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19-1746; Rev 1; 2/01
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers
General Description
The MAX4295/MAX4297 mono/stereo, switch-mode (Class-D) audio power amplifiers operate from a single +2.7V to +5.5V supply. They have >85% efficiency and are capable of delivering 2W continuous power to a 4 load, making them ideal for portable multimedia and general-purpose high-power audio applications. The MAX4295/MAX4297 feature a total harmonic distortion plus noise (THD+N) of 0.4% (fOSC = 125kHz), low quiescent current of 2.8mA (MAX4295) or 4.6mA (MAX4297), high efficiency, and clickless power-up and shutdown. The SHDN input disables the device and limits supply current to <1.5A (MAX4295) or <2.3A (MAX4297). Other features include a 1A current limit, thermal protection, and under-voltage lockout. The MAX4295 (mono) and MAX4297 (stereo) reduce the number of required external components. Both devices have internal high-speed power-MOS transistors, allowing operation as bridge-tied load (BTL) amplifiers. The BTL configuration eliminates the need for isolation capacitors on the output. The frequency-selectable pulse-width modulator (PWM) allows the user to optimize the size and cost of the output filter. The MAX4295 is offered in a space-saving 16-pin QSOP package, and the MAX4297 is offered in a compact 24-pin SSOP package.
Features
o +2.7V to +5.5V Single-Supply Operation o 2W/Channel Output Power at 5V 0.7W/Channel Output Power at 3V o 87% Efficiency (RL = 4, PO = 2W, MAX4295) o 0.4% THD+N (RL = 4, fOSC = 125kHz) o Logic-Programmable PWM Frequency Selection (125kHz, 250kHz, 500kHz, 1MHz) o Low-Power Shutdown Mode o Clickless Transitions Into and Out of Shutdown o 1A Current Limit and Thermal Protection o Available in Space-Saving Packages 16-Pin QSOP (MAX4295) 24-Pin SSOP (MAX4297)
MAX4295/MAX4297
Ordering Information
PART MAX4295EEE MAX4295ESE MAX4297EAG MAX4297EWG TEMP. RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 16 Narrow SO 24 SSOP 24 Wide SO
Applications
Palmtop/Notebook Computers PDA Audio Sound Cards Game Cards Boom Boxes AC Amplifiers Battery-Powered Speakers Cordless Phones Portable Equipment
Pin Configurations appear at end of data sheet.
Typical Operating Circuit
VCC VPVCC 4, 9, 16, 21 VPVCC OUT+L MAX4297 12 11 22 VCC 14 AOUTR INR SHDN FS1 17 OUT-R 13 VCM* FS2 SS AGND 10 PGND 6, 7, 18, 19 *DO NOT CONNECT. 24 CSS OUT+R 8 L2A C2A L2B C2B OUT-L 20 L1B C1B 5 L1A C1A +
3 RF CIN INPUTL RF CIN INPUTR RIN RIN VCC 1 2 AOUTL INL
VCC
15
________________________________________________________________ Maxim Integrated Products
1
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Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
ABSOLUTE MAXIMUM RATINGS
VCC, PVCC to GND or PGND....................................-0.3V to +6V PGND to GND.....................................................................0.3V PVCC to VCC .......................................................................0.3V VCM, SS, AOUT_, IN_ ................................-0.3V to (VCC + 0.3V) SHDN, FS1, FS2 .......................................................-0.3V to +6V OUT_ _ .....................................................-0.3V to (PVCC + 0.3V) Op Amp Output Short-Circuit Duration (AOUT_) .......Indefinite Short Circuit to Either Supply H-Bridge Short-Circuit Duration (OUT_ _) .............Continuous Short Circuit to PGND, PVCC or between OUT+_ & OUT-_ Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.30mW/C above +70C)........667mW 24-Pin SSOP (derate 9.50mW/C above +70C) ........762mW 16-Pin Narrow SO (derate 9.52mW/C above +70C) ..........................696mW 24-Pin Wide SO (derate 11.76mW/C above +70C) ........................941mW Operating Temperature Range MAX4295E__/MAX4297E__ ............................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C 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
(VCC = PVCC = +5V, SHDN = VCC, FS1 = GND, FS2 = VCC (fOSC = 250kHz), input amplifier gain = -1V/V, TA = TMIN to TMAX, unless otherwise noted. Typical values are TA = +25C.) (Note 1)
PARAMETER GENERAL Supply Voltage Range Quiescent Supply Current Shutdown Supply Current Voltage at VCM Pin FS1 = GND, FS2 = GND PWM Frequency FS1 = GND, FS2 = VCC FS1 = VCC, FS2 = GND FS1 = VCC, FS2 = VCC PWM Frequency Change with VCC Duty Cycle Duty Cycle Change with VCC Switch On-Resistance (each power device) H-Bridge Output Leakage H-Bridge Current Limit Soft-Start Capacitor Charging Current Undervoltage Lockout Thermal Shutdown Trip Point VSS = 0 0.75 1.8 VCC = 2.7V to 5.5V VIN = 0.06 x VCC VIN = 0.30 x VCC VIN = 0.54 x VCC VIN = 0.3 x VCC, VCC = 2.7V to 5.5V IOUT = 150mA SHDN = GND VCC = 5V VCC = 2.7V 10.2 49.2 86.2 (Note 2) Output load not connected SHDN = GND MAX4295 MAX4297 MAX4295 MAX4297 0.285 x VCC 105 210 420 840 2.7 2.8 4.6 1.5 2.5 0.3 x VCC 125 250 500 1000 1 12 50 88 0.02 0.25 0.35 0 1 1.35 2.2 145 1.95 2.6 5.5 4 8 8 15 0.315 x VCC 145 290 580 1160 3 13.8 50.8 89.8 0.15 0.5 1.0 5 %/V A A A V C % kHz/V kHz V mA A V CONDITIONS MIN TYP MAX UNITS
2
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Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers
ELECTRICAL CHARACTERISTICS (continued)
(VCC = PVCC = +5V, SHDN = VCC, FS1 = GND, FS2 = VCC (fOSC = 250kHz), input amplifier gain = -1V/V, TA = TMIN to TMAX, unless otherwise noted. Typical values are TA = +25C.)
PARAMETER Input Voltage Range VCC = +3V, fIN = 1kHz Maximum Output Power VCC = +5V, fIN = 1kHz THD Plus Noise Efficiency Channel Isolation Logic Input Current Logic Input High Voltage Logic Input Low Voltage INPUT AMPLIFIER Input Offset Voltage VOS Temp Coefficient Input Bias Current Input Noise Voltage Density Input Capacitance Output Resistance AOUT Disabled Mode Leakage Current Short-Circuit Current Large-Signal Voltage Gain AOUT Voltage Swing Gain Bandwidth Product Power-Supply Rejection Maximum Capacitive Load VCC = +2.7V to +5.5V No sustained oscillations 66 SHDN = GND, VAOUT = 0 to VCC AOUT to GND AOUT to VCC VOUT = 0.2V to 4.6V, RL(OPAMP) = 10k VDIFF 10mV, RL(OPAMP) = 10k VCC - VOH VOL 78 (Note 3) f = 10kHz 0.5 5 0.05 32 2.5 0.01 0.1 8 65 115 40 40 1.25 90 200 250 100 1 25 4 mV V/C nA nV/Hz pF A mA dB mV MHz dB pF RL = 8 RL = 4 RL = 8 RL = 4 CONDITIONS MIN TYP 0 to 0.6 x VCC 0.4 0.7 1.2 2 0.4 87 45 1 0.7 x VCC 0.3 x VCC 100 % % dB nA V V W MAX UNITS V
MAX4295/MAX4297
RL = 4, fIN = 1kHz, PO = 1W, fOSC = 125kHz MAX4295, RL = 4, fIN = 1kHz, PO = 2W MAX4297, fIN = 1kHz, PO = 2W VLOGIC = 0 to VCC
LOGIC INPUTS (SHDN, FS1, FS2)
Note 1: All devices are 100% production tested at TA = 25C. All temperature limits are guaranteed by design. Note 2: Supply Voltage Range guaranteed by PSRR of input amplifier, frequency, duty cycle, and H-bridge on-resistance. Note 3: Guaranteed by design, not production tested.
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3
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Typical Operating Characteristics
(VCC = PVCC = +3V, input amplifier gain = -1, SHDN = VCC , TA = +25C, unless otherwise noted.)
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 2.5Vp-p)
MAX4295/7-01
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 2.5Vp-p)
MAX4295/7-02
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 2.5Vp-p)
VCC = +5V RL = 32
MAX4295/7-03
10
VCC = +5V RL = 4 1MHz 125kHz
10
VCC = +5V RL = 8 1MHz 125kHz
10
1 THD + N (%) THD + N (%)
1 THD + N (%)
1
1MHz
125kHz
0.1
500kHz
250kHz
0.1
500kHz
250kHz
0.1 500kHz 250kHz
0.01 10 1k INPUT FREQUENCY (Hz) 100k
0.01 10 1k INPUT FREQUENCY (Hz) 100k
0.01 10 1k INPUT FREQUENCY (Hz) 100k
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-04
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-05
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
VCC = +5V RL = 32 500kHz
MAX4295/7-06
100
VCC = +5V RL = 4 1MHz
100
VCC = +5V RL = 8
100
10 THD + N (%) THD + N (%)
10 THD + N (%) 125kHz 1MHz 1
10
1
250kHz 125kHz 500kHz
1
1MHz 250kHz
0.1
0.1
500kHz 250kHz
0.1 125kHz
0.10 0 0.5 1.0 1.5 2.0 2.5 OUTPUT POWER (W)
0.10 0 0.3 0.6 0.9 1.2 1.5 1.8 OUTPUT POWER (W)
0.10 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W)
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-07
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-08
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
VCC = +5V RL = 32 1MHz
MAX4295/7-09
100
VCC = +5V RL = 4
10
VCC = +5V RL = 8
100
1MHz
10 1 THD + N (%) 1MHz 1 125kHz 250kHz 0.1 500kHz 500kHz 0.10 0 0.5 1.0 1.5 2.0 2.5 OUTPUT POWER (W) 0.01 0 0.3 0.6 0.9 1.2 1.5 1.8 OUTPUT POWER (W) THD + N (%) 125kHz THD + N (%)
10
1 125kHz 0.1 250kHz 500kHz
0.1 250kHz
0.10 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W)
4
_______________________________________________________________________________________
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Typical Operating Characteristics (continued)
(VCC = PVCC = +3V, input amplifier gain = -1, SHDN = VCC , TA = +25C, unless otherwise noted.)
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 1.5Vp-p)
MAX4295/7-10
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 1.5Vp-p)
MAX4295/7-11
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 1.5Vp-p)
VCC = +3V RL = 32 1MHz 1 THD + N (%) 125kHz
MAX4295/7-12
10 125kHz 1MHz 1 THD + N (%) 500kHz 0.1
VCC = +3V RL = 4
10 1MHz 125kHz 1 THD + N (%)
VCC = +3V RL = 8
10
250kHz
0.1
500kHz 250kHz
0.1 250kHz 500kHz
0.01 10 1k INPUT FREQUENCY (Hz) 100k
0.01 10 1k INPUT FREQUENCY (Hz) 100k
0.01 10 1k INPUT FREQUENCY (Hz) 100k
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-13
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-14
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
VCC = +3V RL = 32 1MHz 10 THD + N (%)
MAX4295/7-15
100
VCC = +3V RL = 4 1MHz
100
VCC = +3V RL = 8
100
1MHz
10 THD + N (%) 500kHz 1 125kHz
10 THD + N (%) 250kHz 500kHz 1 0.1 125kHz 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 OUTPUT POWER (W) 0.10 0 0.1
500kHz 1 125kHz
250kHz
0.1 250kHz 0.10
0.2
0.3
0.4
0.5
0.6 0.7
0.8
0
0.05
0.10
0.15
0.20
OUTPUT POWER (W)
OUTPUT POWER (W)
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-16
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-17
MAX4295 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
VCC = +3V RL = 32 1MHz
MAX4295/7-18
100
VCC = +3V RL = 4 1MHz 250kHz
100
VCC = +3V RL = 8 1MHz
100
10 THD + N (%) THD + N (%)
10 125kHz 1
10 THD + N (%)
1 500kHz 0.1 125kHz
1 125kHz 0.1 250kHz 500kHz
500kHz 0.1 250kHz
0.10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 OUTPUT POWER (W)
0.10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 OUTPUT POWER (W)
0.10 0 0.05 0.10 0.15 0.20 OUTPUT POWER (W)
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5
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Typical Operating Characteristics (continued)
(VCC = PVCC = +3V, input amplifier gain = -1, SHDN = VCC , TA = +25C, unless otherwise noted.)
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 2.5Vp-p)
MAX4295/7-19
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 2.5Vp-p)
MAX4295/7-20
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 2.5Vp-p)
VCC = +5V RL = 32 250kHz 1MHz
MAX4295/7-21
10
VCC = +5V RL = 4 1MHz 250kHz
10
VCC = +5V RL = 8 1MHz 250kHz
10
1 THD + N (%) THD + N (%)
1
1 THD + N (%)
125kHz 0.1 500kHz
0.1
125kHz 500kHz
0.1
500kHz
125kHz
0.01 10 1k INPUT FREQUENCY (Hz) 100k
0.01 10 1k INPUT FREQUENCY (Hz) 100k
0.01 10 1k INPUT FREQUENCY (Hz) 100k
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-22
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-23
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
VCC = +5V RL = 32 1MHz 250kHz THD + N (%) 1 500kHz 0.1 125kHz
MAX4295/7-24
100
VCC = +5V RL = 4 250kHz 1MHz
100
VCC = +5V RL = 8 250kHz 1MHz
100
10 THD + N (%)
10 THD + N (%)
10
1 125kHz 500kHz 0.1
1 500kHz 0.1 125kHz
0.10 0 0.5 1.0 1.5 2.0 2.5 OUTPUT POWER (W)
0.10 0 0.3 0.6 0.9 1.2 1.5 OUTPUT POWER (W)
0.10 0 0.1 0.2 0.3 0.4 0.5 OUTPUT POWER (W)
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-25
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-26
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
VCC = +5V RL = 32 1MHz 125kHz 1
MAX4295/7-27
100
VCC = +5V RL = 4 1MHz
100
VCC = +5V RL = 8
100
10 THD + N (%)
10 THD + N (%) THD + N (%) 250kHz 0.1 500kHz 1MHz 1 125kHz
10
125kHz 1 250kHz 0.1 500kHz
0.1 500kHz 0.10
250kHz
0.10 0 0.5 1.0 1.5 2.0 2.5 OUTPUT POWER (W)
0.10 0 0.3 0.6 0.9 1.2 1.5 OUTPUT POWER (W)
0
0.1
0.2
0.3
0.4
0.5
OUTPUT POWER (W)
6
_______________________________________________________________________________________
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Typical Operating Characteristics (continued)
(VCC = PVCC = +3V, input amplifier gain = -1, SHDN = VCC , TA = +25C, unless otherwise noted.)
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 1.5Vp-p)
MAX4295/7-28
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 1.5Vp-p)
MAX4295/7-29
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. INPUT FREQUENCY (VIN = 1.5Vp-p)
VCC = +3V RL = 32 250kHz 1 THD + N (%)
MAX4295/7-30
10
VCC = +3V RL = 4
10
VCC = +3V RL = 8 250kHz
10
1MHz
1MHz
THD + N (%)
1
THD + N (%)
250kHz
1MHz
1
500kHz 0.1
125kHz
125kHz 0.1 500kHz
500kHz 125kHz 0.1 10 1k INPUT FREQUENCY (Hz) 100k 0.01 10 1k INPUT FREQUENCY (Hz) 100k 0.01 10 1k INPUT FREQUENCY (Hz) 100k
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-31
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-32
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 1kHz)
VCC = +3V RL = 32 250kHz 1MHz
MAX4295/7-33
100
VCC = +3V RL = 4
100
VCC = +3V RL = 8
100
10 10 THD + N (%) 1MHz 1 500kHz 125kHz 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 OUTPUT POWER (W) 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 OUTPUT POWER (W) 125kHz 0.10 0 250kHz THD + N (%) 10 1MHz 250kHz 1 500kHz 0.1 THD + N (%) 1
500kHz 125kHz
0.05
0.10
0.15
0.20
OUTPUT POWER (W)
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-34
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
MAX4295/7-35
MAX4297 TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER (fIN = 20kHz)
VCC = +3V RL = 32
MAX4295/7-36
100
VCC = +3V RL = 4 1MHz
100
VCC = +3V RL = 8 1MHz
100
10 THD + N (%) 125khz 1
10 1MHz THD + N (%) 125kHz 1
10 THD + N (%) 125kHz 1 0.1 500kHz 250kHz 0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 OUTPUT POWER (W) 0.10 0 0.1
500kHz 250kHz 0.1
500kHz 250kHz
0.10 0.2 0.3 0.4 0.5 0.6 0 0.05 0.10 0.15 0.20 OUTPUT POWER (W) OUTPUT POWER (W)
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7
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Typical Operating Characteristics (continued)
(VCC = PVCC = +3V, input amplifier gain = -1, SHDN = VCC , TA = +25C, unless otherwise noted.)
MAX4295 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-37
MAX4295/7-38
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 0.5
500kHz
90 80 EFFICIENCY (%) 70 60 50 40 30
500kHz
90 80 EFFICIENCY (%) 70 60 50 40 30 20
250kHz
250kHz 1MHz
250kHz 1MHz
500kHz
1MHz
125kHz
125kHz
125kHz VCC = +5V RL = 8 0 0.3 0.6 0.9 1.2 1.5 1.8
VCC = +5V RL = 4 1.0 1.5 2.0 2.5
20 10 0
10 0 0 0.1 0.2 0.3
VCC = +5V RL = 32 0.4 0.5
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
MAX4295 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-40
MAX4295 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-41
MAX4295 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 125kHz VCC = +3V RL = 32 0 0.05 0.10 0.15 0.20 1MHz 500kHz 250kHz
MAX4295/7-42
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 0.2 0.4 OUTPUT POWER (W) 0.6 125kHz VCC = +3V RL = 4 250kHz 1MHz 500kHz
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VCC = +3V RL = 8 0 0.2 0.4 OUTPUT POWER (W) 0.6 125kHz 250kHz 1MHz 500kHz
100
10 0 0.8 OUTPUT POWER (W)
0.8
MAX4297 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-43
MAX4297 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-44
MAX4297 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 1MHz 125kHz 500kHz 250kHz
MAX4295/7-45
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 0.5 1.0 1.5 2.0 125kHz VCC = +5V RL = 4 250kHz 1MHz 500kHz
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VCC = +5V RL = 8 0 0.3 0.6 0.9 1.2 125kHz 1MHz 250kHz 500kHz
100
10 0 1.5 0 0.1 0.2 0.3 OUTPUT POWER (W)
VCC = +5V RL = 32 0.4 0.5
2.5
OUTPUT POWER (W)
OUTPUT POWER (W)
8
_______________________________________________________________________________________
MAX4295/7-39
100
MAX4295 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
100 100
MAX4295 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers
Typical Operating Characteristics (continued)
(VCC = PVCC = +3V, input amplifier gain = -1, SHDN = VCC , TA = +25C, unless otherwise noted.)
MAX4297 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-46
MAX4295/MAX4297
MAX4297 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
MAX4295/7-47
MAX4297 EFFICIENCY vs. OUTPUT POWER (fIN = 1kHz)
500kHz 90 80 EFFICIENCY (%) 70 60 50 40 30 20 125kHz VCC = +3V RL = 8 0 0.1 0.2 0.3 0.4 0.5 0.6 250kHz 1MHz
MAX4295/7-48
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 0.1 0.2 0.3 0.4 0.5 125kHz VCC = +3V RL = 4 250kHz 1MHz 500kHz
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VCC = +3V RL = 32 0 0.05 0.10 0.15 125kHz 1MHz 250kHz 500kHz
100
10 0 0.20
0.6
OUTPUT POWER (W)
OUTPUT POWER (W)
OUTPUT POWER (W)
MAX4295 SUPPLY CURRENT vs. SUPPLY VOLTAGE
A: fOSC = 125kHz B: fOSC = 250kHz C: fOSC = 500kHz D: fOSC = 1MHz D
MAX4295/7-49
MAX4297 SUPPLY CURRENT vs. TEMPERATURE
MAX4295/7-50
OSCILLATOR FREQUENCY DEVIATION vs. SUPPLY VOLTAGE
0.01 FREQUECNY DEVIATION (%) 125kHz 0.005 0 -0.005 -0.01 -0.015 -0.02 -0.025 250kHz 500kHz 1MHz 2.5 3.0 3.5 4.0 4.5 5.0 5.5
MAX4295/7-51 MAX4295/7 toc54 MAX4295/7 toc53
10 8 SUPPLY CURRENT (mA)
7 6 SUPPLY CURRENT (mA) 5 4 3 2 1 0 MAX4295 VCC = +3V -40 -15 10 35 60 MAX4297 VCC = +3V MAX4295 VCC = +5V MAX4297 VCC = +5V
0.015
6
C
4
B
2 A 0 0 1 2 3 4 5 SUPPLY VOLTAGE (V)
85
TEMPERATURE (C)
SUPPLY VOLTAGE (V)
MAX4297 SUPPLY CURRENT vs. SUPPLY VOLTAGE
18 16 SUPPLY CURRENT (mA) 14 12 10 8 6 4 2 0 0 1 2 3 4 5 SUPPLY VOLTAGE (V) A 1 0 -40 B C A: fOSC = 125kHz B: fOSC = 250kHz C: fOSC = 500kHz D: fOSC = 1MHz
MAX4295/7-52
MAX4297 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
8 7 SUPPLY CURRENT (A) 6 5 4 3 2 MAX4295 VCC = +3V -15 10 35 60 85 MAX4297 VCC = +3V MAX4295 VCC = +5V MAX4297 VCC = +5V
START-UP/SHUTDOWN WAVEFORM
20
D
VOUT
4V/div
SHDN
RL = 4 fOSC = 250kHz fIN = 10kHz CSS = 560pF 400s/div
2.5V/div
TEMPERATURE (C)
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9
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Pin Description
PIN NAME MAX4295 1, 12 2, 15 3 -- -- 4, 13 5 6 7 -- -- 8 -- -- 9 10 11 14 -- -- 16 MAX4297 10 4, 9, 16, 21 -- 5 8 6, 7, 18, 19 3, 23 13 -- 2 11 -- 1 12 22 14 15 -- 20 17 24 GND PVCC OUT+ OUT+L OUT+R PGND VCC VCM IN INL INR AOUT AOUTL AOUTR SHDN FS1 FS2 OUTOUT-L OUT-R SS Analog Ground H-Bridge Power Supply Positive H-Bridge Output Positive Left-Channel H-Bridge Output Positive Right-Channel H-Bridge Output Power Ground Analog Power Supply Audio Input Common-Mode Voltage. Do not connect. Minimize parasitic coupling to this pin. Audio Input Left-Channel Audio Input Right-Channel Audio Input Input Amplifier Output Left-Channel Input Amplifier Output Right-Channel Input Amplifier Output Active-Low Shutdown Input. Connect to VCC for normal operation. Do not leave floating. Frequency Select Input 1 Frequency Select Input 2 Negative H-Bridge Output Negative Left-Channel H-Bridge Output Negative Right-Channel H-Bridge Output Soft-Start FUNCTION
Detailed Description
The MAX4295/MAX4297 switch-mode, Class-D audio power amplifiers are intended for portable multimedia and general-purpose audio applications. Linear amplifiers in the 1W to 2W output range are inefficient; they overheat when operated near rated output power levels. The efficiency of linear amplifiers is <50% when the output voltage is equal to 1/2 the supply. The MAX4295/MAX4297 Class-D amplifiers achieve efficiencies of 87% or greater and are capable of delivering up to 2W of continuous maximum power to a 4 load. The lost power is due mainly to the on-resistance of the power switches and ripple current in the output. In a Class-D amplifier, a PWM controller converts the analog input to a variable pulse-width signal. The pulse width is proportional to the input voltage, ideally 0% for
10
a 0V input signal and 100% for full-scale input voltages. A passive lowpass LC network filters the PWM output waveform to reconstruct the analog signal. The switching frequency is selected much higher than the maximum input frequencies so that intermodulation products are outside the input signal bandwidth. Higher switching frequencies also simplify the filtering requirements. The MAX4295/MAX4297 consist of an inverting input operational amplifier, a PWM ramp oscillator, a controller that converts the analog input to a variable pulse width signal, and a MOSFET H-bridge power stage (Figures 1a and 1b). The control signal is generated by the PWM comparator; its pulse width is proportional to the input voltage. Ideally the pulse width varies linearly between 0% for a 0V input signal and 100% for fullscale input voltages (Figure 2). This signal controls the
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Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
AOUT IN GATE DRIVE OUT+
PVCC
PGND 0.3 VCC (VCM) PVCC
FS1 FS2
PWM OSC
GATE DRIVE
OUT-
VCC SS CSS POWER MANAGEMENT AND PROTECTION GND PGND
Figure 1a. MAX4295 Functional Diagram
H-bridge. The switches work in pairs to reverse the polarity of the signal in the load. Break-before-make switching of the H-bridge MOSFETs by the driver circuit keeps supply current glitches and crowbar current in the MOSFETs at a low level. The output swing of the Hbridge is a direct function of the supply voltage. Varying the oscillator swing in proportion to the supply voltage maintains constant gain with varying supply voltage. FS1 and FS2 program the oscillator to a frequency of 125kHz, 250kHz, 500kHz, and 1MHz. The sawtooth oscillator swings between GND and 0.6 VCC. The input signal is typically AC-coupled to the internal input op amp, whose gain can be controlled through external feedback components. The common-mode voltage of the input amplifier is 0.3 VCC and is internally generated from the same resistive divider used to generate the 0.6 VCC reference for the PWM oscillator.
100s. A continuous short circuit at the output results in a pulsating output.
Thermal Overload Protection
Thermal overload protection limits total power dissipation in the MAX4295/MAX4297. When the junction temperature exceeds +145C, the thermal detection disables the H-bridge transistors. The H-bridge transistors are enabled after the IC's junction temperature cools by 10C. This results in a pulsating output under continuous thermal overload conditions. Junction temperature does not exceed the thermal overload trip point in normal operation, but only in the event of fault conditions, such as when the H-bridge outputs are short circuited.
Undervoltage Lockout
At low supply voltages, the MOSFETs in the H-bridge may have inadequate gate drive thus dissipating excessive power. The undervoltage lockout circuit prevents the device from operating at supply voltages below +2.2V.
Current Limit
A current-limiting circuit in the H-bridge monitors the current in the H-bridge transistors and disables the Hbridge if the current in any of the H-bridge transistors exceeds 1A. The H-bridge is enabled after a period of
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11
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
PVCC OUT+R OUT-R
GATE DRIVE AOUTR INR
GATE DRIVE
PGND
VCC FS1 FS2 PWM OSC POWER MANAGEMENT AND PROTECTION GND SS CSS
PGND INL AOUTL 0.3 VCC (VCM) GATE DRIVE GATE DRIVE
PVCC OUT+L OUT-L
Figure 1b. MAX4297 Functional Diagram
Low-Power Shutdown Mode
The MAX4295/MAX4297 have a shutdown mode that reduces power consumption and extends battery life. Driving SHDN low disables the H-bridge, turns off the circuit, and places the MAX4295/MAX4297 in a lowpower shutdown mode. Connect SHDN to VCC for normal operation.
Applications Information
Component Selection
Gain Setting External feedback components set the gain of the MAX4295/MAX4297. Resistors RF and RIN set the gain of the input amplifier to -(RF/RIN). The amplifier's noninverting input is connected to the internally generated 0.3 V CC (VCM) that sets the amplifier's commonmode voltage.
12
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Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers
The amplifier's input bias current is low, 50pA, and does not affect the choice of feedback resistors. The noise in the circuit increases as the value of RF increases. The optimum impedance seen by the inverting input is between 5k and 20k. The effective impedance is given by (RF RIN)/(RF + RIN). For values of RF > 50k, a small capacitor (3pF) connected across RF compensates for the pole formed by the input capacitance and the effective resistance at the inverting input. Soft-Start (Clickless Startup) The H-bridge is disabled under any of the following conditions: * SHDN low * H-bridge current exceeds the 1A current limit * Thermal overload * Undervoltage lockout The circuit re-enters normal operation if none of the above conditions are present. A soft-start function prevents an audible pop on restart. An external capacitor connected to SS is charged by an internal 1.2A current source and controls the soft-start rate. VSS is held low while the H-bridge is disabled and allowed to ramp up to begin a soft-start. Until VSS reaches 0.3 VCC, the H-bridge output is limited to a 50% duty cycle, independent of the input voltage. The H-bridge duty cycle is then gradually allowed to track the input signal at a rate determined by the ramp on SS. The soft-start cycle is complete after VSS reaches 0.6 VCC. Input Filter High-fidelity audio applications require gain flatness between 20Hz to 20kHz. Set the low-frequency cutoff point with an AC-coupling capacitor in series with the input resistor of the amplifier, creating a highpass filter (Figure 3). Assuming the input node of the amplifier is a virtual ground, the -3dB point of the highpass filter is determined by: fLO = 1/(2 RIN CIN), where RIN is the input resistor, and CIN is the AC-coupling capacitor. Choose RIN as described in the Gain Setting section. Choose CIN such that the corner frequency is below 20Hz.
MAX4295/MAX4297
Frequency Selection
The MAX4295/MAX4297 have an internal logic-programmable oscillator controlled by FS1 and FS2 (Table 1). The oscillator can be programmed to frequencies of 125kHz, 250kHz, 500kHz, and 1MHz. The frequency should be chosen to best fit the application. As a rule of thumb, choose fOSC to be 10 times the audio bandwidth. A lower switching frequency offers higher amplifier efficiency and lower THD but requires larger external filter components. A higher switching frequency reduces the size and cost of the filter components at the expense of THD and efficiency. In most applications, the optimal fOSC is 250kHz.
Table 1. Frequency Select Logic
FS1 0 0 1 1 FS2 0 1 0 1 FREQUENCY (Hz) 125k 250k 500k 1M
RF
AOUT
INPUT CIN
RIN
IN
VIN VRAMP
VCM
+5V VOUT 0
Figure 3. Input Amplifier Configuration
Figure 2. PWM Waveforms ______________________________________________________________________________________ 13
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Output Filter
An output filter is required to attenuate the PWM switching frequency. Without the filter, the ripple in the load can substantially degrade efficiency and may cause interference problems with other electronic equipment. A Butterworth lowpass filter is chosen for its flat pass band and nice phase response, though other filter implementations may also be used. Three examples are presented below. The filter parameters for balanced 2-pole (Figure 4b) and 4-pole (Figure 4d) Butterworth filters are taken from Electronic Filter Design Handbook by Arthur B. Williams, McGraw Hill, Inc. These filter designs assume that the load is purely resistive and load impedance is constant over frequency. Calculation of filter component values should include the DC resistance of the inductors and take into account the worst-case load scenario: * Single Ended 2-Pole Filter (Figure 4a) C = 1 / (2 RL o), L = 2 RL / o where o = 2 fo (fo = filter cutoff frequency); choosing fo = 30kHz and RL = 4, C = 0.937F, L = 30H. A single-ended 2-pole filter uses the minimum number of external components, but the load (speaker) sees the large common-mode switching voltage, which can increase power dissipation and cause EMI problems. * Balanced 2-Pole (Figure 4b): A balanced 2-Pole filter does not have the commonmode swing problem of the single-ended filter. C = 2 / (2 RL o), L = (2 RL)/(2 o); choosing fo = 30kHz and RL = 4, C1a = C1b = 2.0F, L1a = L1b = 15H. A single capacitor connected across RL, with a value of CL = 1/(2 RL o), can be used in place of C1a and C1b. However, the configuration as shown gives an improved rejection to common-mode signal components of OUT+_ and OUT-_. If the single capacitor scheme is used, additional capacitors (Ca and Cb) can be added from each side of RL, providing a high-frequency short to ground (Figure 4c). These capacitors should be approximately 0.2 CL. * Balanced 4-Pole Filter (Figure 4d) A balanced 4-pole filter is more effective in suppressing the switching frequency and its harmonics. For the 4-pole Butterworth filter, the normalized values are: L1N = 1.5307, L2N = 1.0824, C1N = 1.5772, C2N = 0.3827. The actual inductance and capacitance values for fo = 30kHz and a bridge-tied load of RL = 4 are given by: L1 = (L1N RL ) / (2 o) = 16.24H, L2 = (L2N RL) / (2 o) = 11.5H, C1 = C1N / (RL o) = 2.1F, C2a = C2b = (2 C2N) / (RL o) = 1.0F.
L OUT+ OUT+
L1
Ca C RL Cb OUTOUTCL RL
L2
Figure 4a. Single-Ended 2-Pole Filter
Figure 4c. Alternate Balanced 2-Pole Filter
L1 OUT+ C1a RL C1b OUTOUTL2 OUT+
L1a
L2a
C2a C1 C2b RL
L1b
L2b
Figure 4b. Balanced 2-Pole Filter 14
Figure 4d. Balanced 4-Pole Filter
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Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers
Filter Components The inductor current rating should be higher than the peak current for a given output power requirement and should have relatively constant inductance over temperature and frequency. Typically, an open-core inductor is desirable since these types of inductors are more linear. Toroidal inductors without an air gap are not recommended. Q-shielded inductors may be required if the amplifier is placed in an EMI-sensitive system. The series resistance of the inductors will reduce the attenuation of the switching frequency and reduce efficiency due to the ripple current in the inductor. The capacitors should have a voltage rating 2 to 3 times the maximum expected RMS voltage--allowing for high peak voltages and transient spikes--and be stable over-temperature. Good quality capacitors with low equivalent series resistance (ESR) and equivalent series inductance (ESL) are necessary to achieve optimum performance. Low-ESR capacitors will decrease power dissipation. High ESL will shift the cutoff frequency, and high ESR will reduce filter rolloff.
MAX4295/MAX4297
TIP RING (LEFT) (RIGHT)
SLEEVE (GND)
Figure 6. Typical 3-Wire Headphone Plug
OUT+L
5
L1 C1a L2 C2a
CC
HEADPHONE JACK LEFT GND
OUT-L 20
MAX4297
OUT+R
8
CC
RIGHT
OUT-R 17
Figure 7. Headphone Application Circuit
Bridge-Tied Load/Single-Ended Configuration
The MAX4295/MAX4297 can be used as either a BTL or single-ended configured amplifier. The BTL configuration offers several advantages over a single-ended configuration. By driving the load differentially, the output voltage swing is doubled and the output power is quadrupled in comparison to a single-ended configuraL1a C1 Cc
must also be left open (Figure 5). Do not connect the unused output pin to ground.
Headphone Applications
The MAX4295/MAX4297 can be used to drive a set of headphones. A typical 3-wire headphone plug consists of a tip, ring, and sleeve. The tip and ring are signal carriers, while the sleeve is the ground connection (Figure 6). Figure 7 shows the MAX4297 configured to drive a set of headphones. The OUT+L and OUT+R pins are connected to the tip and ring and deliver the signal to the headphone jack, while the OUT-L and OUT-R pins remain unconnected. The ground connection in the jack should be connected to the same ground plane as the output filter.
OUT+
1
MAX4295
OUT16
RL
Total Harmonic Distortion
The MAX4295/MAX4297 exhibit typical THD plus noise of <1% for input frequencies <10kHz. The PWM frequency affects THD performance. THD can be reduced by limiting the input bandwidth through the input highpass filter, choosing the lowest fOSC possible, and carefully selecting the output filter and its components.
Figure 5. MAX4295 Single-Ended Configuration
tion. Because the differential outputs are biased at half supply, there is no DC voltage across the load, eliminating the need for large DC blocking capacitors at the output. The MAX4295/MAX4297 can be configured as singleended amplifiers. In such a case, the load must be capacitively coupled to the filter to block the half-supply DC voltage from the load. The unused output pin
Bypassing and Layout Considerations
Distortion caused by supply ripple due to H-bridge switching can be reduced through proper bypassing of PV CC . For optimal performance, a 330F, low-ESR POSCAP capacitor to PGND and a 1F ceramic capacitor to GND at each PVCC input is suggested. Place the 1F capacitor close to the PVCC pin. Bypass VCC with
15
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Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
a 10F capacitor in parallel with a 1F capacitor to GND. Ceramic capacitors are recommended due to their low ESR. Good PC board layout techniques optimize performance by decreasing the amount of stray capacitance at the amplifier's inputs and outputs. To decrease stray capacitance, minimize trace lengths by placing external components as close as possible to the amplifier. Surface-mount components are recommended. The MAX4295/MAX4297 require two separate ground planes to prevent switching noise from the MOSFETs in the H-bridge from coupling into the rest of the circuit. PGND, the power ground, is utilized by the H-bridge and any external output components, while GND is used by the rest of the circuit. Connect the PGND and GND planes at only one point, as close to the power supply as possible. Any external components associated with the output of the MAX4295/MAX4297 must be connected to the PGND plane where applicable. Use the Typical Operating Circuit diagram as a reference. Refer to the evaluation kit manual for suggested component values, component suppliers, and layout.
Chip Information
TRANSISTOR COUNT: MAX4295: 846 MAX4297: 1191 PROCESS: BiCMOS
Pin Configurations
TOP VIEW
AOUTL 1 GND 1 PVCC 2 OUT+ 3 PGND 4 VCC 5 VCM 6 IN 7 AOUT 8 16 SS 15 PVCC 14 OUTINL 2 VCC 3 PVCC 4 OUT+ L 5 PGND 6 PGND 7 OUT+ R 8 PVCC 9 GND 10 INR 11 AOUTR 12 24 SS 23 VCC 22 SHDN 21 PVCC
MAX4295
13 PGND 12 GND 11 FS2 10 FS1 9 SHDN
MAX4297
20 OUT- L 19 PGND 18 PGND 17 OUT-R 16 PVCC 15 FS2 14 FS1 13 VCM
SO/QSOP
SO/SSOP
16
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Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Package Information
SSOP.EPS
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QSOP.EPS
17
Mono/Stereo 2W Switch-Mode (Class-D) Audio Power Amplifiers MAX4295/MAX4297
Package Information (continued)
SOICN.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.
18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SOICW.EPS

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