MAX9770_V01 [MAXIM]
1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers;
| 型号： | MAX9770_V01 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | 1.2W, Low-EMI, Filterless, Mono Class D Amplifier with Stereo DirectDrive Headphone Amplifiers |
| 文件： | 总22页 (文件大小：468K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3134; Rev 2; 4/08
EVALUATION KIT
AVAILABLE
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
General Description
Features
♦ 1.2W Filterless Class D Amplifiers Pass FCC
The MAX9770 combines a mono, filterless, Class D
speaker amplifier and stereo DirectDrive® headphone
amplifier in a single device. The MAX9770 operates
from a single 2.5V to 5.5V supply and includes features
that reduce external component count, system cost,
board space, and offer improved audio reproduction.
Class B Radiated EMI Standards with 100mm
of Cable
♦ Spread-Spectrum Mode Offers 5dB EMI
Improvement over Conventional Methods
♦ 80mW DirectDrive Headphone Amplifier
Eliminates Bulky DC-Blocking Capacitors
♦ High 85dB PSRR at 217Hz
The speaker amplifier makes use of Maxim’s Class D
architecture, providing Class AB performance with Class
D efficiency, conserving board space, and extending
battery life. The speaker amplifier delivers 1.2W into an
8Ω load while offering efficiencies above 85%. A spread-
spectrum modulation scheme reduces radiated emis-
sions caused by the modulation frequency. Furthermore,
the MAX9770 oscillator can be synchronized to an exter-
nal clock through the SYNC input, avoiding possible
problem frequencies inside a system. The speaker
amplifier features THD+N as low as 0.025%, high 70dB
PSRR, and SNR in excess of 90dB.
♦ 85% Efficiency
♦ Low 0.015% THD+N
♦ Industry-Leading Click-and-Pop Suppression
♦ Integrated 3-Way Input Mixer/Multiplexer
(MAX9770)
♦ Logic-Adjustable Gain
♦ Short-Circuit and Thermal Protection
♦ Available in Space-Saving, Thermally Efficient
Packages
The headphone amplifiers feature Maxim’s DirectDrive
architecture that produces a ground-referenced output
from a single supply, eliminating the need for large DC-
blocking capacitors. The headphone amplifiers deliver up
to 80mW into a 16Ω load, feature low 0.015% THD+N,
high 85dB PSRR, and 8kV ESD-protected outputs. A
headphone sense input detects the presence of a head-
phone, and automatically configures the amplifiers for
either speaker or headphone mode.
Ordering Information
PART
PIN-PACKAGE
28 TQFN-EP*
28 TSSOP
SELECTABLE INPUTS
2 stereo, 1 mono
MAX9770ETI+
MAX9770EUI
2 stereo, 1 mono
Note: All devices specified over the -40°C to +85°C operating
temperature range.
*EP = Exposed pad.
+
Denotes a lead-free package.
The MAX9770 includes internally set, logic-selectable
gain, and a comprehensive input multiplexer/mixer, allow-
ing multiple audio sources to be selected and for true
mono reproduction of a stereo source in speaker mode.
Industry-leading click-and-pop suppression eliminates
audible transients during power and shutdown cycles. A
low-power shutdown mode decreases supply current
consumption to 0.1µA, further extending battery life.
Pin Configuration appears at end of data sheet.
Simplified Block Diagram
V
DD
DirectDrive
STEREO
HEADPHONE
IN1L
IN2L
The MAX9770 is offered in space-saving, thermally effi-
cient 28-pin TQFN (5mm x 5mm x 0.8mm) and 28-pin
TSSOP packages. The MAX9770 features thermal-over-
load and output short-circuit protection, and is speci-
fied over the extended -40°C to +85°C temperature
range.
MONO
IN1R
IN2R
Applications
Cellular Phones
Compact Notebooks
PDAs
GAIN SEL
INPUT SEL
MUTE
SPKR
(MONO)
CLASS
D
SHDN
HPS
MAX9770
________________________________________________________________ Maxim Integrated Products
1
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.
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
ABSOLUTE MAXIMUM RATINGS
GND to PGND to CPGND......................................-0.3V to +0.3V
Duration of Short Circuit Between
V
V
PV
to PV
to CPV ..........................................-0.3V to +0.3V
HPOUTL and HPOUTR ..........................................Continuous
DD
DD
DD
DD
to GND ...........................................................................+6V
Duration of OUT_ Short Circuit to V , PV , GND, PGND ..10s
DD DD
to PGND.......................................................................+6V
Duration of Short Circuit Between OUT+ and OUT-...............10s
DD
CPV
to CPGND..................................................................+6V
Continuous Power Dissipation (T = +70°C)
DD
A
CPV to CPGND....................................................................-6V
28-Pin TQFN (derate 20.8mW/°C above +70°C) .......1667mW
28-Pin TSSOP (derate 12.8mW°C above +70°C) ......1026mW
Junction Temperature......................................................+150°C
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
SS
SV to GND...........................................................................-6V
SS
C1N..........................................(PV - 0.3V) to (CPGND + 0.3V)
HPOUT_ to GND .................................................................... 3V
All Other Pins to GND.................................-0.3V to (V
Continuous Current Into/Out of:
SS
MAX970
+ 0.3V)
DD
PV , PGND, OUT_......................................................600mA
DD
PV ..............................................................................260mA
SS
Duration of HPOUT_ Short Circuit to V , PV
,
DD
DD
GND, PGND ...........................................................Continuous
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
(V
DD
= PV
= CPV
= 3.3V, GND = PGND = CPGND = 0V, SHDN = 3.3V, C1 = C2 = 1µF, C
= 0.047µF, SYNC = GND, R = ∞,
DD
DD
BIAS L
speaker load connected between OUT+ and OUT-, headphone load connected between HPOUT_ and GND, T = T
to T
,
A
MIN
MAX
unless otherwise noted. Typical values are at T = +25°C.) (Notes 1, 2)
A
PARAMETER
GENERAL
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage Range
V
Inferred from PSRR test
2.5
5.5
10
V
DD
Headphone mode
5.5
5.2
0.1
50
Quiescent Supply Current
I
No load
mA
DD
Speaker mode
7.5
10
Shutdown Supply Current
Shutdown to Full Operation
I
SHDN = HPS = GND
µA
ms
SHDN
t
ON
MONO
7
10
Input Impedance
Bias Voltage
R
(Note 3)
kΩ
V
IN
INL_, INR_
14
1.1
20
V
1.25
1.4
70
BIAS
From any unselected input to any output,
f = 10kHz
Feedthrough
70
dB
SPEAKER AMPLIFIER (GAIN1 = GAIN2 = V , HPS = GND)
DD
Output Offset Voltage
V
15
70
mV
dB
OS
V
= 2.5V to 5.5V,
= +25°C
DD
50
T
A
Power-Supply Rejection Ratio
PSRR
(Note 4)
V
V
V
= 200mV , f = 217Hz
70
68
RIPPLE
RIPPLE
RIPPLE
P-P
= 200mV , f = 1kHz
P-P
= 200mV , f = 20kHz
P-P
50
R = 8Ω
550
900
f = 1kHz,
L
V
V
= 3.3V
= 5V
DD
DD
THD+N = 1%,
GAIN1 = 1,
GAIN2 = 0
R = 4Ω
L
Output Power
P
mW
OUT
R = 8Ω
L
1200
2
_______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= PV
= CPV
= 3.3V, GND = PGND = CPGND = 0V, SHDN = 3.3V, C1 = C2 = 1µF, C
= 0.047µF, SYNC = GND, R = ∞,
DD
DD
BIAS L
speaker load connected between OUT+ and OUT-, headphone load connected between HPOUT_ and GND, T = T
to T
,
A
MIN
MAX
unless otherwise noted. Typical values are at T = +25°C.) (Notes 1, 2)
A
PARAMETER
SYMBOL
THD+N
SNR
CONDITIONS
MIN
TYP
0.025
0.03
MAX
UNITS
%
R = 8Ω, P
= 300mW, f = 1kHz
= 300mW, f = 1kHz
= 500mW,
L
OUT
OUT
OUT
Total Harmonic Distortion Plus
Noise
R = 4Ω, P
L
R = 8Ω, P
L
0.1
f = 1kHz
Signal-to-Noise Ratio
R = 8Ω, V
L
= 2V , A-weighted
RMS
85.9
1100
1450
dB
OUT
SYNC = GND
SYNC = unconnected
980
1220
1620
1280
Output Switching Frequency
f
S
kHz
1220
120kHz
SYNC = V
DD
SYNC Frequency Lock Range
Efficiency
800
2000
kHz
%
η
P
= 1000mW, f = 1kHz
85
6
O
GAIN1 = 0, GAIN2 = 0
GAIN1 = 0, GAIN2 = 1
GAIN1 = 1, GAIN2 = 0
GAIN1 = 1, GAIN2 = 1
3
Gain (MAX9770)
A
dB
V
9
0
Gain Accuracy
5
%
HPS = V , headphone amplifier active,
DD
f = 1kHz
Speaker Path Off-Isolation
102
dB
Into shutdown
Out of shutdown
Into mute
-76
-55
-83
-69
Peak voltage,
A-weighted, 32
samples per second
(Notes 4, 5)
Click-and-Pop Level
K
dB
CP
Out of mute
HEADPHONE AMPLIFIER (GAIN1 = 1, GAIN2 = 0, HPS = V
)
DD
Output Offset Voltage
V
5
76
10
mV
dB
OS
V
V
V
V
= 2.5V to 5.5V, T = +25°C
65
40
DD
A
= 200mV , f = 217Hz
75
RIPPLE
RIPPLE
RIPPLE
P-P
Power-Supply Rejection Ratio
PSRR
(Note 4)
= 200mV , f = 1kHz
82
P-P
= 200mV , f = 20kHz
56
P-P
R = 32Ω
55
L
T
= +25°C,
A
V
V
= 3.3V
= 5V
DD
DD
R = 16Ω
L
40
f = 1kHz,
Output Power
P
mW
%
OUT
THD+N = 1%
(Note 3)
R = 32Ω
L
60
R = 16Ω
L
80
R = 32Ω, P
= 50mW, f = 1kHz
= 35mW, f = 1kHz
0.015
0.03
L
OUT
Total Harmonic Distortion Plus
Noise
THD+N
R = 16Ω, P
L
OUT
_______________________________________________________________________________________
3
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= PV
= CPV
= 3.3V, GND = PGND = CPGND = 0V, SHDN = 3.3V, C1 = C2 = 1µF, C
= 0.047µF, SYNC = GND, R = ∞,
DD
DD
BIAS L
speaker load connected between OUT+ and OUT-, headphone load connected between HPOUT_ and GND, T = T
to T
,
A
MIN
MAX
unless otherwise noted. Typical values are at T = +25°C.) (Notes 1, 2)
A
PARAMETER
SYMBOL
CONDITIONS
= 300mV ,
RMS
MIN
TYP
MAX
UNITS
R = 32Ω, V
L
OUT
Signal-to-Noise Ratio
SNR
101
dB
BW = 22Hz to 22kHz
Between channels, f = 1kHz,
= 200mV
MAX970
Crosstalk
80
96
dB
dB
V
IN
P-P
HPS = GND, speaker amplifier active,
f = 1kHz
Headphone Off-Isolation
Into shutdown
Out of shutdown
Into mute
-58
-53
-92
Peak voltage, A-
weighted, 32
samples per second
(Notes 4, 5)
Click-and-Pop Level
K
dBV
pF
CP
Out of mute
-73
Capacitive-Load Drive
C
1000
L
GAIN1 = 0, GAIN2 = 0
GAIN1 = 0, GAIN2 = 1
GAIN1 = 1, GAIN2 = 0
GAIN1 = 1, GAIN2 = 1
7
4
Gain
A
dB
V
-2
1
Gain Accuracy
ESD Protection
2.5
%
HPOUTR, HPOUTL, IEC Air Discharge
8
kV
DIGITAL INPUTS (SHDN, SYNC, HPS, GAIN_, SEL_)
Input Voltage High
Input Voltage Low
V
2
V
V
IH
V
0.8
25
1
IL
SYNC input
Input Leakage Current (Note 6)
HPS Input Current
µA
µA
All other logic inputs
HPS = GND
-10
Note 1: All devices are 100% production tested at +25°C. All temperature limits are guaranteed by design.
Note 2: Speaker amplifier testing performed with a resistive load in series with an inductor to simulate an actual speaker load. For
R = 4Ω, L = 47µH. For R = 8Ω, L = 68µH.
L
L
Note 3: Guaranteed by design, not production tested.
Note 4: Inputs AC-coupled to GND.
Note 5: Speaker mode testing performed with an 8Ω resistive load in series with a 68µH inductive load connected across BTL output.
Headphone mode testing performed with a 32Ω resistive load connected to GND. Mode transitions are controlled by SHDN. K
level is calculated as: 20 x log [(peak voltage during mode transition, no input signal)/(peak voltage under normal operation at
CP
rated power level)]. Units are expressed in dB. Measured with V = 5V.
DD
Note 6: SYNC has a 200kΩ resistor to V
= 1.25V.
REF
4
_______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Typical Operating Characteristics
(V
DD
= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise
noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY (SPEAKER MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY (SPEAKER MODE)
vs. FREQUENCY (SPEAKER MODE)
10
10
10
R = 8Ω
L
V
= +5V
R = 4Ω
L
DD
L
R = 4Ω
1
1
1
P
= 25mW
OUT
P
= 40mW
OUT
P
OUT
= 100mW
0.1
0.1
0.1
0.01
0.01
0.01
P
OUT
= 500mW
P
OUT
= 400mW
P
OUT
= 1000mW
0.001
0.001
0.001
10
100
1k
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (SPEAKER MODE)
100
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY (SPEAKER MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (SPEAKER MODE)
100
10
V
= 5V
V
P
= 5V
DD
DD
R = 4Ω
L
R = 8Ω
L
= 1W
OUT
R = 8Ω
L
10
1
10
1
1
f = 1kHz
f = 1kHz
0.1
SSM MODE
f = 20Hz
f = 20Hz
0.1
0.1
0.01
FFM MODE
0.01
f = 10kHz
1200
0.01
f = 10kHz
0.001
0.001
0.001
0
1600
400
800
10
100
1k
10k
100k
0
800 1000
200
600
400
OUTPUT POWER (mW)
FREQUENCY (Hz)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (SPEAKER MODE)
100
OUTPUT POWER
vs. LOAD RESISTANCE (SPEAKER MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (SPEAKER MODE)
1.75
1.50
100
10
1
V
= 5V
R = 8Ω
L
DD
V
= 5V
DD
f = 1kHz
f = 1kHz
R = 8Ω
10
L
THD+N = 10%
1.25
1.00
1
f = 1kHz
SSM MODE
0.75
0.50
0.25
f = 20Hz
THD+N = 1%
0.1
0.1
0.01
0.01
f = 10kHz
FFM MODE
0.001
0
0.001
0
800
1
10
LOAD RESISTANCE (Ω)
100
200
400
600
0
1600
400
800
1200
OUTPUT POWER (mW)
OUTPUT POWER (mW)
_______________________________________________________________________________________
5
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise
noted.)
OUTPUT POWER
vs. LOAD RESISTANCE (SPEAKER MODE)
OUTPUT POWER
vs. SUPPLY VOLTAGE (SPEAKER MODE)
EFFICIENCY vs. OUTPUT POWER
1.0
0.8
0.6
0.4
0.2
100
90
80
70
60
50
40
30
20
10
0
2.0
1.5
1.0
0.5
0
f = 1kHz
f = 1kHz
R = 8Ω
L
THD+N = 10%
MAX970
THD+N = 10%
THD+N = 1%
THD+N = 1%
V
= 5V
DD
f = 1kHz
R = 8Ω
L
0
0
0.2 0.4 0.6 0.8 1.0 1.2 1.4
OUTPUT POWER (W)
1
10
100
2.5
10
0
3.0
3.5
4.0
4.5
5.0
5.5
100k
20
LOAD RESISTANCE (Ω)
SUPPLY VOLTAGE (V)
OUTPUT SPECTRUM
(SPEAKER MODE)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY (SPEAKER MODE)
EFFICIENCY vs. OUTPUT POWER
100
0
0
R = 8Ω
L
V
= 200mV
P-P
90
80
70
60
50
40
30
20
10
0
RIPPLE
R = 8Ω
f = 1kHz
FFM MODE
L
-10
-20
-30
-40
-50
-60
-70
-80
R = 8Ω
L
-20
-40
V
= -60dBV
IN
R = 4Ω
L
-60
-80
-100
-120
-140
f = 1kHz
0
0.2
0.4
0.6
0.8
1.0
100
1k
FREQUENCY (Hz)
10k
15
0
5
10
FREQUENCY (kHz)
20
OUTPUT POWER (W)
OUTPUT SPECTRUM
(SPEAKER MODE)
OUTPUT SPECTRUM
(SPEAKER MODE)
WIDEBAND OUTPUT SPECTRUM
(SPEAKER MODE)
40
0
0
FFM MODE
RBW = 10kHz
R = 8Ω
L
R = 8Ω
L
30
20
-20
f = 1kHz
-20
f = 1kHz
SSM MODE
A-WEIGHTED
SSM MODE
-40
V
IN
= -60dBV
-40
-60
10
V
IN
= -60dBV
-60
-80
0
-10
-20
-30
-40
-80
-100
-120
-140
-100
-120
-140
-50
-60
-160
1M
10M
FREQUENCY (Hz)
100M
0
5
10
FREQUENCY (kHz)
15
5
10
FREQUENCY (kHz)
15
20
6
_______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise
noted.)
STARTUP WAVEFORM
(SPEAKER MODE)
WIDEBAND OUTPUT SPECTRUM
(SPEAKER MODE)
MAX9770 toc20
40
SSM MODE
RBW = 10kHz
30
20
SHDN
2V/div
10
0
-10
-20
-30
-40
OUT+ - OUT-
500mV/div
R = 8Ω
L
-50
-60
f = 1kHz
1M
10M
FREQUENCY (Hz)
100M
4ms/div
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY (HEADPHONE MODE)
MIXER OUTPUT (SPEAKER MODE)
MAX9770 toc21
10
10kHz
1V/div
V
= 5V
DD
IN1_
R = 16Ω
L
1
IN2_
4kHz
1V/div
P
OUT
= 10mW
0.1
MONO
1kHz
2V/div
0.01
OUT
P
OUT
= 50mW
1V/div
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
400μs/div
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY (HEADPHONE MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY (HEADPHONE MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. FREQUENCY (HEADPHONE MODE)
10
10
10
V
= 5V
R = 16Ω
L
DD
L
R = 32Ω
L
R = 32Ω
1
1
1
P = 10mW
OUT
P
OUT
= 10mW
P
OUT
= 10mW
0.1
0.1
0.1
0.01
0.01
0.01
P
OUT
= 35mW
P
= 50mW
OUT
P
OUT
= 50mW
0.001
0.001
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
_______________________________________________________________________________________
7
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise
noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (HEADPHONE MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (HEADPHONE MODE)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (HEADPHONE MODE)
100
10
1
100
10
1
100
10
1
V
= 5V
DD
R = 16Ω
L
V
= 5V
DD
L
R = 32Ω
L
R = 16Ω
MAX970
f = 10kHz
f = 1kHz
f = 10kHz
f = 1kHz
f = 1kHz
f = 10kHz
0.1
0.1
0.1
0.01
0.01
0.01
f = 20Hz
20
f = 20Hz
20
f = 20Hz
0.001
0.001
0.001
60
0
40
80
10
20
50
0
30
40
60
0
40
60
80
100
OUTPUT POWER (mW)
OUTPUT POWER (mW)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS NOISE
vs. OUTPUT POWER (HEADPHONE MODE)
OUTPUT POWER
vs. LOAD RESISTANCE (HEADPHONE MODE)
OUTPUT POWER
vs. LOAD RESISTANCE (HEADPHONE MODE)
100
10
1
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
R = 32Ω
L
V
= 5V
f = 1kHz
DD
f = 1kHz
THD+N = 10%
THD+N = 1%
THD+N = 10%
THD+N = 1%
f = 10kHz
f = 1kHz
0.1
0.01
f = 20Hz
0.001
60
10
100
1000
0
20
40
80
10
100
1000
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
LOAD RESISTANCE (Ω)
OUTPUT POWER
OUTPUT POWER
POWER DISSIPATION
vs. SUPPLY VOLTAGE (HEADPHONE MODE)
vs. SUPPLY VOLTAGE (HEADPHONE MODE)
vs. OUTPUT POWER (HEADPHONE MODE)
100
80
70
60
50
40
30
20
10
0
300
250
200
150
100
50
R = 16Ω
R = 32Ω
L
L
THD+N = 10%
90
80
70
60
50
40
30
20
10
0
f = 1kHz
f = 1kHz
THD+N = 10%
R = 16Ω
L
THD+N = 1%
THD+N = 1%
R = 32Ω
L
f = 1kHz
P
OUT
= P
+ P
OUTL OUTR
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
0
30
60
90
120
150
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
8
_______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Typical Operating Characteristics (continued)
(V
DD
= 3.3V, BW = 22Hz to 22kHz, GAIN1 = 1, GAIN2 = 0, spread-spectrum mode, headphone outputs in phase, unless otherwise
noted.)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY (HEADPHONE MODE)
CROSSTALK vs. FREQUENCY
(HEADPHONE MODE)
FEEDTHROUGH vs. FREQUENCY
0
0
0
-10
-20
-30
-40
-50
-60
-70
-80
-90
-100
V
V
= 3.3V
SEL1 = 0
SEL2 = 1
IN1_ = GND
IN2_ = DRIVEN
DD
R = 32Ω
f = 1kHz
L
-10
-20
-30
-40
-50
-60
-70
-80
-10
-20
-30
-40
-50
-60
-70
-80
= 200mV
RIPPLE
P-P
R = 32Ω
L
V
IN
= 200mV
P-P
V
= 2V
IN
P-P
MAX9770
= 0.047μF
C
BIAS
HEADPHONE MODE
SPEAKER MODE
LEFT TO RIGHT
-90
-90
RIGHT TO LEFT
100
-100
-100
10
100
1k
10k
100k
10
100
1k
10k
100k
10
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
OUTPUT POWER
EXITING SHUTDOWN
(HEADPHONE MODE)
OUTPUT SPECTRUM
(HEADPHONE MODE)
vs. CHARGE-PUMP CAPACITANCE
AND LOAD RESISTANCE
MAX9770 toc40
0
-20
60
50
40
30
20
10
0
R = 32Ω
L
R = 32Ω
C1 = C2 = 1μF
L
f = 1kHz
SHDN
2V/div
V
IN
= -60dBV
-40
C1 = C2 = 0.47μF
-60
-80
-100
-120
-140
OUT_
10mV/div
f = 1kHz
THD+N = 1%
20
30
40
50
0
5
10
15
20
2μs/div
FREQUENCY (kHz)
LOAD RESISTANCE (Ω)
ENTERING SHUTDOWN
(HEADPHONE MODE)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9770 toc41
0.5
10
8
R = 32Ω
L
0.4
0.3
0.2
0.1
0
SHDN
2V/div
SPEAKER MODE
6
HEADPHONE MODE
4
2
OUT_
10mV/div
0
2.5
3.5
4.5
5.5
2.5
3.5
4.5
5.5
2μs/div
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
9
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
Pin Description
PIN
NAME
FUNCTION
TQFN-EP
TSSOP
1
2
4
5
BIAS
Common-Mode Bias Voltage. Bypass with a 0.047µF capacitor to GND.
Power Supply
V
DD
3
6
HPOUTR
HPOUTL
Right-Channel Headphone Output
Left-Channel Headphone Output
4
7
MAX970
5
8
SV
Headphone Amplifier Negative Power Supply
Headphone Sense Input
SS
6
9
HPS
CPV
7
10
11
12
13
14
Positive Charge-Pump Power Supply
DD
8
CPV
Charge-Pump Output. Connect to SV
.
SS
SS
9
C1N
Charge-Pump Flying Capacitor Negative Terminal
Charge-Pump Flying Capacitor Positive Terminal
Charge-Pump Ground
10
11
C1P
CPGND
Select Stereo Channel 1 Inputs. Digital input. Drive SEL1 high to select inputs IN1L and
IN1R.
12
13
14
15
15
16
17
18
SEL1
SEL2
SELM
SHDN
Select Stereo Channel 2 Inputs. Digital input. Drive SEL2 high to select inputs IN2L and
IN2R.
Select Mono Channel Input. Digital input. Drive SELM high to select the MONO input.
Shutdown. Drive SHDN low to disable the device. Connect SHDN to V
for normal
DD
operation.
Frequency Select and External Clock Input:
SYNC = GND: fixed-frequency PWM mode with f = 1100kHz.
S
16
19
SYNC
SYNC = Unconnected: fixed-frequency PWM mode with f = 1450kHz.
S
SYNC = V : spread-spectrum PWM mode with f = 1220kHz 120kHz.
DD
S
SYNC = Clocked: fixed-frequency PWM mode with f = external clock frequency.
S
17
18
19
20
21
22
23
24
25
26
27
28
20
21
22
23
24
25
26
27
28
1
PGND
OUT+
OUT-
Speaker Amplifier Power Ground
Speaker Amplifier Positive Output
Speaker Amplifier Negative Output
Speaker Amplifier Power Supply
Gain Control Input 2
PV
DD
GAIN2
GAIN1
MONO
IN2L
Gain Control Input 1
Mono Channel Input
Stereo Channel 2, Left Input
Stereo Channel 1, Left Input
Ground
IN1L
GND
2
IN2R
Stereo Channel 2, Right Input
Stereo Channel 1, Right Input
3
IN1R
Exposed Paddle. Can be left unconnected or connected to GND. Connect to ground
plane for improved thermal performance.
—
—
EP
10 ______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Detailed Description
Table 1. Operating Modes
The MAX9770 combines a mono 1.2W Class D speaker
amplifiers and stereo 80mW DirectDrive headphone
amplifiers with integrated headphone sensing and
comprehensive click-and-pop suppression. A
mixer/multiplexer allows for selection and mixing
between two stereo input sources and a single mono
source. The MAX9770 features PSRR as high as 85dB,
THD as low as 0.015%, industry-leading click-and-pop
suppression, and a low-power shutdown mode.
SYNC INPUT
MODE
FFPWM with f = 1100kHz
GND
S
Unconnected
FFPWM with f = 1450kHz
S
V
SSPWM with f = 1220kHz 120kHz
S
DD
Clocked
FFPWM with f = external clock frequency
S
second comparator trip point, generating a minimum-
width pulse t at the output of the second com-
ON(MIN)
parator (Figure 1). As the input voltage increases or
decreases, the duration of the pulse at one output
increases (the first comparator trip point) while the
Class D Speaker Amplifier
The MAX9770 Class D amplifier features true filterless,
low-EMI, switch-mode architecture that provides Class
AB-like performance with Class D efficiency.
Comparators monitor the MAX9770 input and compare
the input voltage to a sawtooth waveform. The com-
parators trip when the input magnitude of the sawtooth
exceeds the corresponding input voltage. The com-
parator resets at a fixed time after the rising edge of the
other output pulse duration remains at t
. This
-
ON(MIN)
causes the net voltage across the speaker (V
OUT+
V
) to change.
OUT-
t
SW
V
IN-
V
IN+
OUT-
OUT+
t
ON(MIN)
V
- V
OUT-
OUT+
Figure 1. MAX9770 Outputs with an Input Signal Applied
______________________________________________________________________________________ 11
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
Applying an external clock of 800kHz to 2MHz to SYNC
synchronizes the switching frequency of both the Class
D and charge pump. The period of the SYNC clock can
be randomized, enabling the MAX9770 to be synchro-
nized to another spread-spectrum Class D amplifier
operating in SSM mode.
Operating Modes
The switching frequency of the charge pump is 1/2 the
switching frequency of the Class D amplifier, regard-
less of the operating mode. When SYNC is driven exter-
nally, the charge pump switches at 1/2 f
. When
SYNC
SYNC = V , the charge pump switches with a spread-
DD
spectrum pattern.
Filterless Modulation/Common-Mode Idle
The MAX9770 uses Maxim’s unique 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
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, increasing power con-
sumption. When no signal is present at the device input,
the outputs switch as shown in Figure 4. Because the
MAX9770 drives the speaker differentially, the two out-
puts cancel each other, resulting in no net idle mode volt-
age across the speaker, minimizing power consumption.
Fixed-Frequency Modulation (FFM) Mode
The MAX9770 features two FFM modes. The FFM
modes are selected by setting SYNC = GND for a
1.1MHz switching frequency, and SYNC = unconnect-
ed for a 1.45MHz switching frequency. In FFM mode,
the frequency spectrum of the Class D output consists
of the fundamental switching frequency and its associ-
ated harmonics (see the Wideband Output Spectrum
(Speaker Mode) graph in the Typical Operating
Characteristics). The MAX9770 allows the switching fre-
quency to be changed by +32% should the frequency
of one or more harmonics fall in a sensitive band. This
can be done during operation and does not affect
audio reproduction.
MAX970
Efficiency
The 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 out-
put stage is mostly due to the I*R loss of the MOSFET
on-resistance, and quiescent current overhead.
Spread-Spectrum Modulation (SSM) Mode
The MAX9770 features a unique spread-spectrum
mode that flattens the wideband spectral components,
improving EMI emissions radiated by the speaker and
cables by 5dB. Proprietary techniques ensure that the
cycle-to-cycle variation of the switching period does
not degrade audio reproduction or efficiency (see the
Typical Operating Characteristics). Select SSM mode
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 MAX9770 still exhibits > 80% efficiencies
under the same conditions (Figure 5).
by setting SYNC = V . In SSM mode, the switching
DD
frequency varies randomly by 120kHz around the cen-
ter frequency (1.22MHz). The modulation scheme
remains the same, but the period of the sawtooth wave-
form 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 MHz, the wideband spectrum looks like white
noise for EMI purposes (Figure 3).
DirectDrive
Traditional single-supply headphone drivers have their
outputs biased about a nominal DC voltage (typically
half the supply) for maximum dynamic range. Large
coupling capacitors are needed to block this DC bias
from the headphone. Without these capacitors, a signif-
icant amount of DC current flows to the headphone,
resulting in unnecessary power dissipation and possi-
ble damage to both headphone and headphone driver.
External Clock Mode
The SYNC input allows the MAX9770 to be synchro-
nized to a system clock (allowing a fully synchronous
system), or allocating the spectral components of the
switching harmonics to insensitive frequency bands.
12 ______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
t
t
t
t
SW
SW
SW
SW
V
IN-
V
IN+
OUT-
OUT+
t
ON(MIN)
V
- V
OUT-
OUT+
Figure 2. MAX9770 Output with an Input Signal Applied (SSM Mode)
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
FCC LIMIT
MAX9770
30.0
60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0 220.0 240.0 260.0 280.0 300.0
FREQUENCY (MHz)
Figure 3. MAX9770 EMI with 75mm of Speaker Cable
______________________________________________________________________________________ 13
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
EFFICIENCY vs. OUTPUT POWER
100
90
80
70
60
50
40
30
20
10
0
V
= 0V
IN
MAX9770
OUT-
MAX970
CLASS AB
OUT+
V
= 3.3V
DD
f = 1kHz
R - 8Ω
L
0
0.1
0.2
0.3
0.4
0.5
0.6
OUTPUT POWER (W)
V
- V = 0V
OUT+ OUT-
Figure 5. MAX9770 Efficiency vs. Class AB Efficiency
Figure 4. MAX9770 Output with No Signal Applied
Maxim’s DirectDrive architecture uses a charge pump to
create an internal negative supply voltage. This allows
the headphone outputs of the MAX9770 to be biased
about GND, almost doubling dynamic range while oper-
ating from a single supply. With no DC component, there
is no need for the large DC-blocking capacitors. Instead
of two large (220µF, typ) tantalum capacitors, the
MAX9770 charge pump requires two small ceramic
capacitors, which conserves board space, reduces cost,
and improves the frequency response of the headphone
driver. See the Output Power vs. Charge-Pump
Capacitance and Load Resistance graph in the Typical
Operating Characteristics for details of the possible
capacitor sizes. There is a low DC voltage on the driver
outputs due to amplifier offset. However, the offset of the
MAX9770 is typically 5mV, which, when combined with a
32Ω load, results in less than 160µA of DC current flow
to the headphones.
V
DD
MAX9770
800kΩ
SHDN
SHUTDOWN
CONTROL
HPS
HPOUTL
HPOUTR
10kΩ
10kΩ
Figure 6. HPS Configuration
In addition to the cost and size disadvantages of the DC-
blocking capacitors required by conventional head-
phone amplifiers, these capacitors limit the amplifier’s
low-frequency response and can distort the audio signal.
2) The sleeve is typically grounded to the chassis.
Using the midrail biasing approach, the sleeve must
be isolated from system ground, complicating prod-
uct design.
Previous attempts at eliminating the output-coupling
capacitors involved biasing the headphone return
(sleeve) to the DC bias voltage of the headphone
amplifiers. This method raises some issues:
3) During an ESD strike, the driver’s ESD structures are
the only path to system ground. Thus, the driver
must be able to withstand the full ESD strike.
1) When combining a microphone and headphone on a
single connector, the microphone bias scheme typi-
cally requires a 0V reference.
4) When using the headphone jack as a line out to
other equipment, the bias voltage on the sleeve may
conflict with the ground potential from other equip-
ment, resulting in possible damage to the drivers.
14 ______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Table 2. MAX9770 Multiplexer/Mixer Settings
HEADPHONE MODE
SEL1 SEL2 SELM
SPEAKER MODE
HPOUTL
HPOUTR
0
1
0
0
1
1
0
1
0
0
1
0
1
0
1
1
0
0
0
1
0
1
1
1
MUTE
IN1L
MUTE
IN1R
MUTE
(IN1L + IN1R) / 2
IN2L
IN2R
(IN2L + IN2R) / 2
MONO
MONO
MONO
(IN1L + IN2L) / 2
(IN1R + IN2R) / 2
(IN1L + IN1R + IN2L + IN2R) / 4
(IN1L + IN1R + MONO x 2) / 4
(IN2L + IN2R + MONO x 2) / 4
(IN1L + IN1R + IN2L + IN2R + MONO x 2) / 6
(IN1L + MONO) /2
(IN2L + MONO) / 2
(IN1L + IN2L + MONO) / 3
(IN1R + MONO) / 2
(IN2R + MONO) / 2
(IN1R + IN2R + MONO) / 3
Charge Pump
Headphone Sense Input (HPS)
The headphone sense input (HPS) monitors the head-
phone jack, and automatically configures the device
based upon the voltage applied at HPS. A voltage of
less than 0.8V sets the device to speaker mode. A volt-
age of greater than 2V disables the bridge amplifiers
and enables the headphone amplifiers.
The MAX9770 features a low-noise charge pump. The
switching frequency of the charge pump is 1/2 the
switching frequency of the Class D amplifier, regardless
of the operating mode. When SYNC is driven externally,
the charge pump switches at 1/2 f
DD
. When SYNC =
, the charge pump switches with a spread-spectrum
SYNC
V
pattern. The nominal switching frequency is well beyond
the audio range, and thus does not interfere with the
audio signals, resulting in an SNR of 101dB. The switch
drivers feature a controlled switching speed that mini-
mizes noise generated by turn-on and turn-off tran-
sients. By limiting the switching speed of the charge
pump, the di/dt noise caused by the parasitic bond wire
and trace inductance is minimized. Although not typical-
ly required, additional high-frequency noise attenuation
can be achieved by increasing the size of C2 (see the
Block Diagram). The charge pump is active in both
speaker and headphone modes.
For automatic headphone detection, connect HPS to the
control pin of a 3-wire headphone jack as shown in
Figure 6. With no headphone present, the output imped-
ance of the headphone amplifier pulls HPS to less than
0.8V. When a headphone plug is inserted into the jack,
the control pin is disconnected from the tip contact and
HPS is pulled to V
through the internal 800kΩ pullup.
DD
When driving HPS from an external logic source, ground
HPS when the MAX9770 is shut down. Place a 10kΩ
resistor in series with HPS and the headphone jack to
ensure 8kV ESD protection.
BIAS
The MAX9770 features internally generated, power-sup-
ply independent, common-mode bias voltages refer-
enced to GND. BIAS provides both click-and-pop
suppression and sets the DC bias level for the amplifiers.
Choose the value of the bypass capacitor as described in
the BIAS Capacitor section. No external load should be
applied to BIAS. Any load lowers the BIAS voltage, affect-
ing the overall performance of the device.
Input Multiplexer/Mixer
The MAX9770 features an input multiplexer/mixer that
allows multiple audio sources to be selected/mixed.
Driving a SEL_ input high selects the input channel (see
Table 2), and the audio signal is output to the active
amplifier. When a stereo path is selected in speaker
mode, the left and right inputs are attenuated by 6dB and
mixed together, resulting in a true mono reproduction of a
stereo signal. When more than one signal path is select-
ed, the sources are attenuated before mixing to preserve
overall amplitude. For example, selecting two sources in
headphone mode results in 6dB attenuation of the inputs,
while selecting three sources in headphone mode results
in 9.5dB attenuation of the inputs. Table 2 shows how the
input signals are attenuated and mixed for each possible
input selection combination.
Gain Selection
The MAX9770 features logic-selectable, internally set
gains. GAIN1 and GAIN2 set the gain of the MAX9770
speaker and headphone amplifiers as shown in Table 3.
The MAX9770 can be configured to automatically
switch between two gain settings depending on
whether the device is in speaker or headphone mode.
By driving one or both gain inputs with HPS, the gain of
______________________________________________________________________________________ 15
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
up or power-up, the input amplifiers are muted and an
Table 3. Gain Selection
internal loop sets the modulator bias voltages to the cor-
MAX9770
SPEAKER GAIN
(dB)
HEADPHONE
GAIN
rect levels, preventing clicks and pops when the H-
bridge is subsequently enabled. A soft-start function
unmutes the input amplifiers 30ms after startup.
GAIN1
GAIN2
(dB)
0
0
1
1
0
1
0
1
6
3
9
0
7
4
Headphone Amplifier
In conventional single-supply headphone drivers, the
output-coupling capacitor is a major contributor of
audible clicks and pops. Upon startup, the driver
charges the coupling capacitor to its bias voltage, typi-
cally half the supply. Likewise, during shutdown, the
capacitor is discharged to GND. This results in a DC
shift across the capacitor, which in turn, appears as an
audible transient at the speaker. Since the MAX9770
headphone amplifier does not require output-coupling
capacitors, this does not arise.
-2
1
MAX970
Table 4. Gain Settings with HPS
Connection
MAX9770 SPEAKER HEADPHONE MODE
MODE GAIN
(HPS = 0)
(dB)
GAIN
(HPS = 1)
(dB)
GAIN1 GAIN2
Additionally, the MAX9770 features extensive click-and-
pop suppression that eliminates any audible transient
sources internal to the device. The Exiting Shutdown
(Headphone Mode) and Entering Shutdown (Headphone
Mode) graphs in the Typical Operating Characteristics
shows that there are minimal spectral components in the
audible range at the output upon startup or shutdown.
HPS
HPS
0
0
1
6
3
6
9
6
6
3
9
0
-2
1
HPS
HPS
HPS
0
4
1
1
HPS
0
1
In most applications, the output of the preamplifier dri-
ving the MAX9770 has a DC bias of typically half the
supply. During startup, the input-coupling capacitor is
charged to the preamplifier’s DC bias voltage through
7
0
1
4
1
0
-2
1
the R of the MAX9770, resulting in a DC shift across the
F
1
1
capacitor and an audible click-and-pop. An internal
delay of 50ms eliminates the click-and-pop caused by
the input filter.
the device changes when a headphone is inserted or
removed. For example, the block diagram shows HPS
connected to GAIN2, while GAIN1 is connected to V
In this configuration, the gain in speaker mode is 9dB,
while the gain in headphone mode is 1dB. The gain
settings with the HPS connection are shown in Table 4.
Applications Information
.
DD
Filterless Operation
Traditional Class D amplifiers require an output filter to
recover the audio signal from the amplifier’s output. The
filters add cost, increase the solution size of the amplifi-
er, and can decrease efficiency. The traditional PWM
Shutdown
The MAX9770 features a 0.1µA, low-power shutdown
mode that reduces quiescent current consumption and
extends battery life. Drive SHDN low to disable the
drive amplifiers, bias circuitry, and charge pump. Bias
is driven to GND and the headphone amplifier output
impedance is 10kΩ in shutdown. Connect SHDN to
scheme uses large differential output swings (2 x V
DD
peak-to-peak) at idle and causes large ripple currents.
Any parasitic resistance in the filter components results
in a loss of power, lowering efficiency.
The MAX9770 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, and more efficient solution.
V
for normal operation.
DD
Click-and-Pop Suppression
Speaker Amplifier
The MAX9770 speaker amplifier features comprehen-
sive 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 start-
Because the frequency of the MAX9770 output is well
beyond the bandwidth of most speakers, voice coil
movement due to the square-wave frequency is minimal.
16 ______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Although this movement is small, a speaker not designed
to handle the additional power may be damaged. For
optimum results, use a speaker with a series inductance
>10µH. Typical small 8Ω speakers exhibit series induc-
tances in the range of 20µH to 100µH.
affects the amplifier’s low-frequency response. Setting
too low can affect the click-and-pop performance.
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.
f
-3dB
Output Offset
Unlike Class AB amplifiers, 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, a
15mV DC offset across an 8Ω load results in 1.9mA extra
current consumption in a Class AB device. In the Class D
case, a 15mV offset into 8Ω equates to an additional
power drain of 28µW. Due to the high efficiency of the
Class D amplifier, this represents an additional quiescent
Output Filter
The MAX9770 speaker amplifier does not require an out-
put filter for normal operation and audio reproduction. The
device passes FCC Class B radiated emissions stan-
dards with 100mm 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 com-
mon-mode choke connected in series with the speaker
outputs if board space is limited and emissions are a
concern. Use of an LC filter is necessary if excessive
speaker cable is used.
current draw of 28µW/(V
/ 100 x η), which is on the
DD
order of a few microamps.
Power Supplies
The MAX9770 has different supplies for each portion of
the device, allowing for the optimum combination of
headroom and power dissipation and noise immunity.
BIAS Capacitor
BIAS is the output of the internally generated DC bias
voltage. The BIAS bypass capacitor, C
improves
BIAS
The speaker amplifier is powered from PV . PV
PSRR and THD+N by reducing power supply and other
noise sources at the common-mode bias node, and
also generates the clickless/popless, startup/shutdown
DC bias waveforms for the speaker amplifiers. Bypass
BIAS with a 0.047µF capacitor to GND.
DD
DD
ranges from 2.5V to 5.5V. The headphone amplifiers
are powered from V and SV . V is the positive
DD
SS
DD
supply of the headphone amplifiers and ranges from
2.5V to 5.5V. SV is the negative supply of the head-
SS
phone amplifiers. Connect SV to CPV . The charge
SS
SS
pump is powered by CPV . CPV
ranges from 2.5V
DD
DD
to 5.5V and should be the same potential as V . The
DD
charge pump inverts the voltage at CPV , and the
DD
resulting voltage appears at CPV . The remainder of
SS
the device is powered by V
.
DD
Component Selection
Input Filter
The input capacitor (C ), in conjunction with the ampli-
IN
fier input resistance (R ), forms a highpass filter that
IN
removes the DC bias from an incoming signal (see the
Block Diagram). 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:
1
f
=
−3dB
2πR C
IN IN
R
is the amplifier’s internal input resistance value
IN
given in the Electrical Characteristics. Be aware that
the MONO input has a lower input impedance than the
other inputs. Choose C such that f
is below the
-3dB
IN
lowest frequency of interest. Setting f
too high
-3dB
______________________________________________________________________________________ 17
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
Table 5. Suggested Capacitor Manufacturers
SUPPLIER
Taiyo Yuden
TDK
PHONE
FAX
WEBSITE
www.t-yuden.com
www.component.tdk.com
800-348-2496
807-803-6100
847-925-0899
847-390-4405
Charge-Pump Capacitor Selection
parasitic trace resistance, as well as route the head
away from the device. Good grounding improves audio
performance, minimizes crosstalk between channels,
and prevents any switching noise from coupling into the
audio signal. Connect CPGND, PGND, and GND
together at a single point on the PC board. Route
CPGND and all traces that carry switching transients
away from GND, PGND, and the traces and compo-
nents in the audio signal path.
Use capacitors with an ESR less than 100mΩ for opti-
mum performance. Low-ESR ceramic capacitors mini-
mize the output resistance of the charge pump. Most
surface-mount ceramic capacitors satisfy the ESR
requirement. For best performance over the extended
temperature range, select capacitors with an X7R
dielectric. Table 5 lists suggested manufacturers.
MAX970
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the load
regulation and output resistance of the charge pump. A
C1 value that is too small degrades the device’s ability to
provide sufficient current drive, which leads to a loss of
output voltage. Increasing the value of C1 may improve
load regulation and reduces the charge-pump output
resistance to an extent. Above 1µF, the on-resistance of
the switches and the ESR of C1 and C2 dominate.
Connect all components associated with the charge
pump (C2 and C3) to the CPGND plane. Connect SV
SS
and CPV
together at the device. Place the charge-
SS
pump capacitors (C1, C2, and C3) as close to the
device as possible. Bypass V and PV with a 1µF
DD
DD
capacitor to GND. Place the bypass capacitors as
close to the device as possible.
Use large, low-resistance output traces. As load imped-
ance decreases, the current drawn from the device out-
puts increase. At higher current, the resistance of the
output traces decrease the power delivered to the load.
Large output, supply, and GND traces also improve the
power dissipation of the device.
Output Capacitor (C2)
The output capacitor value and ESR directly affect the
ripple at CPV . Increasing the value of C2 reduces
SS
output ripple. Likewise, decreasing the ESR of C2
reduces both ripple and output resistance. Lower
capacitance values can be used in systems with low
maximum output power levels. See the Output Power
vs. Charge-Pump Capacitance and Load Resistance
graph in the Typical Operating Characteristics.
The MAX9770 thin QFN package features an exposed
thermal pad on its underside. This pad lowers the pack-
age’s thermal resistance by providing a direct heat con-
duction path. Due to the high efficiency of the MAX9770’s
Class D amplifier, additional heatsinking is not required. If
additional heatsinking is required, connect the exposed
paddle to GND. See the MAX9770 EV kit data sheet for
suggested component values and layout guidelines.
CPV
Bypass Capacitor
DD
The CPV
bypass capacitor (C3) lowers the output
DD
impedance of the power supply and reduces the impact
of the MAX9770’s charge-pump switching transients.
Bypass CPV
with C3, the same value as C1, and
DD
place it physically close to the CPV
and PGND (refer
DD
to the MAX9770 EV kit for a suggested layout).
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
18 ______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Block Diagram
2.5V TO 5.5V
1μF
V
DD
16
(19)
2
(5)
20
(23)
SYNC
V
C
0.47μF
DD
PV
DD
OSCILLATOR
2.5V TO 5.5V
0.1μF
IN
25
IN1L (28)
LEFT-CHANNEL
AUDIO INPUT 1
18
(21)
OUT+
OUT-
PGND
C
IN
19
(22)
28
CLASS D
MODULATOR
0.47μF
H-BRIDGE
IN1R (3)
RIGHT-CHANNEL
AUDIO INPUT 1
17
(20)
C
IN
23
1μF
MONO (26)
MONO
AUDIO INPUT
MIXER/
MUX/GAIN
CONTROL
1
(4)
BIAS
C
IN
24
C
BIAS
0.47μF
IN2L (27)
LEFT-CHANNEL
AUDIO INPUT 2
0.047μF
V
DD
C
IN
27
(2)
0.47μF
IN2R
RIGHT-CHANNEL
AUDIO INPUT 2
21
(24)
GAIN2
GAIN1
SELM
SEL1
HPS
6
(9)
22
(25)
MUX AND
GAIN CONTROL
HPS
V
V
DD
DD
14
(17)
4
(7)
HPOUTL
HEADPHONE
DETECTION
12
(15)
GND
GND
13
(16)
SEL2
3
(6)
SHUTDOWN
CONTROL
15
(18)
HPOUTR
SHDN
V
DD
7
(10)
CPV
DD
V
DD
10
(13)
MAX9770
1μF
C1P
CHARGE
PUMP
C1
1μF
9
(12)
OSC/2
C1N
11
(14)
CPGND
26
(1)
8
5
(11) (8)
GND
CPV
SV
SS
SS
C2
1μF
( ) FOR TSSOP PIN.
______________________________________________________________________________________ 19
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
System Diagram
2.5V TO 5.5V
1μF
1μF
MAX970
V
DD
PV
DD
HPV
DD
0.47μF
OUT+
OUT-
IN1R
IN1L
AUDIO DAC
0.47μF
0.47μF
MAX9770
HPOUTL
HPS
IN2R
IN2L
HPOUTR
FM RADIO
MODULE
0.47μF
1μF
CPV
SV
SS
1μF
1μF
SS
CPGND
C1P
MONO
BASEBAND
PROCESSOR
SHDN
SEL1
SEL2
SELM
1μF
C1N
CPV
DD
2.5V TO 5.5V
V
V
GAIN1
GAIN2
DD
BIAS
DD
0.047μF
GND
PGND
20 ______________________________________________________________________________________
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
MAX970
Pin Configurations
TOP VIEW
GND
IN2R
IN1R
BIAS
1
2
28 IN1L
27 IN2L
20
18
16 15
19
17
21
3
26 MONO
25 GAIN1
24 GAIN2
GAIN1 22
MONO 23
SELM
SEL2
14
13
4
V
DD
5
MAX9770
HPOUTR
HPOUTL
6
23 PV
DD
12 SEL1
IN2L
24
7
22 OUT-
21 OUT+
20 PGND
19 SYNC
18 SHDN
17 SELM
16 SEL2
15 SEL1
IN1L 25
11 CPGND
MAX9770
SV
SS
8
C1P
C1N
CPV
10
9
26
27
GND
IN2R
HPS
CPV
9
10
DD
IN1R 28
8
SS
CPV 11
SS
C1N 12
C1P 13
5
6
7
4
1
2
3
CPGND 14
TQFN
TSSOP
Package Information
Chip Information
For the latest package outline information, go to
TRANSISTOR COUNT: 7020
www.maxim-ic.com/packages.
PROCESS: BiCMOS
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
28 TQFN-EP
T2855N-1
21-0140
21-0066
28 TSSOP
U28-1
______________________________________________________________________________________ 21
1.2W, Low-EMI, Filterless, Mono Class D Amplifier
with Stereo DirectDrive Headphone Amplifiers
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
Removing MAX9772 from data sheet
2
4/08
1–21
MAX970
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
© 2008 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
相关型号：
MAX9773ETG+T
Audio Amplifier, 1.8W, 2 Channel(s), 1 Func, BICMOS, 4 X 4 MM, 0.80 MM HEIGHT, LEAD FREE, MO-220WGGD-2, TQFN-24
MAXIM
©2020 ICPDF网 联系我们和版权申明