3
FN8200.0
March 28, 2005
PIN CONFIGURATION
PIN NAMES
PRINCIPLES OF OPERATION
The X9440 is a highly integrated microcircuit incorpo-
rating two resistor arrays, two voltage comparators
and their associated registers and counters; and the
serial interface logic providing direct communication
between the host and the digitally-controlled potenti-
ometers and voltage comparators.
Serial Interface
The X9440 supports the SPI interface hardware con-
ventions. The device is accessed via the SI input with
data clocked in on the rising SCK. CS
must be LOW
and the HOLD
and WP pins must be HIGH during the
entire operation.
The SO and SI pins can be connected together, since
they have three state outputs. This can help to reduce
system pin count.
Array Description
The X9440 is comprised of two resistor arrays and two
voltage comparators. Each array contains 63 discrete
resistive segments that are connected in series. The
physical ends of each array are equivalent to the fixed
terminals of a mechanical potentiometer (V
H
and V
L
inputs).
At both ends of each array and between each resistor
segment is a CMOS switch connected to the wiper
(V
W
) output. Within each individual array only one
switch may be turned on at a time. These switches are
controlled by a volatile wiper counter register (WCR).
The six bits of the WCR are decoded to select, and
enable, one of sixty-four switches.
The WCR may be written directly, or it can be changed
by transferring the contents of one of four associated
data registers into the WCR. These data registers and
the WCR can be read and written by the host system.
Voltage Comparator
The comparator compares the wiper voltage V
W
with
the external input voltage V
NI
. The comparator and its
logic level output are controlled by the shutdown,
latch, and enable bits of the analog control register
(ACR). Enable connects the comparator output to the
V
OUT
pin, Latch memorizes the output logic state, and
shutdown removes the analog section supply voltages
to save power. The analog control register (ACR) is
programmed using the SPI serial interface.
The ACR may be written directly, or it can be changed
by transferring the contents of one of four associated
data registers into the ACR. These data registers and
the ACR may be read and written by the host system.
Symbol Description
SCK Serial Clock
S1, SO Serial Data
A0-A1 Device Address
V
H0
-V
H1
,
V
L0
-V
L1
Potentiometers (terminal equivalent)
V
W0
–V
W1
Potentiometers (wiper equivalent)
V
NI0
, V
NI1
Comparator Input Voltages
V
OUT0,
V
OUT1
Buffered Comparator Outputs
WP Hardware Write Protection
V+,V- Analog and Voltage Comparator
Supplies
V
CC
System Supply Voltage
V
SS
System Ground
NC No Connection
V
CC
V
L0
V
H0
WP
SI
A1
1
2
3
4
5
6
7
8
9
10
24
23
22
21
20
19
18
17
16
15
V+
V
OUT0
V
NI0
NC
A0
SO
HOLD
SCK
NC
V
NI1
SOIC
X9440
V
SS
V
W0
14
13
11
12
CS
V
L1
V
H1
V
W1
V
OUT1
V-
1
2
3
4
5
6
7
8
9
10
24
23
22
21
20
19
18
17
16
15
TSSOP
X9440
14
13
11
12
SI
A1
V
L1
V
H1
V
W1
V
SS
NC
V-
V+
V
OUT1
V
OUT0
SCK
HOLD
V
NI1
V
NI0
S0
A0
V
CC
NC
V
L0
V
H0
V
W0
WP
CS
X9440
