7
FN8095.2
March 29, 2006
Principles of Operation
The ISL90843 is an integrated circuit incorporating four
DCPs with their associated registers, and an I2C serial
interface providing direct communication between a host
and the potentiometers.
DCP Description
Each DCP is implemented with a combination of resistor
elements and CMOS switches. The physical ends of each
DCP are equivalent to the fixed terminals of a mechanical
potentiometer (RH and RL pins). The RW pin of each DCP is
connected to intermediate nodes, and is equivalent to the
wiper terminal of a mechanical potentiometer. The position
of the wiper terminal within the DCP is controlled by an 8-bit
volatile Wiper Register (WR). Each DCP has its own WR.
When the WR of a DCP contains all zeroes (WR<7:0>: 00h),
its wiper terminal (RW) is closest to its “Low” terminal (RL).
When the WR of a DCP contains all ones (WR<7:0>: FFh),
its wiper terminal (RW) is closest to its “High” terminal (RH).
As the value of the WR increases from all zeroes (00h) to all
ones (255 decimal), the wiper moves monotonically from the
position closest to RL to the closest to RH. At the same time,
the resistance between RW and RL increases monotonically,
while the resistance between RH and RW decreases
monotonically.
While the ISL90843 is being powered up, all four WRs are
reset to 80h (128 decimal), which locates RW roughly at the
center between RL and RH.
The WRs can be read or written directly using the I2C serial
interface as described in the following sections. The I2C
interface Address Byte has to be set to 00hex, 01hex,
02hex, and 03hex to access the WR of DCP0, DCP1, DCP2,
and DCP3 respectively.
I2C Serial Interface
The ISL90843 supports a bidirectional bus oriented protocol.
The protocol defines any device that sends data onto the
FIGURE 7. END TO END RTOTAL % CHANGE vs
TEMPERATURE
FIGURE 8. TC FOR VOLTAGE DIVIDER MODE IN ppm
FIGURE 9. MIDSCALE GLITCH, CODE 80h TO 7Fh (WIPER 0)
FIGURE 10. LARGE SIGNAL SETTLING TIME
Typical Performance Curves (Continued)
-1.50
-1.00
-0.50
0.00
0.50
1.00
1.50
-40
-20
0
204060
80
TEMPERATURE (°C)
END
TO
E
N
D
R
TOTA
L
CHANGE
(%)
5.5V
2.7V
-20
-10
0
10
20
32
82
132
182
232
TAP POSITION (DECIMAL)
TC
(ppm
/°C)
Wiper Movement Mid Point
From 80h to 7fh
Signal at Wiper (Wiper Unloaded)
SCL
Signal at Wiper
(Wiper Unloaded Movement
From ffh to 00h)
ISL90843