Rainbow Electronics MAX5440 - Manual (Page 12)

MAX5440
Power-On Reset
The power-on comparators monitor (V DD - V SS ) and
(V
LOGIC
- GND). A power-on reset is initiated when
either of the supplies is brought back to the normal
operating voltage. The power-on reset feature sets both
wipers to -12dB. The wipers initially wake up in mute
mode (-90dB) and move to the -12dB position when V
H
= V L to eliminate clicks and pops during power-up.
With DC inputs at V
H
and V
L
, the wipers move after
exceeding the timeout period. A power-on reset places
the MAX5440 in volume-control mode.
Shutdown (
SHDN
)
Upon entering shutdown, the MAX5440 stores the last
wiper settings. The wipers move to the L_ end of the
resistor string. The wipers move to the L_ end of the
resistor string when V
H = V L to eliminate clicks and pops
during shutdown. With DC inputs at V H and V L , the
wipers move after exceeding the timeout period. Exiting
shutdown restores the wipers to their previous settings.
Mute Function (
MUTE
)
The MAX5440 features a mute function input, MUTE.
Successive low pulses on MUTE toggle its setting.
Activating the mute function forces both wipers to maxi-
mum attenuation (-90dB typ). Deactivating the mute
function returns the wipers to their previous settings.
Rotating the encoder clockwise (increasing gray code
count) also deactivates mute, setting the wipers to their
previous positions. MUTE is internally pulled high with a
45k
Ω resistor to V
LOGIC . When both wipers are in the
tap 31 position (-62dB attenuation) further commands
to lower the volume (decreasing gray code count)
place the wipers in the mute position (see
Table 1).
Rotating the encoder to a lower attenuation or a pulse
to MUTE returns the wipers to tap 31.
Mode Indicator (
MODEIND
)
The open-drain MODEIND indicates volume-control
mode or balance-control mode for the MAX5440.
Connect MODEIND to an LED with a series resistor to
V
LOGIC . When the LED is on, the MAX5440 is in balance-
control mode. When the LED is off, the MAX5440 is in
volume-control mode. See the Mode Control (
MODE )
section for more detail on switching between modes.
Level Indicator LEDs
The MAX5440 includes five indicator LED drivers to dis-
play the current wiper settings in either volume or bal-
ance mode. Connect the LEDIND_ outputs to the LEDs
and to V
LOGIC through a series resistor as shown in the
typical application circuits.
In volume-control mode, all LEDs are off when the
wipers reach the highest attenuation levels (mute). All
LEDs are on at the lowest attenuation levels (0dB).
Table 2 shows the LED display as the wipers transition
through various attenuation levels.
In balance-control mode, only one LED is on at a time
to indicate the current balance setting. Figure 5 shows
the LEDs display for the current balance setting. When
LED2 is on, the display indicates that the channels are
centered or balanced at a set volume level. Turning the
encoder clockwise (an increasing gray code count)
turns LED3 on to represent a balance shift towards
channel 1. When LED4 turns on, the balance shifts
completely toward channel 1 and channel 0 is fully
attenuated. From a balanced position, turning the
encoder counterclockwise (a decreasing gray code
count) turns on LED1, and then LED0 to indicate a bal-
ance shift towards channel 0.
Stereo Volume Control
with Rotary Encoder Interface
12 ______________________________________________________________________________________
Table 2. LED Settings in Volume Mode
VOLUME LED OUTPUTS (1 = LED IS ON)
VOLUME POSITION (dB)
LED0 LED1 LED2 LED3 LED4
0 to -8 1 1 1 1 1
-10 to -18 1 1 1 1 0
-20 to -28 1 1 1 0 0
-30 to -38 1 1 0 0 0
-40 to -52 1 0 0 0 0
-54 to mute (-90) 0 0 0 0 0