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19-3465; Rev 0; 11/04
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown
General Description
The MAX9725 fixed-gain, stereo headphone amplifier is ideal for portable equipment where board space is at a premium. The MAX9725 uses a unique, patented 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. Fixed gains of -2V/V (MAX9725A), 1.5V/V (MAX9725B), -1V/V (MAX9725C), and -4V/V (MAX9725D) further reduce external component count. The MAX9725 delivers up to 20mW per channel into a 32 load and achieves 0.006% THD+N. An 80dB at 1kHz power-supply rejection ratio (PSRR) allows the MAX9725 to operate from noisy digital supplies without an additional linear regulator. The MAX9725 includes 8kV ESD protection on the headphone output. Comprehensive click-andpop circuitry suppresses audible clicks and pops at startup and shutdown. A low-power shutdown mode reduces supply current to 0.6A (typ). The MAX9725 operates from a single 0.9V to 1.8V supply, allowing the device to be powered directly from a single AA or AAA battery. The MAX9725 consumes only 2.1mA of supply current, provides short-circuit protection, and is specified over the extended -40C to +85C temperature range. The MAX9725 is available in a tiny (1.54mm x 2.02mm x 0.6mm) 12-bump chip-scale package (UCSPTM) and a 12-pin thin QFN package (4mm x 4mm x 0.8mm).
Features
Low Quiescent Current (2.1mA) Single-Cell, 0.9V to 1.8V Single-Supply Operation Fixed Gain Eliminates External Feedback Network MAX9725A: -2V/V MAX9725B: -1.5V/V MAX9725C: -1V/V MAX9725D: -4V/V Ground-Referenced Outputs Eliminate DC Bias No Degradation of Low-Frequency Response Due to Output Capacitors 20mW per Channel into 32 Low 0.006% THD+N High PSRR (80dB at 1kHz) Integrated Click-and-Pop Suppression Low-Power Shutdown Control Short-Circuit Protection 8kV ESD-Protected Amplifier Outputs Available in Space-Saving Packages 12-Bump UCSP (1.54mm x 2.02mm x 0.6mm) 12-Pin Thin QFN (4mm x 4mm x 0.8mm)
MAX9725
Block Diagram
SINGLE 1.5V CELL AA OR AAA BATTERY
Applications
MP3 Players Cellular Phones PDAs Smart Phones Portable Audio Equipment
INL
VDD
MAX9725
DirectDrive OUTPUTS ELIMINATE DC-BLOCKING CAPACITORS. OUTL
Ordering Information
PART MAX9725AEBC-T* MAX9725AETC MAX9725BEBC-T* MAX9725BETC MAX9725CEBC-T* MAX9725CETC MAX9725DEBC-T* MAX9725DETC PINTEMP RANGE PACKAGE -40C to +85C 12 UCSP-12 -40C to +85C 12 UCSP-12 -40C to +85C 12 TQFN-EP** -40C to +85C 12 UCSP-12 -40C to +85C 12 TQFN-EP** -40C to +85C 12 UCSP-12 -40C to +85C 12 TQFN-EP** TOP GAIN MARK (V/V) ACK ACL AAEX ACM AAEY ACN AAEZ -2 -2 -1.5 -1.5 -1 -1 -4 -4
SGND PGND INR C1N C1P INVERTING CHARGE PUMP
PVSS
-40C to +85C 12 TQFN-EP** AAEW
VSS
OUTR
*Future product--contact factory for availability. **EP = Exposed paddle. UCSP is a trademark of Maxim Integrated Products, Inc. Pin Configurations appear at end of data sheet. 1
________________________________________________________________ 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.
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725
ABSOLUTE MAXIMUM RATINGS
SGND to PGND .....................................................-0.3V to +0.3V VDD to SGND or PGND ............................................-0.3V to +2V VSS to PVSS ...........................................................-0.3V to +0.3V C1P to PGND..............................................-0.3V to (VDD + 0.3V) C1N to PGND............................................(PVSS - 0.3V) to +0.3V VSS, PVSS to GND ....................................................+0.3V to -2V OUTR, OUTL, INR, INL to SGND .....(VSS - 0.3V) to (VDD + 0.3V) SHDN to SGND or PGND .........................................-0.3V to +4V Output Short-Circuit Current ......................................Continuous Continuous Power Dissipation (TA = +70C) 12-Bump UCSP (derate 6.5mW/C above +70C)....518.8mW 12-Pin Thin QFN (derate 16.9mW/C above +70C) ..1349.1mW Junction Temperature ......................................................+150C Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Bump Temperature (soldering) Reflow............................+230C Lead Temperature (soldering, 10s) .................................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1F, CIN = 1F, RL = , TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (See the Functional Diagram.)
PARAMETER Supply Voltage Range Quiescent Supply Current Shutdown Current Shutdown to Full Operation SHDN Thresholds SHDN Input Leakage Current CHARGE PUMP Oscillator Frequency AMPLIFIERS MAX9725A Voltage Gain AV MAX9725B MAX9725C MAX9725D Gain Match Total Output Offset Voltage Input Resistance Power-Supply Rejection Ratio AV VOS RIN PSRR VDD = 0.9V to 1.8V, TA = +25C fIN = 1kHz 100mVP-P ripple fIN = 20kHz VDD = 1.5V Output Power (Note 2) POUT VDD = 1.0V, RL = 32 VDD = 0.9V, RL = 32 Total Harmonic Distortion Plus Noise Signal-to-Noise Ratio THD+N SNR RL = 32, POUT = 12mW, f = 1kHz RL = 16, POUT = 15mW, f = 1kHz BW = 22Hz to 22kHz RL = 32, POUT = 12mW A-weighted filter RL = 32 RL = 16 Input AC-coupled, RL = 32 to GND, TA = +25C MAX9725A/MAX9725D MAX9725B MAX9725C 15 60 -2.04 -1.53 -1.02 -4.08 -2.00 -1.5 -1.00 -4.00 0.5 0.3 0.45 0.6 25 80 70 62 10 20 25 7 6 0.006 0.015 89 92 % dB mW 1.05 1.58 2.1 35 k dB -1.96 -1.47 -0.98 -3.92 % mV V/V SYMBOL VDD IDD ISHDN tON VIH VIL ILEAK fOSC CONDITIONS Guaranteed by PSRR test Both channels active VSHDN = 0V TA = +25C TA = -40C to +85C 180 VDD = 0.9V to 1.8V VDD = 0.9V to 1.8V VDD = 0.9V to 1.8V (Note 1) 493 580 0.7 x VDD 0.3 x VDD 1 667 MIN 0.9 2.1 0.6 TYP MAX 1.8 3.3 10 30 UNITS V mA A s V A kHz
2
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1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown
ELECTRICAL CHARACTERISTICS (continued)
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1F, CIN = 1F, RL = , TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25C.) (See the Functional Diagram.)
PARAMETER Slew Rate Maximum Capacitive Load Crosstalk Click/Pop Level ESD Protection SYMBOL SR CL XTALK KCP VESD No sustained oscillations fIN = 1.0kHz, RL = 32, POUT = 5mW RL = 32, peak voltage, Aweighted, 32 samples per second (Note 3) Into shutdown Out of shutdown CONDITIONS MIN TYP 0.2 150 100 72.8 dB 72.8 8 kV MAX UNITS V/s pF dB
MAX9725
Human Body Model (OUTR, OUTL)
Note 1: Note 2: Note 3:
Input leakage current measurements limited by automated test equipment. fIN = 1kHz, TA = +25C, THD+N < 1%, both channels driven in-phase. Testing performed with 32 resistive load connected to outputs. Mode transitions controlled by SHDN. KCP level calculated as 20 log [peak voltage under normal operation at rated power level / peak voltage during mode transition]. Inputs are ACgrounded.
Typical Operating Characteristics
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1F, CIN = 1F, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25C, unless otherwise noted.) (See the Functional Diagram.) TOTAL HARMONIC DISTORTION PLUS TOTAL HARMONIC DISTORTION PLUS TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY NOISE vs. FREQUENCY NOISE vs. FREQUENCY
MAX9725 toc02 MAX9725 toc01
VDD = 1.5V RL = 16 AV = -2V/V
VDD = 1.5V RL = 32 AV = -2V/V
VDD = 1V RL = 16 AV = -2V/V POUT = 0.7mW
0.1 THD+N (%) POUT = 15mW THD+N (%)
0.1 POUT = 2mW THD+N (%)
0.1
0.01 POUT = 2mW
0.01
0.01 POUT = 4mW POUT = 12mW
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
0.001 10 100 1k FREQUENCY (Hz) 10k 100k
TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY
MAX9725 toc04
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9725 toc05
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
VDD = 1.5V RL = 32 AV = -2V/V fIN = 20Hz fIN = 1kHz
MAX9725 toc06
1
VDD = 1V RL = 32 AV = -2V/V
100
100
10
VDD = 1.5V RL = 16 AV = -2V/V
fIN = 20Hz fIN = 1kHz
10
0.1 THD+N (%) THD+N (%) THD+N (%) POUT = 0.7mW 1 fIN = 10kHz 0.1 1 fIN = 10kHz
0.1
0.01 0.01 POUT = 4mW 0.001 10 100 1k FREQUENCY (Hz) 10k 100k 0.001 0 10 20 30 40 OUTPUT POWER (mW) 0.001 0 10 20 30 40 OUTPUT POWER (mW) 0.01
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3
MAX9725 toc03
1
1
1
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725
Typical Operating Characteristics (continued)
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1F, CIN = 1F, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25C, unless otherwise noted.) (See the Functional Diagram.)
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
MAX9725 toc07
TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER
VDD = 1V RL = 32 AV = -2V/V
MAX9725 toc08
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
-20 -30 -40 VDD = 1.5V RL = 32
MAX9725 toc09
100
10
VDD = 1V RL = 16 AV = -2V/V
100 fIN = 20Hz fIN = 1kHz
-10
fIN = 20Hz fIN = 1kHz
10
THD+N (%)
THD+N (%)
fIN = 10kHz 0.1
fIN = 10kHz 0.1
PSRR (dB) 15
1
1
-50 -60 -70 -80
0.01 0.001 0 5 10 15 OUTPUT POWER (mW)
0.01 0.001 0 5 10 OUTPUT POWER (mW)
-90 -100 -110 10 100 1k FREQUENCY (Hz) 10k 100k
POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX9725 toc10
CROSSTALK vs. FREQUENCY
MAX9725 toc11
OUTPUT POWER vs. SUPPLY VOLTAGE
70 OUTPUT POWER (mW) 60 50 40 30 20 fIN = 1kHz RL = 16 BOTH INPUTS DRIVEN IN-PHASE THD+N = 10%
MAX9725 toc12
0 -10 -20 -30 PSRR (dB)
0 -20 -40 PSRR (dB) -60 -80 -100
VDD = 1V RL = 32
VDD = 1.5V POUT = 5mW RL = 32
80
-40 -50 -60 -70 -80 -90 -100 10 100 1k FREQUENCY (Hz) 10k 100k
LEFT TO RIGHT
RIGHT TO LEFT -120 10 100 1k FREQUENCY (Hz) 10k 100k
10 0 0.9 1.1
THD+N = 1% 1.3 1.5
SUPPLY VOLTAGE (V)
OUTPUT POWER vs. SUPPLY VOLTAGE
MAX9725 toc13
OUTPUT POWER vs. LOAD RESISTANCE
MAX9725 toc14
OUTPUT POWER vs. LOAD RESISTANCE
70 60 OUTPUT POWER (mW) 50 40 30 20 10 0 THD+N = 10% THD+N = 1% VDD = 1V fIN = 1kHz BOTH INPUTS DRIVEN IN-PHASE
MAX9725 toc15
50 45 40 OUTPUT POWER (mW) 35 30 25 20 15 10 5 0 0.9 1.1 1.3 THD+N = 1% fIN = 1kHz RL = 32 BOTH INPUTS DRIVEN IN-PHASE THD+N = 10%
80 70 60 OUTPUT POWER (mW) THD+N = 10% 50 40 30 20 10 0 10 100 THD+N = 1%
VDD = 1.5V fIN = 1kHz BOTH INPUTS DRIVEN IN-PHASE
80
1.5
1k
10
100 LOAD RESISTANCE ()
1k
SUPPLY VOLTAGE (V)
LOAD RESISTANCE ()
4
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1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown
Typical Operating Characteristics (continued)
(VDD = 1.5V, PGND = SGND = 0V, VSHDN = 1.5V, VSS = PVSS, C1 = C2 = 1F, CIN = 1F, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25C, unless otherwise noted.) (See the Functional Diagram.)
POWER DISSIPATION vs. OUTPUT POWER
MAX9725 toc16
MAX9725
POWER DISSIPATION vs. OUTPUT POWER
MAX9725 toc17
GAIN FLATNESS vs. FREQUENCY
2 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 10 100 1k FREQUENCY (Hz) 10k 100k
MAX9725 toc18
80 70 POWER DISSIPATION (mW) 60 50 40 30 20 10 0 0 10 20 30 40 RL = 32 VDD = 1.5V fIN = 1kHz POUT = POUTL + POUTR OUTPUTS IN-PHASE RL = 16
35 30 POWER DISSIPATION (mW) 25 20 15 10 5 0 RL = 32 VDD = 1V fIN = 1kHz POUT = POUTL + POUTR OUTPUTS IN-PHASE 10 15 RL = 16
50
0
5
20
OUTPUT POWER (mW)
OUTPUT POWER (mW)
AMPLITUDE (dB)
OUTPUT POWER vs. CHARGE-PUMP CAPACITANCE AND LOAD RESISTANCE
MAX9725 toc19
OUTPUT SPECTRUM vs. FREQUENCY
MAX9725 toc20
SUPPLY CURRENT vs. SUPPLY VOLTAGE
4.5 4.0 SUPPLY CURRENT (mA) 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 NO LOAD
MAX9725 toc21
40 35 OUTPUT POWER (mW) 30 25 20 15 10 5 0 10 20 30 40 C1 = C2 = 0.68F C1 = C2 = 0.47F VDD = 1.5V fIN = 1kHz THD+N = 1% C1 = C2 = 2.2F C1 = C2 = 1F
0 -20 -40 AMPLITUDE (dB) -60 -80 -100 -120 -140 -160 0 5 10 FREQUENCY (kHz)
5.0
fIN = 1kHz RL = 32 VOUT = -60dBV VDD = 1.5V
50
15
20
0.9
1.0
1.1
1.2
1.3
1.4
1.5
LOAD RESISTANCE ()
SUPPLY VOLTAGE (V)
SHUTDOWN CURRENT vs. SUPPLY VOLTAGE
MAX9725 toc22
EXITING SHUTDOWN
MAX9725 toc23
POWER-UP/-DOWN WAVEFORM
MAX9725toc24
0.7 0.6 SHUTDOWN CURRENT (A) 0.5 0.4 0.3 0.2 0.1 0 0.9 1.1 1.3
OUT_ 1V/div
VDD 1V/div
SHDN 500mV/div OUT_ 10mV/div
1.5
200s/div
200ms/div
SUPPLY VOLTAGE (V)
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5
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725
Pin Description
PIN THIN QFN 1 2 3 4 5 6 7 8 9 10 11 12 EP BUMP NAME UCSP A1 A2 A3 A4 B4 B3 C4 C3 C2 C1 B1 B2 -- C1N PVSS INL INR VSS SGND OUTR OUTL VDD C1P PGND SHDN EP Flying Capacitor Negative Terminal. Connect a 1F capacitor from C1P to C1N. Inverting Charge-Pump Output. Bypass with 1F from PVSS to PGND. PVSS must be connected to VSS. Left-Channel Audio Input Right-Channel Audio Input Amplifier Negative Power Supply. Must be connected to PVSS. Signal Ground. SGND must be connected to PGND. SGND is the ground reference for the input and output signal. Right-Channel Output Left-Channel Output Positive Power-Supply Input. Bypass with a 1F capacitor to PGND. Flying Capacitor Positive Terminal. Connect a 1F capacitor from C1P to C1N. Power Ground. Ground reference for the internal charge pump. PGND must be connected to SGND. Active-Low Shutdown. Connect to VDD for normal operation. Pull low to disable the amplifier and charge pump. Exposed Paddle. Internally connected to VSS. Leave paddle unconnected or solder to VSS. FUNCTION
Detailed Description
The MAX9725 stereo headphone driver features Maxim's patented DirectDrive architecture, eliminating the large output-coupling capacitors required by conventional single-supply headphone drivers. The MAX9725 consists of two 20mW class AB headphone drivers, shutdown control, inverting charge pump, internal gain-setting resistors, and comprehensive click-and-pop suppression circuitry (see the Functional Diagram). A negative power supply (PVSS) is created by inverting the positive supply (VDD). Powering the drivers from VDD and PVSS increases the dynamic range of the drivers to almost twice that of other 1V single-supply drivers. This increase in dynamic range allows for higher output power. The outputs of the MAX9725 are biased about GND (Figure 1). The benefit of this GND bias is that the driver outputs do not have a DC component, thus large DCblocking capacitors are unnecessary. Eliminating the DC-blocking capacitors on the output saves board space, system cost, and improves frequency response.
DirectDrive
Conventional single-supply headphone drivers have their outputs biased about a nominal DC voltage (typically half the supply) for maximum dynamic range. Large coupling capacitors are needed to block the DC bias from the headphones. Without these capacitors, a significant amount of DC current flows to the headphone, resulting in unnecessary power dissipation and possible damage to both headphone and headphone driver. Maxim's DirectDrive architecture uses a charge pump to create an internal negative supply voltage. This allows the MAX9725 outputs to be biased about GND, increasing the dynamic range while operating from a single supply. A conventional amplifier powered from 1.5V ideally provides 18mW to a 16 load. The MAX9725 provides 25mW to a 16 load. The DirectDrive architecture eliminates the need for two large (220F, typ) DC-blocking capacitors on the output. The MAX9725 charge pump requires two small ceramic capacitors, conserving board space, reducing cost, and improving the frequency response of the headphone driver. See the Output Power vs. Charge-
6
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1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown
Low-Frequency Response Large DC-blocking capacitors limit the amplifier's lowfrequency response and can distort the audio signal:
VDD VOUT
MAX9725
1) The impedance of the headphone load and the DCblocking capacitor forms a highpass filter with the -3dB point set by: f-3dB = 1 2RLCOUT
VDD / 2 GND
CONVENTIONAL DRIVER-BIASING SCHEME
VDD
VOUT
GND
-VDD
where RL is the impedance of the headphone and COUT is the value of the DC-blocking capacitor. The highpass filter is required by conventional singleended, single power-supply headphone drivers to block the midrail DC-bias component of the audio signal from the headphones. The drawback to the filter is that it can attenuate low-frequency signals. Larger values of COUT reduce this effect but result in physically larger, more expensive capacitors. Figure 2 shows the relationship between the size of COUT and the resulting low-frequency attenuation. Note that the -3dB point for a 16 headphone with a 100F blocking capacitor is 100Hz, well within the normal audio band, resulting in low-frequency attenuation of the reproduced signal. 2) The voltage coefficient of the DC-blocking capacitor contributes distortion to the reproduced audio signal as the capacitance value varies when the function of the voltage across the capacitor changes. At low frequencies, the reactance of the capacitor dominates at frequencies below the -3dB point and the voltage coefficient appears as frequency-dependent distortion. Figure 3 shows the THD+N introduced by two different capacitor dielectric types. Note that below 100Hz, THD+N increases rapidly. The combination of low-frequency attenuation and frequency-dependent distortion compromises audio reproduction in portable audio equipment that emphasizes low-frequency effects such as multimedia laptops, as well as MP3, CD, and DVD players. These low-frequency, capacitor-related deficiencies are eliminated by using DirectDrive technology. Charge Pump The MAX9725 features a low-noise charge pump. The 580kHz switching frequency is well beyond the audio range, and does not interfere with the audio signals. The switch drivers feature a controlled switching speed that minimizes noise generated by turn-on and turn-off transients. The di/dt noise caused by the parasitic bond wire and trace inductance is minimized by limiting the turn-on/off speed of the charge pump. Additional high7
DirectDrive BIASING SCHEME
Figure 1. Traditional Driver Output Waveform vs. MAX9725 Output Waveform (Ideal Case)
Pump Capacitance and Load Resistance graph in the Typical Operating Characteristics for details of the possible capacitor sizes. Previous attempts to eliminate the output-coupling capacitors involved biasing the headphone return (sleeve) to the DC-bias voltage of the headphone amplifiers. This method raises some issues: * The sleeve is typically grounded to the chassis. Using this biasing approach, the sleeve must be isolated from system ground, complicating product design. * During an ESD strike, the driver's ESD structures are the only path to system ground. The driver must be able to withstand the full ESD strike. When using the headphone jack as a line out to other equipment, the bias voltage on the sleeve may conflict with the ground potential from other equipment, resulting in possible damage to the drivers.
*
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1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725
LF ROLLOFF (16 LOAD)
0 -3 -5 ATTENUATION (dB) -10 100F -15 33F -20 -25 -30 -35 10 100 FREQUENCY (Hz) 1k 0.001 ALUM/ELEC 0.0001 10 100 1k FREQUENCY (Hz) 10k 100k 330F 220F THD+N (%) -3dB CORNER FOR 100F IS 100Hz 1 10
ADDITIONAL THD+N DUE TO DC-BLOCKING CAPACITORS
0.1 TANTALUM 0.01
Figure 2. Low-Frequency Attenuation for Common DC-Blocking Capacitor Values
Figure 3. Distortion Contributed By DC-Blocking Capacitors
frequency noise attenuation can be achieved by increasing the size of C2 (see the Functional Diagram). Extra noise attenuation is not typically required.
Shutdown
The MAX9725's low-power shutdown mode reduces supply current to 0.6A. Driving SHDN low disables the amplifiers and charge pump. The driver's output impedance is typically 50k (MAX9725A), 37.5k (MAX9725B), 25k (MAX9725), or 100k (MAX9725D) when in shutdown mode.
the internal input resistor (25k, typ) causing an audible click and pop. Delaying the rise of SHDN 4 or 5 time constants, based on RIN x CIN, relative to the startup of the preamplifier eliminates any click and pop caused by the input filter (see the Functional Diagram).
Applications Information
Power Dissipation
Linear power amplifiers can dissipate a significant amount of power under normal operating conditions. The maximum power dissipation for each package is given in the Absolute Maximum Ratings section under Continuous Power Dissipation or can be calculated by the following equation: PDISSPKG(MAX) = TJ(MAX) - TA JA
Click-and-Pop Suppression
In conventional single-supply audio drivers, the outputcoupling capacitor is a major contributor of audible clicks and pops. Upon startup, the driver charges the coupling capacitor to its bias voltage, typically half the supply. Likewise, on shutdown, the capacitor is discharged to GND. This results in a DC shift across the capacitor that appears as an audible transient at the speaker. The MAX9725's DirectDrive technology eliminates the need for output-coupling capacitors. The MAX9725 also features extensive click-and-pop suppression that eliminates any audible transient sources internal to the device. The Power-Up/Down Waveform in the Typical Operating Characteristics shows minimal DC shift and no spurious transients at the output upon startup or shutdown. In most applications, the output of the preamplifier driving the MAX9725 has a DC bias of typically half the supply. At startup, the input-coupling capacitor is charged to the preamplifier's DC bias voltage through
8
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 for the thin QFN package is +59.3C/W. The MAX9725 has two power dissipation sources, the charge pump and the two amplifiers. If the power dissipation exceeds the rated package dissipation, reduce VDD, increase load impedance, decrease the ambient temperature, or add heatsinking to the device. Large output, supply, and ground traces decrease JA, allowing more heat to be transferred from the package to surrounding air.
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1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown
Component Selection
OUTPUT POWER vs. SUPPLY VOLTAGE WITH INPUTS IN- AND OUT-OF-PHASE
50 45 40 OUTPUT POWER (mW) 35 30 25 20 15 10 5 0 0.9 1.1 1.3 1.5 SUPPLY VOLTAGE (V) INPUTS IN-PHASE fIN = 1kHz RL = 16 THD+N = 1% INPUTS 180 OUT-OF-PHASE
MAX9725
Input Filtering The AC-coupling capacitor (CIN) and an internal gainsetting resistor form a highpass filter that removes any DC bias from an input signal (see the Functional Diagram). CIN allows the MAX9725 to bias the signal to an optimum DC level. The -3dB point of the highpass filter, assuming zero source impedance, is given by: f-3dB = 1 2 x 25k x CIN
Figure 4. Output Power vs. Supply Voltage with Inputs In-/Outof-Phase
Choose CIN so f-3dB is well below the lowest frequency of interest. Setting f-3dB too high affects the amplifier's lowfrequency response. Use capacitors with low-voltage coefficient dielectrics. Film or C0G dielectric capacitors are good choices for AC-coupling capacitors. Capacitors with high-voltage coefficients, such as ceramics, can result in increased distortion at low frequencies. Charge-Pump Capacitor Selection Use capacitors with less than 100m of ESR. Low-ESR ceramic capacitors minimize the output impedance of the charge pump. Capacitors with an X7R dielectric provide the best performance over the extended temperature range. Table 1 lists suggested capacitor manufacturers. Flying Capacitor (C1) The value of C1 affects the charge pump's load regulation and output impedance. Choosing C1 too small degrades the MAX9725's ability to provide sufficient current drive and leads to a loss of output voltage. Increasing the value of C1 improves load regulation and reduces the charge-pump output impedance. See the Output Power vs. Charge-Pump Capacitance and Load Impedance graph in the Typical Operating Characteristics. Hold Capacitor (C2) The hold capacitor's value and ESR directly affect the ripple at PVSS. Increasing the value of C2 reduces ripple. Choosing a capacitor with lower ESR reduces ripple and output impedance. Lower capacitance values can be used in systems with low maximum output power levels. See the Output Power vs. Charge-Pump Capacitance and Load Impedance graph in the Typical Operating Characteristics.
Output Power The MAX9725's output power increases when the left and right audio signals differ in magnitude and/or phase. Figure 4 shows the two extreme cases for inand out-of-phase input signals. The output power of a typical stereo application lies between the two extremes shown in Figure 4. The MAX9725 is specified to output 20mW per channel when both inputs are in-phase.
Powering Other Circuits from the Negative Supply
The MAX9725 internally generates a negative supply voltage (PVSS) to provide the ground-referenced output signal. Other devices can be powered from PVSS provided the current drawn from the charge pump does not exceed 1mA. Headphone driver output power and THD+N will be adversely affected if more than 1mA is drawn from PVSS. Using PVSS as an LCD bias is a typical application for the negative supply. PVSS is unregulated and proportional to VDD. Connect a 1F capacitor from C1P to C1N for best charge-pump operation.
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9
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725
Table 1. Suggested Capacitor Manufacturers
SUPPLIER Taiyo Yuden TDK PHONE 800-348-2496 847-803-6100 FAX 847-925-0899 847-390-4405 WEBSITE www.t-yuden.com www.component.tdk.com
Power-Supply Bypass Capacitor (C3) The power-supply bypass capacitor (C3) lowers the output impedance of the power supply and reduces the impact of the MAX9725's charge-pump switching transients. Bypass VDD to PGND with the same value as C1. Place C3 as close to VDD as possible.
UCSP Applications Information
For the latest application details on UCSP construction, dimensions, tape carrier information, printed circuit board techniques, bump-pad layout , and recommended reflow temperature profile, as well as the latest information on reliability testing results, go to Maxim's website at www.maxim-ic.com/ucsp for the Application Note: UCSP--A Wafer-Level Chip-Scale Package.
Layout and Grounding
Proper layout and grounding are essential for optimum performance. Connect PGND and SGND together at a single point on the PC board. Connect PVSS to SVSS and bypass with C2 to PGND. Bypass VDD to PGND with C3. Place capacitors C2 and C3 as close to the MAX9725 as possible. Route PGND, and all traces that carry switching transients, away from SGND and the audio signal path. The MAX9725 does not require additional heatsinking. The thin QFN package features an exposed paddle that improves thermal efficiency of the package. Ensure the exposed paddle is electrically isolated from GND and VDD. Connect the exposed paddle to VSS if necessary.
Chip Information
TRANSISTOR COUNT: 2559 PROCESS: BiCMOS
10
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1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown
System Diagram
0.9V TO 1.8V
MAX9725
1F
0.47F MP3 DECODER STEREO DAC 0.47F C1P 1F C1N VSS PVSS 1F INR INL
SHDN
VDD
MAX9725
OUTR OUTL
SGND
PGND
Pin Configurations
TOP VIEW (BUMP-SIDE DOWN)
A C1N B PGND C C1P VDD OUTL SHDN SGND VSS PVSS INL 2 3 PVSS INL INR C1N 1 9 8 7 VDD OUTL OUTR
MAX9725
1 2 3 4
TOP VIEW
SHDN 12
PGND 11
C1P 10
MAX9725
OUTR
UCSP
4 INR
5 VSS
6 SGND
THIN QFN
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11
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725
Functional Diagram
0.9V TO 1.8V LEFTCHANNEL AUDIO IN CIN 0.47F 9 (C2) VDD 12 (B2) SHDN 3 (A3) INL RF*
C3 1F
RIN 25k
VDD 8 OUTL (C3)
10 (C1) C1P
UVLO/ SHUTDOWN CONTROL
SGND
HEADPHONE JACK VSS
C1 1F 1 (A1) C1N
CHARGE PUMP
CLICK-AND-POP SUPPRESSION VDD SGND 7 (C4)
MAX9725
RIN 25k
OUTR
VSS RF*
PVSS 2 (A2) C2 1F
VSS 5 (B4)
PGND 11 (B1)
SGND 6 (B3) CIN 0.47F
INR 4 (A4)
RIGHTCHANNEL AUDIO IN *MAX9725A = 50k. MAX9725B = 37.5k. MAX9725C = 25k. MAX9725D = 100k. ( ) DENOTE BUMPS FOR UCSP.
12
______________________________________________________________________________________
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with 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.)
MAX9725
PACKAGE OUTLINE, 4x3 UCSP 21-0104 F
1 1
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12L, UCSP 4x3.EPS
13
1V, Low-Power, DirectDrive, Stereo Headphone Amplifier with Shutdown MAX9725
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
24L QFN THIN.EPS
PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm
21-0139
C
1
2
PACKAGE OUTLINE 12, 16, 20, 24L THIN QFN, 4x4x0.8mm
21-0139
C
2
2
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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