10
FN6678.2
September 9, 2015
Power-Up and 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
RH and RL
The RH
and RL pins of the ISL22511 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
RH and RL
references the relative position of the terminal in
relation to wiper movement direction.
RW
The RW pin is the wiper terminal of the potentiometer which
is equivalent to the movable terminal of a mechanical
potentiometer.
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.
ASE
The debounced ASE (AUTOSTORE enable) pin can be in
one of two states:
1. AUTOSTORE is enabled if ASE
is held LOW during
power up.
2. AUTOSTORE is disabled if ASE
is held HIGH during
power-up. A LOW to HIGH transition will initiate a manual
store operation. This is for the user who wishes to
connect a push button switch to this pin. For every valid
push, the ISL22511 will store the current wiper position to
the EEPROM.
Device Operation
There are three sections of the ISL22511: the input control,
counter and decode section; the EEPROM memory; 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. Under the proper
conditions, the contents of the counter can be stored in
EEPROM memory and retained for future use. 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 ISL22511 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 depends 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 1 second, the device will go into the
fast scan mode. As soon as the button is released, the
ISL22511 will return to a standby condition.
If two or more buttons are pressed simultaneously, all
commands are ignored upon release of ALL buttons, except
Shutdown Mode condition.
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.
AUTOSTORE
The value of the counter is stored in EEPROM memory after
2 seconds of no activity on PU
or PD inputs while ASE is
enabled (held LOW). When power is restored, the content of
the memory is recalled and the counter resets to the last
value stored.
If AUTOSTORE is to be implemented, ASE
is typically hard
wired to V
SS
. If ASE is held HIGH during power-up and then
taken LOW, the wiper will not respond to the PU
or PD inputs
until ASE
is brought HIGH and held HIGH.
Manual (Push Button) Store
When ASE is not enabled (held HIGH), a push button switch
may be used to pull ASE
LOW for more than 15ms and
released to perform a manual store of the wiper position.
During memory write cycle all inputs will be ignored.
ISL22511
