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
DirectDrive
TM
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
32
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 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 0.6A (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 +85C tem-
perature range. The MAX9725 is available in a tiny
(1.54mm x 2.02mm x 0.6mm) 12-bump chip-scale
package (UCSPTM) 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 32
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 0; 11/04
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 + 85C 12 U
C S P- 12
AC K
- 2
M AX9725AE TC
- 40
C to + 85C 12 TQFN-
EP**
AAEW
- 2
MAX9725BEBC -T*
- 40
C to + 85C 12 U
C S P- 12
AC L
- 1.5
M AX9725BE TC
- 40
C to + 85C 12 TQFN-
EP**
AAEX -
1.5
MAX9725CEBC-T*
- 40
C to + 85C 12 U
C S P- 12
AC M
- 1
M AX9725C E TC
- 40
C to + 85C 12 TQFN-
EP**
AAEY -
1
MAX9725D EBC -T*
- 40
C to + 85C 12 U
C S P- 12
AC N
- 4
M AX9725D E TC
- 40
C to + 85C 12 TQFN-
EP**
AAEZ -
4
UCSP is a trademark of Maxim Integrated Products, Inc.
Pin Configurations appear at end of data sheet.
*Future product--contact factory for availability.
**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
V
DD
PV
SS
V
SS
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
V
DD
to SGND or PGND ............................................-0.3V to +2V
V
SS
to PV
SS
...........................................................-0.3V to +0.3V
C1P to PGND..............................................-0.3V to (V
DD
+ 0.3V)
C1N to PGND............................................(PV
SS
- 0.3V) to +0.3V
V
SS
, PV
SS
to GND ....................................................+0.3V to -2V
OUTR, OUTL, INR, INL to SGND .....(V
SS
- 0.3V) to (V
DD
+ 0.3V)
SHDN to SGND or PGND .........................................-0.3V to +4V
Output Short-Circuit Current ......................................Continuous
Continuous Power Dissipation (T
A
= +70
C)
12-Bump UCSP (derate 6.5mW/
C above +70C)....518.8mW
12-Pin Thin QFN (derate 16.9mW/
C above +70C) ..1349.1mW
Junction Temperature ......................................................+150
C
Operating Temperature Range ...........................-40
C to +85C
Storage Temperature Range .............................-65
C to +150C
Bump Temperature (soldering) Reflow............................+230
C
Lead Temperature (soldering, 10s) .................................+300
C
ELECTRICAL CHARACTERISTICS
(V
DD
= 1.5V, PGND = SGND = 0V, V
SHDN
= 1.5V, V
SS
= PV
SS
, C1 = C2 = 1F, C
IN
= 1F, R
L
=
, T
A
= T
MIN
to T
MAX,
unless otherwise
noted. Typical values are at T
A
= +25
C.) (See the Functional Diagram.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Supply Voltage Range
V
DD
Guaranteed by PSRR test
0.9
1.8
V
Quiescent Supply Current
I
DD
Both channels active
2.1
3.3
mA
T
A
= +25
C
0.6
10
Shutdown Current
I
SHDN
V
SHDN
= 0V
T
A
= -40
C to +85C
30
A
Shutdown to Full Operation
t
ON
180
s
V
IH
V
DD
= 0.9V to 1.8V
0.7 x V
DD
SHDN Thresholds
V
IL
V
DD
= 0.9V to 1.8V
0.3 x V
DD
V
SHDN Input Leakage Current
I
LEAK
V
DD
= 0.9V to 1.8V (Note 1)
1
A
CHARGE PUMP
Oscillator Frequency
f
OSC
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
A
V
MAX9725D
-4.08
-4.00
-3.92
V/V
Gain Match
A
V
0.5
%
MAX9725A/MAX9725D
0.3
1.05
MAX9725B
0.45
1.58
Total Output Offset Voltage
V
OS
Input AC-coupled,
R
L
= 32
to GND,
T
A
= +25
C
MAX9725C
0.6
2.1
mV
Input Resistance
R
IN
15
25
35
k
V
DD
= 0.9V to 1.8V, T
A
= +25
C
60
80
f
IN
= 1kHz
70
Power-Supply Rejection Ratio
PSRR
100mV
P-P
ripple
f
IN
= 20kHz
62
dB
R
L
= 32
10
20
V
DD
= 1.5V
R
L
= 16
25
V
DD
= 1.0V, R
L
= 32
7
Output Power (Note 2)
P
OUT
V
DD
= 0.9V, R
L
= 32
6
mW
R
L
= 32
, P
OUT
= 12mW, f = 1kHz
0.006
Total Harmonic Distortion Plus
Noise
THD+N
R
L
= 16
, P
OUT
= 15mW, f = 1kHz
0.015
%
BW = 22Hz to 22kHz
89
Signal-to-Noise Ratio
SNR
R
L
= 32
, P
OUT
= 12mW
A-weighted filter
92
dB
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
_______________________________________________________________________________________
3
Note 1: Input leakage current measurements limited by automated test equipment.
Note 2: f
IN
= 1kHz, T
A
= +25C, THD+N < 1%, both channels driven in-phase.
Note 3: Testing performed with 32
resistive load connected to outputs. Mode transitions controlled by SHDN. K
CP
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
(V
DD
= 1.5V, PGND = SGND = 0V, V
SHDN
= 1.5V, V
SS
= PV
SS,
C1 = C2 = 1F, C
IN
= 1F, THD+N measurement bandwidth = 22Hz
to 22kHz, T
A
= +25
C, unless otherwise noted.) (See the Functional Diagram.)
10
10k
1k
100
100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc01
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
V
DD
= 1.5V
R
L
= 16
A
V
= -2V/V
P
OUT
= 15mW
P
OUT
= 2mW
10
10k
1k
100
100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc02
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
V
DD
= 1.5V
R
L
= 32
A
V
= -2V/V
P
OUT
= 12mW
P
OUT
= 2mW
10
10k
1k
100
100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc03
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
V
DD
= 1V
R
L
= 16
A
V
= -2V/V
P
OUT
= 0.7mW
P
OUT
= 4mW
10
10k
1k
100
100k
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9725 toc04
FREQUENCY (Hz)
THD+N (%)
1
0.1
0.001
0.01
P
OUT
= 0.7mW
P
OUT
= 4mW
V
DD
= 1V
R
L
= 32
A
V
= -2V/V
100
0
10
20
30
40
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc05
OUTPUT POWER (mW)
THD+N (%)
V
DD
= 1.5V
R
L
= 16
A
V
= -2V/V
f
IN
= 20Hz
f
IN
= 1kHz
f
IN
= 10kHz
100
0
10
20
30
40
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc06
OUTPUT POWER (mW)
THD+N (%)
V
DD
= 1.5V
R
L
= 32
A
V
= -2V/V
f
IN
= 20Hz
f
IN
= 1kHz
f
IN
= 10kHz
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= 1.5V, PGND = SGND = 0V, V
SHDN
= 1.5V, V
SS
= PV
SS
, C1 = C2 = 1F, C
IN
= 1F, R
L
=
, T
A
= T
MIN
to T
MAX,
unless otherwise
noted. Typical values are at T
A
= +25
C.) (See the Functional Diagram.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Slew Rate
SR
0.2
V/s
Maximum Capacitive Load
C
L
No sustained oscillations
150
pF
Crosstalk
XTALK
f
IN
= 1.0kHz, R
L
= 32
, P
OUT
= 5mW
100
dB
Into shutdown
72.8
Click/Pop Level
K
CP
R
L
= 32
, peak voltage, A-
weighted, 32 samples per
second (Note 3)
Out of shutdown
72.8
dB
ESD Protection
V
ESD
Human Body Model (OUTR, OUTL)
8
kV
MAX9725
1V, Low-Power, DirectDrive, Stereo Headphone
Amplifier with Shutdown
4
_______________________________________________________________________________________
Typical Operating Characteristics (continued)
(V
DD
= 1.5V, PGND = SGND = 0V, V
SHDN
= 1.5V, V
SS
= PV
SS,
C1 = C2 = 1F, C
IN
= 1F, THD+N measurement bandwidth = 22Hz
to 22kHz, T
A
= +25
C, unless otherwise noted.) (See the Functional Diagram.)
100
0
5
10
15
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc07
OUTPUT POWER (mW)
THD+N (%)
V
DD
= 1V
R
L
= 16
A
V
= -2V/V
f
IN
= 20Hz
f
IN
= 1kHz
f
IN
= 10kHz
100
0
5
10
15
10
1
0.1
0.01
0.001
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
MAX9725 toc08
OUTPUT POWER (mW)
THD+N (%)
V
DD
= 1V
R
L
= 32
A
V
= -2V/V
f
IN
= 20Hz
f
IN
= 1kHz
f
IN
= 10kHz
10
100
10k
1k
100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9725 toc09
FREQUENCY (Hz)
PSRR (dB)
-10
-110
-60
-50
-40
-30
-20
-70
-80
-90
-100
V
DD
= 1.5V
R
L
= 32
10
100
10k
1k
100k
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9725 toc10
FREQUENCY (Hz)
PSRR (dB)
0
-100
-50
-40
-30
-20
-10
-60
-70
-80
-90
V
DD
= 1V
R
L
= 32
10
100
10k
1k
100k
CROSSTALK vs. FREQUENCY
MAX9725 toc11
FREQUENCY (Hz)
PSRR (dB)
0
-20
-40
-60
-80
-100
-120
V
DD
= 1.5V
P
OUT
= 5mW
R
L
= 32
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)
f
IN
= 1kHz
R
L
= 16
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)
f
IN
= 1kHz
R
L
= 32
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 (
)
OUTPUT POWER (mW)
40
60
10
30
50
V
DD
= 1.5V
f
IN
= 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 (
)
OUTPUT POWER (mW)
40
60
10
30
50
V
DD
= 1V
f
IN
= 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
10
20
30
40
50
POWER DISSIPATION
vs. OUTPUT POWER
MAX9725 toc16
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
V
DD
= 1.5V
f
IN
= 1kHz
P
OUT
= P
OUTL
+ P
OUTR
OUTPUTS IN-PHASE
R
L
= 16
R
L
= 32
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)
V
DD
= 1V
f
IN
= 1kHz
P
OUT
= P
OUTL
+ P
OUTR
OUTPUTS IN-PHASE
R
L
= 16
R
L
= 32
10
100
10k
1k
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 (
)
OUTPUT POWER (mW)
V
DD
= 1.5V
f
IN
= 1kHz
THD+N = 1%
C1 = C2 = 2.2
F
C1 = C2 = 1
F
C1 = C2 = 0.47
F
C1 = C2 = 0.68
F
-160
-140
-120
-100
-80
-60
-40
-20
0
0
5
10
15
20
OUTPUT SPECTRUM
vs. FREQUENCY
MAX9725 toc20
FREQUENCY (kHz)
AMPLITUDE (dB)
f
IN
= 1kHz
R
L
= 32
V
OUT
= -60dBV
V
DD
= 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
1.1
1.0
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 (
A)
1.3
1.1
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
0.9
1.5
EXITING SHUTDOWN
MAX9725 toc23
200
s/div
OUT_
1V/div
SHDN
500mV/div
POWER-UP/-DOWN WAVEFORM
MAX9725toc24
200ms/div
OUT_
10mV/div
V
DD
1V/div
Typical Operating Characteristics (continued)
(V
DD
= 1.5V, PGND = SGND = 0V, V
SHDN
= 1.5V, V
SS
= PV
SS,
C1 = C2 = 1F, C
IN
= 1F, THD+N measurement bandwidth = 22Hz
to 22kHz, T
A
= +25
C, unless otherwise noted.) (See the Functional Diagram.)
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