AD5228 Analog Devices, Inc., AD5228 Datasheet - Page 11

• Manufacturer Part Number: AD5228
• Description: 32-position Manual Up/down Control Potentiometer
• Manufacturer: Analog Devices, Inc.

THEORY OF OPERATION
The AD5228 is a 32-position manual up/down digitally con-
trolled potentiometer with selectable power-on preset. The
AD5228 presets to midscale when the PRE pin is tied to ground
and to zero-scale when PRE is tied to V
is not allowed. The step-up and step-down operations require
the activation of the PU (push-up) and PD (push-down) pins.
These pins have 100 kΩ internal pull-up resistors that the PU
and PD activate at logic low. The common practice is to apply
external pushbuttons (tactile switches) as shown in Figure 30.
Because of the bounce mechanism commonly found in the
switches during contact closures, a single pushbutton press
usually generates numerous bounces during contact closure.
Note that the term pushbutton refers specifically to a
pushbutton tactile switch or a similar switch that has 10 ms or
less bounce time during contact closure. Figure 31 shows the
characteristics of one such switch, the KRS-3550 tactile switch.
Figure 32 and Figure 33 show close ups of the initial bounces
and end bounces, respectively.
PUSH-DOWN
PUSH-UP
1
BUTTON
BUTTON
CH1
1.00V
Figure 31. Typical Tactile Switch Characteristics
V
PU
PD
Figure 30. Typical Pushbutton Interface
DD
R1
R2
SCAN DETECT
DEBOUNCER
STEP/AUTO
CONTROL
DISCRETE
ADAPTIVE
UP/DOWN
M40.0ms
T
LOGIC
20.40%
DD
. Floating the PRE pin
PRE
A CH1
D
E
C
O
D
E
SCALE PRESET
ZERO- OR MID-
AD5228
2.38V
GND
Rev. 0 | Page 11 of 20
A
W
B
The following paragraphs describes the PU incrementing
operation. Similar characteristics apply to the PD decrementing
operation.
The AD5228 features an adaptive debouncer that monitors the
duration of the logic-low level of PU signal between bounces. If
the PU logic-low level signal duration is shorter than 7 ms, the
debouncer ignores it as an invalid incrementing command.
Whenever the logic-low level of PU signal lasts longer than
11 ms, the debouncer assumes that the last bounce is met and
therefore increments R
Repeatedly pressing the PU button for fast adjustment without
missing steps is allowed, provided that each press is not shorter
than t
an advanced video game player can press a pushbutton switch
in 40 ms.
PU
1
1
, which is 12 ms (see Figure 2). As a point of reference,
CH1
CH1
1.00V
1.00V
Figure 32. Close-Up of Initial Bounces
Figure 33. Close-Up of Final Bounces
WB
by one step.
M100µs
M10.0µs
T
T
20.20%
20.20%
A CH1
A CH1
2.38V
2.38V
AD5228