S9518 Datasheet, PDF (3/8 Pages) Summit Microelectronics, Inc. – Nonvolatile DACPOT Electronic Potentiometer With Debounced Push Button Interface

S9518
DEVICE OPERATION
There are five main blocks to the S9518: an 8-bit
EEPROM memory; input debounce circuits, control logic,
and 8-bit counter; 8-bit data register; decode section and
resistor ladder (DAC); and the buffer amplifier. The input
control section operates just like an up/down counter. The
output of this counter is fed to the data register and then
decoded to activate one of 255 electronic switches con-
nected to the resistor ladder. Each switch connects a point
on the ladder to the buffer amplifier input. When re-
quested, the contents of the counter can be stored in
EEPROM memory and retained for future use. The ladder
is comprised of 256 resistors of equal value connected in
series. At the bottom of the ladder and at the junctions of
the resistors there are electronic switches that transfer the
voltage at each point to the buffer amplifier and hence to
the output. The S9518 is designed to interface directly to
two push button switches that effectively move the poten-
tiometer wiper up or down. The UP and DWN inputs
increment or decrement the 8-bit counter respectively.
The data input to the DAC is decoded to select one of the
256 wiper positions along the resistive ladder. The wiper
increment input, UP and the wiper decrement input, DWN
are connected to internal pull-ups 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 UP or DWN remain LOW for less than
30ms (typical). Each of the buttons can be pushed either
once for a single increment/decrement or held low con-
tinuously for a multiple increments/decrements. The
number of increments/decrements of the wiper position
depends on how long the button is 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 one second the device will go into the
fast scan mode. As soon as the button is released the
S9518 will return to a standby condition. The DAC,
whether set to 00 or FF, acts like its mechanical equivalent
and does not move beyond the last position. That is, the
counter does not wrap around when clocked beyond FF
or below 00.
AUTOSTORE
The value of the counter is stored in EEPROM memory
whenever the chip senses a power-down of V_DD while
STR is enabled (held LOW). When power is restored, the
contents of the memory are recalled and the counter reset
to the last value stored. If AUTOSTORE is to be imple-
mented, STR is typically hard wired to GND. If STR is held
HIGH during power-up and then taken LOW, the wiper will
not respond to the UP or DWN inputs until STR is brought
HIGH and the store is complete. Figure 1.
Manual (Push Button) Store
When STR is not enabled (held HIGH) a push button
switch may be used to pull STR LOW and released to
perform a manual store of the wiper position in EEPROM
memory. Figure 2.
Effect of V_DD Removal
The resistor ladder, connected between V_H and V_L, does
not change value when V_DD is removed. However, the
buffer amplifier no longer functions and consequently a
high impedance appears at the V_OUT pin.
Figure 1: Typical circuit with STR store pin used in Figure 2: Typical circuit with STR store pin
AUTOSTORE mode
controlled by push button switch
VCC
3.3µF
8
1
VDD
UP
2 _DWN
7 _STR
GND ⁴
VH ³
VOUT 5
VL ⁶
VCC
20KΩ
8
1
VDD
UP
2 _DWN
7 _STR
VH
VOUT
3
5
VL ⁶
GND
2017 ILL4.0
3
2017 ILL3.0
2017-04 4/24/99