Maxim MAX9721 1v, fixed-gain, directdrive, stereo headphone amplifier with shutdown Datasheet

19-3167; Rev 0; 1/04
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
Features
The MAX9721 fixed-gain, stereo headphone amplifier
is ideal for portable equipment where board space is at a
premium. The MAX9721 uses a unique, patented
DirectDrive architecture to produce a ground-referenced
output from a single supply, eliminating the need for large
DC-blocking capacitors, saving cost, board space, and
component height. Fixed gains of -2V/V (MAX9721A),
-1.5V/V (MAX9721B), and -1V/V (MAX9721C) further
reduce external component count.
♦ Single Cell, 0.9V to 1.8V Single-Supply Operation
♦ Fixed Gain Eliminates External Feedback Network
MAX9721A: -2V/V
MAX9721B: -1.5V/V
MAX9721C: -1V/V
The MAX9721 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
MAX9721 to operate from noisy digital supplies without
an additional linear regulator. The MAX9721 includes
±8kV ESD protection 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
1.0µA (typ).
The MAX9721 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 MAX9721 consumes only
2.2mA of supply current, provides short-circuit protection,
and is specified over the extended -40°C to +85°C temperature range. The MAX9721 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).
♦
♦
♦
♦
♦ 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 Quiescent Current (2.2mA)
♦ 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 Diagram
Applications
MP3 Players
Smart Phones
Cellular Phones
Portable Audio Equipment
SINGLE
1.5V CELL
AA OR AAA
BATTERY
VDD
MAX9721
DirectDrive OUTPUTS
ELIMINATE DC-BLOCKING
CAPACITORS.
INL
PDAs
OUTL
Ordering Information
PART
TEMP RANGE
PINPACKAGE
MAX9721AEBC-T* -40°C to +85°C 12 UCSP-12
MAX9721AETC
-2
ABQ
-1.5
-1.5
ABR
-1
-40°C to +85°C 12 TQFN-EP** AAEB
-1
*Future product—contact factory for availability.
C1P
INVERTING
CHARGE PUMP
C1N
PVSS
VSS
-2
-40°C to +85°C 12 TQFN-EP** AAEA
MAX9721CEBC-T* -40°C to +85°C 12 UCSP-12
MAX9721CETC
ABP
-40°C to +85°C 12 TQFN-EP** AADZ
MAX9721BEBC-T* -40°C to +85°C 12 UCSP-12
MAX9721BETC
TOP GAIN
MARK (V/V)
OUTR
INR
SGND
PGND
**EP = Exposed paddle.
UCSP is a trademark of Maxim Integrated Products, Inc.
Pin Configurations appear at end of data sheet.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX9721
General Description
MAX9721
1V, Fixed-Gain, 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 .....(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
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 = 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.)
PARAMETER
SYMBOL
CONDITIONS
Supply Voltage Range
VDD
Guaranteed by PSRR test
Quiescent Supply Current
IDD
Both channels active
Shutdown Current
Shutdown to Full Operation
SHDN Thresholds
SHDN Input Leakage Current
ISHDN
VSHDN = 0V
MIN
TYP
0.9
TA = +25°C
1.8
V
5
mA
1.0
10
30
180
VIH
VDD = 0.9V to 1.8V
VIL
VDD = 0.9V to 1.8V
UNITS
2.2
TA = -40°C to +85°C
tON
ILEAK
MAX
µA
µs
0.7 x VDD
0.3 x VDD
VDD = 0.9V to 1.8V (Note 1)
V
±1
µA
667
kHz
CHARGE PUMP
Oscillator Frequency
fOSC
493
580
MAX9721A
2.04
-2.00
-1.96
MAX9721B
-1.53
-1.5
-1.47
MAX9721C
-1.02
-1.00
-0.98
MAX9721A
±0.9
±3.8
MAX9721B
±1.3
±5.7
MAX9721C
±1.8
±7.6
15
25
35
60
80
AMPLIFIERS
Voltage Gain
Gain Match
Total Output Offset Voltage
Input Resistance
AV
∆AV
VOS
±0.5
Input AC-coupled,
RL = 32Ω to GND
RIN
VDD = 0.9V to 1.8V, TA = +25°C
Power-Supply Rejection Ratio
PSRR
100mVP-P ripple
VDD = 1.5V
Output Power (Note 2)
POUT
fIN = 1kHz
70
fIN = 20kHz
62
RL = 32Ω
RL = 16Ω
VDD = 1.0V, RL = 32Ω
VDD = 0.9V, RL = 32Ω
Total Harmonic Distortion Plus
Noise
2
THD+N
10
V/V
%
mV
kΩ
dB
20
25
7
mW
6
RL = 32Ω, POUT = 12mW, f = 1kHz
0.006
RL = 16Ω, POUT = 15mW, f = 1kHz
0.015
_______________________________________________________________________________________
%
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
(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.)
PARAMETER
SYMBOL
Signal-to-Noise Ratio
SNR
Slew Rate
SR
Maximum Capacitive Load
CL
Crosstalk
RL = 32Ω, POUT = 12mW
XTALK
ESD Protection
CONDITIONS
VESD
MIN
TYP
BW = 22Hz to 22kHz
89
A-weighted filter
92
MAX
UNITS
dB
0.2
V/µs
No sustained oscillations
150
pF
fIN = 1.0kHz, RL = 32Ω, POUT = 5mW
100
dB
Human body model (OUTR, OUTL)
±8
kV
Note 1: Input leakage current measurements limited by automated test equipment.
Note 2: fIN = 1kHz, TA = +25°C, THD+N < 1%, both channels driven in-phase.
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.)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
VDD = 1.5V
RL = 16Ω
AV = -2V/V
VDD = 1.5V
RL = 32Ω
AV = -2V/V
1
0.1
POUT = 2mW
0.01
0.01
POUT = 0.7mW
THD+N (%)
THD+N (%)
POUT = 15mW
VDD = 1V
RL = 16Ω
AV = -2V/V
0.1
THD+N (%)
0.1
MAX9721toc03
1
MAX9721toc01
1
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
MAX9721toc02
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
0.01
POUT = 2mW
POUT = 4mW
POUT = 12mW
0.001
0.001
10
1k
10k
0.001
10
100k
100
1k
10k
100k
10
100
1k
10k
100k
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
VDD = 1.5V
RL = 16Ω
AV = -2V/V
10
fIN = 20Hz
fIN = 1kHz
100
VDD = 1.5V
RL = 32Ω
AV = -2V/V
10
MAX9721toc06
VDD = 1V
RL = 32Ω
AV = -2V/V
MAX9721toc05
100
MAX9721toc04
1
100
fIN = 20Hz
fIN = 1kHz
POUT = 0.7mW
THD+N (%)
THD+N (%)
THD+N (%)
0.1
1
fIN = 10kHz
0.1
1
fIN = 10kHz
0.1
0.01
0.01
0.01
POUT = 4mW
0.001
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
0.001
0
10
20
30
OUTPUT POWER (mW)
40
0
10
20
30
40
OUTPUT POWER (mW)
_______________________________________________________________________________________
3
MAX9721
ELECTRICAL CHARACTERISTICS (continued)
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.)
10
fIN = 20Hz
fIN = 1kHz
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
100
VDD = 1V
RL = 32Ω
AV = -2V/V
10
-10
MAX9721toc08
VDD = 1V
RL = 16Ω
AV = -2V/V
MAX9721toc07
100
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
fIN = 20Hz
fIN = 1kHz
MAX9721toc09
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
VDD = 1.5V
RL = 32Ω
-20
-30
THD+N (%)
fIN = 10kHz
0.1
1
-50
PSRR (dB)
THD+N (%)
-40
1
fIN = 10kHz
0.1
-60
-70
-80
0.01
-90
0.01
-100
0.001
10
15
-110
0
5
OUTPUT POWER (mW)
-20
1k
-40
-50
-60
LEFT TO RIGHT
-60
-80
-70
10k
100k
OUTPUT POWER vs. SUPPLY VOLTAGE
-40
PSRR (dB)
80
fIN = 1kHz
RL = 16Ω
BOTH INPUTS
DRIVEN IN-PHASE
70
60
50
THD+N = 10%
40
30
20
-100
-90
10
RIGHT TO LEFT
100
1k
10k
10
100k
FREQUENCY (Hz)
OUTPUT POWER
vs. SUPPLY VOLTAGE
fIN = 1kHz
RL = 32Ω
BOTH INPUTS
DRIVEN IN-PHASE
40
35
25
20
15
10
THD+N = 1%
5
THD+N = 10%
50
THD+N = 1%
30
20
10
0.9
1.1
1.3
SUPPLY VOLTAGE (V)
1.5
1.3
80
1.5
VDD = 1V
fIN = 1kHz
BOTH INPUTS
DRIVEN IN-PHASE
70
60
50
40
THD+N = 10%
30
THD+N = 1%
20
10
0
0
1.1
OUTPUT POWER
vs. LOAD RESISTANCE
VDD = 1.5V
fIN = 1kHz
BOTH INPUTS
DRIVEN IN-PHASE
40
0.9
100k
OUTPUT POWER
vs. LOAD RESISTANCE
60
THD+N = 10%
30
10k
SUPPLY VOLTAGE (V)
70
OUTPUT POWER (mW)
45
1k
FREQUENCY (Hz)
80
MAX9721 toc13
50
100
OUTPUT POWER (mW)
10
THD+N = 1%
0
-120
-100
MAX9721toc15
-80
MAX9721toc14
PSRR (dB)
100
FREQUENCY (Hz)
VDD = 1.5V
POUT = 5mW
RL = 32Ω
-20
-30
4
10
CROSSTALK vs. FREQUENCY
0
MAX9721toc10
VDD = 1V
RL = 32Ω
-10
15
OUTPUT POWER (mW)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
0
10
OUTPUT POWER (mW)
5
MAX9721toc11
0
MAX9721toc12
0.001
OUTPUT POWER (mW)
MAX9721
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
0
10
100
LOAD RESISTANCE (Ω)
1k
10
100
LOAD RESISTANCE (Ω)
_______________________________________________________________________________________
1k
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
POWER DISSIPATION
vs. OUTPUT POWER
40
30
VDD = 1.5V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN-PHASE
RL = 32Ω
10
MAX9721toc17
15
10
VDD = 1V
fIN = 1kHz
POUT = POUTL + POUTR
OUTPUTS IN-PHASE
RL = 32Ω
0
0
10
20
30
40
50
2
1
0
-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
0
5
10
15
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
-20
C1 = C2 = 1µF
AMPLITUDE (dB)
30
25
20
15
10
-80
-120
0
20
30
40
4.5
NO LOAD
4.0
3.5
3.0
2.5
2.0
1.5
0.5
-140
10
5.0
1.0
VDD = 1.5V
fIN = 1kHz
THD+N = 1%
C1 = C2 = 0.47µF
-60
-100
C1 = C2 = 0.68µF
5
-40
0
0
50
5
10
15
LOAD RESISTANCE (Ω)
FREQUENCY (kHz)
SHUTDOWN CURRENT
vs. SUPPLY VOLTAGE
EXITING SHUTDOWN
20
0.9
1.0
1.1
1.2
MAX9721toc22
1.2
1.0
1.3
1.4
1.5
SUPPLY VOLTAGE (V)
POWER-UP/-DOWN WAVEFORM
MAX9721toc23
1.4
100k
MAX9721toc21
fIN = 1kHz
RL = 32Ω
POUT = 12mW
VDD = 1.5V
SUPPLY CURRENT (mA)
C1 = C2 = 2.2µF
35
0
MAX9721toc19
40
OUTPUT POWER (mW)
RL = 16Ω
20
5
0
SHUTDOWN CURRENT (µA)
25
AMPLITUDE (dB)
50
MAX9721toc20
POWER DISSIPATION (mW)
60
20
30
POWER DISSIPATION (mW)
RL = 16Ω
70
35
MAX9721toc16
80
GAIN FLATNESS
vs. FREQUENCY
MAX9721toc18
POWER DISSIPATION
vs. OUTPUT POWER
MAX9721
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.)
MAX9721toc24
VDD
1V/div
OUT_
1V/div
0.8
SHDN
500mV/div
0.6
0.4
OUT_
10mV/div
0.2
0
0.9
1.0
1.1
1.2
1.3
1.4
1.5
200µs/div
200ms/div
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
5
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
MAX9721
Pin Description
PIN
BUMP
THIN
QFN
UCSP
1
A1
C1N
Flying Capacitor Negative Terminal. Connect a 1µF capacitor from C1P to C1N.
2
A2
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
4
A4
INR
Right-Channel Audio Input
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
8
C3
OUTL
Left-Channel Output
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
NAME
FUNCTION
Exposed Paddle. Internally connected to VSS. Leave paddle unconnected or solder to VSS.
Detailed Description
The MAX9721 stereo headphone driver features Maxim’s
patented DirectDrive architecture, eliminating the large
output-coupling capacitors required by conventional single-supply headphone drivers. The MAX9721 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 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 MAX9721 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.
6
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 MAX9721 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
MAX9721 provides 25mW to a 16Ω load. The
DirectDrive architecture eliminates the need for two
large (220µF, typ) DC-blocking capacitors on the output. The MAX9721 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, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
VOUT
VDD / 2
GND
CONVENTIONAL DRIVER-BIASING SCHEME
VDD
VOUT
GND
-VDD
DirectDrive BIASING SCHEME
Figure 1. Traditional Driver Output Waveform vs. MAX9721
Output Waveform (Ideal Case)
Pump Capacitance and Load Resistance graph in the
Typical Operating Characteristics for details of the possible 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 equipment, resulting in possible damage to the drivers.
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 as 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
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 MAX9721 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-
_______________________________________________________________________________________
7
MAX9721
VDD
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:
MAX9721
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
ADDITIONAL THD+N DUE
TO DC-BLOCKING CAPACITORS
LF ROLLOFF (16Ω LOAD)
0
10
-3
-5
330µF
1
100µF
-15
-3dB CORNER FOR
100µF IS 100Hz
THD+N (%)
ATTENUATION (dB)
220µF
-10
33µF
-20
0.1
TANTALUM
0.01
-25
0.001
-30
ALUM/ELEC
-35
0.0001
10
100
FREQUENCY (Hz)
1k
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 2. Low-Frequency Attenuation for Common DC-Blocking
Capacitor Values
Figure 3. Distortion Contributed By DC-Blocking Capacitors
frequency noise attenuation can be achieved by
increasing the size of C2 (see the Functional Diagram).
Extra noise attenuation is not typically required.
ble click/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/pop caused by the
input filter (see the Functional Diagram).
Shutdown
The MAX9721’s low-power shutdown mode reduces supply current to 1µA. Driving SHDN low disables the amplifiers and charge pump. The driver’s output impedance is
typically 50kΩ (MAX9721A), 37.5kΩ (MAX9721B), or
25kΩ (MAX9721C) when in shutdown mode.
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 MAX9721’s DirectDrive technology eliminates the need for output-coupling capacitors.
The MAX9721 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 MAX9721 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 audi8
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:
PDISSPKG(MAX) =
TJ(MAX) - TA
θ JA
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 MAX9721 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.
_______________________________________________________________________________________
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
50
45
OUTPUT POWER (mW)
40
fIN = 1kHz
RL = 16Ω
THD+N = 1%
35
INPUTS 180° OUT-OF-PHASE
30
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
Diagram). CIN allows the MAX9721 to bias the signal to
an optimum DC level. The -3dB point of the highpass
filter, assuming zero-source impedance, is given by:
25
20
f-3dB =
15
10
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
Output Power
The MAX9721’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 MAX9721 is specified to output
20mW per channel when both inputs are in-phase.
Powering Other Circuits from
the Negative Supply
The MAX9721 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.
1
2π × 25kΩ × CIN
Choose CIN so f-3dB is well below the lowest frequency of
interest. Setting f-3dB too high affects the amplifier’s lowfrequency 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 MAX9721’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 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 Impedance graph in the Typical
Operating Characteristics.
_______________________________________________________________________________________
9
MAX9721
Component Selection
OUTPUT POWER vs. SUPPLY VOLTAGE
WITH INPUTS IN- AND OUT-OF-PHASE
MAX9721
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
Table 1. Suggested Capacitor Manufacturers
SUPPLIER
PHONE
FAX
Taiyo Yuden
800-348-2496
847-925-0899
www.t-yuden.com
TDK
847-803-6100
847-390-4405
www.component.tdk.com
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 MAX9721’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
MAX9721 as possible. Route PGND, and all traces that
carry switching transients, away from SGND and the
audio signal path.
WEBSITE
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: UCSP—A Wafer-Level Chip-Scale Package.
Chip Information
TRANSISTOR COUNT: 2559
PROCESS: BiCMOS
The MAX9721 does not require additional heatsinking.
The thin QFN package features an exposed paddle that
improves thermal efficiency of the package. Ensure
that the exposed paddle is electrically isolated from
GND and VDD. Connect the exposed paddle to VSS if
necessary.
10
______________________________________________________________________________________
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
0.9V TO 1.8V
1µF
0.47µF
SHDN
RIGHT DAC
VDD
INR
MP3
DECODER
INL
LEFT DAC
C1P
0.47µF
MAX9721
OUTR
1µF
C1N
OUTL
VSS
PVSS
1µF
SGND
PGND
Pin Configurations
MAX9721
TOP VIEW
(BUMPS SIDE
DOWN)
1
2
3
4
TOP VIEW
A
C1N
PVSS
INL
SHDN
PGND
C1P
12
11
10
INR
C1N
1
PVSS
2
INL
3
9
VDD
8
OUTL
7
OUTR
B
PGND
SHDN
SGND
C
C1P
VDD
OUTL
UCSP
VSS
OUTR
MAX9721
4
5
6
INR
VSS
SGND
THIN QFN
______________________________________________________________________________________
11
MAX9721
System Diagram
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
MAX9721
Functional Diagram
LEFT
CHANNEL
AUDIO IN
0.9V TO 1.8V
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
MAX9721
RIN
25kΩ
7
(C4)
VSS
RF*
PVSS
VSS
PGND
SGND
2
(A2)
C2
1µF
5
(B4)
11
(B1)
6
(B3)
INR
4
(A4)
CIN
0.47µF
RIGHT
CHANNEL
AUDIO IN
*MAX9721A = 50kΩ.
MAX9721B = 37.5kΩ.
MAX9721C = 25kΩ.
( ) DENOTE BUMPS FOR UCSP.
12
______________________________________________________________________________________
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
12L, UCSP 4x3.EPS
PACKAGE OUTLINE, 4x3 UCSP
21-0104
F
1
1
______________________________________________________________________________________
13
MAX9721
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.)
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
MAX9721
1V, Fixed-Gain, DirectDrive, Stereo Headphone
Amplifier with Shutdown
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
B
1
2
PACKAGE OUTLINE
12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
B
2
2
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
© 2004 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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