LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier General Description Key Specifications The LM4674 is a single supply, high efficiency, 2.5W/channel, filterless switching audio amplifier. A low noise PWM architecture eliminates the output filter, reducing external component count, board area consumption, system cost, and simplifying design. The LM4674 is designed to meet the demands of mobile phones and other portable communication devices. Operating from a single 5V supply, the device is capable of delivering 2.5W/channel of continuous output power to a 4 load with less than 10% THD+N. Flexible power supply requirements allow operation from 2.4V to 5.5V. The LM4674 features high efficiency compared to conventional Class AB amplifiers. When driving an 8 speaker from a 3.6V supply, the device features 85% efficiency at PO = 500mW. Four gain options are pin selectable through the G0 and G1 pins. Output short circuit protection prevents the device from being damaged during fault conditions. Superior click and pop suppression eliminates audible transients on power-up/down and during shutdown. Independent left/right shutdown control maximizes power savings in mixed mono/stereo applications. Efficiency at 3.6V, 100mW into 8 80% (typ) Efficiency at 3.6V, 500mW into 8 85% (typ) Efficiency at 5V, 1W into 8 85% (typ) Quiescent Power Supply Current at 3.6V supply 4mA Power Output at VDD = 5V, RL = 4, THD 10% 2.5W (typ) Power Output at VDD = 5V, RL = 8, THD 10% 1.5W (typ) Shutdown current 0.03A (typ) Features Output Short Circuit Protection Stereo Class D operation No output filter required Logic selectable gain Independent shutdown control Minimum external components Click and Pop suppression Micro-power shutdown Available in space-saving 2mm x 2mm x 0.6mm micro SMD, and 4mm x 4mm x 0.8mm LLP packages Applications Mobile phones PDAs Laptops Boomer(R) is a registered trademark of National Semiconductor Corporation. (c) 2008 National Semiconductor Corporation 201674 www.national.com LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier July 2, 2008 LM4674 Typical Application 20167463 Ci = 1 F CS1 = 1 F CS2 = 0.1 F FIGURE 1. Typical Audio Amplifier Application Circuit External Components Description (Figure 1) Components Functional Description 1. CS Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for information concerning proper placement and selection of the supply bypass capacitor. 2. Ci Input AC coupling capacitor which blocks the DC voltage at the amplifier's input terminals. www.national.com 2 LM4674 Connection Diagrams TL Package (2mm x 2mm x 0.6mm) LM4674TL Markings 20167462 Top View XY = 2 Digit date code TT = Lot traceability G = Boomer Family G2 = LM4674TL 20167461 Top View Order Number LM4674TL See NS Package Number TL1611A LLP Package (4mm x 4mm x 0.8mm) LM4674SQ Markings 20167465 Top View U = Wafer Fab Code Z = Assembly Plant XY = 2 Digit date code TT = Lot traceability L4674SQ = LM4674SQ 20167466 Top View Order Number LM4674SQ See NS Package Number SQA16A 3 www.national.com LM4674 www.national.com BUMP PIN NAME FUNCTION A1 4 INL+ Non-inverting left channel input A2 6 PVDD Power VDD A3 7 OUTLA Left channel output A A4 8 OUTLB Left channel output B B1 3 INL- Inverting left channel input B2 5 G1 Gain setting input 1 B3 10 SDR Right channel shutdown input B4 9 SDL Left channel shutdown input C1 2 INR- Inverting right channel input C2 16 G0 Gain setting input 0 C3 12 GND Ground C4 11 PGND Power Ground D1 1 INR+ Non-inverting right channel input D2 15 VDD Power Supply D3 14 OUTRA Right channel output A D4 13 OUTRB Right channel output B 4 If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note 1) 6.0V Storage Temperature -65C to +150C Input Voltage -0.3V to VDD +0.3V Power Dissipation (Note 3) Internally Limited ESD Susceptibility, all other pins (Note 4) 2000V ESD Susceptibility (Note 5) 200V 150C JA (SMD) 45.7C/W JA (LLP) 38.9C/W Operating Ratings (Notes 1, 2) Temperature Range TMIN TA TMAX Supply Voltage -40C TA 85C 2.4V VDD 5.5V Electrical Characteristics VDD = 3.6V (Notes 1, 2) The following specifications apply for AV = 6dB, RL = 15H + 8 + 15H, f = 1kHz unless otherwise specified. Limits apply for TA = 25C. LM4674 Symbol VOS IDD Parameter Differential Output Offset Voltage Quiescent Power Supply Current Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) VIN = 0, VDD = 2.4V to 5.0V 5 VIN = 0, RL = , Both channels active, VDD = 3.6V 4 6 mA VIN = 0, RL = , Both channels active, VDD = 5V 5 7.5 mA 0.03 1 A VSDR = VSDL = GND mV ISD Shutdown Current VSDIH Shutdown Voltage Input High 1.4 V (min) VSDIL Shutdown Voltage Input Low 0.4 V (max) TWU Wake Up Time VSDR/SDL = 0.4V 0.5 G0, G1 = GND RL = G0 = VDD, G1 = GND AV Gain RL = G0 = GND, G1 = VDD RL = G0, G1 = VDD RL = RIN Input Resistance ms 6 6 0.5 dB 12 12 0.5 dB 18 18 0.5 dB 24 24 0.5 dB AV = 6dB 28 k AV = 12dB 18.75 k AV = 18dB 11.25 k AV = 24dB 6.25 k 5 www.national.com LM4674 Junction Temperature (TJMAX) Thermal Resistance Absolute Maximum Ratings (Notes 1, 2) LM4674 LM4674 Symbol Parameter Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) RL = 15H + 4 + 15H, THD 10% f = 1kHz, 22kHz BW VDD = 5V 2.5 W VDD = 3.6V 1.2 W VDD = 2.5V 0.530 W 1.5 W RL = 15H + 8 + 15H, THD 10% f = 1kHz, 22kHz BW VDD = 5V PO Output Power VDD = 3.6V 0.78 VDD = 2.5V 0.350 0.6 W W RL = 15H + 4 + 15H, THD 1% f = 1kHz, 22kHz BW VDD = 5V 1.9 W VDD = 3.6V 1 W VDD = 2.5V 0.430 W VDD = 5V 1.25 W VDD = 3.6V 0.63 W VDD = 2.5V RL = 15H + 8 + 15H, THD = 1% f = 1kHz, 22kHz BW THD+N PSRR Total Harmonic Distortion Power Supply Rejection Ratio 0.285 W PO = 500mW, f = 1kHz, RL = 8 0.07 % PO = 300mW, f = 1kHz, RL = 8 0.05 % VRIPPLE = 200mVP-P Sine, fRIPPLE = 217Hz, Inputs AC GND, 75 dB 75 dB 67 dB RL = 8, VDD = 5V 85 % Ci = 1F, input referred VRIPPLE = 1VP-P Sine, fRIPPLE = 1kHz, Inputs AC GND, Ci = 1F, input referred VRIPPLE = 1VP-P fRIPPLE = 217Hz CMRR Common Mode Rejection Ratio Efficiency Xtalk Crosstalk PO = 500mW, f = 1kHz 84 dB SNR Signal to Noise Ratio VDD = 5V, PO = 1W 96 dB OS Output Noise Input referred, A-Weighted Filter 20 V PO = 1W, f = 1kHz, Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: 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 guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, JA, and the ambient temperature, TA. The maximum allowable power dissipation is PDMAX = (TJMAX - TA)/ JA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4674 see power derating currents for more information. Note 4: Human body model, 100pF discharged through a 1.5k resistor. Note 5: Machine Model, 220pF-240pF discharged through all pins. Note 6: Typicals are measured at 25C and represent the parametric norm. Note 7: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level). Note 8: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. www.national.com 6 LM4674 Block Diagrams 20167426 FIGURE 2. Differential Input Configuration 7 www.national.com LM4674 20167464 FIGURE 3. Single-Ended Input Configuration www.national.com 8 LM4674 Typical Performance Characteristics THD+N vs Output Power f = 1kHz, AV = 24dB, RL = 8 THD+N vs Output Power f = 1kHz, AV = 6dB, RL = 8 20167439 20167440 THD+N vs Output Power f= 1kHz, AV = 24dB, RL = 4 THD+N vs Output Power f = 1kHz, AV = 6dB, RL = 4 20167442 20167441 THD+N vs Frequency VDD = 2.5V, POUT = 100mW/ch, RL = 8 THD+N vs Frequency VDD = 3.6V, POUT = 250mW/ch, RL = 8 20167443 20167444 9 www.national.com LM4674 THD+N vs Frequency VDD = 5V, POUT = 375mW/ch, RL = 8 THD+N vs Frequency VDD = 2.5V, POUT = 100mW/ch, RL = 4 20167445 20167446 THD+N vs Frequency VDD = 3.6V, POUT = 250mW/ch, RL = 4 THD+N vs Frequency VDD = 5V, POUT = 375mW/ch, RL = 4 20167448 20167447 Efficiency vs Output Power/channel RL = 4, f = 1kHz Efficiency vs Output Power/channel RL = 8, f = 1kHz 20167449 www.national.com 20167450 10 LM4674 Power Dissipation vs Output Power RL = 4, f = 1kHz Power Dissipation vs Output Power RL = 8, f = 1kHz 20167451 20167452 Output Power/channel vs Supply Voltage RL = 4, f = 1kHz Output Power/channel vs Supply Voltage RL = 8, f = 1kHz 20167453 20167454 PSRR vs Frequency VDD = 3.6V, VRIPPLE= 200mVP-P, RL = 8 Crosstalk vs Frequency VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8 20167422 20167455 11 www.national.com LM4674 CMRR vs Frequency VDD = 3.6V, VCM = 1VP-P, RL = 8 Supply Current vs Supply Voltage RL = 20167457 www.national.com 20167458 12 wanted state changes when SD_ is floating. To minimize shutdown current, SD_ should be driven to GND or left floating. If SD_ is not driven to GND or floating, an increase in shutdown supply current will be noticed. GENERAL AMPLIFIER FUNCTION The LM4674 stereo Class D audio power amplifier features a filterless modulation scheme that reduces external component count, conserving board space and reducing system cost. The outputs of the device transition from VDD to GND with a 300kHz switching frequency. With no signal applied, the outputs for each channel switch with a 50% duty cycle, in phase, causing the two outputs to cancel. This cancellation results in no net voltage across the speaker, thus there is no current to the load in the idle state. With the input signal applied, the duty cycle (pulse width) of the LM4674 outputs changes. For increasing output voltage, the duty cycle of the A output increases, while the duty cycle of the B output decreases for each channel. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION The LM4674 is compatible with single-ended sources. When configured for single-ended inputs, input capacitors must be used to block any DC component at the input of the device. Figure 3 shows the typical single-ended applications circuit. AUDIO AMPLIFIER POWER SUPPLY BYPASSING/ FILTERING Proper power supply bypassing is critical for low noise performance and high PSRR. Place the supply bypass capacitor as close to the device as possible. Typical applications employ a voltage regulator with 10F and 0.1F bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing of the LM4674 supply pins. A 1F capacitor is recommended. DIFFERENTIAL AMPLIFIER EXPLANATION As logic supplies continue to shrink, system designers are increasingly turning to differential analog signal handling to preserve signal to noise ratios with restricted voltage signs. The LM4674 features two fully differential amplifiers. A differential amplifier amplifies the difference between the two input signals. Traditional audio power amplifiers have typically offered only single-ended inputs resulting in a 6dB reduction of SNR relative to differential inputs. The LM4674 also offers the possibility of DC input coupling which eliminates the input coupling capacitors. A major benefit of the fully differential amplifier is the improved common mode rejection ratio (CMRR) over single ended input amplifiers. The increased CMRR of the differential amplifier reduces sensitivity to ground offset related noise injection, especially important in noisy systems. AUDIO AMPLIFIER INPUT CAPACITOR SELECTION Input capacitors may be required for some applications, or when the audio source is single-ended. Input capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of the audio source and the bias voltage of the LM4674. The input capacitors create a highpass filter with the input resistance Ri. The -3dB point of the high pass filter is found using Equation 1 below. f = 1 / 2RiCi (1) The values for Ri can be found in the EC table for each gain setting. The input capacitors can also be used to remove low frequency content from the audio signal. Small speakers cannot reproduce, and may even be damaged by low frequencies. High pass filtering the audio signal helps protect the speakers. When the LM4674 is using a single-ended source, power supply noise on the ground is seen as an input signal. Setting the high-pass filter point above the power supply noise frequencies, 217 Hz in a GSM phone, for example, filters out the noise such that it is not amplified and heard on the output. Capacitors with a tolerance of 10% or better are recommended for impedance matching and improved CMRR and PSRR. POWER DISSIPATION AND EFFICIENCY The major benefit of a Class D amplifier is increased efficiency versus a class AB amplifier. The efficiency of the LM4674 is attributed to the region of operation of the transistors in the output stage. The Class D output stage acts as current steering switches, consuming negligible amounts of power compared to their Class AB counterparts. Most of the power loss associated with the output stage is due to the IR loss of the MOSFET on-resistance (RDS(ON)), along with switching losses due to gate charge. SHUTDOWN FUNCTION The LM4674 features independent left and right channel shutdown controls, allowing each channel to be disabled independently. SDR controls the right channel, while SDL controls the left channel. Driving either low disables the corresponding channel. It is best to switch between ground and VDD for minimum current consumption while in shutdown. The LM4674 may be disabled with shutdown voltages in between GND and VDD, the idle current will be greater than the typical 0.03A value. For logic levels between GND and VDD bypass SD_ with a 0.1F capacitor. The LM4674 shutdown inputs have internal pulldown resistors. The purpose of these resistors is to eliminate any un- AUDIO AMPLIFIER GAIN SETTING The LM4674 features four internally configured gain settings. The device gain is selected through the two logic inputs, G0 and G1. The gain settings are as shown in the following table. LOGIC INPUT 13 GAIN G1 G0 V/V dB 0 0 2 6 0 1 4 12 1 0 8 18 1 1 16 24 www.national.com LM4674 Application Information LM4674 use of power planes creates parasitic capacitors that help to filter the power supply line. The inductive nature of the transducer load can also result in overshoot on one or both edges, clamped by the parasitic diodes to GND and VDD in each case. From an EMI standpoint, this is an aggressive waveform that can radiate or conduct to other components in the system and cause interference. In is essential to keep the power and output traces short and well shielded if possible. Use of ground planes beads and micros-strip layout techniques are all useful in preventing unwanted interference. As the distance from the LM4674 and the speaker increases, the amount of EMI radiation increases due to the output wires or traces acting as antennas become more efficient with length. Ferrite chip inductors places close to the LM4674 outputs may be needed to reduce EMI radiation. PCB LAYOUT GUIDELINES As output power increases, interconnect resistance (PCB traces and wires) between the amplifier, load and power supply create a voltage drop. The voltage loss due to the traces between the LM4674 and the load results in lower output power and decreased efficiency. Higher trace resistance between the supply and the LM4674 has the same effect as a poorly regulated supply, increasing ripple on the supply line, and reducing peak output power. The effects of residual trace resistance increases as output current increases due to higher output power, decreased load impedance or both. To maintain the highest output voltage swing and corresponding peak output power, the PCB traces that connect the output pins to the load and the supply pins to the power supply should be as wide as possible to minimize trace resistance. The use of power and ground planes will give the best THD +N performance. In addition to reducing trace resistance, the www.national.com 14 LM4674 LM4674TL Demo Board Schematic 20167474 LM4674TL Demo Board Schematic 15 www.national.com LM4674 LM4674TL Demonstration Board Layout 20167476 Layer 1 20167477 Layer 2 20167478 Layer 3 www.national.com 16 LM4674 20167479 Layer 4 20167480 Top Silkscreen 20167475 Bottom Silkscreen 17 www.national.com LM4674 LM4674SQ Demo Board Schematic 20167481 LM4674SQ Demo Board Schematic www.national.com 18 LM4674 LM4674SQ Demonstration Board Layout 20167485 Layer 1 20167483 Layer 2 20167484 Layer 3 19 www.national.com LM4674 20167486 Top Silkscreen 20167487 Bottom Layer www.national.com 20 LM4674 Revision Table Rev Date 1.0 12/16/06 Initial release. Description 1.1 05/17/06 Added the LLP package. 1.2 05/31/06 Added the LLP markings. 1.3 09/05/06 Added "No Load" in the Conditions on Av (3.6V table). 1.4 09/21/06 Edited graphics (26, 38, 60) and input some text edits. 1.5 09/27/06 Edited Figure 1 (page 2), TL and LLP pkg/marking drawings (page 3). Input text edits. 1.6 07/13/07 Added the TL and SQ demo boards and schematics diagrams. 1.7 10/30/07 Updated the SQ schematic diagram and replaced the demo boards. 1.8 07/02/08 Text edits (under SHUTDOWN FUNCTION). 21 www.national.com LM4674 Physical Dimensions inches (millimeters) unless otherwise noted 16 Bump micro SMD Order Number LM4674TL NS Package Number TLA1611A X1 = 2mm X2 = 2mm X3 = 0.6mm LLP Package Order Number LM4674SQ NS Package Number SQA16A www.national.com 22 LM4674 Notes 23 www.national.com LM4674 Filterless 2.5W Stereo Class D Audio Power Amplifier Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Design Support Amplifiers www.national.com/amplifiers WEBENCH www.national.com/webench Audio www.national.com/audio Analog University www.national.com/AU Clock Conditioners www.national.com/timing App Notes www.national.com/appnotes Data Converters www.national.com/adc Distributors www.national.com/contacts Displays www.national.com/displays Green Compliance www.national.com/quality/green Ethernet www.national.com/ethernet Packaging www.national.com/packaging Interface www.national.com/interface Quality and Reliability www.national.com/quality LVDS www.national.com/lvds Reference Designs www.national.com/refdesigns Power Management www.national.com/power Feedback www.national.com/feedback Switching Regulators www.national.com/switchers LDOs www.national.com/ldo LED Lighting www.national.com/led PowerWise www.national.com/powerwise Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors Wireless (PLL/VCO) www.national.com/wireless THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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