LM4906 1W, Bypass-Capacitor-less Audio Amplifier with Internal Selectable Gain General Description Key Specifications The LM4906 is an audio power amplifier primarily designed for demanding applications in mobile phones and other portable communication device applications. It is capable of delivering 1W of continuous average power to an 8 BTL load with less than 1% distortion (THD+N) from a +5V power supply. The LM4906 is the first National Semiconductor Boomer Power Amplifier that does not require an external PSRR bypass capacitor. The LM4906 also has an internal selectable gain of either 6dB or 12dB. In addition, no output coupling capacitors or bootstrap capacitors are required which makes the LM4906 ideally suited for cell phone and other low voltage portable applications. The LM4906 contains advanced pop and click circuitry that eliminates noise, which would otherwise occur during turn-on and turn-off transitions. Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. The LM4906 features a low -power consumption shutdown mode (the part is enabled by pulling the SD pin high). Additionally, the LM4906 features an internal thermal shutdown protection mechanism. j Improved PSRR at 217Hz for +3V j Power Output at +5V, THD+N = 1%, 8 71dB 1.0W (typ) j Power Output at +3V, THD+N = 1%, 8 390mW (typ) j Total shutdown power supply current 0.1A (typ) Features n n n n n n n n Selectable gain of 6dB (2V/V) or 12dB (4V/V) No output or PSRR bypass capacitors required Improved "Click and Pop" suppression circuitry Very fast turn on time: 5ms (typ) Minimum external components 2.6 - 5.5V operation BTL output can drive capacitive loads Ultra low current shutdown mode (SD Low) Applications n Portable computers n Desktop computers n Multimedia monitors Typical Application 200571B9 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer (R) is a registered trademark of National Semiconductor Corporation. (c) 2005 National Semiconductor Corporation DS200571 www.national.com LM4906 1W, Bypass-Capacitor-less Audio Amplifier with Internal Selectable Gain January 2005 LM4906 Connection Diagrams MSOP Package MSOP Marking 200571F1 Z - Plant Code X - Date Code T - Die Traceability 20057102 Top View Order Number LM4906MM See NS Package Number MUB08A LLP Package LD Marking 200571F2 Z - Plant Code XY - Date Code T - Die Traceability 200571C3 Top View Order Number LM4906LD See NS Package Number LDA10B Array LLP Package GR Marking 200571F8 200571G2 Top View (Bump_side down) Order Number LM4906GR See NS Package Number GRA16A www.national.com X - Date Code TT - Die Traceability 2 LM4906 LM4906GR Pin Designation Pin (Bump) Number Pin Function A1 Shutdown A2 No Connect A3 VO2 A4 No Connect B1 GND B2 No Connect B3 GND B4 GND C1 Gain Select C2 IN C3 No Connect C4 VDD D1 No Connect D2 No Connect D3 VO1 D4 VDD 3 www.national.com LM4906 Absolute Maximum Ratings (Note 2) JC (MSOP) 56C/W If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. JA (MSOP) 190C/W JC (LLP) 12C/W JA (LLP) 63C/W Supply Voltage (Note 10) 6.0V JA (GRA) TBDC/W -65C to +150C JC (GRA) TBDC/W Storage Temperature -0.3V to VDD +0.3V Input Voltage Power Dissipation (Notes 3, 11) Internally Limited ESD Susceptibility (Note 4) 2000V ESD Susceptibility (Note 5) 200V Junction Temperature Operating Ratings Temperature Range TMIN TA TMAX 150C -40C TA 85C 2.6V VDD 5.5V Supply Voltage 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 = 25C. LM4906 Symbol Parameter IDD Quiescent Power Supply Current ISD Shutdown Current VOS Output Offset Voltage Po Output Power TWU Wake-up time THD+N Conditions Typical Limit (Note 6) (Notes 7, 8) Units (Limits) VIN = 0V, Io = 0A, No Load 3.5 7 mA (max) VIN = 0V, Io = 0A, 8 Load 4 8 mA (max) VSD = GND 0.1 2 A (max) 7 35 mV (max) THD+N = 1% (max); f = 1 kHz RL = 8 1.0 0.9 W (min) 5 ms Total Harmonic Distortion+Noise Po = 0.4 Wrms; f = 1kHz 0.2 % PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p Input terminated with 10 Gain at 6dB 67 (f = 217Hz) 70 (f = 1kHz) dB VSDIH Shutdown Voltage Input High SD Pin High = Part On 1.5 V (min) VSDIL Shutdown Voltage Input Low SD Pin Low = Part Off 1.3 V (max) 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 = 25C. LM4906 Symbol Parameter IDD Quiescent Power Supply Current ISD Shutdown Current VOS Output Offset Voltage Po Output Power TWU Wake-up time THD+N Conditions VIN = 0V, Io = 0A, No Load VIN = 0V, Io = 0A, 8 Load VSD = GND Units (Limits) Typical Limit (Note 6) (Notes 7, 8) 2.6 6 mA (max) mA (max) 3 7 0.1 2 A (max) 7 35 mV (max) THD+N = 1% (max); f = 1 kHz RL = 8 390 mW 4 ms Total Harmonic Distortion+Noise Po = 0.15 Wrms; f = 1kHz 0.1 % PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p Input terminated with 10 Gain at 6dB 71 (f = 217Hz) 73 (f = 1kHz) dB VSDIH Shutdown Voltage Input High SD Pin High = Part On 1.1 V (min) VSDIL Shutdown Voltage Input Low SD Pin Low = Part Off 0.9 V (max) www.national.com 4 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, JA, and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TJMAX-TA)/JA or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4906, see power derating curves for additional information. Note 4: Human body model, 100pF discharged through a 1.5k resistor. Note 5: Machine Model, 220pF-240pF discharged through all pins. Note 6: Typicals are measured at 25C 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 10k output resistors and the two 20k 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. External Components Description Components Functional Description 1. C2 Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a highpass 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. 2. C1 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 www.national.com LM4906 Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. LM4906 Typical Performance Characteristics THD+N vs Frequency VDD = 3V, RL = 8, f = 1kHz, PWR = 250mW THD+N vs Frequency VDD = 5V, RL = 8, f = 1kHz, PWR = 500mW 200571C4 200571C5 THD+N vs Power Out VDD = 3V, RL = 8, f = 1kHz THD+N vs Power Out VDD = 5V, RL = 8, f = 1kHz 200571C6 200571C7 Power Supply Rejection Ratio vs Frequency VDD = 3V, RL = 8 Power Supply Rejection Ratio vs Frequency VDD = 5V, RL = 8 200571E2 www.national.com 200571C9 6 LM4906 Typical Performance Characteristics (Continued) Noise Floor VDD = 5V, RL = 8 80kHz Bandwith, Input to GND Power Derating Curve 200571E4 200571D0 Power Dissipation vs Output Power, VDD = 5V, RL = 8 Power Dissipation vs Output Power, VDD = 3V, RL = 8 200571D2 200571D1 Shutdown Hysteresis Voltage VDD = 5V, SD Mode = VDD (Low) Shutdown Hysteresis Voltage VDD = 5V, SD Mode = VDD (High) 200571D3 200571D4 7 www.national.com LM4906 Typical Performance Characteristics (Continued) Shutdown Hysteresis Voltage VDD = 3V, SD Mode = VDD (High) Shutdown Hysteresis Voltage VDD = 3V, SD Mode = GND (Low) 200571E5 200571D6 Output Power vs Supply Voltage, RL = 32 Output Power vs Supply Voltage, RL = 8 200571D7 200571D9 Frequency Response vs Input Capacitor Size Output Power vs Supply Voltage, RL = 16 200571D8 200571F3 www.national.com 8 LM4906 Typical Performance Characteristics (Continued) PSRR Distribution VDD = 5V, f = 1kHz, RL = 8 PSRR Distribution VDD = 5V, f = 217Hz, RL = 8 200571F4 200571F5 PSRR Distribution VDD = 3V, f = 217Hz, RL = 8 PSRR Distribution VDD = 3V, f = 1kHz, RL = 8 200571F6 200571F7 9 www.national.com LM4906 sinking. If TJMAX still exceeds 150C, 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. Application Information BRIDGE CONFIGURATION EXPLANATION As shown in Figure 2, the LM4906 has two internal operational amplifiers. The first amplifier's gain is either 6dB or 12dB depending on the gain select input (Low = 6dB, High = 12dB). The second amplifier's gain is fixed by the two internal 20k resistors. Figure 2 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 * (20k / 20k) or 2 * (40k / 20k) 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 the power supply pin should be as close to the device as possible. Typical applications employ a 5V regulator with 10F 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 LM4906. 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. TURNING ON THE LM4906 The power supply must first be applied before the application of an input signal to the device and the ramp time to VDD must be less than 4ms, otherwise the wake-up time of the device will be affected. After applying VDD, the LM4906 will turn-on after an initial minimum threshold input signal of 7mVRMS, resulting in a generated output differential signal. An input signal of less than 7mVRMS will result in a negligible output voltage. Once the device is turned on, the input signal can go below the 7mVRMS without shutting the device off. If, however, SHUTDOWN or VDD is cycled, the minimum threshold requirement for the input signal must first be met again, with VDD ramping first. 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 LM4906, 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. (1) SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4906 contains shutdown circuitry that is used to turn off the amplifier's bias circuitry. The device is placed into shutdown mode by toggling the Shutdown pin Low/ground. The trigger point for shutdown low is shown as a typical value in the Supply Current vs Shutdown 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 0.1A. In either case, the shutdown pin should be tied to a definite voltage to avoid unwanted state changes. 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 (or pull-down, depending on shutdown high or low application). This scheme guarantees that the shutdown pin will not float, thus preventing unwanted state changes. It is critical that the maximum junction temperature TJMAX of 150C 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 JA, 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 LM4906. It is especially effective when connected to VDD, GND, and the output pins. Refer to the application information on the LM4906 reference design board for an example of good heat 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. In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, 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 LM4906 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 / (22RL) www.national.com 10 Extra supply voltage creates headroom that allows the LM4906 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. (Continued) 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. The gain of the LM4906 is internally set at either 6dB or 12dB. 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. AUDIO POWER AMPLIFIER DESIGN A 1W/8 Audio Amplifier Given: Power Output Load Impedance Input Level Input Impedance Bandwidth 1 Wrms fL = 100Hz / 5 = 20Hz 8 1 Vrms fH = 20kHz * 5 = 100kHz 20 k 100 Hz-20 kHz 0.25 dB As stated in the External Components section, Rin (20k) in conjunction with C2 create a highpass filter. 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. C2 1 / (2*20k*20Hz) = 0.397F; use 0.39F 200571C0 FIGURE 2. REFERENCE DESIGN BOARD SCHEMATIC 11 www.national.com LM4906 Application Information LM4906 Application Information (Continued) LM4906 MSOP DEMO BOARD ARTWORK Top Layer 200571E6 Bottom Layer 200571E7 www.national.com 12 LM4906 Application Information (Continued) LM4906 LD DEMO BOARD ARTWORK Top Layer 200571E8 Bottom Layer 200571E9 13 www.national.com LM4906 Application Information (Continued) Mono LM4906 Reference Design Boards Bill of Material Quantity Reference Designator LM4906 Audio Amplifier Part Description 1 U1 Tantalum Capcitor, 1F 1 C1 Ceramic Capacitor, 0.39F 1 C2 Jumper Header Vertical Mount 2X1 0.100" spacing 5 J1, J2, Input, Output, VDD PCB LAYOUT GUIDELINES 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. 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 Placement of Digital and Analog Components 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. 14 LM4906 Physical Dimensions inches (millimeters) unless otherwise noted MSOP Order Number LM4906MM NS Package Number MUA08A LLP Order Number LM4906LD NS Package Number LDA10B 15 www.national.com LM4906 1W, Bypass-Capacitor-less Audio Amplifier with Internal Selectable Gain Physical Dimensions inches (millimeters) unless otherwise noted (Continued) micro Array Pkg Order Number LM4906GR NS Package Number GRA16A 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. For the most current product information visit us at www.national.com. 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