MAX9765ETJ MAXIM [Maxim Integrated Products], MAX9765ETJ Datasheet - Page 24

• Manufacturer Part Number: MAX9765ETJ
• Description: 750mW Audio Amplifiers with Headphone Amp, Microphone Preamp, and Input Mux
• Manufacturer: MAXIM [Maxim Integrated Products]

750mW Audio Amplifiers with Headphone Amp,
Microphone Preamp, and Input Mux
section. For example, θ
+42°C/W.
The increase in power delivered by the BTL configura-
tion directly results in an increase in internal power dis-
sipation over the single-ended configuration. The
maximum power dissipation for a given V
given by the following equation:
If the power dissipation for a given application exceeds
the maximum allowed for a given package, either reduce
V
temperature, or add heatsinking to the device. Large
output, supply, and ground PC board traces improve the
maximum power dissipation in the package.
Thermal-overload protection limits total power dissipa-
tion in these devices. When the junction temperature
exceeds +150°C, the thermal-protection circuitry dis-
ables the amplifier output stage. The amplifiers are
enabled once the junction temperature cools by 8°C.
This results in a pulsing output under continuous ther-
mal-overload conditions as the device heats and cools.
External feedback components set the gain of the
MAX9765/MAX9766/MAX9767. Resistor R
gain of the input amplifier (A
the gain of the second-stage amplifier (A
Combining A
ended gain of the device as follows:
24
DD
(
A
MAX
V
, increase load impedance, decrease the ambient
______________________________________________________________________________________
=
A
9765
VIN
A
VIN
×
/
MAX
VIN
A
= −
VOUT
A
and A
P
9766
VIN



DISS MAX
15
R
= −
IN
k
= −
)
(
Ω
VOUT






R
R
,
15
JA
IN
R
F
)
A
Component Selection
, R
IN
k
=
VOUT
Ω
of the QFN package is
VIN
2
(
IN
π

 × −

Gain-Setting Resistors
MAX
V
2
DD
) and resistor R
R
and R
L
= −
2
9767






15
15
F
R
R
VOUT
k
DD
)
F
set the single-
k
F
Ω
Ω

 = +

IN
and load is



):
sets the



F
R
R
IN
sets
F



As shown, the two-stage amplifier architecture results
in a noninverting gain configuration, preserving relative
phase through the MAX9765/MAX9766. The gain of the
device in BTL mode is twice that of the single-ended
mode. Choose R
between 15kΩ and 100kΩ.
The input capacitor (C
a highpass filter that removes the DC bias from an
incoming signal. The AC-coupling capacitor allows the
amplifier to bias the signal to an optimum DC level.
Assuming zero-source impedance, the -3dB point of
the highpass filter is given by:
Choose R
section. Choose the C
the lowest frequency of interest. Setting f
affects the amplifier’s low-frequency response. Use
capacitors whose dielectrics have low-voltage coeffi-
cients, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as
ceramics, may result in an increased distortion at low
frequencies.
Other considerations when designing the input filter
include the constraints of the overall system,
the actual frequency band of interest, and click-and-
pop suppression. Although high-fidelity audio calls for
a flat gain response between 20Hz and 20kHz,
portable voice-reproduction devices such as cellular
phones and two-way radios need only concentrate on
the frequency range of the spoken human voice (typi-
cally 300Hz to 3.5kHz). In addition, speakers used in
portable devices typically have a poor response below
150Hz. Taking these two factors into consideration, the
input filter may not need to be designed for a 20Hz to
20kHz response, saving both board space and cost
due to the use of smaller capacitors.
IN
according to the Gain-Setting Resistors
IN
f
−
3
dB
between 10kΩ and 15kΩ and R
IN
IN
=
), in conjunction with R
2π
such that f
R C
IN IN
1
-3dB
-3dB
is well below
Input Filter
IN
too high
, forms
F