8
FN6588.2
September 9, 2015
Power-up and Power-down Requirements
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
RH
and V
RL
, i.e., V
CC
V
RH,
V
RL
.
The V
CC
ramp rate specification is always in effect.
Pin Descriptions
R
H
and R
L
The R
H
and R
L
pins of the ISL23511 are equivalent to the
fixed terminals of a mechanical potentiometer. The minimum
voltage is V
SS
and the maximum is V
CC
. The terminology of
R
H
and R
L
references the relative position of the terminal in
relation to wiper movement direction.
R
W
The R
W
pin is the wiper terminal of the potentiometer which
is equivalent to the movable terminal of a mechanical
potentiometer. The default wiper position at power-up is at
0tap.
PU
The debounced PU input is used to increment the wiper
position. An on-chip pull-up holds the PU
input HIGH. A
switch closure to ground or a LOW logic level will, after a
debounce time, move the wiper to the next adjacent higher
tap position.
PD
The debounced PD input is used to decrement the wiper
position. An on-chip pull-up holds the PD
input HIGH. A
switch closure to ground or a LOW logic level will, after a
debounce time, move the wiper to the next adjacent lower
tap position.
Device Operation
There are three sections of the ISL23511: the input control,
the counter and decode section and the resistor array. The
input control section operates just like an up/down counter.
The output of this counter is decoded to turn on a single
electronic switch, connecting a point on the resistor array to
the wiper output. The resistor array is comprised of 31
individual resistors connected in series. At either end of the
array and between each resistor is an electronic switch that
transfers the potential at that point to the wiper.
The ISL23511 is designed to interface directly to two push
button switches for effectively moving the wiper up or down.
The PU
and PD inputs increment or decrement a 5-bit
counter respectively. The output of this counter is decoded to
select one of the thirty-two wiper positions along the resistive
array. The wiper increment input, PU
and the wiper
decrement input, PD
are both connected to an internal
pull-up so that they normally remain HIGH. When pulled
LOW by an external push button switch or a logic LOW level
input, the wiper will be switched to the next adjacent tap
position.
Internal debounce circuitry prevents inadvertent switching of
the wiper position if PU
or PD remain LOW for less than
15ms, typical. Each of the buttons can be pushed either
once for a single increment/decrement or continuously for a
multiple increments/decrements. The number of
increments/decrements of the wiper position depend on how
long the button is being pushed. When making a continuous
push, after the first second, the increment/decrement speed
increases. For the first second, the device will be in the slow
scan mode. Then, if the button is held for longer than 1s, the
device will go into the fast scan mode. As soon as the button
is released, the ISL23511 will return to a stand-by condition.
If both PU
and PD buttons are pulled low more than 15ms
from each other, all commands are ignored upon release of
ALL buttons.
The wiper, when at either fixed terminal, acts like its
mechanical equivalent and does not move beyond the last
position. That is, the counter does not wrap around when
clocked to either extreme.
Shutdown Mode
The ISL23511 enters into Shutdown Mode if both PU and PD
inputs are kept LOW for 2s. In this mode, the resistors array
is totally disconnected from its R
H
pin and the wiper is moved
to the position closest to the R
L
pin, as shown in Figure 13.
Note that PU
and PD inputs must be brought LOW within t
DB
time window of 15ms (see “Shutdown Mode Timing” on
page 5) otherwise all commands will be ignored until both
inputs are released.
Holding either PU
or PD input LOW for more than 15ms will
exit shutdown mode and return wiper to prior shutdown
position. If PU
or PD will be held LOW for more than 250ms,
the ISL23511 will start auto-increment or auto-decrement of
wiper position.
R
TOTAL
with V
CC
Removed
The end-to-end resistance of the array will fluctuate once
V
CC
is removed.
R
L
R
W
R
H
FIGURE 13. DCP CONNECTION IN SHUTDOWN MODE
ISL23511
