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MAX4364ESA+T

P1-P3P4-P6P7-P9P10-P12P13-P14
MAX4364/MAX4365
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
CC
and load is
given by the following equation:
If the power dissipation for a given application exceeds
the maximum allowed for a given package, reduce
V
CC
, increase load impedance, decrease the ambient
temperature or add heat sinking 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 the MAX4364/MAX4365. When the junction tem-
perature exceeds +160°C, the thermal protection
circuitry disables the amplifier output stage. The ampli-
fiers are enabled once the junction temperature cools
by 15°C. This results in a pulsing output under continu-
ous thermal overload conditions as the device heats
and cools.
The MAX4365 TDFN package features an exposed
thermal pad on its underside. This pad lowers the ther-
mal resistance of the package by providing a direct
heat conduction path from the die to the PC board.
Connect the exposed thermal pad to circuit ground by
using a large pad, ground plane, or multiple vias to the
ground plane.
Efficiency
The efficiency of the MAX4364/MAX4365 is calculated
by taking the ratio of the power delivered to the load to
the power consumed from the power supply. Output
power is calculated by the following equations:
where V
PEAK
is half the peak-to-peak output voltage. In
BTL amplifiers, the supply current waveform is a full-
wave rectified sinusoid with the magnitude proportional
to the peak output voltage and load. Calculate the sup-
ply current and power drawn from the power supply by
the following:
The efficiency of the MAX4364/MAX4365 is:
The device efficiency values in Table 1 are calculated
based on the previous equation and do include the
effects of quiescent current. Note that efficiency is low
at low output-power levels, but remains relatively con-
stant at normal operating, output-power levels.
Component Selection
Gain-Setting Resistors
External feedback components set the gain of both
devices. Resistors R
F
and R
IN
(see
Typical Application
Circuit/Functional Diagram
) set the gain of the amplifier
as follows:
Optimum output offset is achieved when R
F
= 20kΩ.
Vary the gain by changing the value of R
IN
. When using
the MAX4364/MAX4365 in a high-gain configuration
(greater than 8V/V), a feedback capacitor may be
required to maintain stability (see Figure 2). C
F
and R
F
limit the bandwidth of the device, preventing high-fre-
quency oscillations. Ensure that the pole created by C
F
and R
F
is not within the frequency band of interest.
Input Filter
The input capacitor (C
IN
), in conjunction with R
IN
forms
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
IN
according to the
Gain-Setting Resistors
section. Choose C
IN
such that f
-3dB
is well below the
lowest frequency of interest. Setting f
-3dB
too high
affects the low-frequency response of the amplifier. Use
capacitors whose dielectrics have low-voltage coeffi-
ƒ=
−3
1
2
dB
IN IN
RCπ
A
R
R
VD
F
IN
=×2
η
π
==
P
P
PR
V
OUT
IN
OUT L
CC
2
2
PV
V
R
IN CC
PEAK
L
=
⎛
⎝
⎜
⎞
⎠
⎟
2
π
I
V
R
CC
PEAK
L
=
2
π
P
V
R
OUT
PEAK
L
=
2
2
P
V
R
DISS MAX
CC
L
()
=
2
2
2
π
1.4W and 1W, Ultra-Small, Audio Power
Amplifiers with Shutdown
10 ______________________________________________________________________________________
cients, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as
ceramics, may result in an increase 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 suppres-
sion. 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 (typically 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.
BIAS Capacitor
The BIAS bypass capacitor, C
BIAS
, improves PSRR and
THD+N by reducing power-supply noise at the common-
mode bias node, and serves as the primary click-and-
pop suppression mechanism. C
BIAS
is fed from an
internal 25kΩ source, and controls the rate at which the
common-mode bias voltage rises at startup and falls
during shutdown. For optimum click-and-pop suppres-
sion, ensure that the input capacitor (C
IN
) is fully
charged (ten time constants) before C
BIAS
. The value of
C
BIAS
for best click-and-pop suppression is given by:
In addition, a larger C
BIAS
value yields higher PSRR.
C
CR
k
BIAS
IN IN
≥
⎡
⎣
⎢
⎤
⎦
⎥
10
25 Ω
MAX4364/MAX4365
1.4W and 1W, Ultra-Small, Audio Power
Amplifiers with Shutdown
______________________________________________________________________________________ 11
OUTPUT
POWER (W)
INTERNAL POWER
DISSIPATION (W)
EFFICIENCY (%)
0.25 0.55 31.4
0.50 0.63 44.4
0.75 0.63 54.4
1.00 0.59 62.8
1.25 0.53 70.2
1.40 0.48 74.3
V
CC
V
CC
C
IN
R
IN
R
F
C
F
C
BIAS
6
OUT-
IN+
BIAS
AUDIO INPUT
3
2
CLICKLESS/
POPLESS
SHUTDOWN
CONTROL
GND
SHDN
8
OUT+ 5
7
1
MAX4364
MAX4365
50k
Ω
50k
Ω
10k
Ω
10k
Ω
IN-4
Figure 2. High-Gain Configuration
Table 1. Efficiency in a 5V, 8Ω BTL System
MAX4364/MAX4365
Clickless/Popless Operation
Proper selection of AC-coupling capacitors (C
IN
) and
C
BIAS
achieves clickless/popless shutdown and startup.
The value of C
BIAS
determines the rate at which the
midrail bias voltage rises on startup and falls when enter-
ing shutdown. The size of the input capacitor also affects
clickless/popless operation. On startup, C
IN
is charged
to its quiescent DC voltage through the feedback resistor
(R
F
) from the output. This current creates a voltage tran-
sient at the amplifier’s output, which can result in an
audible pop. Minimizing the size of C
IN
reduces this
effect, optimizing click-and-pop suppression.
Supply Bypassing
Proper supply bypassing ensures low-noise, low-distor-
tion performance. Place a 0.1µF ceramic capacitor in
parallel with a 10µF ceramic capacitor from V
CC
to
GND. Locate the bypass capacitors as close to the
device as possible.
Adding Volume Control
The addition of a digital potentiometer provides simple
volume control. Figure 3 shows the MAX4364/MAX4365
with the MAX5407 log taper digital potentiometer used
as an input attenuator. Connect the high terminal of the
MAX5407 to the audio input, the low terminal to ground
and the wiper to C
IN
. Setting the wiper to the top posi-
tion passes the audio signal unattenuated. Setting the
wiper to the lowest position fully attenuates the input.
Layout Considerations
Good layout improves performance by decreasing the
amount of stray capacitance and noise at the amplifier’s
inputs and outputs. Decrease stray capacitance by min-
imizing PC board trace lengths, using surface-mount
components and placing external components as close
to the device as possible. Also refer to the
Power
Dissipation
section for heatsinking considerations.
1.4W and 1W, Ultra-Small, Audio Power
Amplifiers with Shutdown
12 ______________________________________________________________________________________
OUT+
AUDIO
INPUT
OUT-
IN-
1H
W3
C
IN
R
F
R
IN
4L
MAX4364
MAX4365
MAX5407
Figure 3. MAX4364/MAX4365 and MAX5160 Volume Control
Circuit
Chip Information
PROCESS: BiCMOS
µMAX
TDFN
2 7 SHDNIN+
8 OUT-1
1234
8765
BIAS
+
V
CC
GND 3 6
OUT+
SHDNOUT- V
CC
OUT+
IN-
IN+BIAS GND IN-
EP*
*CONNECT EP TO GND.
+
45
MAX4365
MAX4364
MAX4365
V
CC
OUT+IN-
1
2
8
7
OUT-
+
GNDBIAS
IN+
SHDN
SO
TOP VIEW
3
4
6
5
MAX4364
Pin Configurations
P1-P3P4-P6P7-P9P10-P12P13-P14

MAX4364ESA+T

Mfr. #:
Buy MAX4364ESA+T
Manufacturer:
Maxim Integrated
Description:
Audio Amplifiers 1.4W/1W Audio Power Amplifier
Lifecycle:
New from this manufacturer.
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