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FN6588.1

January 21, 2008

Power-up and Power-down Requirements

There are no restrictions on the power-up or power-down

Pin Descriptions

fixed terminals of a mechanical potentiometer. The minimum

relation to wiper movement direction.

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

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.

The end-to-end resistance of the array will fluctuate once

FIGURE 13. DCP CONNECTION IN SHUTDOWN MODE

ISL23511