Rainbow Electronics MAX9792 - Manual (Page 21)

MAX9791/MAX9792
Windows Vista-Compliant Class D Speaker
Amplifiers with DirectDrive Headphone Amplifiers
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A qualified BEEP signal consists of a 3.3V typical,
215Hz minimum signal that is present at BEEP for four
consecutive cycles. Once the first rising edge transition
is detected at BEEP, the beep circuit wakes up and
begins counting the beep cycles. Once four consecu-
tive cycles of a qualified beep signal are counted, the
device (speaker and headphone amplifiers) enables
within 400µs. If the first rising edge is not followed by
three consecutive rising edges within 16ms, the device
remains shutdown (i.e., glitch protection).
The device (speaker and headphone amplifiers) returns
to its programmed logic state once 246ms has elapsed
from the time the last rising edge was detected. This
246ms amplifier hold time ensures complete beep pro-
files are passed to the amplifier outputs (Figure 7).
Ground BEEP when the wake-on-beep feature is not
used. Do not leave BEEP unconnected.
Low-Dropout Linear Regulator
The LDO regulator can be used to provide a clean
power supply to a CODEC or other circuitry. The LDO
can be enabled independently of the audio amplifiers.
Set LDO_EN = AVDD to enable the LDO or set LDO_EN
= GND to disable the LDO. The LDO can provide up to
120mA of continuous current.
Speaker and Headphone Amplifier Enable
The MAX9791/MAX9792 feature control inputs for the
independent enabling of the speaker and headphone
amplifiers, allowing both to be active simultaneously
if required. Driving SPKR_EN high disables the speaker
amplifiers. Driving HP_EN low independently disables
the headphone amplifiers. For applications that
require only one of the amplifiers to be on at a given
time, connect SPKR_EN and HP_EN together, allowing
a single logic voltage to enable either the speaker or
the headphone amplifier as shown in Figure 8.
Shutdown
The MAX9791/MAX9792 feature a low-power shutdown
mode, drawing 0.1µA of supply current. By disabling
the speaker, headphone amplifiers, and the LDO, the
MAX9791/MAX9792 enter low-power shutdown mode.
Set SPKR_EN to AVDD and HP_EN and LDO_EN to
GND to disable the speaker amplifiers, headphone
amplifiers, and LDO, respectively.
CROSSTALK vs. FREQUENCY
(HEADPHONE MODE)
FREQUENCY (kHz)
CROSSTALK (dB)
10 1 0.1
-90
-80
-70
-60
-50
-40
-30
-20
-100
0.01 100
R L = 32 Ω
FS = 300mV RMS
V OUT = -20dBFS
LEFT TO RIGHT
COM AND SENSE
RIGHT TO LEFT
COM AND SENSE
LEFT TO RIGHT
COM AND SENSE
DISABLED
RIGHT TO LEFT
COM AND SENSE
DISABLED
Figure 6. MAX9791/MAX9792 COM and SENSE Inputs Reduce
Crosstalk
1 2 3 4
BEEP
SPKR AND HP
AMPS ENABLE
400 μs
240ms
16ms
Figure 7. Qualified BEEP Signal Timing