max9706etxt Maxim Integrated Products, Inc., max9706etxt Datasheet - Page 19

• Manufacturer Part Number: max9706etxt
• Description: 3-channel, 2.3w, Filterless Class D Amplifiers With Active Crossover
• Manufacturer: Maxim Integrated Products, Inc.

The headphone sense input (HPS) monitors the head-
phone jack, and automatically configures the MAX9706
based upon the voltage applied at HPS. A voltage of
less than 0.8V sets the MAX9706 to speaker mode and
disables the headphone amplifiers. A voltage of greater
than 2V disables the speaker amplifiers and enables
the headphone amplifiers. The HPS input features a
built-in 65ms debounce period to prevent audible
“chatter” when inserting or removing headphones.
For automatic headphone detection, connect HPS to
the control pin of a 3-wire headphone jack as shown in
Figure 9. With no headphone present, the output
impedance of the headphone amplifier pulls HPS to
less than 0.8V. When a headphone plug is inserted into
the jack, the control pin is disconnected from the tip
contact and HPS is pulled to V
600kΩ pullup. When driving HPS from an external logic
source, drive HPS low when the MAX9706 is shut
down. Place a 10kΩ resistor in series with HPS and the
headphone jack to ensure high ESD protection.
The MAX9706/MAX9707 feature comprehensive click-
and-pop suppression that eliminates audible transients
on startup and shutdown.
While in shutdown, the H-bridge is in a high-impedance
state. During startup or power-up, the input amplifiers
are muted and an internal loop sets the modulator bias
voltages to the correct levels, preventing clicks and
pops when the H-bridge is subsequently enabled.
Figure 9. HPS Configuration
SHDN
3-Channel, 2.3W, Filterless Class D Amplifiers
SHUTDOWN
CONTROL
______________________________________________________________________________________
HPS
HPR
Click-and-Pop Suppression
HPL
MAX9706
Headphone Sense Input (HPS)
1.4kΩ
600kΩ
1.4kΩ
DD
V
DD
through the internal
The MAX9706/MAX9707 feature current limiting and
thermal protection to protect the device from short cir-
cuits and overcurrent conditions. If the current on any
output exceeds the current limit (1.5A typ) the internal
circuitry shuts off for 50µs then turns back on. If the
overload condition is still present after 50µs, the internal
circuitry shuts off again. The amplifier output pulses in
the event of a continuous overcurrent condition. The
headphone amplifier outputs become high impedance
in the event of an overcurrent condition. The speaker
amplifier’s current-limiting protection clamps the output
current without shutting down the outputs.
The MAX9706/MAX9707 feature thermal-shutdown pro-
tection with temperature hysteresis. A rising die tem-
perature shuts down the device at +150°C. When the
die cools down to +143°C, the device is enabled. The
outputs pulsate as the temperature fluctuates between
the thermal limits.
The MAX9706/MAX9707 feature a 0.1µA shutdown
mode that reduces power consumption to extend bat-
tery life. Driving SHDN low disables the drive amplifiers,
bias circuitry, and charge pump and sets the head-
phone amplifier output impedance to 1.4kΩ.
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM out-
put. The filters add cost, increase the solution size of
the amplifier, and can decrease efficiency. The tradi-
tional PWM scheme uses large differential output
swings (2 x V
Any parasitic resistance in the filter components results
in a loss of power, lowering the efficiency.
The MAX9706/MAX9707 do not require an output filter.
The devices rely on the inherent inductance of the
speaker coil and the natural filtering of both the speak-
er and the human ear to recover the audio component
of the square-wave output. Eliminating the output filter
results in a smaller, less costly, more efficient solution.
Because the frequency of the MAX9706/MAX9707 out-
put is well beyond the bandwidth of most speakers,
voice coil movement due to the square-wave frequency
is very small. Although this movement is small, a speak-
er not designed to handle the additional power can be
damaged. For optimum results, use a speaker with a
series inductance >10µH. Typical 8Ω speakers for
portable audio applications exhibit series inductances
in the 20µH to 100µH range.
with Active Crossover
Current Limit and Thermal Protection
DD(P-P)
Applications Information
Filterless Class D Operation
) and causes large ripple currents.
Shutdown
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