19-3465; Rev 4; 3/09
KIT
ATION
EVALU
E
L
B
AVAILA
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
Features
The MAX9725A–MAX9725D fixed-gain, stereo headphone amplifiers are ideal for portable equipment where
board space is at a premium. The MAX9725E offers the
flexibility to adjust the gain with external input and feedback resistors. The MAX9725A–MAX9725E use a unique
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. Fixed gains of -2V/V (MAX9725A),
-1.5V/V (MAX9725B), -1V/V (MAX9725C), and -4V/V
(MAX9725D) further reduce external component count.
The adjustable gain of the MAX9725E DirectDrive headphone amplifier allows for any gain down to -1V/V using
external resistors.
The MAX9725 delivers up to 20mW per channel into a
32Ω load 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 protection on the headphone output. Comprehensive click-andpop 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 temperature 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).
♦ Low Quiescent Current
2.1mA (MAX9725A–MAX9725D)
2.3mA (MAX9725E)
♦ 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
♦ Adjustable Gain with External Input and Feedback
Resistors
MAX9725E: Minimum Stable Gain of -1V/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)
Block Diagrams
MAX9725A–MAX9725D
Applications
Smart Phones
Portable Audio Equipment
MP3 Players
Cellular Phones
PDAs
SINGLE
1.5V CELL
AA OR AAA
BATTERY
C3
VDD
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS.
INL
OUTL
Ordering Information
C1P
PIN-PACKAGE
TOP
MARK
GAIN
(V/V)
MAX9725AEBC+TG45
12 UCSP
+ACK
-2
MAX9725AETC+
12 TQFN-EP*
+AAEW
-2
PART
MAX9725BEBC+TG45
12 UCSP
+ACL
-1.5
Ordering Information continued at end of data sheet.
Note: All devices are specified over the -40°C to +85°C operating
temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.
UCSP is a trademark of Maxim Integrated Products, Inc.
INVERTING
CHARGE PUMP
C1N
PVSS
C2
VSS
OUTR
INR
SGND
PGND
Block Diagrams continued at end of data sheet.
Pin Configurations appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1
MAX9725
General Description
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
ABSOLUTE MAXIMUM RATINGS
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
(MAX9725A–MAX9725D)..............(VSS - 0.3V) to (VDD + 0.3V)
OUTR, OUTL to SGND
(MAX9725E) ..................................(VSS - 0.3V) to (VDD + 0.3V)
INR, INL to SGND (MAX9725E)...................................-4V to +4V
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
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 (MAX9725A–MAX9725D)
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (See the Functional Diagrams.) (Note 1)
PARAMETER
Supply Voltage Range
Quiescent Supply Current
Shutdown Current
Shutdown to Full Operation
SHDN Thresholds
SYMBOL
VDD
IDD
ISHDN
CONDITIONS
Guaranteed by PSRR test
Both channels active
VDD = 0.9V to 1.8V
VIL
VDD = 0.9V to 1.8V
SHDN Input Leakage Current
ILEAK
CHARGE PUMP
Oscillator Frequency
fOSC
TYP
MAX
UNITS
2.1
1.8
3.3
V
mA
0.6
10
0.9
TA = +25°C
VSHDN = 0V
tON
VIH
MIN
TA = -40°C to +85°C
30
180
µA
µs
0.7 x VDD
0.3 x VDD
VDD = 0.9V to 1.8V (Note 2)
V
±1
µA
667
kHz
493
580
MAX9725A
-2.04
-2.00
-1.96
MAX9725B
MAX9725C
-1.53
-1.02
-1.5
-1.00
-1.47
-0.98
MAX9725D
-4.08
-4.00
-3.92
AMPLIFIERS
Voltage Gain
AV
Gain Match
ΔAV
Total Output Offset Voltage
VOS
Input Resistance
Power-Supply Rejection Ratio
±0.5
Input AC-coupled,
RL = 32Ω to GND,
TA = +25°C
PSRR
Output Power (Note 3)
2
±0.3
±0.45
±1.05
±1.58
MAX9725C
±0.6
±2.1
15
25
35
60
80
70
VDD = 0.9V to 1.8V, TA = +25°C
fIN = 1kHz
100mVP-P ripple
fIN = 20kHz
VDD = 1.5V
POUT
%
MAX9725A/MAX9725D
MAX9725B
RIN
RL = 32Ω
RL = 16Ω
V/V
mV
kΩ
dB
62
10
20
VDD = 1.0V, RL = 32Ω
25
7
VDD = 0.9V, RL = 32Ω
6
_______________________________________________________________________________________
mW
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (See the Functional Diagrams.) (Note 1)
PARAMETER
Total Harmonic Distortion Plus
Noise
Signal-to-Noise Ratio
Slew Rate
SYMBOL
THD+N
SNR
CONDITIONS
MIN
TYP
0.006
RL = 16Ω, POUT = 15mW, f = 1kHz
BW = 22Hz to 22kHz
RL = 32Ω, POUT = 12mW
A-weighted filter
0.015
89
92
SR
Maximum Capacitive Load
Crosstalk
CL
XTALK
Click-and-Pop Level
ESD Protection
KCP
VESD
MAX
RL = 32Ω, POUT = 12mW, f = 1kHz
UNITS
%
dB
0.2
V/µs
No sustained oscillations
150
pF
fIN = 1.0kHz, RL = 32Ω, POUT = 5mW
100
dB
RL = 32Ω, peak voltage,
A-weighted, 32 samples per
second (Note 4)
Into shutdown
72.8
Out of shutdown
72.8
dBV
Human Body Model (OUTR, OUTL)
±8
kV
ELECTRICAL CHARACTERISTICS (MAX9725E)
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, RL = 32Ω, RF = 60kΩ, RIN = 10kΩ, TA =
TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (See the Functional Diagrams.) (Note 1)
PARAMETER
Supply Voltage Range
Quiescent Supply Current
Shutdown Current
SYMBOL
VDD
IDD
ISHDN
Shutdown to Full Operation
SHDN Thresholds
CONDITIONS
Guaranteed by PSRR test
Both channels active
VDD = 0.9V to 1.8V
VIL
VDD = 0.9V to 1.8V
SHDN Input Leakage Current
ILEAK
CHARGE PUMP
Oscillator Frequency
fOSC
TYP
MAX
UNITS
2.3
1.8
3.7
V
mA
0.9
TA = +25°C
VSHDN = 0V
tON
VIH
MIN
0.6
1
TA = -40°C to +85°C
10
180
µA
µs
0.7 x VDD
0.3 x VDD
VDD = 0.9V to 1.8V (Note 2)
V
±1
µA
483
592
687
kHz
-6.11
-6.07
-6.00
V/V
AMPLIFIERS
Voltage Gain
AV
Minimum Stable Gain
ΔAV
Total Output Offset Voltage
VOS
Input Resistance
INR, INL Input Leakage
Current
Maximum Input Parasitic
Capacitance
RIN
(Note 5)
-1.0
Input AC-coupled, RL = 32Ω to GND,
TA = +25°C (Note 6)
6.3
±2.1
mV
9.78
14
kΩ
±100
nA
5
VDD = 0.9V to 1.8V, TA = +25°C
Power-Supply Rejection Ratio
±0.63
ILK
CPAR
PSRR
100mVP-P ripple
(Note 5)
52.9
V/V
pF
67.8
fIN = 1kHz
70
fIN = 20kHz
62
dB
_______________________________________________________________________________________
3
MAX9725
ELECTRICAL CHARACTERISTICS (MAX9725A–MAX9725D) (continued)
ELECTRICAL CHARACTERISTICS (MAX9725E) (continued)
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, RL = 32Ω, RF = 60kΩ, RIN = 10kΩ, TA =
TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.) (See the Functional Diagrams.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
RL = 32Ω
VDD = 1.5V
Output Power (Note 3)
POUT
MIN
TYP
10
24
RL = 16Ω
Total Harmonic Distortion Plus
Noise (Note 5)
Signal-to-Noise Ratio
THD+N
SNR
Slew Rate
SR
Maximum Capacitive Load
CL
Crosstalk
XTALK
Click-and-Pop Level
KCP
ESD Protection
VESD
Attenuation in Shutdown
ATT(SD)
MAX
25
7
VDD = 1.0V, RL = 32Ω
VDD = 0.9V, RL = 32Ω
UNITS
mW
6
RL = 32Ω, POUT = 12mW, f = 1kHz
0.006
RL = 16Ω, POUT = 15mW, f = 1kHz
BW = 22Hz to 22kHz
RL = 32Ω, POUT = 12mW
A-weighted filter
0.015
89
92
%
dB
0.3
V/µs
No sustained oscillations
150
pF
fIN = 1.0kHz, RL = 32Ω, POUT = 5mW
100
dB
RL = 32Ω, peak voltage,
A-weighted, 32 samples per
second (Note 4)
Into shutdown
72.8
Out of shutdown
72.8
dBV
Human Body Model (OUTR, OUTL)
VSHDN = 0V
±8
kV
RL = 32Ω
-120
RL = 10kΩ
-75
dB
All specifications are 100% tested at TA = +25°C; temperature limits are guaranteed by design.
Input leakage current measurements limited by automated test equipment.
fIN = 1kHz, TA = +25°C, THD+N < 1%, both channels driven in-phase.
Testing performed with 32Ω resistive 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 ACgrounded.
Note 5: Using existing resistors with 1% precision.
Note 6: RIN = 10Ω, RF =10kΩ.
Note 1:
Note 2:
Note 3:
Note 4:
Typical Operating Characteristics
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth =
22Hz to 22kHz, TA = +25°C, unless otherwise noted.) (See the Functional Diagrams.)
VDD = 1.5V
RL = 16Ω
AV = -2V/V
1
0.1
0.1
THD+N (%)
POUT = 15mW
0.01
VDD = 1V
RL = 16Ω
AV = -2V/V
POUT = 0.7mW
THD+N (%)
0.1
VDD = 1.5V
RL = 32Ω
AV = -2V/V
POUT = 2mW
MAX9725 toc03
1
MAX9725 toc01
1
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc02
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
THD+N (%)
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
0.01
0.01
POUT = 2mW
POUT = 4mW
POUT = 12mW
0.001
100
1k
FREQUENCY (Hz)
4
0.001
0.001
10
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
FREQUENCY (Hz)
_______________________________________________________________________________________
10k
100k
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
THD+N (%)
THD+N (%)
100
fIN = 20Hz
fIN = 1kHz
1
fIN = 10kHz
0.1
VDD = 1.5V
RL = 32Ω
AV = -2V/V
10
MAX9725 toc06
10
0.1
POUT = 0.7mW
VDD = 1.5V
RL = 16Ω
AV = -2V/V
THD+N (%)
VDD = 1V
RL = 32Ω
AV = -2V/V
MAX9725 toc05
100
MAX9725 toc04
1
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
fIN = 20Hz
fIN = 1kHz
1
fIN = 10kHz
0.1
0.01
0.01
0.01
POUT = 4mW
0.001
0.001
10
1k
0.001
0
100k
10
20
30
40
0
10
20
30
OUTPUT POWER (mW)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
VDD = 1V
RL = 32Ω
AV = -2V/V
10
-10
MAX9725 toc08
fIN = 20Hz
fIN = 1kHz
100
fIN = 20Hz
fIN = 1kHz
40
MAX9725 toc09
FREQUENCY (Hz)
VDD = 1V
RL = 16Ω
AV = -2V/V
10
10k
MAX9725 toc07
100
100
VDD = 1.5V
RL = 32Ω
-20
-30
THD+N (%)
fIN = 10kHz
0.1
1
PSRR (dB)
THD+N (%)
-40
1
fIN = 10kHz
0.1
-50
-60
-70
-80
0.01
-90
0.01
-100
0.001
10
15
-110
0
5
OUTPUT POWER (mW)
-20
VDD = 1.5V
POUT = 5mW
RL = 32Ω
-20
-30
100
-40
-50
-60
10k
100k
OUTPUT POWER vs. SUPPLY VOLTAGE
LEFT TO RIGHT
-60
1k
FREQUENCY (Hz)
-40
PSRR (dB)
PSRR (dB)
10
CROSSTALK vs. FREQUENCY
0
MAX9725 toc10
VDD = 1V
RL = 32Ω
-10
15
OUTPUT POWER (mW)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
0
10
80
70
OUTPUT POWER (mW)
5
MAX9725 toc11
0
-80
-70
60
MAX9725 toc12
0.001
fIN = 1kHz
RL = 16Ω
BOTH INPUTS
DRIVEN IN-PHASE
50
THD+N = 10%
40
30
20
-80
-100
10
RIGHT TO LEFT
-90
10
100
1k
FREQUENCY (Hz)
10k
100k
THD+N = 1%
0
-120
-100
10
100
1k
FREQUENCY (Hz)
10k
100k
0.9
1.1
1.3
1.5
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
MAX9725
Typical Operating Characteristics (continued)
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz
to 22kHz, TA = +25°C, unless otherwise noted.) (See the Functional Diagrams.)
Typical Operating Characteristics (continued)
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz
to 22kHz, TA = +25°C, unless otherwise noted.) (See the Functional Diagrams.)
OUTPUT POWER
vs. LOAD RESISTANCE
60
THD+N = 10%
30
25
20
15
10
THD+N = 1%
5
1.1
1.3
30
20
1.5
VDD = 1.5V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN-PHASE
RL = 32Ω
10
MAX9725 toc17
AMPLITUDE (dB)
25
RL = 16Ω
20
15
10
VDD = 1V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN-PHASE
RL = 32Ω
5
0
0
0
10
20
30
40
10
50
0
5
10
15
MAX9725 toc15
100
1k
GAIN FLATNESS
vs. FREQUENCY
30
POWER DISSIPATION (mW)
30
THD+N = 1%
20
LOAD RESISTANCE (Ω)
35
MAX9725 toc16
40
THD+N = 10%
30
1k
POWER DISSIPATION
vs. OUTPUT POWER
50
20
100
POWER DISSIPATION
vs. OUTPUT POWER
60
40
0
10
LOAD RESISTANCE (Ω)
RL = 16Ω
70
50
10
SUPPLY VOLTAGE (V)
80
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
20
10
100
1k
10k
OUTPUT POWER (mW)
OUTPUT POWER (mW)
FREQUENCY (Hz)
OUTPUT POWER vs. CHARGE-PUMP
CAPACITANCE AND LOAD RESISTANCE
OUTPUT SPECTRUM
vs. FREQUENCY
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
AMPLITUDE (dB)
-40
25
20
15
10
VDD = 1.5V
fIN = 1kHz
THD+N = 1%
C1 = C2 = 0.47μF
-80
-100
-120
C1 = C2 = 0.68μF
5
-60
0
20
30
40
LOAD RESISTANCE (Ω)
50
5.0
4.5
NO LOAD
4.0
3.5
3.0
2.5
2.0
1.5
1.0
-140
0.5
0
-160
10
100k
MAX9725 toc21
-20
C1 = C2 = 1μF
30
fIN = 1kHz
RL = 32Ω
VOUT = -60dBV
VDD = 1.5V
SUPPLY CURRENT (mA)
C1 = C2 = 2.2μF
35
0
MAX9725 toc19
40
MAX9725 toc20
POWER DISSIPATION (mW)
THD+N = 1%
0
0.9
6
50
10
0
VDD = 1V
fIN = 1kHz
BOTH INPUTS
DRIVEN IN-PHASE
70
60
THD+N = 10%
40
80
MAX9725 toc18
35
OUTPUT POWER (mW)
OUTPUT POWER (mW)
40
VDD = 1.5V
fIN = 1kHz
BOTH INPUTS
DRIVEN IN-PHASE
70
OUTPUT POWER (mW)
fIN = 1kHz
RL = 32Ω
BOTH INPUTS
DRIVEN IN-PHASE
45
80
MAX9725 toc13
50
OUTPUT POWER
vs. LOAD RESISTANCE
MAX9725 toc14
OUTPUT POWER
vs. SUPPLY VOLTAGE
OUTPUT POWER (mW)
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
0
5
10
FREQUENCY (kHz)
15
20
0.9
1.0
1.1
1.2
1.3
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
1.4
1.5
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN CURRENT (μA)
0.6
POWER-UP/-DOWN WAVEFORM
EXITING SHUTDOWN
MAX9725toc24
MAX9725 toc23
MAX9725 toc22
0.7
VDD
1V/div
OUT_
1V/div
0.5
0.4
SHDN
500mV/div
0.3
0.2
OUT_
10mV/div
0.1
0
1.1
0.9
1.3
1.5
200ms/div
200μs/div
SUPPLY VOLTAGE (V)
Pin Description
PIN
BUMP
THIN
QFN
UCSP
1
A1
NAME
FUNCTION
C1N
Flying Capacitor Negative Terminal. Connect a 1µF capacitor from C1P to C1N.
Inverting Charge-Pump Output. Bypass with 1µF from PVSS to PGND. PVSS must be connected to
VSS.
2
A2
PVSS
3
A3
INL
Left-Amplifier Inverting Input. Connect input resistor RIN from input capacitor C1N to INL (MAX9725E
only).
4
A4
INR
Right-Amplifier Inverting Input. Connect input resistor RIN from input capacitor C1N to INR
(MAX9725E only).
5
B4
VSS
Amplifier Negative Power Supply. Must be connected to PVSS.
6
B3
SGND
Signal Ground. SGND must be connected to PGND. SGND is the ground reference for the input and
output signal.
7
C4
OUTR
Right-Channel Output. Connect feedback resistor RFB between OUTR and INR (MAX9725E only).
8
C3
OUTL
9
C2
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
Left-Channel Output. Connect feedback resistor RFB between OUTL and INL (MAX9725E only).
Exposed Paddle. Internally connected to VSS. Leave paddle unconnected or solder to VSS.
_______________________________________________________________________________________
7
MAX9725
Typical Operating Characteristics (continued)
(VDD = 1.5V, VPGND = VSGND = 0V, VSHDN = 1.5V, VSS = VPVSS, C1 = C2 = 1µF, CIN = 1µF, THD+N measurement bandwidth = 22Hz
to 22kHz, TA = +25°C, unless otherwise noted.) (See the Functional Diagrams.)
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
Detailed Description
The MAX9725 stereo headphone driver features Maxim’s
DirectDrive architecture, eliminating the large output-coupling capacitors required by conventional single-supply
headphone drivers. The MAX9725 consists of two 20mW
class AB headphone drivers, shutdown control, inverting
charge pump, internal gain-setting resistors, and comprehensive click-and-pop suppression circuitry (see the
Functional Diagrams). 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 DCblocking capacitors are unnecessary. Eliminating the
DC-blocking capacitors on the output saves board
space, system cost, and improves frequency response.
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 equipment, resulting in possible damage to the drivers.
VDD
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 16Ω load. The
MAX9725 provides 25mW to a 16Ω load. The
DirectDrive architecture eliminates the need for two
large (220µF, typ) DC-blocking capacitors on the output. 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. ChargePump Capacitance and Load Resistance graph in the
Typical Operating Characteristics for details of the possible capacitor sizes.
8
VOUT
VDD / 2
GND
CONVENTIONAL DRIVER-BIASING SCHEME
VDD
VOUT
GND
-VDD
DirectDrive BIASING SCHEME
Figure 1. Traditional Driver Output Waveform vs. MAX9725
Output Waveform (Ideal Case)
_______________________________________________________________________________________
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
10
-3
-5
330μF
220μF
1
-10
100μF
-15
-3dB CORNER FOR
100μF IS 100Hz
THD+N (%)
ATTENUATION (dB)
MAX9725
ADDITIONAL THD+N DUE
TO DC-BLOCKING CAPACITORS
LF ROLLOFF (16Ω LOAD)
0
33μF
-20
0.1
TANTALUM
0.01
-25
0.001
-30
ALUM/ELEC
-35
10
100
FREQUENCY (Hz)
1k
Figure 2. Low-Frequency Attenuation for Common DC-Blocking
Capacitor Values
Low-Frequency Response
Large DC-blocking capacitors limit the amplifier’s lowfrequency response and can distort the audio signal:
1) The impedance of the headphone load and the DCblocking capacitor forms a highpass filter with the
-3dB point set by:
f-3dB =
1
2πRLCOUT
where RL is the impedance of the headphone and
COUT is the value of the DC-blocking capacitor. The
highpass filter is required by conventional singleended, 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 16Ω headphone 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 dominates at frequencies below the -3dB point and the
0.0001
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 3. Distortion Contributed By DC-Blocking Capacitors
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 frequency-dependent distortion compromises audio
reproduction in portable audio equipment that emphasizes low-frequency effects such as multimedia laptops, as well as MP3, CD, and DVD players. These
low-frequency, capacitor-related deficiencies are eliminated 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 highfrequency noise attenuation can be achieved by
increasing the size of C2 (see the Functional Diagrams).
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 impedance is typically 50kΩ (MAX9725A), 37.5kΩ
(MAX9725B), 25kΩ (MAX9725C), 100kΩ (MAX9725D),
or RF (MAX9725E) when in shutdown mode.
_______________________________________________________________________________________
9
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
OUTPUT POWER vs. SUPPLY VOLTAGE
WITH INPUTS IN- AND OUT-OF-PHASE
50
45
OUTPUT POWER (mW)
40
INPUTS 180° OUT-OF-PHASE
30
25
20
PDISSPKG(MAX) =
15
10
TJ(MAX) - TA
θ JA
INPUTS IN-PHASE
5
0
0.9
1.1
1.3
1.5
SUPPLY VOLTAGE (V)
Figure 4. Output Power vs. Supply Voltage with Inputs In-/Outof-Phase
Click-and-Pop Suppression
In conventional single-supply audio drivers, the outputcoupling 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 discharged 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 eliminates 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 driving 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 for MAX9725AMAX9725D, minimum 10kΩ for MAX9725E) causing an
audible click and pop. Delaying the rise of SHDN 4 or 5
time constants, based on RIN x CIN, relative to the startup of the preamplifier eliminates any click and pop
caused by the input filter (see the Functional Diagrams).
10
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:
fIN = 1kHz
RL = 16Ω
THD+N = 1%
35
Applications Information
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 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 dissipation 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, allowing more heat to be transferred from the package to
surrounding air.
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 inand 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 provided 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 typical 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.
______________________________________________________________________________________
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
Input Filtering
The AC-coupling capacitor (CIN) and an internal gainsetting resistor form a highpass filter that removes any
DC bias from an input signal (see the Functional
Diagrams). CIN allows the MAX9725A–MAX9725D to
bias the signal to an optimum DC level. The -3dB point
of the highpass filter, assuming zero source impedance, is given by:
f-3dB =
1
2π × RIN × CIN
Choose CIN so f-3dB is well below the lowest frequency of
interest. RIN for the MAX9725A–MAX9725D is 25kΩ and a
minimum of 10kΩ for the MAX9725E. 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 100mΩ of 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 regulation 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 Resistance 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 ripple. Choosing a capacitor with lower ESR reduces ripple 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 Resistance graph in the Typical
Operating Characteristics.
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 transients. 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 recommended reflow temperature profile, as well as the latest information on reliability testing results, go to Maxim’s
website at www.maxim-ic.com/ucsp for the
Application Note 1891: Wafer-Level Packaging (WLP)
and Its Applications.
Table 1. Suggested Capacitor Manufacturers
PHONE
FAX
Murata
SUPPLIER
770-436-1300
—
www.murata.com
WEBSITE
Taiyo Yuden
800-348-2496
847-925-0899
www.t-yuden.com
TDK
847-803-6100
847-390-4405
www.component.tdk.com
______________________________________________________________________________________
11
MAX9725
Component Selection
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
MAX9725
System Diagrams
0.9V TO 1.8V
1μF
SHDN
1μF
MP3
DECODER
VDD
INR
STEREO
DAC
INL
1μF
C1P
MAX9725A–
MAX9725D
1μF
OUTR
C1N
VSS
OUTL
PVSS
1μF
SGND
PGND
RF
MAX9725E
1μF
VDD
1μF
SHDN
RIN
INL
OUTL
PVSS
C1N
1μF
1μF
RIN
DIN
CHARGE
PUMP
1μF
VSS
INR
OUTR
SGND
PGND
RF
12
______________________________________________________________________________________
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
0.9V TO 1.8V
LEFTCHANNEL
AUDIO IN
CIN
0.47μF
C3
1μF
9
(C2)
12
(B2)
3
(A3)
VDD
SHDN
INL
RF*
VDD
RIN
25kΩ
8
OUTL (C3)
VSS
CHARGE
PUMP
C1
1μF
HEADPHONE
JACK
SGND
UVLO/
SHUTDOWN
CONTROL
10
(C1) C1P
CLICK-AND-POP
SUPPRESSION
1
(A1) C1N
VDD
SGND
OUTR
MAX9725A–
MAX9725D
RIN
25kΩ
7
(C4)
VSS
RF*
PVSS
VSS
PGND
SGND
2
(A2)
C2
1μF
5
(B4)
11
(B1)
6
(B3)
*MAX9725A = 50kΩ.
MAX9725B = 37.5kΩ.
MAX9725C = 25kΩ.
MAX9725D = 100kΩ.
( ) DENOTE BUMPS FOR UCSP.
INR
4
(A4)
CIN
0.47μF
LEFTCHANNEL
AUDIO IN
______________________________________________________________________________________
13
MAX9725
Functional Diagrams
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
MAX9725
Functional Diagrams (continued)
LEFT-CHANNEL
AUDIO IN
0.9V TO 1.8V
CIN
1μF
RIN
C3
1μF
9
(C2)
12
(B2)
3
(A3)
VDD
SHDN
INL
RF
VDD
8
OUTL (C3)
VSS
CHARGE
PUMP
C1
1μF
HEADPHONE
JACK
SGND
UVLO/
SHUTDOWN
CONTROL
10
(C1) C1P
CLICK-AND-POP
SUPPRESSION
1
(A1) C1N
VSS
SGND
OUTR
MAX9725E
7
(C4)
VDD
RF
PVSS
VSS
PGND
SGND
2
(A2)
C2
1μF
5
(B4)
11
(B1)
6
(B3)
INR
4
(A4)
RIN
( ) DENOTE BUMPS FOR UCSP.
14
RIGHTCHANNEL
AUDIO IN
CIN
1μF
______________________________________________________________________________________
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
3
4
TOP VIEW
OUTR
2
OUTL
1
VDD
MAX9725
TOP VIEW
(BUMP-SIDE DOWN)
9
8
7
A
C1N
PVSS
INL
INR
PGND
SHDN
SGND
VSS
C1P 10
B
PGND 11
C
C1P
VDD
OUTL
MAX9725
6
SGND
5
VSS
4
INR
OUTR
SHDN 12
*EP
+
2
3
INL
C1N
1
PVSS
UCSP
THIN QFN
*EP = EXPOSED PAD.
Block Diagrams (continued)
Ordering Information (continued)
PART
C3
VDD
RFB
SINGLE
1.5V CELL
AA OR AAA
BATTERY
MAX9725E
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS.
INL
OUTL
C1P
INVERTING
CHARGE PUMP
C1N
C2
VSS
TOP
MARK
GAIN
(V/V)
MAX9725BETC+
12 TQFN-EP*
+AAEX
-1.5
MAX9725CEBC+TG45
12 UCSP
+ACM
-1
MAX9725CETC+
12 TQFN-EP*
+AAEY
-1
MAX9725DEBC+TG45
12 UCSP
+ACN
-4
MAX9725DETC+
12 TQFN-EP*
+AAEZ
-4
MAX9725EEBC+TG45
12 UCSP
+AEF
ADJ
MAX9725EETC+**
12 TQFN-EP*
+AAGH
ADJ
Note: All devices are specified over the -40°C to +85°C operating
temperature range.
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
*EP = Exposed pad.
**Future product—contact factory for availability.
OUTR
INR
RFB
PVSS
PIN-PACKAGE
SGND
PGND
______________________________________________________________________________________
15
MAX9725
Pin Configurations
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
Package Information
Chip Information
PROCESS: BiCMOS
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
16
PACKAGE CODE
DOCUMENT NO.
12 UCSP
B12-1
21-0104
12 TQFN-EP
T1244-4
21-0139
______________________________________________________________________________________
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
PAGES
CHANGED
REVISION
NUMBER
REVISION
DATE
0
11/04
Initial release
1
5/05
Removed future product asterisks for UCSP package, added EC table note
1–3, 13, 14
2
11/07
Added MAX9725E packages, MAX9725E EC table, block diagram, functional
diagram, and system diagram. Updated package outlines.
1–3, 6, 8–19
3
8/08
Corrected error in Functional Diagrams
4
3/09
Updated Ordering Information, style changes
DESCRIPTION
—
14
1, 15
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 ____________________ 17
© 2009 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX9725
Revision History
工商网监
湘ICP备2023018690号
