General Description
The MAX9725 fixed-gain, stereo headphone amplifier
is ideal for portable equipment where board space is at a
premium. The MAX9725 uses a unique, patented
DirectDriveTM 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. Fixed gains of -2V/V (MAX9725A),
-1.5V/V (MAX9725B), -1V/V (MAX9725C), and -4V/V
(MAX9725D) further reduce external component count.
The MAX9725 delivers up to 20mW per channel into a
32Ωload and achieves 0.006% THD+N. An 80dB at 1kHz
power-supply rejection ratio (PSRR) allows the MAX9725
to operate from noisy digital supplies without an additional
linear regulator. The MAX9725 includes ±8kV ESD protec-
tion on the headphone output. Comprehensive click-and-
pop circuitry suppresses audible clicks and pops at
startup and shutdown. A low-power shutdown mode
reduces supply current to 0.6µA (typ).
The MAX9725 operates from a single 0.9V to 1.8V supply,
allowing the device to be powered directly from a single
AA or AAA battery. The MAX9725 consumes only
2.1mA of supply current, provides short-circuit protection,
and is specified over the extended -40°C to +85°C tem-
perature range. The MAX9725 is available in a tiny
(1.54mm x 2.02mm x 0.6mm) 12-bump chip-scale
package (UCSP™) and a 12-pin thin QFN package
(4mm x 4mm x 0.8mm).
Applications
Features
♦Low Quiescent Current (2.1mA)
♦Single-Cell, 0.9V to 1.8V Single-Supply Operation
♦Fixed Gain Eliminates External Feedback Network
MAX9725A: -2V/V
MAX9725B: -1.5V/V
MAX9725C: -1V/V
MAX9725D: -4V/V
♦Ground-Referenced Outputs Eliminate DC Bias
♦No Degradation of Low-Frequency Response Due
to Output Capacitors
♦20mW per Channel into 32Ω
♦Low 0.006% THD+N
♦High PSRR (80dB at 1kHz)
♦Integrated Click-and-Pop Suppression
♦Low-Power Shutdown Control
♦Short-Circuit Protection
♦±8kV ESD-Protected Amplifier Outputs
♦Available in Space-Saving Packages
12-Bump UCSP (1.54mm x 2.02mm x 0.6mm)
12-Pin Thin QFN (4mm x 4mm x 0.8mm)
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
________________________________________________________________ Maxim Integrated Products 1
19-3465; Rev 1; 5/05
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.
Ordering Information
PA RT
T EM P R AN G E
PIN-
PA CK A G E
T O P
M A RK
G A IN
( V/V)
MAX9725AEBC -T
- 40°C to + 85°C 12 U C S P- 12 AC K
- 2
M AX9725AE TC
- 40°C to + 85°C 12 TQFN- EP* AAEW
- 2
MAX9725BEBC -T
- 40°C to + 85°C 12 U C S P- 12 AC L
- 1.5
M AX9725BE TC
- 40°C to + 85°C 12 TQFN- EP* AAEX
- 1.5
MAX9725CEBC-T
- 40°C to + 85°C 12 U C S P- 12 AC M
- 1
M AX9725C E TC
- 40°C to + 85°C 12 TQFN- EP* AAEY
- 1
MAX9725D EBC -T
- 40°C to + 85°C 12 U C S P- 12 AC N
- 4
M AX9725D E TC
- 40°C to + 85°C 12 TQFN- EP* AAEZ
- 4
UCSP is a trademark of Maxim Integrated Products, Inc. Pin Configurations appear at end of data sheet.
*EP = Exposed paddle.
MP3 Players
Cellular Phones
PDAs
Smart Phones
Portable Audio Equipment
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS.
C1N
C1P
OUTL
SINGLE
1.5V CELL
AA OR AAA
BATTERY
OUTR
SGND PGND
MAX9725
INVERTING
CHARGE PUMP
INR
INL
VDD
PVSS
VSS
Block Diagram
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
SGND to PGND .....................................................-0.3V to +0.3V
VDD to SGND or PGND ............................................-0.3V to +2V
VSS to PVSS ...........................................................-0.3V to +0.3V
C1P to PGND..............................................-0.3V to (VDD + 0.3V)
C1N to PGND............................................(PVSS - 0.3V) to +0.3V
VSS, PVSS to GND ....................................................+0.3V to -2V
OUTR, OUTL, INR, INL to SGND .....(VSS - 0.3V) to (VDD + 0.3V)
SHDN to SGND or PGND .........................................-0.3V to +4V
Output Short-Circuit Current ......................................Continuous
Continuous Power Dissipation (TA= +70°C)
12-Bump UCSP (derate 6.5mW/°C above +70°C)....518.8mW
12-Pin Thin QFN (derate 16.9mW/°C above +70°C) ..1349.1mW
Junction Temperature......................................................+150°C
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Bump Temperature (soldering) Reflow............................+230°C
Lead Temperature (soldering, 10s) .................................+300°C
ELECTRICAL CHARACTERISTICS
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, RL= ∞, TA= TMIN to TMAX, unless otherwise
noted. Typical values are at TA= +25°C.) (See the Functional Diagram.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
Supply Voltage Range VDD Guaranteed by PSRR test 0.9 1.8 V
Quiescent Supply Current IDD Both channels active 2.1 3.3
mA
TA = +25°C 0.6 10
Shutdown Current
ISHDN
VSHDN = 0V
TA = -40°C to +85°C
30 µA
Shutdown to Full Operation tON
180
µs
VIH VDD = 0.9V to 1.8V
0.7 x VDD
SHDN Thresholds VIL VDD = 0.9V to 1.8V
0.3 x VDD
V
SHDN Input Leakage Current
ILEAK VDD = 0.9V to 1.8V (Note 2) ±1µA
CHARGE PUMP
Oscillator Frequency fOSC
493 580
667
kHz
AMPLIFIERS
MAX9725A
-2.04 -2.00 -1.96
MAX9725B
-1.53 -1.5 -1.47
MAX9725C
-1.02 -1.00 -0.98
Voltage Gain AV
MAX9725D
-4.08 -4.00 -3.92
V/V
Gain Match ∆AV
±0.5
%
MAX9725A/MAX9725D ±0.3 ±1.05
MAX9725B
±0.45 ±1.58
Total Output Offset Voltage VOS
Input AC-coupled,
RL = 32Ω to GND,
TA = +25°CMAX9725C
±0.6 ±2.1
mV
Input Resistance RIN 15 25 35 kΩ
VDD = 0.9V to 1.8V, TA = +25°C6080
fIN = 1kHz 70
Power-Supply Rejection Ratio
PSRR
100mVP-P ripple fIN = 20kHz 62
dB
RL = 32Ω10 20
VDD = 1.5V RL = 16Ω25
VDD = 1.0V, RL = 32Ω7
Output Power (Note 3) POUT
VDD = 0.9V, RL = 32Ω6
mW
RL = 32Ω, POUT = 12mW, f = 1kHz
0.006
Total Harmonic Distortion Plus
Noise
THD+N
RL = 16Ω, POUT = 15mW, f = 1kHz
0.015
%
BW = 22Hz to 22kHz
89
Signal-to-Noise Ratio SNR
RL = 32Ω, POUT = 12mW
A-weighted filter 92 dB
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
_______________________________________________________________________________________ 3
Note 1: All specifications are 100% tested at TA= +25°C; temperature limits are guaranteed by design.
Note 2: Input leakage current measurements limited by automated test equipment.
Note 3: fIN = 1kHz, TA= +25°C, THD+N < 1%, both channels driven in-phase.
Note 4: Testing performed with 32Ωresistive load connected to outputs. Mode transitions controlled by SHDN. KCP level calculated
as 20 log [peak voltage under normal operation at rated power level / peak voltage during mode transition]. Inputs are AC-
grounded. Typical Operating Characteristics
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz
to 22kHz, TA= +25°C, unless otherwise noted.) (See the Functional Diagram.)
10 10k1k100 100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc01
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
VDD = 1.5V
RL = 16Ω
AV = -2V/V
POUT = 15mW
POUT = 2mW
10 10k1k100 100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc03
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
VDD = 1V
RL = 16Ω
AV = -2V/V
POUT = 0.7mW
POUT = 4mW
10 10k1k100 100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc04
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
POUT = 0.7mW
POUT = 4mW
VDD = 1V
RL = 32Ω
AV = -2V/V
100
010203040
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc05
OUTPUT POWER (mW)
THD+N (%)
VDD = 1.5V
RL = 16Ω
AV = -2V/V fIN = 20Hz
fIN = 1kHz
fIN = 10kHz
100
010203040
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc06
OUTPUT POWER (mW)
THD+N (%)
VDD = 1.5V
RL = 32Ω
AV = -2V/V
fIN = 20Hz
fIN = 1kHz
fIN = 10kHz
ELECTRICAL CHARACTERISTICS (continued)
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, RL= ∞, TA= TMIN to TMAX, unless otherwise
noted. Typical values are at TA= +25°C.) (See the Functional Diagram.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Slew Rate SR 0.2
V/µs
Maximum Capacitive Load CLNo sustained oscillations
150
pF
Crosstalk
XTALK
fIN = 1.0kHz, RL = 32Ω, POUT = 5mW
100
dB
Into shutdown
72.8
Click/Pop Level KCP
RL = 32Ω, peak voltage,
A-weighted, 32 samples per
second (Note 4)
Out of shutdown 72.8
dB
ESD Protection VESD Human Body Model (OUTR, OUTL) ±8 kV
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz
to 22kHz, TA= +25°C, unless otherwise noted.) (See the Functional Diagram.)
100
051015
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc07
OUTPUT POWER (mW)
THD+N (%)
VDD = 1V
RL = 16Ω
AV = -2V/V
fIN = 20Hz
fIN = 1kHz
fIN = 10kHz
100
051015
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc08
OUTPUT POWER (mW)
THD+N (%)
VDD = 1V
RL = 32Ω
AV = -2V/V
fIN = 20Hz
fIN = 1kHz
fIN = 10kHz
10 100 10k1k 100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9725 toc09
FREQUENCY (Hz)
PSRR (dB)
-10
-110
-60
-50
-40
-30
-20
-70
-80
-90
-100
VDD = 1.5V
RL = 32Ω
10 100 10k1k 100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9725 toc10
FREQUENCY (Hz)
PSRR (dB)
0
-100
-50
-40
-30
-20
-10
-60
-70
-80
-90
VDD = 1V
RL = 32Ω
10 100 10k1k 100k
CROSSTALK vs. FREQUENCY
MAX9725 toc11
FREQUENCY (Hz)
PSRR (dB)
0
-20
-40
-60
-80
-100
-120
VDD = 1.5V
POUT = 5mW
RL = 32Ω
RIGHT TO LEFT
LEFT TO RIGHT
0
10
20
30
40
50
60
70
80
0.9 1.1 1.3 1.5
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9725 toc12
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
fIN = 1kHz
RL = 16Ω
BOTH INPUTS
DRIVEN IN-PHASE
THD+N = 10%
THD+N = 1%
0
15
10
5
20
25
30
35
40
45
50
0.9 1.1 1.3 1.5
OUTPUT POWER
vs. SUPPLY VOLTAGE
MAX9725 toc13
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
fIN = 1kHz
RL = 32Ω
BOTH INPUTS
DRIVEN IN-PHASE
THD+N = 10%
THD+N = 1%
80
70
0
10 100 1k
OUTPUT POWER
vs. LOAD RESISTANCE
20
MAX9725 toc14
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
40
60
10
30
50
VDD = 1.5V
fIN = 1kHz
BOTH INPUTS
DRIVEN IN-PHASE
THD+N = 10%
THD+N = 1%
80
70
0
10 100 1k
OUTPUT POWER
vs. LOAD RESISTANCE
20
MAX9725 toc15
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
40
60
10
30
50
VDD = 1V
fIN = 1kHz
BOTH INPUTS
DRIVEN IN-PHASE
THD+N = 10%
THD+N = 1%
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
_______________________________________________________________________________________ 5
0
10
20
30
40
50
60
70
80
0 1020304050
POWER DISSIPATION
vs. OUTPUT POWER
MAX9725 toc16
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
VDD = 1.5V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN-PHASE
RL = 16Ω
RL = 32Ω
0
5
10
15
20
25
30
35
0 5 10 15 20
POWER DISSIPATION
vs. OUTPUT POWER
MAX9725 toc17
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
VDD = 1V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN-PHASE
RL = 16Ω
RL = 32Ω
10 100 10k1k 100k
GAIN FLATNESS
vs. FREQUENCY
FREQUENCY (Hz)
AMPLITUDE (dB)
2
1
0
-1
-2
-3
-4
-5
-7
-6
-8
-9
-10
MAX9725 toc18
0
5
10
15
20
25
30
35
40
10 20 30 40 50
OUTPUT POWER vs. CHARGE-PUMP
CAPACITANCE AND LOAD RESISTANCE
MAX9725 toc19
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
VDD = 1.5V
fIN = 1kHz
THD+N = 1%
C1 = C2 = 2.2µF
C1 = C2 = 1µF
C1 = C2 = 0.47µF
C1 = C2 = 0.68µF
-160
-140
-120
-100
-80
-60
-40
-20
0
0 5 10 15 20
OUTPUT SPECTRUM
vs. FREQUENCY
MAX9725 toc20
FREQUENCY (kHz)
AMPLITUDE (dB)
fIN = 1kHz
RL = 32Ω
VOUT = -60dBV
VDD = 1.5V
0
1.5
1.0
0.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0.9 1.11.0 1.2 1.3 1.4 1.5
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9725 toc21
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
NO LOAD
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
MAX9725 toc22
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT (µA)
1.31.1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
0.9 1.5
EXITING SHUTDOWN
MAX9725 toc23
200µs/div
OUT_
1V/div
SHDN
500mV/div
POWER-UP/-DOWN WAVEFORM
MAX9725toc24
200ms/div
OUT_
10mV/div
VDD
1V/div
Typical Operating Characteristics (continued)
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz
to 22kHz, TA= +25°C, unless otherwise noted.) (See the Functional Diagram.)
MAX9725
Detailed Description
The MAX9725 stereo headphone driver features Maxim’s
patented DirectDrive architecture, eliminating the large
output-coupling capacitors required by conventional sin-
gle-supply headphone drivers. The MAX9725 consists of
two 20mW class AB headphone drivers, shutdown con-
trol, inverting charge pump, internal gain-setting resistors,
and comprehensive click-and-pop suppression circuitry
(see the Functional Diagram). A negative power supply
(PVSS) is created by inverting the positive supply (VDD).
Powering the drivers from VDD and PVSS increases the
dynamic range of the drivers to almost twice that of other
1V single-supply drivers. This increase in dynamic range
allows for higher output power.
The outputs of the MAX9725 are biased about GND
(Figure 1). The benefit of this GND bias is that the driver
outputs do not have a DC component, thus large DC-
blocking capacitors are unnecessary. Eliminating the
DC-blocking capacitors on the output saves board
space, system cost, and improves frequency response.
DirectDrive
Conventional 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 the DC bias from the
headphones. 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 driver.
Maxim’s DirectDrive architecture uses a charge pump
to create an internal negative supply voltage. This
allows the MAX9725 outputs to be biased about GND,
increasing the dynamic range while operating from a
single supply. A conventional amplifier powered from
1.5V ideally provides 18mW to a 16Ωload. The
MAX9725 provides 25mW to a 16Ωload. The
DirectDrive architecture eliminates the need for two
large (220µF, typ) DC-blocking capacitors on the out-
put. The MAX9725 charge pump requires two small
ceramic capacitors, conserving board space, reducing
cost, and improving the frequency response of the
headphone driver. See the Output Power vs. Charge-
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
6 _______________________________________________________________________________________
PIN
BUMP
THIN
QFN
UCSP
NAME
FUNCTION
1A1
C1N
Flying Capacitor Negative Terminal. Connect a 1µF capacitor from C1P to C1N.
2A2
PVSS
Inverting Charge-Pump Output. Bypass with 1µF from PVSS to PGND. PVSS must be connected to VSS.
3 A3 INL Left-Channel Audio Input
4A4
INR
Right-Channel Audio Input
5B4
VSS
Amplifier Negative Power Supply. Must be connected to PVSS.
6B3
SGND
Signal Ground. SGND must be connected to PGND. SGND is the ground reference for the input and
output signal.
7C4
OUTR
Right-Channel Output
8C3
OUTL
Left-Channel Output
9C2
VDD
Positive Power-Supply Input. Bypass with a 1µF capacitor to PGND.
10 C1
C1P
Flying Capacitor Positive Terminal. Connect a 1µF capacitor from C1P to C1N.
11 B1
PGND
Power Ground. Ground reference for the internal charge pump. PGND must be connected to SGND.
12 B2
SHDN
Active-Low Shutdown. Connect to VDD for normal operation. Pull low to disable the amplifier and
charge pump.
EP — EP Exposed Paddle. Internally connected to VSS. Leave paddle unconnected or solder to VSS.
Pin Description
Pump Capacitance and Load Resistance graph in the
Typical Operating Characteristics for details of the possi-
ble capacitor sizes.
Previous attempts to eliminate the output-coupling
capacitors involved biasing the headphone return
(sleeve) to the DC-bias voltage of the headphone
amplifiers. This method raises some issues:
• The sleeve is typically grounded to the chassis.
Using this biasing approach, the sleeve must be
isolated from system ground, complicating product
design.
• During an ESD strike, the driver’s ESD structures
are the only path to system ground. The driver must
be able to withstand the full ESD strike.
• 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.
Low-Frequency Response
Large DC-blocking capacitors limit the amplifier’s low-
frequency response and can distort the audio signal:
1) The impedance of the headphone load and the DC-
blocking capacitor forms a highpass filter with the
-3dB point set by:
where RLis the impedance of the headphone and
COUT is the value of the DC-blocking capacitor. The
highpass filter is required by conventional single-
ended, single power-supply headphone drivers to
block the midrail DC-bias component of the audio
signal from the headphones. The drawback to the
filter is that it can attenuate low-frequency signals.
Larger values of COUT reduce this effect but result
in physically larger, more expensive capacitors.
Figure 2 shows the relationship between the size of
COUT and the resulting low-frequency attenuation.
Note that the -3dB point for a 16Ωheadphone with
a 100µF blocking capacitor is 100Hz, well within the
normal audio band, resulting in low-frequency
attenuation of the reproduced signal.
2) The voltage coefficient of the DC-blocking capacitor
contributes distortion to the reproduced audio signal
as the capacitance value varies when the function of
the voltage across the capacitor changes. At low
frequencies, the reactance of the capacitor domi-
nates at frequencies below the -3dB point and the
voltage coefficient appears as frequency-dependent
distortion. Figure 3 shows the THD+N introduced by
two different capacitor dielectric types. Note that
below 100Hz, THD+N increases rapidly.
The combination of low-frequency attenuation and fre-
quency-dependent distortion compromises audio
reproduction in portable audio equipment that empha-
sizes low-frequency effects such as multimedia lap-
tops, as well as MP3, CD, and DVD players. These
low-frequency, capacitor-related deficiencies are elimi-
nated by using DirectDrive technology.
Charge Pump
The MAX9725 features a low-noise charge pump. The
580kHz switching frequency is well beyond the audio
range, and does not interfere with the 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
turn-on/off speed of the charge pump. Additional high-
f2RC
-3dB L OUT
=1
π
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
_______________________________________________________________________________________ 7
Figure 1. Traditional Driver Output Waveform vs. MAX9725
Output Waveform (Ideal Case)
VDD
-VDD
GND
VOUT
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
VDD / 2
VDD
GND
VOUT
MAX9725
frequency noise attenuation can be achieved by
increasing the size of C2 (see the Functional Diagram).
Extra noise attenuation is not typically required.
Shutdown
The MAX9725’s low-power shutdown mode reduces
supply current to 0.6µA. Driving SHDN low disables the
amplifiers and charge pump. The driver’s output imped-
ance is typically 50kΩ(MAX9725A), 37.5kΩ(MAX9725B),
25kΩ(MAX9725), or 100kΩ(MAX9725D) when in shut-
down mode.
Click-and-Pop Suppression
In conventional single-supply audio 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, typically half the
supply. Likewise, on shutdown, the capacitor is dis-
charged to GND. This results in a DC shift across the
capacitor that appears as an audible transient at the
speaker. The MAX9725’s DirectDrive technology elimi-
nates the need for output-coupling capacitors.
The MAX9725 also features extensive click-and-pop
suppression that eliminates any audible transient
sources internal to the device. The Power-Up/Down
Waveform in the Typical Operating Characteristics
shows minimal DC shift and no spurious transients at
the output upon startup or shutdown.
In most applications, the output of the preamplifier dri-
ving the MAX9725 has a DC bias of typically half the
supply. At startup, the input-coupling capacitor is
charged to the preamplifier’s DC bias voltage through
the internal input resistor (25kΩ, typ) causing an audi-
ble click and pop. Delaying the rise of SHDN 4 or 5
time constants, based on RIN x CIN, relative to the start-
up of the preamplifier eliminates any click and pop
caused by the input filter (see the Functional Diagram).
Applications Information
Power Dissipation
Linear power amplifiers can dissipate a significant
amount of power under normal operating conditions.
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:
where TJ(MAX) is +150°C, TAis the ambient tempera-
ture, and θJA is the reciprocal of the derating factor in
°C/W as specified in the Absolute Maximum Ratings
section. For example, θJA for the thin QFN package is
+59.3°C/W.
The MAX9725 has two power dissipation sources, the
charge pump and the two amplifiers. If the power dissi-
pation exceeds the rated package dissipation, reduce
VDD, increase load impedance, decrease the ambient
temperature, or add heatsinking to the device. Large
output, supply, and ground traces decrease θJA, allow-
ing more heat to be transferred from the package to
surrounding air.
PT-T
DISSPKG(MAX)
J(MAX) A
JA
=θ
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
8 _______________________________________________________________________________________
Figure 2. Low-Frequency Attenuation for Common DC-Blocking
Capacitor Values
LF ROLLOFF (16Ω LOAD)
FREQUENCY (Hz)
ATTENUATION (dB)
100
-30
-25
-20
-10 -3dB CORNER FOR
100µF IS 100Hz
-15
-5
-3
0
-35
10 1k
33µF
330µF
220µF
100µF
Figure 3. Distortion Contributed By DC-Blocking Capacitors
ADDITIONAL THD+N DUE
TO DC-BLOCKING CAPACITORS
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.001
0.01
0.1
1
10
0.0001
10 100k
TANTALUM
ALUM/ELEC
Output Power
The MAX9725’s output power increases when the left
and right audio signals differ in magnitude and/or
phase. Figure 4 shows the two extreme cases for in-
and out-of-phase input signals. The output power of a
typical stereo application lies between the two extremes
shown in Figure 4. The MAX9725 is specified to output
20mW per channel when both inputs are in-phase.
Powering Other Circuits from
the Negative Supply
The MAX9725 internally generates a negative supply
voltage (PVSS) to provide the ground-referenced output
signal. Other devices can be powered from PVSS pro-
vided the current drawn from the charge pump does
not exceed 1mA. Headphone driver output power and
THD+N will be adversely affected if more than 1mA is
drawn from PVSS. Using PVSS as an LCD bias is a typi-
cal application for the negative supply.
PVSS is unregulated and proportional to VDD. Connect
a 1µF capacitor from C1P to C1N for best charge-pump
operation.
Component Selection
Input Filtering
The AC-coupling capacitor (CIN) and an internal gain-
setting resistor form a highpass filter that removes any
DC bias from an input signal (see the Functional
Diagram). CIN allows the MAX9725 to bias the signal to
an optimum DC level. The -3dB point of the highpass
filter, assuming zero source impedance, is given by:
Choose CIN so f-3dB is well below the lowest frequency of
interest. Setting f-3dB too high affects the amplifier’s low-
frequency response. Use capacitors with low-voltage
coefficient dielectrics. Film or C0G dielectric capacitors
are good choices for AC-coupling capacitors. Capacitors
with high-voltage coefficients, such as ceramics, can
result in increased distortion at low frequencies.
Charge-Pump Capacitor Selection
Use capacitors with less than 100mΩof ESR. Low-ESR
ceramic capacitors minimize the output impedance of the
charge pump. Capacitors with an X7R dielectric provide
the best performance over the extended temperature
range. Table 1 lists suggested capacitor manufacturers.
Flying Capacitor (C1)
The value of C1 affects the charge pump’s load regula-
tion and output impedance. Choosing C1 too small
degrades the MAX9725’s ability to provide sufficient
current drive and leads to a loss of output voltage.
Increasing the value of C1 improves load regulation
and reduces the charge-pump output impedance. See
the Output Power vs. Charge-Pump Capacitance and
Load Impedance graph in the Typical Operating
Characteristics.
Hold Capacitor (C2)
The hold capacitor’s value and ESR directly affect the
ripple at PVSS. Increasing the value of C2 reduces rip-
ple. Choosing a capacitor with lower ESR reduces rip-
ple and output impedance. Lower capacitance values
can be used in systems with low maximum output
power levels. See the Output Power vs. Charge-Pump
Capacitance and Load Impedance graph in the Typical
Operating Characteristics.
f2 25k C
-3dB IN
=××
1
πΩ
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
_______________________________________________________________________________________ 9
Figure 4. Output Power vs. Supply Voltage with Inputs In-/Out-
of-Phase
0
15
10
5
20
25
30
35
40
45
50
0.9 1.1 1.3 1.5
OUTPUT POWER vs. SUPPLY VOLTAGE
WITH INPUTS IN- AND OUT-OF-PHASE
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
fIN = 1kHz
RL = 16Ω
THD+N = 1%
INPUTS 180° OUT-OF-PHASE
INPUTS IN-PHASE
MAX9725
Power-Supply Bypass Capacitor (C3)
The power-supply bypass capacitor (C3) lowers the
output impedance of the power supply and reduces the
impact of the MAX9725’s charge-pump switching tran-
sients. Bypass VDD to PGND with the same value as
C1. Place C3 as close to VDD as possible.
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 C2 to PGND. Bypass VDD to PGND
with C3. Place capacitors C2 and C3 as close to the
MAX9725 as possible. Route PGND, and all traces that
carry switching transients, away from SGND and the
audio signal path.
The MAX9725 does not require additional heatsinking.
The thin QFN package features an exposed paddle that
improves thermal efficiency of the package. Ensure the
exposed paddle is electrically isolated from GND and
VDD. Connect the exposed paddle to VSS if necessary.
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, printed circuit
board techniques, bump-pad layout , and recommend-
ed reflow temperature profile, as well as the latest infor-
mation on reliability testing results, go to Maxim’s
website at www.maxim-ic.com/ucsp for the Application
Note: UCSP—A Wafer-Level Chip-Scale Package.
Chip Information
TRANSISTOR COUNT: 2559
PROCESS: BiCMOS
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
10 ______________________________________________________________________________________
Table 1. Suggested Capacitor Manufacturers
SUPPLIER PHONE FAX WEBSITE
Taiyo Yuden 800-348-2496 847-925-0899 www.t-yuden.com
TDK 847-803-6100 847-390-4405 www.component.tdk.com
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
______________________________________________________________________________________ 11
OUTR
0.9V TO 1.8V
OUTL
SGND PGND
VDD
INR
INL
C1P
C1N
VSS
PVSS
MP3
DECODER
0.47µF
0.47µF
1µF
1µF
SHDN
1µF
MAX9725
STEREO
DAC
System Diagram
123
C
B
A
UCSP
TOP VIEW
(BUMP-SIDE DOWN) 4
C1N PVSS INL INR
VSS
SGND
C1P VDD OUTL OUTR
PGND SHDN
TOP VIEW
THIN QFN
MAX9725
12
11
10
4
5
PVSS
INL
6
C1N
OUTL
OUTR
VDD
12
PGND
3
987
SHDN
SGND
VSS
INR
MAX9725
C1P
Pin Configurations
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
12 ______________________________________________________________________________________
CHARGE
PUMP
UVLO/
SHUTDOWN
CONTROL
CLICK-AND-POP
SUPPRESSION
C1N
C1P
PVSS VSS PGND SGND
*MAX9725A = 50kΩ.
MAX9725B = 37.5kΩ.
MAX9725C = 25kΩ.
MAX9725D = 100kΩ.
( ) DENOTE BUMPS FOR UCSP.
INR
VDD
VSS
VDD
SGND
RIN
25kΩ
RF*
RIN
25kΩ
OUTR
LEFT-
CHANNEL
AUDIO IN
RIGHT-
CHANNEL
AUDIO IN
HEADPHONE
JACK
12
(B2)
9
(C2)
10
(C1)
11
(B1)
1
(A1)
2
(A2)
5
(B4)
8
(C3)
7
(C4)
6
(B3)
C1
1µF
C2
1µF
0.9V TO 1.8V
C3
1µF
CIN
0.47µF
VSS
VDD
OUTL
CIN
0.47µF
SHDN
3
(A3)
INL
4
(A4)
SGND
RF*
MAX9725
Functional Diagram
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
______________________________________________________________________________________ 13
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.)
12L, UCSP 4x3.EPS
F
1
1
21-0104
PACKAGE OUTLINE, 4x3 UCSP
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
24L QFN THIN.EPS
PACKAGE OUTLINE,
21-0139
2
1
E
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
PACKAGE OUTLINE,
21-0139
2
2
E
12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm
ENGLISH • ???? • ??? • ???
WHAT'S NEW
PRODUCTS
SOLUTIONS
DESIGN
APPNOTES
SUPPORT
BUY
COMPANY
MEMBERS
MAX9725
Part Number Table
Notes:
See the MAX9725 QuickView Data Sheet for further information on this product family or download the
MAX9725 full data sheet (PDF, 452kB).
1.
Other options and links for purchasing parts are listed at: http://www.maxim-ic.com/sales.2.
Didn't Find What You Need? Ask our applications engineers. Expert assistance in finding parts, usually within
one business day.
3.
Part number suffixes: T or T&R = tape and reel; + = RoHS/lead-free; # = RoHS/lead-exempt. More: See full
data sheet or Part Naming Conventions.
4.
* Some packages have variations, listed on the drawing. "PkgCode/Variation" tells which variation the
product uses.
5.
Part Number
Free
Sample
Buy
Direct
Package:
TYPE PINS SIZE
DRAWING CODE/VAR *
Temp
RoHS/Lead-Free?
Materials Analysis
MAX9725DETC+T
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725BETC+
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725BETC+T
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725CETC+
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725CETC+T
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725DETC+
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725AETC+T
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725DETC-T
-40C to +85C
RoHS/Lead-Free: No
MAX9725DETC
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244-4*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725CETC-T
-40C to +85C
RoHS/Lead-Free: No
MAX9725CETC
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244-4*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725AETC+
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244+4*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725AETC
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244-4*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725BETC-T
-40C to +85C
RoHS/Lead-Free: No
MAX9725AETC-T
-40C to +85C
RoHS/Lead-Free: No
MAX9725BETC
THIN QFN;12 pin;4X4X0.8mm
Dwg: 21-0139E (PDF)
Use pkgcode/variation: T1244-4*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725CEBC+
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725CEBC
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725DEBC+
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725DEBC
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725BEBC
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725BEBC+
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725AEBC
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725AEBC+
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725DEBC-T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725AEBC-T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725CEBC-T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725AEBC+T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725BEBC-T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12-1*
-40C to +85C
RoHS/Lead-Free: No
Materials Analysis
MAX9725BEBC+T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725DEBC+T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
MAX9725CEBC+T
UC SP;12 pin;
Dwg: 21-0104F (PDF)
Use pkgcode/variation: B12+1*
-40C to +85C
RoHS/Lead-Free: Yes
Materials Analysis
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