MAXIM MAX9720AEUE

19-2859; Rev 0; 4/03
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
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
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 disabled 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
16Ω load 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.
Ordering Information
PIN/BUMPPACKAGE
GAIN
(V/V)
PART
TEMP RANGE
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
16 TSSOP
-1.41
o
MAX9720BEUE
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 temperature 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.
o
-40 C to +85 C
Simplified Block Diagram
3.6V TO 1.8V
SUPPLY
Applications
MAX9720
RIN
PDAs
Cellular Phones
Smart Phones
Tablet PCs
MP3 Players
Notebook PCs
Portable Audio Equipment
SmartSense and UCSP are trademarks of Maxim Integrated
Products, Inc.
ROUT
+
LIN
SmartSense
HPS
MODE1
MODE2
ALERT
LOUT
Pin Configuration and Typical Application Circuit 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
MAX9720
General Description
The MAX9720 stereo headphone amplifier combines
Maxim’s patented DirectDrive architecture and
SmartSense™, an automatic mono/stereo detection feature. Conventional headphone amplifiers require a bulky
DC-blocking capacitor between the headphone and the
amplifier. DirectDrive produces a ground-referenced output from a single supply, eliminating the need for large
DC-blocking capacitors, saving cost, board space, and
component height.
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
ABSOLUTE MAXIMUM RATINGS
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
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 = 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
3.6
V
Stereo mode
5
8.4
Mono mode (MODE1 = VDD, MODE2 = GND)
3
GENERAL
Supply Voltage Range
Supply Current
Shutdown Supply Current
Turn-On/Turn-Off Time
VDD
IDD
ISHDN
Inferred from PSRR test
1.8
MODE1 = MODE2 = GND
6
tS
10
250
mA
µA
µs
CHARGE PUMP
Oscillator Frequency
fOSC
272
320
368
kHz
HEADPHONE AMPLIFIERS
Voltage Gain
AV
Gain Match
∆AV
Total Output Offset Voltage
(Note 3)
VOS
Input Resistance
RIN
MAX9720A
-1.02
-1
-0.98
MAX9720B
-1.443
-1.415
-1.386
Output Power
2
PSRR
POUT
%
MAX9720A
-5
-0.8
+3.6
MAX9720B
-6.5
-1
+4.5
10
15
20
76
92
1.8V ≤ VDD ≤ 3.6V
(Note 3)
Power-Supply Rejection Ratio
±1
Between OUTL and OUTR
VDD = 3.0V,
200mVP-P ripple
(Note 3)
THD+N = 1%, fIN =
1kHz, TA = +25°C
DC
fRIPPLE = 217Hz
92
fRIPPLE = 1kHz
86
fRIPPLE = 20kHz
61
RL = 32Ω
50
RL = 16Ω
32
50
_______________________________________________________________________________________
V/V
mV
kΩ
dB
mW
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
(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
Total Harmonic Distortion Plus
Noise
SYMBOL
THD+N
Signal-to-Noise Ratio
SNR
Slew Rate
SR
Maximum Capacitive Load
CL
Crosstalk
CONDITIONS
fIN = 1kHz
MIN
TYP
RL = 32Ω,
POUT = 30mW
0.003
RL = 16Ω,
POUT = 30mW
0.005
MAX
UNITS
%
fIN = 1kHz, VOUT = 0.5VRMS, RL = 16Ω,
BW = 22Hz to 22kHz
97
dB
0.8
V/µs
No sustained oscillations
150
pF
75
dB
RL = 32Ω, POUT = 1mW, fIN = 10kHz
Thermal Shutdown Threshold
140
o
C
Thermal Shutdown Hysteresis
15
o
C
SmartSense
Shorted Load Threshold
RSMS
Pulse Duration
tSMS
2.4
4
5.6
3.1
Ω
µs
DEBOUNCE TIME (TIME)
TIME Charging Current
ITIME
TIME Discharge Switch
Resistance
RTIME
TIME Threshold
VTIME
0.7
HPS = GND
1.1
4
1
1.1
1.8
µA
10
kΩ
1.2
V
HEADPHONE SENSE INPUT (HPS)
VIH
HPS Threshold
0.9 x
VDD
V
0.7 x
VDD
VIL
Input Leakage Current
Input Capacitance
IIL
±1
MODE1= MODE2 = GND
CIN
10
µA
pF
ALERT
Output Current High
IOH
VALERT = VDD
Output Voltage Low
VOL
IOL = 3mA
1
µA
0.4
V
MODE_ INPUT
VIH
MODE_ Thresholds
0.7 x
VDD
VIL
MODE_ Input Leakage Current
V
0.3 x
VDD
±1
µA
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.
_______________________________________________________________________________________
3
MAX9720
ELECTRICAL CHARACTERISTICS (continued)
Typical Operating Characteristics
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
VDD = 3V
AV = -1V/V
RL = 16Ω
VDD = 3V
AV = -1V/V
RL = 32Ω
1
THD+N (%)
POUT = 10mW
POUT = 10mW
0.01
VDD = 3V
AV = -1.41V/V
RL = 16Ω
0.1
THD+N (%)
0.1
THD+N (%)
0.1
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc03
1
MAX9720 toc01
1
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
MAX9720 toc02
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.01
POUT = 40mW
POUT = 10mW
0.01
POUT = 40mW
POUT = 40mW
0.001
1k
10k
100k
0.001
10
100
1k
10k
FREQUENCY (Hz)
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
VDD = 3V
AV = -1.41V/V
RL = 32Ω
1
100k
10
VDD = 1.8V
AV = -1V/V
RL = 16Ω
POUT = 40mW
0.01
VDD = 1.8V
AV = -1V/V
RL = 32Ω
THD + N (%)
POUT = 2mW
POUT = 9mW
1k
10k
0.001
10
100k
100
1k
10k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
1
VDD = 3V
AV = -1.41V/V
RL = 32Ω
10
THD+N (%)
POUT = 9mW
0.01
1k
10k
POUT = 2mW
1
OUTPUTS
OUT OF
PHASE
0.1
0.01
VDD = 3V
AV = -1V/V
f = 20Hz
RL = 16Ω
0.01
POUT = 9mW
0.001
0.001
10
100
1k
FREQUENCY (Hz)
4
10k
100k
100k
OUTPUTS
IN PHASE
0.1
POUT = 2mW
100
100
THD+N (%)
0.1
10
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc08
FREQUENCY (Hz)
VDD = 3V
AV = -1.41V/V
RL = 16Ω
100k
POUT = 9mW
FREQUENCY (Hz)
FREQUENCY (Hz)
MAX9720 toc07
1
100
POUT = 2mW
0.01
0.001
10
100k
MAX9720 toc06
1
0.01
0.001
10k
0.1
THD+N (%)
THD+N (%)
POUT = 10mW
1k
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. FREQUENCY
0.1
0.1
100
FREQUENCY (Hz)
MAX9720 toc05
1
100
MAX9720 toc04
10
MAX9720 toc09
0.001
THD+N (%)
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
0.001
10
100
1k
FREQUENCY (Hz)
10k
100k
0
30
60
90
OUTPUT POWER (mW)
_______________________________________________________________________________________
120
150
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
OUTPUTS
OUT OF
PHASE
VDD = 3V
AV = -1V/V
f = 1kHz
RL = 16Ω
0.01
30
60
90
120
150
0.001
0
30
60
90
120
150
0
80
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
OUTPUTS
IN PHASE
1
OUTPUTS
OUT OF
PHASE
0.1
0.01
0.001
40
60
80
100
1
OUTPUTS
OUT OF
PHASE
0.1
VDD = 3V
AV = -1.41V/V
f = 20Hz
RL = 16Ω
0.01
0.001
20
OUTPUTS
IN PHASE
10
THD+N (%)
THD+N (%)
10
MAX9720 toc15
VDD = 3V
AV = -1V/V
f = 10kHz
RL = 32Ω
0.001
0
20
40
60
80
100
0
30
60
90
120
OUTPUT POWER (mW)
OUTPUT POWER (mW)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
VDD = 3V
AV = -1.41V/V
f = 1kHz
RL = 16Ω
0.01
0.001
60
90
OUTPUT POWER (mW)
120
150
1
OUTPUTS
OUT OF
PHASE
0.1
VDD = 3V
AV = -1.41V/V
f = 10kHz
RL = 16Ω
0.01
0.001
0
30
60
90
OUTPUT POWER (mW)
120
150
150
100
OUTPUTS
IN PHASE
10
THD+N (%)
OUTPUTS
OUT OF
PHASE
OUTPUTS
IN PHASE
10
THD+N (%)
OUTPUTS
IN PHASE
30
100
MAX9720 toc16
100
100
100
MAX9720 toc14
MAX9720 toc13
100
VDD = 3V
AV = -1V/V
f = 1kHz
RL = 32Ω
0.01
0
60
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
OUTPUTS
OUT OF
PHASE
0.1
40
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
1
1
20
OUTPUT POWER (mW)
OUTPUTS
IN PHASE
10
VDD = 3V
AV = -1V/V
f = 20Hz
RL = 32Ω
0.01
OUTPUT POWER (mW)
10
0
OUTPUTS
OUT OF
PHASE
0.1
OUTPUT POWER (mW)
100
0.1
OUTPUTS
IN PHASE
1
VDD = 3V
AV = -1V/V
f = 10kHz
RL = 16Ω
0.001
0
THD+N (%)
OUTPUTS
OUT OF
PHASE
0.01
0.001
THD+N (%)
1
0.1
10
MAX9720 toc18
0.1
OUTPUTS
IN PHASE
THD+N (%)
THD+N (%)
1
10
MAX9720 toc11
OUTPUTS
IN PHASE
100
MAX9720 toc17
THD+N (%)
10
100
MAX9720 toc10
100
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc12
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
1
OUTPUTS
OUT OF
PHASE
0.1
VDD = 3V
AV = -1.41V/V
f = 20Hz
RL = 32Ω
0.01
0.001
0
20
40
60
80
100
120
OUTPUT POWER (mW)
_______________________________________________________________________________________
5
MAX9720
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
0.1
VDD = 3V
AV = -1.41V/V
f = 10kHz
RL = 32Ω
20
40
60
80
100
120
VDD = 1.8V
AV = -1V/V
f = 20Hz
RL = 16Ω
0.001
0
20
40
60
80
100
0
120
10
20
30
40
50
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
OUTPUTS
OUT OF
PHASE
0.1
OUTPUTS
OUT OF
PHASE
0.001
10
20
30
50
40
0
10
20
30
1
0.1
VDD = 1.8V
AV = -1V/V
f = 20Hz
RL = 32Ω
0.001
0
50
40
OUTPUTS
OUT OF
PHASE
0.01
0.001
0
OUTPUTS
IN PHASE
10
VDD = 1.8V
AV = -1V/V
f = 10kHz
RL = 16Ω
0.01
MAX9720 toc24
1
0.1
VDD = 1.8V
AV = -1V/V
f = 1kHz
RL = 16Ω
0.01
OUTPUTS
IN PHASE
THD+N (%)
THD+N (%)
1
10
100
MAX9720 toc23
100
MAX9720 toc22
10
5
10
15
20
25
30
OUTPUT POWER (mW)
OUTPUT POWER (mW)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
VDD = 1.8V
AV = -1V/V
f = 1kHz
RL = 32Ω
0.01
10
15
20
25
OUTPUT POWER (mW)
30
1
OUTPUTS
OUT OF
PHASE
0.1
VDD = 1.8V
AV = -1V/V
f = 10kHz
RL = 32Ω
35
MAX9720 toc27
10
1
OUTPUTS
OUT OF
PHASE
0.1
VDD = 1.8V
AV = -1.41V/V
f = 20Hz
RL = 16Ω
0.01
0.001
35
OUTPUTS
IN PHASE
OUTPUTS
IN PHASE
0.01
0.001
100
THD+N (%)
OUTPUTS
OUT OF
PHASE
5
10
THD+N (%)
OUTPUTS
IN PHASE
10
100
MAX9720 toc25
100
0
0.1
OUTPUT POWER (mW)
OUTPUTS
IN PHASE
0.1
OUTPUTS
OUT OF
PHASE
OUTPUT POWER (mW)
100
1
1
0.01
0.001
0
THD+N (%)
OUTPUTS
OUT OF
PHASE
0.01
0.001
6
1
VDD = 3V
AV = -1.41V/V
f = 1kHz
RL = 32Ω
0.01
10
OUTPUTS
IN PHASE
THD+N (%)
THD+N (%)
OUTPUTS
OUT OF
PHASE
0.1
10
OUTPUTS
IN PHASE
MAX9720 toc26
THD+N (%)
1
100
MAX9720 toc20
OUTPUTS
IN PHASE
10
100
MAX9720 toc19
100
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc21
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
THD+N (%)
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
0.001
0
5
10
15
20
25
OUTPUT POWER (mW)
30
35
0
10
20
30
OUTPUT POWER (mW)
_______________________________________________________________________________________
40
50
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
0
10
20
30
50
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
THD+N (%)
OUTPUTS
OUT OF
PHASE
VDD = 1.8V
AV = -1.41V/V
f = 1kHz
RL = 32Ω
0.01
1
VDD = 1.8V
AV = -1.41V/V
f = 10kHz
RL = 32Ω
0.01
0.001
160
15
20
25
30
35
40
0
5
OUTPUT POWER (mW)
OUTPUT POWER vs. SUPPLY VOLTAGE
25
30
35
140
OUTPUT POWER (mW)
80
60
40
20
0
2.1
2.4
2.7
3.0
SUPPLY VOLTAGE (V)
STEREO
IN PHASE
80
60
0
40
1.8
2.1
fIN = 1kHz
RL = 32Ω
THD+N = 1%
STEREO
OUT OF
PHASE
120
100
80
3.3
3.6
2.4
2.7
3.0
3.3
3.6
OUTPUT POWER vs. SUPPLY VOLTAGE
STEREO
IN PHASE
60
160
140
fIN = 1kHz
RL = 32Ω
THD+N = 10%
120
100
STEREO
OUT OF
PHASE
STEREO
IN PHASE
80
60
40
40
20
20
0
1.8
100
SUPPLY VOLTAGE (V)
160
MAX9720 toc34
STEREO
OUT OF
PHASE
STEREO
IN PHASE
100
20
40
120
OUTPUT POWER vs. SUPPLY VOLTAGE
140
120
15
35
STEREO
OUT OF
PHASE
140
OUTPUT POWER (mW)
200
fIN = 1kHz
RL = 16Ω
THD+N = 10%
10
30
20
OUTPUT POWER (mW)
10
25
40
MAX9720 toc35
5
20
fIN = 1kHz
RL = 16Ω
THD+N = 1%
180
0.001
0
15
200
MAX9720 toc32
OUTPUTS
OUT OF
PHASE
0.1
10
OUTPUT POWER vs. SUPPLY VOLTAGE
OUTPUTS
IN PHASE
10
5
0
OUTPUT POWER (mW)
100
MAX9720 toc31
OUTPUTS
IN PHASE
0.1
OUTPUT POWER (mW)
40
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
1
160
30
OUTPUT POWER (mW)
10
180
20
OUTPUT POWER (mW)
100
THD+N (%)
0.001
10
0
50
40
VDD = 1.8V
AV = -1.41V/V
f = 20Hz
RL = 32Ω
0.01
0.001
0.001
0.1
VDD = 1.8V
AV = -1.41V/V
f = 10kHz
RL = 16Ω
0.01
OUTPUTS
OUT OF
PHASE
MAX9720 toc33
VDD = 1.8V
AV = -1.41V/V
f = 1kHz
RL = 16Ω
0.01
0.1
1
MAX9720 toc36
0.1
THD+N (%)
OUTPUTS
OUT OF
PHASE
OUTPUTS
OUT OF
PHASE
1
OUTPUTS
IN PHASE
10
OUTPUT POWER (mW)
1
THD+N (%)
10
OUTPUTS
IN PHASE
10
100
MAX9720 toc29
OUTPUTS
IN PHASE
THD+N (%)
100
MAX9720 toc28
100
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
MAX9720 toc30
TOTAL HARMONIC DISTORTION
PLUS NOISE vs. OUTPUT POWER
0
1.8
2.1
2.4
2.7
3.0
SUPPLY VOLTAGE (V)
3.3
3.6
1.8
2.1
2.4
2.7
3.0
3.3
3.6
SUPPLY VOLTAGE (V)
_______________________________________________________________________________________
7
MAX9720
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
80
60
40
100
60
INPUTS
IN PHASE
100
100
15
INPUTS
IN PHASE
10
300
RL = 16Ω
250
200
150
100
RL = 32Ω
VDD = 3V
f = 1kHz
POUT = POUTL + POUTR
50
5
POWER DISSIPATION (mW)
20
10
100
150
200
OUTPUT POWER (mW)
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
POWER-SUPPLY REJECTION RATIO
vs. FREQUENCY
VDD = 1.8V
VRIPPLE = 200mVP-P
-10
-20
-40
-50
-60
-80
-90
100
1k
FREQUENCY (Hz)
10k
100k
0
-10
-20
10
100
1k
FREQUENCY (Hz)
10k
40
60
VDD = 3V
RL = 32Ω
VIN = 200mVP-P
80
-30
-40
-50
-60
-70
RIGHT-TO-LEFT
CHANNEL
-80
-90
-100
LEFT-TO-RIGHT
CHANNEL
-110
-120
-100
10
20
CROSSTALK vs. FREQUENCY
-70
-100
-110
-120
VDD = 1.8V
f = 1kHz
POUT = POUTL + POUTR
0
CROSSTALK (dB)
PSRR (dB)
-70
-80
-90
RL = 32Ω
OUTPUT POWER (mW)
-30
-40
-50
-60
50
250
MAX9720 toc44
0
MAX9720 toc43
VDD = 3V
VRIPPLE = 200mVP-P
-10
-20
-30
50
LOAD RESISTANCE (Ω)
0
75
0
0
100
RL = 16Ω
100
25
0
0
MAX9720 toc39
POWER DISSIPATION vs. OUTPUT POWER
125
MAX9720 toc41
MAX9720 toc40
VDD = 1.8V
f = 1kHz
THD+N = 10%
100
LOAD RESISTANCE (Ω)
350
POWER DISSIPATION (mW)
OUTPUT POWER (mW)
25
INPUTS
IN PHASE
10
POWER DISSIPATION vs. OUTPUT POWER
OUTPUT POWER vs. LOAD RESISTANCE
30
15
LOAD RESISTANCE (Ω)
40
INPUTS
OUT OF
PHASE
INPUTS
OUT OF
PHASE
20
0
10
LOAD RESISTANCE (Ω)
35
25
5
0
10
30
10
20
0
8
MAX9720 toc38
80
40
INPUTS
IN PHASE
20
INPUTS
OUT OF
PHASE
120
VDD = 1.8V
f = 1kHz
THD+N = 1%
35
MAX9720 toc42
100
f = 1kHz
THD+N = 10%
140
OUTPUT POWER vs. LOAD RESISTANCE
40
OUTPUT POWER (mW)
120
f = 1kHz
THD+N = 1%
MAX9720 toc37
INPUTS
OUT OF
PHASE
OUTPUT POWER (mW)
OUTPUT POWER (mW)
140
OUTPUT POWER vs. LOAD RESISTANCE
160
100k
MAX9720 toc45
OUTPUT POWER vs. LOAD RESISTANCE
160
PSRR (dB)
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
10
100
1k
FREQUENCY (Hz)
_______________________________________________________________________________________
10k
100k
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
4
AV = -1V/V
RIGHT-TO-LEFT
CHANNEL
1
0
-1
-2
6
4
2
-4
ILOAD = 10mA
-5
1k
10k
0
0.01
100k
0.1
FREQUENCY (Hz)
10
100
1k
10k
OUTPUT SPECTRUM vs. FREQUENCY
OUTPUT SPECTRUM (dB)
1µF
40
30
0.47µF
20
fIN = 1kHz
THD+N = 1%
OUTPUTS
IN PHASE
VIN = 1VP-P
RL = 32Ω
fIN = 1kHz
-20
-40
-60
-80
40
1k
10k
LOAD RESISTANCE (Ω)
FREQUENCY (Hz)
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
EXITING SHUTDOWN
8
7
3.6
5
STEREO MODE
4
3
MONO MODE
2
100k
1.8
2.1
2.4
2.7
3.0
3.3
3.6
SUPPLY VOLTAGE (V)
POWER-UP/DOWN WAVEFORM
MAX9720 toc54
MAX9720 toc53
MAX9720 toc52
9
3.3
0
100
50
3.0
1
-120
30
2.7
SUPPLY CURRENT vs. SUPPLY VOLTAGE
-100
0
2.4
6
SUPPLY CURRENT (mA)
2.2µF
50
20
2.1
SUPPLY VOLTAGE (V)
0
MAx9720 toc49
60
10
1.8
FREQUENCY (Hz)
OUTPUT POWER vs. LOAD RESISTANCE
AND CHARGE-PUMP CAPACITOR SIZE
10
1
MAX9720 toc50
100
10
OUTPUT POWER (mW)
8
-3
LEFT-TO-RIGHT
CHANNEL
-120
SUPPLY CURRENT (µA)
10
MAX9720 toc51
-80
-90
-100
-110
12
OUTPUT IMPEDANCE (Ω)
3
2
-40
-50
-60
-70
14
MAX9720 toc47
VDD = 1.8V
RL = 32Ω
VIN = 200mVP-P
GAIN (dB)
CROSSTALK (dB)
5
MAX9720 toc46
0
-10
-20
-30
CHARGE-PUMP OUTPUT IMPEDANCE
vs. SUPPLY VOLTAGE
GAIN FLATNESS vs. FREQUENCY
MAx9720 toc48
CROSSTALK vs. FREQUENCY
MAX9720
Typical Operating Characteristics (continued)
(VDD = 3V, THD+N bandwidth = 22Hz to 22kHz, MODE1 = MODE2 = VDD.)
3V
3V
MODE1 AND
MODE2
VDD
0V
6
0V
100dB
5
10mV/div
OUT_
4
OUT_
3
500mV/div
2
20dB/div
OUT_FFT
1
0
1.8
2.1
2.4
2.7
3.0
SUPPLY VOLTAGE (V)
3.3
400µs/div
3.6
fIN = 1kHz
RL = 32Ω
VIN = GND
RL = 32Ω
200ms/div
FFT: 25Hz/div
_______________________________________________________________________________________
9
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
MAX9720
Pin Description
PIN
BUMP
TSSOP
UCSP
1
D2
VDD
2
C2
MODE1
3
D1
C1P
4
C1
PGND
Power Ground. Connect to SGND.
5
B1
C1N
Flying Capacitor Negative Terminal
6
A1
PVSS
Charge-Pump Output
7
B2
MODE2
Mode Select 2 Logic Input
8
A2
ALERT
Open-Drain Interrupt Logic Output
NAME
FUNCTION
Positive Power Supply
Mode Select 1 Logic Input
Flying Capacitor Positive Terminal
9
A3
INL
10
B3
TIME
Left-Channel Audio Input
11
A4
INR
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
16
D3
OUTL
Debouncing Timer Capacitor
Right-Channel Audio Input
Headphone Sense Input
Left-Channel Output
Detailed Description
The MAX9720 fixed-gain, stereo headphone amplifier
includes Maxim’s patented DirectDrive architecture and
SmartSense. DirectDrive eliminates the large outputcoupling capacitors required by conventional singlesupply 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 (V DD ), 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 elimi10
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 channel. The device also features an ALERT output that indicates 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
VDD
VOUT
VDD/2
GND
CONVENTIONAL DRIVER-BIASING SCHEME
+VDD
VOUT
GND
-VDD
DirectDrive BIASING SCHEME
Figure 1. Conventional Amplifier Output Waveform vs.
MAX9720 Output Waveform
DirectDrive
Conventional single-supply headphone amplifiers have
their outputs biased about a nominal DC voltage (typically half the supply) for maximum dynamic range. Large
coupling capacitors are needed to block this DC bias
from the headphone. 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 amplifier.
Maxim’s patented DirectDrive architecture uses a
charge pump to create an internal negative supply voltage. 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 ceramic capacitors (1µF typ), conserving board space,
reducing cost, and improving the frequency response
of the headphone amplifier. See the Output Power vs.
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 speaker 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 DCblocking capacitors limit the low-frequency response of
the amplifier and distort the audio signal:
• The impedance of the headphone load and the DCblocking capacitor form a highpass filter with the
-3dB point determined by:
f−3dB =
1
2πRLCOUT
where R L 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-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 16Ω headphone with a 100µF
blocking capacitor is 100Hz, well within the audio
band.
______________________________________________________________________________________
11
MAX9720
Charge-Pump Capacitance and Load Resistance
graph in the Typical Operating Characteristics for
details of the possible capacitor sizes.
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 frequency-dependent distortion compromises audio
reproduction. DirectDrive improves low-frequency
reproduction in portable audio equipment that emphasizes 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 output 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.
LOW-FREQUENCY ROLLOFF
(RL = 16Ω)
0
-3
DirectDrive
-6
ATTENUATION (dB)
•
-9
330µF
-12
220µF
-15
100µF
-18
33µF
-21
-24
-27
-30
0.01
0.1
1
10
100
FREQUENCY (Hz)
MICROPHONE
BIAS
MICROPHONE
AMPLIFIER
Figure 3. Low-Frequency Attenuation of Common DC-Blocking
Capacitor Values
MICROPHONE
AMPLIFIER
OUTPUT
ADDITIONAL THD+N DUE
TO DC-BLOCKING CAPACITORS
10
AUDIO
INPUT
AUDIO
INPUT
1
MAX9720
THD+N (%)
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
0.1
TANTALUM
0.01
0.001
ALUM/ELEC
0.0001
HEADPHONE DRIVER
10
100
1k
10k
100k
FREQUENCY (Hz)
Figure 2. Earbud Speaker/Microphone Combination Headset
Configuration
12
Figure 4. Distortion Contributed by DC-Blocking Capacitors
______________________________________________________________________________________
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
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 threshold is approached, and the output is near GND.
• The die temperature exceeds the thermal limit
(+140°C).
•
Power or shutdown is cycled.
MAX9720
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.
M1 = L
M2 = L
?
N
Y
SHDN
STATUS
CHANGE
?
N
Automatic Detection Mode
A fault condition is defined as a short (under 4Ω) on
either amplifier output to ground. SmartSense automatically 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 maintaining optimum headroom. The mixed mono signal is
output only on the properly loaded channel. If both outputs are shorted then both outputs go into a highimpedance state and no audio playback occurs. In
automatic detection mode (MODE1 = MODE2 = high),
M1 = H
M2 = L
?
N
Y
FORCED MONO
STATUS
CHANGE
?
N
M1 = L
M2 = H
?
N
Y
N
SHORT
DETECTED
?
N
OPERATING
MODE
MODE2
SmartSense
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
—
Y
N
STATUS
CHANGE
?
STATUS
CHANGE
?
Y
MONO MODE
N
STEREO MODE
Y
FORCED STEREO
Table 1. MAX9720 Operating Modes
MODE1
Y
STATUS
CHANGE
?
Y
Y
Reset ALERT
Figure 5. SmartSense Flow Diagram
______________________________________________________________________________________
13
MAX9720
Mode Selection (MODE_)
SmartSense is controlled by the two mode select
inputs, MODE1 and MODE2. Table 1 shows the operating modes in relation to the status of the MODE_ inputs.
When MODE1 = MODE2 = low, the device is in lowpower 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 signal 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.
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
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 impedance 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 100kΩ pullup.
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 debounce 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 supply 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 disabled.
ALERT Output
The MAX9720 includes an active-low, open-drain
ALERT output that indicates to the master device that
SmartSense has detected a fault condition. ALERT triggers 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 output-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 output-coupling capacitors, no audible transient occurs.
14
TIP
(SIGNAL)
SLEEVE
(GND)
Figure 6. Typical 2-Wire (Mono) Headphone Plug
VDD
MAX9720
R1
100kΩ
HPS
OUTL
OUTR
15
16
14
Figure 7. HPS Configuration
Additionally, the MAX9720 features extensive click-andpop 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 shutdown.
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 operation, a low-level audible transient may be heard. To prevent this, a host-controlled SmartSense routine should
only be executed when ALERT asserts.
______________________________________________________________________________________
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
TOTAL HARMONIC DISTORTION PLUS
NOISE vs. OUTPUT POWER
Power Dissipation
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 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 dissipation 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 dissipation in the MAX9720. When the junction temperature
exceeds +140°C, the thermal protection circuitry disables 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 condition—when both inputs are in phase. Under this condition, 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 maximum 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.
100
OUTPUTS
IN PHASE
10
THD+N (%)
Under normal operating conditions, linear power amplifiers 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:
TJ(MAX) − TA
PDISSPKG(MAX) =
θJA
MAX9720
Applications Information
OUTPUTS
OUT OF
PHASE
1
SINGLECHANNEL
0.1
VDD = 3V
AV = -1V/V
f = 1kHz
RL = 16Ω
0.01
0.001
0
20
40
60
80
100 120 140 160
OUTPUT POWER (mW)
Figure 8. THD+N vs. Output Power with Inputs In-/Out-of-Phase
The charge-pump voltage at PVSS is roughly proportional 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 (C IN ), 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:
f−3dB =
1
2πRINCIN
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-frequency response. Use capacitors whose dielectrics
have low-voltage coefficients, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as ceramics, may result in increased
distortion at low frequencies.
______________________________________________________________________________________
15
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
Table 2. Suggested Capacitor Manufacturers
PHONE
FAX
Taiyo Yuden
SUPPLIER
800-348-2498
847-925-0899
www.t-yuden.com
TDK
847-803-6100
847-390-4405
www.component.tdk.com
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mΩ for optimum performance. Low-ESR ceramic capacitors minimize 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 output ripple. Likewise, decreasing the ESR of C2 reduces
both ripple and output impedance. Lower capacitance
values can be used in systems with low maximum output power levels. See the Output Power vs. ChargePump 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 transients. Bypass VDD with C3, the same value as C1, and
place it physically close to the device.
16
WEBSITE
TIME Capacitor
The TIME capacitor (CTIME) sets the HPS debounce
time. The debounce time is the delay between HPS
exceeding 0.8 x V DD and the execution of the
SmartSense routine. The delay ensures that any excessive contact bounce caused by the insertion of a headphone 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 capacitors, C2 and C3 (see Typical Application Circuit). Place
capacitors C1 and C3 as close to the device as possible. Place capacitor C2 as close to PVSS as possible.
Route PGND and all traces that carry switching transients away from SGND, traces, and components in the
audio signal path.
______________________________________________________________________________________
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
MAX9720
LEFT AUDIO 5 H0
INPUT
HEADPHONE
INSERTED
CIN
9
W0A 7
HPS
6
OUTL
16
MAX9720
MAX5408
tDELAY
RIGHT AUDIO 12 H1
INPUT
3.1µs
INL
L0
CIN
W1A 10
11
INR
OUTR
14
11 L1
70mV
OUT_
Figure 9. HPS Debouncing Delay
Figure 10. MAX9720 and MAX5408 Volume Control Circuit
Pin Configurations
TOP VIEW
VDD 1
16 OUTL
MODE1 2
15 HPS
14 OUTR
C1P 3
MAX9720
PGND 4
13 SVSS
12 SGND
C1N 5
11 INR
PVSS 6
10 TIME
MODE2 7
9
ALERT 8
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, printed circuit
board techniques, bump-pad layout, and the 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 and look up
Application Note: UCSP—A Wafer-Level Chip-Scale
Package.
Chip Information
TRANSISTOR COUNT: 4858
PROCESS: BiCMOS
INL
TSSOP
TOP VIEW
(BUMP SIDE DOWN)
1
2
3
4
INL
INR
A
PVSS ALERT
B
C1N MODE2 TIME SGND
C
PGND MODE1 HPS
SVSS
D
C1P
VDD
OUTL OUTR
UCSP
______________________________________________________________________________________
17
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
MAX9720
System Diagram
VDD
VDD
0.1µF
0.1µF
15kΩ
AUX_IN
0.1µF 15kΩ
IN
MAX4063 OUT
2.2kΩ
CODEC/
BASEBAND
PROCESSOR
BIAS
OUT+
OUT-
VDD
0.1µF 15kΩ
BIAS
MAX4365
1µF
2.2kΩ
OUT
0.1µF
SHDN
IN+
VDD
IN-
100kΩ
0.1µF
VDD
MODE1
MODE2
µC
HPS
1µF
VDD
10kΩ
1µF
INL
MAX9720 OUTL
INR
OUTR
ALERT
PVSS
1µF
SVSS
TIME
220nF
C1P
CIN
1µF
1µF
18
______________________________________________________________________________________
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
1.8V TO 3.8V
LOGIC
CONTROL
R4
10kΩ
C3
1µF
1
(D2)
2
(C2)
VDD
MODE1
CIN
1µF
LEFTCHANNEL
AUDIO INPUT
7
(B2)
8
(A2)
MODE2
ALERT
9
(A3)
INL
MAX9720
MIXER
ATTENUATOR
AND
GAIN SETTING
VDD
OUTL
3
(D1) C1P
SVSS
SmartSense
AND
HEADPHONE
DETECTION
CHARGE
PUMP
C1
1µF
VDD
SGND
UVLO
AND
SHUTDOWN
CONTROL
5
(B1) C1N
16
(D3)
R1
100kΩ
HPS
15
(C3)
OUTR
14
(D4)
CLICK-AND-POP
SUPPRESSION
VDD
SGND
MIXER
ATTENUATOR
AND
GAIN SETTING
PVSS
6
(A1)
SVSS
13
(C4)
C2
1µF
PGND
4
(C1)
SGND
TIME
INR
12
(B4)
10
(B3)
C4
220nF
11
(A4)
RIGHTCHANNEL
AUDIO INPUT
SVSS
CIN
1µF
( ) UCSP BUMP.
______________________________________________________________________________________
19
MAX9720
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.)
16L,UCSP.EPS
MAX9720
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
20
______________________________________________________________________________________
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
TSSOP4.40mm.EPS
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.
MAX9720
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.)