OBSOLETE LM4682 www.ti.com LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 10 Watt Stereo CLASS D Audio Power Amplifier with Stereo Headphone Amplifier and DC Volume Control Check for Samples: LM4682 FEATURES DESCRIPTION * * * * * * The LM4682 is a fully integrated single supply, high efficiency audio power amplifier solution. The LM4682 utilizes a proprietary balanced pulse-width modulation technique that lowers output noise and THD and improves PSRR when compared to conventional pulse width modulators. 1 2 Pulse-Width Modulator DC Volume Control Stereo Headphone Amplifier "Click and Pop" Suppression Circuitry Micropower Shutdown Mode 48-Lead WQFN Package (No Heatsink Required) APPLICATIONS * * * Flat Panel Displays Televisions Multimedia Monitors KEY SPECIFICATIONS * * * * * * * PO at THD+N = 10%, VDD = 14V 10W (typ) THD+N at 1kHz at 6W into 8 (Power Amp) 0.2% (typ) Efficiency at 7W into 8 84% (typ) Total Quiescent Power Supply Current 52mA (typ) Total Shutdown Power Supply Current 0.1mA (typ) THD+N 1kHz, 20mW, 32 (Headphone) 0.02% (typ) Single Supply Range 8.5V to 15V The LM4682 also features a stereo headphone amplifier that delivers 60mW into a 32 headset with less than 0.5% THD. The LM4682's DC volume control has a +30dB to -48dB range when speakers are driven and a range of +13dB to -65dB when headphones are connected. All amplifiers are protected by thermal shutdown. Additionally, all amplifiers incorporate output current limiting function to protect their outputs from short circuit. The LM4682 features a low-power consumption shutdown mode. And its efficiency reaches 85% for a 10W output power with an 8 load. External heatsink is not required when playing music. The IC features click and pop reduction circuitry that minimizes audible popping during device turn-on and turn-off. The LM4682 is available in a 48-lead WQFN package, ideal for portable and desktop computer applications. 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 2006-2013, Texas Instruments Incorporated OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Block Diagram Figure 1. Block Diagram for LM4682 2 Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 BST1_B NC IN_B BYPASS_B HPOUT_B HP_VDD HP_GND HPOUT_A BYPASS_A IN_A VREF BST1_A 48 47 46 45 44 43 42 41 40 39 38 37 Connection Diagram PGND_B 7 30 PGND_A OUT2_B 8 29 OUT2_A OUT2_B 9 28 OUT2_A OUT2_B 10 27 OUT2_A PVDD_B 11 26 PVDD_A PVDD_B 12 25 PVDD_A 24 PGND_A BST2_A 31 23 6 NC PGND_B 22 OUT1_A HPSEL 32 21 5 VOL_CTL OUT1_B 20 OUT1_A VOLVDD 33 19 4 GND_A OUT1_B 18 OUT1_A VDD_A 34 17 3 NC OUT1_B 16 PVDD_A SDB 35 15 2 MUTEB PVDD_B 14 PVDD_A NC 36 13 1 BST2_B PVDD_B Figure 2. 48-Lead WQFN - Top View See RHS Package Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 3 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com Typical Application VDD 1 PF 43 VDD 18 1 PF Click-Pop Suppression + + 1 PF 1 PF + Attenuator 40 38 VREF 45 + Attenuator + + 21 0.1 PF 22 48 0.22 PF 0.1 PF 0.22 PF 3,4,5 0.22 PF 8,9,10 PWM 13 + - 44 22 PH 0.22 PF 0.1 PF 100 PF To PWM Power Management Over-Current Protection Thermal Protection 100 k: 25,26, 1,2, 35,36 11,12 10 PF 100 k: 22 PH 22 PH Class D DC Volume Control Shutdown 16 VDD 0.22 PF 27,28,29 24 Balanced PWM B VREF 15 20 HP GND 0.1PF Preamp 5V 0.22 PF 32,33,34 Class D Balanced PWM A VDD/2 46 Mute 0.1 PF 22 PH 39 10 PF To HP Sense Pin on Headphone Jack 41 37 + Preamp 1 PF 1 k: 100 PF + To PWM 19 1 PF 100 k: To Headphone Jack Output Pin 0.1 PF 42 VDD VDD 6,7 30,31 0.1 PF 1 k: HP GND + To HP Sense Circuit From Decoupled HP Output A 14 Stereo Headphone Jack HP GND + 4.7 PF 10 PF + 4.7 PF Figure 3. Typical Stereo Audio Amplifier with Headphone Selection Circuit 4 Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Absolute Maximum Ratings (1) (2) Supply Voltage 15.5V -0.3V to VDD +0.3V Input Voltage Power Dissipation (3) Internally Limited ESD Susceptibility (4) 2000V ESD Susceptibility (5) 200V Junction Temperature (6) 150C -65C TA 150C Storage Temperature Soldering Information (1) (2) (3) (4) (5) (6) WQFN Package Vapor Phase (60 sec.) 215C Infrared (15 sec.) 220C "Absolute Maximum Ratings" indicate limits beyond which damage to the device may occur. "Operating Ratings" indicate conditions for which the device is functional, but do not specify performance limits. "Electrical Characteristics" state DC and AC electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication of device performance. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. For operating at case temperatures above 25C, the device must be derated based on a 150C maximum junction temperature and a thermal resistance of JA = 28C/W (junction to ambient). Human body model, 100pF discharged through a 1.5k resistor. Device pin 16 has ESD HBM rating = 1500V. Machine Model 220pF-240pF discharged through all pins. The operating junction temperature maximum is 150C. Operating Ratings (1) TMIN TA TMAX Temperature Range -40C TA +85C 8.5V VDD 15V Supply Voltage Thermal Resistance (WQFN Package) (1) JA 28C/W JC 20C/W All voltages are measured with respect to the ground pin, unless otherwise specified. Electrical Characteristics (1) (2) The following specifications apply for VDD = 12V, VOLVDD = 5V, RL = 8, LC filter values as shown in Figure 3, unless otherwise specified. Limits apply for TA = 25C. Symbol VDD Parameter Conditions LM4682 Typical Max Min 12 15 8.5 Operating Supply Voltage Range Units V Quiescent Power Supply Current, Class D Mode VIN = 0VRMS, VHPSEL = 0V 52 70 mA Quiescent Power Supply Current, Headphone Mode VIN = 0VRMS, VHPSEL = 12V 30 40 mA ISD Quiescent Power Supply Current, Shutdown Mode SDB = 0V 0.1 RIN Input Resistance in Both Modes VOLVDD DC Reference Supply Voltage VIH Minimum Logic High Input Voltage VIL Maximum Logic Low Input Voltage VHPIH HP Sense High Input Voltage VHPIL HP Sense Low Input Voltage IS mA 8 k 5.5 SDB, MUTEB pins 3 V 0.7xVOLVDD V 0.3xVOLVDD V VDD-1 VDD/2 V V Power Amplifiers POR Output Power, Per Channel THD+N 1%, fIN = 1kHz 6.0 PD1 Power Dissipation PO = 7W/Chan, fIN = 1kHz 2.6 (1) (2) 5.5 W W All voltages are measured with respect to the ground pin, unless otherwise specified. Limits are specified to AOQL (Average Outgoing Quality Level). Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 5 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com Electrical Characteristics(1)(2) (continued) The following specifications apply for VDD = 12V, VOLVDD = 5V, RL = 8, LC filter values as shown in Figure 3, unless otherwise specified. Limits apply for TA = 25C. Symbol Parameter Conditions LM4682 Typical Max Min Units EFF1 Efficiency PO = 7W/Chan, fIN = 1kHz 84.4 % THD+N Harmonic Distortion + Noise PO = 6W/Chan, fIN = 1kHz 0.2 % Output Noise Voltage, RMS. A-Weighted RSOURCE = 50, CIN = 1F, BW = 8Hz to 22kHz A-weighted, input referred 13 V VNOISE VRIPPLE = 200mVpp, 1kHz, VIN = 0, input referred PSRR Power Supply Rejection Ratio f = 50Hz 94 f = 60Hz 94 f 100Hz 93 f = 120Hz 93 f = 1kHz 84 dB Headphone Amplifiers PO Power Out Per Channel THD+N 1%, RL = 32, fIN = 1kHz THD+N Distortion + Noise PO = 20mW, RL = 32, fIN = 1kHz 0.02 % VNOISE Output Noise Voltage, RMS RIN = 50, CIN = 1F, BW = 20Hz to 20kHz A-weighted, input referred 9 V PSRR Power Supply Rejection Ratio (Referred to Input) 200mV, 1kHz, VIN = 0, RL = 32 88 dB 80 60 mW Electrical Characteristics for Volume Control (1) The following specifications apply for VDD = 12V. Limits apply for TA = 25C. Symbol CRANGE AM (1) (2) (3) 6 Parameter Gain Range Mute Gain LM4682 Conditions Typical (2) Limit (3) Units (Limits ) VOL_CTL voltage = VOLVDD voltage, No Load Power Amplifier Headphone Amplifier 30 13 29 12 dB (min) dB (min) VOL_CTL voltage = 0.069 x VOLVDD No Load Power Amplifier Headphone Amplifier -48 -65 -46 -63 dB (min) dB (min) VMUTE voltage = 0V, No Load Power Amplifier Headphone Amplifier -80 -70 -60 -60 dB (max) dB (max) All voltages are measured with respect to the ground pin, unless otherwise specified. Typicals are measured at 25C and represent the parametric norm. Limits are specified to AOQL (Average Outgoing Quality Level). Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Typical Performance Characteristics (Power Amplifier) THD+N vs Frequency VDD = 9V, RL = 8, PO = 1W 1 1 0.5 0.5 0.2 0.2 0.1 0.1 THD+N (%) THD+N (%) THD+N vs Frequency VDD = 12V, RL = 8, PO = 1W 0.05 0.02 0.05 0.02 0.01 0.01 0.005 0.005 0.002 0.002 0.001 20 1 50 100 200 500 1k 2k 0.001 20 5k 10k 20k 50 100 200 500 1k 2k 5k 10k 20k FREQUENCY (Hz) FREQUENCY (Hz) Figure 4. Figure 5. THD+N vs Frequency VDD = 15V, RL = 8, PO = 1W THD+N vs Output Power Per Channel VDD = 9V, fIN = 1kHz, RL = 8 20 0.5 10 0.2 1 THD+N (%) THD+N (%) 0.1 0.05 0.02 0.01 0.1 0.005 0.01 0.002 50 100 200 500 1k 2k 0.002 10m 5k 10k 20k 100m 1 10 FREQUENCY (Hz) OUTPUT POWER PER CHANNEL (W) Figure 6. Figure 7. THD+N vs Output Power Per Channel VDD = 12V, fIN = 1kHz, RL = 8 THD+N vs Output Power Per Channel VDD = 15V, fIN = 1kHz, RL = 8 20 20 10 10 1 1 THD+N (%) THD+N (%) 0.001 20 0.1 0.01 0.1 0.01 0.002 10m 100m 1 0.002 20m 10 200m 2 OUTPUT POWER PER CHANNEL (W) OUTPUT POWER PER CHANNEL (W) Figure 8. Figure 9. 20 Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 7 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com Typical Performance Characteristics (Power Amplifier) (continued) THD+N vs Output Power Per Channel VDD = 12V, fIN = 20Hz, RL = 8 20 20 10 10 1 1 THD+N (%) THD+N (%) THD+N vs Output Power Per Channel VDD = 12V, fIN = 10kHz, RL = 8 0.1 0.01 0.01 0.002 10m 14 100m 1 0.002 10m 10 Figure 10. Figure 11. Output Power vs Supply Voltage fIN = 1kHz, RL = 8 Amplifiers Gain vs Frequency VDD = 9V, RL = 8, PO = 1W 40 10 Class-D Amplifier Gain Po = 1W RL = 8: 30 10 THD+N = 10% 8 6 THD+N = 1% 4 20 10 HP Amplifier Gain Po = 20mW RL = 32: 2 0 0 40 10 11 13 14 12 POWER SUPPLY VOLTAGE (V) 20 15 200 2k FREQUENCY (Hz) 20k Figure 12. Figure 13. Amplifiers Gain vs Frequency VDD = 12V, RL = 8, PO = 1W Amplifiers Gain vs Frequency VDD = 15V, RL = 8, PO = 1W 40 Class-D Amplifier Gain Po = 1W RL = 8: Class-D Amplifier Gain Po = 1W RL = 8: 30 GAIN (dB) 30 GAIN (dB) 1 OUTPUT POWER PER CHANNEL (W) 12 9 20 10 20 10 HP Amplifier Gain Po = 20mW RL = 32: 0 HP Amplifier Gain Po = 20mW RL = 32: 0 20 200 2k FREQUENCY (Hz) 20k Figure 14. 8 100m OUTPUT POWER PER CHANNEL (W) GAIN (dB) CLASS-D AMPLIFIER OUTPUT POWER (W) 0.1 20 200 2k FREQUENCY (Hz) 20k Figure 15. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Typical Performance Characteristics (Power Amplifier) (continued) PSRR vs Frequency VDD = 9V 120 100 100 80 80 PSRR (dB) PSRR (dB) 120 60 60 40 40 20 20 0 0 10 100 1k 10k 10 100k 10k 100k Figure 16. Figure 17. PSRR vs Frequency VDD = 15V Class-D Amplifier Dissipation vs Load Dissipation Per Channel, VDD = 9V, RL = 8 (both channels driven and measured) CLASS-D AMPLIFIER DISSIPATION (W) 80 60 40 20 0 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0 100 1k 10k 100k 0 1 2 3 4 5 6 LOAD DISSIPATION PER CHANNEL (W) FREQUENCY (Hz) Figure 18. Figure 19. Class-D Amplifier Dissipation vs Load Dissipation Per Channel, VDD = 12V, RL = 8 (both channels driven and measured) Class-D Amplifier Dissipation vs Load Dissipation Per Channel, VDD = 15V, RL = 8 (both channels driven and measured) CLASS-D AMPLIFIER DISSIPATION (W) 5.0 CLASS-D AMPLIFIER DISSIPATION 1k FREQUENCY (Hz) 100 10 100 FREQUENCY (Hz) 120 PSRR (dB) PSRR vs Frequency VDD = 12V 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 6 5 4 3 2 1 0 0 2 4 6 8 10 12 0 2 4 6 8 10 12 14 16 LOAD DISSIPATION PER CHANNEL (W) LOAD DISSIPATION PER CHANNEL (W) Figure 20. Figure 21. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 9 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com Typical Performance Characteristics (Power Amplifier) (continued) Efficiency vs Output Power VDD = 9V, RL = 8 (both channels driven and measured) Efficiency vs Output Power VDD = 12V, RL = 8 (both channels driven and measured) 100 90 90 80 80 70 70 EFFICIENCY (%) EFFICIENCY (%) 100 60 50 40 30 60 50 40 30 20 20 10 10 0 0 0 1 2 3 4 5 6 0 OUTPUT POWER PER CHANNEL (W) 4 10 12 Efficiency vs Output Power VDD = 15V, RL = 8 (both channels driven and measured) Output Power vs Load Resistance VDD = 9V, fIN = 1kHz (both channels driven and measured) OUTPUT POWER PER CHANNEL (W) 5 80 70 60 50 40 30 20 10 0 4.5 4 3.5 3 2.5 THD+N = 10% 2 1.5 THD+N = 1% 1 0.5 0 0 4 2 6 8 10 12 14 16 8 12 OUTPUT POWER PER CHANNEL (W) 16 20 24 28 32 LOAD IMPEDANCE (: Figure 24. Figure 25. Output Power vs Load Resistance VDD = 12V, fIN = 1kHz (both channels driven and measured) Output Power vs Load Resistance VDD = 15V, fIN = 1kHz (both channels driven and measured) 14 OUTPUT POWER PER CHANNEL (W) 10 OUTPUT POWER PER CHANNEL (W) 8 Figure 23. 90 9 8 7 6 THD+N = 10% 5 4 3 2 THD+N = 1% 1 12 10 8 THD+N = 10% 6 4 THD+N = 1% 2 0 0 8 12 16 20 24 28 32 LOAD IMPEDANCE (: Figure 26. 10 6 Figure 22. 100 EFFICIENCY (%) 2 OUTPUT POWER PER CHANNEL (W) 8 12 16 24 28 20 LOAD IMPEDANCE (: 32 Figure 27. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Typical Performance Characteristics (Power Amplifier) (continued) 56 40 55 30 54 20 53 10 GAIN (dB) POWER SUPPLY CURRENT (mA) Power Supply Current vs Power Supply Voltage 52 51 50 Class-D Amplifier Gain vs Volume Control Voltage VDD = 15V 0 -10 -20 49 -30 48 -40 47 -50 -60 46 9 10 11 12 13 14 15 0 1 2 3 4 5 VOLUME CONTROL VOLTAGE (V) POWER SUPPLY VOLTAGE (V) Figure 28. Figure 29. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 11 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com Typical Performance Characteristics (Headphone Amplifier) 1 THD+N vs Frequency VDD = 9V, RL = 32, PO = 20mW THD+N vs Frequency VDD = 12V, RL = 32, PO = 20mW 1 0.2 0.2 0.1 0.1 0.05 0.02 0.05 0.02 0.01 0.01 0.005 0.005 0.002 0.002 0.001 20 50 100 200 500 1k 2k 0.001 20 5k 10k 20k Figure 30. Figure 31. THD+N vs Frequency VDD = 15V, RL = 32, PO = 20mW THD+N vs Output Power VDD = 9V, RL = 32, fIN = 1kHz 10 0.5 5 0.2 2 0.1 1 THD+N (%) THD+N (%) 5k 10k 20k FREQUENCY (Hz) 0.05 0.02 0.5 0.2 0.01 0.1 0.005 0.05 0.002 0.02 0.001 20 50 100 200 500 1k 2k 0.01 10P 100P 1m 10m 100m 1 OUTPUT POWER PER CHANNEL (W) 5k 10k 20k FREQUENCY (Hz) Figure 32. Figure 33. THD+N vs Output Power VDD = 12V, RL = 32, fIN = 1kHz THD+N vs Output Power VDD = 15V, RL = 32, fIN = 1kHz 10 10 5 5 2 2 1 THD+N (%) 1 THD+N (%) 50 100 200 500 1k 2k FREQUENCY (Hz) 1 0.5 0.2 0.5 0.2 0.1 0.1 0.05 0.05 0.02 0.02 0.01 10P 100P 1m 10m 100m 1 OUTPUT POWER PER CHANNEL (W) 0.01 10P 100P 1m 10m 100m 1 OUTPUT POWER PER CHANNEL (W) Figure 34. 12 R 0.5 THD+N (%) THD+N (%) 0.5 Figure 35. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Typical Performance Characteristics (Headphone Amplifier) (continued) Output Power vs Supply Voltage Per Channel fIN = 1kHz, RL = 32 Power Supply Current vs Power Supply Voltage 33 87.5 POWER SUPPLY CURRENT (mA) HEADPHONE AMPLIFIER OUTPUT POWER PER CHANNEL (mW) 100 THD+N = 1% 75 62.5 THD+N = 0.1% 50 37.5 25 12.5 0 32.5 32 31.5 31 30.5 30 29.5 29 28.5 28 9 10 11 12 13 14 15 9 POWER SUPPLY VOLTAGE (V) 10 11 12 13 14 15 POWER SUPPLY VOLTAGE (V) Figure 36. Figure 37. 20 Headphone Amplifier Gain vs Volume Control Voltage VDD = 15V 10 0 GAIN (dB) -10 -20 -30 -40 -50 -60 -70 0 1 2 3 4 5 VOLUME CONTROL VOLTAGE (V) Figure 38. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 13 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com GENERAL FEATURES SYSTEM FUNCTIONAL INFORMATION Modulation Technique Unlike typical Class D amplifiers that use single-ended comparators to generate a pulse-width modulated switching waveform and RC timing circuits to set the switching frequency, the LM4682 uses a balanced differential floating modulator. Oscillation is a result of injecting complimentary currents onto the respective plates of a floating, on-die capacitor. The value of the floating capacitor and value of the components in the modulator's feedback network set the nominal switching frequency at 450kHz. Modulation results from imbalances in the injected currents. The amount of current imbalance is directly proportional to the applied input signal's magnitude and frequency. Using a balanced, floating modulator produces a Class D amplifier that is immune to common mode noise sources such as substrate noise. This noise occurs because of the high frequency, high current switching in the amplifier's output stage. The LM4682 is immune to this type of noise because the modulator, the components that set its switching frequency, and even the load all float with respect to ground. The balanced modulator's pulse width modulated output drives the gates of the LM4682's H-bridge configured output power MOSFETs. The pulse-train present at the power MOSFETs' output is applied to an LC low pass filter that removes the 450kHz energy component. The filter's output signal, which is applied to the driven load, is an amplified replica of the audio input signal. Shutdown Function The LM4682's active-low shutdown function allows the user to place the amplifier in a shutdown mode while the system power supply remains active. Activating shutdown stops the output switching waveform and minimizes the quiescent current. Applying logic "0" to SDB pin enables the shutdown function. Applying logic "1" to SDB pin disables the shutdown function and restores full amplifier operation. Mute Function The LM4682's active-low mute function allows the user to place the amplifier outputs in muted mode while the amplifier's analog input signals remain active. Activating mute internally removes the analog input signal from the Class D and headphone amplifier inputs. While muted the amplifier inputs and outputs retain in their VDD/2 operational bias. Applying logic "0" to MUTEB pin activates mute. Applying logic "1" to MUTEB pin deactivates mute. The MUTEB pin is pull-down internally to put both Class D and headphone amplifier outputs mute. Stereo Headphone Amplifier The LM4682's stereo headphone amplifier operates continuously, even while the Class D amplifiers are active. When using headphones to listen to program material, it is usually desirable to stop driving external speakers. This is easily achieved by using the active high HPSEL input. As shown in typical application schematic in Figure 1, with no headphones connected to the headphone jack, the input voltage applied to the HPSEL pin is a logic low. In this state, the Class D amplifiers are active and able to drive external speakers. When headphones are plugged into the headphone jack, the switch inside the jack is opened. This changes the voltage applied to the HPSEL pin to a logic high, shutting off the LM4682's Class D amplifiers. The headphone control of the output configuration is shown in Table 1. Table 1. Headphone Controls HP Sense Pin, HPSEL 14 Output Stage Configuration 0 Class D Amps Active 1 Class D Amps Inactive Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Under Voltage Protection The under voltage protection disables the output driver section of the LM4682 while the supply voltage is below 8V. This condition may occur as power is first applied or during low line conditions, changes in load resistance, or when power supply sag occurs. The under voltage protection ensures that all of the LM4682's power MOSFETs are off. This action eliminates shoot-through current and minimizes output transients during turn-on and turn-off. The under voltage protection gives the digital logic time to stabilize into known states, further minimizing turn on output transients. Power Supply Sequencing In order to stabilize LM4682 before any operation, a power-up sequence for the power supplies is recommended. The Power VDD should be applied first. Without deactivating the mute and shutdown function of the amplifiers, the VOLVDD is then applied. Prior to removing the two supply voltages, activate shutdown and mute. Turn-On Time The LM4682 has an internal timer that determines the amplifier's turn-on time. After power is first applied or the part returns from shutdown, the nominal turn-on time is 600ms. This delay allows all externally applied capacitors to charge to a final value of VDD/2. Further, during turn-on, the outputs are muted. This minimizes output transients that may occur while the part settles into its quiescent operating mode. Output Stage Current Limit and Fault Detection Protection The output stage MOSFETs are protected against output conditions that could otherwise compromise their operational status. The first stage of protection is output current limiting. When conditions that require high currents to drive a load, the LM4682's current limit circuitry clamps the output current at a nominal value of 2.5A. The output waveform is present, but may be clipped or its amplitude reduced. The same 2.5A nominal current limit also occurs if the amplifier outputs are shorted together or either output is shorted to VDD or GND. The second stage of protection is an onboard fault detection circuit that continuously monitors the signal on each output MOSFET's gate and compares it against the respective drain voltage. When a condition is detected that violates a MOSFET's Safe Operating Area (SOA) and the drive signal is disconnected from the output MOSFETs' gates. The fault detect circuit maintains this protective condition for approximately 600ms, at which time the drive signal is reconnected. If the fault condition is no longer present, normal operation resumes. If the fault condition remains, however, the drive signal is again disconnected. Thermal Protection The LM4682 has thermal shutdown circuitry that monitors the die temperature. Once the LM4682 die temperature reaches 170C, the LM4682 disables the output switching waveform and remains disabled until the die temperature falls below 140C (typ). Over-Modulation Protection The LM4682's over-modulation protection is a result of the preamplifier's inability to produce signal magnitudes that equal the power supply voltages. Since the preamplifier's output magnitude will always be less than the supply voltage, the duty cycle of the amplifier's switching output will never reach zero. Peak modulation is limited to a nominal 95%. DC Volume Control The LM4682 has an internal stereo volume control whose setting is a function of the DC voltage applied to the volume control pin VOLCTL. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 15 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com The LM4682 volume control consists of 31 steps, which are individually selected by a variable DC voltage level on the VOLCTL pin. A linear type 100k potentiometer is used to adjust the VOLCTL voltage in the LM4682 demonstration board as shown in application circuit (see Figure 3). The resistance value of potentiometer fall in the range from 10k to 100k is recommended to be used with only small amount of current dissipation and large enough for the VOLCTL pin to function properly. The Volume Control Characteristics of LM4682 can be found in the Typical Performance Characteristics (Headphone Amplifier) section. The gain range of Class D amplifiers are from -48dB to 30dB. The gain range of headphone amplifiers are from -65dB to 13dB. Each gain step corresponds to specific input voltage of both Class D amplifiers and headphone amplifiers are shown in Table 2. To minimize the effect of noise on the volume control VOLCTL pin, which can affect the selected gain level, hysteresis has been implemented. The amount of hysteresis corresponds to half of the step width. For highest accuracy, the voltage shown in the "recommended voltage" column of the table is used to select a desired gain. The recommended voltage is exactly halfway between the two closest transitions to the next highest or next lowest gain levels. Table 2. Volume Control Table Voltage Range (% of VOLVDD) Step 16 Voltage Range (V), VOLVDD = 5V Gain (dB) Low High Recommended Low High Recommended Class D Amplifier 1 77.50% 100.00% 100.000% 3.875 5.000 5.000 29.97 13.06 2 75.00% 78.50% 76.875% 3.750 3.925 3.844 28.97 12.07 3 72.50% 76.25% 74.375% 3.625 3.813 3.719 27.97 11.07 4 70.00% 73.75% 71.875% 3.500 3.688 3.594 26.96 10.06 5 67.50% 71.25% 69.375% 3.375 3.563 3.469 25.98 9.07 6 65.00% 68.75% 66.875% 3.250 3.438 3.344 24.97 8.07 7 62.50% 66.25% 64.375% 3.125 3.313 3.219 23.95 7.05 8 60.00% 63.75% 61.875% 3.000 3.188 3.094 21.98 5.08 9 57.50% 61.25% 59.375% 2.875 3.063 2.969 19.95 3.05 10 55.00% 58.75% 56.785% 2.750 2.983 2.844 17.96 1.06 11 52.50% 56.25% 54.375% 2.625 2.813 2.719 15.97 -0.93 12 50.00% 53.75% 51.875% 2.500 2.688 2.594 13.99 -2.91 13 47.50% 51.25% 49.375% 2.375 2.563 2.469 11.99 -4.91 14 45.00% 48.75% 46.875% 2.250 2.438 2.344 9.95 -6.96 15 42.50% 46.25% 44.375% 2.125 2.313 2.219 7.96 -8.94 16 40.00% 43.75% 41.875% 2.000 2.188 2.094 5.96 -10.95 17 37.50% 41.25% 39.375% 1.875 2.063 1.969 3.99 -12.91 18 35.00% 38.75% 36.875% 1.750 1.938 1.844 2.03 -14.87 19 32.50% 36.25% 34.375% 1.625 1.813 1.719 -0.02 -16.92 20 30.00% 33.75% 31.875% 1.500 1.688 1.594 -2.11 -19.02 21 27.50% 31.25% 29.375% 1.375 1.563 1.469 -4.16 -21.06 22 25.00% 28.75% 26.875% 1.250 1.438 1.344 -5.97 -22.87 23 22.50% 26.25% 24.375% 1.125 1.313 1.219 -8.77 -25.68 24 20.00% 23.75% 21.875% 1.000 1.188 1.094 -12.06 -28.96 25 17.50% 21.25% 19.375% 0.875 1.063 0.969 -14.84 -31.75 26 15.00% 18.75% 16.875% 0.750 0.938 0.844 -17.36 -34.26 27 12.50% 16.25% 14.375% 0.625 0.813 0.719 -20.89 -37.79 28 10.00% 13.75% 11.875% 0.500 0.688 0.594 -26.92 -43.83 29 7.50% 11.25% 9.375% 0.375 0.563 0.469 -32.95 -49.85 30 5.00% 8.75% 6.875% 0.250 0.438 0.344 -38.97 -55.88 31 0.00% 6.25% 0.000% 0.000 0.313 0.000 -48.03 -64.94 Submit Documentation Feedback Headphone Amplifier Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Application Hints SUPPLY BYPASSING The major source of noises to be taken care and applying bypassing technique in using LM4682 are those transients response coming from its output stage. During the switching operations of the output stage of LM4682, the switching frequencies vary when the internal modulator react to the input signals. This creates a band of switching transients giving back to the power supply terminals of LM4682. A single capacitor may not bypass those transients well. Two capacitors which values are closed to each other are used to bypass this range of frequencies to the ground. 10F tantalum capacitors and 4.7F ceramic capacitors are needed for this kind of decoupling of LM4682 switching operation. This results an improvement in terms of both stability and audio performance of LM4682. In addition, these capacitors should be placed as close as possible to each IC's supply pin(s) using leads as short as possible. Apart from the power supply de-coupling capacitors, the four bootstrapping capacitors (at pins BST1_A, BST2_A, BST1_B and BST2_B) should also be placed close to their corresponding pins. This could minimize the undesirable switching noise coupled to the supply rail. The LM4682 has two different sets of VDD pins: a set for power VDD (PVDD_A and P VDD _B) and a set for signal VDD _A and HP_ VDD. The parallel combination of the low value ceramic (4.7F) and high value tantalum (10F) should be used to bypass the power VDD pins. A small value (1F) ceramic or tantalum can be used to bypass the signal VDD _A and HP_ VDD pin. OUTPUT STAGE FILTERING The LM4682 requires a low pass filter connected between the amplifier's bridge output and the load. Figure 3 shows the recommended LC filter. A minimum value of 22H is recommended. As shown in Figure 3, using the values of the components connected between the amplifier BTL outputs and the load achieves a 2nd-order lowpass filter response which optimizes the amplifier's performance within the audio band. THD+N MEASUREMENTS AND OUT OF AUDIO BAND NOISE THD+N (Total Harmonic Distortion plus Noise) is a very important parameter by which all audio amplifiers are measured. Often it is shown as a graph where either the output power or frequency is changed over the operating range. A very important variable in the measurement of THD+N is the bandwidth-limiting filter at the input of the test equipment. Class D amplifiers, by design, switch their output power devices at a much higher frequency than the accepted audio range (20Hz - 20kHz). Alternately switching the output voltage between VDD and GND allows the LM4682 to operate at much higher efficiency than that achieved by traditional Class AB amplifiers. Switching the outputs at high frequency also increases the out-of-band noise. Under normal circumstances the output lowpass filter significantly reduces this out-of-band noise. If the low pass filter is not optimized for a given switching frequency, there can be significant increase in out-of-band noise. THD+N measurements can be significantly affected by out-of-band noise, resulting in a higher than expected THD+N measurement. To achieve a more accurate measurement of THD, the test equipment's input bandwidth of the must be limited. Some common upper filter points are 22kHz, 30kHz, and 80kHz. The input filter limits the noise component of the THD+N measurement to a smaller bandwidth resulting in a more real-world THD+N value. RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT Figure 39 through Figure 43 show the recommended four-layer PCB board layout that is optimized for the 48-pin WQFN packaged LM4682 and associated external components. This circuit is designed for use with an external 12V supply and 8 speakers (or load resistors). Apply 12V and ground to board's VDD and GND terminals respectively. And apply 5V to the VOLVDD (refer to Power Supply Sequencing for details). Connect speakers (or load resistors) between the board's OUTA+ and OUTA-, and between the board's OUTB+ and OUTB-. Apply the stereo input signals to IN_A and IN_B. When designing the layout of the PCB layout, please pay attention to the output terminals of LM4682. Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 17 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com Figure 39. Top Layer Figure 40. Top Silkscreen Layer 18 Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 Figure 41. Upper Middle Layer Figure 42. Lower Middle Layer Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 19 OBSOLETE LM4682 SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 www.ti.com Figure 43. Bottom Layer 20 Submit Documentation Feedback Copyright (c) 2006-2013, Texas Instruments Incorporated Product Folder Links: LM4682 OBSOLETE LM4682 www.ti.com SNAS271E - FEBRUARY 2006 - REVISED APRIL 2013 REVISION HISTORY Rev Date 1.0 02/22/06 Initial WEB release of the document. Description 1.1 02/24/06 Edited art 201196 71 (changed the y-axis unit from mA to mW. 1.2 03/08/06 Did few texts clean-up and re-released D/S to the WEB (per Kevin H.). 1.3 06/29/06 Added 2 columns on ( Gain dB) Table 2 and re-released the D/S to the WEB (per Alex CK Wong). 1.4 04/09/08 Added volume control curves and input some text edits. 1.5 04/15/08 Changed the titles on curves 20119628 and 29. 1.6 04/21/08 Text edits. E 04/10/13 Changed layout of National Data Sheet to TI format. 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