LM48520, LM48520TLBD www.ti.com LM48520 SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 Boosted Stereo Class D Audio Power Amplifier with Output Speaker Protection and Spread Spectrum Check for Samples: LM48520, LM48520TLBD FEATURES DESCRIPTION * * * * * * * The LM48520 integrates a boost converter with a high efficiency Class D stereo audio power amplifier to provide up to 1W/ch continuous power into an 8 speaker when operating from 2.7V to 5.0V power supply with boost voltage (PV1) of 5.0V. The LM48520 utilizes a proprietary spread spectrum pulse width modulation technique that lowers RF interference and EMI levels. The Class D amplifier is a low noise, filterless PWM architecture that eliminates the output filter, reducing external component count, board area, power consumption, system cost, and simplifying design. 1 2 * * * Click and Pop Suppression Low 0.04A Shutdown Current 78% Efficiency Filterless Class D 2.7V - 5.0V Operation 4 Adjustable Gain Settings Adjustable Output Swing Limiter with Soft Clipping Speaker Protection Short Circuit Protection on Audio Amps Independent Boost and Amplifier Shutdown Pins APPLICATIONS * * * * * Mobile Phones PDAs Portable media Cameras Handheld games KEY SPECIFICATIONS * * * Quiescent Power Supply Current: 11.5 mA(typ) Output Power (RL = 8, THD+N 1%, VDD = 3.3V,PV1 = 5.0V): 1.1 W(typ) Shutdown Current: 0.04 A(typ) The LM48520 is designed for use in mobile phones and other portable communication devices. The high (78%) efficiency extends battery life when compared to Boosted Class AB amplifiers. The LM48520 features a low-power consumption shutdown mode. Shutdown may be enabled by driving the Shutdown pin to a logic low (GND). Also, external leakage is minimized via control of the ground reference via the SW-OUT pin . The LM48520 has 4 gain options which are pin selectable via Gain0 and Gain1 pins. Output short circuit prevents the device from damage during fault conditions. Superior click and pop suppression eliminates audible transients during power-up and shutdown. 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 2008-2013, Texas Instruments Incorporated LM48520, LM48520TLBD SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 www.ti.com Typical Application L1 V1 = VFB ( 1+ R1/R2) 6.8 PH Cs1 2.2 PF 2.7V to 5.0V D1 Cf1 330 pF BstFB SW-GND R2 16.2k SS Boost SD Amp SD Gain0 FB-GND Cs Cs2 4.7 PF PV1 Boost SD V1 Amp SD Gain0 Gain1 Gain1 Vlimit Vlimit GND PGND 1 PF INPUT R Co 100 PF SW VDD 0.1 PF R1 40.2k INROUTR+ Ci OUTR- 1 PF INR+ Ci 1 PF INPUT L INLCi OUTL+ 1 PF OUTLINL+ Ci Figure 1. Typical LM48520 Audio Amplifier Application Circuit Connection Diagram Top View 1 2 3 4 5 A VDD BstFB Soft Start SW_ GND SW B INR+ INR- FB_GND INL- INL+ C V1 BstSD GND Gain0 PV1 D AmpSD OUTR+ NC OUTL+ GAIN1 E VLimit OUTR- PGND OUTL- NC Figure 2. DSBGA Package See Package Number YZR0025AAA 2 Submit Documentation Feedback Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD LM48520, LM48520TLBD www.ti.com SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 Pin Descriptions Pin Designator Pin Name Pin Function A1 VDD A2 BstFB A3 Soft Start Soft start capacitor A4 SW_GND Booster ground A5 SW Drain of the Internal FET switch B1 INR+ Non-inverting right channel input B2 INR- Inverting right channel input B3 FB_GND B4 INL- Inverting left channel input Non-inverting left channel input Power Supply Regulator Feedback Input. Connect BstFB to an external resistive voltage divider to set the boost output voltage. Ground return for R1, R2 resistor divider B5 INL+ C1 V1 C2 BstSD C3 GND Ground C4 Gain0 Gain setting input 0 C5 PV1 D1 AmpSD Amplifier active low shutdown D2 OUTR+ Non-inverting right channel output D3 NC D4 OUTL+ Amplifier supply voltage. Connect to PV1. Regulator active low shutdown Amplifier H-bridge power supply. Connect to V1. No connect Non-inverting left channel output D5 Gain1 Gain setting input 1 E1 VLimit Set to control output clipping level E2 OUTR- Inverting right channel output E3 PGND Power ground E4 OUTL- Inverting left channel output E5 NC No connect These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) Supply Voltage (VDD, V1) 6V -65C to +150C Storage Temperature -0.3V to VDD + 0.3V Input Voltage Power Dissipation (3) Internally limited ESD Susceptibility (4) 2000V ESD Susceptibility (5) 200V Junction Temperature 150C Thermal Resistance JA (YZR0025AAA) (1) (2) (3) (4) (5) 40.5 C/W 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication of device performance. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications. 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 given in Absolute Maximum Ratings, whichever is lower. Human body model, 100pF discharged through a 1.5k resistor. Machine Model, 220pF-240pF discharged through all pins. Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD Submit Documentation Feedback 3 LM48520, LM48520TLBD SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 www.ti.com Operating Ratings Temperature Range TMIN TA TMAX -40C TA +85C 2.7V VDD 5.0V Supply Voltage (VDD) Amplifier Voltage (V1 ) 2.4V V1 5.5V Not under Boosted Condition Amplifier Voltage (PV1 ) 3.0V PV1 5.0V Under Boosted Condition Electrical Characteristics VDD = 3.3V (1) (2) The following specifications apply for VDD = 3.3V, AV = 6dB, RL = 15H + 8 +15H, fIN = 1kHz, unless otherwise specified. Limits apply for TA = 25C, R1 = 40.2k, R2 = 16.2k, V1 = PV1 = 5V, Vlimit = GND. All electrical specifications are for amplifier and booster. LM48520 Parameter Test Conditions Typ (3) Limit (4) (5) Units (Limits) 15.5 mA (max) VIN = 0, RLOAD = IDD Quiescent Power Supply Current VDD = 2.7V 14.8 VDD = 3.3V 11.5 VDD = 5.0V 8.0 0.04 ISD Shutdown Current VSHUTDOWN = GND 1.0 A (max) VSDIH Shutdown Voltage Input High For SD Boost, SD Amp 1.4 V VSDIL Shutdown Voltage Input Low For SD Boost, SD Amp 0.4 TWU Wake-up Time Amplifier + Booster Wakeup VOS Output Offset Voltage AV Gain PO Output Power 5 mV 6 dB G0 = VDD, G1 = GND RL = 12 dB G0 = GND, G1 = VDD RL = 18 dB G0, G1 = VDD RL = 24 dB RL = 15H + 8 + 15H THD+N = 1% (max), f = 1kHz, 22kHz, BW VDD = 3.3V 1.1 RL = 15H + 8 + 15H THD+N = 10% (max), f = 1kHz, 22kHz, BW VDD = 3.3V 1.3 W 0.04 % 32 VRMS Total Harmonic Distortion + Noise PO = 500mW, f = 1kHz, RL = 15H + 8 + 15H, VDD = 3.3V OS Output Noise VDD = 3.6V, f = 20Hz - 20kHz Inputs to AC GND, A weighted (3) (4) (5) 4 ms G0, G1 = GND RL = THD+N (1) (2) V 3 0.87 W (min) All voltages are measured with respect to the GND pin, unless otherwise specified. 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication of device performance. Typicals are measured at 25C and represent the parametric norm. Limits are specified to AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are ensured by design, test, or statistical analysis. Submit Documentation Feedback Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD LM48520, LM48520TLBD www.ti.com SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 Electrical Characteristics VDD = 3.3V (1)(2) (continued) The following specifications apply for VDD = 3.3V, AV = 6dB, RL = 15H + 8 +15H, fIN = 1kHz, unless otherwise specified. Limits apply for TA = 25C, R1 = 40.2k, R2 = 16.2k, V1 = PV1 = 5V, Vlimit = GND. All electrical specifications are for amplifier and booster. LM48520 Parameter Test Conditions Typ (3) Limit (4) (5) Units (Limits) VRIPPLE = 200mVP-P Sine, fRIPPLE = = 217Hz 82 dB VRIPPLE = 200mVP-P Sine, fRIPPLE = = 1kHz 79 dB Common Mode Rejection Ratio VRIPPLE = 1VP-P, fRIPPLE = 217Hz 67 dB Efficiency PO = 1W, f = 1kHz, RL = 15H + 8 + 15H VDD = 3.3V VDD = 4.2V 78 % VFB Feedback Pin Reference Voltage See Vout clipped Output Voltage in clipped state with soft clip activated Vlimit = 2V, RL = 8, VIN = 2VP Vout clipped = 8/3 (PV1 - 2Vlimit) PSRR CMRR (6) Power Supply Rejection Ratio (6) 1.24 2.5 V 1.9 3.2 Vpk (min) Vpk (max) Feedback pin reference voltage is measured with the Audio Amplifier disconnected from the Boost converter (the Boost converter is unloaded). Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD Submit Documentation Feedback 5 LM48520, LM48520TLBD SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 www.ti.com Typical Performance Characteristics THD+N vs Frequency VDD = 3.3V, POUT = 900mW, RL = 8 100 100 10 10 THD + N (%) THD + N (%) THD+N vs Frequency VDD = 2.7V, POUT = 800mW, RL = 8 1 0.1 0.01 0.1 0.01 100 1k 0.001 20 10k 20k Figure 4. THD+N vs Frequency VDD = 5.0V, POUT = 1W, RL = 8 THD+N vs Output Power VDD = 2.7V, RL = 8 10 10 1 0.1 0.01 1 0.1 0.01 100 1k 0.001 10m 10k 20k 1 Figure 5. Figure 6. THD+N vs Output Power VDD = 3.3V, RL = 8 THD+N vs Output Power VDD = 5.0V, RL = 8 100 100 10 10 THD + N (%) THD + N (%) 100m 2 OUTPUT POWER (W) FREQUENCY (Hz) 1 0.1 0.01 1 0.1 0.01 100m 1 2 0.001 10m OUTPUT POWER (W) Submit Documentation Feedback 100m 1 2 OUTPUT POWER (W) Figure 7. 6 10k 20k FREQUENCY (Hz) 100 0.001 10m 1k Figure 3. 100 0.001 20 100 FREQUENCY (Hz) THD + N (%) THD + N (%) 0.001 20 1 Figure 8. Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD LM48520, LM48520TLBD www.ti.com SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 Typical Performance Characteristics (continued) Power Dissipation vs Output Power VDD = 2.7V, RL = 8, f = 1kHz Power Dissipation vs Output Power VDD = 3.3V, RL = 8, f = 1kHz 800 750 POWER DISSIPATION (mW) POWER DISSIPATION (mW) 700 600 450 300 150 600 500 400 300 200 100 POUT = POUTL + POUTR POUT = POUTL + POUTR 0 0 0 0 500 1000 1500 2000 2500 500 2000 2500 Figure 9. Figure 10. Power Dissipation vs Output Power VDD = 5.0V, RL = 8, f = 1kHz Efficiency vs Output Power VDD = 2.7V, RL = 8, f = 1kHz 3000 100 800 90 700 80 EFFICIENCY (%) 600 500 400 300 200 70 60 50 40 30 20 100 10 POUT = POUTL + POUTR 0 0 0 500 1000 1500 2000 2500 3000 3500 0 500 Figure 11. Efficiency vs Output Power VDD = 3.3V, RL = 8, f = 1kHz 90 80 80 70 70 EFFICIENCY (%) 90 60 50 40 30 50 40 30 20 10 10 1000 1500 2500 60 20 500 2000 Efficiency vs Output Power VDD = 5.0V, RL = 8, f = 1kHz 100 0 1500 Figure 12. 100 0 1000 OUTPUT POWER (mW) OUTPUT POWER (mW) EFFICIENCY (%) 1500 OUTPUT POWER (mW) OUTPUT POWER (mW) POWER DISSIPATION (mW) 1000 2000 2500 3000 0 0 500 1000 1500 2000 OUTPUT POWER (mW) OUTPUT POWER (mW) Figure 13. Figure 14. Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD 2500 Submit Documentation Feedback 7 LM48520, LM48520TLBD SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 www.ti.com Typical Performance Characteristics (continued) PSRR vs Frequency VDD =3.3V, VRIPPLE = 200mVP-P, RL = 8 0 0 -10 -10 -20 -20 -30 -30 PSRR (dB) CMRR (dB) CMRR vs Frequency VDD =3.3V, VRIPPLE = 1VP-P, RL = 8 -40 -50 -60 -40 -50 -60 -70 -70 -80 -80 -90 -90 10 100 1000 10000 -100 10 100000 100 10000 100000 FREQUENCY (Hz) FREQUENCY (Hz) Figure 15. Figure 16. Supply Current vs Supply Voltage No Load Output Power vs Supply Voltage RL = 8, f = 1kHz 4 16 THD+N = 10% OUTPUT POWER (W) 14 SUPPLY CURRENT (mA) 1000 12 10 8 6 4 3 2 THD+N = 1% 1 2 0 0 2 2.5 3 3.5 4 4.5 5 2 5.5 3.5 4 4.5 5 5.5 Figure 17. Figure 18. Boost Output Voltage vs Load Current VDD = 2.7V Boost Output Voltage vs Load Current VDD = 3.3V 5.4 5.2 BOOST OUTPUT VOLTAGE (V) BOOST OUTPUT VOLTAGE (V) 3 SUPPLY VOLTAGE (V) 5.4 5 4.8 4.6 4.4 4.2 4 0 8 2.5 SUPPLY VOLTAGE (V) 200 400 600 800 1000 1200 1400 5.2 5 4.8 4.6 4.4 0 200 400 600 800 1000 1200 1400 LOAD CURRENT (mA) LOAD CURRENT (mA) Figure 19. Figure 20. Submit Documentation Feedback Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD LM48520, LM48520TLBD www.ti.com SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 Typical Performance Characteristics (continued) Boost Output Voltage vs Load Current VDD = 5.0V BOOST OUTPUT VOLTAGE (V) 5.4 5.3 5.2 5.1 5 0 200 400 600 800 1000 1200 1400 LOAD CURRENT (mA) Figure 21. Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD Submit Documentation Feedback 9 LM48520, LM48520TLBD SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 www.ti.com APPLICATION INFORMATION General Amplifier Function The LM48520 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 LM48520 outputs changes. For increasing output voltage, the duty cycle of VLS+ increases, while the duty cycle of VLS-decreases. For decreasing output voltages, the converse occurs. The difference between the two pulse widths yields the differential output voltage. Differential Amplifier Explanation The amplifier portion of the LM48520 is a 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 amplifier also offers the possibility of DC input coupling which eliminates the two external AC coupling, DC blocking capacitors. The amplifier 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 amplifier portion of the LM48520 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. Amplifier Dissipation and Efficiency The major benefit of a Class D amplifier is increased efficiency versus a Class AB. The efficiency of the LM48520 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. 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 LM48520 FET switch. The switch power dissipation from ON-time conduction is calculated by: PD(SWITCH) = DC x (IINDUCTOR(AVE))2 x RDS(ON) (W) (1) where: Where DC is the duty cycle Shutdown Function The LM48520 features independent amplifier and regulator shutdown controls, allowing each portion of the device to be disabled or enabled independently. AmpSD controls the Class D amplifiers, while BstSD 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. 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: VDD -- [VD + (IL x DCR)] (2) where: VD is the forward voltage of the Schottky diode IL is the current through the inductor 10 Submit Documentation Feedback Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD LM48520, LM48520TLBD www.ti.com SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 DCR is the DC resistance of the inductor Additionally, when the regulator is disabled, an external voltage between 2.4V and 5.5V 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 LM48520 may be disabled with shutdown voltages in between GND and VDD, the idle current will be greater than the typical 0.1A value. Increased THD+N may also be observed when a voltage of less than VDD is applied to AmpSD. 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 LM48520 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, AVX, and Murata. Power Supply Bypassing for Amplifier 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 Input Capacitor for Audio Amplifier Input capacitors, CIN, in conjunction with the input impedance of the LM48520 forms a high pass filter that removes the DC bias from an incoming signal. The AC-coupling capacitor allows the amplifier to bias the signal to an optimal DC level. Assuming zero source impedance, the -3dB point of the high pass filter is given by: f(-3dB) = 1/2RINCIN (3) Choose CIN such that f-3dB is well below that lowest frequency of interest. Setting f-3dB too high affects the lowfrequency responses of the amplifier. Use capacitors with low voltage coefficient dielectrics, such as tantalum or aluminum electrolytic. Capacitors with high-voltage coefficients, such as ceramics, may result in increased distortion at low frequencies. Other factors to consider when designing the input filter include the constraints of the overall system. Although high fidelity audio requires a flat frequency response between 20Hz and 20kHz, portable devices such as cell phones may only concentrate on the frequency range of the frequency range of the spoken human voice (typically 300Hz to 4kHz). In addition, the physical size of the speakers used in such portable devices limits the low frequency response; in this case, frequencies below 150Hz may be filtered out. Selecting Output Capacitor (CO) for Boost Converter A single 100F 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. Selecting Input Capacitor (Cs1) for Boost Converter An input 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 is the best choice. We recommend a nominal value of 2.2F, 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. Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD Submit Documentation Feedback 11 LM48520, LM48520TLBD SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 www.ti.com Selecting Soft-Start (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. 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 (CO). A 0.1uF soft-start capacitor is recommended for a typical application. Setting the Output Voltage (V1) of boost Converter The output voltage is set using the external resistors R1 and R2 (see Figure 1). A value of approximately 13.3k is recommended for R2 to establish a divider current of approximately 92A. R1 is calculated using the formula: R1 = R2 X (V1/1.23 - 1) (4) Feed-Forward Compensation for Boost Converter Although the LM48520's internal Boost converter is internally compensated, the external feed-forward capacitor Cf is required for stability (see Figure 1). Adding this capacitor puts a zero in the loop response of the converter. The recommended frequency for the zero fz should be approximately 6kHz. Cf1 can be calculated using the formula: Cf = 1 / (2 X R1 X fz) (5) Selecting Diodes for Boost The external diode used in Figure 1 should be a Schottky diode. A 20V diode such as the MBRS320T3 is recommended. The MBRS320T3 series of diodes are designed to handle a maximum average current of 3A. 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 as: Duty Cycle = VOUT + VDIODE - VIN/ VOUT + VDIODE - VSW (6) This applies for continuous mode operation. 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: E = L/2 X (IP)2 (7) Where "lp" is the peak inductor current. The LM48520 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. During the TBDs ON-time, the inductor current ramps up TBDA and ramps down an equal amount during the OFF-time. This is defined as the inductor "ripple current". It can also be seen that if the load current drops to about TBDmA, the inductor current will begin touching the zero axis which means it will be in discontinuous mode. A similar analysis can be performed on any boost converter, to make sure the ripple current is reasonable and continuous operation will be maintained at the typical load current values. 12 Submit Documentation Feedback Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD LM48520, LM48520TLBD www.ti.com SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 Maximum Switch Current The maximum FET switch current available before the current limiter cuts in is dependent on duty cycle of the application. This is illustrated in a graph in the Typical Performance Characteristics section which shows typical values of switch current as a function of effective (actual) duty cycle. Calculating Output Current of Boost Converter (IAMP) The load current is related to the average inductor current by the relation: ILOAD = IIND(AVG) x (1 - DC) (8) where: "DC" is the duty cycle of the application The switch current can be found by: ISW = IIND(AVG) + 1/2 (IRIPPLE) (9) Inductor ripple current is dependent on inductance, duty cycle, input voltage and frequency: IRIPPLE = DC x (VIN-VSW) / (f x L) (10) combining all terms, we can develop an expression which allows the maximum available load current to be calculated: ILOAD(max) = (1-DC)x(ISW(max)-DC(VIN-VSW))/fL (11) 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. Design Parameters VSW and ISW The value of the FET "ON" voltage (referred to as VSW in Equation 4 thru Equation 9) is dependent on load current. A good approximation can be obtained by multiplying the "ON Resistance" of the FET times the average inductor current. FET on resistance increases at VIN values below 5V, since the internal N-FET has less gate voltage in this input voltage range (see Typical Performance Characteristics curves). Above VIN = 5V, the FET gate voltage is internally clamped to 5V. The maximum peak switch current the device can deliver is dependent on duty cycle. For higher duty cycles, see Typical Performance Characteristics curves. Inductor Suppliers The recommended inductor for the LM48520 is the NR8040T6R8N from Taiyo Yuden. When selecting an inductor, make certain that the continuous current rating is high enough to avoid saturation at peak currents, where: IIND = (PV1 / VDD) x ILOAD(BOOST) (12) A suitable core type must be used to minimize core (switching) losses, and wire power losses must be considered when selecting the current rating. PCB Layout Guidelines High frequency boost converters require very careful layout of components in order to get stable operation and low noise. All components must be as close as possible to the LM48520 device. It is recommended that a four layer PCB be used so that internal ground planes are available. Some additional guidelines to be observed (all designators are referencing Figure 1): 1. Keep the path between L1, D1, and Co extremely short. Parasitic trace inductance in series with D1 and Co will increase noise and ringing. 2. The feedback components R1, R2 and Cf1 must be kept close to the FB pin to prevent noise injection on the FB pin trace. 3. Since the external components of the boost converter are switching, L1 and D1 should be kept away from Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD Submit Documentation Feedback 13 LM48520, LM48520TLBD SNAS367C - FEBRUARY 2008 - REVISED APRIL 2013 www.ti.com the input traces to prevent the noise from injecting into the input. 4. The power supply bypass capacitors, Cs1 and Cs2 should be placed as close to the LM48520 device as possible. GROUNDING GUIDELINES There are three grounds on the LM48520, GND, SW_GND, and PGND. When laying out the PCB, it is critical to connect the grounds as close to the device as possible. The simplest way to do that is to place vias close to the GND, SW_GND, and PGND bumps and connect the GND, SW_GND, and PGND vias using a single ground plane in an inner layer of the PCB. Output Speaker Protection Function The LM48520's output voltage limiter can be used to set a minimum and maximum output voltage swing magnitude. The voltage applied to the VLimit pin controls the limit on the output voltage level. The output level is determined by the following equation: Vout clipped = 8/3 * (PV1 -- 2 * Vlimit) (13) where: Vout clipped = the desired output level measured in Vpk PV1 = Boost output voltage Vlimit is the voltage applied the the Vlimit pin on the LM48520 or Vout clipped = 1/2 * (PV1 -- 3/8 * Vout clipped) (14) To disable the limiter, set Vlimit = 0V. Figure 22 provides an example of how the output voltage limiter functions with VDD = 3.3V, AV = 6dB, PV1 = 5V, Vlimit = 2V, RL = 8, VIN = 2VP. 4 No Clipping 3 OUTPUT (V) 2 With Soft Clipping 1 0 -1 -2 -3 -4 200 Ps Figure 22. Soft Clipping vs No Clipping Revision History 14 Rev Date 1.0 02/27/08 Initial release. 1.01 03/07/08 Added the Soft clipping vs No clipping curve. 1.02 03/12/08 Text edits. C 04/05/13 Changed layout of National Data Sheet to TI format. Submit Documentation Feedback Description Copyright (c) 2008-2013, Texas Instruments Incorporated Product Folder Links: LM48520 LM48520TLBD PACKAGE OPTION ADDENDUM www.ti.com 24-Sep-2015 PACKAGING INFORMATION Orderable Device Status (1) LM48520TL/NOPB ACTIVE Package Type Package Pins Package Drawing Qty DSBGA YZR 25 250 Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Green (RoHS & no Sb/Br) SNAGCU Level-1-260C-UNLIM Op Temp (C) Device Marking (4/5) -40 to 85 GI5 (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation of the previous line and the two combined represent the entire Device Marking for that device. (6) Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish value exceeds the maximum column width. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals. TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release. In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis. Addendum-Page 1 Samples PACKAGE OPTION ADDENDUM www.ti.com 24-Sep-2015 Addendum-Page 2 PACKAGE MATERIALS INFORMATION www.ti.com 2-Sep-2015 TAPE AND REEL INFORMATION *All dimensions are nominal Device LM48520TL/NOPB Package Package Pins Type Drawing SPQ DSBGA 250 YZR 25 Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 178.0 8.4 Pack Materials-Page 1 2.69 B0 (mm) K0 (mm) P1 (mm) 2.69 0.76 4.0 W Pin1 (mm) Quadrant 8.0 Q1 PACKAGE MATERIALS INFORMATION www.ti.com 2-Sep-2015 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM48520TL/NOPB DSBGA YZR 25 250 210.0 185.0 35.0 Pack Materials-Page 2 MECHANICAL DATA YZR0025xxx 0.6000.075 D E TLA25XXX (Rev D) D: Max = 2.511 mm, Min =2.451 mm E: Max = 2.511 mm, Min =2.451 mm 4215055/A NOTES: A. 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