Rainbow Electronics MAX5440 - Manual (Page 7)

MAX5440
Stereo Volume Control
with Rotary Encoder Interface
Detailed Description
The MAX5440 dual, 40k
Ω logarithmic taper digital
potentiometer features a debounced up/down interface
for use with a simple rotary encoder without using a
microcontroller. Each potentiometer has 32 log-spaced
tap points with a buffered wiper output and replaces
mechanical potentiometers.
Mode Control (
MODE
)
The MAX5440 MODE input toggles between volume
and balance modes. Force MODE low to toggle
between volume and balance modes. For example, dri-
ving MODE low once while in volume-control mode
switches the MAX5440 to balance mode. Driving MODE
low again switches the MAX5440 back to volume mode.
MODE is internally pulled high with a 45k
Ω resistor to
V
LOGIC
. The MAX5440 powers up in volume-control
mode. Leave unconnected or connect to V
LOGIC
if bal-
ance mode is not required.
Rotary Encoder Interface
The MAX5440 interfaces with rotary encoder switches.
The rotary encoder is a contact closure type switch with
two outputs that connect to RENCODEA and
RENCODEB on the device. As the shaft is rotated,
RENCODEA and RENCODEB produce a gray code
count.
Figure 1 shows a typical rotary encoder interface.
State changes trigger a wiper movement and the direc-
tion of the count dictates the direction of wiper move-
ment. An increasing gray code count moves the wiper
up to a lower attenuation setting in volume mode and
towards a full right channel (CH1) in balance mode. A
decreasing gray code count moves the wiper down to a
higher attenuation in volume mode and towards a full left
channel (CH0) in balance mode. Both switch inputs are
internally pulled up to V
LOGIC by internal 45k
Ω resistors.
During rapid rotation, the inputs must be stable for at
least 20ms and have separation between state
changes by at least 40ms for the debounce circuitry to
accurately detect the input states.
Figure 1. Rotary Encoder Interface
MAX5440
B
RENCODEA
RENCODEB
ROTARY
ENCODER
A
GND
V
LOGIC
45k Ω 45k Ω
CLOCKWISE ROTATION
INCREASING GRAY CODE (AB) 11, 10, 00, 01, 11, 10, ETC.
COUNTERCLOCKWISE ROTATION
DECREASING GRAY CODE (AB) 11, 01, 00, 10, 11, 01, ETC.
CW
CLOSED CIRCUIT
OPEN CIRCUIT
OPEN CIRCUIT
CLOSED CIRCUIT
CHANNEL A
CHANNEL B
1/4 CYCLE PER DETENT
D D D D D D D D D D D D D D D D D
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