LM4901IBLX

LM4901 1.6 Watt Audio Power Amplifier with Selectable Shutdown Logic Level December 2002 LM4901 1.6 Watt Audio Power Amplifier with Selectable Shutdown Logic Level General Description The LM4901 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 and 1.6 watts of continuous avearge power to a 4Ω 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 LM4901 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 LM4901 features a low-power consumption shutdown mode. To facilitate this, Shutdown may be enabled by either logic high or low depending on mode selection. Driving the shutdown mode pin either high or low enables the shutdown pin to be driven in a likewise manner to enable shutdown. The LM4901 contains advanced pop & click circuitry which eliminates noise which would otherwise occur during turn-on and turn-off transitions. The LM4901 is unity-gain stable and can be configured by external gain-setting resistors. Key Specifications j Improved PSRR at 217Hz & 1KHz j Power Output at 5.0V, 1% THD, 4Ω j Power Output at 5.0V, 1% THD, 8Ω j Power Output at 3.0V, 1% THD, 4Ω j Power Output at 3.0V, 1% THD, 8Ω j Shutdown Current 62dB 1.6W (typ) 1.07W (typ) 525mW (typ) 390mW (typ) 0.1µA (typ) Features n Available in space-saving packages: LLP, micro SMD, and MSOP n Ultra low current shutdown mode n BTL output can drive capacitive loads n Improved pop & click circuitry eliminates noise during turn-on and turn-off transitions n 2.0 - 5.5V operation n No output coupling capacitors, snubber networks or bootstrap capacitors required n Unity-gain stable n External gain configuration capability n User selectable shutdown High or Low logic Level Applications n Mobile Phones n PDAs n Portable electronic devices Typical Application 20019801 FIGURE 1. Typical Audio Amplifier Application Circuit Boomer ® is a registered trademark of National Semiconductor Corporation. © 2002 National Semiconductor Corporation DS200198 www.national.com LM4901 Connection Diagrams 9 Bump micro SMD Mini Small Outline (MSOP) Package 20019823 20019836 Top View Order Number LM4901IBL, LM4901IBLX See NS Package Number BLA09AAC LLP Package Top View Order Number LM4901MM See NS Package Number MUB10A micro SMD Marking 20019870 Top View X - Date Code T - Die Traceability G - Boomer Family Q - LM4901IBL 200198B3 Top View Order Number LM4901LD See NS Package Number LDA10B MSOP Marking LLP Marking 20019871 200198B4 Top View G - Boomer Family C1 - LM4901MM Top View Z - Plant Code XY - Date Code TT - Die Traceability Bottom Line - Part Number www.national.com 2 LM4901 Absolute Maximum Ratings (Note 2) θJA (MSOP) θJA (LLP) θJC (LLP) Soldering Information 190˚C/W 63˚C/W (Note 14) 12˚C/W (Note 14) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage (Note 11) Storage Temperature Input Voltage Power Dissipation (Notes 3, 13) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature Thermal Resistance θJA (micro SMD) (Note 12) θJC (MSOP) 180˚C/W 56˚C/W 6.0V −65˚C to +150˚C −0.3V to VDD +0.3V Internally Limited 2000V 200V 150˚C See AN-1112 "microSMD Wafers Level Chip Scale Package." See AN-1187 "Leadless Leadframe Package (LLP)." Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage −40˚C ≤ TA ≤ 85˚C 2.0V ≤ VDD ≤ 5.5V 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. LM4901 Symbol Parameter Conditions VIN = 0V, Io = 0A, No Load VIN = 0V, Io = 0A, 8Ω Load VSD = VSD VSD VSD VSD VSD MODE MODE MODE MODE Mode Typical (Note 6) 3 4 0.1 1.5 1.3 1.5 1.3 7 8.5 Limit (Notes 7, 9) 7 10 2.0 Units (Limits) mA (max) mA (max) µA (max) V (min) V (max) V (min) V (max) IDD ISD VSDIH VSDIL VSDIH VSDIL VOS ROUT Quiescent Power Supply Current Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Shutdown Voltage Input High Shutdown Voltage Input Low Output Offset Voltage Resistor Output to GND (Note 10) Output Power (8Ω) Wake-up time Total Harmonic Distortion+Noise Power Supply Rejection Ratio (Note 8) = VDD = VDD = GND = GND 50 9.7 7.0 0.9 mV (max) kΩ (max) kΩ (min) W (min) W mS (max) % Po TWU THD+N PSRR THD = 1% (max); f = 1 kHz 1.07 1.6 100 0.2 60 (f = 217Hz) 64 (f = 1kHz) (4Ω) (Notes 14, 15) THD = 1% (max); f = 1 kHz Po = 0.5 Wrms; f = 1kHz Vripple = 200mV sine p-p Input terminated with 10Ω 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. LM4901 Symbol Parameter Conditions VIN = 0V, Io = 0A, No Load VIN = 0V, Io = 0A, 8Ω Load VSD = VSD VSD VSD VSD VSD MODE MODE MODE MODE Mode Typical (Note 6) 2 3 0.1 1.1 0.9 1.3 1.0 7 Limit (Notes 7, 9) 7 9 2.0 Units (Limits) mA (max) mA (max) µA (max) V (min) V (max) V (min) V (max) IDD ISD VSDIH VSDIL VSDIH VSDIL VOS Quiescent Power Supply Current Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Shutdown Voltage Input High Shutdown Voltage Input Low Output Offset Voltage (Note 8) = VDD = VDD = GND = GND 50 mV (max) 3 www.national.com LM4901 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. (Continued) LM4901 Symbol ROUT Parameter Conditions Typical (Note 6) Resistor Output to GND (Note 10) Output Power (8Ω) (4Ω) Wake-up time Total Harmonic Distortion+Noise Power Supply Rejection Ratio Po = 0.25 Wrms; f = 1kHz Vripple = 200mV sine p-p Input terminated with 10Ω THD = 1% (max); f = 1 kHz THD = 1% (max); f = 1 kHz 8.5 390 525 75 0.1 62 (f = 217Hz) 68 (f = 1kHz) 55 Limit (Notes 7, 9) 9.7 7.0 Units (Limits) kΩ (max) kΩ (min) mW mW mS (max) % dB (min) Po TWU THD+N PSRR 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. LM4901 Symbol Parameter Conditions VIN = 0V, Io = 0A, No Load VIN = 0V, Io = 0A, 8Ω Load VSD = VSD VSD VSD VSD VSD MODE MODE MODE MODE Mode Typical (Note 6) 2.0 3.0 0.1 1.0 0.9 1.2 1.0 5 8.5 Limit (Notes 7, 9) Units (Limits) mA (max) mA (max) µA (max) V (min) V (max) V (min) V (max) IDD ISD VSDIH VSDIL VSDIH VSDIL VOS ROUT Po TWU THD+N PSRR Quiescent Power Supply Current Shutdown Current Shutdown Voltage Input High Shutdown Voltage Input Low Shutdown Voltage Input High Shutdown Voltage Input Low Output Offset Voltage Resistor Output to GND (Note 10) Output Power ( 8Ω ) ( 4Ω ) Wake-up time Total Harmonic Distortion+Noise Power Supply Rejection Ratio (Note 8) = VDD = VDD = GND = GND 50 9.7 7.0 mV (max) kΩ (max) kΩ (min) mW mS (max) % dB (min) THD = 1% (max); f = 1 kHz THD = 1% (max); f = 1 kHz Po = 0.15 Wrms; f = 1kHz Vripple = 200mV sine p-p Input terminated with 10Ω 275 340 70 0.1 51 (f = 217Hz) 51 (f = 1kHz) 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 LM4901, 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, 220 pF–240 pF 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: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 10: RROUT 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 11: 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. www.national.com 4 LM4901 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. (Continued) Note 12: All bumps have the same thermal resistance and contribute equally when used to lower thermal resistance. The LM4901IBL demo board (views featured in the Application Information section) has two inner layers, one for VDD and one for GND. The planes each measure 611mils x 661mils (15.52mm x 16.79mm) and aid in spreading heat due to power dissipation within the IC. Note 13: 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. Note 14: The Exposed-DAP of the LDA10B package should be electrically connected to GND or an electrically isolated copper area. the LM4901LD demo board (views featured in the Application Information section) has the Exposed-DAP connected to GND with a PCB area of 86.7mils x 585mils (2.02mm x 14.86mm) on the copper top layer and 550mils x 710mils (13.97mm x 18.03mm) on the copper bottom layer. Note 15: The thermal performance of the LLP package (LM4901LD) when used with the exposed-DAP connected to a thermal plane is sufficient for driving 4Ω loads. The LM4901LD demo board (views featured in the Application Information section) can drive 4Ω loads at the maximum power dissipation point (1.267W) without thermal shutdown circuitry being activated. The other available packages (MSOP & micro SMD) do not have the thermal performance necessary for driving 4Ω loads with a 5V supply and are not recommended for this application. External Components Description (Figure 1) Components 1. 2. Ri Ci Functional Description 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). 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. Feedback resistance which sets the closed-loop gain in conjunction with Ri. 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. 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. 3. 4. 5. Rf CS CB Typical Performance Characteristics THD+N vs Frequency at VDD = 5V, 8Ω RL, and PWR = 500mW THD+N vs Frequency at VDD = 3V, 8Ω RL, and PWR = 250mW 20019830 20019831 5 www.national.com LM4901 Typical Performance Characteristics THD+N vs Frequency at VDD = 2.6V, 8Ω RL, and PWR = 150mW (Continued) THD+N vs Frequency at VDD = 2.6V, 4Ω RL, and PWR = 150mW 20019832 20019833 THD+N vs Power Out at VDD = 5V, 8Ω RL, 1kHz THD+N vs Power Out at VDD = 3V, 8Ω RL, 1kHz 20019834 20019883 www.national.com 6 LM4901 Typical Performance Characteristics THD+N vs Power Out at VDD = 2.6V, 8Ω RL, 1kHz (Continued) THD+N vs Power Out at VDD = 2.6V, 4Ω RL, 1kHz 20019884 20019885 Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 5V, 8Ω RL Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 5V, 8Ω RL 20019886 20019887 Input terminated with 10Ω Input Floating 7 www.national.com LM4901 Typical Performance Characteristics Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 3V, 8Ω RL (Continued) Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 3V, 8Ω RL 20019888 20019889 Input terminated with 10Ω Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 2.6V, 8Ω RL Input Floating Power Supply Rejection Ratio (PSRR) vs Frequency at VDD = 2.6V, 8Ω RL 20019890 20019891 Input terminated with 10Ω Input Floating www.national.com 8 LM4901 Typical Performance Characteristics Open Loop Frequency Response, 5V (Continued) Open Loop Frequency Response, 3V 20019892 20019893 Open Loop Frequency Response, 2.6V Noise Floor, 5V, 8Ω 80kHz Bandwidth, Input to GND 20019894 20019895 Power Derating Curves Power Dissipation vs Output Power, VDD =5V 20019869 200198B5 9 www.national.com LM4901 Typical Performance Characteristics Power Dissipation vs Output Power, VDD =3V (Continued) Power Dissipation vs Output Power, VDD =2.6V 200198B6 200198B7 Shutdown Hysteresis Voltage 5V, SD Mode = VDD (High) Shutdown Hysteresis Voltage 5V, SD Mode = GND (Low) 200198A0 200198A1 www.national.com 10 LM4901 Typical Performance Characteristics Shutdown Hysteresis Voltage 3V, SD Mode = VDD (High) (Continued) Shutdown Hysteresis Voltage 3V, SD Mode = GND (Low) 200198A2 200198A3 Shutdown Hysteresis Voltage 2.6V, SD Mode = VDD (High) Shutdown Hysteresis Voltage 2.6V, SD Mode = GND (Low) 200198A4 200198A5 11 www.national.com LM4901 Typical Performance Characteristics Output Power vs. Supply Voltage, 4Ω (Continued) Output Power vs Supply Voltage, 8Ω 200198B8 200198A6 Output Power vs Supply Voltage, 16Ω Output Power vs Supply Voltage, 32Ω 200198A7 200198A8 www.national.com 12 LM4901 Typical Performance Characteristics Frequency Response vs Input Capacitor Size (Continued) 20019854 13 www.national.com LM4901 Application Information BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4901 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 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 LM4901, 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. 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 LM4901 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) (1) especially effective when connected to VDD, GND, and the output pins. Refer to the application information on the LM4901 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. 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 LM4901. 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. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4901 contains shutdown circuitry that is used to turn off the amplifier’s bias circuitry. In addition, the LM4901 contains a Shutdown Mode pin, allowing the designer to designate whether the part will be driven into shutdown with a high level logic signal or a low level logic signal. This allows the designer maximum flexibility in device use, as the Shutdown Mode pin may simply be tied permanently to either VDD or GND to set the LM4901 as either a "shutdown-high" device or a "shutdown-low" device, respectively. The device may then be placed into shutdown mode by toggling the Shutdown pin to the same state as the Shutdown Mode pin. For simplicity’s sake, this is called "shutdown same", as the LM4901 enters shutdown mode whenever the two pins are in the same logic state. The trigger point for either shutdown high or 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 0.1µA. 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 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. 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 LM4901 is tolerant of 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 LM4901. It is www.national.com 14 LM4901 Application Information (Continued) Load Impedance Input Level Input Impedance Bandwidth 8Ω 1 Vrms 20 kΩ 100 Hz–20 kHz ± 0.25 dB external component combinations, consideration to component values must be used to maximize overall system quality. The LM4901 is unity-gain stable which gives the designer maximum system flexibility. The LM4901 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. 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 100 Hz to 150 Hz. 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, 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 LM4901 turns on. The slower the LM4901’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. AUDIO POWER AMPLIFIER DESIGN A 1W/8Ω Audio Amplifier Given: Power Output 1 Wrms 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. 5V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the LM4901 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. (2) Rf/Ri = AVD/2 From Equation 2, the minimum AVD is 2.83; use AVD = 3. Since the desired input impedance was 20 kΩ, and with a AVD impedance of 2, 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 = 300kHz which is much smaller than the LM4901 GBWP of 2.5MHz. This figure displays that if a designer has a need to design an amplifier with a higher differential gain, the LM4901 can still be used without running into bandwidth limitations. 15 www.national.com LM4901 Application Information (Continued) 20019824 FIGURE 2. HIGHER GAIN AUDIO AMPLIFIER The LM4901 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 320 kHz. www.national.com 16 LM4901 Application Information (Continued) 20019829 FIGURE 3. DIFFERENTIAL AMPLIFIER CONFIGURATION FOR LM4901 20019825 FIGURE 4. REFERENCE DESIGN BOARD SCHEMATIC 17 www.national.com LM4901 Application Information LM4901 micro SMD BOARD ARTWORK Silk Screen (Continued) Top Layer 20019878 20019876 Bottom Layer Inner Layer VDD 20019881 20019880 Inner Layer Ground 20019882 www.national.com 18 LM4901 Application Information Silk Screen (Continued) LM4901 MSOP DEMO BOARD ARTWORK Top Layer 20019875 20019879 Bottom Layer 20019877 19 www.national.com LM4901 Application Information LM4901 LLP DEMO BOARD ARTWORK Composite View (Continued) Silk Screen 200198A9 200198B0 Top Layer Bottom Layer 200198B1 200198B2 www.national.com 20 LM4901 Application Information (Continued) Mono LM4901 Reference Design Boards Bill of Material Part Description LM4901 Audio AMP Tantalum Capcitor, 1µF Ceramic Capacitor, 0.39µF Resistor, 20kΩ, 1/10W Resistor, 100kΩ, 1/10W Jumper Header Vertical Mount 2X1 0.100“ spacing PCB LAYOUT GUIDELINES Quantity 1 2 1 2 2 2 Reference Designator U1 C1, C3 C2 R2, R3 R1, R4 J1, J2 Single-Point Power / Ground Connections The analog power traces should be connected to the digital traces through a single point (link). A "Pi-filter" can be helpful in minimizing High Frequency noise coupling between the analog and digital sections. It is further recommended to put digital and analog power traces over the corresponding digital and analog ground traces to minimize noise coupling. Placement of Digital and Analog Components All digital components and high-speed digital 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. 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 (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. 21 www.national.com LM4901 Physical Dimensions inches (millimeters) unless otherwise noted Note: Unless otherwise specified. 1. Epoxy coating. 2. Recommend non-solder mask defined landing pad. 3. Pin 1 is established by lower left corner with respect to text orientation pins are numbered counterclockwise. 4. 63Sn/37Pb eutectic bump. 5. Reference JEDEC registration MO-211, variation BC. 9-Bump micro SMD Order Number LM4901IBL, LM4901IBLX NS Package Number BLA09AAC X1 = 1.514, X2 = 1.514, X3 = 0.600 www.national.com 22 LM4901 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) MSOP Order Number LM4901MM NS Package Number MUB10A 23 www.national.com LM4901 1.6 Watt Audio Power Amplifier with Selectable Shutdown Logic Level Physical Dimensions inches (millimeters) unless otherwise noted (Continued) LLP Order Number LM4901LD NS Package Number LDA10B 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. 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