General Description
The MAX9715 high-efficiency, stereo, Class D audio
power amplifier provides up to 2.8W per channel into a
4Ω speaker with a 5V supply. Maxim’s second-generation
Class D technology features robust output protection,
high efficiency, and high power-supply rejection (PSRR)
while eliminating the need for output filters. Selectable
gain settings, +10.5dB or +9.0dB, adjust the amplifier
gain to suit the audio input level and speaker load.
The MAX9715 features high PSRR (71dB at 1kHz),
allowing for operation from noisy supplies without additional regulation. Comprehensive click-and-pop suppression eliminates audible clicks and pops at startup
and shutdown. The MAX9715 operates from a single 5V
supply and consumes only 12mA of supply current.
Integrated shutdown control reduces supply current to
less than 100nA.
The MAX9715 is fully specified over the extended
-40°C to +85°C temperature range and is available in a
thermally enhanced 16-pin TQFN-EP package.
Applications
High-End Notebook Audio
LCD Projectors
Portable Audio
Multimedia Docking Stations
Features
♦ 5V Single-Supply Operation
♦ Spread-Spectrum Modulator Reduces EMI
♦ 2.8W, Class D, Stereo Speaker Amplifier (4Ω)
♦ Filterless Class D Requires No LC Output Filter
♦ High PSRR (71dB at 1kHz)
♦ 86% Efficiency (R
L
= 8Ω, P
OUT
= 1W)
♦ Low-Power Shutdown Mode
♦ Integrated Click-and-Pop Suppression
♦ Low Total Harmonic Distortion: 0.06% at 1kHz
♦ Short-Circuit and Thermal Protection
♦ Internal Gain, +9.0dB or +10.5dB
♦ Available in Space-Saving Package
16-Pin Thin QFN-EP (5mm x 5mm x 0.8mm)
MAX9715
2.8W, Low-EMI, Stereo, Filterless
Class D Audio Amplifier
________________________________________________________________
Maxim Integrated Products
1
Pin Configurations
Ordering Information
Block Diagram
19-3589; Rev 2; 7/08
+
Denotes a lead-free/RoHS-compliant package.
*
EP = Exposed pad.
PART TEMP RANGE PIN-PACKAGE
MAX9715ETE+ -40°C to +85°C 16 TQFN-EP*
Typical Operating Circuit/Functional Diagram appears at
end of data sheet.
EVALUATION KIT
AVAILABLE
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim's website at www.maxim-ic.com.
4.5V TO 5.5V SUPPLY
INR
GAIN
INL
CLASS D
AMPLIFIER
MAX9715
OUTR+
OUTR-
OUTL+
OUTL-
TOP VIEW
BIAS
V
INR
INL
PGND
OUTR+
12 11 10 9
13
DD
14
15
16
+
MAX9715
1234
PGND
OUTL+
TQFN
OUTR-
OUTL-
DD
PV
8
SHDN
GND
7
GAIN
6
N.C.
5
DD
PV
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD= PVDD= 5.0V, GND = PGND = 0V, V
SHDN
= VDD, C
BIAS
= 1μF, speaker impedance = 8Ω in series with 68μH connected between
OUT_+ and OUT_-, GAIN = +10.5dB, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
VDD, PVDD, to GND ...............................................................+6V
GND to PGND .......................................................-0.3V to +0.3V
Any Other Pin to PGND ............................. -0.3V to (V
DD
+ 0.3V)
Duration of OUT__ Short Circuit to PGND or PV
DD
....Continuous
Duration of OUT_+ Short Circuit between OUT_- ......Continuous
Continuous Current Into/Out of (PV
DD
, OUT__, PGND)........1.7A
Continuous Input Current (All Other Pins) ....................... ±20mA
Continuous Power Dissipation (T
A
= +70°C)
16-Pin TQFN-EP (derate 20.8mW/°C above +70°C)..1666mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL
Supply Voltage Range V
Quiescent Current I
Shutdown Supply Current I
Input Resistance R
Turn-On Time t
BIAS Voltage V
CLASS D SPEAKER AMPLIFIERS
Output Offset Voltage V
Maximum Speaker Amplifier Gain
(Note 3)
Power-Supply Rejection Ratio PSRR V
Output Power P
Total Harmonic Distortion Plus
Noise
Signal-to-Noise Ratio SNR
Maximum Capacitive Load C
Switching Frequency f
THD+N f = 1kHz
DD
DD
SHDN
IN
ON
BIAS
OS
A
V
OUT
L_MAX
SW
Inferred from PSRR test 4.5 5.5 V
No load 12.8 16 mA
V
SHDN
TA = +25°C 12.6 45
TA = T
GAIN = 0 10.5
GAIN = 1 9.0
IN_
THD+N = 1%
THD+N = 10%
P
OUT
P
OUT
Average frequency in spread-spectrum
operation
= 0V 0.1 2 μA
to T
MIN
MAX
PVDD or VDD = 4.5V to
= 0V
= 1W, BW = 22Hz to 22kHz 89
= 1W, A-weighted 93
5.5V
f = 1kHz, 100mV
f = 20kHz, 100mV
RL = 8Ω 1.4
= 4Ω 2.3
R
L
RL = 8Ω 1.7
= 4Ω 2.8
R
L
RL = 8Ω, P
= 4Ω, P
R
L
P-P
P-P
= 1.2W 0.06
OUT
= 2W 0.07
OUT
6.5 10 13.5 kΩ
25 ms
1.8 V
70
52.4 75
71
60
200 pF
1.00 1.22 1.40 MHz
mV
dB
dB
W
%
dB
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD= PVDD= 5.0V, GND = PGND = 0V, V
SHDN
= VDD, C
BIAS
= 1μF, speaker impedance = 8Ω in series with 68μH connected between
OUT_+ and OUT_-, GAIN = +10.5dB, T
A
= T
MIN
to T
MAX
, unless otherwise noted. Typical values are at TA= +25°C.) (Notes 1, 2)
Note 1: All devices are 100% production tested at TA= +25°C. All temperature limits are guaranteed by design.
Note 2: Speaker amplifier gain is defined as A
V
= (V
OUT_+
- V
OUT_-
) / VIN.
Note 3: Click-and-pop level testing performed with an 8Ω resistive load in series with 68μH inductive load connected across the
Class D BTL outputs. Mode transitions are controlled by the SHDN pin. Inputs AC-coupled to GND.
Note 4: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For R
L
= 4Ω, L = 33μH.
For R
L
= 8Ω, L = 68μH.
Typical Operating Characteristics
(VDD= 5.0V, C
VDD
= 3 x 0.1μF, C
BIAS
= 1μF, C
INL
= C
INR
= 1μF, AV= +10.5dB, TA= +25°C, unless otherwise noted.) (See the
Typical Operating Circuit/Functional Diagram
)
10 1k 100k10k100
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9715toc01
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
P
OUT
= 0.35W
P
OUT
= 2W
VDD = 5V
R
L
= 4
Ω
10 1k 100k10k100
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9715toc02
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
P
OUT
= 0.5W
P
OUT
= 1.25W
VDD = 5V
R
L
= 8
Ω
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Spread-Spectrum Modulation ±120 kHz
Crosstalk
Click-and-Pop Level K
Efficiency η
DIGITAL INPUTS (GAIN and SHDN)
Input High Voltage V
Input Low Voltage V
Input Leakage Current I
CP
IH
IL
LEAK
Channel-to-channel, f = 10kHz, P
left to right or right to left
Peak voltage,
= 1W,
OUT
72 dB
Into shutdown -64
A-weighted,
32 samples per
second (Note 4)
R
= 8Ω in series with 68μH, P
L
per channel, f = 1kHz
Out of shutdown -46
= 1W
OUT
86 %
2.0 V
SHDN ±1
GAIN ±1.5
0.8 V
dBV
μA
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
100
10
1
THD+N (%)
0.1
0.01
0.001
fIN = 1kHz AND 20Hz
01.00.5 2.0 3.0 4.03.5
1.5 2.5
OUTPUT POWER (W)
fIN = 10kHz
VDD = 5V
R
L
MAX9715toc03
= 4Ω
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD= 5.0V, C
VDD
= 3 x 0.1μF, C
BIAS
= 1μF, C
INL
= C
INR
= 1μF, AV= +10.5dB, TA= +25°C, unless otherwise noted.) (See the
Typical Operating Circuit/Functional Diagram
)
EFFICIENCY
vs. OUTPUT POWER
MAX9715toc05
OUTPUT POWER (W)
EFFICIENCY (%)
10
20
30
40
50
60
70
80
90
100
0
0
1
23
4
5
6
VDD = 5V
f
IN
= 1kHz
P
OUT
= P
OUTL
+ P
OUTR
OUTPUTS IN-PHASE
RL = 4
Ω
RL = 8
Ω
0
0.5
1.0
2.0
1.5
2.5
4.5 4.8 5.0 5.3 5.5
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9715toc09
SUPPLY VOLTAGE (V)
OUTPUT POWER (W)
THD+N = 1%
fIN = 1kHz
R
L
= 8Ω
THD+N = 10%
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
100
fIN = 1kHz
10
fIN = 20Hz
1
THD+N (%)
0.1
0.01
0.001
0 0.5 1.0 1.5 2.52.0
OUTPUT POWER (W)
fIN = 10kHz
VDD = 5V
= 8
R
L
Ω
MAX9715toc04
EFFICIENCY
vs. SUPPLY VOLTAGE
100
90
80
70
60
50
40
EFFICIENCY (%)
30
fIN = 1kHz
20
10
= P
P
OUT
OUTPUTS IN-PHASE
THD+N = 1%
0
4.5 5.5
RL = 8
Ω
RL = 4
Ω
+ P
OUTL
OUTR
SUPPLY VOLTAGE (V)
OUTPUT POWER
vs. SUPPLY VOLTAGE
5.0
4.5
4.0
3.5
3.0
2.5
2.0
OUTPUT POWER (W)
1.5
1.0
0.5
0
4.5 4.8 5.0 5.3 5.5
THD+N = 10%
THD+N = 1%
SUPPLY VOLTAGE (V)
5.35.04.8
fIN = 1kHz
R
= 4Ω
L
MAX9715 toc06
MAX9715toc08
4.0
3.5
3.0
2.5
2.0
1.5
OUTPUT POWER (W)
1.0
THD+N = 1%
0.5
0
11k10010
OUTPUT POWER
vs. LOAD RESISTANCE
VDD = 5V
f
IN
L
LOAD
THD+N = 10%
LOAD RESISTANCE (Ω)
= 1kHz
= 33μH
MAX9715toc07
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
_______________________________________________________________________________________
5
Typical Operating Characteristics (continued)
(VDD= 5.0V, C
VDD
= 3 x 0.1μF, C
BIAS
= 1μF, C
INL
= C
INR
= 1μF, AV= +10.5dB, TA= +25°C, unless otherwise noted.) (See the
Typical Operating Circuit/Functional Diagram
)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
0
RL = 8Ω
-10
-20
-30
-40
-50
PSRR (dB)
-60
-70
-80
-90
-100
0.01 0.1 10 100
1
FREQUENCY (Hz)
MAX9715toc10
OUTPUT SPECTRUM
vs. FREQUENCY (A-WEIGHTED)
-40
-50
-60
-70
-80
-90
-100
AMPLITUDE (dBV)
-110
-120
-130
-140
0 5 10 15 20
FREQUENCY (kHz)
RL = 8Ω
= 5V
V
DD
= 1kHz
f
IN
MAX9715toc13
0
-20
-40
-60
CROSSTALK (dB)
-80
-100
-120
0
-20
-40
-60
AMPLITUDE (dBV)
-80
-100
-120
0.01
OUTPUT SPECTRUM
vs. FREQUENCY
FREQUENCY (kHz)
P
= 1W
OUT
= 8
R
L
A
= +10.5dB
V
= 10kHz
f
IN
CROSSTALK
vs. FREQUENCY
Ω
RIGHT TO LEFT
LEFT TO RIGHT
FREQUENCY (kHz)
-40
-50
MAX9715 toc11
-60
-70
-80
-90
-100
AMPLITUDE (dBV)
-110
-120
-130
1010.1
100
-140
0 5 10 15 20
SUPPLY CURRENT
WIDEBAND SPECTRUM
VDD = 5V
INPUTS AC GROUNDED
= 8
R
Ω
L
1 1000
FREQUENCY (MHz)
10010
20
18
MAX9715 toc14
16
14
12
10
8
6
SUPPLY CURRENT (mA)
4
2
0
4.5 4.8 5.0 5.3 5.5
vs. SUPPLY VOLTAGE
NO LOAD
INPUTS AC GROUNDED
SUPPLY VOLTAGE (V)
RL = 8Ω
= 5V
V
DD
= 1kHz
f
IN
MAX9715toc12
MAX9715toc15
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
6 _______________________________________________________________________________________
Pin Description
Typical Operating Characteristics (continued)
(VDD= 5.0V, C
VDD
= 3 x 0.1μF, C
BIAS
= 1μF, C
INL
= C
INR
= 1μF, AV= +10.5dB, TA= +25°C, unless otherwise noted.) (See the
Typical Operating Circuit/Functional Diagram
)
0.40
0.35
0.30
0.25
0.20
0.15
SHUTDOWN CURRENT (μA)
0.10
0.05
0
4.5 5.5
PIN NAME FUNCTION
1, 12 PGND Power Ground
2 OUTL+ Left-Channel Positive Speaker Output
3 OUTL- Left-Channel Negative Speaker Output
4, 9 PV
5 N.C. No connection. Not internally connected.
6 GAIN Gain Select. Sets the internal amplifier gain. See the Gain Selection section.
7 GND Ground
8 SHDN Shutdown Control. Drive SHDN low to shut down the MAX9715.
10 OUTR- Right-Channel Negative Speaker Output
11 OUTR+ Right-Channel Positive Speaker Output
13 BIAS Bias Voltage Output. V
14 V
15 INR Right-Channel Input
16 INL Left-Channel Input
— EP Exposed Paddle. Connect EP to an electrically isolated copper pad or GND.
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
SUPPLY VOLTAGE (V)
DD
DD
Positive Speaker Power-Supply Input. Power-supply input for speaker amplifier output stages. Connect
to V
Positive Power-Supply Input. Bypass to GND with a 0.1μF ceramic capacitor.
MAX9715 toc16
5.35.04.8
and bypass with 0.1μF to PGND.
DD
= 1.8V, bypass BIAS to GND with a 1μF ceramic capacitor.
BIAS
POWER-ON/OFF WAVEFORM
10ms/div
MAX9715 toc17
SHDN
5V/div
I
OUT
200mA/div
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
_______________________________________________________________________________________ 7
Detailed Description
The MAX9715 2.8W, Class D speaker amplifier with
gain control offers Class AB performance with Class D
efficiency while occupying minimal board space. A
unique modulation scheme and spread-spectrum
switching allow filterless operation to create a compact,
flexible, low-noise, efficient audio power amplifier. The
MAX9715 features high 71dB at 1kHz PSRR, low 0.06%
THD+N, industry-leading click-and-pop performance
and a low-power shutdown mode.
The MAX9715 features an undervoltage lockout that prevents operation from an insufficient power supply and
click-and-pop suppression that eliminates audible transients at startup and shutdown. The speaker amplifier
includes thermal-overload and short-circuit protection.
The MAX9715 features unique, spread-spectrum operation that reduces the amplitude of spectral components at
high frequencies, reducing EMI emissions that might otherwise be radiated by the speaker and cables. The
switching frequency varies randomly by ±120kHz around
the center frequency (1.22MHz). The modulation scheme
is consistent with Maxim’s Class D amplifiers but the period of the triangle waveform changes from cycle to cycle.
Audio reproduction is not affected by the spread-spectrum switching scheme. Instead of a large amount of
spectral energy present at multiples of the switching frequency that energy is now spread over a range of frequencies. The spreading is increased with frequency so
that above a few megahertz, the wideband spectrum
looks like white noise for EMI purposes (Figure 1).
Filterless Modulation/Common-Mode Idle
The spread-spectrum modulation scheme eliminates the
LC filter required by traditional Class D amplifiers, improving efficiency, reducing component count, conserving
board space and system cost. Conventional Class D
amplifiers output a 50% duty cycle square wave when no
signal is present. With no filter, the output square wave
appears across the load, resulting in finite load current,
which increases power consumption. When no signal is
present at the input, the MAX9715 outputs switch as
shown in Figure 2. The two outputs cancel each other
because the MAX9715 drives the speaker differently,
minimizing power consumption as there is no net idlemode voltage across the speaker.
Figure 1. MAX9715 Radiated Emissions with 75mm of Speaker Cable
Figure 2. MAX9715 Output without Input Signal Applied
50
45
40
35
30
AMPLITUDE (dBμV/m)
25
20
15
30
60
80
100
120
FREQUENCY (MHz)
MAX9715 fig01
260
280
300140
VIN = 0V
OUT-
OUT+
OUT-
220
240
= 0V
160 180
V
OUT+
200
- V
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
8 _______________________________________________________________________________________
Efficiency
Efficiency of a Class D amplifier is attributed to the region
of operation of the output-stage transistors. In a Class D
amplifier, the output transistors act as current-steering
switches and consume negligible additional power. Any
power loss associated with the Class D output stage is
mostly due to the I2R loss of the MOSFET on-resistance,
switching losses, and quiescent current overhead.
The theoretical best efficiency of a linear amplifier is
78%, however, that efficiency is only exhibited at peak
output powers. Under normal operating levels (typical
music or voice reproduction levels), efficiency falls
below 30%. Under the same conditions, the MAX9715
still exhibits >80% efficiencies (Figure 3).
Gain Selection
Drive GAIN high to set the gain of the speaker amplifiers to +9dB, drive GAIN low to set the gain of the
speaker amplifiers to +10.5dB (see Table 1). The gain
of the MAX9715 is calculated by the following equation:
Table 2 shows the speaker amplifier input voltage needed to attain maximum output power from a given gain setting and load.
Shutdown
The MAX9715 features a 0.1μA low-power shutdown
mode that reduces quiescent current consumption and
extends battery life. Driving SHDN low disables the output amplifiers, bias circuitry, and drives BIAS to GND.
Connect SHDN to logic 1 for normal operation.
Click-and-Pop Suppression
The MAX9715 speaker amplifiers feature Maxim’s comprehensive, industry-leading click-and-pop suppression
that eliminates any audible transients at startup. The outputs are high-impedance while in shutdown. During
startup or power-up, the modulator bias voltage is set to
the correct level while the input amplifiers are muted. The
input amplifiers are muted for 25ms allowing the input
capacitors to charge to the bias voltage (V
BIAS
). The
amplifiers are then unmuted, ensuring click-free startup.
Applications Information
Filterless Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s PWM output.
The filters add cost, increase the solution size of the
amplifier, and can decrease efficiency. The traditional
PWM scheme uses large differential output swings (2 x
V
DD(P-P)
), which causes large ripple currents. Any parasitic resistance in the filter components results in a loss
of power, lowering the efficiency.
The MAX9715 does not require an output filter. The
device relies on the inherent inductance of the speaker
coil and the natural filtering of both the speaker and the
human ear to recover the audio component of the
square-wave output. The elimination of the output filter
results in a smaller, less costly, more efficient solution.
Figure 3. MAX9715 Class D Efficiency vs. Typical Class AB
Efficiency
Table 1. MAX9715 Maximum Gain Settings
Table 2. MAX9715 Input Voltage and Gain
Settings for Maximum Output Power
20 log×
⎛
VV
⎜
⎝
−
+
OUT OUT
V
IN
⎞
−
⎟
⎠
EFFICIENCY
vs. OUTPUT POWER
100
90
MAX9715
80
70
60
50
40
EFFICIENCY (%)
30
20
10
0
0 2.00
CLASS AB
OUTPUT POWER (W)
VDD = 5V
R
L
f
IN
= 8
Ω
= 1kHz
1.751.501.00 1.250.50 0.750.25
MAX9715 fig03
GAIN SPEAKER MODE GAIN (dB)
0 +10.5
1 +9.0
GAIN (dB) INPUT (V
10.5 0.90 4 2.3
9.0 1.08 4 2.3
10.5 1.00 8 1.4
9.0 1.19 8 1.4
)RL (Ω)P
RMS
OUT
(W)
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
_______________________________________________________________________________________ 9
Voice coil movement due to the square-wave frequency
is very small because the switching frequency of the
MAX9715 is well beyond the bandwidth of most speakers. Although this movement is small, a speaker not
designed to handle the additional power may be
damaged. Use a speaker with a series inductance
> 30μH for optimum efficiency. Typical 8Ω speakers
exhibit series inductances in the 30μH to 100μH range.
The highest efficiency is achieved with speaker inductances > 60μH.
Component Selection
Input Filter
The input capacitor (CIN), in conjunction with the amplifier
input resistance (RIN), forms a highpass filter that
removes the DC bias from an incoming signal (see the
Typical Application Circuit
). 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:
RINis the amplifier’s internal input resistance value given
in the
Electrical Characteristics
table. Choose CINso
f
-3dB
is well below the lowest frequency of interest.
Setting f
-3dB
too high affects the amplifier’s low-frequency
response. Use capacitors with low-voltage coefficient
dielectrics, such as tantalum or aluminum electrolytic.
Capacitors with high-voltage coefficients, such as ceramics, may result in increased distortion at low frequencies.
The inability of small diaphragm speakers to reproduce
low frequencies can be exploited to improve click-andpop performance. Set the cutoff frequency of the
MAX9715’s input highpass filter to match the speaker’s
frequency response. Doing so will allow for smaller C
IN
values and reduce click-and-pop.
Output Filter
The MAX9715 speaker amplifiers do not require output
filters. However, output filtering can be used if a design
is failing radiated emissions due to board layout, cable
length, or the circuit is near EMI-sensitive devices. Use
a ferrite bead filter or a common-mode choke when radiated frequencies above 10MHz are of concern. Use an
LC filter when radiated frequencies below 10MHz are of
concern, or when long cables (>75mm) connect the
amplifier to the speaker. Figure 4 shows possible output
filter connections.
Figure 4. Optional Speaker Amplifier Output Filter—Guidelines for FCC Compliance
f
=
dB
−
3
1
RC
××
2π
IN IN
OUTL+
OUTL-
MAX9715
OUTR+
OUTR-
(a)
TYPICAL APPLICATION
<75mm OF SPEAKER CABLE.
OUTL+
OUTL-
MAX9715
OUTR+
OUTR-
COMMON-MODE CHOKE FOR
APPLICATIONS USING CABLE LENGTHS
(b)
GREATER THAN 150mm.
MAX9715
OUTL+
OUTL-
OUTR+
OUTR-
LC FILTER WHEN USING LONG CABLE
LENGTHS OR IN APPLICATIONS
THAT ARE SENSITIVE TO EMI.
(c)
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
10 ______________________________________________________________________________________
Supply Bypassing, Layout,
and Grounding
Proper layout and grounding are essential for optimum
performance. Use large traces for the power-supply
inputs and amplifier outputs to minimize losses due to
parasitic trace resistance. Large traces also aid in moving
heat away from the package. Proper grounding improves
audio performance, minimizes crosstalk between channels, and prevents any switching noise from coupling into
the audio signal. Route ground return paths that carry
switching transients to power ground (PGND). Keep highcurrent return paths that connect to PGND short and
route them away from analog ground (GND) and any
traces or components in the audio input signal path. Use
a star connection to connect GND and PGND together at
one point on the PC board.
Bypass each PV
DD
with a 0.1μF capacitor to PGND.
Bypass VDDto GND with a 0.1μF capacitor. Place a bulk
capacitor between VDDand PGND. Place the bypass
capacitors as close to the MAX9715 as possible.
Use large, low-resistance output traces. Current drawn
from the output increases as load impedance decreases.
High-output-trace resistance decreases the power delivered to the load. For example, when compared to a 0Ω
trace, a 100mΩ trace reduces the power delivered to a
4Ω load from 2.1W to 2.0W. Large output, supply, and
GND traces decrease the thermal impedance of the circuit and allow more heat to be radiated from the MAX9715
to the air.
The MAX9715 thin QFN-EP package features an
exposed thermal pad on its underside. This pad lowers
the package’s thermal impedance by providing a direct-
heat conduction path from the die to the PC board.
Connect the exposed thermal pad to an electrically isolated pad of copper. A bigger pad area provides better
thermal performance. Connect EP to GND if PC board
layout rules do not allow for isolated pads of copper. If
EP is connected to GND, ensure that high-current return
paths do not flow through EP.
Biamp Configuration
The
Typical Application Circuit
shows the MAX9715
configured as a mid-/high-frequency amplifier and the
MAX9713 is configured as a mono bass amplifier.
Capacitors C1 and C2 set the highpass cutoff frequency according to the following equation:
where RINis the input resistance of the MAX9715 and
C1 = C2. The 10μF capacitors on the output of the
MAX9715 ensure a two-pole roll-off with the 5Ω load
shown.
The stereo signal is summed to a mono signal and then
sent to a two-pole lowpass filter. The filtered signal is
then amplified by the MAX9713. The passband gain of
the lowpass filter, for coherent left and right signals is
(-2 x R3) / R1, where R1 = R2. The cutoff frequency of
the lowpass filter is set by the following equation:
f
=
××
21π
1
f
=×
CCRR
2
3434π
1
RC
IN
1
×××
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
______________________________________________________________________________________ 11
Typical Application Circuit
LEFT IN
RIGHT IN
C5
1μF
C6
1μF
R1
15kΩ
R2
15kΩ
22nF
5V
C4
2.2nF
22μF
22μF
MAX4480
1μF
1μF
8Ω
8Ω
12V
MAX9713
C1
15nF
C2
15nF
C3
MAX9715
R3
7.5kΩ
R4
15kΩ
2.5V
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
12 ______________________________________________________________________________________
Typical Operating Circuit/Functional Diagram
Chip Information
TRANSISTOR COUNT: 11,721
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns, go
to www.maxim-ic.com/packages
.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
16 TQFN-EP T1655-2
21-0140
4.5V TO 5.5V
*
0.1μF
0.1μF
0.1μF
SHUTDOWN
CONTROL
MAX9715
LEFT
AUDIO
GAIN-SELECT
LOGIC
RIGHT
AUDIO
1μF
1μF
1μF
INL
GAIN
INR
BIAS
V
BIAS
R
IN
GAIN
SELECT
R
IN
BIAS
GENERATOR
V
BIAS
*BULK PC BOARD DECOUPLING, TYPICALLY GREATER THAN 10μF.
V
DD
V
DD
V
DD
GND PGND PGND
PV
DDPVDD
SHDN
CONTROL
CLASS D
MODULATOR
AND H-BRIDGE
OSCILLATOR
CLASS D
MODULATOR
AND H-BRIDGE
SHDN
OUTL+
OUTL-
OUTR+
OUTR-
MAX9715
2.8W, Low-EMI, Stereo, Filterless Class D
Audio Amplifier
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________
13
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
2 7/08 Removed TSSOP package option 1, 2, 6, 12
REVISION
DATE
DESCRIPTION
PAGES
CHANGED
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