LM4894IBP

LM4894 LM4894 1 Watt Fully Differential Audio Power Amplifier With Shutdown Select Literature Number: SNAS134H October 5, 2011 1 Watt Fully Differential Audio Power Amplifier With Shutdown Select General Description Key Specifications The LM4894 is a fully differential 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 LM4894 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 LM4894 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 select pin to be driven in a likewise manner to enable Shutdown. Additionally, the LM4894 features an internal thermal shutdown protection mechanism. The LM4894 contains advanced pop & click circuitry which eliminates noises which would otherwise occur during turn-on and turn-off transitions. The LM4894 is unity-gain stable and can be configured by external gain-setting resistors. ■ Improved PSRR at 217Hz 80dB(typ) ■ Power Output at 5.0V & 1% THD 1.0W(typ) ■ Power Output at 3.3V & 1% THD 400mW(typ) ■ Shutdown Current 0.1µA(typ) Features ■ Fully differential amplification ■ Available in space-saving packages micro SMD, MSOP, ■ ■ ■ ■ ■ ■ ■ ■ ■ and LLP Ultra low current shutdown mode Can drive capacitive loads up to 500pF Improved pop & click circuitry eliminates noises during turn-on and turn-off transitions 2.2 - 5.5V operation No output coupling capacitors, snubber networks or bootstrap capacitors required Unity-gain stable External gain configuration capability Shutdown high or low selectivity High CMRR Applications ■ Mobile phones ■ PDAs ■ Portable electronic devices Connection Diagrams Mini Small Outline (MSOP) Package LLP Package 20013723 Top View Order Number LM4894MM See NS Package Number MUB10A 20013735 Top View Order Number LM4894LD See NS Package Number LDA10B Boomer® is a registered trademark of National Semiconductor Corporation. © 2011 National Semiconductor Corporation 200137 200137 Version 9 Revision 5 www.national.com Print Date/Time: 2011/10/05 07:59:55 LM4894 1 Watt Fully Differential Audio Power Amplifier With Shutdown Select OBSOLETE LM4894 LM4894 9 Bump micro SMD Package 9 Bump micro SMD Package 20013794 Top View Order Number LM4894ITL, LM4894ITLX See NS Package Number TLA09AAA 20013736 Top View Order Number LM4894IBP See NS Package Number BPA09CDB Typical Application 20013701 FIGURE 1. Typical Audio Amplifier Application Circuit www.national.com 2 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55  θJC (MSOP) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage Storage Temperature Input Voltage Power Dissipation (Note 3) ESD Susceptibility (Note 4) ESD Susceptibility (Note 5) Junction Temperature Thermal Resistance 12°C/W  θJA (LLP) 63°C/W Electrical Characteristics VDD = 5V 56°C/W 190°C/W  θJA (MSOP) Soldering Information See AN-1112 "microSMD Wafers Level Chip Scale Package." See AN-1187 "Leadless Leadframe Package (LLP)." 6.0V −65°C to +150°C −0.3V to VDD +0.3V Internally Limited 2000V 200V 150°C  θJC (LLP) 220°C/W Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX Supply Voltage −40°C ≤ TA ≤ 85°C 2.2V ≤ VDD ≤ 5.5V (Note 1, Note 2, Note 8) The following specifications apply for VDD = 5V, AV = 1, and 8Ω load unless otherwise specified. Limits apply for TA = 25°C. LM4894 Symbol Parameter Conditions Typical Limit Units (Limits) (Note 6) (Note 7) IDD Quiescent Power Supply Current VIN = 0V, Io = 0A 4 8 mA (max) ISD Shutdown Current Vshutdown = GND 0.1 1 µA (max) Po Output Power THD = 1% (max); f = 1 kHz    LM4894LD, RL= 4Ω (Note 11)    LM4894, RL= 8Ω THD+N Total Harmonic Distortion+Noise Po = 0.4 Wrms; f = 1kHz PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p CMRR Common_Mode Rejection Ratio 1.4 W (min) 1 0.850 0.1 %    f = 217Hz (Note 9) 87 dB (min)    f = 1kHz (Note 9) 83    f = 217Hz (Note 10) 83    f = 1kHz (Note 10) 80   f = 217Hz 50 Electrical Characteristics VDD = 3V 63 dB (Note 1, Note 2, Note 8) The following specifications apply for VDD = 3V, AV = 1, and 8Ω load unless otherwise specified. Limits apply for TA = 25°C. LM4894 Symbol Parameter Conditions Units (Limits) Typical Limit (Note 6) (Note 7) 3.5 6 mA (max) 1 µA (max) IDD Quiescent Power Supply Current VIN = 0V, Io = 0A ISD Shutdown Current Vshutdown = GND 0.1 Po Output Power THD = 1% (max); f = 1kHz 0.35 W THD+N Total Harmonic Distortion+Noise Po = 0.25Wrms; f = 1kHz 0.325 % PSRR Power Supply Rejection Ratio Vripple = 200mV sine p-p    f = 217Hz (Note 9) 87 dB    f = 1kHz (Note 9) 83    f = 217Hz (Note 10) 80    f = 1kHz (Note 10) 78    f = 217Hz 49 CMRR Common-Mode Rejection Ratio 3 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 dB www.national.com LM4894  θJA (micro SMD) Absolute Maximum Ratings (Note 2) LM4894 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 LM4894, see power derating currents 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: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. 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: Unterminated input. Note 10: 10Ω terminated input. Note 11: When driving 4Ω loads from a 5V supply, the LM4894LD must be mounted to a circuit board. External Components Description (Figure 1) Components Functional Description 1. Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. 2. Rf Feedback resistance which sets the closed-loop gain in conjunction with Ri. 3. 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. 4. 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. www.national.com 4 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 LM4894 Typical Performance Characteristics LD Specific Characteristics LM4894LD THD+N vs Frequency VDD = 5V, 4Ω RL, and Power = 1W LM4894LD THD+N vs Output Power VDD = 5V, 4Ω RL 20013790 20013791 LM4894LD Power Dissipation vs Output Power LM4894LD Power Derating Curve 20013793 20013792 5 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 www.national.com LM4894 Typical Performance Characteristics Non-LD Specific Characteristics THD+N vs Frequency at VDD = 5V, 8Ω RL, and PWR = 400mW THD+N vs Frequency at VDD = 3V, 8Ω RL, and PWR = 250mW 20013737 20013738 THD+N vs Frequency at VDD = 3V, 4Ω RL, and PWR = 225mW THD+N vs Frequency at VDD = 2.6V, 8Ω RL, and PWR = 150mW 20013739 www.national.com 20013740 6 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 LM4894 THD+N vs Frequency @ VDD = 2.6V, 4Ω RL, and PWR = 150mW THD+N vs Output Power @ VDD = 5V, 8Ω RL 20013741 20013742 THD+N vs Output Power @ VDD = 3V, 8Ω RL THD+N vs Output Power @ VDD = 3V, 4Ω RL 20013743 20013744 7 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 www.national.com LM4894 THD+N vs Output Power @ VDD = 2.6V, 8Ω RL THD+N vs Output Power @ VDD = 2.6V, 4Ω RL 20013745 20013773 Power Supply Rejection Ratio (PSRR) @ VDD = 5V Input 10Ω Terminated Power Supply Rejection Ratio (PSRR) @ VDD = 5V Input Floating 20013746 20013747 www.national.com 8 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 Power Supply Rejection Ratio (PSRR) @ VDD = 3V Input Floating 20013748 20013749 Output Power vs Supply Voltage Output Power vs Supply Voltage 20013751 20013750 9 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 www.national.com LM4894 Power Supply Rejection Ratio (PSRR) @ VDD = 3V Input 10Ω Terminated LM4894 Power Dissipation vs Output Power Power Dissipation vs Output Power 20013753 20013752 Power Dissipation vs Output Power Output Power vs Load Resistance 20013755 20013754 Supply Current vs Shutdown Voltage Shutdown Low Supply Current vs Shutdown Voltage Shutdown High 20013769 www.national.com 20013756 10 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 LM4894 Clipping (Dropout) Voltage vs Supply Voltage Open Loop Frequency Response 20013784 20013774 Power Derating Curve Noise Floor 20013776 20013777 Input CMRR vs Frequency Input CMRR vs Frequency 20013778 20013779 11 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 www.national.com LM4894 PSRR vs DC Common-Mode Voltage PSRR vs DC Common-Mode Voltage 20013780 20013781 THD vs Common-Mode Voltage THD vs Common-Mode Voltage 20013782 www.national.com 20013783 12 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 DIFFERENTIAL AMPLIFIER EXPLANATION The LM4894 is a fully differential audio amplifier that features differential input and output stages. Internally this is accomplished by two circuits: a differential amplifier and a common mode feedback amplifier that adjusts the output voltages so that the average value remains VDD/2. When setting the differential gain, the amplifier can be considered to have "halves". Each half uses an input and feedback resistor (Ri1and RF1) to set its respective closed-loop gain (see Figure 1). With Ri1 = Ri2 and RF1 = RF2, the gain is set at -RF/Ri for each half. This results in a differential gain of AVD = -RF/Ri (1) It is extremely important to match the input resistors to each other, as well as the feedback resistors to each other for best amplifier performance. See the Proper Selection of External Components section for more information. A differential amplifier works in a manner where the difference between the two input signals is amplified. In most applications, this would require input signals that are 180° out of phase with each other. The LM4894 can be used, however, as a single ended input amplifier while still retaining its fully differential benefits. In fact, completely unrelated signals may be placed on the input pins. The LM4894 simply amplifies the difference between them. Figures 2 and 3 show single-ended applications of the LM4894 that still take advantage of the differential nature of the amplifier and the benefits to PSRR, common-mode noise reduction, and "click and pop" reduction. All of these applications, either single-ended or fully differential, provide what is known as a "bridged mode" output (bridge-tied-load, BTL). This results in output signals at Vo1 and Vo2 that are 180° out of phase with respect to each other. Bridged mode operation is different from the single-ended amplifier configuration that connects the load between the amplifier output and ground. A bridged amplifier design has distinct advantages over the single-ended configuration: it provides differential drive to the load, thus doubling maximum possible output swing for a specific supply voltage. Four times the output power is possible compared with 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 closedloop gain without causing excess clipping, please refer to the Audio Power Amplifier Design section. A bridged configuration, such as the one used in the LM4894, 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 assumes that the input resistor pair and the feedback resistor pair are properly matched (see Proper Selection of External Components). BTL configuration eliminates the output coupling capacitor required in single-supply, single-ended amplifier configurations. If an output coupling capacitor is not used in a single-ended output configuration, the half-supply bias across the load would result in both increased internal IC power dissipation as well as permanent loudspeaker damage. Further advantages of bridged mode operation specific to fully differential amplifiers like the LM4894 include increased power supply rejection ratio, common-mode noise reduction, and click and pop reduction. PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3Ω AND 4Ω LOADS Power dissipated by a load is a function of the voltage swing across the load and the load's impedance. As load impedance decreases, load dissipation becomes increasingly de-pendent on the interconnect (PCB trace and wire) resistance between the amplifier output pins and the load's connections. Residual trace resistance causes a voltage drop, which results in power dissipated in the trace and not in the load as desired. For example, 0.1Ω trace resistance reduces the output power dissipated by a 4Ω load from 1.4W to 1.37W. This problem of decreased load dissipation is exacerbated as load impedance decreases. Therefore, to maintain the highest load dissipation and widest output voltage swing, PCB traces that connect the output pins to a load must be as wide as possible. Poor power supply regulation adversely affects maximum output power. A poorly regulated supply's output voltage decreases with increasing load current. Reduced supply voltage causes decreased headroom, output signal clipping, and reduced output power. Even with tightly regulated supplies, trace resistance creates the same effects as poor sup-ply regulation. Therefore, making the power supply traces as wide as possible helps maintain full output voltage swing. 13 200137 Version 9 Revision 5 Print Date/Time: 2011/10/05 07:59:55 www.national.com LM4894 EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS The LM4894's exposed-DAP (die attach paddle) package (LD) provide a low thermal resistance between the die and the PCB to which the part is mounted and soldered. This allows rapid heat transfer from the die to the surrounding PCB copper traces, ground plane and, finally, surrounding air. The result is a low voltage audio power amplifier that produces 1.4W at ≤ 1% THD with a 4Ω load. This high power is achieved through careful consideration of necessary thermal design. Failing to optimize thermal design may compromise the LM4894's high power performance and activate unwanted, though necessary, thermal shutdown protection. The LD package must have its DAP soldered to a copper pad on the PCB. The DAP's PCB copper pad is connected to a large plane of continuous unbroken copper. This plane forms a thermal mass and heat sink and radiation area. Place the heat sink area on either outside plane in the case of a two-sided PCB, or on an inner layer of a board with more than two layers. Connect the DAP copper pad to the inner layer or backside copper heat sink area with 4 (2x2) vias. The via diameter should be 0.012in - 0.013in with a 0.050in pitch. Ensure efficient thermal conductivity by plating-through and solder-filling the vias. Best thermal performance is achieved with the largest practical copper heat sink area. If the heatsink and amplifier share the same PCB layer, a nominal 2.5in2 (min) area is necessary for 5V operation with a 4Ω load. Heatsink areas not placed on the same PCB layer as the LM4894 should be 5in2 (min) for the same supply voltage and load resistance. The last two area recommendations apply for 25°C ambient temperature. In all circumstances and conditions, the junction temperature must be held below 150°C to prevent activating the LM4894's thermal shutdown protection. The LM4894's power de-rating curve in the Typical Performance Characteristics shows the maximum power dissipation versus temperature. Example PCB layouts for the exposed-DAP TSSOP and LLP packages are shown in the Demonstration Board Layout section. Further detailed and specific information concerning PCB layout, fabrication, and mounting an LLP package is available from National Semiconductor's package Engineering Group under application note AN1187. Application Information LM4894 lection is thus dependant upon desired PSRR and click and pop performance as explained in the section Proper Selection of External Components. POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifer, whether the amplifier is bridged or singleended. Equation 2 states the maximum power dissipation point for a single-ended amplifier operating at a given supply voltage and driving a specified output load. PDMAX=(VDD)2/(2π2RL) Single-Ended SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4894 contains shutdown circuitry that is used to turn off the amplifier's bias circuitry. In addition, the LM4894 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 LM4894 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 Select pin to the same state as the Shutdown Mode pin. For simplicity's sake, this is called "shutdown same", as the LM4894 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. (2) However, a direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation versus a single-ended amplifier operating at the same conditions. PDMAX = 4*(VDD)2/(2π2RL) Bridge Mode (3) Since the LM4894 has bridged outputs, the maximum internal power dissipation is 4 times that of a single-ended amplifier. Even with this substantial increase in power dissipation, the LM4894 does not require additional heatsinking under most operating conditions and output loading. From Equation 3, assuming a 5V power supply and an 8Ω load, the maximum power dissipation point is 625mW. The maximum power dissipation point obtained from Equation 3 must not be greater than the power dissipation results from Equation 4: PDMAX = (TJMAX - TA)/θJA (4) The LM4894's θJA in an MUA10A package is 190°C/W. Depending on the ambient temperature, TA, of the system surroundings, Equation 4 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 3 is greater than that of Equation 4, then either the supply voltage must be decreased, the load impedance increased, the ambient temperature reduced, or the θJA reduced with heatsinking. In many cases, larger traces near the output, VDD, and GND pins can be used to lower the θJA. The larger areas of copper provide a form of heatsinking allowing higher power dissipation. For the typical application of a 5V power supply, with an 8Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 30°C provided that device operation is around the maximum power dissipation point. Recall that internal power dissipation is a function of output power. If typical operation is not around the maximum power dissipation point, the LM4894 can operate at higher ambient temperatures. Refer to the Typical Performance Characteristics curves for power dissipation information. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components in applications using integrated power amplifiers is critical when optimizing device and system performance. Although the LM4894 is tolerant to a variety of external component combinations, consideration of component values must be made when maximizing overall system quality. The LM4894 is unity-gain stable, giving the designer maximum system flexibility. The LM4894 should be used in low closed-loop gain configurations to minimize THD+N values and maximize signal to noise ratio. Low gain configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1Vrms are available from sources such as audio codecs. Please refer to the Audio Power Amplifier Design section for a more complete explanation of proper gain selection. When used in its typical application as a fully differential power amplifier the LM4894 does not require input coupling capacitors for input sources with DC common-mode voltages of less than VDD. Exact allowable input common-mode voltage levels are actually a function of VDD, Ri, and Rf and may be determined by Equation 5: POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection ratio (PSRR). The capacitor location on both the bypass and power supply pins should be as close to the device as possible. A larger half-supply bypass capacitor improves PSRR because it increases half-supply stability. Typical applications employ a 5V regulator with 10µF and 0.1µF bypass capacitors that increase supply stability. This, however, does not eliminate the need for bypassing the supply nodes of the LM4894. Although the LM4894 will operate without the bypass capacitor CB, although the PSRR may decrease. A 1µF capacitor is recommended for CB. This value maximizes PSRR performance. Lesser values may be used, but PSRR decreases at frequencies below 1kHz. The issue of CB sewww.national.com VCMi