LM4906 NSC | Alldatasheet
Document overview
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Technical content
Features
n Selectable gain of 6dB (2V/V) or 12dB (4V/V) n No output or PSRR bypass capacitors required n Improved “Click and Pop” suppression circuitry n Very fast turn on time: 5ms (typ) n Minimum external components n 2.6 - 5.5V operation n BTL output can drive capacitive loads n Ultra low current shutdown mode (SD Low)
Applications
Boomer® is a registered trademark of National Semiconductor Corporation. 200571B9 FIGURE 1. Typical Audio Amplifier Application Circuit
See NS Package Number MUB08A 200571F1 Z - Plant Code X - Date Code T - Die Traceability 200571C3 Top View Order Number LM4906LD See NS Package Number LDA10B 200571F2 Z - Plant Code XY - Date Code T - Die Traceability LM4906 www.national.com 2
Absolute Maximum Ratings(Note 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note 10) 6.0V Storage Temperature −65˚C to +150˚C Input Voltage −0.3V to V DD +0.3V Power Dissipation (Notes 3, 11) Internally Limited ESD Susceptibility (Note 4) 2000V ESD Susceptibility (Note 5) 200V Junction Temperature 150˚C Thermal Resistance θ JC (MSOP) 56˚C/W θJA (MSOP) 190˚C/W θJC (LLP) 12˚C/W θJA (LLP) 63˚C/W Operating Ratings Temperature Range Supply Voltage 2.6V ≤ VDD ≤ 5.5V Electrical Characteristics VDD =5 V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for T A = 25˚C. Symbol Parameter Conditions LM4906 Units (Limits)Typical Limit (Note 6) (Notes 7, 8) IDD Quiescent Power Supply Current VIN = 0V, Io = 0A, No Load 3.5 7 mA (max) VIN = 0V, Io = 0A, 8Ω Load 4 8 mA (max) ISD Shutdown Current V SD = GND 0.1 2 µA (max) VOS Output Offset Voltage 7 35 mV (max) Po Output Power THD+N = 1% (max) ;f=1k H z RL =8 Ω 1.0 0.9 W (min) TWU Wake-up time 5 ms THD+N Total Harmonic Distortion+Noise P o = 0.4 Wrms; f = 1kHz 0.2 % PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p Input terminated with 10 Ω Gain at 6dB 67 (f = 217Hz) 70 (f = 1kHz) dB V SDIH 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 =3 V (Notes 1, 2) The following specifications apply for the circuit shown in Figure 1, unless otherwise specified. Limits apply for T A = 25˚C. Symbol Parameter Conditions LM4906 Units (Limits)Typical Limit (Note 6) (Notes 7, 8) IDD Quiescent Power Supply Current VIN = 0V, Io = 0A, No Load 2.6 6 mA (max) VIN = 0V, Io = 0A, 8Ω Load 3 7 mA (max) ISD Shutdown Current V SD = GND 0.1 2 µA (max) VOS Output Offset Voltage 7 35 mV (max) Po Output Power THD+N = 1% (max) ;f=1k H z RL =8 Ω 390 mW TWU Wake-up time 4 ms THD+N Total Harmonic Distortion+Noise P o = 0.15 Wrms; f = 1kHz 0.1 % PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p Input terminated with 10 Ω Gain at 6dB 71 (f = 217Hz) 73 (f = 1kHz) dB V SDIH 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) LM4906 www.national.com3
Note 1: All voltages are measured with respect to the ground pin, unless otherwise specified. Note 2: Absolute Maximum Ratingsindicate limits beyond which damage to the device may occur. Operating Ratingsindicate conditions for which the device is functional, but do not guarantee specific performance limits.Electrical Characteristicsstate 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 LM4906, see power derating curves for additional information. Note 4: Human body model, 100pF discharged through a 1.5k Ω 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 10k Ω output resistors and the two 20k Ω 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 (P DMAX) occurs at an output power level significantly below full output power. P DMAX can be calculated using Equation 1 shown in the Application Informationsection. It may also be obtained from the power dissipation graphs. External Components Description Components Functional Description 1. C 2 Input coupling capacitor which blocks the DC voltage at the amplifiers input terminals. Also creates a highpass filter with R i at fc =1 / (2πRiCi). Refer to the section, Proper Selection of External Components, for an explanation of how to determine the value of C i. 2. C 1 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. LM4906 www.national.com 4
Typical Performance Characteristics THD+N vs Frequency VDD = 5V, RL =8 Ω, f = 1kHz, PWR = 500mW THD+N vs Frequency VDD = 3V, RL =8 Ω, f = 1kHz, PWR = 250mW 200571C4 200571C5 THD+N vs Power Out VDD = 5V, RL =8 Ω, f = 1kHz THD+N vs Power Out VDD = 3V, RL =8 Ω, f = 1kHz 200571C6 200571C7 Power Supply Rejection Ratio vs Frequency VDD = 5V, RL =8 Ω Power Supply Rejection Ratio vs Frequency VDD = 3V, RL =8 Ω 200571E2 200571C9 LM4906 www.national.com5
Typical Performance Characteristics (Continued) Noise Floor VDD = 5V, RL =8 Ω 80kHz Bandwith, Input to GND Power Derating Curve 200571D0 200571E4 Power Dissipation vs Output Power, VDD =5 V Power Dissipation vs Output Power, VDD =3 V 200571D1 200571D2 Shutdown Hysteresis Voltage VDD = 5V, SD Mode = VDD (High) Shutdown Hysteresis Voltage VDD = 5V, SD Mode = VDD (Low) 200571D3 200571D4 LM4906 www.national.com 6
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 =8 Ω Output Power vs Supply Voltage, RL =1 6Ω 200571D7 200571D9 Output Power vs Supply Voltage, RL =3 2Ω Frequency Response vs Input Capacitor Size 200571D8 200571F3 LM4906 www.national.com7
Typical Performance Characteristics (Continued) PSRR Distribution VDD = 5V, f = 1kHz, RL =8 Ω PSRR Distribution VDD = 5V, f = 217Hz, RL =8 Ω 200571F4 200571F5 PSRR Distribution VDD = 3V, f = 1kHz, RL =8 Ω PSRR Distribution VDD = 3V, f = 217Hz, RL =8 Ω 200571F6 200571F7 LM4906 www.national.com 8
Application Information
BRIDGE CONFIGURATION EXPLANATION As shown in Figure 2, the LM4906 has two internal opera- tional 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 inter- nal 20kΩ resistors. Figure 2shows that the output of ampli- fier 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 A VD = 2 * (20k / 20k) o r 2 * (40k / 20k) 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 configura- tion 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 con- ditions. 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 ex- cessive 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 amplifi- ers. 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 configura- tion. 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. 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 opera- tional 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 Equa- tion 1. P DMAX =4*( V DD)2 /( 2π2RL) (1) It is critical that the maximum junction temperature T JMAX of 150˚C is not exceeded. T JMAX 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 θ JA, resulting in higher P DMAX 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 V DD, GND, and the output pins. Refer to the application information on the LM4906 reference design board for an example of good heat sinking. If T JMAX still exceeds 150˚C, then additional changes must be made. These changes can include re- duced supply voltage, higher load impedance, or reduced ambient temperature. Internal power dissipation is a function of output power. Refer to the Typical Performance Charac- teristics curves for power dissipation information for differ- ent output powers and output loading. 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 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 LM4906. 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 V DD must be less than 4ms, otherwise the wake-up time of the device will be affected. After applying V DD, the LM4906 will turn-on after an initial minimum threshold input signal of 7mV RMS, 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 7mV RMS without shutting the device off. If, however, SHUTDOWN or V DD is cycled, the minimum threshold requirement for the input signal must first be met again, with V DD ramping first. 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 shut- down 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 Typi- cal Performance Characteristics section. It is best to switch between ground and supply for maximum perfor- mance. 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. In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry, which pro- vides a quick, smooth transition to shutdown. Another solu- tion is to use a single-throw switch in conjunction with an external pull-up resistor (or pull-down, depending on shut- down high or low application). This scheme guarantees that the shutdown pin will not float, thus preventing unwanted state changes. 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 attenu- ation. 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 perfor- mance. In addition to system cost and size, click and pop perfor- mance is effected by the size of the input coupling capacitor, LM4906 www.national.com9
turn-on pops can be minimized. in the Power Dissipationsection. conjunction with C2 create a highpass filter. FIGURE 2. REFERENCE DESIGN BOARD SCHEMATIC
Application Information (Continued) LM4906 MSOP DEMO BOARD ARTWORK Top Layer 200571E6 Bottom Layer 200571E7 LM4906 www.national.com11
Application Information (Continued) LM4906 LD DEMO BOARD ARTWORK Top Layer 200571E8 Bottom Layer 200571E9 LM4906 www.national.com 12
Application Information (Continued) Mono LM4906 Reference Design Boards Bill of Material Part Description Quantity Reference Designator LM4906 Audio Amplifier 1 U1 Tantalum Capcitor, 1µF 1 C1 Ceramic Capacitor, 0.39µF 1 C2 Jumper Header Vertical Mount 2X1 0.100“ spacing 5 J1, J2, Input, Output, V DD 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 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 (bring- ing 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. 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 digi- tal and analog ground traces to minimize noise coupling. 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. 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. LM4906 www.national.com13
Physical Dimensions inches (millimeters) unless otherwise noted MSOP Order Number LM4906MM LM4906 www.national.com 14
Physical Dimensions inches (millimeters) unless otherwise noted (Continued) LLP Order Number LM4906LD 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. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: europe.support@nsc.com Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: ap.support@nsc.com National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: jpn.feedback@nsc.com Tel: 81-3-5639-7560 www.national.com LM4906 1W, Bypass-Capacitor-less Audio Amplifier with Internal Selectable Gain National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the righ t at any time without notice to change said circuitry and specifications.