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19-3597; Rev 3; 3/07
60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
General Description
The MAX9724A/MAX9724B stereo headphone amplifiers are designed for portable equipment where board space is at a premium. These devices use a unique, patented DirectDriveTM architecture to produce a ground-referenced output from a single supply, eliminating the need for large DC-blocking capacitors, saving cost, board space, and component height. The MAX9724 suppresses RF radiation received by input and supply traces acting as antennas and prevents the amplifer from demodulating the coupled noise. The MAX9724A offers an externally adjustable gain while the MAX9724B has an internally preset gain of -1.5V/V. The MAX9724A/MAX9724B deliver up to 60mW per channel into a 32 load and have low 0.02% THD+N. An 80dB at 1kHz power-supply rejection ratio (PSRR) allows these devices to operate from noisy digital supplies without an additional linear regulator. Comprehensive click-and-pop circuitry suppresses audible clicks and pops on startup and shutdown. The MAX9724A/MAX9724B operate from a single 2.7V to 5.5V supply, consume only 3.5mA of supply current, feature short-circuit and thermal-overload protection, and are specified over the extended -40C to +85C temperature range. The devices are available in tiny 12bump UCSPTM (1.5mm x 2mm) and 12-pin thin QFN (3mm x 3mm x 0.8mm) packages.
Features
Improved RF Noise Rejection (Up to 67dB Over Typical Amplifiers) No Bulky DC-Blocking Capacitors Required Low-Power Shutdown Mode, < 0.1A Adjustable Gain (MAX9724A) or Fixed -1.5V/V Gain (MAX9724B) Low 0.02% THD+N High PSRR (80dB at 1kHz) Eliminates LDO Integrated Click-and-Pop Suppression 2.7V to 5.5V Single-Supply Operation Low Quiescent Current (3.5mA) Available in Space-Saving Packages: 12-Bump UCSP (1.5mm x 2mm) 12-Pin Thin QFN (3mm x 3mm x 0.8mm)
MAX9724A/MAX9724B
Ordering Information
PART MAX9724AEBC+T MAX9724AETC+ MAX9724BEBC+T MAX9724BETC+ GAIN PIN(V/V) PACKAGE Adj. Adj. -1.5 -1.5 12 UCSP-12 12 UCSP-12 PKG CODE B12-1 B12-1 TOP MARK +ADH +AAT +ADI +AAU
12 TQFN-EP* T1233-1 12 TQFN-EP* T1233-1
Applications
Cellular Phones MP3 Players Notebook PCs Handheld Gaming Consoles DVD Players Smart Phones PDAs
Note: All devices specified over the -40C to +85C operating range. +Denotes lead-free package. *EP = Exposed paddle. Pin Configurations appear at end of data sheet.
U.S. Patent# 7,061,327 UCSP is a trademark of Maxim Integrated Products, Inc.
Block Diagrams
MAX9724B MAX9724A
LEFT AUDIO INPUT DirectDrive OUTPUTS ELIMINATE DC-BLOCKING CAPACITORS LEFT AUDIO INPUT DirectDrive OUTPUTS ELIMINATE DC-BLOCKING CAPACITORS
SHDN
SHDN
RIGHT AUDIO INPUT
RIGHT AUDIO INPUT
FIXED GAIN ELIMINATES EXTERNAL RESISTOR NETWORK
________________________________________________________________ Maxim Integrated Products
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
ABSOLUTE MAXIMUM RATINGS
VDD to GND ..............................................................-0.3V to +6V PVSS to SVSS .........................................................-0.3V to +0.3V PGND to SGND .....................................................-0.3V to +0.3V C1P to PGND..............................................-0.3V to (VDD + 0.3V) C1N to PGND............................................(PVSS - 0.3V) to +0.3V PVSS and SVSS to PGND..........................................-6V to +0.3V IN_ to SGND (MAX9724A)..........................-0.3V to (VDD + 0.3V) IN_ to SGND (MAX9724B) .............(SVSS - 0.3V) to (VDD + 0.3V) OUT_ to SVSS (Note 1) ....-0.3V to Min (VDD - SVSS + 0.3V, +9V) OUT_ to VDD (Note 2) ......+0.3V to Max (SVSS - VDD - 0.3V, -9V) SHDN to _GND.........................................................-0.3V to +6V OUT_ Short Circuit to GND ........................................Continuous Short Circuit between OUTL and OUTR ....................Continuous Continuous Input Current into PVSS ..................................260mA Continuous Input Current (any other pin) .........................20mA Continuous Power Dissipation (TA = +70C) 12-Bump USCP (derate 6.5mW/C above +70C) ........519mW 12-Pin TQFN (derate 14.7mW/C above +70C) .........1177mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Junction Temperature ......................................................+150C Lead Temperature (soldering, 10s) .................................+300C Bump Temperature (soldering) Reflow............................+235C
Note 1: OUTR and OUTL should be limited to no more than 9V above SVSS, or above VDD + 0.3V, whichever limits first. Note 2: OUTR and OUTL should be limited to no more than 9V below VDD, or below SVSS - 0.3V, whichever limits first.
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 = 5V, PGND = SGND, SHDN = 5V, C1 = C2 = 1F, RL = , resistive load reference to ground; for MAX9724A gain = -1.5V/V (RIN = 20k, RF = 30k); for MAX9724B gain = -1.5V/V (internally set), TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C, unless otherwise noted.) (Note 3)
PARAMETER GENERAL Supply Voltage Range Quiescent Current Shutdown Current Shutdown to Full Operation Input Impedance Output Offset Voltage Power-Supply Rejection Ratio VDD ICC ISHDN tSON RIN VOS PSRR MAX9724B, measured at IN_ (Note 4) VDD = 2.7V to 5.5V, TA = +25C f = 1kHz, 100mVP-P (Note 4) f = 20kHz, 100mVP-P (Note 4) Output Power (TQFN) Output Power (UCSP) Voltage Gain Channel-to-Channel Gain Tracking Total Harmonic Distortion Plus Noise (Note 6) THD+N POUT POUT AV RL = 32, THD+N = 1% RL = 16, THD+N = 1% RL = 32, THD+N = 1% RL = 16, THD+N = 1% MAX9724B (Note 5) MAX9724B RL = 1k, VOUT = 2VRMS, fIN = 1kHz RL = 32, POUT = 50mW, fIN = 1kHz RL = 16, POUT = 35mW, fIN = 1kHz -1.52 25 30 69 12 SHDN = SGND = PGND Guaranteed by PSRR test 2.7 3.5 0.1 180 19 1.5 86 80 65 63 42 45 35 -1.5 0.15 0.003 0.02 0.04 % -1.48 mW mW V/V % dB 28 10 5.5 5.5 1 V mA A s k mV SYMBOL CONDITIONS MIN TYP MAX UNITS
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
ELECTRICAL CHARACTERISTICS (continued)
(VDD = 5V, PGND = SGND, SHDN = 5V, C1 = C2 = 1F, RL = , resistive load reference to ground; for MAX9724A gain = -1.5V/V (RIN = 20k, RF = 30k); for MAX9724B gain = -1.5V/V (internally set), TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C, unless otherwise noted.) (Note 3)
PARAMETER SYMBOL RL = 1k, VOUT = 2VRMS RL = 32, POUT = 50mW CONDITIONS BW = 22Hz to 22kHz A-weighted BW = 22Hz to 22kHz A-weighted MIN TYP 102 105 98 101 0.5 No sustained oscillations L to R, R to L, f = 10kHz, RL = 16, POUT = 15mW fOSC Into shutdown RL = 32, peak voltage, A-weighted, 32 samples per Out of second (Notes 4, 7) shutdown (TQFN only) (TQFN only) (UCSP only) (UCSP only) 1.4 0.9 1 2 0.8 190 100 -70 270 -67 -64 dB 400 V/s pF dB kHz MAX UNITS
MAX9724A/MAX9724B
Signal-to-Noise Ratio
SNR
dB
Slew Rate Capacitive Drive Crosstalk Charge-Pump Oscillator Frequency Click-and-Pop Level DIGITAL INPUTS (SHDN) Input-Voltage High Input-Voltage Low Input-Voltage High Input-Voltage Low Input Leakage Current
SR CL
KCP
VINH VINL VINH VINL
V V V V A
ELECTRICAL CHARACTERISTICS
(VDD = 3V, PGND = SGND, SHDN = 3V, C1 = C2 = 1F, RL = , resistive load reference to ground; for MAX9724A gain = -1.5V/V (RIN = 20k, RF = 30k); for MAX9724B gain = -1.5V/V (internally set), TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C, unless otherwise noted.) (Note 3)
PARAMETER Quiescent Current Shutdown Current Power-Supply Rejection Ratio (Note 4) Output Power Total Harmonic Distortion Plus Noise (Note 6) SYMBOL ICC ISHDN PSRR POUT SHDN = SGND = PGND f = 1kHz, 100mVP-P f = 20kHz, 100mVP-P RL = 32, THD+N = 1% RL = 16, THD+N = 1% RL = 1k, VOUT = 2VRMS, fIN = 1kHz THD+N RL = 32, POUT = 15mW, fIN = 1kHz RL = 16, POUT = 10mW, fIN = 1kHz CONDITIONS MIN TYP 3.0 0.1 80 65 20 14 0.05 0.03 0.06 % MAX UNITS mA A dB mW
Note 3: Note 4: Note 5: Note 6: Note 7:
All specifications are 100% tested at TA = +25C; temperature limits are guaranteed by design. The amplifier inputs are AC-coupled to GND. Gain for the MAX9724A is adjustable. Measurement bandwidth is 22Hz to 22kHz. Test performed with a 32 resistive load connected to GND. Mode transitions are controlled by SHDN. KCP level is calculated as 20log[(peak voltage during mode transition, no input signal)/(peak voltage under normal operation at rated power level)]. Units are expressed in dB. _______________________________________________________________________________________ 3
60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
Typical Operating Characteristics
(VDD = 5V, PGND = SGND = 0V, SHDN = VDD, C1 = C2 = 1F, RL = , gain = -1.5V/V (RIN = 20k, RF = 30k for the MAX9724A), THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25C, unless otherwise noted.)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (TQFN ONLY)
MAX9724toc01
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (TQFN ONLY)
MAX9724toc02
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (TQFN ONLY)
VDD = 5V RL = 16 10
MAX9724toc03
100 VDD = 3V RL = 16 10
100 VDD = 3V RL = 32 10
100
THD+N (%)
THD+N (%)
1 fIN = 1kHz 0.1 fIN = 10kHz
1 fIN = 1kHz 0.1 fIN = 10kHz
THD+N (%)
1 fIN = 1kHz 0.1 fIN = 10kHz 0.01 fIN = 20Hz
0.01 fIN = 20Hz 0.001 0 10 20 30 40 OUTPUT POWER (mW)
0.01 0.001 0 fIN = 20Hz 10 20 30 40 50
0.001 0 20 40 60 80 100 OUTPUT POWER (mW)
OUTPUT POWER (mW)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (TQFN ONLY)
MAX9724toc04
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (TQFN ONLY)
MAX9724toc05
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (TQFN ONLY)
VDD = 3V RL = 32
MAX9724toc06
100 VDD = 5V RL = 32 10
1
VDD = 3V RL = 16
1
0.1 THD+N (%) THD+N (%) 1 fIN = 1kHz
THD+N (%)
POUT = 5mW
0.1 POUT = 8mW 0.01
0.1
0.01 POUT = 10mW 0.01 fIN = 20Hz 0.001 0 20 40 60 80 100 120 OUTPUT POWER (mW) 0.001 10 100 1k FREQUENCY (Hz) 10k 100k fIN = 10kHz
POUT = 15mW
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (TQFN ONLY)
MAX9724toc07
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY (TQFN ONLY)
MAX9724toc08
OUTPUT POWER vs. SUPPLY VOLTAGE (TQFN ONLY)
fIN = 1kHz RL = 16
MAX9724toc09
1
VDD = 5V RL = 16 POUT = 20mW
1 VDD = 5V RL = 32
70 60 OUTPUT POWER (mW) 50 10% THD+N 40 30 20 1% THD+N 10
0.1 THD+N (%) THD+N (%)
0.1
POUT = 30mW
0.01
POUT = 37mW
0.01 POUT = 50mW
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
Typical Operating Characteristics (continued)
(VDD = 5V, PGND = SGND = 0V, SHDN = VDD, C1 = C2 = 1F, RL = , gain = -1.5V/V (RIN = 20k, RF = 30k for the MAX9724A), THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25C, unless otherwise noted.)
OUTPUT POWER vs. SUPPLY VOLTAGE (TQFN ONLY)
fIN = 1kHz RL = 32
MAX9724toc10
OUTPUT POWER vs. LOAD RESISTANCE (TQFN ONLY)
10% THD+N VDD = 3V fIN = 1kHz
MAX9724toc11
OUTPUT POWER vs. LOAD RESISTANCE (TQFN ONLY)
90 80 OUTPUT POWER (mW) 70 60 50 40 30 20 VDD = 5V fIN = 1kHz 10 LOAD RESISTANCE () 100 THD+N = 1% THD+N = 10%
MAX9724toc12
120 100 OUTPUT POWER (mW) 80
35 30 25 20 15 1% THD+N 10 5 0
100
10% THD+N 60 40 20 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) 1% THD+N
OUTPUT POWER (mW)
10 0 10 100 LOAD RESISTANCE () 1000
POWER DISSIPATION vs. OUTPUT POWER (TQFN ONLY)
MAX9724toc13
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY (TQFN ONLY)
MAX9724toc14
CROSSTALK vs. FREQUENCY (TQFN ONLY)
POUT = 15mW RL = 16
MAX9724toc15
250
0 RL = 32 -20 -40
0 -20 CROSSTALK (dB) -40 -60 -80 -100 -120 LEFT TO RIGHT
POWER DISSIPATION (mW)
200 RL = 16 RL = 32
PSRR (dB)
150
-60 -80
100 VDD = 3V fIN = 1kHz POUT = POUTL + POUTR OUTPUTS IN PHASE 0 20 40 60 80
VDD = 5V
RIGHT TO LEFT
50
-100 -120 10 100
VDD = 3V 1k FREQUENCY (Hz) 10k 100k
0 OUTPUT POWER (mW)
10
100
1k FREQUENCY (Hz)
10k
100k
OUTPUT POWER vs. LOAD RESISTANCE AND CHARGE-PUMP CAPACITOR SIZE (TQFN ONLY)
MAX9724toc16
OUTPUT SPECTRUM vs. FREQUENCY (TQFN ONLY)
MAX9724toc17
SUPPLY CURRENT vs. SUPPLY VOLTAGE (TQFN ONLY)
MAX9724toc18
80 C1 = C2 = 2.2F 70 OUTPUT POWER (mW) 60 50 C1 = C2 = 0.47F 40 30 20 0 50 100 VDD = 5V fIN = 1kHz THD+N = 1% C1 = C2 = 1F
-40 -50 -60 AMPLITUDE (dBV) -70 -80 -90 -100 -110 -120 -130 -140 RL = 32 VDD = 3V fIN = 1kHz VOUT = -60dBV
3.5 3.4 SUPPLY CURRENT (mA) 3.3 3.2 3.1 3.0 2.9 2.8 NO LOAD INPUTS GROUND 2.5 3.0 3.5 4.0 4.5 5.0
150
0
5
10 FREQUENCY (kHz)
15
20
5.5
LOAD RESISTANCE ()
SUPPLY VOLTAGE (V)
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
Typical Operating Characteristics (continued)
(VDD = 5V, PGND = SGND = 0V, SHDN = VDD, C1 = C2 = 1F, RL = , gain = -1.5V/V (RIN = 20k, RF = 30k for the MAX9724A), THD+N measurement bandwidth = 22Hz to 22kHz, both outputs driven in phase, TA = +25C, unless otherwise noted.)
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE (TQFN ONLY)
NO LOAD INPUTS GND 120 SHUTDOWN CURRENT (nA) 100 80 60 40 20 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) VOUT_ 500mV/div VOUT_ 500mV/div
MAX9724 toc19
EXITING SHUTDOWN
MAX9724toc20
ENTERING SHUTDOWN
MAX9724toc21
140
VSHDN 5V/div VIN_ 1V/div
VSHDN 5V/div VIN_ 1V/div
40s/div
20s/div
Pin Description
PIN TQFN 1 2 3 4 5 6 7 8 9 10 11 12 EP UCSP A1 A2 A3 A4 C2 B3 C1 B2 B4 C3 C4 B1 -- NAME C1P PGND C1N PVSS SHDN INL SGND INR SVSS OUTR OUTL VDD EP FUNCTION Flying Capacitor Positive Terminal. Connect a 1F ceramic capacitor from C1P to C1N. Power Ground. Connect to SGND. Flying Capacitor Negative Terminal. Connect a 1F ceramic capacitor from C1P to C1N. Charge-Pump Output. Connect to SVSS and bypass with a 1F ceramic capacitor to PGND. Active-Low Shutdown Input Left-Channel Input Signal Ground. Connect to PGND. Right-Channel Input Amplifier Negative Supply. Connect to PVSS. Right-Channel Output Left-Channel Output Positive Power-Supply Input. Bypass with a 1F capacitor to PGND. Exposed Paddle. Internally connected to SVSS. Connect to SVSS or leave unconnected.
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
Detailed Description
The MAX9724A/MAX9724B stereo headphone amplifiers feature Maxim's patented DirectDrive architecture, eliminating the large output-coupling capacitors required by conventional single-supply headphone amplifiers. The device consists of two 60mW Class AB headphone amplifiers, undervoltage lockout (UVLO)/shutdown control, charge pump, and comprehensive click-and-pop suppression circuitry (see the Functional Diagram/Typical Operating Circuits). 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 PGND (Figure 1). The benefit of this PGND bias is that the amplifier outputs do not have a DC component. The large DC-blocking capacitors required with conventional headphone amplifiers are unnecessary, conserving board space, reducing system cost, and improving frequency response. The MAX9724A/MAX9724B feature an undervoltage lockout that prevents operation from an insufficient power supply and click-and-pop suppression that eliminates audible transients on startup and shutdown. The MAX9724A/MAX9724B also feature thermal-overload and short-circuit protection.
MAX9724A/MAX9724B
VOUT VDD VDD
VDD/2 GND
CONVENTIONAL DRIVER-BIASING SCHEME VOUT
VDD
GND
2VDD
-VDD
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, allowing the MAX9724A/MAX9724B outputs to be biased about GND. With no DC component, there is no need for the large DC-blocking capacitors. The MAX9724A/MAX9724B charge pumps require two small ceramic capacitors, conserving board space, reducing cost, and improving the frequency response of the headphone amplifier. See the Output Power vs. Load Resistance and Charge-Pump Capacitor Size graph in the Typical Operating Characteristics for details of the possible capacitor sizes. There is a low DC voltage on the amplifier outputs due to amplifier offset. However, the offsets of the MAX9724A/MAX9724B are typically 1.5mV, which, when combined with a 32 load, results in less than 47A of DC current flow to the headphones.
DirectDrive BIASING SCHEME
Figure 1. Conventional Driver Output Waveform vs. MAX9724A/MAX9724B Output Waveform
Charge Pump The MAX9724A/MAX9724B feature a low-noise charge pump. The 270kHz switching frequency is well beyond the audio range and does not interfere with audio signals. The switch drivers feature a controlled switching speed that minimizes noise generated by turn-on and turn-off transients. The di/dt noise caused by the parasitic bond wire and trace inductance is minimized by limiting the switching speed of the charge pump. Although not typically required, additional high-frequency noise attenuation can be achieved by increasing the value of C2 (see the Functional Diagram/Typical Operating Circuits).
RF Susceptibility
Modern audio systems are often subject to RF radiation from sources like wireless networks and cellular phone networks. Although the RF radiation is out of the audio band, many signals, in particular GSM signals, contain bursts or modulation at audible frequencies. Most analog amplifiers demodulate the low-frequency envelope, adding noise to the audio signal. The architecture of
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
the MAX9724 addresses the problem of the RF susceptibility by rejecting RF noise and preventing it from coupling into the audio band. The RF susceptibility of an amplifier can be measured by placing the amplifier in an isolated chamber and subjecting it to an electric field of known strength. If the electric field is modulated with an audio band signal, a percentage of the modulated signal will be demodulated and amplified by the device in the chamber. Figure 2 shows the signal level at the outputs of an unoptimized amplifier and the MAX9724. The test conditions are shown in Table 1. Typically, the output of the device driving the MAX9724A/MAX9724B has a DC bias of half the supply voltage. At startup, the input-coupling capacitor is charged to the preamplifier's DC-bias voltage through the input and feedback resistors of the MAX9724A/ MAX9724B, resulting in a DC shift across the capacitor and an audible click/pop. Delay the rise of SHDN 4 to 5 time constants based on RIN and CIN, relative to the startup of the preamplifier, to eliminate clicks-and-pops caused by the input filter.
Shutdown
The MAX9724A/MAX9724B feature a <0.1A, lowpower shutdown mode that reduces quiescent current consumption and extends battery life for portable applications. Drive SHDN low to disable the amplifiers and the charge pump. In shutdown mode, the amplifier output impedance is set to 14k||RF (RF is 30k for the MAX9724B). The amplifiers and charge pump are enabled once SHDN is driven high.
Table 1. RF Susceptibility Test Conditions
TEST PARAMETER RF Field Strength RF Modulation Type RF Modulation Index RF Modulation Frequency SETTING 50V/m Sine wave 100% 1kHz
Applications Information
Power Dissipation
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: PDISSPKG(MAX) = TJ(MAX) - TA JA
Click-and-Pop Suppression
In conventional single-supply audio amplifiers, the output-coupling capacitor contributes significantly to audible clicks and pops. Upon startup, the amplifier charges the coupling capacitor to its bias voltage, typically half the supply. Likewise, on shutdown, the capacitor is discharged. This results in a DC shift across the capacitor, which appears as an audible transient at the speaker. Since the MAX9724A/ MAX9724B do not require outputcoupling capacitors, this problem does not arise. Additionally, the MAX9724A/MAX9724B feature extensive click-and-pop suppression that eliminates any audible transient sources internal to the device.
AMPLIFIER OUTPUT AMPLITUDE (dBV)
20 0 -20 -40 -60
62dB IMPROVEMENT AT 850MHz RF SUSCEPTIBLE AMPLIFIER
39dB IMPROVEMENT AT 900MHz 67dB IMPROVEMENT AT 1800MHz
49dB IMPROVEMENT AT 1900MHz
MAX9724 -80 -100 100 600 1100 1600 2100 2600 RF CARRIER FREQUENCY (MHz)
Figure 2. RF Susceptibility of the MAX9724 and a Typical Headphone Amplifier 8 _______________________________________________________________________________________
MAX9724 fig02
40
60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
where TJ(MAX) is +150C, TA is the ambient temperature, and JA is the reciprocal of the derating factor in C/W as specified in the Absolute Maximum Ratings section. For example, JA of the thin QFN package is +68C/W, and 154.2C/W for the UCSP package. The MAX9724A/MAX9724B have two power dissipation sources; a charge pump and the two output amplifiers. If power dissipation for a given application exceeds the maximum allowed for a particular package, reduce VDD, increase load impedance, decrease the ambient temperature, or add heatsinking to the device. Large output, supply, and ground traces decrease JA, allowing more heat to be transferred from the package to the surrounding air. Thermal-overload protection limits total power dissipation in the MAX9724A/MAX9724B. When the junction temperature exceeds +150C, the thermal protection circuitry disables the amplifier output stage. The amplifiers are enabled once the junction temperature cools by approximately 12C. This results in a pulsing output under continuous thermal-overload conditions. supply voltages greater than 4.35V. The output must not be driven such that the peak output voltage exceeds the opposite supply voltage by 9V. For example, if VDD = 5V, the charge pump sets PVSS = -5V. Therefore, the peak output swing must be less than 4V to prevent exceeding the absolute maximum ratings.
MAX9724A/MAX9724B
UVLO
The MAX9724A/MAX9724B feature an undervoltage lockout (UVLO) function that prevents the device from operating if the supply voltage is less than 2.7V. This feature ensures proper operation during brownout conditions and prevents deep battery discharge. Once the supply voltage exceeds the UVLO threshold, the MAX9724A/MAX9724B charge pump is turned on and the amplifiers are powered, provided that SHDN is high.
Component Selection
Input-Coupling Capacitor The input capacitor (CIN), in conjunction with the input resistor (RIN), forms a highpass filter that removes the DC bias from an incoming signal (see the Functional Diagram/Typical Operating Circuits). The AC-coupling capacitor allows the device 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 2RINCIN
Output Dynamic Range
Dynamic range is the difference between the noise floor of the system and the output level at 1% THD+N. Determine the system's dynamic range before setting the maximum output gain. Output clipping occurs if the output signal is greater than the dynamic range of the system. The DirectDrive architecture of the MAX9724A/ MAX9724B has increased the dynamic range compared to other single-supply amplifiers.
Maximum Output Swing
VDD < 4.35V If the output load impedance is greater than 1k, the MAX9724A/MAX9724B can swing within a few millivolts of their supply rail. For example, with a 3.3V supply, the output swing is 2VRMS, or 2.83V peak while maintaining a low 0.003% THD+N. If the supply voltage drops to 3V, the same 2.83V peak has only 0.05% THD+N. VDD > 4.35V Internal device structures limit the maximum voltage swing of the MAX9724A/MAX9724B when operated at
Choose the CIN such that f-3dB is well below the lowest frequency of interest. Setting f-3dB too high affects the device'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, can result in increased distortion at low frequencies. Charge-Pump Capacitor Selection Use ceramic capacitors with a low ESR for optimum performance. For optimal performance over the extended temperature range, select capacitors with an X7R dielectric. Table 2 lists suggested manufacturers.
Table 2. Suggested Capacitor Manufacturers
SUPPLIER Taiyo Yuden TDK Murata PHONE 800-348-2496 847-803-6100 770-436-1300 FAX 847-925-0899 847-390-4405 770-436-3030 WEBSITE www.t-yuden.com www.component.tdk.com www.murata.com
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
Flying Capacitor (C1) The value of the flying capacitor (see the Functional Diagram/Typical Operating Circuits) affects the charge pump's load regulation and output resistance. 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. Increasing the value of C1 improves load regulation and reduces the charge-pump output resistance to an extent. See the Output Power vs. Load Resistance and Charge-Pump Capacitor Size graph in the Typical Operating Characteristics. Above 1F, the on-resistance of the switches and the ESR of C1 and C2 dominate. Hold Capacitor (C2) The hold capacitor value (see the Functional Diagram/Typical Operating Circuits) and ESR directly affect the ripple at PVSS. Increasing the value of C2 reduces output ripple. Likewise, decreasing the ESR of C2 reduces both ripple and output resistance. Lower capacitance values can be used in systems with low maximum output power levels. See the Output Power vs. Load Resistance and Charge-Pump Capacitor Size graph in the Typical Operating Characteristics. Power-Supply Bypass Capacitor (C3) The power-supply bypass capacitor (see the Functional Diagram/Typical Operating Circuits) lowers the output impedance of the power supply, and reduces the impact of the MAX9724A/MAX9724B's charge-pump switching transients. Bypass VDD with C3, the same value as C1, and place it physically close to the VDD and PGND pins. The gain of the MAX9724A amplifier is set externally as shown in Figure 3, the gain is: AV = -RF/RIN (V/V) Choose feedback resistor values in the tens of k range. Lower values may cause excessive power dissipation and require impractically small values of RIN for large gain settings. The high-impedance state of the outputs can also be degraded during shutdown mode if an inadequate feedback resistor is used since the equivalent output impedance during shutdown is 14k||Rf (RF is equal to 30k for the MAX9724B). The source resistance of the input device may also need to be taken into consideration. Since the effective value of RIN is equal to the sum of the source resistance of the input device and the value of the input resistor connected to the inverting terminal of the headphone amplifier (20k for the MAX9724B), the overall closed-loop gain of the headphone amplifier can be reduced if the input resistor is not significantly larger than the source resistance of the input device.
RF
MAX9724A
LEFT AUDIO INPUT RIN INL OUTL
Amplifier Gain
The gain of the MAX9724B amplifier is internally set to -1.5V/V. All gain-setting resistors are integrated into the device, reducing external component count. The internally set gain, in combination with DirectDrive, results in a headphone amplifier that requires only five small capacitors to complete the amplifier circuit: two for the charge pump, two for audio input coupling, and one for power-supply bypassing (see the Functional Diagram/Typical Operating Circuits).
RIGHT AUDIO INPUT RIN INR
OUTR
RF
Figure 3. Gain Setting for the MAX9724A
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
Lineout Amplifier and Filter Block
The MAX9724A can be used as an audio line driver capable of providing 2VRMS into 10k loads with a single 5V supply (see Figure 4 for the RMS Output Voltage vs. Supply Voltage plot). 2VRMS is a popular audio line level, first used in CD players, but now common in DVD and set-top box (STB) interfacing standards. A 2VRMS
RMS OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
3.5 fIN = 1kHz RMS OUTPUT VOLTAGE (V) 3.0 RL = 10k 1% THD+N LIMITED BY ABS. MAXIMUM RATINGS RL = 1k 1% THD+N
2.5
2.0
1.5 2.5 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V)
sinusoidal signal equates to approximately 5.7VP-P, which means that the audio system designer cannot simply run the lineout stage from a (typically common) 5V supply--the resulting output swing would be inadequate. A common solution to this problem is to use op amps driven from split supplies (5V typically), or to use a high-voltage supply rail (9V to 12V). This can mean adding extra cost and complexity to the system power supply to meet this output level requirement. Having the ability to derive 2VRMS from a 5V supply, or even 3.3V supply, can often simplify power-supply design in some systems. When the MAX9724A is used as a line driver to provide outputs that feed stereo equipment (receivers, STBs, notebooks, and desktops) with a digital-to-analog converter (DAC) used as an audio input source, it is often desirable to eliminate any high-frequency quantization noise produced by the DAC output before it reaches the load. This high-frequency noise can cause the input stages of the line-in equipment to exceed slew-rate limitations or create excessive EMI emissions on the cables between devices.
MAX9724A/MAX9724B
Figure 4. RMS Output Voltage vs. Supply Voltage
15k 220pF
LEFT AUDIO INPUT
1F
7.5k 1.2nF
7.5k
MAX9724A
INL OUTL LINE IN DEVICE
STEREO DAC
10k 1.2nF RIGHT AUDIO INPUT 1F OUTR 7.5k 7.5k INR 10k 220pF
15k
Figure 5. MAX9724A Line Out Amplifier and Filter Block Configuration
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
To suppress this noise, and to provide a 2VRMS standard audio output level from a single 5V supply, the MAX9724A can be configured as a line driver and active lowpass filter. Figure 5 shows the MAX9724A connected as 2-pole Rauch/multiple feedback filter with a passband gain of 6dB and a -3dB (below passband) cutoff frequency of approximately 27kHz (see Figure 6 for the Gain vs. Frequency plot).
MAX9724A ACTIVE FILTER GAIN vs. FREQUENCY
10 5 0 -5 GAIN (dB) -10 -15 -20 -25 -30 -35 1k 10k 100k 1M FREQUENCY (Hz) RL = 10k
Layout and Grounding
Proper layout and grounding are essential for optimum performance. Connect PGND and SGND together at a single point on the PC Board. Connect PVSS to SVSS and bypass with a 1F capacitor. Place the power-supply bypass capacitor and the charge-pump hold capacitor as close to the MAX9724 as possible. Route PGND and all traces that carry switching transients away from SGND and the audio signal path. The thin QFN package features an exposed paddle that improves thermal efficiency. Ensure that the exposed paddle is electrically isolated from PGND, SGND, and VDD. Connect the exposed paddle to SVSS only when the board layout dictates that the exposed paddle cannot be left floating.
Figure 6. Frequency Response of Active Filter of Figure 4
UCSP Applications Information
For the latest application details on UCSP construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout, and recommended reflow temperature profile, as well as the latest information on reliability testing results, refer to the Application Note UCSP--A Wafer-Level Chip-Scale Package available on Maxim's website at www.maximic.com/ucsp.
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
System Diagram
VDD 0.1F 15k 1F 15k INR VDD PVDD BIAS 1F OUTR+ OUTR-
MAX9724A/MAX9724B
MAX9710
PGND MUTE 0.1F 15k SHDN INL 15k CONTROLLER
GND OUTLOUTL+ VDD 100k 100k 0.1F
STEREO DAC O.47F
SHDN
OUTL
MAX9724B OUTR
INL SGND INR PGND PVSS SVSS C1P C1N VDD 1F 1F VDD
O.47F
1F
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
Functional Diagram/Typical Operating Circuits
2.7V TO 5.5V LEFT AUDIO INPUT CIN R IN* 0.47F 20k RF* 30k
ON C3 1F 12 (B1) VDD OFF 5 (C2) SHDN
6 (B3) INL VDD 11 OUTL (C4)
1 (A1) C1P
HEADPHONE JACK SVSS UVLO/ SHUTDOWN CONTROL CHARGE PUMP SGND VDD 10 (C3) CLICK-AND-POP SUPPRESSION
C1 1F 3 (A3) C1N
OUTR
MAX9724A
PVSS 4 (A4) C2 1F SVSS PGND 2 9 (B4) (A2) SVSS SGND 7 (C1) RIGHT AUDIO INPUT CIN RIN* 0.47F 20k INR 8 (B2) RF* 30k
*RIN AND RF VALUES ARE CHOSEN FOR A GAIN -1.5V/V. ( ) UCSP PACKAGE
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
Functional Diagram/Typical Operating Circuits (continued)
2.7V TO 5.5V LEFT AUDIO INPUT CIN 0.47F
MAX9724A/MAX9724B
C3 1F
ON OFF 12 (B1) VDD 5 (C2) SHDN
6 (B3) INL RF* 30k VDD 11 OUTL (C4)
RIN* 20k
1 (A1) C1P
HEADPHONE JACK VSS UVLO/ SHUTDOWN CONTROL CHARGE PUMP SGND VDD 10 (C3) CLICK-AND-POP SUPPRESSION
C1 1F 3 (A3) C1N
MAX9724B
RIN 20k SVSS RF 30k
OUTR
PVSS 4 (A4) C2 1F
SVSS 9 (B4)
PGND 2 (A2)
SGND 7 (C1)
INR 8 (B2) CIN RIGHT 0.47F AUDIO INPUT
( ) UCSP PACKAGE
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
Pin Configurations
INR
TOP VIEW
SGND
SVSS
TOP VIEW
(BUMPS ON BOTTOM) 1 2 3 4
9
8
7
MAX9724A/MAX9724B
OUTR 10 OUTL 11 VDD 12
6
INL SHDN PVSS
A C1P PGND C1N PVSS
MAX9724A MAX9724B +
1 C1P 2 PGND 3 C1N
5
B VDD C SGND SHDN OUTR OUTL INR INL SVSS
4
TQFN
UCSP
Chip Information
TRANSISTOR COUNT: 993 PROCESS: BiCMOS
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
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.)
MAX9724A/MAX9724B
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12x16L QFN THIN.EPS
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown MAX9724A/MAX9724B
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.)
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60mW, DirectDrive, Stereo Headphone Amplifier with Low RF Susceptibility and Shutdown
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.)
12L, UCSP 4x3.EPS
MAX9724A/MAX9724B
PACKAGE OUTLINE, 4x3 UCSP 21-0104 F
1 1
Revision History
Pages changed at Rev 2: 1, 2, 3, 6, 9, 12, 14-19 Pages changed at Rev 3: 1-6, 19
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 ____________________ 19 (c) 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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