LM48310 Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S General Description Key Specifications The LM48310 is a single supply, high efficiency, mono, 2.6W, filterless switching audio amplifier. The LM48310 features National’s Enhanced Emissions Suppression (E2S) system, that features a unique patent-pending ultra low EMI, spread spectrum, PWM architecture, that significantly reduces RF emissions while preserving audio quality and efficiency. The E2S system improves battery life, reduces external component count, board area consumption, system cost, and simplifying design. The LM48310 is designed to meet the demands of portable multimedia devices. Operating from a single 5V supply, the device is capable of delivering 2.6W 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 LM48310 offers two logic selectable modulation schemes, fixed frequency mode, and an EMI suppressing spread spectrum mode. The E2S system includes an advanced, patentpending edge rate control (ERC) architecture that further reduce emissions by minimizing the high frequency component of the device output, while maintaining high quality audio reproduction (THD+N = 0.03%) and high efficiency (η = 88%). The LM48310 also features a SYNC_IN input and SYNC_OUT, which allows multiple devices to operate with the same switching frequency, eliminating beat frequencies and any other interference caused by clock intermodulation. The LM48310 features high efficiency compared to conventional Class AB amplifiers, and other low EMI Class D amplifiers. When driving and 8Ω speaker from a 5V supply, the device operates with 88% efficiency at PO = 1W. The gain of the LM48310 is internally set to 12dB, further reducing external component count. A low power shutdown mode reduces supply current consumption to 0.01μA. Advanced output short circuit protection with auto-recovery prevents the device from being damaged during fault conditions. Superior click and pop suppression eliminates audible transients on power-up/down and during shutdown. ■ Efficiency at 3.6V, 400mW into 8Ω 85% (typ) ■ Efficiency at 5V, 1W into 8Ω 88% (typ) ■ Quiescent Power Supply Current at 5V 3.2mA ■ Power Output at VDD = 5V, RL = 4Ω, THD+N ≤ 10% 2.6W (typ) ■ Power Output at VDD = 5V, RL = 8Ω, THD+N ≤ 10% 1.6W (typ) ■ Shutdown current 0.01μA (typ) Features ■ Passes FCC Class B Radiated Emissions with 20 inches of cable ■ E2S System Reduces EMI while Preserving Audio Quality ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ and Efficiency Output Short Circuit Protection with Auto-Recovery Stereo Class D operation No output filter required Internally Configured Gain (12dB) Synchronizable Oscillator for Multi-Channel operation Low power shutdown mode Minimum external components "Click and pop" suppression Micro-power shutdown Available in space-saving LLP package Applications ■ Mobile phones ■ PDAs ■ Laptops EMI Graph 20in of Speaker Cable 300374a0 Boomer® is a registered trademark of National Semiconductor Corporation. © 2008 National Semiconductor Corporation 300374 www.national.com LM48310 Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S March 4, 2008 LM48310 Typical Application 30037459 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 LM48310 Connection Diagram LLP Package 3mm x 3mm x 0.8mm 30037458 Top View Order Number LM48310SD See NS Package Number SDA010 Pin Descriptions TABLE 1. Pin Name 1 IN+ Non-Inverting Input Description 2 IN- Inverting Input 3 VDD Power Supply 4 SD Active Low Shutdown Input. Connect to VDD for normal operation. 5 SYNC_IN Mode Select and External Oscillator Input. SYNC_IN = VDD: Spread spectrum mode with fS = 300kHz ± 30% SYNC_IN = GND: Fixed frequency mode with fS = 300kHz SYNC_IN = Clocked: fS = external clock frequency 6 SYNC_OUT 7 OUTB Inverting Output 8 GND Ground 9 PVDD H-Bridge Power Supply 10 OUTA Non-Inverting Output Clock Output 3 www.national.com LM48310 Junction Temperature Thermal Resistance 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 Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Rating (Note 4) ESD Rating (Note 5) 6.0V −65°C to +150°C − 0.3V to VDD +0.3V Internally Limited 2000V 200V 150°C θJC 49.2°C/W θJA 8.2°C/W Operating Ratings (Notes 1, 2) Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage −40°C ≤ TA ≤ +85°C 2.4V ≤ VDD ≤ 5.5V Electrical Characteristics VDD = PVDD = 5V (Notes 2, 8) The following specifications apply for AV = 12dB, (RL = 8Ω, SYNC_IN = VDD (Spread Spectrum mode), f = 1kHz, unless otherwise specified. Limits apply for TA = 25°C. LM48310 Symbol VOS IDD Parameter Differential Output Offset Voltage Quiescent Power Supply Current IDD Quiescent Power Supply Current ISD Conditions VIN = 0 Typical Limit (Note 6) (Notes 7, 8) Units (Limits) 1 3 mV (max) VIN = 0, RL = ∞ VDD = 3.6V 2.7 3.9 mA (max) VIN = 0, RL = ∞ VDD = 5V 3.2 4.4 mA (max) VIN = 0, VDD = 3.6V 2.7 mA VIN = 0, VDD = 5V 3.2 Shutdown Current VSD = GND 0.01 VIH Logic Input High Voltage SD input, VDD = 3.6V 1.4 V (min) VIL Logic Input Low Voltage SD input, VDD = 3.6V 0.4 V (max) TWU Wake Up Time fSW Switching Frequency mA 1.0 μA 7.5 ms SYNC_IN = VDD (Spread Spectrum) 300±30 kHz SYNC_IN = GND (Fixed Frequency) 300 kHz SYNC_IN = External Clock Minimum Frequency 200 kHz SYNC_IN = External Clock Maximum Frequency 1000 kHz AV Gain 12 11 13 dB (min) dB (max) RIN Input Resistance 20 17 kΩ (min) www.national.com 4 Symbol PO THD+N PSRR Parameter Output Power Total Harmonic Distortion + Noise Power Supply Rejection Ratio (Input Referred) Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) RL = 4Ω, THD = 10% f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V 2.6 1.3 555 W W mW RL = 8Ω, THD = 10% (max) f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V 1.6 800 354 W mW mW RL = 4Ω, THD = 1% (max) f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V 2.1 1 446 W W mW RL = 8Ω, THD = 1% (max) f = 1kHz, 22kHz BW VDD = 5V VDD = 3.6V VDD = 2.5V 1.3 640 286 PO = 200mW, RL = 8Ω, f = 1kHz 0.03 % (max) PO = 100mW, RL = 8Ω, f = 1kHz 0.03 % VRIPPLE = 200mVP-P Sine, fRIPPLE = 217Hz, Inputs AC GND, 82 dB 80 dB 70 dB 88 % 85 % VDD = 5V, PO = 1W, Fixed Frequency Mode 97 dB VDD = 5V, PO = 1W, Spread Spectrum Mode 97 dB Input referred, Fixed Frequency Mode, A-weighted Filter 14 μV Input referred, Spread Spectrum Mode, Unweighted 28 μV 1.1 W (min) mW mW CIN = 1μF, Input referred VRIPPLE = 200mVP-P Sine, fRIPPLE = 1kHz, Inputs AC GND, CIN = 1μF, Input referred CMRR Common Mode Rejection Ratio VRIPPLE = 1VP-P fRIPPLE = 217Hz VDD = 5V, POUT = 1W η Efficiency RL = 8Ω, f = 1kHz VDD = 3.6V, POUT = 400mW RL = 8Ω, f = 1kHz SNR εOS Signal to Noise Ratio Output Noise 5 www.national.com LM48310 LM48310 LM48310 Note 1: “Absolute Maximum Ratings” indicate limits beyond which damage to the device may occur, including inoperability and degradation of device reliability and/or performance. Functional operation of the device and/or non-degradation at the Absolute Maximum Ratings or other conditions beyond those indicated in the Recommended Operating Conditions is not implied. The Recommended Operating Conditionsindicate conditions at which the device is functional and the device should not be operated beyond such conditions. All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: The Electrical Characteristics tables list guaranteed specifications under the listed Recommended Operating Conditions except as otherwise modified or specified by the Electrical Characteristics Conditions and/or Notes. Typical specifications are estimations only and are not guaranteed. 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. Note 4: Human body model, applicable std. JESD22-A114C. Note 5: Machine model, applicable std. JESD22-A115-A. Note 6: Typical values represent most likely parametric norms at TA = +25°C, and at the Recommended Operation Conditions at the time of product characterization and are not guaranteed. Note 7: Datasheet min/max specification limits are guaranteed by test or statistical analysis. Note 8: RL is a resistive load in series with two inductors to simulate an actual speaker load. For RL = 8Ω, the load is 15µH + 8Ω, +15µH. For RL = 4Ω, the load is 15µH + 4Ω + 15µH. www.national.com 6 LM48310 Typical Performance Characteristics THD+N vs Frequency VDD = 2.5V, POUT = 300mW, RL = 4Ω THD+N vs Frequency VDD = 3.6V, POUT = 700mW, RL = 4Ω 30037466 30037467 THD+N vs Frequency VDD = 5.0V, POUT = 1.2W, RL = 4Ω THD+N vs Frequency VDD = 2.5V, POUT = 150mW, RL = 8Ω 30037468 30037469 THD+N vs Frequency VDD = 3.6V, POUT = 400mW, RL = 8Ω THD+N vs Frequency VDD = 5V, POUT = 650mW, RL = 8Ω 30037470 30037471 7 www.national.com LM48310 THD+N vs Output Power f = 1kHz, RL = 4Ω THD+N vs Output Power f = 1kHz, RL = 8Ω 30037464 30037465 Efficiency vs Output Power f = 1kHz, RL = 4Ω Efficiency vs Output Power f = 1kHz, RL = 8Ω 30037473 30037472 Power Dissipation vs Output Power f = 1kHz, RL = 4Ω Power Dissipation vs Output Power f = 1kHz, RL = 8Ω 30037475 30037474 www.national.com 8 LM48310 Output Power vs Supply Voltage f = 1kHz, RL = 4Ω Output Power vs Supply Voltage f = 1kHz, RL = 8Ω 30037476 30037477 PSRR vs Frequency VDD = 3.6V, VRIPPLE = 200mVP-P, RL = 8Ω PSRR vs Frequency VDD = 5.0V, VRIPPLE = 200mVP-P, RL = 8Ω 30037498 30037497 CMRR vs Frequency VDD = 3.6V, VRIPPLE = 1VP-P, RL = 8Ω CMRR vs Frequency VDD = 5.0V, VRIPPLE = 1VP-P, RL = 8Ω 30037463 30037480 9 www.national.com LM48310 Fixed Frequency Output Spectrum vs Frequency VDD = 5.0V, VIN = 1VRMS, RL = 8Ω Spread Spectrum Output Spectrum vs Frequency VDD = 5.0V, VIN = 1VRMS, RL = 8Ω 30037482 30037483 Wideband Fixed Frequency Output Spectrum vs Frequency VDD = 5.0V, RL = 8Ω Wideband Spread Spectrum Output Spectrum vs Frequency VDD = 5.0V, RL = 8Ω 30037484 30037485 Supply Current vs Supply Voltage No Load Shutdown Supply Current vs Supply Voltage No Load 30037499 30037486 www.national.com 10 spectrum mode, the switching frequency varies randomly by 30% about a 300kHz center frequency, reducing the wideband spectral contend, improving EMI emissions radiated by the speaker and associated cables and traces. Where a fixed frequency class D exhibits large amounts of spectral energy at multiples of the switching frequency, the spread spectrum architecture of the LM48310 spreads that energy over a larger bandwidth (See Typical Performance Characteristics). The cycle-to-cycle variation of the switching period does not affect the audio reproduction, efficiency, or PSRR. Set SYNC_IN = VDD for spread spectrum mode. GENERAL AMPLIFIER FUNCTION The LM48310 mono Class D audio power amplifier features a filterless modulation scheme that reduces external component count, conserving board space and reducing system cost. With no signal applied, the outputs (VOUTA and VOUTB) switch between VDD and GND 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 LM48310 outputs changes. For increasing output voltage, the duty cycle of VOUTAincreases, while the duty cycle of VOUTB decreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. EXTERNAL CLOCK MODE (SYNC_IN = CLOCK) Connecting a clock signal to SYNC_IN synchronizes the LM48310 oscillator to an external clock, moving the output spectral components out of a sensitive frequency band, and minimizing audible beat frequencies when multiple LM48310s are used in a single system. The LM48310 accepts an external clock frequency between 200kHz and 1MHz. The LM48310 can be synchronized to a spread spectrum clock, allowing multiple LM48310s to be synchronized in spread spectrum mode (see SYNC_OUT section). ENHANCED EMISSIONS SUPPRESSION SYSTEM (E2S) The LM48310 features National’s patent-pending E2S system that reduces EMI, while maintaining high quality audio reproduction and efficiency. The E2S system features a synchronizable oscillator with selectable spread spectrum, and advanced edge rate control (ERC). The LM48310 ERC greatly reduces the high frequency components of the output square waves by controlling the output rise and fall times, slowing the transitions to reduce RF emissions, while maximizing THD+N and efficiency performance. The overall result of the E2S system is a filterless Class D amplifier that passes FCC Class B radiated emissions standards with 20in of twisted pair cable, with excellent 0.03% THD+N and high 88% efficiency. SYNC_OUT SYNC_OUT is a clock output for synchronizing external devices. The SYNC_OUT signal is identical in frequency and duty cycle of the amplifier’s switching frequency. When the LM48310 is in fixed frequency mode, SYNC_OUT is a fixed, 300kHz clock. When the LM48310 is in spread spectrum mode, SYNC_OUT is an identical spread spectrum clock. When the LM48310 is driven by an external clock, SYNC_OUT is identical to the external clock. If unused, leave SYNC_OUT floating. Multiple LM48310s can be synchronized to a single clock. In Figure 2, device U1 is the master, providing a spread spectrum clock to the slave device (U2). This configuration synchronizes the switching frequencies of the two devices, eliminating any audible beat frequencies. Because SYNC_OUT has no audio content, there is minimal THD+N degredation or crosstalk between the devices, Figure 3-5. FIXED FREQUENCY MODE (SYNC_IN = GND) The LM48310 features two modulations schemes, a fixed frequency mode and a spread spectrum mode. Select the fixed frequency mode by setting SYNC_IN = GND. In fixed frequency mode, the amplifier output switch at a constant 300kHz. In fixed frequency mode, the output spectrum consists of the fundamental and its associated harmonics (see Typical Performance Characteristics). SPREAD SPECTRUM MODE (SYNC_IN = VDD) The logic selectable spread spectrum mode eliminates the need for output filters, ferrite beads or chokes. In spread 11 www.national.com LM48310 Application Information LM48310 30037460 FIGURE 2. Cascaded LM48310 www.national.com 12 LM48310 30037438 300374a1 FIGURE 4. THD+N vs Frequency FIGURE 3. THD+N vs Output Power 30037496 FIGURE 5. Crosstalk vs Frequency 13 www.national.com LM48310 Where RIN is the value of the input resistor given in the Electrical Characteristics table. 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 LM48310 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. 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 LM48310 features a fully differential speaker amplifier. 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 LM48310 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 GAIN The gain of the LM48310 is internally set to 12dB. The gain can be reduced by adding additional input resistance (Figure 6). In this configuration, the gain of the device is given by: POWER DISSIPATION AND EFFICIENCY The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the LM48310 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 onresistance, along with switching losses due to gate charge. AV = 2 x [RF / (RINEXT + RIN)] Where RF is 40kΩ, RIN is 20kΩ, and RINEXT is the value of the additional external resistor. SHUTDOWN FUNCTION The LM48310 features a low current shutdown mode. Set SD = GND to disable the amplifier and reduce supply current to 0.01µA. Switch SD between GND and VDD for minimum current consumption is shutdown. The LM48310 may be disabled with shutdown voltages in between GND and VDD, the idle current will be greater than the typical 0.1µA value. The LM48310 shutdown input has and internal pulldown resistor. The purpose of this resistor 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. 30037461 FIGURE 6. Reduced Gain Configuration SINGLE-ENDED AUDIO AMPLIFIER CONFIGURATION The LM48310 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 7 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 capacitors 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 LM48310 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 LM48310. The input capacitors create a highpass filter with the input resistors RIN. The -3dB point of the high pass filter is found using Equation (1) below. f = 1 / 2πRINCIN www.national.com 30037462 FIGURE 7. Single-Ended Input Configuration 14 As the distance from the LM48310 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 LM48310 outputs may be needed to reduce EMI radiation. 15 Designator Quantity Description C1 1 10μF ±10% 16V 500Ω Tantalum Capacitor (B Case) AVX TPSB106K016R0500 C2, C3 2 1μF ±10% 16V X7R Ceramic Capacitor (603) Panasonic ECJ-1VB1C105K C4, C5 2 1μF ±10% 16V X7R Ceramic Capacitor (1206) Panasonic ECJ-3YB1C105K C6 1 Not Installed Ceramic Capacitor (603) R1 1 0Ω ±1% resistor (603) JP1 — JP2 2 3 Pin Headers LM48310SDL 1 LM48310SD (10-pin LLP) www.national.com LM48310 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 LM48310 and the load results in lower output power and decreased efficiency. Higher trace resistance between the supply and the LM48310 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. LM48310 LM48310 Demo Board Schematic 30037489 FIGURE 8. LM48310 DEMO BOARD SCHEMATIC www.national.com 16 LM48310 Demo Boards 30037491 30037490 FIGURE 10. Top Layer FIGURE 9. Top Silkscreen 30037493 30037492 FIGURE 12. Layer 3 (VDD ) FIGURE 11. Layer 2 (GND) 30037494 30037495 FIGURE 13. Bottom Layer FIGURE 14. Bottom Silkscreen 17 www.national.com LM48310 Revision History Rev Date 1.0 11/13/07 Initial release. 1.01 02/26/08 Fixed few typos (Pin Description table). 1.02 03/04/08 Text edits under SHUTDOWN FUNCTION (Application Information section). www.national.com Description 18 LM48310 Physical Dimensions inches (millimeters) unless otherwise noted LLP Order Number LM48310SD NS Package Number SDA08A 19 www.national.com LM48310 Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S 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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