X9268_06 Datasheet, PDF (6/22 Pages) Intersil Corporation – Dual Digitally-Controlled Potentiometers

X9268
PRINCIPLES OF OPERATION
The X9268 is a integrated microcircuit incorporating
four resistor arrays and their associated registers and
counters 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 X9268 is comprised of a resistor array (See
Figure 1). Each array contains 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).
Figure 1. Detailed Potentiometer Block Diagram
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.
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 Requirements.
At all times, the voltages on the potentiometer pins
must be less than V+ and more than V-. During power-
up and power-down, V_CC, V+, and V- must reach their
final values within 1msecs of each other. The V_CC
ramp rate spec is always in effect.
One of Two Potentiometers
SERIAL DATA PATH
SERIAL
R_H
FROM INTERFACE
CIRCUITRY
BUS
INPUT
REGISTER 0
(DR0)
REGISTER 1
(DR1)
C
O
U
8
8
PARALLEL
BUS
INPUT
N
T
E
R
REGISTER 2
(DR2)
REGISTER 3
(DR3)
WIPER
D
COUNTER
E
REGISTER ^C
(WCR)
O
D
E
INC/DEC
IF WCR = 00[H] THEN R_W = R_L
IF WCR = FF[H] THEN R_W = R_H
UP/DN
LOGIC
UP/DN
MODIFIED SCL _CLK
R_L
R_W
6
FN8172.4
August 29, 2006