19-3963; Rev 1; 7/09
KIT
ATION
EVALU
E
L
B
A
AVAIL
60mW, DirectDrive, Stereo
Headphone Amplifiers with Shutdown
The MAX9728A/MAX9728B stereo headphone amplifiers are designed for display and notebook applications or portable equipment where board space is at a
premium. These devices use a unique DirectDrive ®
architecture to produce a ground-referenced output
from a single supply, eliminating the need for large DCblocking capacitors, saving cost, board space, and
component height. The MAX9728A offers an externally
adjustable gain, while the MAX9728B has an internally
preset gain of -1.5V/V. The MAX9728A/MAX9728B
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 MAX9728A/MAX9728B operate from a single 4.5V
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 12pin Thin QFN (3mm x 3mm x 0.8mm) and 14-pin
TSSOP packages (5mm x 4.4mm x 1.1mm).
Applications
Notebook PCs
CRT TVs
DVD Players
Multimedia Monitors
LCD/PDP Displays
DirectDrive is a registered trademark of Maxim Integrated
Product, Inc.
Features
♦ No Bulky DC-Blocking Capacitors Required
♦ Low-Power Shutdown Mode, < 0.1µA
♦ Adjustable Gain (MAX9728A) or Fixed -1.5V/V
Gain (MAX9728B)
♦ Low 0.02% THD+N
♦ High PSRR (80dB at 1kHz) Eliminates LDO
♦ Integrated Click-and-Pop Suppression
♦ 4.5V to 5.5V Single-Supply Operation
♦ Low Quiescent Current (3.5mA)
♦ Available in Space-Saving Packages
12-Pin Thin QFN (3mm x 3mm x 0.8mm)
14-Pin TSSOP (5mm x 4.4mm x 1.1mm)
Ordering Information
PART
GAIN (V/V) PIN-PACKAGE
MAX9728AETC+
Adj.
12 TQFN-EP*
MAX9728AEUD+
Adj.
14 TSSOP
MAX9728BETC+
-1.5
12 TQFN-EP*
MAX9728BEUD+
-1.5
14 TSSOP
TOP MARK
ABC
—
ABD
—
Note: All devices specified over the -40°C to +85°C operating
range.
+Denotes lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Pin Configurations appear at end of data sheet.
Block Diagrams
MAX9728B
MAX9728A
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
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.
MAX9728A/MAX9728B
General Description
MAX9728A/MAX9728B
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
ABSOLUTE MAXIMUM RATINGS
VDD to PGND............................................................-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 (MAX9728A)..........................-0.3V to (VDD + 0.3V)
IN_ to SGND (MAX9728B) .............(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 SGND ......................................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-Pin TQFN (derate 14.7mW/°C above +70°C) .........1177mW
14-Pin TSSOP (derate 9.1mW/°C above +70°C) ...........727mW
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
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 MAX9728A gain = -1.5V/V
(RIN = 20kΩ, RF = 30kΩ); for MAX9728B 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
GENERAL
Supply Voltage Range
VDD
Quiescent Current
ICC
Shutdown Current
ISHDN
Shutdown to Full Operation
RIN
Output Offset Voltage
VOS
PSRR
Output Power
POUT
Voltage Gain
AV
Channel-to-Channel Gain
Tracking
Total Harmonic Distortion Plus
Noise
2
SHDN = SGND = PGND
tSON
Input Impedance
Power-Supply Rejection Ratio
4.5
THD+N
180
MAX9728B, measured at IN_
15
19
25
kΩ
±1.5
±10
mV
VDD = 4.5V to 5.5V
86
f = 1kHz, 100mVP-P
80
f = 20kHz, 100mVP-P
65
RL = 32Ω, THD+N = 1%
30
RL = 16Ω, THD+N = 1%
MAX9728B (Note 4)
µs
dB
63
mW
42
-1.52
-1.5
MAX9728B
±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 Shutdown
(VDD = 5V, PGND = SGND, SHDN = 5V, C1 = C2 = 1µF, RL = ∞, resistive load reference to ground; for MAX9728A gain = -1.5V/V
(RIN = 20kΩ, RF = 30kΩ); for MAX9728B 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
Click-and-Pop Level
CONDITIONS
TYP
RL = 1kΩ,
VOUT = 2VRMS
BW = 22Hz to 22kHz
102
A-weighted
105
RL = 32Ω,
POUT = 50mW
BW = 22Hz to 22kHz
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
fOSC
KCP
MIN
190
Into shutdown
RL = 32Ω, peak voltage,
A-weighted, 32 samples per Out of
second (Note 5)
shutdown
270
400
kHz
-67
dB
-64
DIGITAL INPUTS (SHDN)
Input Voltage High
VINH
Input Voltage Low
VINL
Input Leakage Current
2
V
0.8
V
±1
µA
Note 3: All specifications are 100% tested at TA = +25°C; temperature limits are guaranteed by design.
Note 4: Gain for the MAX9728A is adjustable.
Note 5: Test performed with a 32Ω resistive load connected to SGND. 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
MAX9728A/MAX9728B
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 MAX9728A),
THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25°C, unless otherwise noted.)
VDD = 5V
RL = 16Ω
10
1
MAX9728A/28B toc02
100
MAX9728A/28B toc01
100
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
VDD = 5V
RL = 32Ω
10
MAX9728A/28B toc03
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
VDD = 5V
RL = 16Ω
POUT = 20mW
fIN = 1kHz
0.1
1
THD+N (%)
THD+N (%)
fIN = 1kHz
0.1
0.01
0.01
fIN = 10kHz
fIN = 20Hz
fIN = 20Hz
0.001
0.001
0.001
40
60
80
100
0
OUTPUT POWER (mW)
80
POUT = 30mW
0.01
POUT = 50mW
THD+N = 10%
60
50
30
100
1k
FREQUENCY (Hz)
10k
100k
100
1k
10k
100k
FREQUENCY (Hz)
OUTPUT POWER vs. SUPPLY VOLTAGE
THD+N = 1%
20
fIN = 1kHz
RL = 16Ω
120
THD+N = 10%
100
80
60
40
THD+N = 1%
20
0
0.001
10
10
120
40
10
4
100
70
OUTPUT POWER (mW)
0.1
60
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9728A/28B toc04
VDD = 5V
RL = 32Ω
40
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
1
20
OUTPUT POWER (mW)
20
MAX9728A/28B toc05
0
POUT = 37mW
0.01
fIN = 10kHz
MAX9728A/28B toc06
THD+N (%)
0.1
1
THD+N (%)
MAX9728A/MAX9728B
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
fIN = 1kHz
RL = 32Ω
0
4.5
5.0
SUPPLY VOLTAGE (V)
5.5
4.5
5.0
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5.5
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
POWER-SUPPLY REJECTION
RATIO vs. FREQUENCY
THD+N = 10%
70
50
40
-60
-80
30
POUT = 15mW
RL = 16Ω
-20
CROSSTALK (dB)
-40
60
-40
-60
LEFT TO RIGHT
-80
THD+N = 1%
20
-100
VDD = 5V
fIN = 1kHz
10
10
100
-120
10
1000
RIGHT TO LEFT
-100
-120
0
100
1k
10k
100k
10
100
1k
10k
FREQUENCY (Hz)
FREQUENCY (Hz)
OUTPUT POWER vs. LOAD RESISTANCE
AND CHARGE-PUMP CAPACITOR SIZE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
50
C1 = C2 = 0.47μF
40
VDD = 5V
fIN = 1kHz
THD+N = 1%
30
3.40
3.35
3.30
50
250
100
200
150
LOAD RESISTANCE (Ω)
300
8
7
6
5
4
3
1
NO LOAD INPUTS GROUND
3.20
0
9
2
3.25
20
MAX9728A/28B toc12
3.45
100k
10
SHUTDOWN CURRENT (nA)
60
MAX9728A/28B toc11
C1 = C2 = 1μF
70
3.50
SUPPLY CURRENT (mA)
C1 = C2 = 2.2μF
MAX9728A/28B toc10
LOAD RESISTANCE (Ω)
80
OUTPUT POWER (mW)
RL = 32Ω
VDD = 5V
-20
PSRR (dB)
OUTPUT POWER (mW)
80
CROSSTALK vs. FREQUENCY
0
MAX9728A/28B toc09
90
0
MAX9728A/28B toc07
100
MAX9728A/28B toc08
OUTPUT POWER
vs. LOAD RESISTANCE
NO LOAD INPUTS GROUND
0
4.5
5.0
SUPPLY VOLTAGE (V)
5.5
4.5
5.0
5.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
MAX9728A/MAX9728B
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 MAX9728A),
THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25°C, unless otherwise noted.)
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 MAX9728A),
THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25°C, unless otherwise noted.)
ENTERING SHUTDOWN
VSHDN
5V/div
MAX9728A/28B toc14
EXITING SHUTDOWN
MAX9728A/28B toc13
MAX9728A/MAX9728B
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
VSHDN
5V/div
VIN_
1V/div
VIN_
1V/div
VOUT_
500mV/div
VOUT_
500mV/div
40μs/div
20μs/div
Pin Description
PIN
TQFN
6
TSSOP
NAME
FUNCTION
1
3
C1P
2
4
PGND
3
5
C1N
Flying Capacitor Negative Terminal. Connect a 1µF ceramic capacitor from C1P to C1N.
4
7
PVSS
Charge-Pump Output. Connect to SVSS and bypass with a 1µF ceramic capacitor to PGND.
5
8
SHDN
Active-Low Shutdown Input
6
9
INL
7
10
SGND
8
11
INR
Flying Capacitor Positive Terminal. Connect a 1µF ceramic capacitor from C1P to C1N.
Power Ground. Connect to SGND.
Left-Channel Input
Signal Ground. Connect to PGND.
Right-Channel Input
9
12
SVSS
Amplifier Negative Supply. Connect to PVSS.
10
14
OUTR
Right-Channel Output
11
1
OUTL
Left-Channel Output
12
2
VDD
—
6,13
N.C.
EP
—
EP
Positive Power-Supply Input. Bypass with a 1µF capacitor to PGND.
No Connection. Not internally connected.
Exposed Paddle. Leave this connection floating or connect it to SVSS.
_______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone
Amplifier with Shutdown
The MAX9728A/MAX9728B stereo headphone amplifiers feature Maxim’s DirectDrive architecture, eliminating the large output-coupling capacitors required by
conventional single-supply headphone amplifiers.
These devices consist 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
SGND (Figure 1). The benefit of this SGND 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 MAX9728A/MAX9728B 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 MAX9728A/MAX9728B also feature
thermal-overload and short-circuit protection.
MAX9728A/MAX9728B
Detailed Description
VOUT
VDD
VDD
VDD/2
SGND
CONVENTIONAL DRIVER-BIASING SCHEME
VOUT
VDD
SGND
2VDD
-VDD
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typically half the supply) for maximum dynamic range. Largecoupling 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 DirectDrive architecture uses a charge pump
to create an internal negative supply voltage, allowing
the MAX9728A/MAX9728B outputs to be biased about
SGND. With no DC component, there is no need for the
large DC-blocking capacitors. The MAX9728A/
MAX9728B 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 MAX9728A/MAX9728B are typically
1.5mV, which, when combined with a 32Ω load, results
in less than 47µA of DC current flow to the headphones.
DirectDrive BIASING SCHEME
Figure 1. Conventional Driver Output Waveform vs.
MAX9728A/MAX9728B Output Waveform
Charge Pump
The MAX9728A/MAX9728B 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).
Click-and-Pop Suppression
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.
_______________________________________________________________________________________
7
MAX9728A/MAX9728B
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
Since the MAX9728A/MAX9728B do not require outputcoupling capacitors, this problem does not arise.
Additionally, the MAX9728A/MAX9728B feature extensive click-and-pop suppression that eliminates any
audible transient sources internal to the device.
Typically, the output of the device driving the
MAX9728A/MAX9728B 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 MAX9728A/
MAX9728B, 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 MAX9728A/MAX9728B 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
MAX9728B). The amplifiers and charge pump are
enabled once SHDN is driven high.
Applications Information
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) =
TJ(MAX) − TA
θJA
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 +110°C/W for the TSSOP package.
The MAX9728A/MAX9728B 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
8
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 MAX9728A/MAX9728B. 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 MAX9728A/
MAX9728B has increased the dynamic range compared
to other single-supply amplifiers.
Maximum Output Swing
Internal device structures limit the maximum voltage
swing of the MAX9728A/MAX9728B. 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.
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.
_______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone
Amplifier with Shutdown
switching transients. Bypass VDD with C3, the same
value as C1, and place it physically close to the VDD
and PGND pins.
Amplifier Gain
The gain of the MAX9728B 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).
The gain of the MAX9728A amplifier is set externally as
shown in Figure 2, the gain is:
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.
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 MAX9728B). 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 MAX9728B), 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.
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 MAX9728A/MAX9728Bs’ charge-pump
Table 1. Suggested Capacitor Manufacturers
SUPPLIER
Taiyo Yuden
PHONE
FAX
800-348-2496
847-925-0899
WEBSITE
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
MAX9728A/MAX9728B
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 1 lists suggested manufacturers.
Lineout Amplifier and Filter Block
To suppress this noise, and to provide a 2VRMS standard audio output level from a single 5V supply, the
MAX9728A can be configured as a line driver and
active lowpass filter. Figure 4 shows the MAX9728A
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 5
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 MAX9728 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.
10
RF
MAX9728A
LEFT
AUDIO
INPUT
RIN
RIGHT
AUDIO
INPUT
RIN
INL
OUTL
OUTR
INR
RF
Figure 2. Gain Setting for the MAX9728A
RMS OUTPUT VOLTAGE
vs. SUPPLY VOLTAGE
4.1
MAX9728A/28B fig03
The MAX9728A can be used as an audio line driver
capable of providing 2VRMS into 10kΩ loads with a single 5V supply (see Figure 3 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
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 can often simplify power-supply design in some systems.
When the MAX9728A 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.
fIN = 1kHz
3.9
RMS OUTPUT VOLTAGE (V)
MAX9728A/MAX9728B
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
RL = 10kΩ
1% THD+N
3.7
3.5
RL = 1kΩ
1% THD+N
3.3
3.1
2.9
2.7
2.5
4.5
5.0
SUPPLY VOLTAGE (V)
Figure 3. RMS Output Voltage vs. Supply Voltage
______________________________________________________________________________________
5.5
60mW, DirectDrive, Stereo Headphone
Amplifier with Shutdown
MAX9728A/MAX9728B
15kΩ
220pF
LEFT
AUDIO
INPUT
1μF
7.5kΩ
7.5kΩ
MAX9728A
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 4. MAX9728A Line-Out Amplifier and Filter Block Configuration
MAX9728A ACTIVE FILTER GAIN
vs. FREQUENCY
10
RL = 10kΩ
5
0
GAIN (dB)
-5
-10
-15
-20
-25
-30
-35
1k
10k
100k
1M
FREQUENCY (Hz)
Figure 5. Frequency Response of Active Filter of Figure 4
______________________________________________________________________________________
11
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
MAX9728A/MAX9728B
System Diagram
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
MAX9728B OUTR
INL
SGND
O.47μF
INR
PGND
VDD
PVSS
1μF
SVSS
C1P
C1N
VDD
1μF
1μF
12
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone
Amplifier with Shutdown
4.5V TO 5.5V
ON
C3
1μF
OFF
CIN R
IN*
0.47μF 20kΩ
LEFT
AUDIO
INPUT
RF*
30kΩ
12
(2)
5
(8)
6
(9)
VDD
SHDN
INL
VDD
11
OUTL (1)
HEADPHONE
JACK
1
(3) C1P
SVSS
UVLO/
SHUTDOWN
CONTROL
CLICK-AND-POP
SUPPRESSION
CHARGE
PUMP
C1
1μF
SGND
VDD
3
(5) C1N
OUTR
10
(14)
MAX9728A
PVSS
4
(7)
SVSS PGND
2
9
(12) (4)
C2
1μF
SVSS
SGND
7
(10)
INR
8
(11)
RIGHT
AUDIO
INPUT
CIN
RIN*
0.47μF 20kΩ
RF*
30kΩ
*RIN AND RF VALUES ARE CHOSEN FOR A GAIN -1.5V/V.
( ) TSSOP PACKAGE
______________________________________________________________________________________
13
MAX9728A/MAX9728B
Functional Diagram/Typical Operating Circuits
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
MAX9728A/MAX9728B
Functional Diagram/Typical Operating Circuits (continued)
4.5V TO 5.5V
ON
C3
1μF
OFF
LEFT
AUDIO
INPUT
CIN
0.47μF
12
(2)
5
(8)
6
(9)
VDD
SHDN
INL
RIN*
20kΩ
RF*
30kΩ
VDD
11
OUTL (1)
HEADPHONE
JACK
1
(3) C1P
VSS
UVLO/
SHUTDOWN
CONTROL
CLICK-AND-POP
SUPPRESSION
CHARGE
PUMP
C1
1μF
SGND
VDD
3
(5) C1N
MAX9728B
OUTR
RIN
20kΩ
10
(14)
SVSS
RF
30kΩ
PVSS
SVSS
PGND
SGND
4
(7)
C2
1μF
9
(12)
2
(4)
7
(10)
CIN
RIGHT 0.47μF
AUDIO
INPUT
INR
8
(11)
( ) TSSOP PACKAGE
14
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
SVSS
INR
SGND
TOP VIEW
9
8
7
TOP VIEW
+
14 OUTR
OUTL 1
OUTR 10
6
MAX9728A
MAX9728B
OUTL 11
INL
5
SHDN
4
PVSS
VDD
2
13 N.C.
C1P
3
12 SVSS
PGND 4
C1N 5
VDD 12
1
2
3
C1P
PGND
C1N
+
MAX9728A
MAX9728B
11 INR
10 SGND
N.C. 6
9
INL
PVSS 7
8
SHDN
TSSOP
TQFN
Chip Information
TRANSISTOR COUNT: 993
PROCESS: BiCMOS
______________________________________________________________________________________
15
MAX9728A/MAX9728B
Pin Configurations
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.
12 TQFN-EP
T1233-1
21-0136
14 TSSOP
U14-1
21-0066
(NE - 1) X e
E
MARKING
12x16L QFN THIN.EPS
MAX9728A/MAX9728B
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
E/2
D2/2
(ND - 1) X e
D/2
AAAA
e
CL
D
D2
k
CL
b
0.10 M C A B
E2/2
L
E2
0.10 C
C
L
C
L
0.08 C
A
A2
A1
L
L
e
e
PACKAGE OUTLINE
8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
16
______________________________________________________________________________________
I
1
2
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
PKG
8L 3x3
12L 3x3
16L 3x3
REF.
MIN. NOM. MAX.
MIN. NOM. MAX.
MIN. NOM. MAX.
A
0.70
0.75
0.80
0.70
0.75
0.80
0.70
0.75
0.80
b
0.25
0.30
0.35
0.20
0.25
0.30
0.20
0.25
0.30
D
2.90
3.00
3.10
2.90
3.00
3.10
2.90
3.00
3.10
E
2.90
3.00
3.10
2.90
3.00
3.10
2.90
3.00
3.10
e
L
0.65 BSC.
0.35
0.55
0.50 BSC.
0.75
0.45
0.55
0.50 BSC.
0.65
0.30
0.40
N
8
12
16
ND
2
3
4
2
NE
0
A1
A2
k
3
0.05
0.02
0
-
-
0.25
-
0.50
4
0.05
0
0.20 REF
0.20 REF
0.25
0.02
EXPOSED PAD VARIATIONS
0.02
0.05
0.20 REF
-
0.25
-
PKG.
CODES
TQ833-1
D2
E2
PIN ID
JEDEC
MIN.
NOM.
MAX.
MIN.
NOM.
MAX.
0.25
0.70
1.25
0.25
0.70
1.25
0.35 x 45°
WEEC
WEED-1
T1233-1
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
T1233-3
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-1
T1233-4
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-1
T1633-2
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-2
T1633F-3
0.65
0.80
0.95
0.65
0.80
0.95
0.225 x 45°
WEED-2
T1633FH-3
0.65
0.80
0.95
0.65
0.80
0.95
0.225 x 45°
WEED-2
T1633-4
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-2
T1633-5
0.95
1.10
1.25
0.95
1.10
1.25
0.35 x 45°
WEED-2
-
NOTES:
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994.
ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES.
N IS THE TOTAL NUMBER OF TERMINALS.
THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO
JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED
WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR
MARKED FEATURE.
DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.20 mm AND 0.25 mm
FROM TERMINAL TIP.
ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY.
DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION.
COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS
.
DRAWING CONFORMS TO JEDEC MO220 REVISION C.
MARKING IS FOR PACKAGE ORIENTATION REFERENCE ONLY.
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY.
WARPAGE NOT TO EXCEED 0.10mm.
PACKAGE OUTLINE
8, 12, 16L THIN QFN, 3x3x0.8mm
21-0136
I
2
2
______________________________________________________________________________________
17
MAX9728A/MAX9728B
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.
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.
TSSOP4.40mm.EPS
MAX9728A/MAX9728B
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
18
______________________________________________________________________________________
60mW, DirectDrive, Stereo Headphone
Amplifiers with Shutdown
PAGES
CHANGED
REVISION
NUMBER
REVISION
DATE
0
1/06
Initial release
—
1
7/09
Corrected top mark designations
1
DESCRIPTION
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
© 2009 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX9728A/MAX9728B
Revision History
工商网监
湘ICP备2023018690号
