9-0731; Rev 0; 1/07 KIT ATION EVALU E L B AVAILA Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs Features The MAX9742 stereo Class D audio power amplifier delivers up to 2 x 16W into 4Ω loads. The MAX9742 features high-power efficiency (92% with 8Ω loads), eliminating the need for a bulky heatsink and conserving power. The MAX9742 operates from a 20V to 40V single supply or a ±10V to ±20V dual supply.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs ABSOLUTE MAXIMUM RATINGS VDD to VSS, NSENSE ..............................................-0.3V to +45V MID, LGND, LVDD, REGM, REGP, OUTR, OUTL to VSS .......................................................-0.3V to +45V MID, LGND, LVDD, REGM, REGP, OUTR, OUTL to VDD.......................................................-45V to +0.3V REGLS to VSS .........................................................-0.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs (VDD = 24V, VSS = VSUB = LGND = 0V, VSHDN = 3.3V, VMID = 12V, CVDD = 660µF, CMID1 = 10µF, CMID2 = 10µF, R1 = R2 = R3 = 10kΩ, CSFT = 0.47µF, COUT = 1000µF, CFB_1 = 150pF, CFB_2 = 10pF, CBOOT = 0.1µF, CREGP = CREGM = 1µF, RIN_ = 30.1kΩ, RF1A = 121kΩ, RF1B = 562kΩ, RF2 = 681kΩ, RREF = 68kΩ, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs ELECTRICAL CHARACTERISTICS—Dual Supplies (continued) (VDD = 15V, VSS = VSUB = -15V, VSHDN = 3.3V, VMID = LGND = 0V, CVDD = CVSS = 1000µF, CBYP = 1µF, CSFT = 0.22µF, CFB_1 = 150pF, CFB_2 = 10pF, CBOOT = 0.1µF, CREGP = CREGM = 1µF, RIN_ = 30.1kΩ, RF1A = 121kΩ, RF1B = 562kΩ, RF2 = 681kΩ, RREF = 68kΩ, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs (VDD = 24V, VSS = VSUB = LGND = 0V, VSHDN = 3.3V, VMID = 12V, CVDD = 660µF, CMID1 = 10µF, CMID2 = 10µF, R1 = R2 = R3 = 10kΩ, CSFT = 0.47µF, COUT = 1000µF, CFB_1 = 150pF, CFB_2 = 10pF, CBOOT = 0.1µF, CREGP = CREGM = 1µF, RIN_ = 30.1kΩ, RF1A = 121kΩ, RF1B = 562kΩ, RF2 = 681kΩ, RREF = 68kΩ, RL = ∞, TA = TMIN to TMAX, unless otherwise noted. Typical values are at TA = +25°C.
Typical Operating Characteristics (24V single-supply mode, ±15V dual-supply mode, both channels driven in phase, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25°C, unless otherwise noted. See Figure 1 for test circuits, see Typical Application Circuits/Functional Diagrams for test circuit component values.) SINGLE SUPPLY VDD = 24V f = 1kHz SINGLE SUPPLY VDD = 32V f = 1kHz SINGLE SUPPLY VDD = 36V f = 1kHz 10 10 RL = 6Ω 1 RL = 8Ω RL = 6Ω 1 THERMALLY LIMITED RL = 4Ω 0.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs 1 f = 1kHz 0.1 f = 100Hz 1 f = 1kHz 1 f = 100Hz f = 100Hz 0 10 20 30 5 10 0 15 5 OUTPUT POWER PER CHANNEL (W) OUTPUT POWER PER CHANNEL (W) TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs. FREQUENCY DUAL SUPPLY RL = 4Ω 10 0.1 f = 100Hz 1 THD+N (%) THD+N (%) f = 1kHz POUT = 8W POUT = 13W 1 0.1 0.1 0.
Typical Operating Characteristics (continued) (24V single-supply mode, ±15V dual-supply mode, both channels driven in phase, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25°C, unless otherwise noted. See Figure 1 for test circuits, see Typical Application Circuits/Functional Diagrams for test circuit component values.) TOTAL HARMONIC DISTORTION PLUS NOISE vs. OUTPUT POWER WITH AND WITHOUT T-NETWORK TOTAL HARMONIC DISTORTION PLUS NOISE vs.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs 6 60 SYSTEM POWER DISSIPATION 4 30 3 BTL CONFIGURATION VDD = 24V RL = 8Ω fIN = 1kHz 20 10 0 20 30 10 1% THD+N 5 0 10% THD+N 15 1% THD+N 10 5 0 0 50 40 ±10 ±12 ±14 ±16 ±18 ±10 ±20 ±12 ±14 ±16 ±18 OUTPUT POWER (W) SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) OUTPUT POWER vs. SUPPLY VOLTAGE OUTPUT POWER vs. SUPPLY VOLTAGE OUTPUT POWER vs.
Typical Operating Characteristics (continued) (24V single-supply mode, ±15V dual-supply mode, both channels driven in phase, THD+N measurement bandwidth = 22Hz to 22kHz, TA = +25°C, unless otherwise noted. See Figure 1 for test circuits, see Typical Application Circuits/Functional Diagrams for test circuit component values.) 0.2 MAX9742 toc36 -60 -80 30 35 1.0 5k 10k 20k 15k POWER-SUPPLY REJECTION RATIO vs. FREQUENCY POWER-SUPPLY REJECTION RATIO vs. FREQUENCY POWER-SUPPLY REJECTION RATIO vs.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs MAX9742 toc45 MAX9742 toc44 DUAL SUPPLY RL = 8Ω VOUT_ 20V/div FILTERED VOUT_ 5V/div VOUT_ 10V/div VOUT_ 10V/div FILTERED VOUT_ 5V/div FILTERED VOUT_ 5V/div 10ms/div CASE TEMPERATURE vs. OUTPUT POWER CASE TEMPERATURE vs.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs Pin Description PIN NAME 1, 6, 18, 27, 28, 36 N.C. 2, 3 OUTL 4 SUB 5 BOOTL 7 INL+ Left-Channel Positive Input 8 INL- Left-Channel Negative Input. Connect an external feedback capacitor between INL- and FBL. See the Feedback Capacitor (CFB_) section. 9 FBL Left-Channel Feedback Capacitor Terminal. Connect an external feedback capacitor between FBL and INL-. See the Feedback Capacitor (CFB_) section.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs PIN NAME 24 BOOTR FUNCTION 25, 26 OUTR 29, 30, 34, 35 VDD Positive Power-Supply Input. Bypass VDD to LGND with a 0.1µF plus additional bulk capacitance. See the Supply Pumping Effects section. 31, 32, 33 VSS Negative Power-Supply Input. For dual-supply operation, connect to negative power-supply voltage and bypass VSS to LGND with a 0.1µF plus additional bulk capacitance. For single-supply operation, connect to LGND.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs efficiency of a linear amplifier is 78%; however, that efficiency is only exhibited at peak output powers. Under normal operating levels (typical music reproduction levels), efficiency falls below 30%, whereas the MAX9742 still exhibits 80% efficiency under the same conditions.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs MAX9742 1 fSW INTERNAL TRIANGLE WAVE OSCILLATOR INPUT SIGNAL VDD VOUT_ VDD + VSS 2 VSS NOTE: FOR CLARITY, SIGNAL PERIODS ARE NOT SHOWN TO ACTUAL SCALE. Figure 3a. MAX9742 Output with an Applied Input Signal VOUT_ VDD AVERAGE VALUE OF VOUT_ VDD + VSS 2 VSS NOTE: FOR CLARITY, SIGNAL PERIODS ARE NOT SHOWN TO ACTUAL SCALE. Figure 3b.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs Shutdown Mode The MAX9742 features a low-power shutdown mode that reduces quiescent current consumption to less than 0.5mA in single-supply mode and less than 1µA in dual-supply mode. Drive SHDN low to place the device into shutdown mode. Connect SHDN to a logic-high for normal operation. The maximum voltage that may be applied to the SHDN input is 4V (see the Absolute Maximum Ratings section).
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs ( ) VOUT_P−P = 2 2 POUT_10% × RL (V) where POUT_10% is the output power that causes 10% THD+N, RL is the load resistance, and VOUT_P-P is the peak-to-peak output voltage.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs Summing Configuration (Audio Mixer) Figure 6 shows the MAX9742 configured as a summing amplifier, which allows multiple audio sources to be linearly mixed together.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs Component Selection Feedback Capacitor (CFB_) To maximize dynamic range, an external feedback capacitor (CFB_) is needed to generate an error signal for the Class D modulator. The feedback capacitor configures the input amplifier stage as an integrator whose output is equal to an error signal consisting of the sum of the integrated input audio and PWM output signals.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs To guarantee stability and minimize distortion, select the external feedback resistor (R F_ ) and capacitor (CFB_) so that the following conditions are met: RF_ × CFB_ ≥ 21.5 and RF _ > 400kΩ fSW where f SW is the output switching frequency determined by R REF (see the Setting the Switching Frequency and Output Current Limit (RREF) section).
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs 1 (F) 4 × π × fC × RSPKR × ζ 1 LF = (H) 2 4 × π × fC2 × CF CF = Since the frequency response of the output filter is dependent on the speaker resistance, it is best to optimize the LC filter for a particular load resistance. To calculate the component values of the LC filter for a given speaker load resistance, first select an appropriate cutoff frequency for the filter.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs To maximize the performance of the differential output filter and minimize EMI radiation, keep the ground connections of the CF capacitors close together on the PCB and place the filter near the MAX9742. The component ratings for CF and LF follow the same requirements mentioned in the Single-Ended LC Output Filter Design (LF and CF) section.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs Capacitor (CBOOT) For most applications, use a CBOOT capacitor ≥ 0.1µF and ≤ 0.22µF. For proper operation, use capacitors with low ESR and voltage ratings greater than 7V for CBOOT. Output-Coupling Capacitors (COUT, Single-Ended, Single-Supply Operation) The MAX9742 requires output-coupling capacitors for single-supply operation.
Multiple-Pole MID Network vs. Single-Pole VMID Network for Increased PSRR Performance (Single-Supply Operation) A multiple-pole MID network improves PSRR performance over a single-pole network. Since the input amplifiers of the MAX9742 are biased at V MID, any noise coupled into the MID input using the MID bias network supply appears at the outputs of the MAX9742.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs For dual-supply operation, the startup time of the MAX9742 is primarily dependent on the value of CSFT since it controls the rate of the soft-start sequencing. In single-supply operation, the overall startup time is affected by the values of CMID1, CMID2, CSFT, COUT (single-ended outputs) and the value of the resistors used to bias the MID input.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs IPUMP = DUTY CYCLE x IAVG VDD CVDD OFF VDD CVDD ON LF IAVG IAVG LF CF CF OFF ON VSS CVSS VSS CVSS CASE 1: IAVG FLOWING INTO HALF-BRIDGE CAUSING VOLTAGE ACROSS CVDD TO INCREASE (DUTY CYCLE < 50%). IAVG = AVERAGE (CONTINUOUS) OUTPUT CURRENT DURING ONE SWITCHING CYCLE. IPUMP = AMOUNT OF CURRENT PUMPED INTO SUPPLY BYPASS CAPACITOR. Figure 13a.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs capacitor decreases the supply voltage variations due to supply pumping. Using large bypass capacitors helps minimize supply voltage variations by providing sufficient supply decoupling at low output frequencies.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs T-Network for Low THD Performance at Low Output Powers (Optional) If low THD+N performance is needed at low-output powers, replace the feedback resistor (RF1) in each channel with the T-network shown in Figure 15. The T-network provides additional attenuation of audio band noise, therefore, providing improved THD+N performance at lower output powers.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs Thermal Considerations Class D amplifiers provide much better efficiency and thermal performance than a comparable Class AB amplifier. However, the system’s thermal performance must be considered with realistic expectations along with its many parameters. Continuous Sine Wave vs. Music When a Class D amplifier is evaluated in the lab, often a continuous sine wave is used as the signal source.
28 N.C. 29 VDD 30 VDD 31 VSS 32 VSS 33 VSS 34 VDD 35 VDD 27 N.C. 2 26 OUTR 3 25 OUTR 4 24 BOOTR 5 23 REGLS 22 NSENSE 7 21 INR+ 8 20 INR- 9 19 FBR 1 + MAX9742 12 13 14 15 16 17 18 REGP REFCUR SFT LGND LVDD SHDN N.C. 6 11 N.C. OUTL OUTL SUB BOOTL N.C. INL+ INLFBL 36 N.C. TOP VIEW 10 Auxiliary Heatsinking If operating in higher ambient temperatures, it is possible to improve the thermal performance of a PCB with the addition of an external heatsink.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs RF1 CFBL 10V TO 20V FBL VDD LEFT NEGATIVE AUDIO INPUT LEFT POSITIVE AUDIO INPUT CIN CIN RIN1 INL- RIN2 MAX9742 CLASS D MODULATOR AND HALF-BRIDGE INL+ RF2 OUTL LF RZBL CFBL CF CZBL MID RF2 RIGHT POSITIVE AUDIO INPUT RIGHT NEGATIVE AUDIO INPUT CIN RIN2 CIN RIN1 CFBR CLASS D MODULATOR AND HALF-BRIDGE INR+ OUTR LF RZBL INRCONTROL LOGIC/ POWER-UP SEQUENCING FBR VSS CZBL SFT SHDN CFBR CF ON CSFT -10V
CMID1 10µF R2 10kΩ R1 10kΩ VDD CMID2 10µF R3 10kΩ = PGND RIN1 30.1kΩ RIN2 30.1kΩ RIN2 30.1kΩ RIN1 30.1kΩ CFBL 150pF CFBR 150pF RF2 681kΩ RF2 681kΩ CONNECT PGND AND SGND TO A SINGLE POINT ON THE PCB NEAR THE MAX9742 CIN 0.47µF CIN 0.47µF CIN 0.47µF = SGND RIGHT NEGATIVE AUDIO INPUT RIGHT POSITIVE AUDIO INPUT LEFT POSITIVE AUDIO INPUT LEFT NEGATIVE AUDIO INPUT CIN 0.
= PGND CFBL1 150pF CFBR1 150pF RF2 681kΩ RF2 681kΩ CONNECT PGND AND SGND TO A SINGLE POINT ON THE PCB NEAR THE MAX9742 CIN 0.47µF RIN2 30.1kΩ CIN 0.47µF RIN1 30.1kΩ RIN2 30.1kΩ RIN1 30.1kΩ CIN 0.47µF = SGND RIGHT NEGATIVE AUDIO INPUT RIGHT POSITIVE AUDIO INPUT LEFT POSITIVE AUDIO INPUT LEFT NEGATIVE AUDIO INPUT CIN 0.47µF DUAL-SUPPLY OPERATION DEVICE CONNECTED FOR AV = 22V/V. 20 INR- VMID - 5V - + 17 14 SFT OPTIONAL ON CFBR2 10pF RF1a 121kΩ OFF SHDN 19 VDD CSFT 0.
CMID1 10µF R2 10kΩ R1 10kΩ VDD CMID2 10µF R3 10kΩ POSITIVE AUDIO INPUT NEGATIVE AUDIO INPUT = PGND RF2 681kΩ RF2 681kΩ CONNECT PGND AND SGND TO A SINGLE POINT ON THE PCB NEAR THE MAX9742 RIN1 30.1kΩ CIN 0.47µF = SGND RIN2 30.1kΩ RIN2 30.1kΩ RIN1 30.1kΩ CIN 0.47µF CIN 0.47µF CIN 0.47µF BRIDGE-TIED-LOAD (BTL), SINGLE-SUPPLY OPERATION DEVICE CONNECTED FOR AV = 44V/V.
Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs QFN THIN.EPS ______________________________________________________________________________________ 35 MAX9742 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.
MAX9742 Single-/Dual-Supply, Stereo 16W, Class D Amplifier with Differential Inputs 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.) Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.
