LM48511 3W, Ultra-Low EMI, Filterless, Mono, Class D Audio Power Amplifier with Spread Spectrum General Description Key Specifications The LM48511 integrates a boost converter with a high efficiency Class D audio power amplifier to provide 3W continuous power into an 8Ω speaker when operating from a 5V power supply. When operating from a 3V to 4V power supply, the LM48511 can be configured to drive 1 to 2.5W into an 8Ω load with less than 1% distortion (THD+N). The Class D amplifier features a low noise PWM architecture that eliminates the output filter, reducing external component count, board area consumption, system cost, and simplifying design. A selectable spread spectrum modulation scheme suppresses RF emissions, further reducing the need for output filters. The LM48511’s switching regulator is a current-mode boost converter operating at a fixed frequency of 1MHz. Two selectable feedback networks allow the LM48511 regulator to dynamically switch between two different output voltages, improving efficiency by optimizing the amplifier’s supply voltage based on battery voltage and output power requirements. The LM48511 is designed for use in portable devices, such as GPS, mobile phones, and MP3 players. The high, 80% efficiency at 5V, extends battery life when compared to Boosted Class AB amplifiers. Independent regulator and amplifier shutdown controls optimize power savings by disabling the regulator when high output power is not required. The gain of the LM48511 is set by external resistors, which allows independent gain control from multiple sources by summing the signals. Output short circuit and thermal overload protection prevent the device from damage during fault conditions. Superior click and pop suppression eliminates audible transients during power-up and shutdown. ■ Quiescent Power Supply Current VDD = 3V VDD = 5V 9mA (typ) 13.5mA (typ) ■ PO at VDD = 5V, PV1 = 7.8V RL = 8Ω, THD+N = 1% 3.0W (typ) ■ PO at VDD = 3V, PV1 = 4.8V RL = 8Ω, THD+N = 1% 1W (typ) ■ PO at VDD = 5V, PV1 = 7.8V RL = 4Ω, THD+N = 1% ■ Shutdown Current at VDD = 3V 5.4W (typ) 0.01μA (typ) Features ■ ■ ■ ■ ■ ■ ■ ■ ■ 3W Output into 8Ω at 5V with THD+N = 1% Selectable spread spectrum mode reduces EMI 80% Efficiency Independent Regulator and Amplifier Shutdown Controls Dynamically Selectable Regulator Output Voltages Filterless Class D 3.0V – 5.5V operation Low Shutdown Current Click and Pop Suppression Applications ■ ■ ■ ■ ■ GPS Portable media Cameras Mobile Phones Handheld games EMI Graph 300222h5 FIGURE 1. LM48511 RF Emissions — 3 inch cable Boomer® is a registered trademark of National Semiconductor Corporation. © 2008 National Semiconductor Corporation 300222 www.national.com LM48511 3W, Ultra-Low EMI, Filterless, Mono, Class D Audio Power Amplifier with Spread Spectrum February 25, 2008 LM48511 Typical Application 300222i3 FIGURE 2. Typical LM48511 Audio Amplifier Application Circuit www.national.com 2 LM48511 Connection Diagrams SQ Package 300222d4 Top View Order Number LM48511SQ See NS Package Number SQA24B SQ Package Marking 300222d5 Top View U — Wafer fab code Z — Assembly plant XY — 2 Digit date code TT — Lot traceability 3 www.national.com LM48511 Pin Descriptions LLP-24 Pin Name Function Regulator Feedback Select. Connect to VDD to select feedback network connected to FB_GND1. Connect to GND to select feedback network connected to FB_GND0. 1 FB_SEL 2,3 SW 4 SOFTSTART 5 SD_AMP 6 SS/FF 7 GND Signal Ground 8 LS+ Amplifier Non-Inverting Output 9, 11 LSGND 10 PV1 Amplifier H-Bridge Power Supply. Connect to V1. 12 LS- Amplifier Inverting Output 13 V1 Amplifier Supply Voltage. Connect to PV1 14 VG0+ 15 IN- Amplifier Inverting Input 16 IN+ Amplifier Non-Inverting Input 17 VG0– Amplifier Inverting Gain Output 18 VDD Power Supply 19 FB 20 FB_GND1 Ground return for R3, R1 resistor divider Drain of the Internal FET Switch Soft Start Capacitor Amplifier Active Low Shutdown. Connect to VDD for normal operation. Connect to GND to disable amplifier. Modulation Mode Select. Connect to VDD for spread spectrum mode (SS). Connect to GND for fixed frequency mode (FF). Amplifier H-Bridge Ground Amplifier Non-Inverting Gain Output Regulator Feedback Input. Connect FB to an external resistive voltage divider to set the boost output voltage. 21 FB_GND0 Ground return for R3, R2 resistor divider 22,23 REGGND Power Ground (Booster) 24 SD_BOOST DAP www.national.com Regulator Active Low Shutdown. Connect to VDD for normal operation. Connect to GND to disable regulator. To be soldered to board for enhanced thermal dissipation. Connect to GND plane. 4 Thermal Resistance If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. θJC (SQ) 3.8°C/W θJA (SQ) 32.8°C/W Supply Voltage (VDD, PV1, V1) Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature Operating Ratings 9V −65°C to +150°C −0.3V to VDD + 0.3V Internally limited 2000V 200V 150°C Electrical Characteristics VDD = 5.0V Temperature Range TMIN ≤ TA ≤ TMAX −40°C ≤ TA ≤ +85°C 3.0V ≤ VDD ≤ 5.5V Supply Voltage (VDD) 4.8V ≤ PV1 ≤ 8.0V Amplifier Voltage (PV1, V1) (Notes 1, 2, 10) The following specifications apply for VDD = 5.0V, PV1 = 7.8V (continuos mode), AV = 2V/V, R3 = 25.5kΩ, RLS = 4.87kΩ, RL = 8Ω, f = 1kHz, SS/FF = GND, unless otherwise specified. Limits apply for TA = 25°C. LM48511 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) VIN = 0, RLOAD = ∞ IDD Quiescent Power Supply Current Fixed Frequency Mode (FF) 13.5 mA (max) Spread Spectrum Mode (SS) 14.5 22 mA (max) VSD_BOOST = VSD_AMP = SS = FB_SEL = GND 0.11 1 μA (max) ISD Shutdown Current VIH Logic Voltage Input High 1.03 1.4 V (min) VIL Logic Voltage Input Low 0.92 0.4 V (min) TWU Wake-up Time CSS = 0.1μF VOS Output Offset Voltage Note 12 49 ms 0.01 3 mV THD+N = 1% FF SS 3.0 3.0 2.6 W (min) W THD+N = 10% FF SS 3.8 3.8 W W THD+N = 1% FF SS 5.4 5.4 W W THD+N = 10% FF SS 6.7 6.7 W W 0.03 0.03 % % 0.04 0.05 % % RL = 8Ω f = 1kHz, BW = 22kHz PO Output Power RL = 4Ω f = 1kHz, BW = 22kHz PO = 2W, f = 1kHz, RL = 8Ω THD+N Total Harmonic Distortion + Noise FF SS PO = 3W, f = 1kHz, RL = 4Ω FF SS 5 www.national.com LM48511 Absolute Maximum Ratings (Notes 2, 2) LM48511 LM48511 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) f = 20Hz to 20kHz Inputs to AC GND, No weighting εOS Output Noise 32 32 µVRMS µVRMS 22 22 µVRMS µVRMS VRIPPLE = 200mVP-P Sine, fRIPPLE = = 217Hz, FF SS 88 87 dB dB VRIPPLE = 200mVP-P Sine, fRIPPLE = = 1kHz, FF SS 88 85 dB dB VRIPPLE = 200mVP-P Sine, fRIPPLE = = 10kHz, FF SS 77 76 73 dB 80 % 1.23 V FF SS f = 20Hz to 20kHz Inputs to AC GND, A weighted FF SS PSRR Power Supply Rejection Ratio (Input Referred) CMRR Common Mode Rejection Ratio (Input Referred) VRIPPLE = 1VP-P, fRIPPLE = 217Hz η Efficiency f = 1kHz, RL = 8Ω, PO = 1W VFB Feedback Pin Reference Voltage Electrical Characteristics VDD = 3.6V dB dB (Notes 1, 2, 10) The following specifications apply for VDD = 3.6V, PV1 = 7V (continuous mode), AV = 2V/V, R3 = 25.5kΩ, RLS = 5.36kΩ, RL = 8Ω, f = 1kHz, SS/FF = GND, unless otherwise specified. Limits apply for TA = 25°C. LM48511 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) VIN = 0, RLOAD = ∞ IDD Quiescent Power Supply Current ISD Shutdown Current VIH Fixed Frequency Mode (FF) 16 Spread Spectrum Mode (SS) 17.5 26.6 mA (max) mA (max) VSD_BOOST = VSD_AMP = SS = FB_SEL = GND 0.03 1 μA (max) Logic Voltage Input High 0.96 1.4 V (min) VIL Logic Voltage Input Low 0.84 0.4 V (min) TWU Wake-up Time CSS = 0.1μF VOS Output Offset Voltage Note 12 www.national.com 6 50 ms 0.04 mV Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) RL = 8Ω, f = 1kHz, BW = 22kHz PO Output Power THD+N = 1% FF SS 2.5 2.5 W W THD+N = 10% FF SS 3.0 3.0 W W THD+N = 1% FF SS 4.3 4.2 W W THD+N = 10% FF SS 5.4 5.3 W W 0.03 0.03 % % 0.04 0.05 % % 35 36 µVRMS µVRMS 25 26 µVRMS µVRMS VRIPPLE = 200mVP-P Sine, fRIPPLE = = 217Hz FF SS 85 86 dB dB VRIPPLE = 200mVP-P Sine, fRIPPLE = = 1kHz FF SS 87 86 dB dB VRIPPLE = 200mVP-P Sine, fRIPPLE = = 10kHz FF SS 78 77 dB dB RL = 4Ω, f = 1kHz, BW = 22kHz PO = 1.5W, f = 1kHz, RL = 8Ω THD+N Total Harmonic Distortion + Noise FF SS PO = 3W, f = 1kHz, RL = 4Ω FF SS f = 20Hz to 20kHz Inputs to AC GND, No weighting εOS Output Noise FF SS f = 20Hz to 20kHz Inputs to AC GND, A weighted FF SS PSRR Power Supply Rejection Ratio (Input Referred) CMRR Common Mode Rejection Ratio (Input Referred) VRIPPLE = 1VP-P, fRIPPLE = 217Hz 73 dB η Efficiency f = 1kHz, RL = 8Ω, PO = 1W 77 % VFB Feedback Pin Reference Voltage 1.23 V 7 www.national.com LM48511 LM48511 Symbol LM48511 Electrical Characteristics VDD = 3.0V (Notes 1, 2, 10) The following specifications apply for VDD = 3.0V, PV1 = 4.8V (continuos mode), AV = 2V/V, R3 = 25.5kΩ, RLS = 9.31kΩ, RL = 8Ω, f = 1kHz, SS/FF = GND, unless otherwise specified. Limits apply for TA = 25°C. LM48511 Symbol Parameter Conditions Typical (Note 6) Limit (Note 7) Units (Limits) VIN = 0, RLOAD = ∞ IDD Quiescent Power Supply Current Fixed Frequency Mode (FF) 9 mA (max) Spread Spectrum Mode (SS) 9.5 mA (max) VSD_BOOST = VSD_AMP = SS = FB_SEL = GND 0.01 μA ISD Shutdown Current VIH Logic Voltage Input High 0.91 V (min) VIL Logic Voltage Input Low 0.79 V TWU Wake-up Time CSS = 0.1μF VOS Output Offset Voltage Note 12 1 49 ms 0.04 mV RL = 8Ω, f = 1kHz, BW = 22kHz PO Output Power THD+N = 1% FF SS 1 1 THD+N = 10% FF SS 1.3 1.3 W W THD+N = 1% FF SS 1.8 1.8 W W THD+N = 10% FF SS 2.2 2.2 W W 0.02 0.03 % % 0.04 0.06 % % 35 35 µVRMS µVRMS 25 25 µVRMS µVRMS 0.84 W (min) W RL = 4Ω, f = 1kHz, BW = 22kHz PO = 500mW, f = 1kHz, RL = 8Ω THD+N Total Harmonic Distortion + Noise FF SS PO = 500mW, f = 1kHz, RL = 4Ω FF SS f = 20Hz to 20kHz Inputs to AC GND, No weighting εOS Output Noise FF SS f = 20Hz to 20kHz Inputs to AC GND, A weighted FF SS www.national.com 8 Parameter Conditions VRIPPLE = 200mVP-P Sine, fRIPPLE = = 217Hz FF SS PSRR Power Supply Rejection Ratio (Input Referred) Typical (Note 6) Units (Limits) Limit (Note 7) 89 89 dB dB VRIPPLE = 200mVP-P Sine, fRIPPLE = = 1kHz FF SS 88 88 dB dB VRIPPLE = 200mVP-P Sine, fRIPPLE = = 10kHz FF SS 78 78 dB dB CMRR Common Mode Rejection Ratio (Input Referred) VRIPPLE = 1VP-P, fRIPPLE = 217Hz 71 dB η Efficiency f = 1kHz, RL = 8Ω, PO = 1W 75 % VFB Feedback Pin Reference Voltage 1.23 V 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. TheRecommended Operating Conditions indicate 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, θJJA, 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 LM48511, see power derating curves for additional information. 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 = +25ºC, 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: Shutdown current is measured with components R1 and R2 removed. Note 9: Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is unloaded). Note 10: 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. Note 11: Offset voltage is determined by: (IDD (with load) — IDD (no load)) x RL. 9 www.national.com LM48511 LM48511 Symbol LM48511 Typical Performance Characteristics THD+N vs Frequency VDD = 5V, RL = 8Ω PO = 2W, filter = 22kHz, PV1 = 7.8V THD+N vs Frequency VDD = 3.6V, RL = 8Ω PO = 500mW, filter = 22kHz, PV1 = 4.8V 300222g7 300222g9 THD+N vs Frequency VDD = 3V, RL = 8Ω PO = 1.5W, filter = 22kHz, PV1 = 7V THD+N vs Output Power VDD = 5V, RL = 8Ω PO = 1.5W, f = 1kHz, filter = 22kHz, PV1 = 7.8V 300222g8 300222h4 THD+N vs Output Power VDD = 3.6V, RL = 8Ω f = 1kHz, filter = 22kHz, PV1 = 7V THD+N vs Output Power VDD = 3V, RL = 8Ω f = 1kHz, filter = 22kHz, PV1 = 4.8V 300222h1 www.national.com 300222h3 10 THD+N vs Output Power VDD = 3.6V, RL = 8Ω filter = 22kHz, PV1 = 7.8V, PV1 = 7V, PV1 = 4.8V, FF 300222i0 300222i1 Boost Amplifier vs Output Power VDD = 5V, RL = 8Ω f = 1kHz, PV1 = 7.8V Boost Amplifier vs Output Power VDD = 3.6V, RL = 8Ω f = 1kHz, PV1 = 7V 300222f7 300222f5 Boost Amplifier vs Output Power VDD = 3V, RL = 8Ω f = 1kHz, PV1 = 4.8V PSRR vs Frequency VDD = 5V, RL = 8Ω VRIPPLE = 200mVPP, PV1 = 7.8V 300222g3 300222f6 11 www.national.com LM48511 THD+N vs Output Power VDD = 3V, 3.6V, 5V, RL = 8Ω f = 1kHz, filter = 22kHz, R1 = 4.87kΩ, FF LM48511 PSRR vs Frequency VDD = 3.6V, RL = 8Ω VRIPPLE = 200mVPP, PV1 = 7V PSRR vs Frequency VDD = 3V, RL = 8Ω VRIPPLE = 200mVPP, PV1 = 4.8V 300222g1 300222g2 Supply Current vs Supply Voltage PV1 = 7.8V Supply Current vs Supply Voltage PV1 = 7V 300222g5 300222g6 Supply Current vs Supply Voltage PV1 = 4.8V Power Dissipation vs Output Power VDD = 5V, RL = 8Ω PV1 = 7.8V, FF 300222g4 300222g0 www.national.com 12 LM48511 Power Dissipation vs Output Power VDD = 3.6V, RL = 8Ω PV1 = 7V, FF Power Dissipation vs Output Power VDD = 3V, RL = 8Ω PV1 = 4.8V, FF 300222f8 300222f9 Boost Converter Efficiency vs ILOAD(DC) VDD = 5V, PV1 = 7.8V Boost Converter Efficiency vs ILOAD(DC) VDD = 3.6V, PV1 =7V 300222h8 300222h6 Boost Converter Efficiency vs ILOAD(DC) VDD = 3V, PV1 = 4.8V 300222h7 13 www.national.com LM48511 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. Application Information GENERAL AMPLIFIER FUNCTION The LM48511 features a Class D audio power amplifier that utilizes a filterless modulation scheme, reducing external component count, conserving board space and reducing system cost. The outputs of the device transition from PV1 to GND with a 300kHz switching frequency. With no signal applied, the outputs (VLS+ and VLS-) 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 LM48511 outputs changes. For increasing output voltage, the duty cycle of VLS+ increases, while the duty cycle of VLSdecreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. REGULATOR POWER DISSIPATION At higher duty cycles, the increased ON-time of the switch FET means the maximum output current will be determined by power dissipation within the LM48511 FET switch. The switch power dissipation from ON-time conduction is calculated by: PD(SWITCH) = DC x (IINDUCTOR(AVE))2 x RDS(ON) (W) where DC is the duty cycle. SHUTDOWN FUNCTION The LM48511 features independent amplifier and regulator shutdown controls, allowing each portion of the device to be disabled or enabled independently. SD_AMP controls the Class D amplifiers, while SD_BOOST controls the regulator. Driving either inputs low disables the corresponding portion of the device, and reducing supply current. When the regulator is disabled, both FB_GND switches open, further reducing shutdown current by eliminating the current path to GND through the regulator feedback network. Without the GND switches, the feedback resistors as shown in Figure 1 would consume an additional 165μA from a 5V supply. With the regulator disabled, there is still a current path from VDD, through the inductor and diode, to the amplifier power supply. This allows the amplifier to operate even when the regulator is disabled. The voltage at PV1 and V1 will be: FIXED FREQUENCY The LM48511 features two modulations schemes, a fixed frequency mode (FF) and a spread spectrum mode (SS). Select the fixed frequency mode by setting SS/FF = GND. In fixed frequency mode, the amplifier outputs 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 The logic selectable spread spectrum mode eliminates the need for output filters, ferrite beads or chokes. In spread spectrum mode, the switching frequency varies randomly by 10% about a 330kHz 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 LM48511 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 SS/FF = VDD for spread spectrum mode. (VDD - [VD + (IL x DCR)] (2) Where VD is the forward voltage of the Schottky diode, IL is the current through the inductor, and DCR is the DC resistance of the inductor. Additionally, when the regulator is disabled, an external voltage between 5V and 8V can be applied directly to PV1 and V1 to power the amplifier. It is best to switch between ground and VDD for minimum current consumption while in shutdown. The LM48511 may be disabled with shutdown voltages in between GND and VDD, the idle current will be greater than the typical 0.1µA value. Increased THD+N may also be observed when a voltage of less than VDD is applied to SD_AMP . DIFFERENTIAL AMPLIFIER EXPLANATION The LM48511 includes fully differential amplifier that features differential input and output stages. 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 in signal to noise ratio relative to differential inputs. The LM48511 also offers the possibility of DC input coupling which eliminates the two external AC coupling, DC blocking capacitors. The LM48511 can be used, however, as a single ended input amplifier while still retaining it's fully differential benefits. In fact, completely unrelated signals may be placed on the input pins. The LM48511 simply amplifies the difference between the signals. A major benefit of a differential amplifier is the improved common mode rejection ratio (CMRR) over single input amplifiers. The common-mode rejection characteristic of the differential amplifier reduces sensitivity to ground offset related noise injection, especially important in high noise applications. REGULATOR FEEDBACK SELECT The LM45811 regulator features two feedback paths as shown in Figure 1, which allow the regulator to easily switch between two different output voltages. The voltage divider consists of the high side resistor, R3, and the low side resistors (RLS), R1 and R2. R3 is connected to the output of the boost regulator, the mid-point of each divider is connected to FB, and the low side resistors are connected to either FB_GND1 or FB_GND0. FB_SEL determines which FB_GND switch is closed, which in turn determines which feedback path is used. For example if FB_SEL = VDD, the FB_GND1 switch is closed, while the FB_GND0 switch remains open, creating a current path through the resistors connected to FB_GND1. Conversely, if FB_SEL = GND, the FB_GND0 switch is closed, while the FB_GND1 switch remains open, creating a current path through the resistors connected to FB_GND0. AUDIO AMPLIFIER POWER DISSIPATION AND EFFICIENCY The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the LM48511 is attributed to the region of operation of the transistors in the output stage. www.national.com (1) 14 tween the resistors results in a differential gain error that leads to an increase in THD+N, decrease in PSRR and CMRR, as well as an increase in output offset voltage. Resistors with a tolerance of 1% or better are recommended. The gain setting resistors should be placed as close to the device as possible. Keeping the input traces close together and of the same length increases noise rejection in noisy environments. Noise coupled onto the input traces which are physically close to each other will be common mode and easily rejected. 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 LM48511. The input capacitors create a highpass filter with the input resistors RIN. The -3dB point of the high pass filter is found by: f = 1 / 2πRINCIN In single-ended configurations, the input capacitor value affects click-and-pop performance. The LM48511 features a 50mg turn-on delaly. Choose the input capacitor / input resistor values such that the capacitor is charged before the 50ms turn-on delay expires. A capacitor value of 0.18μF and a 20kΩ input resistor are recommended. In differential applications, the charging of the input capacitor does not affect click-and-pop significantly. The input capacitors can also be used to remove low frequency content from the audio signal. High pass filtering the audio signal helps protect speakers that can not reproduce or may be damaged by low frequencies. When the LM48511 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. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components in applications using integrated power amplifiers, and switching DC-DC converters, is critical for optimizing device and system performance. Consideration to component values must be used to maximize overall system quality. The best capacitors for use with the switching converter portion of the LM48511 are multi-layer ceramic capacitors. They have the lowest ESR (equivalent series resistance) and highest resonance frequency, which makes them optimum for high frequency switching converters. When selecting a ceramic capacitor, only X5R and X7R dielectric types should be used. Other types such as Z5U and Y5F have such severe loss of capacitance due to effects of temperature variation and applied voltage, they may provide as little as 20% of rated capacitance in many typical applications. Always consult capacitor manufacturer’s data curves before selecting a capacitor. High-quality ceramic capacitors can be obtained from Taiyo-Yuden and Murata. SELECTING REGULATOR OUTPUT CAPACITOR A single 100µF low ESR tantalum capacitor provides sufficient output capacitance for most applications. Higher capacitor values improve line regulation and transient response. Typical electrolytic capacitors are not suitable for switching converters that operate above 500kHz because of significant ringing and temperature rise due to self-heating from ripple current. An output capacitor with excessive ESR reduces phase margin and causes instability. POWER SUPPLY BYPASSING As with any amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. The capacitor location on both PV1, V1 and VDD pins should be as close to the device as possible. SELECTING REGULATING BYPASS CAPACITOR A supply bypass capacitor is required to serve as an energy reservoir for the current which must flow into the coil each time the switch turns on. This capacitor must have extremely low ESR, so ceramic capacitors are the best choice. A nominal value of 10μF is recommended, but larger values can be used. Since this capacitor reduces the amount of voltage ripple seen at the input pin, it also reduces the amount of EMI passed back along that line to other circuitry. AUDIO AMPLIFIER GAIN SETTING RESISTOR SELECTION The amplifier gain of the LM48511 is set by four external resistors, the input resistors, R5 and R7, and the feed back resistors R6 and R8.. The amplifier gain is given by: Where RIN is the input resistor and RF is the feedback resistor. AVD = 2 X RF / RIN (4) (3) SELECTING THE SOFTSTART (CSS) CAPACITOR The soft-start function charges the boost converter reference voltage slowly. This allows the output of the boost converter to ramp up slowly thus limiting the transient current at startup. Careful matching of the resistor pairs, R6 and R8, and R5 and R7, is required for optimum performance. Any mismatch be15 www.national.com LM48511 FB_SEL can be susceptible to noise interference. To prevent an accidental state change, either bypass FB_SEL with a 0.1µF capacitor to GND, or connect the higher voltage feedback network to FB_GND0, and the lower voltage feedback network to FB_GND1. Because the higher output voltage configuration typically generates more noise on VDD, this configuration minimizes the VDD noise exposure of FB_SEL, as FB_SEL = GND for FB_GND0 (high voltage output) and FB_SEL = VDD for FB_GND1 (low voltage output). The selectable feedback networks maximize efficiency in two ways. In applications where the system power supply voltage changes, such as a mobile GPS receiver, that transitions from battery power, to AC line, to a car power adapter, the LM48511 can be configured to generate a lower voltage when the system power supply voltages is lower, and conversely, generate a higher voltage when the system power supply is higher. See the Setting the Regulator Output Voltage (PV1) section. In applications where the same speaker/amplifier combination is used for different purposes with different audio power requirements, such as a cell phone ear piece/speaker phone speaker, the ability to quickly switch between two different voltages allows for optimization of the amplifier power supply, increasing overall system efficiency. When audio power demands are low (ear piece mode) the regulator output voltage can be set lower, reducing quiescent current consumption. When audio power demands increase (speaker phone mode), a higher voltage increases the amplifier headroom, increasing the audio power delivered to the speaker. LM48511 be considered when selecting the current rating. Use shielded inductors in systems that are susceptible to RF interference. Selecting a soft-start capacitor (CSS) value presents a trade off between the wake-up time and the startup transient current. Using a larger capacitor value will increase wake-up time and decrease startup transient current while the apposite effect happens with a smaller capacitor value. A general guideline is to use a capacitor value 1000 times smaller than the output capacitance of the boost converter (C2). A 0.1uF softstart capacitor is recommended for a typical application. The following table shows the relationship between CSS startup time and surge current. (μF) CSS Boost Set-up Time (ms) Input Surge Current (mA) 0.1 5.1 330 0.22 10.5 255 0.47 21.7 220 SETTING THE REGULATOR OUTPUT VOLTAGE (PV1) The output voltage of the regulator is set through one of two external resistive voltage-dividers (R3 in combination with either R1 or R2) connected to FB (Figure 1). The resistor, R4 is only for compensation purposes and does not affect the regulator output voltage. The regulator output voltage is set by the following equation: PV1 = VFB [1+R3/RLS] Where VFB is 1.23V, and RLS is the low side resistor (R1 or R2). To simplify resistor selection: VDD = 5V, PV1 = 7.8V (continuous mode) RLS = (R3VFB) / (PV1–VFB) SELECTING DIODE (D1) Use a Schottkey diode, as shown in Figure 1. A 30V diode such as the DFLS230LH from Diodes Incorporated is recommended. The DFLS230LH diodes are designed to handle a maximum average current of 2A. VDD (V) PV1 (V) R3(kΩ) RLS (kΩ) POUT into 8Ω (W) (5) SELECTING INDUCTOR VALUE Inductor value involves trade-offs in performance. Larger inductors reduce inductor ripple current, which typically means less output voltage ripple (for a given size of output capacitor). Larger inductors also mean more load power can be delivered because the energy stored during each switching cycle is: 4.8 25.5 9.31 1 3.6 7.1 25.5 5.35 2.5 5 7.8 25.5 4.87 3 DISCONTINUOUS/CONTINUOUS OPERATION The LM48511 regulator features two different switching modes. Under light load conditions, the regulator operates in a variable frequency, discontinuous, pulse skipping mode, that improves light load efficiency by minimizing losses due to MOSFET gate charge. Under heavy loads, the LM48511 regulator automatically switches to a continuous, fixed frequency PWM mode, improving load regulation. In discontinuous mode, the regulator output voltage is typically 400mV higher than the expected (calculated) voltage in continuous mode. (6) Where “lp” is the peak inductor current. The LM48511 will limit its switch current based on peak current. With IP fixed, increasing L will increase the maximum amount of power available to the load. Conversely, using too little inductance may limit the amount of load current which can be drawn from the output. Best performance is usually obtained when the converter is operated in “continuous” mode at the load current range of interest, typically giving better load regulation and less output ripple. Continuous operation is defined as not allowing the inductor current to drop to zero during the cycle. Boost converters shift over to discontinuous operation if the load is reduced far enough, but a larger inductor stays continuous over a wider load current range. ISWFEED-FORWARD COMPENSATION FOR BOOST CONVERTER Although the LM48511 regulator is internally compensated, an external feed-forward capacitor, (C1) may be required for stability (Figure 1). The compensation capacitor places a zero in regulator loop response. The recommended frequency of the zero (fZ) is 22.2kHz. The value of C1 is given by: C1 =1 / 2πR3fZ (9) In addition to C1, a compensation resistor, R4 is required to cancel the zero contributed by the ESR of the regulator output capacitor. Calculate the zero frequency of the output capacitor by: INDUCTOR SUPPLIES The recommended inductor for the LM48511 is the IHLP-2525CZ-01 from Vishay Dale. When selecting an inductor, the continuous current rating must be high enough to avoid saturation at peak currents. A suitable core type must be used to minimize switching losses, and DCR losses must www.national.com 3.0 The values of PV1 are for continuous mode operation. For feedback path selection, see Regulator Feedback Select section. This applies for continuous mode operation. E = L/2 x IP2 (8) A value of approximately 25.5kΩ is recommended for R3. The quiescent current of the boost regulator is directly related to the difference between its input and output voltages, the larger the difference, the higher the quiescent current. For improved power consumption the following regulator input/ output voltage combinations are recommended: DUTY CYCLE The maximum duty cycle of the boost converter determines the maximum boost ratio of output-to-input voltage that the converter can attain in continuous mode of operation. The duty cycle for a given boost application is defined by: Duty Cycle = (PV1+VD-VDD)/(PV1+VD-VSW) (7) fCO =1 / 2πRCOCO 16 (10) R4 =1 / 2πfCOC1 where f = switching frequency = 1MHz combining all terms, we can develop an expression which allows the maximum available load current to be calculated: (11) CALCULATING REGULATOR OUTPUT CURRENT The load current of the boost converter is related to the average inductor current by the relation: IAMP = IINDUCTOR(AVE) x (1 - DC) (A) IAMP(max) = (1–DC)x[ISW(max)–DC(V-VSW)]/2fL (A) (15) The equation shown to calculate maximum load current takes into account the losses in the inductor or turn-off switching losses of the FET and diode. (12) Where "DC" is the duty cycle of the application. The switch current can be found by: ISW = IINDUCTOR(AVE) + 1/2 (IRIPPLE) (A) (14) DESIGN PARAMETERS VSW AND ISW The value of the FET "ON" voltage (referred to as VSW in equations 9 thru 12) is dependent on load current. A good approximation can be obtained by multiplying the on resistance (RDS(ON) of the FET times the average inductor current. The maximum peak switch current the device can deliver is dependent on duty cycle. (13) Inductor ripple current is dependent on inductance, duty cycle, supply voltage and frequency: 17 www.national.com LM48511 IRIPPLE = DC x (VDD-VSW) / (f x L) (A) Where R CO is the ESR of the output capacitor. The value of RFB3 is given by: LM48511 Build Of Materials Designator Description Footprint Quantity Value Cf1 CHIP CAPACITOR GENERIC CAP 0805 1 470pF CINA CHIP CAPACITOR GENERIC CAP 1210 1 1μF CINB CHIP CAPACITOR GENERIC CAP 1210 1 1μF Co CHIP CAPACITOR GENERIC CAP 1210 1 10μF Cs1 CHIP CAPACITOR GENERIC CAP 1210 1 2.2μF Cs2 CHIP CAPACITOR GENERIC CAP 1210 1 4.7μF D1 SCHOTTKY DIO DIODE MBR0520 IR 1 IND_COILCRAFT-DO1813P 1 4.7μH L1 R1 CHIP RESISTOR GENERIC RES 0805 1 41.2K R2 CHIP RESISTOR GENERIC RES 0805 1 13.3K RINA CHIP RESISTOR GENERIC RES 0805 1 150K RINB CHIP RESISTOR GENERIC RES 0805 1 150K www.national.com 18 LM48511 Revision History Rev Date 1.0 07/24/07 Initial release. Description 1.1 07/25/07 Input some text edits. 1.2 09/25/07 Changed the Amplifier Voltage (Operating Ratings section) from 5.0V to 4.8V. 1.3 11/06/07 Added another Po (@Vdd = 5V, Rl = 4Ω) section in the Key Specification division. 1.4 02/25/08 Edited the Notes section. 19 www.national.com LM48511 Physical Dimensions inches (millimeters) unless otherwise noted SQ Package Order Number LM48511SQ NS Package Number SQA24B www.national.com 20 LM48511 Notes 21 www.national.com LM48511 3W, Ultra-Low EMI, Filterless, Mono, Class D Audio Power Amplifier with Spread Spectrum 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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