LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 LM4818 350mW Audio Power Amplifier with Shutdown Mode Check for Samples: LM4818 FEATURES DESCRIPTION * * * * The LM4818 is a mono bridged power amplifier that is capable of delivering 350mWRMS output power into a 16 load or 300mWRMS output power into an 8 load with 10% THD+N from a 5V power supply. 1 23 SOIC Surface Mount Packaging. Switch On/Off Click Suppression. Unity-Gain Stable. Minimum External Components. APPLICATIONS * * * General Purpose Audio Portable Electronic Devices Information Appliances (IA) KEY SPECIFICATIONS * * * THD+N at 1kHz, 350mW Continuous Average Output Power into 16 10% (max) THD+N at 1kHz, 300mW Continuous Average Output Power into 8 10% (max) Shutdown Current 0.7A (typ) The LM4818 BoomerTM audio power amplifier is designed specifically to provide high quality output power and minimize PCB area with surface mount packaging and a minimal amount of external components. Since the LM4818 does not require output coupling capacitors, bootstrap capacitors or snubber networks, it is optimally suited for low-power portable applications. The closed loop response of the unity-gain stable LM4818 can be configured using external gain-setting resistors. The device is available in SOIC package type to suit various applications. Typical Application Figure 1. Typical Audio Amplifier Application Circuit 1 2 3 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. Boomer is a trademark of Texas Instruments. All other 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) 2002-2013, Texas Instruments Incorporated LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com Connection Diagram Figure 2. SOIC Package - Top View See Package Number D 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) (3) Supply Voltage 6.0V -65C to +150C Storage Temperature -0.3V to VDD +0.3V Input Voltage Power Dissipation (PD) (4) Internally Limited ESD Susceptibility (5) ESD Susceptibility 2.5kV (6) 200V Junction Temperature (TJ) Soldering Information 150C Small Outline Package Vapor Phase (60 seconds) Infrared (15 seconds) Thermal Resistance (1) (2) (3) (4) (5) (6) 215C 220C JC (SOIC) 35C/W JA (SOIC) 170C/W All voltages are measured with respect to the ground 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's 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. For the LM4818, TJMAX = 150C and the typical junction-toambient thermal resistance (JA) when board mounted is 170C/W for the SOIC package. Human body model, 100pF discharged through a 1.5 k resistor. Machine Model, 220pF-240pF capacitor is discharged through all pins. OPERATING RATINGS (1) (2) Temperature Range TMIN TA TMAX -40C TA 85C 2.0V VCC 5.5V Supply Voltage (1) (2) 2 All voltages are measured with respect to the ground 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's performance. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 ELECTRICAL CHARACTERISTICS VDD = 5V (1) (2) The following specifications apply for VDD = 5V, RL = 16 unless otherwise stated. Limits apply for TA = 25C. Symbol Parameter Conditions LM4818 Typical (3) Limit (4) (5) Units (Limits) IDD Quiescent Power Supply Current VIN = 0V, Io = 0A 1.5 3.0 mA (max) ISD Shutdown Current VPIN1 = VDD (6) 1.0 5.0 A (max) ISDIH Shutdown Voltage Input High 4.0 V (min) ISDIL Shutdown Voltage Input Low VOS Output Offset Voltage PO Output Power THD+N Total Harmonic Distortion + Noise (1) (2) (3) (4) (5) (6) VIN = 0V 5 1.0 V (max) 50 mV (max) THD = 10%, fIN = 1kHz 350 mW THD = 10%, fIN = 1kHz, RL = 8 300 mW 1 % PO = 270mWRMS, AVD = 2, fIN = 1kHz All voltages are measured with respect to the ground 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's performance. Typical specifications are specified at 25C and represent the parametric norm. Tested limits are specified to TI's AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are specified by designs, test, or statistical analysis. The Shutdown pin (pin 1) should be driven as close as possible to VDD for minimum current in Shutdown Mode. ELECTRICAL CHARACTERISTICS VDD = 3V (1) (2) The following specifications apply for VDD = 3V and RL = 16 load unless otherwise stated. Limits apply to TA = 25C. Symbol Parameter Conditions LM4818 Typical (3) Limit (4) (5) Units (Limits) IDD Quiescent Power Supply Current VIN = 0V, Io = 0A 1.0 3.0 mA (max) ISD Shutdown Current VPIN1 = VDD (6) 0.7 5.0 A (max) ISDIH Shutdown Voltage Input High 2.4 V (min) ISDIL Shutdown Voltage Input Low 0.6 V (max) VOS Output Offset Voltage PO Output Power THD+N Total Harmonic Distortion + Noise (1) (2) (3) (4) (5) (6) VIN = 0V 5 50 mV THD = 10%, fIN = 1kHz 110 mW THD = 10%, fIN = 1kHz, RL = 8 90 mW PO = 80mWRMS, AVD = 2, fIN = 1kHz 1 % All voltages are measured with respect to the ground 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's performance. Typical specifications are specified at 25C and represent the parametric norm. Tested limits are specified to TI's AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are specified by designs, test, or statistical analysis. The Shutdown pin (pin 1) should be driven as close as possible to VDD for minimum current in Shutdown Mode. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 3 LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com EXTERNAL COMPONENTS DESCRIPTION (Figure 1) Components 4 Functional Description 1. Ri Combined with Rf, this inverting input resistor sets the closed-loop gain. Ri also forms a high pass filter with Ci at fc = 1/(2RiCi). 2. Ci This input coupling capacitor blocks DC voltage at the amplifier's terminals. Combined with Ri, it creates a high pass filter with Ri at fc = 1/(2RiCi). Refer to the section, PROPER SELECTION OF EXTERNAL COMPONENTS for an explanation of how to determine the value of Ci. 3. Rf Combined with Ri, this is the feedback resistor that sets the closed-loop gain: Av = 2(RF/Ri). 4. CS This is the power supply bypass capacitor that filters the voltage applied to the power supply pin. Refer to the APPLICATION INFORMATION section for proper placement and selection of Cs. 5. CB This is the bypass pin capacitor that filters the voltage at the BYPASS pin. Refer to the section, PROPER SELECTION OF EXTERNAL COMPONENTS for information concerning proper placement and selection of CB. 6. CB2 This is an optional capacitor that is not needed in the majority of applications. If the capacitor is not used, pin 3 should be connected directly to pin2. Refer to the section PROPER SELECTION OF EXTERNAL COMPONENTS for more information concerning CB2. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 TYPICAL PERFORMANCE CHARACTERISTICS Figure 3. Figure 4. Figure 5. Figure 6. Figure 7. Figure 8. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 5 LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) 6 Figure 9. Figure 10. Figure 11. Figure 12. Figure 13. Figure 14. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 TYPICAL PERFORMANCE CHARACTERISTICS (continued) Output Power vs Supply Voltage RL = 8 Output Power vs Supply Voltage RL = 16 Figure 15. Figure 16. Output Power vs Supply Voltage RL = 32 Output Power vs Load Resistance Figure 17. Figure 18. Power Dissipation vs Output Power VDD = 5V Power Dissipation vs Output Power VDD = 3V Figure 19. Figure 20. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 7 LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS (continued) Power Derating Curves Frequency Response vs Input Capacitor Size Figure 21. Figure 22. Supply Current vs Supply Voltage Figure 23. 8 Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 APPLICATION INFORMATION BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4818 consist of two operational amplifiers. External resistors, Ri and RF set the closed-loop gain of the first amplifier (and the amplifier overall), whereas two internal 20k resistors set the second amplifier's gain at -1. The LM4818 is typically used to drive a speaker connected between the two amplifier outputs. Figure 1 shows that the output of Amp1 servers as the input to Amp2, which results in both amplifiers producing signals identical in magnitude but 180 out of phase. Taking advantage of this phase difference, a load is placed between V01 and V02 and driven differentially (commonly referred to as "bridge mode"). This results in a differential gain of AVD= 2 *(Rf/Ri) (1) Bridge mode is different from single-ended amplifiers that drive loads connected between a single amplifier's output and ground. For a given supply voltage, bridge mode has a distinct advantage over the single-ended configuration: its differential output doubles the voltage swing across the load. This results in four times the output power when compared to a single-ended amplifier under the same conditions. This increase in attainable output assumes that the amplifier is not current limited or the output signal is not clipped. To ensure minimum output signal clipping when choosing an amplifier's closed-loop gain, refer to the AUDIO POWER AMPLIFIER DESIGN EXAMPLE section. Another advantage of the differential bridge output is no net DC voltage across the load. This results from biasing V01 and V02 at half-supply. This eliminates the coupling capacitor that single supply, single-ended amplifiers require. Eliminating an output coupling capacitor in a single-ended configuration forces a single supply amplifier's half-supply bias voltage across the load. The current flow created by the half-supply bias voltage increases internal IC power dissipation and may permanently damage loads such as speakers. POWER DISSIPATION Power dissipation is a major concern when designing a successful bridged or single-ended amplifier. Equation 2 states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and driving a specified load. PDMAX = (VDD)2 /(22RL ) (W) Single-ended (2) However, a direct consequence of the increased power delivered to the load by a bridged amplifier is an increase in the internal power dissipation point for a bridge amplifier operating at the same given conditions. Equation 3 states the maximum power dissipation point for a bridged amplifier operating at a given supply voltage and driving a specified load. PDMAX = 4(VDD)2/(22 RL ) (W) Bridge Mode (3) The LM4818 has two operational amplifiers in one package and the maximum internal power dissipation is four times that of a single-ended amplifier. However, even with this substantial increase in power dissipation, the LM4818 does not require heatsinking. From Equation 3, assuming a 5V power supply and an 8 load, the maximum power dissipation point is 633mW. The maximum power dissipation point obtained from Equation 3 must not exceed the power dissipation predicted by Equation 4: PDMAX = (TJMAX - TA)/JA (W) (4) For the D package, JA = 170C/W and TJMAX = 150C for the LM4818. For a given ambient temperature, TA, Equation 4 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 3 is greater than the result of Equation 4, then decrease the supply voltage, increase the load impedance, or reduce the ambient temperature. For a typical application using the D packaged LM4818 with a 5V power supply and an 8 load, the maximum ambient temperature that does not violate the maximum junction temperature is approximately 42C. It is assumed that a device is a surface mount part operating around the maximum power dissipation point. The assumption that the device is operating around the maximum power dissipation point is incorrect for an 8 load. The maximum power dissipation point occurs when the output power is equal to the maximum power dissipation or 50% efficiency. The LM4818 is not capable of the output power level (633mW) required to operate at the maximum power dissipation point for an 8 load. To find the maximum Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 9 LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com power dissipation, the graph Figure 20 must be used. From the graph, the maximum power dissipation for an 8 load and a 5V supply is approximately 575mW. Substituting this value back into Equation 4 for PDMAX and using JA = 170C/W for the D package, the maximum ambient temperature is 52C. Refer to the TYPICAL PERFORMANCE CHARACTERISTICS curves for power dissipation information for lower output powers and maximum power dissipation for each package at a given ambient temperature. POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. The capacitors connected to the bypass and power supply pins should be placed as close to the LM4818 as possible. The capacitor connected between the bypass pin and ground improves the internal bias voltage's stability, producing improved PSRR. The improvements to PSRR increase as the bypass pin capacitor value increases. Typical applications employ a 5V regulator with 10F and 0.1F filter capacitors that aid in supply stability. Their presence, however, does not eliminate the need for bypassing the supply nodes of the LM4818. The selection of bypass capacitor values, especially CB , depends on desired PSRR requirements, click and pop performance as explained in the section, PROPER SELECTION OF EXTERNAL COMPONENTS, as well as system cost and size constraints. SHUTDOWN FUNCTION The voltage applied to the LM4818's SHUTDOWN pin controls the shutdown function. Activate micro-power shutdown by applying VDD to the SHUTDOWN pin. When active, the LM4818's micro-power shutdown feature turns off the amplifier's bias circuitry, reducing the supply current. The logic threshold is typically 1/2VDD. The low 0.7A typical shutdown current is achieved by applying a voltage that is as near as VDD as possible to the SHUTDOWN pin. A voltage that is less than VDD may increase the shutdown current. Avoid intermittent or unexpected micro-power shutdown by ensuring that the SHUTDOWN pin is not left floating but connected to either VDD or GND. There are a few ways to activate micro-power shutdown. These included using a single-pole, single-throw switch, a microcontroller, or a microprocessor. When using a switch, connect an external 10k to 100k pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select normal amplifier operation by closing the switch. Opening the switch connects the shutdown pin to VDD through the pull-up resistor, activating micro-power shutdown. The switch and resistor ensure that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or a microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active circuitry eliminates the pull-up resistor PROPER SELECTION OF EXTERNAL COMPONENTS Optimizing the LM4818's performance requires properly selecting external components. Though the LM4818 operates well when using external components with wide tolerances, best performance is achieved by optimizing component values. The LM4818 is unity gain stable, giving the designer maximum design flexibility. The gain should be set to no more than a given application requires. This allows the amplifier to achieve minimum THD+N and maximum signal-to-noise ratio. These parameters are compromised as the closed-loop gain increases. However, low gain demands input signals with greater voltage swings to achieve maximum output power. Fortunately, many signal sources such as audio CODECs have outputs of 1VRMS (2.83VP-P). Please refer to the AUDIO POWER AMPLIFIER DESIGN EXAMPLE section for more information on selecting the proper gain. Another important consideration is the amplifier's close-loop bandwidth. To a large extent, the bandwidth is dictated by the choice of external components shown in Figure 1. The input coupling capacitor, Ci, forms a first order high pass filter that limits low frequency response. This value should be chosen based on needed frequency response for a few distinct reasons discussed below Input Capacitor Value Selection Amplifying the lowest audio frequencies requires a high value input coupling capacitor (Ci in Figure 1). A high value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 150Hz. Applications using speakers with limited frequency response reap little improvement by using a large input capacitor. 10 Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 Besides affecting system cost and size, Ci has an effect on the LM4818's click and pop performance. When the supply voltage is first applied, a transient (pop) is created as the charge on the input capacitor changes from zero to a quiescent state. The magnitude of the pop is directly proportional to the input capacitor's value. Higher value capacitors need more time to reach a quiescent DC voltage (usually 1/2 VDD) when charged with a fixed current. The amplifier's output charges the input capacitor through the feedback resistor, RF. Thus, selecting an input capacitor value that is no higher than necessary to meet the desired -3dB frequency can minimize pops. As shown in Figure 1, the input resistor (Ri) and the input capacitor, Ci produce a -3dB high pass filter cutoff frequency that is found using Equation 5. f-3dB = 1/(2 RiCi) (Hz) (5) As an example when using a speaker with a low frequency limit of 150Hz, Ci, using Equation 5 is 0.063F. The 0.39F Ci shown in Figure 1 allows the LM4818 to drive a high efficiency, full range speaker whose response extends down to 20Hz. Besides optimizing the input capacitor value, the bypass capacitor value, CB requires careful consideration. The bypass capacitor's value is the most critical to minimizing turn-on pops because it determines how fast the LM4818 turns on. The slower the LM4818's outputs ramp to their quiescent DC voltage (nominally 1/2VDD), the smaller the turn-on pop. While the device will function properly (no oscillations or motorboating), with CB less than 1.0F, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to or greater than 1.0F is recommended in all but the most cost sensitive designs. Bypass Capacitor Value Selection Besides minimizing the input capacitor size, careful consideration should be paid to the value of CB, the capacitor connected to the BYPASS pin. Since CB determines how fast the LM4818 settles to quiescent operation, its value is critical when minimizing turn-on pops. The slower the LM4818's outputs ramp to their quiescent DC voltage (nominally 1/2VDD), the smaller the turn-on pop. Choosing CB equal to 1.0F along with a small value of Ci (in the range of 0.1F to 0.39F) produces a click-less and pop-less shutdown function. As discussed above, choosing Ci no larger than necessary for the desired bandwidth helps minimize clicks and pops. If using the optional capacitor, CB2, the total capacitance see at the BYPASS pin is CB + CB2. When using the values shown in Figure 1 for CB and CB2 the change in the capacitance seen by the BYPASS pin is not significant relative to capacitor value tolerances. Optimizing Click and Pop Reduction Performance The LM4818 contains circuitry that minimizes turn-on and shutdown transients or "clicks and pops". For this discussion, turn on refers to either applying the power or supply voltage or when the shutdown mode is deactivated. While the power supply is ramping to it's final value, the LM4818's internal amplifiers are configured as unity gain buffers. An internal current source charges the voltage of the bypass capacitor, CB, connected to the BYPASS pin in a controlled, linear manner. Ideally, the input and outputs track the voltage charging on the bypass capacitor. The gain of the internal amplifiers remains unity until the bypass capacitor is fully charged to 1/2VDD. As soon as the voltage on the bypass capacitor is stable, the device becomes fully operational. Although the BYPASS pin current cannot be modified, changing the size of the bypass capacitor, CB, alters the device's turn-on time and magnitude of "clicks and pops". Increasing the value of CB reduces the magnitude of turn-on pops. However, this presents a tradeoff: as the size of CB increases, the turn-on time (Ton) increases. There is a linear relationship between the size of CB and the turn on time. If using the optional capacitor, CB2, the total capacitance see at the BYPASS pin is CB and CB2. The total capacitance see at the BYPASS pin must be considered for the table below and when optimizing click and pop performance. Below are some typical turn-on times for various values of CB: CB TON 0.01F 20ms 0.1F 200ms 0.22F 440ms 0.47F 940ms 1.0F 2S Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 11 LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com In order to eliminate "clicks and pops", all capacitors must be discharged before turn-on. Rapidly switching VDD may not allow the capacitors to fully discharge, which may cause "clicks and pops". AUDIO POWER AMPLIFIER DESIGN EXAMPLE The following are the desired operational parameters: Given: Power Output 100mW Load Impedance 16 Input Level 1Vrms (max) Input Impedance 20k Bandwidth 100Hz-20kHz 0.25dB The design begins by specifying the minimum supply voltage necessary to obtain the specified output power. To find this minimum supply voltage, use the Output Power vs. Supply Voltage graph in the TYPICAL PERFORMANCE CHARACTERISTICS section. From the graph for a 16 load, (graphs are for 8, 16, and 32 loads) the supply voltage for 100mW of output power with 1% THD+N is approximately 3.15 volts. Additional supply voltage creates the benefit of increased headroom that allows the LM4818 to reproduce peaks in excess of 100mW without output signal clipping or audible distortion. The choice of supply voltage must also not create a situation that violates maximum dissipation as explained above in the Power Dissipation section. For example, if a 3.3V supply is chosen for extra headroom then according to Equation 3 the maximum power dissipation point with a 16 load is 138mW. Using Equation 4 the maximum ambient temperature is 126C for the D package. After satisfying the LM4818's power dissipation requirements, the minimum differential gain is found using Equation 6. (6) Thus a minimum gain of 1.27 V/V allows the LM4818 to reach full output swing and maintain low noise and THD+N performance. For this example, let AVD = 1.27. The amplifier's overall gain is set using the input (Ri) and feedback (RF) resistors. With the desired input impedance set to 20k, the feedback resistor is found using Equation 7. RF/Ri = AVD/2 (V/V) (7) The value of RF is 13k. The last step in this design example is setting the amplifier's -3dB frequency bandwidth. To achieve the desired 0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the lower bandwidth limit and the high frequency response must extend to at least five times the upper bandwidth limit. The gain variation for both response limits is 0.17dB, well with in the 0.25dB desired limit. The results are: fL = 100Hz/5 = 20Hz fH = 20 kHz*5 = 100kHz (8) (9) As mentioned in the PROPER SELECTION OF EXTERNAL COMPONENTS section, Ri and Ci create a high pass filter that sets the amplifier's lower band pass frequency limit. Find the coupling capacitor's value using Equation 10. Ci 1/(2Rifc) (F) (10) Ci 0.398F, a standard value of 0.39F will be used. The product of the desired high frequency cutoff (100kHz in this example) and the differential gain, AVD, determines the upper pass band response limit. With AVD = 1.27 and fH = 100kHz, the closed-loop gain bandwidth product (GBWP) is 127kHz. This is less than the LM4818's 900kHz GBWP. With this margin the amplifier can be used in designs that require more differential gain while avoiding performance restricting bandwidth limitations. 12 Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 Figure 24. HIGHER GAIN AUDIO AMPLIFIER The LM4818 is unity-gain stable and requires no external components besides gain-setting resistors, an input coupling capacitor, and proper supply bypassing in the typical application. However, if a closed-loop differential gain of greater than 10 is required, a feedback capacitor (C4) may be needed as shown in Figure 24 to bandwidth limit the amplifier. This feedback capacitor creates a low pass filter that eliminates possible high frequency oscillations. Care should be taken when calculating the -3dB frequency in that an incorrect combination of R3 and C4 will cause rolloff before 20kHz. A typical combination of feedback resistor and capacitor that will not produce audio band high frequency rolloff is R3 = 20k and C4 = 25pF. These components result in a -3dB point of approximately 320 kHz. It is not recommended that the feedback resistor and capacitor be used to implement a band limiting filter below 100kHz. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 13 LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com Figure 25. REFERENCE DESIGN BOARD and PCB LAYOUT GUIDELINES LM4818 SOIC DEMO BOARD ARTWORK Composite View 14 Silk Screen Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 Top Layer Bottom Layer Table 1. Mono LM4818 Reference Design Boards Bill of Material for all Demo Boards Item Part Number Part Description Qty Ref Designator 1 551011208-001 LM4818 Mono Reference Design Board 1 10 482911183-001 LM4818 Audio AMP 1 U1 20 151911207-001 Tant Cap 1uF 16V 10 1 C1 21 151911207-002 Cer Cap 0.39uF 50V Z5U 20% 1210 1 C2 25 152911207-001 Tant Cap 1uF 16V 10 1 C3 30 472911207-001 Res 20K Ohm 1/10W 5 3 R1, R2, R3 35 210007039-002 Jumper Header Vertical Mount 2X1 0.100 2 J1 PCB LAYOUT GUIDELINES This section provides practical guidelines for mixed signal PCB layout that involves various digital/analog power and ground traces. Designers should note that these are only "rule-of-thumb" recommendations and the actual results will depend heavily on the final layout. General Mixed Signal Layout Recommendation Power and Ground Circuits For two layer mixed signal design, it is important to isolate the digital power and ground trace paths from the analog power and ground trace paths. Star trace routing techniques (bringing individual traces back to a central point rather than daisy chaining traces together in a serial manner) can have a major impact on low level signal performance. Star trace routing refers to using individual traces to feed power and ground to each circuit or even device. This technique will take require a greater amount of design time but will not increase the final price of the board. The only extra parts required will be some jumpers. Single-Point Power / Ground Connections The analog power traces should be connected to the digital traces through a single point (link). A "Pi-filter" can be helpful in minimizing high frequency noise coupling between the analog and digital sections. It is further recommended to put digital and analog power traces over the corresponding digital and analog ground traces to minimize noise coupling. Placement of Digital and Analog Components All digital components and high-speed digital signals traces should be located as far away as possible from analog components and circuit traces. Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 15 LM4818 SNAS163B - APRIL 2002 - REVISED MAY 2013 www.ti.com Avoiding Typical Design / Layout Problems Avoid ground loops or running digital and analog traces parallel to each other (side-by-side) on the same PCB layer. When traces must cross over each other do it at 90 degrees. Running digital and analog traces at 90 degrees to each other from the top to the bottom side as much as possible will minimize capacitive noise coupling and cross talk. 16 Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 LM4818 www.ti.com SNAS163B - APRIL 2002 - REVISED MAY 2013 REVISION HISTORY Changes from Revision A (May 2013) to Revision B * Page Changed layout of National Data Sheet to TI format .......................................................................................................... 16 Submit Documentation Feedback Copyright (c) 2002-2013, Texas Instruments Incorporated Product Folder Links: LM4818 17 PACKAGE OPTION ADDENDUM www.ti.com 2-May-2013 PACKAGING INFORMATION Orderable Device Status (1) LM4818MX/NOPB ACTIVE Package Type Package Pins Package Drawing Qty SOIC D 8 2500 Eco Plan Lead/Ball Finish (2) Green (RoHS & no Sb/Br) MSL Peak Temp Op Temp (C) Top-Side Markings (3) CU SN Level-1-260C-UNLIM (4) -40 to 85 LM48 18M (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) Multiple Top-Side Markings will be inside parentheses. Only one Top-Side 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 Top-Side Marking for that device. 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. 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Addendum-Page 1 Samples PACKAGE MATERIALS INFORMATION www.ti.com 8-May-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device LM4818MX/NOPB Package Package Pins Type Drawing SOIC D 8 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2500 330.0 12.4 Pack Materials-Page 1 6.5 B0 (mm) K0 (mm) P1 (mm) 5.4 2.0 8.0 W Pin1 (mm) Quadrant 12.0 Q1 PACKAGE MATERIALS INFORMATION www.ti.com 8-May-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM4818MX/NOPB SOIC D 8 2500 367.0 367.0 35.0 Pack Materials-Page 2 IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services per JESD46, latest issue, and to discontinue any product or service per JESD48, latest issue. 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