General Description
The MAX9701 stereo Class D audio power amplifier pro-
vides 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 8Ωload while
offering 87% efficiency. Maxim’s next-generation, low-
EMI 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-fre-
quency (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 fea-
tures a fully differential architecture, a full bridge-tied load
(BTL) output, and comprehensive click-and-pop suppres-
sion. 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),
and 20-bump UCSP™ (2mm x 2.5mm x 0.6mm) pack-
ages. The MAX9701 is specified over the extended
-40°C to +85°C temperature range.
Applications
Cellular Phones
Notebooks
Handheld Gaming Consoles
Docking Stations
MP3 Players
Features
oPatented Spread-Spectrum Modulation Lowers
Radiated Emissions
oSingle-Supply Operation (2.5V to 5.5V)
o1.3W Stereo Output (8Ω, VDD = 5V, THD+N = 1%)
oNo LC Output Filter Required
o87% Efficiency (RL= 8Ω, POUT = 1000mW)
oLess Than 0.1% THD+N
oHigh 80dB PSRR
oFully Differential Inputs
oIntegrated Click-and-Pop Suppression
oTypical Low Quiescent Current (9mA)
oTypical Low-Power Shutdown Mode (0.1µA)
oShort-Circuit and Thermal-Overload Protection
oAvailable in Thermally Efficient, Space-Saving
Packages
24-Pin Thin QFN-EP (4mm x 4mm x 0.8mm)
20-Bump UCSP (2mm x 2.5mm x 0.6mm)
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
________________________________________________________________
Maxim Integrated Products
1
MAX9701
GAIN2
GAIN1
VDD
GAIN
RIGHT
MODULATOR
AND H-BRIDGE
SYNC OSCILLATOR
LEFT
MODULATOR
AND H-BRIDGE
INR+
INR-
INL+
INL-
SYNC_OUT
Block Diagram
Ordering Information
19-3457; Rev 3; 3/09
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.
PART TEMP RANGE PIN-PACKAGE
MAX9701EBP+TG45 -40°C to +85°C
20 UCSP
MAX9701ETG+ -40°C to +85°C
24 TQFN-EP*
Pin Configurations appear at end of data sheet.
UCSP is a trademark of Maxim Integrated Products, Inc.
+
Denotes lead(Pb)-free/RoHS-compliant package.
*
EP = Exposed pad.
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RLconnected between
OUT+ and OUT-, RL= ∞, TA= TMIN to TMAX, 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 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
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
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
GENERAL
Supply Voltage Range VDD Inferred from PSRR test 2.5 5.5 V
VDD = 3.3V, per channel 4.5 8
Quiescent Current IDD VDD = 5V, per channel 6.3 10 mA
Shutdown Current ISHDN 0.1 10 µA
Common-Mode Rejection Ratio CMRR fIN = 1kHz 66 dB
Input Bias Voltage VBIAS
1.125 1.25 1.375
V
Turn-On Time tON 40 ms
TA = +25oC
±10 ±30
Output Offset Voltage VOS TMIN < TA < TMAX
±55
mV
VDD = 2.5V to 5.5V, VIN = 0V 60 80
fRIPPLE = 217Hz 72Power-Supply Rejection Ratio PSRR 100mVP-P ripple,
VIN = 0V fRIPPLE = 20kHz 50
dB
RL = 8Ω460
VDD = 3.3V RL = 4Ω750
RL = 8Ω1300
Output Power (Note 3) POUT THD+N = 1%,
TA = +25oCVDD = 5V
RL = 4Ω2200
mW
RL = 8Ω (POUT = 300mW), f = 1kHz
0.08
Total Harmonic Distortion Plus
Noise (Note 3)
THD+N
RL = 4Ω (POUT = 400mW), f = 1kHz
0.15
%
FFM 86
BW = 22Hz
to 22kHz SSM 86
FFM
88.5
Signal-to-Noise Ratio SNR VOUT = 1VRMS
A-weighted
SSM
88.5
dB
SYNC = GND
950 1100 1250
SYNC = unconnected
1200 1400 1600
Oscillator Frequency fOSC
SYNC = VDD
1200
±60
kHz
Minimum On-Time tMIN
200
ns
SYNC Frequency Lock Range fSYNC
1000 1600
kHz
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
_______________________________________________________________________________________ 3
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 4Ωwith large signals, exercise care to avoid violating the absolute maximum rating for continuous
output current.
Note 4: Testing performed with 8Ωresistive load in series with 68µH inductive load connected across the BTL output. Mode transi-
tions 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.
ELECTRICAL CHARACTERISTICS (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = 0V (FFM), gain = 6dB (GAIN1 = 0, GAIN2 = 1), RLconnected 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
SYNC_OUT Capacitance Drive
CSYNC_OUT 100
pF
Bridge-tied capacitance
200
Capacitive Drive CLSingle ended
400
pF
Into shutdown 66.16
Click-and-Pop Level KCP
Peak reading, TH D + N = 1%
A-weighted, 32 samples
per second (Note 4) Out of
shutdown
66.26
dB
VDD = 3.3V, POUT = 500mW per channel,
fIN = 1kHz, RL = 8Ω87
Efficiency η
VDD = 5V, POUT = 1000mW per channel,
fIN = 1kHz, RL = 8Ω
87.4
%
GAIN1 = 0, GAIN2 = 0
10.5
15
19.5
GAIN1 = 1, GAIN2 = 0 25
GAIN1 = 0, GAIN2 = 1
37.4
Input Resistance RIN
GAIN1 = 1, GAIN2 = 1 50
kΩ
GAIN1 = 0, GAIN2 = 0 18
GAIN1 = 1, GAIN2 = 0 12
GAIN1 = 0, GAIN2 = 1 6
Gain AV
GAIN1 = 1, GAIN2 = 1 0
dB
Channel-to-Channel Gain
Tracking 1%
Crosstalk L to R, R to L, f = 10kHz, RL = 8Ω,
POUT = 300mW 70 dB
DIGITAL INPUTS (SHDN, SYNC, GAIN1, GAIN2)
Input-Voltage High VINH 2V
Input-Voltage Low VINL 0.8 V
Input Leakage Current
(SHDN, GAIN1, GAIN2) ±1µA
VIN = GND, normal operation -15 -7
Input Leakage Current (SYNC) VIN = VDD, normal operation 12 25 µA
DIGITAL OUTPUTS (SYNC_OUT)
Output-Voltage High VOH IOH = 3mA, VDD = 3.3V 2.4 V
Output-Voltage Low VOL IOL = 3mA
0.08
V
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
_______________________________________________________________________________________
5
Typical Operating Characteristics (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
CROSSTALK vs. INPUT AMPLITUDE
MAX9701 toc20
INPUT AMPLITUDE (dB)
CROSSTALK (dB)
-14-34-54-74
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-130
-94 6
RL = 8Ω
fIN = 1kHz
RIGHT TO LEFT
LEFT TO RIGHT
OUTPUT FREQUENCY SPECTRUM
MAX9701 toc22
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-140
0 20k
FFM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
OUTPUT FREQUENCY SPECTRUM
MAX9701 toc24
FREQUENCY (Hz)
OUTPUT MAGNITUDE (dBV)
15k10k5k
-120
-100
-80
-60
-40
-20
0
-140
0 20k
SSM MODE
VOUT = -60dBV
f = 1kHz
RL = 8Ω
A-WEIGHTED
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
_______________________________________________________________________________________
7
TURN-ON/TURN-OFF RESPONSE
MAX9701 toc27
MAX9701
OUTPUT
SHDN
0V
250mV/div
2V/div
10ms/div
Typical Operating Characteristics (continued)
(VDD = PVDD = SHDN = 3.3V, GND = PGND = 0V, SYNC = VDD (SSM), gain = 6dB (GAIN1 = 0, GAIN2 = 1)).
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
8 _______________________________________________________________________________________
Pin Description
PIN
TQFN UCSP NAME FUNCTION
1A2SHDN Active-Low Shutdown. Connect to VDD for normal operation.
2 B3 SYNC
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.
3, 8, 11, 16
— N.C. No Connection. Not internally connected.
4 A3 OUTL+ Left-Channel Amplifier Output Positive Phase
5, 14 A4, D4 PVDD H-Bridge Power Supply. Connect to VDD. Bypass with a 0.1µF capacitor to PGND.
6, 13 B4, C4 PGND Power Ground
7 A5 OUTL- Left-Channel Amplifier Output Negative Phase
9, 22 B1, B5 GND Analog Ground
10 C5
SYNC_OUT
Clock Signal Output
12 D5 OUTR- Right-Channel Amplifier Output Negative Phase
15 D3 OUTR+ Right-Channel Amplifier Output Positive Phase
17 C3 GAIN1 Gain-Select Input 1
18 D2 GAIN2 Gain-Select Input 2
19 D1 INR- Right-Channel Inverting Input
20 C2 INR+ Right-Channel Noninverting Input
21 C1 VDD Analog Power Supply. Connect to PVDD. Bypass with a 10µF capacitor to GND.
23 B2 INL+ Left-Channel Noninverting Input
24 A1 INL- Left-Channel Inverting Input
EP — EP Exposed Pad. Connect the exposed thermal pad to the GND plane (see the Supply
Bypassing, Layout, and Grounding section).
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
_______________________________________________________________________________________ 9
Functional Diagram
VBIAS
VBIAS
CLASS D
MODULATOR
AND H-BRIDGE
CLASS D
MODULATOR
AND H-BRIDGE
BIAS
GENERATOR
OSCILLATOR
AND
SAWTOOTH
GAIN
CONTROL
OUTL+
VBIAS
MAX9701
GND PGND
OUTR+
OUTL-
OUTR-
SYNC_OUT
PVDD
SYNC
INL+
INL-
INR+
INR-
GAIN1
GAIN2
SHDN
RIN
RIN
RIN
RIN
470nF
470nF
470nF
470nF
VDD
VDD
10μF 0.1μF
MAX9701
Detailed Description
The MAX9701 filterless, stereo Class D audio power
amplifier features several improvements to switch-mode
amplifier technology. The MAX9701 offers Class AB per-
formance with Class D efficiency, while occupying mini-
mal 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.
Comparators monitor the MAX9701 inputs and compare
the complementary input voltages to the sawtooth wave-
form. 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 sec-
ond 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
10 ______________________________________________________________________________________
OUT+
OUT-
VIN-
VIN+
VOUT+ - VOUT-
tON(MIN)
tSW
Figure 1. MAX9701 Outputs with an Input Signal Applied
Operating Modes
Fixed-Frequency (FFM) Mode
The MAX9701 features two fixed-frequency modes.
Connect SYNC to GND to select a 1.1MHz switching fre-
quency. Leave SYNC unconnected to select a 1.4MHz
switching frequency. The frequency spectrum of the
MAX9701 consists of the fundamental switching frequen-
cy and its associated harmonics (see the Wideband
Output Spectrum (FFM Mode) graph in the
Typical
Operating Characteristics
). Program the switching fre-
quency so the harmonics do not fall within a sensitive fre-
quency band (Table 1). Audio reproduction is not
affected by changing the switching frequency.
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
______________________________________________________________________________________ 11
VOUT_+ - VOUT_-
tSW tSW tSW tSW
VIN_-
VIN_+
OUT_+
OUT_-
tON(MIN)
Figure 2. MAX9701 Outputs with an Input Signal Applied (SSM Mode)
Table 1. Operating Modes
SYNC MODE
GND FFM with fOSC = 1100kHz
Unconnected FFM with fOSC = 1400kHz
VDD SSM with fOSC = 1200kHz ±60kHz
Clocked FFM with fOSC = external clock frequency
MAX9701
Spread-Spectrum (SSM) Mode
The MAX9701 features a unique, patented spread-
spectrum 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 = VDD (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 ampli-
fier, creating a fully synchronous system, minimizing
clock intermodulation, and allocating spectral compo-
nents 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.
SYNC_OUT
SYNC_OUT allows several MAX9701s as well as other
Class D amplifiers (such as the MAX9700) to be cas-
caded. The synchronized output minimizes interfer-
ence 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 compo-
nent 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 pre-
sent. 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 I2R loss of the MOSFET on-
resistance, and quiescent-current overhead.
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
12 ______________________________________________________________________________________
VIN_ = 0V
OUT_-
OUT_+
VOUT_+ - VOUT_- = 0V
Figure 4. MAX9701 Outputs with No Input Signal
FREQUENCY (MHz)
AMPLITUDE (dBμV/m)
280260240200 22080 100 120 140 160 18060
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
0.0
30 300
Figure 3. MAX9701 with 76mm of Speaker Cable with TDK
Common-Mode Choke: TDK ACM4532-801-20-X
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.
Applications Information
Filterless Operation
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 VDD(P-P)) and causes large ripple currents.
Any parasitic resistance in the filter components results
in a loss of power, lowering the efficiency.
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 dam-
aged. For optimum results, use a speaker with a series
inductance >10µH. Typical 8Ωspeakers, 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 8Ωload results in 1mA extra
current consumption in a Class AB device. In the Class D
case, an 8mV offset into 8Ωequates 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%.
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
______________________________________________________________________________________ 13
0
30
20
10
50
40
90
80
70
60
100
0 0.1 0.2 0.40.3 0.5
EFFICIENCY vs. OUTPUT POWER
OUTPUT POWER (W)
EFFICIENCY (%)
MAX9701
CLASS AB VDD = 3.3V
f = 1kHz
RL - 8Ω
Figure 5. MAX9701 Efficiency vs. Class AB Efficiency
GAIN1
GAIN2
GAIN
(dB)
INPUT
(VRMS)
RL
(Ω)
POUT
(mW)
0 0 +18
0.305
41100
1 0 +12
0.615
41100
01+6
1.213
41100
110
2.105
41100
0 0 +18
0.345
8725
1 0 +12
0.686
8725
01+6
1.360
8725
110
2.705
8725
Table 2. Gain Settings
MAX9701
Input Amplifier
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-fre-
quency 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 differ-
ential input amplifier amplifies the difference of the two
inputs, any signal common to both inputs is canceled.
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 cou-
pling eliminates the input-coupling capacitors, reduc-
ing 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.
Component Selection
Input Filter
An input capacitor, CIN, 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 automati-
cally bias the signal to an optimum DC level. Assuming
zero-source impedance, the -3dB point of the highpass
filter is given by:
Choose CIN so f-3dB is well below the lowest frequency of
interest. Use capacitors whose dielectrics have low-volt-
age coefficients, such as tantalum or aluminum electrolyt-
ic. Capacitors with high-voltage coefficients, such as
ceramics, may result in increased distortion at low fre-
quencies.
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 concen-
trate on the frequency range of the spoken human voice
(typically 300Hz to 3.5kHz). In addition, speakers used
fRC
dB IN IN
−=
3
1
2π
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
14 ______________________________________________________________________________________
MAX9701
0.1μF10μF
2.5V TO 5.5V
0.47μF
0.47μF
0.47μF
0.47μF
SINGLE-ENDED
LEFT AUDIO INPUT
SINGLE-ENDED
RIGHT AUDIO INPUT
OUTL+
OUTL-
OUTR+
OUTR-
GAIN1
GND
PGND
SYNC
INL+
INR+
INL-
INR-
GAIN2
SHDN
VDD
PVDD
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB.
Figure 6. Single-Ended Input
MAX9701
0.1μF10μF
2.5V TO 5.5V
OUTL+
OUTL-
OUTR+
OUTR-
GAIN1
GND
PGND
SYNC
INL+
INR+
INL-
INR-
GAIN2
SHDN
VDD
PVDD
FFM MODE WITH fOSC = 1100kHz, GAIN = 6dB
CODEC BIASED TO 1/2 MAX9701 COMMON-MODE VOLTAGE.
CODEC
Figure 7. DC-Coupled Inputs
in portable devices typically have a poor response
below 300Hz. Taking these two factors into considera-
tion, 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:
where RIN is the typical input resistance of the
MAX9701. The 10µF capacitors on the output of the
MAX9701 ensure a two-pole highpass filter.
fRC
IN IN
=××
1
2π
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
______________________________________________________________________________________ 15
MAX9701
MAX9700
MAX4238
INR+
INL+
INL-
INR-
SYNC
5V
OUTL+
OUTL-
OUTR+
OUTR-
8Ω
8Ω
SYNC_OUT
10μF
10μF
CIN
2200pF
1μF
1μF
5V
NOTE: VALUES SHOWN ARE FOR A LOWPASS CUTOFF OF 2Hz AND A BASS GAIN OF -1V/V.
FFM MODE WITH fOSC = 1100kHz.
OUT+
OUT-
SYNC
IN+
IN-
1.25V
R3
10kΩ
C2
1nF
R1
20kΩ
R2
20kΩ
R4
39kΩ
C2
0.01μF
VDD
CIN
2200pF
CIN
2200pF
CIN
2200pF
4Ω
Figure 8. 2.1 Channel Application Circuit
MAX9701
Low frequencies are summed through a two-pole low-
pass filter and sent to the MAX9700 mono speaker
amplifier. The passband gain of the lowpass filter is
unity for in-phase stereo signals,
where R1 = R2 and R3 = R1//R2. The cutoff frequency
of the lowpass filter is set by the following equation:
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 chan-
nels, 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/com-
ponents in the audio signal path.
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 imped-
ance 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.
fCC R R
=× ×××
1
2
1
12 34π
−×23
1
R
R
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
16 ______________________________________________________________________________________
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
______________________________________________________________________________________ 17
MAX4060
MAX9701
MAX9722B
CODEC
AUX_IN
BIAS
IN+
IN-
VCC
OUTL-
OUTL+
OUTR+
OUTR-
INL
INR
C1P CIN
SVSS
PVSS
OUTR
OUTL
VDD
0.1μF
0.1μF
0.1μF
2.2kΩ
2.2kΩ
VDD
μCONTROLLER
INL+
SYNC
OUT
1μF
1μF
1μF
1μF
1μF
SHDN
SHDN
GND
470nF
470nF
470nF
470nF
GAIN1
GAIN2
INL-
INR-
INR+
0.1μF10μF
VDD
VDD PVDD
GND PGND
0.1μF
System Diagram
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
18 ______________________________________________________________________________________
Chip Information
TRANSISTOR COUNT: 5688
PROCESS: BiCMOS
GND INL+ SYNC PGND GND
VDD INR+ GAIN1 PGND SYNC
_OUT
INR- GAIN2 OUTR+ PVDD OUTR-
INL- SHDN OUTL+ PVDD OUTL-A
B
C
D
12345
MAX9701
UCSP
TOP VIEW
(BUMPS ON BOTTOM)
MAX9701
18 17 16 15 14
19
TQFN
TOP VIEW
13
1 2 3 4 5 6
24
23
22
21
20
12
7
8
9
10
11
INL+
VDD
INR+
INR-
INL-
GND
N.C.
SYNC_OUT
N.C.
OUTR-
OUTL-
GND
SHDN
SYNC
N.C.
OUTL+
PVDD
PGND
GAIN2
GAIN1
N.C.
OUTR+
PVDD
PGND
Pin Configurations
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
______________________________________________________________________________________ 19
24L QFN THIN.EPS
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the
package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
24 TQFN-EP T2444-4 21-0139
20 UCSP B20-1 21-0095
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
20 ______________________________________________________________________________________
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the
package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power Amplifier
______________________________________________________________________________________ 21
5x4 UCSP.EPS
Package Information (continued)
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a "+", "#", or "-" in the
package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the
package regardless of RoHS status.
MAX9701
1.3W, Filterless, Stereo Class D Audio
Power 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.
22
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2009 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
3 3/09 Added G45 option to Ordering Information 1