APPLICATION NOTES
A V A I L A B L E
AN42 • AN44–48 • AN50 • AN52 • AN53 • AN71 • AN73
TerminalX9312 Voltage 0V to +15V, 100 Taps
X9312
E2POT™ Nonvolatile Digital Potentiometer
FEATURES
•Compatible with X9C102/103/104/503
•Low Power CMOS —Active Current, 3mA Max
—Standby Current, 1mA Max
•99 Resistive Elements —Temperature Compensated
—±20% End to End Resistance Range
—0 to +15V Range
•100 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
•X9312Z = 1KΩ
•X9312W = 10KΩ
•X9312U = 50KΩ
•X9312T = 100KΩ
DESCRIPTION
The Xicor X9312 is a solid state nonvolatile potentiometer and is ideal for digitally controlled resistance trimming.
The X9312 is a resistor array composed of 99 resistive elements. Between each element and at either end are tap points accessible to the wiper element. 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 resolution of the X9312 is equal to the maximum resistance value divided by 99. As an example, for the X9312U (50KΩ) each tap point represents 505Ω.
All Xicor nonvolatile memories are designed and tested for applications requiring extended endurance and data retention.
FUNCTIONAL DIAGRAM
U/D |
7-BIT |
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99 |
VH |
INC |
UP/DOWN |
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CS |
COUNTER |
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98 |
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97 |
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7-BIT |
ONE |
96 |
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NONVOLATILE |
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OF |
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MEMORY |
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ONE- |
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HUNDRED |
TRANSFER |
RESISTOR |
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DECODER |
GATES |
ARRAY |
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2 |
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STORE AND |
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1 |
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RECALL |
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VCC |
CONTROL |
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GND |
CIRCUITRY |
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0 |
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VL |
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VW |
3865 FHD F01
E2POT™ is a trademark of Xicor, Inc.
©Xicor, Inc. 1994, 1995 Patents Pending |
Characteristics subject to change without notice |
3865-2.4 12/1/95 T1/C0/D0 NS |
1 |
X9312
PIN DESCRIPTIONS
VH and VL
The high (VH) and low (VL) terminals of the X9312 are equivalent to the fixed terminals of a mechanical potentiometer. The minimum voltage is 0V and the maximum is +15V. 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 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 X9312 will be placed in the low power standby mode until the device is selected once again.
PIN CONFIGURATION
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DIP/SOIC |
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INC |
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8 |
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VCC |
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U/D |
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CS |
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VH |
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3 |
X9312 |
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VL |
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VSS |
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VW |
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3863 FHD F02.1 |
PIN NAMES
Symbol |
Description |
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VH |
High Terminal |
VW |
Wiper Terminal |
VL |
Low Terminal |
VSS |
Ground |
VCC |
Supply Voltage |
U/D |
Up/Down Input |
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INC |
Increment Input |
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CS |
Chip Select Input |
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3865 PGM T01
2
X9312
DEVICE OPERATION
There are three sections of the X9312: 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 INC, U/D and CS inputs control the movement of the wiper along the resistor array. With CS set LOW the X9312 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 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 X9312 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 X9312, 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-up/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 X9312 and then move the wiper up and down until the proper trim is attained.
TIW/RTOTAL
The electronic switches on the X9312 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.
RTOTAL with VCC Removed
The end to end resistance of the array will fluctuate once VCC is removed.
SYMBOL TABLE
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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 |
from LOW |
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to HIGH |
to HIGH |
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May change |
Will change |
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from HIGH |
from HIGH |
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to LOW |
to 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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