LM4893 1.1 Watt Audio Power Amplifier General Description Key Specifications The LM4893 is an audio power amplifier primarily designed for demanding applications in mobile phones and other portable communication device applications. It is capable of delivering 1.1 watt of continuous average power to an 8Ω BTL load with less than 1% distortion (THD+N) from a 5VDC power supply. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4893 does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for lower-power portable applications where minimal space and power consumption are primary requirements. The LM4893 features a low-power consumption global shutdown mode, which is achieved by driving the shutdown pin with logic low. Additionally, the LM4893 features an internal thermal shutdown protection mechanism. The LM4893 contains advanced pop & click circuitry which eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM4893 is unity-gain stable and can be configured by external gain-setting resistors. j Improved PSRR at 5V, 3V, & 217Hz 62dB (typ) j Higher Power Output at 5V & 1% THD 1.1W (typ) j Higher Power Output at 3V & 1% THD 350mW (typ) j Shutdown Current 0.1µA (typ) Features n No output coupling capacitors, snubber networks or bootstrap capacitors required n Unity gain stable n Ultra low current shutdown mode n Instantaneous turn-on time n BTL output can drive capacitive loads up to 100pF n Advanced pop & click circuitry eliminates noises during turn-on and turn-off transitions n 2.2V - 5.5V operation n Available in space-saving µSMD, SO, and MSOP packages Applications n Mobile Phones n PDAs n Portable electronic devices Typical Application 20038001 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2004 National Semiconductor Corporation DS200380 www.national.com LM4893 1.1 Watt Audio Power Amplifier August 2004 LM4893 Connection Diagrams 9 Bump micro SMD Marking 9 Bump micro SMD 20038087 Top View X - Date Code T - Die Traceability G - Boomer Family 93 - LM4893ITL 20038086 Top View Order Number LM4893ITL, LM4893ITLX See NS Package Number TLA09AAA SO Marking Small Outline (SO) Package 20038092 Top View XY - Date Code TT - Die Traceability Bottom 2 lines - Part Number 20038091 MSOP Marking Top View Order Number LM4893MA See NS package Number M08A Mini Small Outline (MSOP) Package 20038085 Top View G - Boomer Family 93 - LM4893MM 20038084 Top View NC = No Connect Order Number LM4893MM See NS Package Number MUB10A www.national.com 2 θJA (TLA09AAA) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. θJC (MUB10A) 56˚C/W θJA (MUB10A) 190˚C/W θJC (M08A) 35˚C/W Supply Voltage (Note 9) θJA (M08A) 150˚C/W 6.0V Storage Temperature 180˚C/W (Note 10) −65˚C to +150˚C −0.3V to VDD +0.3V Input Voltage Power Dissipation (Note 3) Internally Limited ESD Susceptibility (Note 4) 2000V ESD Susceptibility (Note 5) 200V Junction Temperature Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX −40˚C ≤ TA ≤ 85˚C 2.2V ≤ VDD ≤ 5.5V Supply Voltage 150˚C Thermal Resistance Electrical Characteristics VDD = 5V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1 unless otherwise specified. Limits apply for TA = 25˚C. LM4893 Symbol Parameter Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) IDD Quiescent Power Supply Current VIN = 0V, 8Ω BTL 5 10 mA (max) ISD Shutdown Current Vshutdown = GND 0.1 2.0 µA (max) VOS Output Offset Voltage 5 40 mV (max) Po Output Power THD = 1% (max); f = 1kHz 1.1 0.9 W (min) THD+N Total Harmonic Distortion+Noise Po = 0.4Wrms; f = 1kHz 0.1 PSRR Power Supply Rejection Ratio Vripple = 200mVsine p-p, CB = 1.0µF Input terminated with 10Ω to ground VSDIH Shutdown High Input Voltage VSDIL Shutdown Low Input Voltage NOUT Output Noise A-Weighted; Measured across 8Ω BTL Input terminated with 10Ω to ground % 68 (f = 1kHz) 62 (f = 217Hz) 55 dB (min) 1.4 V (min) 0.4 V (max) 26 µVRMS Electrical Characteristics VDD = 3.0V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1 unless otherwise specified. Limits apply for TA = 25˚C. LM4893 Symbol Parameter Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) IDD Quiescent Power Supply Current VIN = 0V, 8Ω BTL 4.5 9 mA (max) ISD Shutdown Current Vshutdown = GND 0.1 2.0 µA (max) VOS Output Offset Voltage 5 40 mV (max) Po Output Power THD = 1% (max); f = 1kHz 350 320 mW THD+N Total Harmonic Distortion+Noise Po = 0.15Wrms; f = 1kHz 0.1 PSRR Power Supply Rejection Ratio Vripple = 200mVsine p-p, CB = 1.0µF Input terminated with 10Ω to ground VSDIH Shutdown High Input Voltage 1.4 V (min) VSDIL Shutdown Low Input Voltage 0.4 V (max) 3 68 (f = 1kHz) 62 (f = 217Hz) % 55 dB (min) www.national.com LM4893 Absolute Maximum Ratings (Note 2) LM4893 Electrical Characteristics VDD = 3.0V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1 unless otherwise specified. Limits apply for TA = 25˚C. (Continued) LM4893 Symbol NOUT Parameter Output Noise Conditions A-Weighted; Measured across 8Ω BTL Input terminated with 10Ω to ground Typical Limit (Note 6) (Notes 7, 8) 26 Units (Limits) µVRMS Electrical Characteristics VDD = 2.6V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1 unless otherwise specified. Limits apply for TA = 25˚C. LM4893 Symbol Parameter Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) IDD Quiescent Power Supply Current VIN = 0V, 8Ω BTL 3.5 ISD Shutdown Current Vshutdown = GND 0.1 µA VOS Output Offset Voltage 5 mV Po Output Power mA THD = 1% (max); f = 1kHz THD+N PSRR RL = 8Ω 250 RL = 4Ω 350 Total Harmonic Distortion+Noise Po = 0.1Wrms; f = 1kHz Power Supply Rejection Ratio Vripple = 200mVsine p-p, CB = 1.0µF Input terminated with 10Ω to ground 0.1 55 (f = 1kHz) 55 (f = 217Hz) mW % dB Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit is given, however, the typical value is a good indication of device performance. Note 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TJMAX–TA)/θJA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4893, see power derating curves for additional information. Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor. Note 5: Machine Model, 220pF–240pF discharged through all pins. Note 6: Typicals are measured at 25˚C and represent the parametric norm. Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level). Note 8: For micro SMD only, shutdown current is measured in a Normal Room Environment. Exposure to direct sunlight will increase ISD by a maximum of 2µA. Note 9: If the product is in shutdown mode, and VDD exceeds 6V (to a max of 8V VDD), then most of the excess current will flow through the ESD protection circuits. If the source impedance limits the current to a max of 10ma, then the part will be protected. If the part is enabled when VDD is above 6V, circuit performance will be curtailed or the part may be permanently damaged. Note 10: All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. Note 11: Maximum power dissipation (PDMAX) in the device occurs at an output power level significantly below full output power. PDMAX can be calculated using Equation 1 shown in the Application section. It may also be obtained from the power dissipation graphs. www.national.com 4 LM4893 External Components Description (Figure 1) Components Functional Description 1. Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a high pass filter with Ci at fC= 1/(2π RiCi). 2. Ci Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a highpass filter with Ri at fc = 1/(2π RiCi). Refer to the section, Proper Selection of External Components, for an explanation of how to determine the value of Ci. 3. Rf Feedback resistance which sets the closed-loop gain in conjunction with Ri. 4. CS Supply bypass capacitor which provides power supply filtering. Refer to the Power Supply Bypassing section for information concerning proper placement and selection of the supply bypass capacitor. 5. CB Bypass pin capacitor which provides half-supply filtering. Refer to the section, Proper Selection of External Components, for information concerning proper placement and selection of CB. Typical Performance Characteristics THD+N vs Frequency at VDD = 3.0V, 8Ω RL, and PWR = 150mW THD+N vs Frequency at VDD = 5V, 8Ω RL, and PWR = 250mW 20038037 20038038 THD+N vs Frequency at VDD = 2.6V, 4Ω RL, and PWR = 100mW THD+N vs Frequency at VDD = 2.6V, 8Ω RL, and PWR = 100mW 20038039 20038040 5 www.national.com LM4893 Typical Performance Characteristics (Continued) THD+N vs Power Out THD+N vs Power Out @ VDD = 5V, 8Ω RL, 1kHz @ VDD = 3.0V, 8Ω RL, 1kHz 20038041 20038042 THD+N vs Power Out THD+N vs Power Out @ VDD = 2.6V, 8Ω RL, 1kHz @ VDD = 2.6V, 4Ω RL, 1kHz 20038043 www.national.com 20038044 6 (Continued) Power Supply Rejection Ratio (PSRR) @ VDD = 5V Power Supply Rejection Ratio (PSRR) @ VDD = 3V 20038045 20038073 Input terminated with 10Ω R Input terminated with 10Ω R Power Supply Rejection Ratio (PSRR) @ VDD = 2.6V Power Dissipation vs Output Power @ VDD = 5V 20038046 20038047 Input terminated with 10Ω R 7 www.national.com LM4893 Typical Performance Characteristics LM4893 Typical Performance Characteristics (Continued) Power Dissipation vs Output Power @ VDD = 2.6V Power Dissipation vs Output Power VDD = 3.0V 20038049 20038048 Power Derating - SOP PDMAX = 670mW for 5V, 8Ω Power Derating - MSOP PDMAX = 670mW for 5V, 8Ω 20038079 www.national.com 20038093 8 LM4893 Typical Performance Characteristics (Continued) Power Derating - 9 Bump µSMD PDMAX = 670mW for 5V, 8Ω Output Power vs Supply Voltage 20038051 20038081 Output Power vs Supply Voltage Output Power vs Load Resistance 20038050 20038074 9 www.national.com LM4893 Typical Performance Characteristics (Continued) Clipping (Dropout) Voltage vs Supply Voltage Supply Current vs Shutdown Voltage 20038075 20038052 Shutdown Hysterisis Voltage VDD = 3V Shutdown Hysterisis Voltage VDD = 5V 20038076 www.national.com 20038077 10 LM4893 Typical Performance Characteristics (Continued) Shutdown Hysterisis Voltage VDD = 2.6V Open Loop Frequency Response 20038078 20038054 Frequency Response vs Input Capacitor Size 20038056 11 www.national.com LM4893 duced supply voltage, higher load impedance, or reduced ambient temperature. Internal power dissipation is a function of output power. Refer to the Typical Performance Characteristics curves for power dissipation information for different output powers and output loading. Application Information BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4893 has two operational amplifiers internally, allowing for a few different amplifier configurations. The first amplifier’s gain is externally configurable, while the second amplifier is internally fixed in a unity-gain, inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri while the second amplifier’s gain is fixed by the two internal 20 kΩ resistors. Figure 1 shows that the output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude, but out of phase by 180˚. Consequently, the differential gain for the IC is AVD= 2 *(Rf/Ri) 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 the bypass and power supply pins should be as close to the device as possible. Typical applications employ a 5V regulator with 10 µF tantalum or electrolytic capacitor and a ceramic bypass capacitor which aid in supply stability. This does not eliminate the need for bypassing the supply nodes of the LM4893. The selection of a bypass capacitor, especially CB, is dependent upon PSRR requirements, click and pop performance (as explained in the section, Proper Selection of External Components), system cost, and size constraints. By driving the load differentially through outputs Vo1 and Vo2, an amplifier configuration commonly referred to as “bridged mode” is established. Bridged mode operation is different from the classical single-ended amplifier configuration where one side of the load is connected to ground. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4893 contains a SHUTDOWN pin to externally turn off the amplifier’s bias circuitry. This shutdown feature turns the amplifier off when a logic low is placed on the SHUTDOWN pin. By switching the SHUTDOWN pin to ground, the LM4893 supply current draw will be minimized in idle mode. While the device will be disabled with SHUTDOWN pin voltages less than 0.4VDC, the idle current may be greater than the typical value of 0.1µA. (Idle current is measured with the SHUTDOWN pin tied to ground). In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry to provide a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch in conjunction with an external pull-up resistor. When the switch is closed, the SHUTDOWN pin is connected to ground which disables the amplifier. If the switch is open, then the external pull-up resistor to VDD will enable the LM4893. This scheme guarantees that the SHUTDOWN pin will not float thus preventing unwanted state changes. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage. Four times the output power is possible as compared to a single-ended amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not current limited or clipped. In order to choose an amplifier’s closed-loop gain without causing excessive clipping, please refer to the Audio Power Amplifier Design section. A bridge configuration, such as the one used in LM4893, also creates a second advantage over single-ended amplifiers. Since the differential outputs, Vo1 and Vo2, are biased at half-supply, no net DC voltage exists across the load. This eliminates the need for an output coupling capacitor which is required in a single supply, single-ended amplifier configuration. Without an output coupling capacitor, the half-supply bias across the load would result in both increased internal IC power dissipation and also possible loudspeaker damage. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components in applications using integrated power amplifiers is critical to optimize device and system performance. While the LM4893 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The LM4893 is unity-gain stable which gives the designer maximum system flexibility. The LM4893 should be used in low gain configurations to minimize THD+N values, and maximize the signal to noise ratio. Low gain configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1 Vrms are available from sources such as audio codecs. Please refer to the section, Audio Power Amplifier Design, for a more complete explanation of proper gain selection. Besides gain, one of the major considerations is the closedloop bandwidth of the amplifier. 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 which limits low frequency response. This value should be chosen based on needed frequency response for a few distinct reasons. POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation. Since the LM4893 has two operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a single-ended amplifier. The maximum power dissipation for a given application can be derived from the power dissipation graphs or from Equation 1. (1) PDMAX = 4*(VDD)2/(2π2RL) It is critical that the maximum junction temperature (TJMAX) of 150˚C is not exceeded. TJMAX can be determined from the power derating curves by using PDMAX and the PC board foil area. By adding additional copper foil, the thermal resistance of the application can be reduced from a free air value of 150˚C/W, resulting in higher PDMAX. Additional copper foil can be added to any of the leads connected to the LM4893. It is especially effective when connected to VDD, GND, and the output pins. Refer to the application information on the LM4893 reference design board for an example of good heat sinking. If TJMAX still exceeds 150˚C, then additional changes must be made. These changes can include rewww.national.com 12 (Continued) LM4893 Application Information AUDIO POWER AMPLIFIER DESIGN Selection Of Input Capacitor Size A 1W/8Ω Audio Amplifier Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 100 Hz to 150 Hz. Thus, using a large input capacitor may not increase actual system performance. Given: Power Output Load Impedance Input Level Input Impedance Bandwidth In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally 1/2 VDD). This charge comes from the output via the feedback and is apt to create pops upon device enable. Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be minimized. Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value. Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the LM4893 turns on. The slower the LM4893’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn-on pop. Choosing CB equal to 1.0 µF along with a small value of Ci (in the range of 0.1 µF to 0.39 µF), should produce a virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or motorboating), with CB equal to 0.1 µF, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 1.0 µF is recommended in all but the most cost sensitive designs. Figure 2 shows the LM4893’s turn-on characteristics when coming out of shutdown mode. Trace B is the differential output signal across a BTL 8Ω load. The LM4893’s activelow SHUTDOWN pin is driven by the logic signal shown in Trace A. Trace C is the Vo1- output signal and Trace D is the Vo2+ output signal. A shown in Figure 2, the differential output signal Trace B appears just as Trace A transitions from logic low to logic high (turn-on condition). 1 Wrms 8Ω 1 Vrms 20 kΩ 100 Hz–20 kHz ± 0.25 dB A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating from the Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply rail can be easily found. A second way to determine the minimum supply rail is to calculate the required Vopeak using Equation 2 and add the output voltage. Using this method, the minimum supply voltage would be (Vopeak + (VODTOP + VODBOT)), where VODBOT and VODTOP are extrapolated from the Dropout Voltage vs Supply Voltage curve in the Typical Performance Characteristics section. (2) 5V is a standard voltage, in most applications, chosen for the supply rail. Extra supply voltage creates headroom that allows the LM4893 to reproduce peaks in excess of 1W without producing audible distortion. At this time, the designer must make sure that the power supply choice along with the output impedance does not violate the conditions explained in the Power Dissipation section. Once the power dissipation equations have been addressed, the required differential gain can be determined from Equation 3. (3) AVD = (Rf/Ri) 2 From Equation 3, the minimum AVD is 2.83; use AVD = 3. Since the desired input impedance was 20 kΩ, and with a AVD of 3, a ratio of 1.5:1 of Rf to Ri results in an allocation of Ri = 20 kΩ and Rf = 30 kΩ. The final design step is to address the bandwidth requirements which must be stated as a pair of −3 dB frequency points. Five times away from a −3 dB point is 0.17 dB down from passband response which is better than the required ± 0.25 dB specified. fL = 100 Hz/5 = 20 Hz fH = 20 kHz * 5 = 100 kHz As stated in the External Components section, Ri in conjunction with Ci create a highpass filter. Ci ≥ 1/(2π*20 kΩ*20 Hz) = 0.397 µF; use 0.39 µF The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain, AVD. With a AVD = 3 and fH = 100 kHz, the resulting GBWP = 300 kHz which is much smaller than the LM4893 GBWP of 10 MHz. This figure displays that if a designer has a need to design an amplifier with a higher differential gain, the LM4893 can still be used without running into bandwidth limitations. 20038097 FIGURE 2. LM4893 Turn-on Characteristics Differential output signal (Trace B) is devoid of transients. The SHUTDOWN pin is driven by a shutdown signal (Trace A). The inverting output (Trace C) and the non-inverting output (Trace D) are applied across an 8Ω BTL load. 13 www.national.com LM4893 Application Information (Continued) 20038088 FIGURE 3. HIGHER GAIN AUDIO AMPLIFIER nates 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 = 20kΩ and C4 = 25pf. These components result in a -3dB point of approximately 320 kHz. The LM4893 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 2 to bandwidth limit the amplifier. This feedback capacitor creates a low pass filter that elimi- www.national.com 14 LM4893 Application Information (Continued) 20038089 FIGURE 4. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4893 20038090 FIGURE 5. REFERENCE DESIGN BOARD and LAYOUT - micro SMD 15 www.national.com LM4893 Application Information (Continued) LM4893 SO BOARD ARTWORK Silk Screen 20038098 Top Layer 20038095 Bottom Layer 20038096 www.national.com 16 LM4893 Application Information (Continued) 20038068 FIGURE 6. REFERENCE DESIGN BOARD and PCB LAYOUT GUIDELINES - MSOP & SO Boards 17 www.national.com LM4893 Application Information (Continued) LM4893 MSOP DEMO BOARD ARTWORK Silk Screen 20038065 Top Layer 20038066 Bottom Layer 20038067 www.national.com 18 LM4893 Application Information (Continued) Mono LM4893 Reference Design Boards Bill of Material for all 3 Demo Boards Item Part Number 1 551011208-001 LM4893 Mono Reference Design Board Part Description 1 Qty 10 482911183-001 LM4893 Audio AMP 1 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 1.0uF 16V 10 1 C3 30 472911207-001 Res 20K Ohm 1/10W 5 3 35 210007039-002 Jumper Header Vertical Mount 2X1 0.100 2 PCB LAYOUT GUIDELINES Ref Designator U1 R1, R2, R3 J1, J2 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. 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. 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. General Mixed Signal Layout Recommendations POWER AND GROUND CIRCUITS For 2 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 may be some jumpers. 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. 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 19 www.national.com LM4893 Physical Dimensions inches (millimeters) unless otherwise noted 9-Bump micro SMD Order Number LM4893ITL, LM4893ITLX NS Package Number TLA09AAA X1 = 1.514 ± 0.03 X2 = 1.514 ± 0.03 X3 = 0.60 ± 0.075 www.national.com 20 LM4893 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) SO Order Number LM4893MA NS Package Number M08A 21 www.national.com LM4893 1.1 Watt Audio Power Amplifier Physical Dimensions inches (millimeters) unless otherwise noted (Continued) MSOP Order Number LM4893MM NS Package Number MUB10A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. 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