EVALUATION KIT AVAILABLE MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier General Description The MAX9708 mono/stereo, Class D audio power amplifier delivers up to 2 x 21W into an 8Ω stereo mode and 1 x 42W into a 4Ω load in mono mode while offering up to 87% efficiency. The MAX9708 provides Class AB amplifier performance with the benefits of Class D efficiency, eliminating the need for a bulky heatsink and conserving power.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier ABSOLUTE MAXIMUM RATINGS Continuous Power Dissipation (TA = +70°C) 56-Pin TQFN (derate 47.6mW/°C above +70°C) ............3.81W Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range .............................-65°C to +150°C Junction Temperature ......................................................+150°C Thermal Resistance (θJC) 56-Pin TQFN… ..............................................
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier ELECTRICAL CHARACTERISTICS (continued) (PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, MONO = low (stereo mode), SHDN = MUTE = high, G1 = low, G2 = high (AV = 22dB), FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are connected between OUT_+ and OUT_-, unless otherwise stated. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier ELECTRICAL CHARACTERISTICS (continued) (PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, MONO = low (stereo mode), SHDN = MUTE = high, G1 = low, G2 = high (AV = 22dB), FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are connected between OUT_+ and OUT_-, unless otherwise stated. TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Typical Operating Characteristics (PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO = low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and OUT_-, TA = +25°C, unless otherwise stated.) 10 RL = 8Ω THD+N (%) 1 1 PVDD = 18V, 8Ω STEREO MODE, POUT = 8.3W PER CHANNEL 0.01 0.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Typical Operating Characteristics (continued) (PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO = low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and OUT_-, TA = +25°C, unless otherwise stated.) 0.1 0.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Typical Operating Characteristics (continued) (PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO = low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and OUT_-, TA = +25°C, unless otherwise stated.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Typical Operating Characteristics (continued) (PVDD = VDD = +18V, PGND = GND = 0V, CSS = 0.47µF, CREG = 0.01µF, C1 = 0.1µF, C2 = 1µF, RLOAD = ∞, SHDN = high, MONO = low, MUTE = high, G1 = low, G2 = high, FS1 = FS2 = high (SSM), SYNCIN = low. All load resistors (RL) are between OUT_+ and OUT_-, TA = +25°C, unless otherwise stated.) POWER-SUPPLY REJECTION RATIO vs.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Pin Description (continued) PIN NAME 8 C1N Charge-Pump Flying Capacitor C1, Negative Terminal FUNCTION 9 C1P Charge-Pump Flying Capacitor C1, Positive Terminal 10 CPVDD 11 SYNCOUT Charge-Pump Power Supply. Bypass to PVDD with a 1µF capacitor as close to the pin as possible.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Typical Application Circuits/Functional Diagrams VDD PVDD 0.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Typical Application Circuits/Functional Diagrams (continued) VDD PVDD 47μF* 0.1μF 0.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Detailed Description The MAX9708 filterless, Class D audio power amplifier features several improvements to switch-mode amplifier technology. The MAX9708 is a two-channel, stereo amplifier with 21W output power on each channel. The amplifier can be configured to output 42W output power in mono mode. The device offers Class AB performance with Class D efficiency, while occupying minimal board space.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier TEMP returns high once the junction temperature cools below the set threshold minus the thermal hysteresis. If TEMP is connected to either MUTE or SS, the audio output resumes. The temperature threshold is set by the TH0, TH1, and TH2 inputs as shown in Table 1. An RC filter may be used to eliminate any transient at the TEMP output as shown in Figure 3.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Linear Regulator (REG) The supply voltage range for the MAX9708 is from 10V to 18V to achieve high-output power. An internal linear regulator reduces this voltage to 6.3V for use with small-signal and digital circuitry that does not require a high-voltage supply. Bypass a 0.01µF capacitor from REG to GND.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Sharing Input Sources In certain systems, a single audio source can be shared by multiple devices (speaker and headphone amplifiers). When sharing inputs, it is common to mute the unused device, rather than completely shutting it down, preventing the unused device inputs from distorting the input signal. Mute the MAX9708 by driving MUTE low.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Auxiliary Heatsinking If operating in higher ambient temperatures, it is possible to improve the thermal performance of a PC board with the addition of an external heatsink. The thermal resistance to this heatsink must be kept as low as possible to maximize its performance. With a bottom-side exposed pad, the lowest resistance thermal path is on the bottom of the PC board.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Mismatch in the components can cause discrepancies between the nominal transfer function and actual performance. Also, the mismatch of the input resistors (R15, R17, R19, and R21 in Figure 6) of the summing amplifier and lowpass filter will cause some high-frequency sound to be sent to the subwoofer. The circuit in Figure 6 drives a pair of MAX9708 devices similar to the circuit in Figure 5.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier R1 56.2kΩ R2, 56.2kΩ R3 28kΩ C1 47nF C2 47nF 2 U1A MAX4478 R4 28kΩ RIGHT AUDIO INPUT R5 56.2kΩ BIAS 1 3 RIGHT AUDIO OUTPUT R6, 56.2kΩ R7 28kΩ C3 47nF C4 47nF 6 U1B MAX4478 R8 56.2kΩ BIAS 7 5 RIGHT AND LEFT OUTPUTS ARE AC-COUPLED TO A MAX9708 CONFIGURED AS A STEREO AMPLIFIER R9, 56.2kΩ R10 28kΩ C5 47nF C6 47nF 9 U1C MAX4478 R11 28kΩ LEFT AUDIO INPUT R12 56.2kΩ BIAS 8 10 LEFT AUDIO OUTPUT R13, 56.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Pin Configuration 35 34 33 G2 36 SHDN 37 TEMP 38 MUTE PVDD 39 TH1 PVDD 40 TH2 PGND 41 PVDD PGND 42 TH0 N.C. PGND TOP VIEW 32 31 30 29 N.C. 43 28 G1 N.C. 44 27 INR+ OUTR- 45 26 INR- OUTR- 46 25 VDD OUTR+ 47 24 SS OUTR+ 48 23 GND PGND 49 22 GND MAX9708 PGND 50 21 REG OUTL- 51 20 REG 6 7 8 9 10 11 12 13 14 FS2 5 SYNCIN 4 N.C. 3 SYNCOUT 2 C1P 1 CPVDD 15 FS1 C1N N.C.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. 20 PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Package Information (continued) For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status.
MAX9708 20W/40W, Filterless, Spread-Spectrum, Mono/Stereo, Class D Amplifier Revision History REVISION NUMBER REVISION DATE 3 4/13 DESCRIPTION Added automotive qualified part and removed TQFP package PAGES CHANGED 1, 2, 8–11, 20 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied.
