X90100 Datasheet, PDF (6/7 Pages) Xicor Inc. – NV Electronically Programmable Capacitor

X90100
and retained for future use. The capacitor array is comprised
of 31 individual capacitors connected in parallel. At one end
of each element is an electronic switch that connects it to the
sum.
The capacitor, when at either end of the range, 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 counter changes positions. If
the counter is moved several positions, multiple units are
connected to the total for t_IW (INC to C_TOTAL change). The
C_TOTAL value for the device can temporarily be increased by
a significant amount if the counter 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 capacitor is set to the value last stored.
Instructions and Programming
The INC, U/D and CS inputs control the movement of the
capacitor total value. 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 five bit counter.
The output of this counter is decoded to select one of thirty
two capacitor combinations for the capacitor array.
The value of the counter is stored in nonvolatile memory
whenever CS transitions HIGH while the INC input is also
HIGH.
Table of Values
Single-Ended Mode
Code
C_OUT = ₃₁ • 7.0 + 7.5 (pF)
0 ≤ Code ≤ 31
The system may select the X90100, move the capacitor
value and deselect the device without having to store the
latest count total in nonvolatile memory. After the count
movement is performed as described above and once the
new position is reached, the system must keep INC LOW
while taking CS HIGH. The new C_TOTAL value will be
maintained until changed by the system or until a power-
up/down cycle recalled the previously stored data.
This procedure allows the system to always power-up to a
preset value stored in nonvolatile memory; then during
system operation minor adjustments can 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 counter up and down until the proper trim is
attained.
Mode Selection
CS INC U/D
MODE
L
H Cap Value Up
L
L Cap Value Down
H
X Store Cap Position
H
X
X Standby Current
L
X No Store, Return To Standby
L
H Cap Value Up (not recommended)
L
L Cap Value Down (not recommended)
Differential Mode
C_OUT = Code • 0.35 + 1.00 (pF)
0 ≤ Code ≤ 31
C_p
X90100
C_m
X1
Oscillator
Circuit
X2
Example of a single-ended circuit
C_m
C_p
X90100
C_p
Oscillator
Circuit
C_s
Example of a differential mode circuit
6
FN8156.0
February 2, 2005