MAXIM MAX9701

19-3457; Rev 0; 6/05
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
The MAX9701 stereo class D audio power amplifier provides class AB amplifier audio performance with the
benefits of class D efficiency, eliminating the need for a
heatsink while extending battery life. The MAX9701
delivers up to 1.3W per channel into an 8Ω load while
offering 87% efficiency. Maxim’s next-generation, lowEMI modulation scheme allows the amplifier to operate
without an external LC filter while still meeting FCC EMI
emission levels.
The MAX9701 offers two modulation schemes: a fixed-frequency (FFM) mode, and a spread-spectrum (SSM)
mode that reduces EMI-radiated emissions. The
MAX9701 oscillator can be synchronized to an external
clock through the SYNC input, allowing synchronization of
multiple Maxim class D amplifiers. The sync output
(SYNC_OUT) can be used for a master-slave application
where more channels are required. The MAX9701 features a fully differential architecture, a full bridge-tied load
(BTL) output, and comprehensive click-and-pop suppression. The device features internally set gains of 0dB, 6dB,
12dB, and 18dB selected through two gain-select inputs,
further reducing external component count.
The MAX9701 features high 80dB PSRR, less than 0.1%
THD+N, and SNR in excess of 88dB. Short-circuit and
thermal-overload protection prevent the device from
being damaged during a fault condition. The MAX9701 is
available in 24-pin thin QFN-EP (4mm x 4mm x 0.8mm),
20-pin TSSOP, and 20-bump UCSP™ (2mm x 2.5mm x
0.6mm) packages. The MAX9701 is specified over the
extended -40°C to +85°C temperature range.
Applications
Cellular Phones
Features
♦ Patented Spread-Spectrum Modulation Lowers
Radiated Emissions
♦ Single-Supply Operation (2.5V to 5.5V)
♦ 1.3W Stereo Output (8Ω, VDD = 5V, THD+N = 1%)
♦ No LC Output Filter Required
♦ 87% Efficiency (RL = 8Ω, PO = 1000mW)
♦ Less Than 0.1% THD+N
♦ High 80dB PSRR
♦ Fully Differential Inputs
♦ Integrated Click-and-Pop Suppression
♦ Typical Low Quiescent Current (9mA)
♦ Typical Low-Power Shutdown Mode (0.1µA)
♦ Short-Circuit and Thermal-Overload Protection
♦ Available in Thermally Efficient, Space-Saving
Packages
24-Pin Thin QFN-EP (4mm x 4mm x 0.8mm)
20-Pin TSSOP
20-Bump UCSP (2mm x 2.5mm x 0.6mm)
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX9701EBP-T
-40°C to +85°C
20 UCSP-20
MAX9701EUP+
-40°C to +85°C
20 TSSOP
MAX9701ETG+
-40°C to +85°C
24 TQFN-EP
+ Denotes lead-free package.
Block Diagram
Notebooks
Handheld Gaming Consoles
VDD
Docking Stations
MP3 Players
MAX9701
INR+
RIGHT
MODULATOR
AND H-BRIDGE
INR-
Pin Configurations appear at end of data sheet.
GAIN1
GAIN2
GAIN
INL+
LEFT
MODULATOR
AND H-BRIDGE
INL-
SYNC
OSCILLATOR
SYNC_OUT
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX9701
General Description
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
ABSOLUTE MAXIMUM RATINGS
VDD to GND..............................................................................6V
VDD to PVDD ..........................................................-0.3V to +0.3V
PVDD to PGND .........................................................................6V
GND to PGND .......................................................-0.3V to +0.3V
All Other Pins to GND.................................-0.3V to (VDD + 0.3V)
Continuous Current In/Out of PVDD, PGND, OUT_ .........±800mA
Continuous Input Current (all other pins)..........................±20mA
Duration of OUT_ Short Circuit to GND or PVDD ........Continuous
Duration of Short Circuit Between OUT+ and OUT- ......Continuous
Continuous Power Dissipation (TA = +70°C)
20-Bump UCSP (derate 10mW/°C above +70°C) ...........800mW
20-Pin TSSOP (derate 11mW/°C above +70°C) ...........879.1mW
24-Pin Thin QFN (derate 20.8mW/°C above +70°C) ..1666.7mW
Junction Temperature ......................................................+150°C
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Bump Temperature (soldering) Reflow............................+235°C
Lead Temperature (soldering, 10s) .................................+300°C
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.
ELECTRICAL CHARACTERISTICS
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected between
OUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
5.5
V
GENERAL
Supply Voltage Range
Quiescent Current
VDD
IDD
Shutdown Current
ISHDN
Common-Mode Rejection Ratio
CMRR
Input Bias Voltage
VBIAS
Turn-On Time
Output Offset Voltage
Inferred from PSRR test
2.5
VDD = 3.3V, per channel
4.5
8
VDD = 5V, per channel
6.3
10
0.1
10
fIN = 1kHz
66
1.125
tON
VOS
Output Power (Note 3)
Total Harmonic Distortion Plus
Noise (Note 3)
PSRR
POUT
THD+N
100mVP-P ripple,
VIN = 0V
THD+N = 1%,
TA = +25oC
SNR
VDD = 3.3V
VDD = 5V
460
RL = 4Ω
750
RL = 8Ω
1300
RL = 4Ω
2200
RL = 4Ω (POUT = 400mW), f = 1kHz
0.15
FFM
86
SSM
86
FFM
88.5
SSM
SYNC Frequency Lock Range
fOSC
2
%
dB
1100
1400
1250
1600
kHz
1200
±60
tMIN
fSYNC
mW
88.5
950
1200
SYNC = VDD
Minimum On-Time
dB
50
RL = 8Ω
0.08
SYNC = GND
SYNC = unconnected
mV
80
RL = 8Ω (POUT = 300mW), f = 1kHz
VOUT = 1VRMS
V
ms
±30
72
fRIPPLE = 20kHz
A-weighted
Oscillator Frequency
60
fRIPPLE = 217Hz
BW = 22Hz
to 22kHz
Signal-to-Noise Ratio
1.375
±55
TMIN < TA < TMAX
µA
dB
40
±10
TA = +25oC
VDD = 2.5V to 5.5V, VIN = 0V
Power-Supply Rejection Ratio
1.25
mA
200
1000
_______________________________________________________________________________________
ns
1600
kHz
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RL connected between
OUT+ and OUT-, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (Notes 1, 2)
PARAMETER
SYNC_OUT Capacitance Drive
Capacitive Drive
SYMBOL
KCP
η
Efficiency
RIN
Gain
AV
MAX
100
200
Single ended
400
Peak reading, THD+N = 1% Into shutdown
A-weighted, 32 samples
Out of
per second (Note 4)
shutdown
UNITS
pF
pF
66.16
dB
66.26
VDD = 3.3V, POUT = 500mW per channel,
fIN = 1kHz, RL = 8Ω
87
VDD = 5V, POUT = 1000mW per channel,
fIN = 1kHz, RL = 8Ω
87.4
%
10.5
15
GAIN1 = 1, GAIN2 = 0
25
GAIN1 = 0, GAIN2 = 1
37.4
GAIN1 = 1, GAIN2 = 1
50
GAIN1 = 0, GAIN2 = 0
18
GAIN1 = 1, GAIN2 = 0
12
GAIN1 = 0, GAIN2 = 1
6
GAIN1 = 1, GAIN2 = 1
0
Channel-to-Channel Gain
Tracking
L to R, R to L, f = 10kHz, RL = 8Ω,
POUT = 300mW
Crosstalk
TYP
Bridge-tied capacitance
GAIN1 = 0, GAIN2 = 0
Input Resistance
MIN
CSYNC_OUT
CL
Click-and-Pop Level
CONDITIONS
19.5
kΩ
dB
1
%
70
dB
DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)
Input-Voltage High
VINH
Input-Voltage Low
VINL
2
V
Input Leakage Current
(SHDN, GAIN1, GAIN2)
VIN = GND, normal operation
Input Leakage Current (SYNC)
-15
0.8
V
±1
µA
-7
µA
VIN = VDD, normal operation
12
25
DIGITAL OUTPUTS (SYNC_OUT)
Output-Voltage High
VOH
IOH = 3mA, VDD = 3.3V
Output-Voltage Low
VOL
IOL = 3mA
2.4
V
0.08
V
Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Note 2: Testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For RL = 4Ω, L = 33µH.
For RL = 8Ω, L = 68µH.
Note 3: When driving speakers below 4Ω with large signals, exercise care to avoid violating the absolute maximum rating for continuous
output current.
Note 4: Testing performed with 8Ω resistive load in series with 68µH inductive load connected across the BTL output. Mode transitions are controlled by SHDN. KCP level is calculated as: 20 x log[(peak voltage under normal operation at rated power
level) / (peak voltage during mode transition, no input signal)]. Units are expressed in dB.
_______________________________________________________________________________________
3
MAX9701
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
VDD = 5V
RL = 4Ω
VDD = 5V
RL = 8Ω
VDD = 3.3V
RL = 4Ω
OUTPUT POWER = 600mW
0.1
THD+N (%)
1
THD+N (%)
1
OUTPUT POWER = 500mW
0.1
0.1
OUTPUT POWER = 100mW
OUTPUT POWER = 100mW
0.01
0.01
100
1k
10k
100k
OUTPUT POWER = 300mW
OUTPUT POWER = 100mW
OUTPUT POWER = 250mW
OUTPUT POWER = 300mW
10
100
1k
10k
0.01
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
10
MAX9701 toc04
10
VDD = 3.3V
RL = 8Ω
100
MAX9701 toc05
10
OUTPUT POWER = 600mW
VDD = 5V
RL = 8Ω
POUT = 800mW
MAX9701 toc06
THD+N (%)
1
10
MAX9701 toc02
10
MAX9701 toc01
10
MAX9701 toc03
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
VDD = 5V
RL = 4Ω
10
OUTPUT POWER = 400mW
0.1
THD+N (%)
THD+N (%)
1
THD+N (%)
1
FFM
fIN = 10kHz
1
0.1
0.1
OUTPUT POWER = 100mW
fIN = 1kHz
SSM
fIN = 20kHz
OUTPUT POWER = 250mW
0.01
0.01
0.01
100
1k
10k
100k
10
100
1k
10k
0
100k
0.5
1.0
1.5
2.0
2.5
FREQUENCY (Hz)
FREQUENCY (Hz)
OUTPUT POWER (W)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
VDD = 5V
RL = 8Ω
10
VDD = 3.3V
RL = 4Ω
100
VDD = 3.3V
RL = 8Ω
10
3.0
MAX9701 toc09
100
MAX9701 toc07
100
MAX9701 toc08
10
10
1
0.1
fIN = 1kHz
fIN = 10kHz
0.1
fIN = 1kHz
fIN = 20kHz
0.01
1
THD+N (%)
THD+N (%)
fIN = 10kHz
THD+N (%)
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
fIN = 10kHz
1
0.1
fIN = 20kHz
fIN = 1kHz
fIN = 20kHz
0.01
0.001
0
0.5
1.0
OUTPUT POWER (W)
4
1.5
2.0
0.01
0
0.2
0.4
0.6
0.8
OUTPUT POWER (W)
1.0
1.2
0
100
200
300
400
500
OUTPUT POWER (mW)
_______________________________________________________________________________________
600
700
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
EFFICIENCY vs. OUTPUT POWER
0.1
MAX9701 toc11
80
RL = 4Ω
70
60
50
40
80
30
FFM
0.01
1.2
0.5
1.0
2.0
2.5
0
2.5
THD+N = 10%
1.5
RL = 8Ω
AV = 12dB
fIN = 1kHz
1.6
1.2
THD+N = 1%
THD+N = 10%
0.8
0
3.5
4.0
4.5
5.0
2.0
THD+N = 10%
1.5
THD+N = 1%
1.0
3.0
3.5
4.0
4.5
5.0
5.5
0
20
40
60
SUPPLY VOLTAGE (V)
LOAD RESISTANCE (Ω)
OUTPUT POWER vs. LOAD RESISTANCE
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
COMMON-MODE REJECTION RATIO
vs. FREQUENCY
-20
-30
CMRR (dB)
THD+N = 1%
-40
-50
-60
-40
-60
-70
-70
-80
-80
-90
-90
0
-100
-100
20
40
60
LOAD RESISTANCE (Ω)
80
100
10
100
1k
FREQUENCY (Hz)
10k
100k
VDD = 5V
-50
0.4
0
VCM = 100mVP-P
RL = 8Ω
-10
-30
PSRR (dB)
0.8
MAX9701 toc18
-20
THD+N = 10%
1.2
VRIPPLE = 100mVP-P
RL = 8Ω
-10
0
MAX9701 toc17
1.6
0
MAX9701 toc16
fIN = 1kHz
100
80
SUPPLY VOLTAGE (V)
2.0
OUTPUT POWER (W)
VDD = 5V
fIN = 1kHz
0
2.5
5.5
1.2
1.0
0.5
0.5
0
0.8
2.5
THD+N = 1%
0.4
0.6
OUTPUT POWER vs. LOAD RESISTANCE
1.0
3.0
0.4
3.0
MAX9701 toc14
MAX9701 toc13
RL = 4Ω
AV = 12dB
fIN = 1kHz
2.5
0.2
OUTPUT POWER (W)
2.0
OUTPUT POWER (W)
OUTPUT POWER (W)
1.5
OUTPUT POWER vs. SUPPLY VOLTAGE
OUTPUT POWER vs. SUPPLY VOLTAGE
3.5
2.0
VDD = 3.3V
fIN = 1kHz
POUT = POUTLEFT + POUTRIGHT
OUTPUT POWER (W)
OUTPUT POWER (W)
3.0
40
0
0
2.0
1.6
OUTPUT POWER (W)
0.8
50
10
0
0.4
RL = 4Ω
60
20
VDD = 5V
fIN = 1kHz
POUT = POUTLEFT + POUTRIGHT
10
0
70
30
20
0.001
RL = 8Ω
90
MAX9701 toc15
SSM
100
EFFICIENCY (%)
THD+N (%)
1
EFFICIENCY vs. OUTPUT POWER
RL = 8Ω
90
EFFICIENCY (%)
VDD = 5V
RL = 8Ω
fIN = 1kHz
10
100
MAX9701 toc10
100
MAX9701 toc12
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
VDD = 3.3V
10
100
1k
10k
100k
FREQUENCY (Hz)
_______________________________________________________________________________________
5
MAX9701
Typical Operating Characteristics (continued)
Typical Operating Characteristics (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
CROSSTALK vs. FREQUENCY
-60
-70
-80
LEFT TO RIGHT
-90
RL = 8Ω
fIN = 1kHz
-40
-50
CROSSTALK (dB)
-100
-60
-70
LEFT TO RIGHT
-80
-90
-100
-110
-110
RIGHT TO LEFT
-120
RIGHT TO LEFT
-120
-130
-130
100
1k
10k
100k
-94
FREQUENCY (Hz)
MAX9701 toc21
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
-60
-80
-100
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
-20
OUTPUT MAGNITUDE (dBV)
OUTPUT MAGNITUDE (dBV)
6
-14
0
-40
-60
-80
-100
-120
-120
-140
-140
0
5k
10k
15k
0
20k
5k
OUTPUT FREQUENCY SPECTRUM
20k
OUTPUT FREQUENCY SPECTRUM
-60
-80
-100
-120
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
-20
OUTPUT MAGNITUDE (dBV)
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
UNWEIGHTED
-40
15k
0
MAX9701 toc23
0
-20
10k
FREQUENCY (Hz)
FREQUENCY (Hz)
-40
-60
-80
-100
-120
-140
-140
0
5k
10k
FREQUENCY (Hz)
6
-34
OUTPUT FREQUENCY SPECTRUM
OUTPUT FREQUENCY SPECTRUM
-40
-54
INPUT AMPLITUDE (dB)
0
-20
-74
MAX9701 toc22
10
MAX9701 toc24
CROSSTALK (dB)
-50
MAX9701 toc20
POUT = 300mW
RL = 8Ω
-40
CROSSTALK vs. INPUT AMPLITUDE
-30
MAX9701 toc19
-30
OUTPUT MAGNITUDE (dBV)
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
15k
20k
0
5k
10k
15k
20k
FREQUENCY (Hz)
_______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
WIDEBAND OUTPUT SPECTRUM
(SSM MODE)
WIDEBAND OUTPUT SPECTRUM
(FFM MODE)
-20
RBW = 10kHz
INPUT AC GROUNDED
-10
-30
-40
-50
-60
-70
MAX9701 toc26
RBW = 10kHz
INPUT AC GROUNDED
-20
OUTPUT MAGNITUDE (dB)
-30
-40
-50
-60
-70
-80
-80
-90
-90
-100
-100
10k
1k
1M
100k
10k
FREQUENCY (Hz)
TURN-ON/TURN-OFF RESPONSE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SHDN
20
BOTH CHANNELS
17
SUPPLY CURRENT (mA)
2V/div
0V
MAX9701
OUTPUT
1M
100k
FREQUENCY (Hz)
MAX9701 toc27
1k
MAX9701 toc28
OUTPUT MAGNITUDE (dB)
0
MAX9701 toc25
0
-10
250mV/div
14
SSM
11
FFM
8
5
10ms/div
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX9701 toc29
5
SHUTDOWN CURRENT (µA)
BOTH CHANNELS
4
3
2
1
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
7
MAX9701
Typical Operating Characteristics (continued)
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
MAX9701
Pin Description
PIN
8
NAME
FUNCTION
TSSOP
TQFN
UCSP
1, 10
9, 22
B1, B5
GND
Analog Ground
2
23
B2
INL+
Left-Channel Noninverting Input
3
24
A1
INL-
4
1
A2
SHDN
Active-Low Shutdown. Connect to VDD for normal operation.
Frequency Select and External Clock Input.
SYNC = GND: Fixed-frequency mode with fS = 1100kHz.
SYNC = Unconnected: Fixed-frequency mode with fS = 1400kHz.
SYNC = VDD: Spread-spectrum mode with fS = 1200kHz ±60kHz.
SYNC = Clocked: Fixed-frequency mode with fS = external clock
frequency.
5
2
B3
SYNC
6
4
A3
OUTL+
Left-Channel Inverting Input
Left-Channel Amplifier Output Positive Phase
7, 14
5, 14
A4, D4
PVDD
H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1µF capacitor
to PGND.
8, 13
6, 13
B4, C4
PGND
Power Ground
9
7
A5
OUTL-
11
10
C5
SYNC_OUT
Left-Channel Amplifier Output Negative Phase
12
12
D5
OUTR-
15
15
D3
OUTR+
Right-Channel Amplifier Output Positive Phase
16
17
C3
GAIN1
Gain-Select Input 1
17
18
D2
GAIN2
Gain-Select Input 2
18
19
D1
INR-
Right-Channel Inverting Input
19
20
C2
INR+
Right-Channel Noninverting Input
20
21
C1
VDD
—
3, 8, 11, 16
—
N.C.
—
EP
—
EP
Clock Signal Output
Right-Channel Amplifier Output Negative Phase
Analog Power Supply. Connect to PVDD. Bypass with a 10µF capacitor to
GND.
No Connection. Not internally connected.
Exposed Pad. Connect the exposed thermal pad to the GND plane (see
the Supply Bypassing, Layout, and Grounding section).
_______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
VDD
10µF
0.1µF
VDD
INL+
470nF
CLASS D
MODULATOR
AND H-BRIDGE
INL-
INR+
RIN
INR-
RIN
470nF
VBIAS
RIN
RIN
470nF
SYNC_OUT
OSCILLATOR
AND
SAWTOOTH
SYNC
470nF
PVDD
CLASS D
MODULATOR
AND H-BRIDGE
VBIAS
OUTL+
OUTL-
OUTR+
OUTR-
VBIAS
BIAS
GENERATOR
GAIN1
GAIN2
GAIN
CONTROL
MAX9701
SHDN
GND
PGND
_______________________________________________________________________________________
9
MAX9701
Functional Diagram
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
tSW
VIN-
VIN+
OUT-
OUT+
tON(MIN)
VOUT+ - VOUT-
Figure 1. MAX9701 Outputs with an Input Signal Applied
Detailed Description
The MAX9701 filterless, stereo class D audio power
amplifier features several improvements to switch-mode
amplifier technology. The MAX9701 offers class AB performance with class D efficiency, while occupying minimal board space. A unique, filterless modulation
scheme, synchronizable switching frequency, and
spread-spectrum switching mode create a compact,
flexible, low-noise, efficient audio power amplifier. The
differential input architecture reduces common-mode
noise pickup, and can be used without input-coupling
capacitors. The inputs can also be configured to accept
a single-ended input signal.
10
Comparators monitor the MAX9701 inputs and compare
the complementary input voltages to the sawtooth waveform. The comparators trip when the input magnitude of
the sawtooth exceeds their corresponding input voltage.
Both comparators reset at a fixed time after the rising
edge of the second comparator trip point, generating a
minimum-width pulse (tON(MIN)) at the output of the second comparator (Figure 1). As the input voltage increases
or decreases, the duration of the pulse at one output
increases while the other output pulse duration remains
the same. This causes the net voltage across the speaker
(VOUT+ - VOUT-) to change. The minimum-width pulse
helps the device to achieve high levels of linearity.
______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
tSW
tSW
MAX9701
tSW
tSW
VIN_-
VIN_+
OUT_-
OUT_+
tON(MIN)
VOUT_+ - VOUT_-
Figure 2. MAX9701 Outputs with an Input Signal Applied (SSM Mode)
Operating Modes
Fixed-Frequency (FFM) Mode
The MAX9701 features two fixed-frequency modes.
Connect SYNC to GND to select a 1.1MHz switching frequency. Leave SYNC unconnected to select a 1.4MHz
switching frequency. The frequency spectrum of the
MAX9701 consists of the fundamental switching frequency and its associated harmonics (see the Wideband FFT
graph in the Typical Operating Characteristics). Program
the switching frequency so the harmonics do not fall
within a sensitive frequency band (Table 1). Audio reproduction is not affected by changing the switching frequency.
Table 1. Operating Modes
SYNC
MODE
GND
FFM with fOSC = 1100kHz
Unconnected
FFM with fOSC = 1400kHz
VDD
Clocked
SSM with fOSC = 1200kHz ±60kHz
FFM with fOSC = external clock frequency
______________________________________________________________________________________
11
VIN_ = 0V
50.0
45.0
40.0
AMPLITUDE (dBµV/m)
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
35.0
30.0
OUT_-
25.0
20.0
15.0
10.0
5.0
OUT_+
0.0
30
60
80
100
120
140
160
180
200
220
240
260
280
300
FREQUENCY (MHz)
VOUT_+ - VOUT_- = 0V
Figure 3. MAX9701 with 76mm of Speaker Cable with TDK
Common-Mode Choke: TDK ACM4532-801-20-X
Spread-Spectrum (SSM) Mode
The MAX9701 features a unique, patented spreadspectrum mode that flattens the wideband spectral
components, improving EMI emissions that may be
radiated by the speaker and cables. This mode is
enabled by setting SYNC = V DD (Table 1). In SSM
mode, the switching frequency varies randomly by
±60kHz around the center frequency (1.2MHz). The
modulation scheme remains the same, but the period
of the sawtooth waveform changes from cycle to cycle
(Figure 2). Instead of a large amount of spectral energy
present at multiples of the switching frequency, the
energy is now spread over a bandwidth that increases
with frequency. Above a few megahertz, the wideband
spectrum looks like white noise for EMI purposes
(Figure 3). A proprietary amplifier topology ensures this
does not corrupt the noise floor in the audio bandwidth.
Synchronous Switching Mode
SYNC
The SYNC input allows the MAX9701 to be synchronized
to a user-defined clock, or another Maxim class D amplifier, creating a fully synchronous system, minimizing
clock intermodulation, and allocating spectral components of the switching harmonics to insensitive frequency
bands. Applying a TTL clock signal between 1000kHz
and 1600kHz to SYNC synchronizes the MAX9701. The
period of the SYNC clock can be randomized, allowing
the MAX9701 to be synchronized to another Maxim class
D amplifier operating in SSM mode.
12
Figure 4. MAX9701 Outputs with No Input Signal
SYNC_OUT
SYNC_OUT allows several MAX9701s as well as other
class D amplifiers (such as the MAX9700) to be cascaded. The synchronized output minimizes interference due to clock intermodulation caused by the
switching spread between single devices. Using
SYNC_OUT, the modulation scheme remains the same
and audio reproduction is not affected by changing the
switching frequency.
Filterless Modulation/Common-Mode Idle
The MAX9701 uses Maxim’s unique, patented modulation
scheme that 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,
180° out-of-phase square wave when no signal is present. With no filter, the square wave appears across the
load as a DC voltage, resulting in finite load current,
which increases power consumption especially when
idling. When no signal is present at the input of the
MAX9701, the amplifiers will output an in-phase square
wave as shown in Figure 4. Because the MAX9701 drives
the speaker differentially, the two outputs cancel each
other, resulting in no net idle mode voltage across the
speaker, minimizing power consumption.
Efficiency
Efficiency of a class D amplifier is due to the switching
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 I*R loss of the MOSFET onresistance, and quiescent-current overhead.
______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
100
90
EFFICIENCY (%)
80
70
MAX9701
60
50
40
30
CLASS AB
20
10
VDD = 3.3V
f = 1kHz
RL - 8Ω
0
0
0.1
0.2
0.3
0.4
0.5
OUTPUT POWER (W)
Figure 5. MAX9701 Efficiency vs. Class AB Efficiency
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 reproduction levels), efficiency falls below 30%,
whereas the MAX9701 still exhibits >80% efficiencies
under the same conditions (Figure 5).
Shutdown
The MAX9701 has a shutdown mode that reduces power
consumption and extends battery life. Driving SHDN low
places the MAX9701 in a low-power (0.1µA) shutdown
mode. Connect SHDN to VDD for normal operation.
Click-and-Pop Suppression
The MAX9701 features 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. For 40ms following startup, a soft-start function
gradually unmutes the input amplifiers.
The MAX9701 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. Eliminating the output filter results
in a smaller, less costly, more efficient solution.
Because the frequency of the MAX9701 output 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 speaker 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
range of 20µH to 100µH.
Output Offset
Unlike a class AB amplifier, the output offset voltage of a
class D amplifier does not noticeably increase quiescent
current draw when a load is applied. This is due to the
power conversion of the class D amplifier. For example,
an 8mV DC offset across an 8Ω load results in 1mA extra
current consumption in a class AB device. In the class D
case, an 8mV offset into 8Ω equates to an additional
power drain of 8µW. Due to the high efficiency of the
class D amplifier, this represents an additional quiescent
current draw of: 8µW/(VDD / 100 x η), which is on the
order of a few µA.
Selectable Gain
The MAX9701 features four selectable gain settings,
minimizing external component count. Gains of 0dB,
3dB, 12dB, and 18dB are set through gain-select
inputs, GAIN1 and GAIN2. GAIN1 and GAIN2 can be
hard-wired or digitally controlled. Table 2 shows the
suggested gain settings to attain a maximum output
power from a given peak input voltage and given load
at VDD = 3.3V and THD+N = 10%.
Table 2. Gain Settings
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 VDD(P-P)) and causes large ripple currents.
Any parasitic resistance in the filter components results
in a loss of power, lowering the efficiency.
GAIN1
GAIN2
GAIN
(dB)
INPUT
(VRMS)
RL
(Ω)
POUT
(mW)
0
0
+18
0.305
4
1100
1
0
+12
0.615
4
1100
0
1
+6
1.213
4
1100
1
1
0
2.105
4
1100
0
0
+18
0.345
8
725
8
725
1
0
+12
0.686
0
1
+6
1.360
8
725
1
1
0
2.705
8
725
______________________________________________________________________________________
13
MAX9701
EFFICIENCY vs. OUTPUT POWER
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
0.47µF
SINGLE-ENDED
LEFT AUDIO INPUT
INL+
INL+
OUTL+
INL-
OUTL+
0.47µF
SINGLE-ENDED
RIGHT AUDIO INPUT
CODEC
INR+
INL-
0.47µF
INR-
MAX9701
INR+
MAX9701
OUTLINR-
OUTLOUTR+
OUTR+
0.47µF
OUTR-
OUTR-
GAIN2
GAIN2
GAIN1
GAIN1
SHDN
SHDN
2.5V TO 5.5V
VDD
PVDD
10µF
GND
PVDD
PGND
10µF
0.1µF
GND
VDD
2.5V TO 5.5V
PGND
0.1µF
SYNC
SYNC
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB
CODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE.
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB.
Figure 6. Single-Ended Input
Figure 7. DC-Coupled Inputs
Input Amplifier
Component Selection
Differential Input
The MAX9701 features a differential input structure,
making it compatible with many CODECs and offers
improved noise immunity over a single-ended input
amplifier. In devices such as cellular phones, high-frequency signals from the RF transmitter can be picked
up by the amplifier’s input traces. The signals appear at
the amplifier’s inputs as common-mode noise. A differential input amplifier amplifies the difference of the two
inputs, any signal common to both inputs is canceled.
Input Filter
An input capacitor, C IN , in conjunction with the
MAX9701 input impedance (RIN) forms a highpass filter
that removes the DC bias from an incoming signal. The
AC-coupling capacitor allows the amplifier to automatically bias the signal to an optimum DC level. Assuming
zero-source impedance, the -3dB point of the highpass
filter is given by:
Single-Ended Input
The MAX9701 can be configured as a single-ended
input amplifier by capacitively coupling either input to
GND, and driving the other input (Figure 6).
DC-Coupled Inputs
The input amplifier can accept DC-coupled inputs that
are biased within the amplifier’s common-mode range
(see the Typical Operating Characteristics). DC coupling eliminates the input-coupling capacitors, reducing component count to potentially two external
components (Figure 7). However, the highpass filtering
effect of the capacitors is lost, allowing low-frequency
signals to feed through to the load.
14
f−3dB =
1
2πRINCIN
Choose CIN so f-3dB is well below the lowest frequency of
interest. Use capacitors whose dielectrics have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as
ceramics, may result in increased distortion at low frequencies.
Other considerations when designing the input filter
include the constraints of the overall system and the
actual frequency band of interest. 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
______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
MAX9701
5V
CIN
2200pF
10µF
INL+
OUTL+
CIN
2200pF
8Ω
MAX9701
INR+
OUTL-
CIN
2200pF
10µF
INLOUTR+
CIN
2200pF
8Ω
INROUTRSYNC
SYNC_OUT
R3
10kΩ
5V
R1
20kΩ
VDD
R4
39kΩ
R2
20kΩ
SYNC
C2
1nF
1µF
IN+
C2
0.01µF
1.25V
MAX4238
MAX9700
OUT+
4Ω
1µF
IN-
OUT-
NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V.
FFM MODE WITH fOSC = 1100kHz.
Figure 8. 2.1 Channel Application Circuit
in portable devices typically have a poor response
below 300Hz. 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.
Output Filter
The MAX9701 does not require an output filter. The
device passes FCC emissions standards with 76mm of
unshielded speaker cables. However, output filtering
can be used if a design is failing radiated emissions due
to board layout or cable length, or if the circuit is near
EMI-sensitive devices. Use a ferrite bead filter when
radiated frequencies above 10MHz are of concern. Use
an LC filter or a common-mode choke when radiated
emissions below 10MHz are of concern, or when long
leads (>76mm) connect the amplifier to the speaker.
2.1 Channel Configuration
The typical 2.1 channel application circuit (Figure 8)
shows the MAX9701 configured as a mid-/high-frequency
amplifier and the MAX9700 configured as a mono bass
amplifier. Input capacitors (CIN) set the highpass cutoff
frequency according to the following equation:
f=
1
2π × RIN × CIN
where R IN is the typical input resistance of the
MAX9701. The 10µF capacitors on the output of the
MAX9701 ensure a two-pole highpass filter.
______________________________________________________________________________________
15
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
Low frequencies are summed through a two-pole lowpass filter and sent to the MAX9700 mono speaker
amplifier. The passband gain of the lowpass filter is
unity for in-phase stereo signals,
−2 × R3
R1
where R1 = R2 and R3 = R1//R2. The cutoff frequency
of the lowpass filter is set by the following equation:
f=
1
×
2π
1
C1 × C2 × R 3 × R4
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. Connect PGND and GND together at a
single point on the PC board. Route all traces that carry
switching transients away from GND and the traces/components in the audio signal path.
16
Bypass VDD with 10µF to GND and PVDD with 0.1µF to
PGND. Place the bypass capacitors as close to the
MAX9701 as possible. Use large, low-resistance output
traces. Current drawn from the outputs increases as load
impedance decreases. High-output trace resistance
decreases the power delivered to the load. Large output,
supply, and GND traces allow more heat to move from
the MAX9701 to the air, decreasing the thermal impedance of the circuit.
The MAX9701 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 printed
circuit board. Connect the exposed thermal pad to the
GND plane.
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, printed circuit board
techniques, bump-pad layout, and recommended reflow
temperature profile as well as the latest information on
reliability testing results, refer to Application Note:
UCSP—A Wafer-Level Chip-Scale Package available on
Maxim’s website at www.maxim-ic.com/ucsp.
______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
VDD
10µF
0.1µF
0.1µF
VDD
PVDD
0.1µF
AUX_IN
VCC
470nF
INR+
2.2kΩ
MAX4060
BIAS
MAX9701
470nF
OUTR-
INROUT
CODEC
OUTR+
470nF
INL-
2.2kΩ
OUTL-
470nF
0.1µF
IN+
IN-
INL+
OUTL+
GAIN1
GND
GAIN2
0.1µF
SHDN
SYNC
GND
PGND
VDD
1µF
VDD
SHDN
1µF
INL
OUTL
1µF
MAX9722B
INR
OUTR
µCONTROLLER
PVSS
SVSS
C1P
CIN
1µF
1µF
______________________________________________________________________________________
17
MAX9701
System Diagram
Pin Configurations
TOP VIEW
(BUMPS ON BOTTOM)
INL-
INL+
GND
VDD
INR+
INR-
TOP VIEW
24
23
22
21
20
19
GND 1
20 VDD
INL+ 2
19 INR+
SHDN
1
18 GAIN2
INL- 3
18 INR-
SHDN 4
17 GAIN1
3
16 N.C.
OUTL+
4
15 OUTR+
PVDD
5
14 PVDD
PVDD 7
14 PVDD
PGND
6
13 PGND
PGND 8
13 PGND
7
8
9
10
11
12
OUTL- 9
12 OUTR-
SYNC_OUT
N.C.
OUTR-
MAX9701
16 GAIN1
OUTL+ 6
N.C.
MAX9701
2
N.C.
GND
SYNC 5
SYNC
17 GAIN2
OUTL-
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
GND 10
11 SYNC_OUT
TSSOP
MAX9701
1
2
3
4
5
A
INL-
SHDN
OUTL+
PVDD
OUTL-
B
GND
INL+
SYNC
PGND
GND
C
VDD
INR+
GAIN1
PGND
SYNC
_OUT
D
INR-
GAIN2
OUTR+
PVDD
OUTR-
15 OUTR+
UCSP
TQFN
Chip Information
TRANSISTOR COUNT: 5688
PROCESS: BiCMOS
18
______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
TSSOP4.40mm.EPS
PACKAGE OUTLINE, TSSOP 4.40mm BODY
21-0066
G
1
1
______________________________________________________________________________________
19
MAX9701
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
24L QFN THIN.EPS
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
D
1
2
PACKAGE OUTLINE,
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
21-0139
20
D
2
2
______________________________________________________________________________________
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
5x4 UCSP.EPS
PACKAGE OUTLINE, 5x4 UCSP
21-0095
I
1
1
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 ____________________ 21
© 2005 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products, Inc.
MAX9701
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)