) The device is selected when the CS input is LOW. The current counter value is stored in nonvolatile memory when CS is returned HIGH while the INC input is also HIGH. After the store operation is complete the device will be placed in the low power standby mode until the device is selected once again. PIN CONFIGURATION DIP/SOIC/(TSSOP) (CS) INC (VCC) U/D (INC) VH (U/D) V SS 1 2 3 4 X9C303 8 7 6 5 VCC (VL) CS (VW) VL (VSS) VW (VH) VL R1 + R2 + . . . + Ri VW G i = 20Log ------------------------------------------------ = --------- ( V L = 0V ) R TOTAL VS R 1 + R 2 + . . . + R 99 @ 33KΩ = R TOTAL (Refer Test Circuit 1) PIN NAMES Symbol VH VW VL VSS VCC U/D INC CS NC Description High Terminal (Potentiometer) Wiper Terminal (Potentiometer) Low Terminal (Potentiometer) Ground Supply Voltage Up/Down Control Input Increment Control Input Chip Select Control Input No Connection POTENTIOMETER RELATIONSHIPS S100 VH (VS) S99 S98 VW R99 R98 S3 R2 R1 S2 S1 REV 1.1 4/27/01 www.xicor.com Characteristics subject to change without notice. 2 of 10 X9C303 PRINCIPLES OF OPERATION There are three sections of the X9C303: the input control, counter and decode section; the nonvolatile memory; and the resistor array. The input control section operates just like an up/down counter. The output of this counter is decoded to turn on a single electronic switch connecting a point on the resistor array to the wiper output. Under the proper conditions the contents of the counter can be stored in nonvolatile memory and retained for future use. The resistor array is comprised of 99 individual resistors connected in series. At either end of the array and between each resistor is an electronic switch that transfers the potential at that point to the wiper. The wiper, when at either fixed terminal, acts like its mechanical equivalent and does not move beyond the last position. That is, the counter does not wrap around when clocked to either extreme. The electronic switches on the device operate in a “make before break” mode when the wiper changes tap positions. If the wiper is moved several positions, multiple taps are connected to the wiper for tIW (INC to VW change). The RTOTAL value for the device can temporarily be reduced by a significant amount if the wiper is moved several positions. When the device is powered-down, the last counter position stored will be maintained in the nonvolatile memory. When power is restored, the contents of the memory are recalled and the counter is reset to the value last stored. Instructions and Programming The INC, U/D and CS inputs control the movement of the wiper along the resistor array. With CS set LOW the device is selected and enabled to respond to the U/D and INC inputs. HIGH to LOW transitions on INC will increment or decrement (depending on the state of the U/D input) a seven-bit counter. The output of this counter is decoded to select one of one-hundred wiper positions along the resistive array. The value of the counter is stored in nonvolatile memory whenever CS transitions HIGH while the INC input is also HIGH. The system may select the X9C303, move the wiper, and deselect the device without having to store the latest wiper position in nonvolatile memory. The wiper movement is performed as described above; once the new position is reached, the system would the keep INC LOW while taking CS HIGH. The new wiper position would be maintained until changed by the system or until a power-down/up cycle recalled the previously stored data. This would allow the system to always power-up to a preset value stored in nonvolatile memory; then during system operation minor adjustments could be made. The adjustments might be based on user preference: system parameter changes due to temperature drift, etc... The state of U/D may be changed while CS remains LOW. This allows the host system to enable the device and then move the wiper up and down until the proper trim is attained. MODE SELECTION CS L L H H X L INC U/D H L X X X Wiper Up Mode Wiper Down Store Wiper Position Standby Current No Store, Return to Standby SYMBOL TABLE WAVEFORM INPUTS Must be steady May change from Low to High May change from High to Low Don’t Care: Changes Allowed N/A OUTPUTS Will be steady Will change from Low to High Will change from High to Low Changing: State Not Known Center Line is High Impedance REV 1.1 4/27/01 www.xicor.com Characteristics subject to change without notice. 3 of 10 X9C303 ABSOLUTE MAXIMUM RATINGS Temperature under bias ....................–65°C to +135°C Storage temperature .........................–65°C to +150°C Voltage on CS, INC, U/D and VCC with respect to VSS .................................. –1V to +7V Voltage on VH and VL referenced to VSS ................................... –8V to +8V ∆V = |VH–VL| X9C303 .......................................... 10V Lead temperature (soldering, 10 seconds)...... +300°C Wiper current ..................................................... ±1mA COMMENT Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only; functional operation of the device (at these or any other conditions above those listed in the operational sections of this specification) is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ANALOG CHARACTERISTICS Electrical Characteristics End-to-end resistance tolerance ....................... ±15% Power rating at 25°C X9C303 ........................... 10mW Wiper current ............................................ ±1mA Max. Typical Electrical Taper 100.0% 90.0% 80.0% 70.0% % Total Resistance 60.0% 50.0% 40.0% 30.0% 20.0% 10.0% 0.0% 0 3 6 9 12 15 18 21 24 27 30 33 36 39 42 45 48 51 54 57 60 63 66 69 72 75 78 81 84 87 90 93 96 R(VH–VW) R(VW–VL) 99 4 of 10 Typical wiper resistance ...........................40Ω at 1mA Typical resistor noise ........................ 23 nV (RMS)/÷Hz at 1kHzPHZ Typical charge pump noise.. 20 mV (RMS) @ 2.5 MHz Relative Variation Relative variation is a measure of the error in step size between taps = log (Vw(n)) – log (Vw(n-1)) = 0.045 ± 0.003 for tap n = 2 – 99 Temperature Coefficient (–40°C to +85°C) X9C303 .......... ±400 ppm/°C Typical Ratiometric temperature coefficient ..............±20 ppm Wiper Adjustability Unlimited Wiper Adjustment (Non-Store operation) Wiper Position Store Operations ...................100,000 Data Changes per Bit Physical Characteristics Marking Includes Manufacturer’s Trademark Resistance Value or Code Date Code Tap REV 1.1 4/27/01 www.xicor.com Characteristics subject to change without notice. X9C303 Test Circuit #1 VH Test Circuit #2 VH Test Point Circuit #3SPICE Macro Model RTO