General Description
The MAX9720 stereo headphone amplifier combines
Maxim’s patented DirectDrive architecture and
SmartSense™, an automatic mono/stereo detection fea-
ture. Conventional headphone amplifiers require a bulky
DC-blocking capacitor between the headphone and the
amplifier. DirectDrive produces a ground-referenced out-
put from a single supply, eliminating the need for large
DC-blocking capacitors, saving cost, board space, and
component height.
SmartSense automatically detects the presence of a
short at either the left or right amplifier output. Under a
fault condition, the shorted output is automatically dis-
abled and the stereo input signal is automatically mixed
and routed to the remaining active channel. This feature
is useful in cell phone and PDA applications where a
variety of headphone jacks with unknown loads can be
inserted into the headphone jack socket. SmartSense
prevents both damage to the amplifier and eliminates
battery drain into a shorted load.
The MAX9720 delivers up to 50mW per channel into a
16Ωload and has an ultra-low 0.003% THD+N. A high
(92dB at 217kHz) power-supply rejection ratio (PSRR)
allows the device to operate from noisy digital supplies
without additional power conditioning. The gain of the
MAX9720 is set internally, further reducing component
count. Two gain options are available (-1V/V, MAX9720A
and -1.41V/V, MAX9720B). The headphone outputs
include a comprehensive click-and-pop circuitry that
eliminates audible glitches on startup and shutdown. A
shutdown mode provides a fast 250µs turn-on time.
The MAX9720 operates from a single 1.8V to 3.6V
supply and consumes only 5mA of supply current. The
MAX9720 also features thermal overload protection,
and is specified over the extended -40°C to +85°C tem-
perature range. The MAX9720 is available in a tiny
(2mm x 2mm x 0.6mm) 16-bump chip-scale package
(UCSP™) and a 16-pin TSSOP package.
Applications
Features
♦DirectDrive Eliminates Bulky DC-Blocking
Capacitors
♦SmartSense Automatic Short Detection
♦Low 5mA Quiescent Current
♦Fixed Gain Eliminates External Feedback Network
MAX9720A: -1V/V
MAX9720B: -1.41V/V
♦50mW per Channel Output Power
♦Ultra-Low 0.003% THD+N
♦High PSRR (92dB at 217Hz)
♦Integrated Click-and-Pop Suppression
♦1.8V to 3.6V Single-Supply Operation
♦Thermal Overload Protection
♦Available in Space-Saving Packages
16-Bump UCSP (2mm x 2mm x 0.6mm)
16-Pin TSSOP
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2859; Rev 0; 4/03
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.
Pin Configuration and Typical Application Circuit appear at
end of data sheet.
PART TEMP RANGE PIN/BUMP-
PACKAGE
GAIN
(V/V)
MAX9720AEBE-T -40oC to +85oC 16 UCSP-16 -1
MAX9720BEBE-T -40oC to +85oC 16 UCSP-16 -1.41
MAX9720AEUE -40oC to +85oC 16 TSSOP -1
MAX9720BEUE -40oC to +85oC 16 TSSOP -1.41
PDAs
Cellular Phones
MP3 Players
Notebook PCs
Smart Phones
Tablet PCs
Portable Audio Equipment
SmartSense and UCSP are trademarks of Maxim Integrated
Products, Inc.
RIN
+
LIN
ROUT
HPS
MODE1
MODE2
ALERT
3.6V TO 1.8V
SUPPLY
MAX9720
SmartSense
LOUT
Simplified Block Diagram
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VDD = VMODE1 = VMODE2 = 3.0V, PGND = SGND = 0V, RL= ∞, C1 = C2 = 2.2µF. TA= TMIN to TMAX, unless otherwise noted.
Typical values are at TA= +25°C.) (Note 1)
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.
PGND to SGND .....................................................-0.3V to +0.3V
PVSS to SVSS .........................................................-0.3V to +0.3V
VDD to PGND or SGND ............................................-0.3V to +4V
PVSS and SVSS to PGND or SGND ..........................-4V to +0.3V
IN_, OUT_, and HPS to SGND .......(SVSS - 0.3V) to (VDD + 0.3V)
C1P to PGND ...............................(PGND - 0.3V) to (VDD + 0.3V)
C1N to PGND .............................(PVSS - 0.3V) to (PGND + 0.3V)
ALERT to PGND .......................................................-0.3V to +4V
MODE_ to PGND........................................-0.3V to (VDD + 0.3V)
TIME to SGND ............................................-0.3V to (VDD + 0.3V)
Output Short Circuit to GND or VDD ...............................Continuous
Continuous Power Dissipation (TA= +70°C)
16-Bump UCSP (derate 8.2mW/°C above +70°C) .......659mW
16-Pin TSSOP (derate 9.4mW/°C above +70°C) .......754.7mW
Junction Temperature......................................................+150°C
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-65°C to +150°C
Bump Temperature (soldering)
Reflow ...........................................................................+235°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
GENERAL
Supply Voltage Range VDD Inferred from PSRR test 1.8 3.6 V
Stereo mode 5 8.4
Supply Current IDD M ono m od e ( M OD E 1 = V
D D
, M OD E 2 = GN D ) 3 mA
Shutdown Supply Current ISHDN MODE1 = MODE2 = GND 6 10 µA
Turn-On/Turn-Off Time tS250 µs
CHARGE PUMP
Oscillator Frequency fOSC 272 320 368 kHz
HEADPHONE AMPLIFIERS
MAX9720A -1.02 -1 -0.98
Voltage Gain AVMAX9720B -1.443 -1.415 -1.386 V/V
Gain Match ∆AVBetween OUTL and OUTR ±1%
MAX9720A -5 -0.8 +3.6
Total Output Offset Voltage
(Note 3) VOS MAX9720B -6.5 -1 +4.5 mV
Input Resistance RIN 10 15 20 kΩ
1.8V ≤ VDD ≤ 3.6V
(Note 3) DC 76 92
fRIPPLE = 217Hz 92
fRIPPLE = 1kHz 86
Power-Supply Rejection Ratio PSRR VDD = 3.0V,
200mVP-P ripple
(Note 3) fRIPPLE = 20kHz 61
dB
RL = 32Ω50
Output Power POUT THD+N = 1%, fIN =
1kHz, TA = +25°CRL = 16Ω32 50 mW
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
_______________________________________________________________________________________ 3
Note 1: All specifications are 100% tested at TA= +25oC; temperature limits are guaranteed by design.
Note 2: Inputs are AC-coupled to ground.
Note 3: Inputs are connected directly to ground.
ELECTRICAL CHARACTERISTICS (continued)
(VDD = VMODE1 = VMODE2 = 3.0V, PGND = SGND = 0V, RL= ∞, C1 = C2 = 2.2µF. TA= TMIN to TMAX, unless otherwise noted.
Typical values are at TA= +25°C.) (Note 1)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
RL = 32Ω,
POUT = 30mW 0.003
Total Harmonic Distortion Plus
Noise THD+N fIN = 1kHz
RL = 16Ω,
POUT = 30mW 0.005
%
Signal-to-Noise Ratio SNR fIN = 1kHz, VOUT = 0.5VRMS, RL = 16Ω,
BW = 22Hz to 22kHz 97 dB
Slew Rate SR 0.8 V/µs
Maximum Capacitive Load CLNo sustained oscillations 150 pF
Crosstalk RL = 32Ω, POUT = 1mW, fIN = 10kHz 75 dB
Thermal Shutdown Threshold 140 oC
Thermal Shutdown Hysteresis 15 oC
SmartSense
Shorted Load Threshold RSMS 2.4 4 5.6 Ω
Pulse Duration tSMS 3.1 µs
DEBOUNCE TIME (TIME)
TIME Charging Current ITIME 0.7 1.1 1.8 µA
TIME Discharge Switch
Resistance RTIME HPS = GND 4 10 kΩ
TIME Threshold VTIME 1 1.1 1.2 V
HEADPHONE SENSE INPUT (HPS)
VIH 0.9 x
VDD
HPS Threshold
VIL 0.7 x
VDD
V
Input Leakage Current IIL MODE1= MODE2 = GND ±1µA
Input Capacitance CIN 10 pF
ALERT
Output Current High IOH VALERT = VDD 1µA
Output Voltage Low VOL IOL = 3mA 0.4 V
MODE_ INPUT
VIH 0.7 x
VDD
MODE_ Thresholds
VIL 0.3 x
VDD
V
MODE_ Input Leakage Current ±1µA
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
4 _______________________________________________________________________________________
Typical Operating Characteristics
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc01
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
AV = -1V/V
RL = 16Ω
POUT = 10mW
POUT = 40mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc02
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
AV = -1V/V
RL = 32Ω
POUT = 10mW
POUT = 40mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc03
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
AV = -1.41V/V
RL = 16Ω
POUT = 10mW
POUT = 40mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc04
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
AV = -1.41V/V
RL = 32Ω
POUT = 10mW
POUT = 40mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc05
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 1.8V
AV = -1V/V
RL = 16Ω
POUT = 2mW
POUT = 9mW
FREQUENCY (Hz)
10k1k10010 100k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc06
THD + N (%)
1
0.1
0.001
0.01
VDD = 1.8V
AV = -1V/V
RL = 32Ω
POUT = 2mW
POUT = 9mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc07
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
AV = -1.41V/V
RL = 16Ω
POUT = 2mW
POUT = 9mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc08
FREQUENCY (Hz)
THD+N (%)
10k1k100
0.01
0.1
1
0.001
10 100k
VDD = 3V
AV = -1.41V/V
RL = 32Ω
POUT = 2mW
POUT = 9mW
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc09
OUTPUT POWER (mW)
THD+N (%)
120906030
0.01
0.1
1
10
100
0.001
0 150
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE VDD = 3V
AV = -1V/V
f = 20Hz
RL = 16Ω
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
_______________________________________________________________________________________ 5
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc10
OUTPUT POWER (mW)
THD+N (%)
120906030
0.01
0.1
1
10
100
0.001
0 150
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE VDD = 3V
AV = -1V/V
f = 1kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc11
OUTPUT POWER (mW)
THD+N (%)
120906030
0.01
0.1
1
10
100
0.001
0 150
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 3V
AV = -1V/V
f = 10kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc12
OUTPUT POWER (mW)
THD+N (%)
80604020
0.01
0.1
1
10
100
0.001
0 100
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE VDD = 3V
AV = -1V/V
f = 20Hz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc13
OUTPUT POWER (mW)
THD+N (%)
80604020
0.01
0.1
1
10
100
0.001
0 100
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE VDD = 3V
AV = -1V/V
f = 1kHz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc14
OUTPUT POWER (mW)
THD+N (%)
80604020
0.01
0.1
1
10
100
0.001
0 100
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 3V
AV = -1V/V
f = 10kHz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc15
OUTPUT POWER (mW)
THD+N (%)
120906030
0.01
0.1
1
10
100
0.001
0 150
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 3V
AV = -1.41V/V
f = 20Hz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc16
OUTPUT POWER (mW)
THD+N (%)
120906030
0.01
0.1
1
10
100
0.001
0 150
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 3V
AV = -1.41V/V
f = 1kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc17
OUTPUT POWER (mW)
THD+N (%)
120906030
0.01
0.1
1
10
100
0.001
0 150
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 3V
AV = -1.41V/V
f = 10kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc18
OUTPUT POWER (mW)
THD+N (%)
0.01
0.1
1
10
100
0.001
010080604020 120
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE VDD = 3V
AV = -1.41V/V
f = 20Hz
RL = 32Ω
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
6 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc19
OUTPUT POWER (mW)
THD+N (%)
0.01
0.1
1
10
100
0.001
0 120
10080604020
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE VDD = 3V
AV = -1.41V/V
f = 1kHz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc20
OUTPUT POWER (mW)
THD+N (%)
0.01
0.1
1
10
100
0.001
0 120
10080604020
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 3V
AV = -1.41V/V
f = 10kHz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc21
OUTPUT POWER (mW)
THD+N (%)
40302010
0.01
0.1
1
10
100
0.001
050
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1V/V
f = 20Hz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc22
OUTPUT POWER (mW)
THD+N (%)
40302010
0.01
0.1
1
10
100
0.001
050
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1V/V
f = 1kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc23
OUTPUT POWER (mW)
THD+N (%)
40302010
0.01
0.1
1
10
100
0.001
050
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1V/V
f = 10kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc24
OUTPUT POWER (mW)
THD+N (%)
25155302010
0.01
0.1
1
10
100
0.001
035
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1V/V
f = 20Hz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc25
OUTPUT POWER (mW)
THD+N (%)
25155302010
0.01
0.1
1
10
100
0.001
035
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1V/V
f = 1kHz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc26
OUTPUT POWER (mW)
THD+N (%)
25155302010
0.01
0.1
1
10
100
0.001
035
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1V/V
f = 10kHz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc27
OUTPUT POWER (mW)
THD+N (%)
40302010
0.01
0.1
1
10
100
0.001
050
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1.41V/V
f = 20Hz
RL = 16Ω
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
_______________________________________________________________________________________ 7
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc28
OUTPUT POWER (mW)
THD+N (%)
40302010
0.01
0.1
1
10
100
0.001
050
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1.41V/V
f = 1kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc29
OUTPUT POWER (mW)
THD+N (%)
40302010
0.01
0.1
1
10
100
0.001
050
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1.41V/V
f = 10kHz
RL = 16Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc30
OUTPUT POWER (mW)
THD+N (%)
25155302010
0.01
0.1
1
10
100
0.001
04035
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1.41V/V
f = 20Hz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc31
OUTPUT POWER (mW)
THD+N (%)
25155302010
0.01
0.1
1
10
100
0.001
04035
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1.41V/V
f = 1kHz
RL = 32Ω
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc32
OUTPUT POWER (mW)
THD+N (%)
25155302010
0.01
0.1
1
10
100
0.001
04035
OUTPUTS
IN PHASE
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1.41V/V
f = 10kHz
RL = 32Ω
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9720 toc33
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.33.02.72.42.1
20
40
60
80
100
120
140
160
180
200
0
1.8 3.6
fIN = 1kHz
RL = 16Ω
THD+N = 1% STEREO
OUT OF
PHASE
STEREO
IN PHASE
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9720 toc34
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.33.02.72.42.1
20
40
60
80
100
120
140
160
180
200
0
1.8 3.6
fIN = 1kHz
RL = 16Ω
THD+N = 10%
STEREO
OUT OF
PHASE
STEREO
IN PHASE
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9720 toc35
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.33.02.72.42.1
20
40
60
80
100
120
140
160
0
1.8 3.6
fIN = 1kHz
RL = 32Ω
THD+N = 1% STEREO
OUT OF
PHASE
STEREO
IN PHASE
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9720 toc36
SUPPLY VOLTAGE (V)
OUTPUT POWER (mW)
3.33.02.72.42.1
20
40
60
80
100
120
140
160
0
1.8 3.6
fIN = 1kHz
RL = 32Ω
THD+N = 10%
STEREO
OUT OF
PHASE
STEREO
IN PHASE
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
8 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
OUTPUT POWER vs. LOAD RESISTANCE
MAX9720 toc37
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
20
40
60
80
100
120
140
160
0
10 100
f = 1kHz
THD+N = 1%
INPUTS
OUT OF
PHASE
INPUTS
IN PHASE
OUTPUT POWER vs. LOAD RESISTANCE
MAX9720 toc38
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
20
40
60
80
100
120
140
160
0
10 100
f = 1kHz
THD+N = 10%
INPUTS
OUT OF
PHASE
INPUTS
IN PHASE
OUTPUT POWER vs. LOAD RESISTANCE
MAX9720 toc39
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
5
10
15
20
25
30
35
40
0
10 100
VDD = 1.8V
f = 1kHz
THD+N = 1%
INPUTS
OUT OF
PHASE
INPUTS
IN PHASE
OUTPUT POWER vs. LOAD RESISTANCE
MAX9720 toc40
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
5
10
15
20
25
30
35
40
0
10 100
VDD = 1.8V
f = 1kHz
THD+N = 10%
INPUTS
OUT OF
PHASE
INPUTS
IN PHASE
POWER DISSIPATION vs. OUTPUT POWER
MAX9720 toc41
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
20015010050
50
100
150
200
250
300
350
0
0 250
RL = 16Ω
RL = 32Ω
VDD = 3V
f = 1kHz
POUT = POUTL + POUTR
POWER DISSIPATION vs. OUTPUT POWER
MAX9720 toc42
OUTPUT POWER (mW)
POWER DISSIPATION (mW)
604020
25
50
75
100
125
0
080
RL = 16Ω
RL = 32Ω
VDD = 1.8V
f = 1kHz
POUT = POUTL + POUTR
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9720 toc43
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-120
10 100k
VDD = 3V
VRIPPLE = 200mVP-P
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
MAX9720 toc44
FREQUENCY (Hz)
PSRR (dB)
10k1k100
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
10 100k
VDD = 1.8V
VRIPPLE = 200mVP-P
CROSSTALK vs. FREQUENCY
MAX9720 toc45
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-120
10 100k
VDD = 3V
RL = 32Ω
VIN = 200mVP-P
RIGHT-TO-LEFT
CHANNEL
LEFT-TO-RIGHT
CHANNEL
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
_______________________________________________________________________________________ 9
CROSSTALK vs. FREQUENCY
MAX9720 toc46
FREQUENCY (Hz)
CROSSTALK (dB)
10k1k100
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-120
10 100k
VDD = 1.8V
RL = 32Ω
VIN = 200mVP-P
RIGHT-TO-LEFT
CHANNEL
LEFT-TO-RIGHT
CHANNEL
GAIN FLATNESS vs. FREQUENCY
MAX9720 toc47
FREQUENCY (Hz)
GAIN (dB)
1k1001010.1
-4
-3
-2
-1
0
1
2
3
4
5
-5
0.01 10k
AV = -1V/V
CHARGE-PUMP OUTPUT IMPEDANCE
vs. SUPPLY VOLTAGE
MAx9720 toc48
SUPPLY VOLTAGE (V)
OUTPUT IMPEDANCE (Ω)
3.33.02.72.42.1
2
4
6
8
10
12
14
0
1.8 3.6
ILOAD = 10mA
0.47µF
OUTPUT POWER vs. LOAD RESISTANCE
AND CHARGE-PUMP CAPACITOR SIZE
MAx9720 toc49
LOAD RESISTANCE (Ω)
OUTPUT POWER (mW)
403020
10
20
30
40
50
60
0
10 50
2.2µF
1µF
fIN = 1kHz
THD+N = 1%
OUTPUTS
IN PHASE
OUTPUT SPECTRUM vs. FREQUENCY
MAX9720 toc50
FREQUENCY (Hz)
OUTPUT SPECTRUM (dB)
10k1k
-100
-80
-60
-40
-20
0
-120
100 100k
VIN = 1VP-P
RL = 32Ω
fIN = 1kHz
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX9720 toc51
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
3.33.02.72.42.1
1
2
3
4
5
6
0
1.8 3.6
STEREO MODE
MONO MODE
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX9720 toc52
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
3.33.02.72.42.1
1
2
3
4
5
6
7
8
9
0
1.8 3.6
EXITING SHUTDOWN
MAX9720 toc53
400µs/div
OUT_ 500mV/div
3V
0V
fIN = 1kHz
RL = 32Ω
MODE1 AND
MODE2
POWER-UP/DOWN WAVEFORM
MAX9720 toc54
200ms/div
FFT: 25Hz/div
OUT_FFT
OUT_
20dB/div
3V
0V
10mV/div
VIN = GND
RL = 32Ω
VDD
100dB
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
MAX9720
Detailed Description
The MAX9720 fixed-gain, stereo headphone amplifier
includes Maxim’s patented DirectDrive architecture and
SmartSense. DirectDrive eliminates the large output-
coupling capacitors required by conventional single-
supply headphone amplifiers. SmartSense automatically
detects the presence of a short at either output. Under a
fault condition, the shorted output is automatically
disabled and the stereo input signal is automatically
mixed and routed to the remaining active channel. This
prevents damage to the amplifier and optimizes power
savings by eliminating battery drain into a shorted load.
The device consists of two 50mW Class AB headphone
amplifiers, an internal feedback network (MAX9720A:
fixed -1V/V gain, MAX9720B: fixed -1.41V/V gain), a
mono mixer/attenuator, undervoltage lockout (UVLO)/
shutdown control, SmartSense, a charge pump, and
comprehensive click-and-pop suppression circuitry
(see Functional Diagram). The charge pump inverts the
positive supply (VDD), creating a negative supply
(PVSS). The headphone amplifiers operate from these
bipolar supplies with their outputs biased about GND
(Figure 1). The amplifiers have almost twice the supply
range compared to other single-supply amplifiers,
nearly quadrupling the available output power. The
benefit of the GND bias is that the amplifier outputs do
not have a DC component (typically VDD/2). This elimi-
nates the large DC-blocking capacitors required with
conventional headphone amplifiers, conserving board
space, system cost, and improving frequency
response.
The noninvasive SmartSense feature of the MAX9720
detects a short on either output. The SmartSense routine
executes when the device is powered up or brought out
of shutdown (see the SmartSense section). If a fault is
detected, the shorted channel is shut down, the output
goes high impedance, and the stereo audio input is
mixed/attenuated and fed to the remaining active chan-
nel. The device also features an ALERT output that indi-
cates to a host µC that SmartSense has detected a
short-circuit condition on either amplifier output.
Forced stereo and forced mono modes can also be
selected through the two MODE_ inputs. In forced
operation mode, SmartSense is disabled and the
device operates as specified by the MODE_ inputs,
regardless of output load conditions. A fast low-power
shutdown mode is also selected through the MODE_
inputs (see the Mode_ Selection section).
The UVLO prevents operation from an insufficient
power supply and click-and-pop suppression, which
eliminates audible transients on startup and shutdown.
Additionally, the MAX9720 features thermal overload
protection and can withstand ±4kV ESD strikes on the
output.
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
10 ______________________________________________________________________________________
Pin Description
PIN BUMP
TSSOP UCSP NAME FUNCTION
1D2V
DD Positive Power Supply
2 C2 MODE1 Mode Select 1 Logic Input
3 D1 C1P Flying Capacitor Positive Terminal
4 C1 PGND Power Ground. Connect to SGND.
5 B1 C1N Flying Capacitor Negative Terminal
6A1PV
SS Charge-Pump Output
7 B2 MODE2 Mode Select 2 Logic Input
8A2ALERT Open-Drain Interrupt Logic Output
9 A3 INL Left-Channel Audio Input
10 B3 TIME Debouncing Timer Capacitor
11 A4 INR Right-Channel Audio Input
12 B4 SGND Signal Ground. Connect to PGND.
13 C4 SVSS Amplifier Negative Power Supply. Connect to PVSS.
14 D4 OUTR Right-Channel Output
15 C3 HPS Headphone Sense Input
16 D3 OUTL Left-Channel Output
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typical-
ly half the supply) for maximum dynamic range. Large
coupling capacitors are needed to block this DC bias
from the headphone. Without these capacitors, a signifi-
cant amount of DC current flows to the headphone,
resulting in unnecessary power dissipation and possible
damage to both headphone and headphone amplifier.
Maxim’s patented DirectDrive architecture uses a
charge pump to create an internal negative supply volt-
age. This allows the MAX9720 output to be biased
about GND, almost doubling dynamic range while
operating from a single supply. With no DC component,
there is no need for the large DC-blocking capacitors.
Instead of two large capacitors (220µF typ), the
MAX9720 charge pump requires only two, small ceram-
ic capacitors (1µF typ), conserving board space,
reducing cost, and improving the frequency response
of the headphone amplifier. See the Output Power vs.
Charge-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 raised 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 amplifier’s ESD structures
are the only path to system ground. The amplifier
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 large ground-loop current
and possible damage to the amplifiers.
•When using a combination microphone and speak-
er headset (in a cell phone or PDA application), the
microphone typically requires a GND return. Any
DC bias on the sleeve conflicts with the microphone
requirements (Figure 2).
Low-Frequency Response
In addition to the cost and size disadvantages, the DC-
blocking capacitors limit the low-frequency response of
the amplifier and distort the audio signal:
•The impedance of the headphone load and the DC-
blocking capacitor form a highpass filter with the
-3dB point determined 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-supply headphone amplifiers to block
the midrail DC component of the audio signal from the
headphones. Depending on the -3dB point, the filter
can attenuate low-frequency signals within the audio
band. Larger values of COUT reduce the attenuation,
but are physically larger, more expensive capacitors.
Figure 3 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 audio
band.
fRC
dB L OUT
−=
3
1
2
π
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
______________________________________________________________________________________ 11
+VDD
-VDD
GND
VOUT
CONVENTIONAL DRIVER-BIASING SCHEME
DirectDrive BIASING SCHEME
VDD/2
VDD
GND
VOUT
Figure 1. Conventional Amplifier Output Waveform vs.
MAX9720 Output Waveform
MAX9720
•The voltage coefficient of the capacitor, the change
in capacitance due to a change in the voltage
across the capacitor, distorts the audio signal. At
frequencies around the -3dB point, the reactance of
the capacitor dominates, and the voltage coefficient
appears as frequency-dependent distortion. Figure
4 shows the THD+N introduced by two different
capacitor dielectrics. Note that around the -3dB
point, THD+N increases dramatically.
The combination of low-frequency attenuation and fre-
quency-dependent distortion compromises audio
reproduction. DirectDrive improves low-frequency
reproduction in portable audio equipment that empha-
sizes low-frequency effects such as multimedia laptops
and MP3, CD, and DVD players.
Charge Pump
The MAX9720 features a low-noise charge pump. The
320kHz 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. Limiting the switching speed of the charge
pump minimizes the di/dt noise caused by the parasitic
bond wire and trace inductance. Although not typically
required, additional high-frequency ripple attenuation
can be achieved by increasing the size of C2 (see
Typical Application Circuit).
SmartSense
The SmartSense feature detects a short on either out-
put and automatically reconfigures the MAX9720 for
optimum power savings. If an output short circuit is
detected during the SmartSense routine, the shorted
channel is disabled, ALERT is asserted, and the device
is set to mono mode (assuming the other channel is not
shorted). SmartSense works by applying an inaudible
3µs test voltage pulse to the load. The resulting current
from the test pulse and load is sensed. If the load
impedance is less than 4Ω, the output is determined to
be a short.
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
12 ______________________________________________________________________________________
HEADPHONE DRIVER
MICROPHONE
AMPLIFIER
MICROPHONE
AMPLIFIER
OUTPUT
AUDIO
INPUT
AUDIO
INPUT
MICROPHONE
BIAS
MAX9720
Figure 2. Earbud Speaker/Microphone Combination Headset
Configuration
0
-30
0.01 0.1 1 10 100
LOW-FREQUENCY ROLLOFF
(RL = 16Ω)
-24
-27
-12
-15
-18
-21
-6
-9
-3
FREQUENCY (Hz)
ATTENUATION (dB)
DirectDrive
330µF
220µF
100µF
33µF
Figure 3. Low-Frequency Attenuation of Common DC-Blocking
Capacitor Values
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
Figure 4. Distortion Contributed by DC-Blocking Capacitors
Mode Selection (MODE_)
SmartSense is controlled by the two mode select
inputs, MODE1 and MODE2. Table 1 shows the operat-
ing modes in relation to the status of the MODE_ inputs.
When MODE1 = MODE2 = low, the device is in low-
power shutdown mode. When MODE1 = high and
MODE2 = low, the device is in forced mono mode. The
right channel is disabled, OUTR goes high impedance,
and the stereo audio input is mixed, and the audio sig-
nal is reproduced on OUTL. SmartSense is disabled in
this mode. When MODE1 = low and MODE2 = high, the
device is in forced stereo mode, and SmartSense is
disabled. When the device detects the presence of a
short BEFORE forced stereo mode is selected, the
device remains in mono mode (Figure 5). When
MODE1 = MODE2 = high, the device is in automatic
detection mode; the operating mode of the device is
determined by SmartSense.
MODE1 is also used to execute a host-controlled
SmartSense routine and reset the ALERT output. On the
rising edge of MODE1, the device invokes a
SmartSense routine. The falling edge of MODE1 resets
the ALERT output to its idle state.
Automatic Detection Mode
A fault condition is defined as a short (under 4Ω) on
either amplifier output to ground. SmartSense automati-
cally detects and disables the shorted output. The
mixer/attenuator combines the two stereo inputs (INL
and INR), attenuates the resultant signal by a factor of
2, and redirects the audio playback to the remaining
active channel. This allows for full reproduction of a
stereo signal through a single headphone while main-
taining optimum headroom. The mixed mono signal is
output only on the properly loaded channel. If both out-
puts are shorted then both outputs go into a high-
impedance state and no audio playback occurs. In
automatic detection mode (MODE1 = MODE2 = high),
any of the following events trigger a SmartSense test
sequence:
•HPS rises above 0.8 x VDD, indicating a headphone
jack has been inserted into the socket.
•The 180mA high-side (sourcing) overcurrent thresh-
old is approached, and the output is near GND.
•The die temperature exceeds the thermal limit
(+140°C).
•Power or shutdown is cycled.
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
______________________________________________________________________________________ 13
M1 = L
M2 = L
?
M1 = H
M2 = L
?
M1 = L
M2 = H
?
SHORT
DETECTED
?
STATUS
CHANGE
?
SHDN
SmartSense
FORCED MONO
FORCED STEREO
MONO MODE
STATUS
CHANGE
?
STATUS
CHANGE
?
STATUS
CHANGE
?
STEREO MODE
STATUS
CHANGE
?
N
N
N
N
N
N
N
N
N
Y
Y
Y
Y
Y
Y
Y
Y
Y
MAX9720
Figure 5. SmartSense Flow Diagram
MODE1 MODE2 SmartSense OPERATING
MODE
High High Enabled Automatic
detection mode
Low Low Disabled Shutdown
High Low Disabled Forced left mono
Low High Disabled Forced stereo
High Enabled Host controlled
X—Reset ALERT
Table 1. MAX9720 Operating Modes
MAX9720
For automatic headphone detection, connect HPS to the
control pin of a 3-wire headphone jack, as shown in
Figure 7. With no headphone present, the output imped-
ance of the amplifier pulls HPS to less than 0.8 x VDD.
When a headphone plug is inserted into the jack, the
control pin is disconnected from the tip contact, and
HPS is pulled to VDD through the internal 100kΩpullup.
A debounce delay controls the time between HPS going
high and the initiation of the SmartSense test sequence.
This time is controlled by an external capacitor on the
TIME pin and allows the user to customize the de-
bounce time (see the TIME Capacitor section).
Shutdown
Driving MODE1 and MODE2 to GND shuts down the
MAX9720, disconnects the internal HPS pullup resistor,
disables the charge pump and amplifiers, sets the
amplifier output impedance to 1kΩ, and reduces sup-
ply current to less than 6µA.
Forced Mono Mode
In forced left mono mode (MODE1 = high, MODE2 =
low), the right channel is disabled and OUTR goes high
impedance. The stereo signal inputs are combined
through the mixer/attenuator and output on the left
channel. In forced mono mode, the SmartSense routine
is disabled.
Forced Stereo Mode
In forced stereo mode (MODE1 = low, MODE2 = high),
the device operates as a stereo headphone amplifier.
In forced stereo mode, the SmartSense routine is dis-
abled.
AALLEERRTTOutput
The MAX9720 includes an active-low, open-drain
ALERT output that indicates to the master device that
SmartSense has detected a fault condition. ALERT trig-
gers when an output short circuit is detected through
the SmartSense routine. During normal operation,
ALERT idles high. If a fault condition is detected,
ALERT pulls the line low. ALERT remains low until
MODE1 is toggled from high to low.
Click-and-Pop Suppression
In conventional single-supply audio amplifiers, the out-
put-coupling capacitor is a major contributor of audible
clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically half
the supply. Likewise, during shutdown, the capacitor is
discharged to GND. A DC shift across the capacitor
results, which in turn appears as an audible transient at
the speaker. Since the MAX9720 does not require out-
put-coupling capacitors, no audible transient occurs.
Additionally, the MAX9720 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 that there are minimal spectral components in
the audible range at the output upon startup and shut-
down.
In most applications, the preamplifier output driving the
MAX9720 has a DC bias of typically half the supply.
During startup, the input-coupling capacitor is charged
to the preamplifier’s DC bias voltage through the input
resistor of the MAX9720, resulting in a DC shift across
the capacitor and an audible click/pop. Delaying the
startup of the MAX9720 by 4 to 5 time constants (80ms
to 100ms) based on RIN and CIN, relative to the startup
of the preamplifier, eliminates this click/pop caused by
the input filter.
If the SmartSense routine occurs during normal opera-
tion, a low-level audible transient may be heard. To pre-
vent this, a host-controlled SmartSense routine should
only be executed when ALERT asserts.
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
14 ______________________________________________________________________________________
TIP
(SIGNAL)
SLEEVE
(GND)
Figure 6. Typical 2-Wire (Mono) Headphone Plug
OUTR
OUTL 16
14
15
MAX9720
VDD
HPS
R1
100kΩ
Figure 7. HPS Configuration
Applications Information
Power Dissipation
Under normal operating conditions, linear power ampli-
fiers can dissipate a significant amount of power. The
maximum power dissipation for each package is given
in the Absolute Maximum Ratings section under
Continuous Power Dissipation or can be calculated by
the following equation:
where TJ(MAX) is +150°C, TAis the ambient temperature,
and θJA is the reciprocal of the derating factor in °C/W as
specified in the Absolute Maximum Ratings section. For
example, θJA of the TSSOP package is +106.38°C/W.
The MAX9720 has two power dissipation sources: the
charge pump and the two amplifiers. If the power dissipa-
tion for a given application exceeds the maximum
allowed for a given package, either reduce VDD, increase
load impedance, decrease the ambient temperature, or
add heat sinking to the device. Large output traces
improve the maximum power dissipation in the package.
Thermal overload protection limits total power dissipa-
tion in the MAX9720. When the junction temperature
exceeds +140°C, the thermal protection circuitry dis-
ables the amplifier output stage. The amplifiers are
enabled once the junction temperature cools by 15°C,
resulting in a pulsing output under continuous thermal
overload conditions.
Output Power
The MAX9720 is specified for the worst-case condi-
tion—when both inputs are in phase. Under this condi-
tion, the amplifiers simultaneously draw current from
the charge pump, leading to a slight loss in headroom
of VSS. In typical stereo audio applications, the left and
right signals present differences in both magnitude and
phase, subsequently leading to an increase in the max-
imum attainable output power. Figure 8 shows the two
extreme cases for in- and out-of-phase. In reality, the
available power lies between these extremes.
Powering Other Circuits from
a Negative Supply
An additional benefit of the MAX9720 is the internally
generated, negative supply voltage (PVSS). PVSS is the
negative supply for the MAX9720 headphone amplifiers.
PVSS can power other devices within a system. Limit the
current drawn from PVSS to 5mA. Exceeding this affects
the operation of the headphone amplifiers. A typical
application is a negative supply to adjust the contrast of
LCD modules.
The charge-pump voltage at PVSS is roughly propor-
tional to VDD and is not a regulated voltage. Consider
the charge-pump output impedance when powering
other devices from PVSS. See the Charge-Pump Output
Impedance graph in the Typical Operating
Characteristics. Use 2.2µF charge-pump capacitors for
the highest output power; 1µF or lower capacitors can
also be used for most applications. See the Output
Power vs. Load Resistance and Charge-Pump
Capacitance graph for details of the output power vs.
capacitor size.
Component Selection
Input Filtering
The input capacitor (CIN), in conjunction with the
MAX9720 input impedance, forms a highpass filter that
removes the DC bias from an incoming signal (see
Typical Application Circuit). The AC-coupling capacitor
allows the amplifier to bias the signal to an optimum DC
level. Assuming zero-source impedance, the
-3dB point of the highpass filter is given by:
RIN is the amplifier’s internal input impedance value
given in the Electrical Characteristics. Chose CIN such
that f-3dB is well below the lowest frequency of interest.
Setting f-3dB too high affects the amplifier’s low-fre-
quency response. Use capacitors whose dielectrics
have low-voltage coefficients, such as tantalum or alu-
minum electrolytic. Capacitors with high-voltage coeffi-
cients, such as ceramics, may result in increased
distortion at low frequencies.
fRC
dB IN IN
−=
3
1
2
π
P
TT
DISSPKG MAX
J MAX A
JA
()
()
=
−
θ
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
______________________________________________________________________________________ 15
100
0.001
04020 80 120 160140
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
0.01
0.1
1
10
OUTPUT POWER (mW)
THD+N (%)
60 100
VDD = 3V
AV = -1V/V
f = 1kHz
RL = 16Ω
OUTPUTS
IN PHASE
SINGLE-
CHANNEL
OUTPUTS
OUT OF
PHASE
Figure 8. THD+N vs. Output Power with Inputs In-/Out-of-Phase
MAX9720
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩfor opti-
mum performance. Low-ESR ceramic capacitors mini-
mize the output resistance of the charge pump. For
best performance over the extended temperature
range, select capacitors with an X7R dielectric. Table 2
lists suggested manufacturers.
Flying Capacitor (C1)
The value of the flying capacitor (C1) affects the charge
pump’s load regulation and output impedance. A C1
value that is too small degrades the device’s ability to
provide sufficient current drive, which leads to a loss of
output voltage. In most applications, 1µF for both C1
and C2 provides adequate performance. Increasing
the value of C1 improves load regulation and reduces
the charge-pump output resistance to an extent. See
the Output Power vs. Charge Pump Capacitance and
Load Resistance graph in the Typical Operating
Characteristics. Above 2.2µF, the on-resistance of the
switches and the ESR of C1 and C2 dominate.
Hold Capacitor (C2)
The hold capacitor value and ESR directly affect the
ripple on PVSS. Increasing the value of C2 reduces out-
put ripple. Likewise, decreasing the ESR of C2 reduces
both ripple and output impedance. Lower capacitance
values can be used in systems with low maximum out-
put power levels. See the Output Power vs. Charge-
Pump Capacitance and Load Resistance graph in the
Typical Operating Characteristics.
Power-Supply Bypass Capacitor
The power-supply bypass capacitor (C3) lowers the
output impedance of the power supply and reduces the
impact of the MAX9720’s charge-pump switching tran-
sients. Bypass VDD with C3, the same value as C1, and
place it physically close to the device.
TIME Capacitor
The TIME capacitor (CTIME) sets the HPS debounce
time. The debounce time is the delay between HPS
exceeding 0.8 x VDD and the execution of the
SmartSense routine. The delay ensures that any exces-
sive contact bounce caused by the insertion of a head-
phone plug into the jack does not cause HPS to
register an invalid state (Figure 9). The value of the
CTIME in nF equals the nominal delay time in ms, i.e.,
CTIME = 10nF = tDELAY = 10ms. CTIME values in the
200nF to 600nF range are recommended.
Adding Volume Control
The addition of a digital potentiometer provides simple,
digital volume control. Figure 10 shows the MAX9720
with the MAX5408 dual log taper digital potentiometer
used as an input attenuator. Connect the high terminal
of the MAX5408 to the audio input, the low terminal to
GND, and the wiper to CIN. Setting the wiper to the top
position passes the audio signal unattenuated. Setting
the wiper to the lowest position fully attenuates the input.
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 all components
associated with the charge pump (C2 and C3) to the
PGND plane. Connect PVSS and SVSS together at the
device. Bypassing of both the positive and negative
supplies is accomplished by the charge-pump capaci-
tors, C2 and C3 (see Typical Application Circuit). Place
capacitors C1 and C3 as close to the device as possi-
ble. Place capacitor C2 as close to PVSS as possible.
Route PGND and all traces that carry switching tran-
sients away from SGND, traces, and components in the
audio signal path.
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
16 ______________________________________________________________________________________
SUPPLIER PHONE FAX WEBSITE
Taiyo Yuden 800-348-2498 847-925-0899 www.t-yuden.com
TDK 847-803-6100 847-390-4405 www.component.tdk.com
Table 2. Suggested Capacitor Manufacturers
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, printed circuit
board techniques, bump-pad layout, and the recom-
mended reflow temperature profile, as well as the latest
information on reliability testing results, go to Maxim’s
website at www.maxim-ic.com/ucsp and look up
Application Note: UCSP—A Wafer-Level Chip-Scale
Package.
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
______________________________________________________________________________________ 17
tDELAY
3.1µs
70mV
OUT_
HPS
HEADPHONE
INSERTED
Figure 9. HPS Debouncing Delay
OUTL
MAX9720
INL
9
MAX5408
H0
L0
5
6
W0A 7
LEFT AUDIO
INPUT
11
W1A 10
CIN
CIN
RIGHT AUDIO
INPUT
INR OUTR 14
16
H1
L1
12
11
Figure 10. MAX9720 and MAX5408 Volume Control Circuit
Chip Information
TRANSISTOR COUNT: 4858
PROCESS: BiCMOS
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
VDD OUTL
HPS
OUTR
SVSS
SGND
INR
TIME
INL
TOP VIEW
TOP VIEW
(BUMP SIDE DOWN)
MAX9720
TSSOP
MODE1
C1P
PVSS
PGND
C1N
MODE2
ALERT
UCSP
A
B
C
D
1234
PVSS ALERT INL INR
C1N MODE2 TIME SGND
PGND MODE1 HPS SVSS
C1P VDD OUTL OUTR
Pin Configurations
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
18 ______________________________________________________________________________________
MAX4365
OUT+
OUT-
IN
BIAS
VDD
SHDN
15kΩ
15kΩ
VDD
0.1µF
0.1µF
15kΩ
0.1µF
1µF
220nF
MAX4063
MAX9720 OUTL
HPS
OUTR
C1P CIN
PVSS
SVSS
MODE1
MODE2
1µF
1µF
100kΩ
10kΩ
1µF
INL
INR
ALERT
TIME
AUX_IN
BIAS
IN+
IN-
2.2kΩ
2.2kΩ
0.1µF
0.1µF
VDD
0.1µF
CODEC/
BASEBAND
PROCESSOR
µC
OUT
OUT
1µF
1µF
VDD
VDD
VDD
System Diagram
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
______________________________________________________________________________________ 19
CHARGE
PUMP
UVLO
AND
SHUTDOWN
CONTROL
CLICK-AND-POP
SUPPRESSION
SmartSense
AND
HEADPHONE
DETECTION
MIXER
ATTENUATOR
AND
GAIN SETTING
MIXER
ATTENUATOR
AND
GAIN SETTING
C1N
C1P
PVSS SVSS PGND SGND TIME INR
VDD
SVSS
VDD
SGND
INL
MODE1 MODE2
LOGIC
CONTROL
ALERT
R4
10kΩ
OUTR
LEFT-
CHANNEL
AUDIO INPUT
RIGHT-
CHANNEL
AUDIO INPUT
1
(D2)
2
(C2)
7
(B2)
8
(A2)
3
(D1)
4
(C1)
5
(B1)
6
(A1)
13
(C4)
16
(D3)
15
(C3)
9
(A3)
14
(D4)
12
(B4)
10
(B3)
MAX9720
C1
1µF
C2
1µFC4
220nF
( ) UCSP BUMP.
1.8V TO 3.8V
C3
1µF
CIN
1µF
SVSS
VDD
VDD
HPS
OUTL
CIN
1µF
11
(A4)
SGND
R1
100kΩ
Typical Application Circuit
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.)
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
20 ______________________________________________________________________________________
16L,UCSP.EPS
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and 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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 21
© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
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.)
TSSOP4.40mm.EPS
