LM4674ATL

LM4674A Filterless 2.5W Stereo Class D Audio Power Amplifier September 2006 LM4674A Filterless 2.5W Stereo Class D Audio Power Amplifier General Description The LM4674A 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 LM4674A 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 4Ω load with less than 10% THD+N. Flexible power supply requirements allow operation from 2.4V to 5.5V. The LM4674A features high efficiency compared to conventional Class AB amplifiers. When driving an 8Ω speaker from a 3.6V supply, the device features 85% efficiency at PO = 500mW. Four gain options are pin selectable through the GAIN0 and GAIN1 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 controls maximizes power savings in mixed mono/stereo applications. Key Specifications j Efficiency at 3.6V, 100mW into 8Ω j Efficiency at 3.6V, 500mW into 8Ω j Efficiency at 5V, 1W into 8Ω j Quiescent Power Supply Current 80% (typ) 85% (typ) 85% (typ) 4mA 2.5W (typ) 1.5W (typ) 0.1µA (typ) at 3.6V supply j Power Output at VDD = 5V, RL = 4Ω, THD ≤ 10% j Power Output at VDD = 5V, RL = 8Ω, THD ≤ 10% j Shutdown current Features n n n n n n n n n 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 package Applications n Mobile phones n PDAs n Laptops Boomer ® is a registered trademark of National Semiconductor Corporation. © 2006 National Semiconductor Corporation DS201961 www.national.com LM4674A Typical Application 20196103 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM4674A Connection Diagrams TL Package (2mmx2mmx0.6mm) 20196101 Top View Order Number LM4674ATL See NS Package Number TL1611A LM4674ATL Markings 20196125 Top View XY = 2 digit datecode TT = Die traceability G = Boomer Family I2 = LM4674ATL 3 www.national.com LM4674A Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note 1) Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Susceptibility, all other pins (Note 4) ESD Susceptibility (Note 5) 6.0V −65˚C to +150˚C –0.3V to VDD +0.3V Internally Limited 2000V 200V Junction Temperature (TJMAX) Thermal Resistance θJA 150˚C 45.7˚C/W Operating Ratings (Note 1) (Note 2) Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage −40˚C ≤ TA ≤ 85˚C 2.4V ≤ VDD ≤ 5.5V Electrical Characteristics VDD = 3.6V (Notes 1, 2) The following specifications apply for AV = 6dB, RL = 15µH + 8Ω + 15µH, f = 1kHz unless otherwise specified. Limits apply for TA = 25˚C. LM4674A Symbol VOS Parameter Differential Output Offset Voltage Conditions VIN = 0, VDD = 2.4V to 5.0V VIN = 0, RL = ∞, Both channels active, VDD = 3.6V VIN = 0, RL = ∞, Both channels active, VDD = 5V VSD1 = VSD2 = GND Typical (Note 6) 5 4 5 0.03 6 7.5 1 1.4 0.4 VSHUTDOWN = 0.4V GAIN0, GAIN1 = GND AV Gain GAIN0 = VDD, GAIN1 = GND GAIN0 = GND, GAIN1 = VDD GAIN0, GAIN1 = VDD AV = 6dB RIN Input Resistance AV = 12dB AV = 18dB AV = 24dB 4.2 6 12 18 24 28 18.75 11.25 6.25 6 ± 0.5 12 ± 0.5 18 ± 0.5 24 ± 0.5 Limit (Note 7) Units (Limits) mV mA mA µA V (min) V (max) ms dB dB dB dB kΩ kΩ kΩ kΩ IDD Quiescent Power Supply Current ISD VSDIH VSDIL TWU Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Wake Up Time www.national.com 4 LM4674A Electrical Characteristics VDD = 3.6V (Notes 1, 2) The following specifications apply for AV = 6dB, RL = 15µH + 8Ω + 15µH, f = 1kHz unless otherwise specified. Limits apply for TA = 25˚C. (Continued) LM4674A Symbol Parameter Conditions RL = 15µH + 4Ω + 15µH, THD = 10% f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V RL = 15µH + 8Ω + 15µH, THD = 10% f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V PO Output Power VDD = 2.5V RL = 15µH + 4Ω + 15µH, THD = 1% f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V RL = 15µH + 8Ω + 15µH, THD = 1% f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V THD+N Total Harmonic Distortion PO = 500mW, f = 1kHz, RL = 8Ω PO = 300mW, f = 1kHz, RL = 8Ω VRIPPLE = 200mVP-P Sine, fRipple = 217Hz, Inputs AC GND, CI = 1µF, input referred VRIPPLE = 1VP-P Sine, fRipple = 1kHz, Inputs AC GND, CI = 1µF, input referred VRIPPLE = 1VP-P fRIPPLE = 217Hz PO = 1W, f = 1kHz, RL = 8Ω, VDD = 5V PO = 500mW, f = 1kHz VDD = 5V, PO = 1W Input referred, A-Weighted Filter 1.25 0.63 0.285 0.07 0.05 75 W W W % % dB 1.9 1 0.430 W W W 1.5 0.78 0.350 0.6 W W W 2.5 1.2 0.530 W W W Typical (Note 6) Limit (Note 7) Units (Limits) PSRR Power Supply Rejection Ratio 75 dB CMRR η Common Mode Rejection Ratio Efficiency Crosstalk 67 85 84 96 20 dB % dB dB µV SNR eOS Signal to Noise Ratio Output Noise 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, θJA, and the ambient temperature, TA. The maximum allowable power dissipation is PDMAX = (TJMAX – TA)/ θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4674A see power derating currents for more information. Note 4: Human body model, 100pF discharged through a 1.5kΩ resistor. Note 5: Machine Model, 220pF–240pF discharged through all pins. Note 6: Typicals are measured at 25˚C and represent the parametric norm. Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). 5 www.national.com LM4674A External Components Description (Figure 1) Components 1. 2. CS CI Functional Description 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. Input AC coupling capacitor which blocks the DC voltage at the amplifier’s input terminals. www.national.com 6 LM4674A Block Diagrams 20196137 7 www.national.com LM4674A Block Diagrams (Continued) 20196138 Differential Input Configuration www.national.com 8 LM4674A Typical Performance Characteristics THD+N vs Output Power f = 1kHz, AV = 24dB, RL = 8Ω THD+N vs Output Power f = 1kHz, AV = 6dB, RL = 8Ω 20196139 20196140 THD+N vs Output Power f= 1kHz, AV = 24dB, RL = 4Ω THD+N vs Output Power f = 1kHz, AV = 6dB, RL = 4Ω 20196141 20196142 THD+N vs Frequency VDD = 2.5V, POUT = 100mW, RL = 8Ω THD+N vs Frequency VDD = 3.6V, POUT = 250mW, RL = 8Ω 20196143 20196144 9 www.national.com LM4674A Typical Performance Characteristics THD+N vs Frequency VDD = 5V, POUT = 375mW, RL = 8Ω (Continued) THD+N vs Frequency VDD = 2. 5V, POUT = 100mW, RL = 4Ω 20196145 20196146 THD+N vs Frequency VDD = 3.6V, POUT = 250mW, RL = 4Ω THD+N vs Frequency VDD = 5V, POUT = 375mW, RL = 4Ω 20196147 20196148 Efficiency vs. Output Power RL = 4Ω, f = 1kHz Efficiency vs. Output Power RL = 8Ω, f = 1kHz 20196149 20196150 www.national.com 10 LM4674A Typical Performance Characteristics Power Dissipation vs. Output Power RL = 4Ω, f = 1kHz (Continued) Power Dissipation vs. Output Power RL = 8Ω, f = 1kHz 20196151 20196152 Output Power vs. Supply Voltage RL = 4Ω, f = 1kHz Output Power vs. Supply Voltage RL = 8Ω, f = 1kHz 20196153 20196154 PSRR vs. Frequency VDD = 3.6V, VRIPPLE= 200mVP-P, RL = 8Ω Crosstalk vs. Frequency VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8Ω 20196155 20196122 11 www.national.com LM4674A Typical Performance Characteristics CMRR vs. Frequency VDD = 3.6V, VCM = 1VP-P, RL = 8Ω (Continued) Supply Current vs. Supply Voltage No Load 20196157 20196158 www.national.com 12 LM4674A Application Information GENERAL AMPLIFIER FUNCTION The LM4674A 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 (OUT_A and OUT_B) 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 LM4674A outputs changes. For increasing output voltage, the duty cycle of OUT_A increases, while the duty cycle of OUT_B decreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. 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 LM4674A 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 LM4674A 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. POWER DISSIPATION AND EFFICIENCY The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the LM4674A 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, along with switching losses due to gate charge. SHUTDOWN FUNCTION The LM4674A 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, reducing supply current to 0.03µA. It is best to switch between ground and VDD for minimum current consumption while in shutdown. The LM4674A may be disabled with shutdown voltages in between GND and VDD, the idle current will be greater than the typical 0.03µA value. Increased THD+N may also be observed when a voltage of less than VDD is applied to /SD_ for logic levels between GND and VDD Bypass /SD_ with a 0.1µF capacitor. The LM4674A shutdown inputs have internal pulldown resistors. The purpose of these resistors is to eliminate any unwanted 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. SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION The LM4674A is compatible with single-ended sources. When configured for single-ended inputs, input capacitors must be used to block and 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 10µF and 0.1µF bypass capacitors that increase supply stability. These capacitors do not eliminate the need for bypassing of the LM4674A supply pins. A 1µF capacitor is recommended. 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 LM4674A. The input capacitors create a high-pass filter with the input resistors RI. The -3dB point of the high pass filter is found using Equation 1 below. (1) f = 1 / 2πRINCIN 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 LM4674A 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, 217Hz 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. AUDIO AMPLIFIER GAIN SETTING The LM4674A 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. G1 0 0 1 1 G0 V/V 0 1 0 1 2 4 8 16 GAIN dB 6 12 18 24 13 www.national.com LM4674A Application Information PCB LAYOUT GUIDELINES (Continued) 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 LM4674A and the load results in lower output power and decreased efficiency. Higher trace resistance between the supply and the LM4674A 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 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 of 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 LM4674A 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 LM4674A outputs may be needed to reduce EMI radiation. www.national.com 14 LM4674A Application Information (Continued) 20196126 Differential Input Configuration FIGURE 2. 15 www.national.com LM4674A Application Information (Continued) 20196138 Single-Ended Input Configuration FIGURE 3. www.national.com 16 LM4674A Revision Table Rev 1.0 Date 9/13/06 Description Initial WEB release. 17 www.national.com LM4674A Filterless 2.5W Stereo Class D Audio Power Amplifier Physical Dimensions inches (millimeters) unless otherwise noted 16 Bump micro SMD Order Number LM4674ATL NS Package Number TLA1611A X1 = 2mm X2 = 2mm X3 = 0.6mm National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. 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