LM4903 1 Watt Audio Power Amplifier General Description Key Specifications The LM4903 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 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 LM4903 does not require output coupling capacitors or bootstrap capacitors, and therefore is ideally suited for mobile phone and other low voltage applications where minimal power consumption is a primary requirement. The LM4903 features a low-power consumption shutdown mode, which is achieved by driving the shutdown pin with logic low. Additionally, the LM4903 features an internal thermal shutdown protection mechanism. The LM4903 contains advanced pop & click circuitry which eliminates noise which would otherwise occur during turn-on and turn-off transitions. The LM4903 is unity-gain stable and can be configured by external gain-setting resistors. j Improved PSRR at 217Hz & 1KHz 62dB j Power Output at 5.0V, 1% THD, 8Ω 1.07W (typ) j Power Output at 3.0V, 1% THD, 4Ω 525mW (typ) j Power Output at 3.0V, 1% THD, 8Ω 390mW (typ) j Shutdown Current 0.1µA (typ) Features n n n n n n n n Available in space-saving MSOP package Ultra low current shutdown mode BTL output can drive capacitive loads Improved pop & click circuitry eliminates noise during turn-on and turn-off transitions 2.0 - 5.5V operation No output coupling capacitors, snubber networks or bootstrap capacitors required Unity-gain stable External gain configuration capability Applications n Mobile Phones n PDAs n Portable electronic devices Typical Application 200467D3 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2003 National Semiconductor Corporation DS200467 www.national.com LM4903 1 Watt Audio Power Amplifier February 2003 LM4903 Connection Diagrams Mini Small Outline (MSOP) Package 200467D1 Top View Order Number LM4903MM See NS Package Number MUA08A MSOP Marking 200467D2 Top View G - Boomer Family A4 - LM4903MM www.national.com 2 Junction Temperature (Note 2) Thermal Resistance If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note 10) θJC (MSOP) 56˚C/W θJA (MSOP) 190˚C/W 6.0V Storage Temperature −65˚C to +150˚C Operating Ratings −0.3V to VDD +0.3V Input Voltage 150˚C Power Dissipation (Notes 3, 11) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Temperature Range Internally Limited TMIN ≤ TA ≤ TMAX 2000V −40˚C ≤ TA ≤ 85˚C 2.0V ≤ VDD ≤ 5.5V Supply Voltage 200V 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. LM4903 Symbol Parameter Conditions Typical Limit (Note 6) (Notes 7, 8) VIN = 0V, Io = 0A, No Load 3 7 mA (max) VIN = 0V, Io = 0A, 8Ω Load 4 10 mA (max) 0.8 2.0 µA (max) IDD Quiescent Power Supply Current ISD Shutdown Current VSDIH Shutdown Voltage Input High 1.5 VSDIL Shutdown Voltage Input Low 1.3 VOS Output Offset Voltage ROUT Output Power TWU Wake-up time THD+N Total Harmonic Distortion+Noise Power Supply Rejection Ratio PSRR VSD = VGND V (min) V (max) 7 Resistor Output to GND (Note 9) Po Units (Limits) 8.5 THD = 1% (max); f = 1 kHz 1.07 50 mV (max) 9.7 kΩ (max) 7.0 kΩ (min) 0.9 W 100 mS (max) Po = 0.5 Wrms; f = 1kHz 0.2 % Vripple = 200mV sine p-p Input terminated with 10Ω 60 (f = 217Hz) 64 (f = 1kHz) 55 dB (min) Electrical Characteristics VDD = 3V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for TA = 25˚C. LM4903 Symbol Parameter Conditions VIN = 0V, Io = 0A, No Load Units (Limits) Typical Limit (Note 6) (Notes 7, 8) 2 7 mA (max) 3 9 mA (max) 0.1 2.0 µA (max) IDD Quiescent Power Supply Current ISD Shutdown Current VSDIH Shutdown Voltage Input High 1.3 V (min) VSDIL Shutdown Voltage Input Low 1.0 V (max) VOS Output Offset Voltage ROUT Po VIN = 0V, Io = 0A, 8Ω Load VSD = VGND 7 Resistor Output to GND (Note 9) Output Power (8Ω) (4Ω) 8.5 THD = 1% (max); f = 1 kHz 390 THD = 1% (max); f = 1 kHz 525 50 mV (max) 9.7 kΩ (max) 7.0 kΩ (min) mW TWU Wake-up time 75 mS (max) THD+N Total Harmonic Distortion+Noise Po = 0.25 Wrms; f = 1kHz 0.1 % PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p Input terminated with 10Ω 70 (f = 217Hz) 65 (f = 1kHz) 3 55 dB (min) www.national.com LM4903 Absolute Maximum Ratings LM4903 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. LM4903 Symbol Parameter Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) VIN = 0V, Io = 0A, No Load 2.0 mA (max) VIN = 0V, Io = 0A, 8Ω Load 3.0 mA (max) VSD = VGND 0.01 IDD Quiescent Power Supply Current ISD Shutdown Current VSDIH Shutdown Voltage Input High 1.2 V (min) VSDIL Shutdown Voltage Input Low 1.0 V (max) VOS Output Offset Voltage ROUT Po 5 Resistor Output to GND (Note 9) 8.5 Output Power ( 8Ω ) THD = 1% (max); f = 1 kHz 270 ( 4Ω ) THD = 1% (max); f = 1 kHz 325 2.0 µA (max) 50 mV (max) 9.7 kΩ (max) 7.0 kΩ (min) mW TWU Wake-up time 70 mS (max) THD+N Total Harmonic Distortion+Noise Po = 0.15 Wrms; f = 1kHz 0.1 % Power Supply Rejection Ratio Vripple = 200mV sine p-p Input terminated with 10Ω 51 (f = 217Hz) 51 (f = 1kHz) dB (min) PSRR 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 LM4903, see power derating curves for additional information. Note 4: Human body model, 100pF discharged through a 1.5kΩ 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: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 9: ROUT is measured from the output pin to ground. This value represents the parallel combination of the 10kΩ output resistors and the two 20kΩ resistors. Note 10: 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 device will be protected. If the device is enabled when VDD is greater than 5.5V and less than 6.5V, no damage will occur, although operation life will be reduced. Operation above 6.5V with no current limit will result in permanent damage. Note 11: Maximum power dissipation in the device (PDMAX) occurs at an output power level significantly below full output power. PDMAX can be calculated using Equation 1 shown in the Application Information section. It may also be obtained from the power dissipation graphs. www.national.com 4 LM4903 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 = 3V, 8Ω RL, and PWR = 250mW THD+N vs Frequency at VDD = 5V, 8Ω RL, and PWR = 500mW 20046730 20046731 THD+N vs Frequency at VDD = 2.6V, 4Ω RL, and PWR = 150mW THD+N vs Frequency at VDD = 2.6V, 8Ω RL, and PWR = 150mW 20046732 20046733 5 www.national.com LM4903 Typical Performance Characteristics (Continued) THD+N vs Power Out at VDD = 5V, 8Ω RL, 1kHz THD+N vs Power Out at VDD = 3V, 8Ω RL, 1kHz 20046734 20046783 THD+N vs Power Out at VDD = 2.6V, 4Ω RL, 1kHz THD+N vs Power Out at VDD = 2.6V, 8Ω RL, 1kHz 20046784 20046785 Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 5V, 8Ω RL Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 5V, 8Ω RL 20046786 20046787 Input terminated with 10Ω www.national.com Input Floating 6 (Continued) Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 3V, 8Ω RL Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 3V, 8Ω RL 20046788 20046789 Input terminated with 10Ω Input Floating Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 2.6V, 8Ω RL Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 2.6V, 8Ω RL 20046790 20046791 Input terminated with 10Ω Input Floating Open Loop Frequency Response, 5V Open Loop Frequency Response, 3V 20046792 20046793 7 www.national.com LM4903 Typical Performance Characteristics LM4903 Typical Performance Characteristics (Continued) Open Loop Frequency Response, 2.6V Noise Floor, 5V, 8Ω 80kHz Bandwidth, Input to GND 20046794 20046795 Power Derating Curves Power Dissipation vs Output Power, 5V, 8Ω 20046769 20046797 Power Dissipation vs Output Power, VDD =2.6V Power Dissipation vs Output Power, VDD =3V 200467C8 www.national.com 200467C9 8 LM4903 Typical Performance Characteristics (Continued) Shutdown Hysteresis Voltage 5V Shutdown Hysteresis Voltage 3V 200467A1 200467A3 Shutdown Hysteresis Voltage 2.6V Output Power vs Supply Voltage, 8Ω 200467A5 200467A6 Output Power vs Supply Voltage, 16Ω Output Power vs Supply Voltage, 32Ω 200467A7 200467A8 9 www.national.com LM4903 Typical Performance Characteristics (Continued) Frequency Response vs Input Capacitor Size 20046754 www.national.com 10 output pins. Refer to the application information on the LM4903 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 reduced 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. BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4903 has two internal operational amplifiers. 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 20kΩ 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 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 10µF 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 LM4903. 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. AVD= 2 *(Rf/Ri) 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. 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 LM4903, 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. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4903 contains shutdown circuitry that is used to turn off the amplifier’s bias circuitry. This shutdown feature turns the amplifier off when logic low is placed on the shutdown pin. By switching the shutdown pin to GND, the LM4903 supply current draw will be minimized in idle mode. Idle current is measured with the shutdown pin connected to GND. The trigger point for shutdown is shown as a typical value in the Shutdown Hysteresis Voltage graphs in the Typical Performance Characteristics section. It is best to switch between ground and supply for maximum performance. While the device may be disabled with shutdown voltages in between ground and supply, the idle current may be greater than the typical value of 0.1µA. In either case, the shutdown pin should be tied to a definite voltage to avoid unwanted state changes. 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 LM4903 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. PDMAX = 4*(VDD)2/(2π2RL) In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry, which provides a quick, smooth transition to shutdown. Another solution is to use a single-throw switch in conjunction with an external pull-up resistor. This scheme guarantees that the shutdown pin will not float, thus preventing unwanted state changes. 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 LM4903 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The LM4903 is unity-gain stable which gives the designer maximum system flexibility. The LM4903 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 (1) 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 copper foil, the thermal resistance of the application can be reduced from the free air value of θJA, resulting in higher PDMAX values without thermal shutdown protection circuitry being activated. Additional copper foil can be added to any of the leads connected to the LM4903. It is especially effective when connected to VDD, GND, and the 11 www.national.com LM4903 Application Information LM4903 Application Information Output Power vs Supply Voltage graphs in the Typical Performance Characteristics section, the supply rail can be easily found. 5V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the LM4903 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 2. (Continued) 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. Selection Of Input Capacitor Size 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 100Hz to 150Hz. Thus, using a large input capacitor may not increase actual system performance. (2) Rf/Ri = AVD/2 From Equation 2, the minimum AVD is 2.83; use AVD = 3. Since the desired input impedance was 20kΩ, and with a AVD impedance of 2, a ratio of 1.5:1 of Rf to Ri results in an allocation of Ri = 20kΩ and Rf = 30kΩ. The final design step is to address the bandwidth requirements which must be stated as a pair of −3dB frequency points. Five times away from a −3dB point is 0.17dB down from passband response which is better than the required ± 0.25dB specified. fL = 100Hz/5 = 20Hz fH = 20kHz * 5 = 100kHz As stated in the External Components section, Ri in conjunction with Ci create a highpass filter. Ci ≥ 1/(2π*20kΩ*20Hz) = 0.397µF; use 0.39µF 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 = 100kHz, the resulting GBWP = 300kHz which is much smaller than the LM4903 GBWP of 2.5MHz. This figure displays that if a designer has a need to design an amplifier with a higher differential gain, the LM4903 can still be used without running into bandwidth limitations. The LM4903 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 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 = 20kΩ and C4 = 25pf. These components result in a -3dB point of approximately 320kHz. 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 LM4903 turns on. The slower the LM4903’s outputs ramp to their quiescent DC voltage (nominally 1/2 VDD), the smaller the turn-on pop. Choosing CB equal to 1.0µF along with a small value of Ci (in the range of 0.1µF to 0.39µF), should produce a virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or motorboating), with CB equal to 0.1µF, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 1.0µF is recommended in all but the most cost sensitive designs. AUDIO POWER AMPLIFIER DESIGN A 1W/8Ω Audio Amplifier Given: Power Output Load Impedance Input Level Input Impedance Bandwidth 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 www.national.com 12 LM4903 Application Information (Continued) 200467D4 FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER 200467D5 FIGURE 3. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4903 13 www.national.com LM4903 Application Information (Continued) 200467D6 FIGURE 4. REFERENCE DESIGN BOARD SCHEMATIC www.national.com 14 LM4903 Application Information (Continued) LM4903 MSOP BOARD ARTWORK Composite View Silk Screen 200467E0 200467D8 Top Layer Bottom Layer 200467D9 200467D7 Mono LM4903 Reference Design Boards Bill of Material Part Description Quantity Reference Designator LM4903 Audio AMP 1 U1 Tantalum Capcitor, 1µF 2 C1, C3 Ceramic Capacitor, 0.39µF 1 C2 Resistor, 20kΩ, 1/10W 2 R2, R3 Resistor, 100kΩ, 1/10W 1 R1 Jumper Header Vertical Mount 2X1 0.100“ spacing 1 J1 15 www.national.com LM4903 Application Information Single-Point Power / Ground Connections (Continued) 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. 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. Placement of Digital and Analog Components GENERAL MIXED SIGNAL LAYOUT RECOMMENDATION All digital components and high-speed digital signal traces should be located as far away as possible from analog components and circuit traces. 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 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. www.national.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 LM4903 1 Watt Audio Power Amplifier Physical Dimensions inches (millimeters) unless otherwise noted MSOP Order Number LM4903MM NS Package Number MUA08A 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. 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National Semiconductor Asia Pacific Customer Support Center Fax: +65-6250 4466 Email: [email protected] Tel: +65-6254 4466 National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: [email protected] Tel: 81-3-5639-7560 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.