CAT5120, CAT5121, CAT5122
16-Tap MiniPot™ Digitally Programmable
Potentiometers with 2-Wire Interface
FEATURES
0.3µA Ultra-low standby current
Single-supply operation: 2.7V to 5.5V
Glitchless switching between resistor taps
Power-on reset to midscale
2-wire up/down serial interface
Resistance values: 10kΩ, 50kΩ and 100kΩ
Available in SC-70 and SOT-23 packages
DESCRIPTION
CAT5120/5121/5122 linear-taper digitally programmable
potentiometers perform the same function as a
mechanical potentiometer or a variable resistor. These
devices consist of a fixed resistor and a wiper contact
with 16-tap points that are digitally controlled through a
2-wire up/down serial interface.
The CAT5120 is configured as a potentiometer. The
CAT5121 and CAT5122 are configured as variable
resistors. See
Pin Configurations
for part functionality.
Three resistance values are available: 10kΩ, 50kΩ and
100kΩ. These are available in space-saving 5-pin and
6-pin SC-70 and SOT-23 packages.
APPLICATIONS
LCD screen adjustment
Volume control
Mechanical potentiometer replacement
Gain adjustment
Line impedance matching
FUNCTIONAL DIAGRAM
H
V
DD
GND
For Ordering Information details, see page 10.
16-POSITION
DECODER
CS
UP-DOWN
COUNTER
W
U/D
PIN CONFIGURATION
SC-70
SOT-23
V
DD
1
6
H
V
DD
1
SC-70
SOT-23
5
H
L
PIN DESCRIPTIONS
Name
V
DD
GND
4
CS
Description
Power Supply
Ground
¯¯¯¯¯
¯¯
Up/Down Control Input. With CS low, a
low-to-high transition increments or
decrements the wiper position.
¯¯
Chip Select Input. A high-to-low CS
transition determines the mode:
¯
increment if U/D is high, or decrement if
¯
U/D is low.
Low Terminal of Resistor
Wiper Terminal of Resistor
High Terminal of Resistor
GND 2
5 W
GND 2
CAT5120
U/D 3
4
CS
U/D 3
CAT5122
¯
U/D
SC-70
SOT-23
V
DD
1
6
H
¯¯
CS
L
W
H
GND 2
5 L
CAT5121
U/D 3
4
CS
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
1
Doc. No. MD-2121 Rev. E
CAT5120, CAT5121, CAT5122
ABSOLUTE MAXIMUM RATINGS
(1)
Parameters
V
DD
to GND
All Other Pins to GND
Input and Output Latch-Up Immunity
Maximum Continuous Current into H, L and W
100kΩ
50kΩ
10kΩ
Continuous Power Dissipation (T
A
= +70ºC)
5-pin SC-70
(2)
6-pin SC-70
(2)
Operating Temperature Range
Junction Temperature
Storage Temperature Range
Soldering Temperature (soldering, 10s)
Ratings
-0.3 to +6
-0.3 to (V
DD
+ 0.3)
±200
±0.6
±1.3
±1.3
247
245
-40 to +85
+150
-65 to +150
+300
Units
V
V
mA
mA
mW
ºC
ºC
ºC
ºC
ELECTRICAL CHARACTERISTICS
V
DD
= 2.7V to 5.5V, V
H
= V
DD
, V
L
= 0, T
A
= -40ºC to +85ºC. Typical values are at V
DD
= 2.7V, T
A
= 25ºC, unless
otherwise noted.
Parameter
DC Performance
Resolution
End-to-End Resistance (-00)
End-to-End Resistance (-50)
End-to-End Resistance (-10)
End-to-End Resistance Tempco
Ratiometric Resistance Tempco
Integral Nonlinearity
Differential Nonlinearity
Zero/Full-Scale Error
Wiper Resistance
Digital Inputs
Input High Voltage
Input Low Voltage
V
IH
V
IL
0.7 x V
DD
0.3 x V
DD
V
V
R
W
INL
DNL
±0.1
200
TC
R
16
75
37.5
7.5
100
50
10
200
5
±0.5
±0.5
±0.5
600
125
62.5
12.5
ppm/ºC
ppm/ºC
LSB
LSB
LSB
Ω
kΩ
Taps
Symbol
Conditions
Min
Typ
Max
Units
Notes:
(1) Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings
only, and functional operation of the device at these or any other conditions outside of those listed in the operational sections of this
specification is not implied. Exposure to any absolute maximum rating for extended periods may affect device performance and reliability.
(2) Derate 3.1mW/ºC above T
A
= +70ºC
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
2
Doc. No. MD-2121 Rev. E
CAT5120, CAT5121, CAT5122
ELECTRICAL CHARACTERISTICS
(continued)
Parameter
¯
¯¯
U/D Mode to CS Setup
¯¯
¯
CS to U/D Step Setup
¯¯
¯
CS to U/D Step Hold
¯
U/D Step Low Period
¯
U/D Step High Period
(1)
¯¯¯¯¯
Up/Down Toggle Rate
Output Settling Time
Power Supply
Supply Voltage
Active Supply Current
(3)
(4)
(2)
Symbol
t
CU
t
CI
t
IC
t
IL
t
IH
f
TOGGLE
t
SETTLE
Conditions
Min
25
50
25
25
25
Typ
Max
Units
ns
ns
ns
ns
ns
Timing Characteristics (Figures 1, 2)
1
100kΩ variable resistor
configuration, C
L
= 10pF
100kΩ potentiometer
configuration, C
L
= 10pF
2.7
V
DD
= +5V
0.3
1
MHz
μs
0.25
V
DD
I
DD
I
SB
5.5
25
1
V
µA
µA
Standby Supply Current
TYPICAL OPERATING CHARACTERISTICS
T
A
= 25ºC, unless otherwise noted.
V
DD
= 2.7V
50K
V
DD
= 5.5V
0
4
8 12 16 20 24
WIPER POSITION
28
32
TEMPERATURE (ºC)
V
DD
= 5.5V
V
DD
= 2.7V
TEMPERATURE (ºC)
Notes:
(1)
(2)
(3)
(4)
Up/Down Toggle Rate:
f
TOGGLE
=
1
t
SETTLE
Typical settling times are dependent on end-to-end resistance.
Supply current measured while changing wiper tap, f
TOGGLE
= 1MHz.
Supply current measured while wiper position is fixed.
3
Doc. No. MD-2121 Rev. E
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT5120, CAT5121, CAT5122
FUNCTIONAL DESCRIPTION
The CAT5120/5121/5122 consist of a fixed resistor and
a wiper contact with 16-tap points that are digitally
controlled through a2-wire up/down serial interface.
Three end-to-end resistance values are available: 10kΩ,
50kΩ and 100kΩ.
The CAT5120 is designed to operate as a potentiometer.
In this configuration, the low terminal of the resistor array
is connected to ground (pin 2).
The CAT5122 performs as a variable resistor. In this
device, the wiper terminal and high terminal of the
resistor array is connected at pin 5. The CAT5121 is a
similar variable resistor, except the low terminal is
connected to pin 5.
Digital Interface Operation
The MiniPots have two modes of operation when the
serial interface is active: increment and decrement
¯¯
mode. The serial interface is only active when CS is low.
¯¯
¯
The CS and U/D inputs control the position of the
¯¯
wiper along the resistor array. When CS transitions
from high to low, the part will go into increment mode
¯
if U/D input is high, and into decrement mode when
¯
U/D input is low. Once the mode is set, the device will
¯¯
remain in that mode until CS goes high again. A low-
¯
to-high transition at the U/D pin will increment or
decrement the wiper position depending on the
current mode (Figures 1 and 2).
¯¯
When the CS input transitions to high (serial interface
inactive), the value of the counter is stored and the
wiper position is maintained.
Note that when the wiper reaches the maximum (or
minimum) tap position, the wiper will not wrap around
to the minimum (or maximum) position.
Power-On Reset
All parts in this family feature power-on reset (POR)
circuitry that sets the wiper position to midscale at
power-up. By default, the chip is in the increment mode.
CS
t
CU
t
IL
U/D
t
IC
t
CI
t
SETTLE
W
Note: "W" is not a digital signal. It represents wiper transitions.
t
IH
t
SETTLE
Figure 1. Serial Interface Timing Diagram, Increment Mode
CS
t
CU
t
IH
U/D
t
IC
t
IL
W
t
CI
t
SETTLE
t
SETTLE
Note: "W" is not a digital signal. It represents wiper transitions.
Figure 2. Serial Interface Timing Diagram, Decrement Mode
Doc. No. MD-2121 Rev. E
4
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
CAT5120, CAT5121, CAT5122
APPLICATIONS INFORMATION
The MiniPots are intended for circuits requiring
digitally controlled adjustable resistance, such as LCD
contrast control, where voltage biasing adjusts the
display contrast.
Alternative Positive LCD Bias Control
Use an op amp to provide buffering and gain on the
output of the CAT5120. Connect the mechanical
potentiometer to the positive input of a noninverting op
amp (Figure 3) to select a portion of the input signal
by digitally controlling the wiper terminal. Figure 4
shows a similar circuit for the CAT5121.
Adjustable Gain
Figure 5 shows how to use the variable resistor to
digitally adjust the gain of a noninverting op amp
configuration. Connect the CAT5121 in series with a
resistor to ground to form the adjustable gain control
of a noninverting amplifier. The Minipots have a low
5ppm/°C ratiometric tempco that allows for a very
stable adjustable gain configuration over temperature.
+5V
+5V
H
30V
W
V
OUT
CAT5121
L
30V
V
OUT
H
CAT5120
L
Figure 3. Positive LCD Bias Control
Figure 4. Positive LCD Bias Control
V
CC
V
IN
V
OUT
V
IN
V
CC
V
OUT
H
W
L
H
CAT5121
L
CAT5120
Figure 5a. Adjustable Gain Circuit
Figure 5b. Adjustable Gain Circuit
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice
5
Doc. No. MD-2121 Rev. E
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