A
PPLICATION
N
OTES AND
D
EVELOPMENT
S
YSTEM
A V A I L A B L E
AN99 • AN115 • AN124 •AN133 • AN134 • AN135
Single Supply / Low Power / 256-tap / 2-Wire Bus
X9279
Single Digitally-Controlled (XDCP
TM
) Potentiometer
FEATURES
• 256 Resistor Taps
• 2-Wire Serial Interface for write, read, and
transfer operations of the potentiometer
• Wiper Resistance, 100
Ω
typical @ 5V
• 16 Nonvolatile Data Registers for Each
Potentiometer
• Nonvolatile Storage of Multiple Wiper Positions
• Power On Recall. Loads Saved Wiper Position on
Power Up.
• Standby Current < 5µA Max
• V
CC
: 2.7V to 5.5V Operation
• 50K
Ω
, 100K
Ω
versions of End to End Resistance
• Endurance: 100,000 Data Changes per Bit per
Register
• 100 yr. Data Retention
• 14-Lead TSSOP, 16-Lead CSP (Chip Scale
Package)
• Low Power CMOS
DESCRIPTION
The X9279 integrates a single digitally controlled
potentiometer (XDCP) on a monolithic CMOS
integrated circuit.
The digital controlled potentiometer is implemented
using 255 resistive elements in a series array. Between
each element are tap points connected to the wiper
terminal through switches. The position of the wiper on
the array is controlled by the user through the 2-Wire
bus interface. The potentiometer has associated with it
a volatile Wiper Counter Register (WCR) and a four
nonvolatile Data Registers that can be directly written
to and read by the user. The contents of the WCR
controls the position of the wiper on the resistor array
though the switches. Powerup recalls the contents of
the default data register (DR0) to the WCR.
The XDCP can be used as a three-terminal
potentiometer or as a two terminal variable resistor in
a wide variety of applications including control,
parameter adjustments, and signal processing.
FUNCTIONAL DIAGRAM
V
CC
R
H
2-Wire
Bus
Interface
Address
Data
Status
Write
Read
Transfer
Inc/Dec
Bus
Interface
and Control
Control
Power On Recall
Wiper Counter
Register (WCR)
Data Registers
16 Bytes
wiper
50KΩ and 100KΩ
256-taps
POT
V
SS
R
W
R
L
REV 1.1.7 2/6/03
www.xicor.com
Characteristics subject to change without notice.
1 of 24
X9279
DETAILED FUNCTIONAL DIAGRAM
V
CC
Bank 0
DR0 DR1
Power On Recall
WIPER
COUNTER
REGISTER
(WCR)
50KΩ and 100KΩ
256-taps
R
H
SCL
SDA
A2
A1
A0
WP
INTERFACE
AND
CONTROL
CIRCUITRY
DATA
DR2 DR3
R
L
R
W
Bank 1
DR0 DR1
Bank 2
DR0 DR1
Bank 3
DR0 DR1
DR2 DR3
Control
DR2 DR3
DR2 DR3
12 additional nonvolatile registers
3 Banks of 4 registers x 8-bits
V
SS
CIRCUIT LEVEL APPLICATIONS
• Vary the gain of a voltage amplifier
• Provide programmable dc reference voltages for
comparators and detectors
• Control the volume in audio circuits
• Trim out the offset voltage error in a voltage amplifier
circuit
• Set the output voltage of a voltage regulator
• Trim the resistance in Wheatstone bridge circuits
• Control the gain, characteristic frequency and
Q-factor in filter circuits
• Set the scale factor and zero point in sensor signal
conditioning circuits
• Vary the frequency and duty cycle of timer ICs
• Vary the dc biasing of a pin diode attenuator in RF
circuits
• Provide a control variable (I, V, or R) in feedback
circuits
SYSTEM LEVEL APPLICATIONS
• Adjust the contrast in LCD displays
• Control the power level of LED transmitters in
communication systems
• Set and regulate the DC biasing point in an RF power
amplifier in wireless systems
• Control the gain in audio and home entertainment
systems
• Provide the variable DC bias for tuners in RF wireless
systems
• Set the operating points in temperature control
systems
• Control the operating point for sensors in industrial
systems
• Trim offset and gain errors in artificial intelligent
systems
REV 1.1.7 2/6/03
www.xicor.com
Characteristics subject to change without notice.
2 of 24
X9279
PIN CONFIGURATION
CSP
4
3
2
1
TSSOP
NC
A0
NC
A2
SCL
SDA
V
SS
14
1
X9279
13
2
3
12
4
11
5
10
6
9
8
7
V
CC
R
L
R
H
R
W
A3
A1
WP
A
B
C
D
A0
A2
SCL
V
CC
NC
NC
R
L
NC
NC
WP
R
H
R
W
A3
A1
SDA VSS
PIN ASSIGNMENTS
Pin
TSSOP
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Pin
CSP
B2, B3
A4
C2, C3
B4
C4
D4
D3
D2
D1
C1
B1
A1
A2
A3
Symbol
NC
A0
NC
A2
SCL
SDA
V
SS
WP
A1
A3
R
W
R
H
R
L
V
CC
No Connect
Function
Device Address for 2-Wire bus.
No Connect
Device Address for 2-Wire bus.
Serial Clock for 2-Wire bus.
Serial Data Input/Output for 2-Wire bus.
System Ground.
Hardware Write Protect
Device Address for 2-Wire bus.
Device Address for 2 wire-bus.
Wiper Terminal of the Potentiometer.
High Terminal of the Potentiometer.
Low Terminal of the Potentiometer.
System Supply Voltage.
REV 1.1.7 2/6/03
www.xicor.com
Characteristics subject to change without notice.
3 of 24
X9279
PIN DESCRIPTIONS
Bus Interface Pins
S
ERIAL
D
ATA
I
NPUT
/O
UTPUT
(SDA)
The SDA is a bidirectional serial data input/output pin
for a 2-Wire slave device and is used to transfer data
into and out of the device. It receives device address,
opcode, wiper register address and data sent from an
2-Wire master at the rising edge of the serial clock
SCL, and it shifts out data after each falling edge of the
serial clock SCL.
It is an open drain output and may be wire-ORed with
any number of open drain or open collector outputs. An
open drain output requires the use of a pull-up resistor.
For selecting typical values, refer to the guidelines for
calculating typical values on the bus pull-up resistors
graph.
S
ERIAL
C
LOCK
(SCL)
This input is used by 2-Wire master to supply 2-Wire
serial clock to the X9279.
D
EVICE
A
DDRESS
(A2 - A0)
The Address inputs are used to set the least significant
3 bits of the 8-bit slave address. A match in the slave
address serial data stream must be made with the
Address input in order to initiate communication with
the X9279. A maximum of 8 devices may occupy the 2-
Wire serial bus.
Potentiometer Pins
R
H
, R
L
The R
H
and R
L
pins are equivalent to the terminal
connections on a mechanical potentiometer.
R
W
The wiper pin is equivalent to the wiper terminal of a
mechanical potentiometer.
Bias Supply Pins
S
YSTEM
S
UPPLY
V
OLTAGE
(V
CC
)
AND
S
UPPLY
G
ROUND
(V
SS
)
The V
CC
pin is the system supply voltage. The V
SS
pin
is the system ground.
Other Pins
N
O
C
ONNECT
No connect pins should be left open. This pins are used
for Xicor manufacturing and testing purposes.
H
ARDWARE
W
RITE
P
ROTECT
I
NPUT
(WP)
The WP pin when LOW prevents nonvolatile writes to
the Data Registers.
REV 1.1.7 2/6/03
www.xicor.com
Characteristics subject to change without notice.
4 of 24
X9279
PRINCIPLES OF OPERATION
The X9279 is a integrated microcircuit incorporating a
resistor array and associated registers and counter
and the serial interface logic providing direct
communication between the host and the digitally
controlled potentiometers. This section provides detail
description of the following:
– Resistor Array Description.
– Serial Interface Description.
– Instruction and Register Description.
Array Description
The X9279 is comprised of a resistor array (see Figure
1). The array contains, in effect, 255 discrete resistive
segments that are connected in series. The physical
ends of each array are equivalent to the fixed terminals
of a mechanical potentiometer (R
H
and R
L
inputs).
At both ends of each array and between each resistor
segment is a CMOS switch connected to the wiper
(R
W
) output. Within each individual array only one
switch may be turned on at a time.
Figure 1. Detailed Potentiometer Block Diagram
These switches are controlled by a Wiper Counter
Register (WCR). The 8-bits of the WCR (WCR[7:0])
are decoded to select, and enable, one of 256 switches
(see Table 1).
The WCR may be written directly. These Data
Registers can the WCR can be read and written by the
host system.
Power Up and Down Recommendations.
There are no restrictions on the power-up or power-
down conditions of V
CC
and the voltages applied to the
potentiometer pins provided that V
CC
is always more
positive than or equal to V
H
, V
L
, and V
W
, i.e., V
CC
≥
V
H
,
V
L
, V
W
. The V
CC
ramp rate specification is always in
effect.
SERIAL DATA PATH
FROM INTERFACE
CIRCUITRY
REGISTER 0
(DR0)
8
BANK_0 Only
SERIAL
BUS
INPUT
REGISTER 1
(DR1)
8
PARALLEL
BUS
INPUT
WIPER
COUNTER
REGISTER
(WCR)
INC/DEC
LOGIC
UP/DN
MODIFIED SCK
UP/DN
CLK
C
O
U
N
T
E
R
D
E
C
O
D
E
R
H
REGISTER 2
(DR2)
REGISTER 3
(DR3)
IF WCR = 00[H] THEN R
W
= R
L
IF WCR = FF[H] THEN R
W
= R
H
R
L
R
W
REV 1.1.7 2/6/03
www.xicor.com
Characteristics subject to change without notice.
5 of 24
京公网安备 11010802033920号
EEWORLD
