APPLICATION NOTE
A V A I L A B L E
AN104
Low Noise, Low Power, 32 Taps
X9315
E2POTTM Nonvolatile Digital Potentiometer
FEATURES
•Low Power CMOS
—VCC = 2.7V to 5.5V, Single Supply
—Active Current, 50µA (Increment) max
—Active Current, 400µA (Store) Max
—Standby Current, 1µA Max
•Low Noise
•31 Resistive Elements
—Temperature Compensated
—± 20% End to End Resistance Range
—VSS to VCC Range
•32 Wiper Tap Points
—Wiper Positioned via Three-Wire Interface
—Similar to TTL Up/Down Counter
—Wiper Position Stored in Nonvolatile Memory and Recalled on Power-Up
•100 Year Wiper Position Data Retention
•X9315Z = 1KΩ
•X9315W = 10KΩ
•Packages
—8-Lead SOIC
—8-Lead MSOP
—8-Pin DIP
DESCRIPTION
The Xicor X9315 is a solid state "micropower" nonvolatile potentiometer and is ideal for digitally controlled resistance trimming.
The X9315 is a resistor array composed of 31 resistive elements. Between each element and at either end are tap points accessible to the wiper element. The posi- tion 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 resolution of the X9315 is equal to the maximum resistance value divided by 31. As an example, for the X9315W (10KΩ) each tap point represents 323Ω.
All Xicor nonvolatile digital potentiometers are designed and tested for applications requiring extended endurance and data retention.
FUNCTIONAL DIAGRAM
U/D |
5-BIT |
CMOS SWITCH |
VH |
INC |
UP/DOWN |
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CS |
COUNTER |
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5-BIT |
ONE |
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OF |
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NONVOLATILE |
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THIRTY- |
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MEMORY |
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TWO |
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RESISTOR |
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WIPER |
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ARRAY |
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POSITION |
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DECODER |
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STOREAND |
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RECALL |
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CONTROL |
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CIRCUITRY |
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VL
VW
6732 FM1
E2POT™ is a trademark of Xicor, Inc.
6732-2.0 5/30/97 T1/C0/D0 SH |
1 |
Characteristics subject to change without notice |
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X9315
PIN DESCRIPTIONS
VH and VL
The high (VH) and low (VL) terminals of the X9315 are equivalent to the fixed terminals of a mechanical potentiometer. The minimum voltage is VSS and the maximum is VCC. 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 400Ω.
Up/Down (U/D)
The U/D input controls the direction of the wiper movement and whether the counter is incremented 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 X9315 will be placed in the low power standby mode until the device is selected once again.
PIN CONFIGURATION
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DIP/SOIC/MSOP |
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1 |
8 |
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VCC |
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INC |
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U/D |
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7 |
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CS |
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X9315 |
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VH |
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3 |
6 |
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VL |
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VSS |
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4 |
5 |
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VW |
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6732 FM2
PIN NAMES
Symbol |
Description |
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VH |
High Terminal |
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VW |
Wiper Terminal |
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VL |
Low Terminal |
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VSS |
Ground |
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VCC |
Supply Voltage |
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Up/Down Input |
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U/D |
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Increment Input |
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INC |
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Chip Select Input |
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CS |
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6732 FM T01
2
X9315
DEVICE OPERATION
There are three sections of the X9315: 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 31 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 INC, U/D and CS inputs control the movement of the wiper along the resistor array. With CS set LOW the X9315 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 thirty two wiper positions along the resistive array.
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 value of the counter is stored in nonvolatile memory whenever CS transistions HIGH while the INC input is also HIGH.
When the X9315 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.
Operation Notes
The system may select the X9315, 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 powerup/down 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 X9315 and then move the wiper up and down until the proper trim is attained.
SYMBOL TABLE
WAVEFORM |
INPUTS |
OUTPUTS |
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Must be |
Will be |
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steady |
steady |
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May change |
Will change |
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from Low to |
from Low to |
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High |
High |
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May change |
Will change |
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from High to |
from High to |
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Low |
Low |
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Don’t Care: |
Changing: |
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Changes |
State Not |
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Allowed |
Known |
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N/A |
Center Line |
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is High |
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Impedance |
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6732 FM 3
3
X9315
ABSOLUTE MAXIMUM RATINGS* |
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Temperature under Bias ......................... |
–65°C to +135°C |
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Storage Temperature.............................. |
–65°C to +150°C |
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Voltage on |
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VH, VL and VCC |
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CS, |
INC, |
U/D |
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with Respect to VSS.................................. |
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–1V to +7V |
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V = |VH–VL| ................................................................. |
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5V |
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Lead Temperature (Soldering 10 seconds) |
............. 300°C |
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Wiper Current ........................................................... |
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±1mA |
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ANALOG CHARACTERISTICS |
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Electrical Characteristics |
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Temperature under Bias......................... |
–65°C to +135°C |
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End-to-End Resistance Tolerance |
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±20% |
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Power Rating at 25°C .............................................. |
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10mW |
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Wiper Current ................................................. |
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± 1mA Max. |
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Typical Wiper Resistance ............................ |
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400 Ω at 1mA |
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Typical Noise.................................. |
< –140dB√ Hz Ref: 1V |
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Resolution |
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Resistance ................................................................... |
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3% |
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Linearity |
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Absolute Linearity(1)........................................... |
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± 1.0 Ml(2) |
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Relative Linearity(3) ........................................... |
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± 0.2 Ml(2) |
*COMMENT
Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress rating only and the functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied.
Temperature Coefficient |
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(–40°C to +85°C) .............................. |
+300 ppm/°C Typical |
Ratiometric Temperature Coefficient |
.................. ±20 ppm |
Wiper Adjustability
Unlimited Wiper Adjustment (Non-Store operation)
Wiper Position Store Operations .......................... |
100,000 |
Physical Characteristics
Marking Includes
Manufacturer’s Trademark
Resistance Value or Code
Date Code
Test Circuit #1 |
Test Circuit #2 |
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VH |
VH |
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TEST POINT |
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TEST POINT |
VW |
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VW |
FORCE |
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CURRENT |
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VL |
VL |
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6732 FM 5 |
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6732 FM 4 |
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Notes: (1) Absolute Linearity is utilized to determine actual wiper voltage versus expected voltage |
= (Vw(n)(actual) – Vw(n)(expected)) = ±1 Ml Maximum.
(2)1 Ml = Minimum Increment = RTOT/31.
(3)Relative Linearity is a measure of the error in step size between taps = VW(n+1) – [Vw(n) + Ml] = +0.2 Ml.
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