MAXIM MAX9724AEBC+T

19-3597; Rev 3; 3/07
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
The MAX9724A/MAX9724B stereo headphone amplifiers are designed for portable equipment where board
space is at a premium. These devices use a unique,
patented † DirectDrive™ architecture to produce a
ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors, saving cost, board space, and component height. The
MAX9724 suppresses RF radiation received by input
and supply traces acting as antennas and prevents the
amplifer from demodulating the coupled noise. The
MAX9724A offers an externally adjustable gain while
the MAX9724B has an internally preset gain of -1.5V/V.
The MAX9724A/MAX9724B deliver up to 60mW per
channel into a 32Ω load and have low 0.02% THD+N.
An 80dB at 1kHz power-supply rejection ratio (PSRR)
allows these devices to operate from noisy digital supplies without an additional linear regulator.
Comprehensive click-and-pop circuitry suppresses
audible clicks and pops on startup and shutdown.
The MAX9724A/MAX9724B operate from a single 2.7V
to 5.5V supply, consume only 3.5mA of supply current,
feature short-circuit and thermal-overload protection,
and are specified over the extended -40°C to +85°C
temperature range. The devices are available in tiny 12bump UCSP™ (1.5mm x 2mm) and 12-pin thin QFN
(3mm x 3mm x 0.8mm) packages.
Applications
Cellular Phones
MP3 Players
Notebook PCs
Handheld Gaming Consoles
DVD Players
Smart Phones
PDAs
Features
♦ Improved RF Noise Rejection (Up to 67dB Over
Typical Amplifiers)
♦ No Bulky DC-Blocking Capacitors Required
♦ Low-Power Shutdown Mode, < 0.1µA
♦ Adjustable Gain (MAX9724A) or Fixed -1.5V/V
Gain (MAX9724B)
♦ Low 0.02% THD+N
♦ High PSRR (80dB at 1kHz) Eliminates LDO
♦ Integrated Click-and-Pop Suppression
♦ 2.7V to 5.5V Single-Supply Operation
♦ Low Quiescent Current (3.5mA)
♦ Available in Space-Saving Packages:
12-Bump UCSP (1.5mm x 2mm)
12-Pin Thin QFN (3mm x 3mm x 0.8mm)
Ordering Information
PART
GAIN PIN(V/V) PACKAGE
PKG
CODE
B12-1
TOP
MARK
MAX9724AEBC+T
Adj.
12 UCSP-12
MAX9724AETC+
Adj.
12 TQFN-EP* T1233-1
+AAT
MAX9724BEBC+T
-1.5
12 UCSP-12
+ADI
MAX9724BETC+
-1.5
12 TQFN-EP* T1233-1
B12-1
+ADH
+AAU
Note: All devices specified over the -40°C to +85°C operating
range.
+Denotes lead-free package.
*EP = Exposed paddle.
Pin Configurations appear at end of data sheet.
†U.S. Patent# 7,061,327
UCSP is a trademark of Maxim Integrated Products, Inc.
Block Diagrams
MAX9724B
MAX9724A
LEFT
AUDIO
INPUT
SHDN
RIGHT
AUDIO
INPUT
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS
LEFT
AUDIO
INPUT
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS
SHDN
RIGHT
AUDIO
INPUT
FIXED GAIN ELIMINATES
EXTERNAL RESISTOR
NETWORK
________________________________________________________________ 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
MAX9724A/MAX9724B
General Description
MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..............................................................-0.3V to +6V
PVSS to SVSS .........................................................-0.3V to +0.3V
PGND to SGND .....................................................-0.3V to +0.3V
C1P to PGND..............................................-0.3V to (VDD + 0.3V)
C1N to PGND............................................(PVSS - 0.3V) to +0.3V
PVSS and SVSS to PGND..........................................-6V to +0.3V
IN_ to SGND (MAX9724A)..........................-0.3V to (VDD + 0.3V)
IN_ to SGND (MAX9724B) .............(SVSS - 0.3V) to (VDD + 0.3V)
OUT_ to SVSS (Note 1) ....-0.3V to Min (VDD - SVSS + 0.3V, +9V)
OUT_ to VDD (Note 2) ......+0.3V to Max (SVSS - VDD - 0.3V, -9V)
SHDN to _GND.........................................................-0.3V to +6V
OUT_ Short Circuit to GND ........................................Continuous
Short Circuit between OUTL and OUTR ....................Continuous
Continuous Input Current into PVSS ..................................260mA
Continuous Input Current (any other pin) .........................±20mA
Continuous Power Dissipation (TA = +70°C)
12-Bump USCP (derate 6.5mW/°C above +70°C) ........519mW
12-Pin TQFN (derate 14.7mW/°C above +70°C) .........1177mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
Bump Temperature (soldering) Reflow............................+235°C
Note 1: OUTR and OUTL should be limited to no more than 9V above SVSS, or above VDD + 0.3V, whichever limits first.
Note 2: OUTR and OUTL should be limited to no more than 9V below VDD, or below SVSS - 0.3V, whichever limits first.
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 = 5V, PGND = SGND, SHDN = 5V, C1 = C2 = 1µF, RL = ∞, resistive load reference to ground; for MAX9724A gain = -1.5V/V
(RIN = 20kΩ, RF = 30kΩ); for MAX9724B gain = -1.5V/V (internally set), TA = -40°C to +85°C, unless otherwise noted. Typical values
are at TA = +25°C, unless otherwise noted.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
5.5
V
3.5
5.5
mA
0.1
1
µA
19
28
kΩ
±1.5
±10
mV
GENERAL
Supply Voltage Range
VDD
Quiescent Current
ICC
Shutdown Current
ISHDN
Guaranteed by PSRR test
SHDN = SGND = PGND
Shutdown to Full Operation
tSON
Input Impedance
RIN
MAX9724B, measured at IN_
Output Offset Voltage
VOS
(Note 4)
180
VDD = 2.7V to 5.5V, TA = +25°C
Power-Supply Rejection Ratio
PSRR
2.7
12
69
f = 1kHz, 100mVP-P (Note 4)
Output Power (TQFN)
POUT
Output Power (UCSP)
POUT
Voltage Gain
AV
Channel-to-Channel Gain
Tracking
Total Harmonic Distortion Plus
Noise (Note 6)
2
THD+N
63
mW
42
25
RL = 16Ω, THD+N = 1%
MAX9724B (Note 5)
dB
65
30
RL = 16Ω, THD+N = 1%
RL = 32Ω, THD+N = 1%
86
80
f = 20kHz, 100mVP-P (Note 4)
RL = 32Ω, THD+N = 1%
µs
45
mW
35
-1.52
-1.5
MAX9724B
±0.15
RL = 1kΩ, VOUT = 2VRMS, fIN = 1kHz
0.003
RL = 32Ω, POUT = 50mW, fIN = 1kHz
0.02
RL = 16Ω, POUT = 35mW, fIN = 1kHz
0.04
_______________________________________________________________________________________
-1.48
V/V
%
%
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
(VDD = 5V, PGND = SGND, SHDN = 5V, C1 = C2 = 1µF, RL = ∞, resistive load reference to ground; for MAX9724A gain = -1.5V/V
(RIN = 20kΩ, RF = 30kΩ); for MAX9724B gain = -1.5V/V (internally set), TA = -40°C to +85°C, unless otherwise noted. Typical values
are at TA = +25°C, unless otherwise noted.) (Note 3)
PARAMETER
Signal-to-Noise Ratio
SYMBOL
SNR
Slew Rate
SR
Capacitive Drive
CL
Crosstalk
Charge-Pump Oscillator
Frequency
CONDITIONS
RL = 1kΩ,
VOUT = 2VRMS
RL = 32Ω,
POUT = 50mW
TYP
BW = 22Hz to 22kHz
A-weighted
BW = 22Hz to 22kHz
102
105
98
A-weighted
101
MAX
UNITS
dB
0.5
V/µs
No sustained oscillations
100
pF
L to R, R to L, f = 10kHz, RL = 16Ω,
POUT = 15mW
-70
dB
190
fOSC
KCP
Into shutdown
RL = 32Ω, peak voltage,
A-weighted, 32 samples per Out of
second (Notes 4, 7)
shutdown
VINH
(TQFN only)
Input-Voltage Low
VINL
(TQFN only)
Input-Voltage High
VINH
(UCSP only)
Input-Voltage Low
VINL
(UCSP only)
Click-and-Pop Level
MIN
270
400
kHz
-67
dB
-64
DIGITAL INPUTS (SHDN)
Input-Voltage High
2
V
0.8
1.4
V
V
Input Leakage Current
0.9
V
±1
µA
ELECTRICAL CHARACTERISTICS
(VDD = 3V, PGND = SGND, SHDN = 3V, C1 = C2 = 1µF, RL = ∞, resistive load reference to ground; for MAX9724A gain = -1.5V/V
(RIN = 20kΩ, RF = 30kΩ); for MAX9724B gain = -1.5V/V (internally set), TA = -40°C to +85°C, unless otherwise noted. Typical values
are at TA = +25°C, unless otherwise noted.) (Note 3)
PARAMETER
SYMBOL
Quiescent Current
ICC
Shutdown Current
ISHDN
Power-Supply Rejection Ratio
(Note 4)
PSRR
Output Power
POUT
Total Harmonic Distortion Plus
Noise (Note 6)
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
THD+N
CONDITIONS
MIN
TYP
MAX
UNITS
3.0
mA
SHDN = SGND = PGND
0.1
µA
f = 1kHz, 100mVP-P
80
f = 20kHz, 100mVP-P
65
RL = 32Ω, THD+N = 1%
20
RL = 16Ω, THD+N = 1%
14
RL = 1kΩ, VOUT = 2VRMS, fIN = 1kHz
0.05
RL = 32Ω, POUT = 15mW, fIN = 1kHz
0.03
RL = 16Ω, POUT = 10mW, fIN = 1kHz
0.06
dB
mW
%
All specifications are 100% tested at TA = +25°C; temperature limits are guaranteed by design.
The amplifier inputs are AC-coupled to GND.
Gain for the MAX9724A is adjustable.
Measurement bandwidth is 22Hz to 22kHz.
Test performed with a 32Ω resistive load connected to GND. Mode transitions are controlled by SHDN. KCP level is calculated as 20log[(peak voltage during mode transition, no input signal)/(peak voltage under normal operation at rated power
level)]. Units are expressed in dB.
_______________________________________________________________________________________
3
MAX9724A/MAX9724B
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VDD = 5V, PGND = SGND = 0V, SHDN = VDD, C1 = C2 = 1µF, RL = ∞, gain = -1.5V/V (RIN = 20kΩ, RF = 30kΩ for the MAX9724A),
THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25°C, unless otherwise noted.)
VDD = 3V
RL = 32Ω
1
fIN = 1kHz
0.1
fIN = 10kHz
100
VDD = 5V
RL = 16Ω
10
THD+N (%)
10
THD+N (%)
10
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER (TQFN ONLY)
MAX9724toc02
VDD = 3V
RL = 16Ω
THD+N (%)
100
MAX9724toc01
100
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER (TQFN ONLY)
1
fIN = 1kHz
0.1
MAX9724toc03
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER (TQFN ONLY)
1
fIN = 1kHz
0.1
fIN = 10kHz
fIN = 10kHz
0.01
0.01
0.01
fIN = 20Hz
fIN = 20Hz
0.001
fIN = 20Hz
0.001
30
40
0
10
OUTPUT POWER (mW)
40
50
0
20
40
VDD = 5V
RL = 32Ω
1
10
VDD = 3V
RL = 16Ω
0.1
fIN = 1kHz
100
1
VDD = 3V
RL = 32Ω
0.1
POUT = 8mW
0.01
0.01
POUT = 10mW
0.01
80
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY (TQFN ONLY)
POUT = 5mW
THD+N (%)
1
60
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY (TQFN ONLY)
MAX9724toc04
100
THD+N (%)
30
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER (TQFN ONLY)
0.1
0.001
20
MAX9724toc06
20
THD+N (%)
10
MAX9724toc05
0
POUT = 15mW
fIN = 10kHz
fIN = 20Hz
0.001
20
40
60
80
100
0.001
10
120
100
POUT = 20mW
1k
10k
100k
OUTPUT POWER
vs. SUPPLY VOLTAGE (TQFN ONLY)
VDD = 5V
RL = 32Ω
POUT = 30mW
THD+N (%)
POUT = 37mW
100
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY (TQFN ONLY)
0.1
0.01
10
FREQUENCY (Hz)
1
0.1
100k
70
MAX9724toc08
VDD = 5V
RL = 16Ω
MAX9724toc07
1
10k
FREQUENCY (Hz)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY (TQFN ONLY)
1k
0.01
POUT = 50mW
fIN = 1kHz
RL = 16Ω
60
OUTPUT POWER (mW)
0
MAX9724toc09
0.001
THD+N (%)
MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
50
10% THD+N
40
30
20
1% THD+N
10
0.001
100
1k
FREQUENCY (Hz)
4
0
0.001
10
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5.0
5.5
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
(VDD = 5V, PGND = SGND = 0V, SHDN = VDD, C1 = C2 = 1µF, RL = ∞, gain = -1.5V/V (RIN = 20kΩ, RF = 30kΩ for the MAX9724A),
THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25°C, unless otherwise noted.)
30
10% THD+N
60
40
20
15
1% THD+N
10
1% THD+N
80
70
60
50
40
THD+N = 1%
30
5
0
3.0
3.5
4.0
4.5
5.0
0
10
5.5
100
10
1000
100
SUPPLY VOLTAGE (V)
LOAD RESISTANCE (Ω)
LOAD RESISTANCE (Ω)
POWER DISSIPATION
vs. OUTPUT POWER (TQFN ONLY)
POWER-SUPPLY REJECTION
RATIO vs. FREQUENCY (TQFN ONLY)
CROSSTALK vs. FREQUENCY
(TQFN ONLY)
RL = 32Ω
-20
RL = 16Ω
RL = 32Ω
100
-60
VDD = 5V
-80
VDD = 3V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN PHASE
50
-100
0
40
60
80
-40
-60
RIGHT TO LEFT
-80
LEFT TO RIGHT
-100
VDD = 3V
-120
20
POUT = 15mW
RL = 16Ω
-20
CROSSTALK (dB)
PSRR (dB)
-40
150
MAX9724toc15
200
0
MAX9724toc14
0
MAX9724toc13
250
0
VDD = 5V
fIN = 1kHz
10
0
2.5
-120
10
100
10k
1k
100k
10
100
10k
1k
100k
OUTPUT POWER (mW)
FREQUENCY (Hz)
FREQUENCY (Hz)
OUTPUT POWER vs. LOAD RESISTANCE AND
CHARGE-PUMP CAPACITOR SIZE (TQFN ONLY)
OUTPUT SPECTRUM
vs. FREQUENCY (TQFN ONLY)
SUPPLY CURRENT
vs. SUPPLY VOLTAGE (TQFN ONLY)
-60
60
50
C1 = C2 = 0.47µF
40
-70
-80
-90
-100
-110
-140
50
100
LOAD RESISTANCE (Ω)
3.3
3.2
3.1
3.0
150
NO LOAD
INPUTS
GROUND
2.9
-130
20
0
3.4
-120
VDD = 5V
fIN = 1kHz
THD+N = 1%
30
3.5
MAX9724toc18
C1 = C2 = 1µF
RL = 32Ω
VDD = 3V
fIN = 1kHz
VOUT = -60dBV
-50
SUPPLY CURRENT (mA)
70
-40
AMPLITUDE (dBV)
C1 = C2 = 2.2µF
MAX9724toc16
80
MAX9724toc17
POWER DISSIPATION (mW)
THD+N = 10%
90
20
20
OUTPUT POWER (mW)
100
OUTPUT POWER (mW)
25
OUTPUT POWER (mW)
80
VDD = 3V
fIN = 1kHz
10% THD+N
MAX9724toc11
fIN = 1kHz
RL = 32Ω
100
OUTPUT POWER (mW)
35
MAX9724toc10
120
OUTPUT POWER
vs. LOAD RESISTANCE (TQFN ONLY)
OUTPUT POWER
vs. LOAD RESISTANCE (TQFN ONLY)
MAX9724toc12
OUTPUT POWER
vs. SUPPLY VOLTAGE (TQFN ONLY)
2.8
0
5
10
FREQUENCY (kHz)
15
20
2.5
3.0
3.5
4.0
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
MAX9724A/MAX9724B
Typical Operating Characteristics (continued)
Typical Operating Characteristics (continued)
(VDD = 5V, PGND = SGND = 0V, SHDN = VDD, C1 = C2 = 1µF, RL = ∞, gain = -1.5V/V (RIN = 20kΩ, RF = 30kΩ for the MAX9724A),
THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25°C, unless otherwise noted.)
EXITING SHUTDOWN
NO LOAD INPUTS GND
120
100
80
ENTERING SHUTDOWN
MAX9724toc20
MAX9724 toc19
140
VSHDN
5V/div
MAX9724toc21
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE (TQFN ONLY)
SHUTDOWN CURRENT (nA)
MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
VSHDN
5V/div
VIN_
1V/div
VIN_
1V/div
VOUT_
500mV/div
VOUT_
500mV/div
60
40
20
0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
40µs/div
20µs/div
SUPPLY VOLTAGE (V)
Pin Description
PIN
6
NAME
FUNCTION
TQFN
UCSP
1
A1
C1P
2
A2
PGND
3
A3
C1N
Flying Capacitor Negative Terminal. Connect a 1µF ceramic capacitor from C1P to C1N.
Charge-Pump Output. Connect to SVSS and bypass with a 1µF ceramic capacitor to PGND.
4
A4
PVSS
5
C2
SHDN
6
B3
INL
7
C1
SGND
8
B2
INR
Flying Capacitor Positive Terminal. Connect a 1µF ceramic capacitor from C1P to C1N.
Power Ground. Connect to SGND.
Active-Low Shutdown Input
Left-Channel Input
Signal Ground. Connect to PGND.
Right-Channel Input
9
B4
SVSS
Amplifier Negative Supply. Connect to PVSS.
10
C3
OUTR
Right-Channel Output
11
C4
OUTL
Left-Channel Output
12
B1
VDD
EP
—
EP
Positive Power-Supply Input. Bypass with a 1µF capacitor to PGND.
Exposed Paddle. Internally connected to SVSS. Connect to SVSS or leave unconnected.
_______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
The MAX9724A/MAX9724B stereo headphone amplifiers feature Maxim’s patented DirectDrive architecture,
eliminating the large output-coupling capacitors
required by conventional single-supply headphone
amplifiers. The device consists of two 60mW Class AB
headphone amplifiers, undervoltage lockout
(UVLO)/shutdown control, charge pump, and comprehensive click-and-pop suppression circuitry (see the
Functional Diagram/Typical Operating Circuits). The
charge pump inverts the positive supply (VDD), creating a negative supply (PVSS). The headphone amplifiers operate from these bipolar supplies with their
outputs biased about PGND (Figure 1). The benefit of
this PGND bias is that the amplifier outputs do not have
a DC component. The large DC-blocking capacitors
required with conventional headphone amplifiers are
unnecessary, conserving board space, reducing system cost, and improving frequency response. The
MAX9724A/MAX9724B feature an undervoltage lockout
that prevents operation from an insufficient power supply and click-and-pop suppression that eliminates audible transients on startup and shutdown. The
MAX9724A/MAX9724B also feature thermal-overload
and short-circuit protection.
DirectDrive
Conventional single-supply headphone amplifiers 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
significant amount of DC current flows to the headphone, resulting in unnecessary power dissipation and
possible damage to both headphone and headphone
amplifier.
Maxim’s patented DirectDrive architecture uses a
charge pump to create an internal negative supply voltage, allowing the MAX9724A/MAX9724B outputs to be
biased about GND. With no DC component, there is no
need for the large DC-blocking capacitors. The
MAX9724A/MAX9724B charge pumps require two
small ceramic capacitors, conserving board space,
reducing cost, and improving the frequency response
of the headphone amplifier. See the Output Power vs.
Load Resistance and Charge-Pump Capacitor Size
graph in the Typical Operating Characteristics for
details of the possible capacitor sizes. There is a low
DC voltage on the amplifier outputs due to amplifier offset. However, the offsets of the MAX9724A/MAX9724B
are typically 1.5mV, which, when combined with a 32Ω
load, results in less than 47µA of DC current flow to the
headphones.
MAX9724A/MAX9724B
Detailed Description
VOUT
VDD
VDD
VDD/2
GND
CONVENTIONAL DRIVER-BIASING SCHEME
VOUT
VDD
GND
2VDD
-VDD
DirectDrive BIASING SCHEME
Figure 1. Conventional Driver Output Waveform vs.
MAX9724A/MAX9724B Output Waveform
Charge Pump
The MAX9724A/MAX9724B feature a low-noise charge
pump. The 270kHz switching frequency is well beyond
the audio range and does not interfere with audio signals. The switch drivers feature a controlled switching
speed that minimizes noise generated by turn-on and
turn-off transients. The di/dt noise caused by the parasitic bond wire and trace inductance is minimized by
limiting the switching speed of the charge pump.
Although not typically required, additional high-frequency noise attenuation can be achieved by increasing the value of C2 (see the Functional Diagram/Typical
Operating Circuits).
RF Susceptibility
Modern audio systems are often subject to RF radiation
from sources like wireless networks and cellular phone
networks. Although the RF radiation is out of the audio
band, many signals, in particular GSM signals, contain
bursts or modulation at audible frequencies. Most analog amplifiers demodulate the low-frequency envelope,
adding noise to the audio signal. The architecture of
_______________________________________________________________________________________
7
the MAX9724 addresses the problem of the RF susceptibility by rejecting RF noise and preventing it from coupling into the audio band.
The RF susceptibility of an amplifier can be measured
by placing the amplifier in an isolated chamber and subjecting it to an electric field of known strength. If the
electric field is modulated with an audio band signal, a
percentage of the modulated signal will be demodulated and amplified by the device in the chamber. Figure 2
shows the signal level at the outputs of an unoptimized
amplifier and the MAX9724. The test conditions are
shown in Table 1.
Table 1. RF Susceptibility Test Conditions
TEST PARAMETER
SETTING
RF Field Strength
50V/m
RF Modulation Type
Sine wave
RF Modulation Index
100%
RF Modulation Frequency
1kHz
Typically, the output of the device driving the
MAX9724A/MAX9724B has a DC bias of half the supply
voltage. At startup, the input-coupling capacitor is
charged to the preamplifier’s DC-bias voltage through
the input and feedback resistors of the MAX9724A/
MAX9724B, resulting in a DC shift across the capacitor
and an audible click/pop. Delay the rise of SHDN 4 to 5
time constants based on RIN and CIN, relative to the
startup of the preamplifier, to eliminate clicks-and-pops
caused by the input filter.
Shutdown
The MAX9724A/MAX9724B feature a <0.1µA, lowpower shutdown mode that reduces quiescent current
consumption and extends battery life for portable applications. Drive SHDN low to disable the amplifiers and
the charge pump. In shutdown mode, the amplifier output impedance is set to 14kΩ||RF (RF is 30kΩ for the
MAX9724B). The amplifiers and charge pump are
enabled once SHDN is driven high.
Applications Information
Click-and-Pop Suppression
40
62dB IMPROVEMENT
AT 850MHz
RF SUSCEPTIBLE
AMPLIFIER
20
0
Power Dissipation
Under normal operating conditions, linear power amplifiers can dissipate a significant amount of power. The
maximum power dissipation for each package is given
in the Absolute Maximum Ratings section under
Continuous Power Dissipation or can be calculated by
the following equation:
PDISSPKG(MAX) =
39dB IMPROVEMENT
AT 900MHz
67dB IMPROVEMENT
AT 1800MHz
49dB IMPROVEMENT
AT 1900MHz
TJ(MAX) − TA
θJA
MAX9724 fig02
In conventional single-supply audio amplifiers, the output-coupling capacitor contributes significantly to audible clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically half
the supply. Likewise, on shutdown, the capacitor is discharged. This results in a DC shift across the capacitor,
which appears as an audible transient at the speaker.
Since the MAX9724A/ MAX9724B do not require outputcoupling capacitors, this problem does not arise.
Additionally, the MAX9724A/MAX9724B feature extensive click-and-pop suppression that eliminates any audible transient sources internal to the device.
AMPLIFIER OUTPUT AMPLITUDE (dBV)
MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
-20
-40
-60
MAX9724
-80
-100
100
600
1100
1600
2100
2600
RF CARRIER FREQUENCY (MHz)
Figure 2. RF Susceptibility of the MAX9724 and a Typical Headphone Amplifier
8
_______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
The MAX9724A/MAX9724B have two power dissipation
sources; a charge pump and the two output amplifiers.
If power dissipation for a given application exceeds the
maximum allowed for a particular package, reduce
VDD, increase load impedance, decrease the ambient
temperature, or add heatsinking to the device. Large
output, supply, and ground traces decrease θJA, allowing more heat to be transferred from the package to the
surrounding air.
Thermal-overload protection limits total power dissipation in the MAX9724A/MAX9724B. When the junction
temperature exceeds +150°C, the thermal protection
circuitry disables the amplifier output stage. The amplifiers are enabled once the junction temperature cools
by approximately 12°C. This results in a pulsing output
under continuous thermal-overload conditions.
Output Dynamic Range
Dynamic range is the difference between the noise floor
of the system and the output level at 1% THD+N.
Determine the system’s dynamic range before setting the
maximum output gain. Output clipping occurs if the output signal is greater than the dynamic range of the system. The DirectDrive architecture of the MAX9724A/
MAX9724B has increased the dynamic range compared
to other single-supply amplifiers.
Maximum Output Swing
VDD < 4.35V
If the output load impedance is greater than 1kΩ, the
MAX9724A/MAX9724B can swing within a few millivolts
of their supply rail. For example, with a 3.3V supply, the
output swing is 2VRMS, or 2.83V peak while maintaining
a low 0.003% THD+N. If the supply voltage drops to
3V, the same 2.83V peak has only 0.05% THD+N.
VDD > 4.35V
Internal device structures limit the maximum voltage
swing of the MAX9724A/MAX9724B when operated at
supply voltages greater than 4.35V. The output must not
be driven such that the peak output voltage exceeds the
opposite supply voltage by 9V. For example, if VDD =
5V, the charge pump sets PVSS = -5V. Therefore, the
peak output swing must be less than ±4V to prevent
exceeding the absolute maximum ratings.
UVLO
The MAX9724A/MAX9724B feature an undervoltage
lockout (UVLO) function that prevents the device from
operating if the supply voltage is less than 2.7V. This feature ensures proper operation during brownout conditions and prevents deep battery discharge. Once the
supply voltage exceeds the UVLO threshold, the
MAX9724A/MAX9724B charge pump is turned on and
the amplifiers are powered, provided that SHDN is high.
Component Selection
Input-Coupling Capacitor
The input capacitor (CIN), in conjunction with the input
resistor (RIN), forms a highpass filter that removes the
DC bias from an incoming signal (see the Functional
Diagram/Typical Operating Circuits). The AC-coupling
capacitor allows the device to bias the signal to an optimum DC level. Assuming zero-source impedance, the 3dB point of the highpass filter is given by:
f−3dB =
1
2πRINCIN
Choose the CIN such that f-3dB is well below the lowest
frequency of interest. Setting f-3dB too high affects the
device’s low-frequency response. Use capacitors
whose dielectrics have low-voltage coefficients, such
as tantalum or aluminum electrolytic. Capacitors with
high-voltage coefficients, such as ceramics, can result
in increased distortion at low frequencies.
Charge-Pump Capacitor Selection
Use ceramic capacitors with a low ESR for optimum
performance. For optimal performance over the extended temperature range, select capacitors with an X7R
dielectric. Table 2 lists suggested manufacturers.
Table 2. Suggested Capacitor Manufacturers
SUPPLIER
WEBSITE
PHONE
FAX
Taiyo Yuden
800-348-2496
847-925-0899
www.t-yuden.com
TDK
847-803-6100
847-390-4405
www.component.tdk.com
Murata
770-436-1300
770-436-3030
www.murata.com
_______________________________________________________________________________________
9
MAX9724A/MAX9724B
where TJ(MAX) is +150°C, TA is the ambient temperature, and θJA is the reciprocal of the derating factor in
°C/W as specified in the Absolute Maximum Ratings
section. For example, θJA of the thin QFN package is
+68°C/W, and 154.2°C/W for the UCSP package.
MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
Flying Capacitor (C1)
The value of the flying capacitor (see the Functional
Diagram/Typical Operating Circuits) affects the charge
pump’s load regulation and output resistance. 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 improves load
regulation and reduces the charge-pump output resistance to an extent. See the Output Power vs. Load
Resistance and Charge-Pump Capacitor Size graph in
the Typical Operating Characteristics. Above 1µF, the
on-resistance of the switches and the ESR of C1 and C2
dominate.
Hold Capacitor (C2)
The hold capacitor value (see the Functional
Diagram/Typical Operating Circuits) and ESR directly
affect the ripple at PVSS. Increasing the value of C2
reduces 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. Load Resistance and Charge-Pump Capacitor Size
graph in the Typical Operating Characteristics.
Power-Supply Bypass Capacitor (C3)
The power-supply bypass capacitor (see the Functional
Diagram/Typical Operating Circuits) lowers the output
impedance of the power supply, and reduces the
impact of the MAX9724A/MAX9724B’s charge-pump
switching transients. Bypass VDD with C3, the same
value as C1, and place it physically close to the VDD
and PGND pins.
The gain of the MAX9724A amplifier is set externally as
shown in Figure 3, the gain is:
AV = -RF/RIN (V/V)
Choose feedback resistor values in the tens of kΩ
range. Lower values may cause excessive power dissipation and require impractically small values of RIN for
large gain settings. The high-impedance state of the
outputs can also be degraded during shutdown mode
if an inadequate feedback resistor is used since the
equivalent output impedance during shutdown is
14kΩ||Rf (RF is equal to 30kΩ for the MAX9724B). The
source resistance of the input device may also need to
be taken into consideration. Since the effective value of
RIN is equal to the sum of the source resistance of the
input device and the value of the input resistor connected to the inverting terminal of the headphone amplifier
(20kΩ for the MAX9724B), the overall closed-loop gain
of the headphone amplifier can be reduced if the input
resistor is not significantly larger than the source resistance of the input device.
RF
MAX9724A
LEFT
AUDIO
INPUT
RIN
RIGHT
AUDIO
INPUT
RIN
INL
OUTL
Amplifier Gain
The gain of the MAX9724B amplifier is internally set to
-1.5V/V. All gain-setting resistors are integrated into the
device, reducing external component count. The internally set gain, in combination with DirectDrive, results in
a headphone amplifier that requires only five small
capacitors to complete the amplifier circuit: two for the
charge pump, two for audio input coupling, and one for
power-supply bypassing (see the Functional
Diagram/Typical Operating Circuits).
10
OUTR
INR
RF
Figure 3. Gain Setting for the MAX9724A
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
RMS OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
3.5
RMS OUTPUT VOLTAGE (V)
fIN = 1kHz
RL = 10kΩ
1% THD+N
3.0
LIMITED BY
ABS. MAXIMUM
RATINGS
2.5
RL = 1kΩ
1% THD+N
2.0
1.5
2.5
3.0
3.5
4.0
4.5
5.0
sinusoidal signal equates to approximately 5.7VP-P,
which means that the audio system designer cannot
simply run the lineout stage from a (typically common)
5V supply—the resulting output swing would be inadequate. A common solution to this problem is to use op
amps driven from split supplies (±5V typically), or to
use a high-voltage supply rail (9V to 12V). This can
mean adding extra cost and complexity to the system
power supply to meet this output level requirement.
Having the ability to derive 2VRMS from a 5V supply, or
even 3.3V supply, can often simplify power-supply
design in some systems.
When the MAX9724A is used as a line driver to provide
outputs that feed stereo equipment (receivers, STBs,
notebooks, and desktops) with a digital-to-analog converter (DAC) used as an audio input source, it is often
desirable to eliminate any high-frequency quantization
noise produced by the DAC output before it reaches
the load. This high-frequency noise can cause the input
stages of the line-in equipment to exceed slew-rate limitations or create excessive EMI emissions on the
cables between devices.
5.5
SUPPLY VOLTAGE (V)
Figure 4. RMS Output Voltage vs. Supply Voltage
15kΩ
220pF
LEFT
AUDIO
INPUT
1µF
7.5kΩ
7.5kΩ
MAX9724A
INL
OUTL
1.2nF
STEREO
DAC
LINE IN DEVICE
10kΩ
1.2nF
RIGHT
AUDIO
INPUT
1µF
OUTR
7.5kΩ
7.5kΩ
INR
10kΩ
220pF
15kΩ
Figure 5. MAX9724A Line Out Amplifier and Filter Block Configuration
______________________________________________________________________________________
11
MAX9724A/MAX9724B
Lineout Amplifier and Filter Block
The MAX9724A can be used as an audio line driver
capable of providing 2VRMS into 10kΩ loads with a single 5V supply (see Figure 4 for the RMS Output Voltage
vs. Supply Voltage plot). 2VRMS is a popular audio line
level, first used in CD players, but now common in DVD
and set-top box (STB) interfacing standards. A 2VRMS
To suppress this noise, and to provide a 2VRMS standard audio output level from a single 5V supply, the
MAX9724A can be configured as a line driver and
active lowpass filter. Figure 5 shows the MAX9724A
connected as 2-pole Rauch/multiple feedback filter with
a passband gain of 6dB and a -3dB (below passband)
cutoff frequency of approximately 27kHz (see Figure 6
for the Gain vs. Frequency plot).
Layout and Grounding
Proper layout and grounding are essential for optimum
performance. Connect PGND and SGND together at a
single point on the PC Board. Connect PVSS to SVSS
and bypass with a 1µF capacitor. Place the power-supply bypass capacitor and the charge-pump hold
capacitor as close to the MAX9724 as possible. Route
PGND and all traces that carry switching transients
away from SGND and the audio signal path. The thin
QFN package features an exposed paddle that
improves thermal efficiency. Ensure that the exposed
paddle is electrically isolated from PGND, SGND,
and VDD. Connect the exposed paddle to SVSS only
when the board layout dictates that the exposed
paddle cannot be left floating.
MAX9724A ACTIVE FILTER GAIN
vs. FREQUENCY
10
RL = 10kΩ
5
0
-5
GAIN (dB)
MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
-10
-15
-20
-25
-30
-35
1k
10k
100k
Figure 6. Frequency Response of Active Filter of Figure 4
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 the
Application Note UCSP—A Wafer-Level Chip-Scale
Package available on Maxim’s website at www.maximic.com/ucsp.
12
1M
FREQUENCY (Hz)
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
VDD
0.1µF
15kΩ
1µF
15kΩ
INR
VDD
PVDD
BIAS
OUTR+
OUTR-
1µF
MAX9710
GND
PGND
MUTE
0.1µF 15kΩ
OUTL-
SHDN
OUTL+
INL
VDD
15kΩ
µCONTROLLER
100kΩ
100kΩ
0.1µF
STEREO
DAC
OUTL
SHDN
O.47µF
MAX9724B OUTR
INL
SGND
O.47µF
INR
PGND
VDD
PVSS
1µF
SVSS
C1P
C1N
VDD
1µF
1µF
______________________________________________________________________________________
13
MAX9724A/MAX9724B
System Diagram
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
MAX9724A/MAX9724B
Functional Diagram/Typical Operating Circuits
2.7V TO 5.5V
ON
C3
1µF
OFF
CIN R
IN*
0.47µF 20kΩ
LEFT
AUDIO
INPUT
RF*
30kΩ
12
(B1)
5
(C2)
6
(B3)
VDD
SHDN
INL
VDD
11
OUTL (C4)
HEADPHONE
JACK
1
(A1) C1P
SVSS
UVLO/
SHUTDOWN
CONTROL
CLICK-AND-POP
SUPPRESSION
CHARGE
PUMP
C1
1µF
SGND
VDD
3
(A3) C1N
OUTR
10
(C3)
MAX9724A
PVSS
4
(A4)
SVSS PGND
2
9
(B4) (A2)
C2
1µF
SVSS
SGND
7
(C1)
INR
8
(B2)
RIGHT
AUDIO
INPUT
CIN
RIN*
0.47µF 20kΩ
RF*
30kΩ
*RIN AND RF VALUES ARE CHOSEN FOR A GAIN -1.5V/V.
( ) UCSP PACKAGE
14
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
2.7V TO 5.5V
ON
C3
1µF
OFF
LEFT
AUDIO
INPUT
CIN
0.47µF
12
(B1)
5
(C2)
6
(B3)
VDD
SHDN
INL
RIN*
20kΩ
RF*
30kΩ
VDD
11
OUTL (C4)
HEADPHONE
JACK
1
(A1) C1P
VSS
UVLO/
SHUTDOWN
CONTROL
CLICK-AND-POP
SUPPRESSION
CHARGE
PUMP
C1
1µF
SGND
VDD
3
(A3) C1N
MAX9724B
OUTR
RIN
20kΩ
10
(C3)
SVSS
RF
30kΩ
PVSS
SVSS
PGND
SGND
4
(A4)
C2
1µF
9
(B4)
2
(A2)
7
(C1)
INR
8
(B2)
CIN
RIGHT 0.47µF
AUDIO
INPUT
( ) UCSP PACKAGE
______________________________________________________________________________________
15
MAX9724A/MAX9724B
Functional Diagram/Typical Operating Circuits (continued)
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
INR
SGND
TOP VIEW
SVSS
MAX9724A/MAX9724B
Pin Configurations
9
8
7
TOP VIEW
(BUMPS ON BOTTOM)
1
2
3
4
MAX9724A/MAX9724B
OUTR 10
MAX9724A
MAX9724B
OUTL 11
VDD 12
+
6
INL
5
SHDN
4
PVSS
A
C1P
PGND
C1N
PVSS
VDD
INR
INL
SVSS
SGND
SHDN
OUTR
OUTL
B
3
C1N
C1P
2
PGND
C
1
TQFN
UCSP
Chip Information
TRANSISTOR COUNT: 993
PROCESS: BiCMOS
16
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
12x16L QFN THIN.EPS
______________________________________________________________________________________
17
MAX9724A/MAX9724B
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.)
MAX9724A/MAX9724B
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
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.)
18
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone Amplifier
with Low RF Susceptibility and Shutdown
12L, UCSP 4x3.EPS
PACKAGE OUTLINE, 4x3 UCSP
21-0104
F
1
1
Revision History
Pages changed at Rev 2: 1, 2, 3, 6, 9, 12, 14–19
Pages changed at Rev 3: 1–6, 19
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 ____________________ 19
© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.
MAX9724A/MAX9724B
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.)