LM4835 LM4835 Stereo 2W Audio Power Amplifierswith DC Volume Control and Selectable Gain Literature Number: SNAS019E LM4835 Stereo 2W Audio Power Amplifiers with DC Volume Control and Selectable Gain General Description Key Specifications The LM4835 is a monolithic integrated circuit that provides DC volume control, and stereo bridged audio power amplifiers capable of producing 2W into 4 (Note 1) with less than 1.0% THD or 2.2W into 3 (Note 2) with less than 1.0% THD. Boomer (R) audio integrated circuits were designed specifically to provide high quality audio while requiring a minimum amount of external components. The LM4835 incorporates a DC volume control, stereo bridged audio power amplifiers and a selectable gain or bass boost, making it optimally suited for multimedia monitors, portable radios, desktop, and portable computer applications. The LM4835 features an externally controlled, low-power consumption shutdown mode, and both a power amplifier and headphone mute for maximum system flexibility and performance. n PO at 1% THD+N n into 3 (LM4835LQ, LM4835MTE) 2.2W (typ) n into 4 (LM4835LQ, LM4835MTE) 2.0W (typ) n into 8 (LM4835) 1.1W (typ) n Single-ended mode - THD+N at 85mW into 32 1.0% (typ) n Shutdown current 0.7A (typ) Note 1: When properly mounted to the circuit board, the LM4835LQ and LM4835MTE will deliver 2W into 4. The LM4835MT will deliver 1.1W into 8. See the Application Information section LM4835LQ and for LM4835MTE usage information. Note 2: An LM4835LQ and LM4835MTE that have been properly mounted to the circuit board and forced-air cooled will deliver 2.2W into 3. Features PC98 Compliant DC Volume Control Interface System Beep Detect Stereo switchable bridged/single-ended power amplifiers Selectable internal/external gain and bass boost configurable n "Click and pop" suppression circuitry n Thermal shutdown protection circuitry n n n n n Applications n Portable and Desktop Computers n Multimedia Monitors n Portable Radios, PDAs, and Portable TVs Connection Diagrams LLP Package TSSOP Package 10013902 10013935 Top View Order Number LM4835LQ See NS Package LQA028AA for Exposed-DAP LLP Top View Order Number LM4835MT or LM4835MTE See NS Package MTC28 for TSSOP or See NS Package MXA28A for Exposed-DAP TSSOP Boomer (R) is a registered trademark of NationalSemiconductor Corporation. (c) 2003 National Semiconductor Corporation DS100139 www.national.com LM4835 Stereo 2W Audio Power Amplifiers with DC Volume Control and Selectable Gain February 2003 LM4835 Block Diagram 10013901 FIGURE 1. LM4835 Block Diagram www.national.com 2 (Note 12) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Supply Voltage 6.0V Storage Temperature JC (typ) -- LQA028AA 3.0C/W JA (typ) -- LQA028AA (Note 7) 42C/W JC (typ) -- MTC28 20C/W JA (typ) -- MTC28 80C/W JC (typ) -- MXA28A 2C/W -65C to +150C JA (typ) -- MXA28A (Note 4) 41C/W -0.3V to VDD +0.3V JA (typ) -- MXA28A (Note 3) 54C/W Internally limited JA (typ) -- MXA28A (Note 5) 59C/W ESD Susceptibility (Note 14) 2000V JA (typ) -- MXA28A (Note 6) 93C/W ESD Susceptibility (Note 15) 200V Input Voltage Power Dissipation Junction Temperature 150C Soldering Information Small Outline Package Vapor Phase (60 sec.) Infrared (15 sec.) Operating Ratings 215C Temperature Range TMIN TA TMAX -40C TA 85C 220C Supply Voltage 2.7V VDD 5.5V See AN-450 "Surface Mounting and their Effects on Product Reliability" for other methods of soldering surface mount devices. Electrical Characteristics for Entire IC (Notes 8, 12) The following specifications apply for VDD = 5V unless otherwise noted. Limits apply for TA = 25C. LM4835 Symbol Parameter Conditions Typical (Note 16) Limit (Note 17) Units (Limits) VDD Supply Voltage 5.5 V (max) IDD Quiescent Power Supply Current VIN = 0V, IO = 0A 15 30 mA (max) ISD Shutdown Current Vpin 0.7 2.0 A (max) VIH Headphone Sense High Input Voltage 4 V (min) VIL Headphone Sense Low Input Voltage 0.8 V (max) 2.7 2 = VDD V (min) Electrical Characteristics for Volume Attenuators (Notes 8, 12) The following specifications apply for VDD = 5V. Limits apply for TA = 25C. LM4835 Symbol Parameter Conditions CRANGE Attenuator Range Gain with Vpin AM Mute Attenuation Vpin Vpin 7 Typical (Note 16) Limit (Note 17) 0 0.5 = 5V Attenuation with Vpin dB (max) -81 -80 dB (min) 5 = 5V, Bridged Mode -88 -80 dB (min) 5 = 5V, Single-Ended Mode -88 -80 dB (min) 7 = 0V Units (Limits) Electrical Characteristics for Single-Ended Mode Operation (Notes 8, 12) The following specifications apply for VDD = 5V. Limits apply for TA = 25C. LM4835 Symbol PO Parameter Output Power Conditions Typical (Note 16) Limit (Note 17) Units (Limits) THD = 1.0%; f = 1kHz; RL = 32 85 mW THD = 10%; f = 1 kHz; RL = 32 95 mW 0.065 % 58 dB THD+N Total Harmonic Distortion+Noise VOUT = 1VRMS, f=1kHz, RL = 10k, AVD = 1 PSRR Power Supply Rejection Ratio CB = 1.0 F, f =120 Hz, VRIPPLE = 200 mVrms 3 www.national.com LM4835 Absolute Maximum Ratings LM4835 Electrical Characteristics for Single-Ended Mode Operation (Continued) (Notes 8, 12) The following specifications apply for VDD = 5V. Limits apply for TA = 25C. LM4835 Symbol Parameter Conditions SNR Signal to Noise Ratio POUT =75 mW, R Filter Xtalk Channel Separation f=1kHz, CB = 1.0 F L Typical (Note 16) = 32, A-Wtd Units (Limits) Limit (Note 17) 102 dB 65 dB Electrical Characteristics for Bridged Mode Operation (Notes 8, 12) The following specifications apply for VDD = 5V, unless otherwise noted. Limits apply for TA = 25C. LM4835 Symbol Parameter Conditions Typical (Note 16) Limit (Note 17) 5 30 Units (Limits) VOS Output Offset Voltage VIN = 0V PO Output Power THD + N = 1.0%; f=1kHz; RL = 3 (Notes 9, 11) 2.2 W THD + N = 1.0%; f=1kHz; RL = 4 (Notes 10, 11) 2 W THD+N Total Harmonic Distortion+Noise mV (max) THD = 0.5% (max);f = 1 kHz; RL = 8 1.1 1.0 W (min) THD+N = 10%;f = 1 kHz; RL = 8 1.5 W PO = 1W, 20 Hz < f < 20 kHz, 0.3 % RL = 8, AVD = 2 PO = 340 mW, RL = 32 1.0 % PSRR Power Supply Rejection Ratio CB = 1.0 F, f = 120 Hz, VRIPPLE = 200 mVrms; RL = 8 74 dB SNR Signal to Noise Ratio VDD = 5V, POUT = 1.1W, RL = 8, A-Wtd Filter 93 dB Xtalk Channel Separation f=1kHz, CB = 1.0 F 70 dB Note 3: The JA given is for an MXA28A package whose exposed-DAP is soldered to an exposed 2in 2 piece of 1 ounce printed circuit board copper. Note 4: The JA given is for an MXA28A package whose exposed-DAP is soldered to a 2in2 piece of 1 ounce printed circuit board copper on a bottom side layer through 21 8mil vias. Note 5: The JA given is for an MXA28A package whose exposed-DAP is soldered to an exposed 1in 2 piece of 1 ounce printed circuit board copper. Note 6: The JA given is for an MXA28A package whose exposed-DAP is not soldered to any copper. Note 7: The given JA is for an LM4835 packaged in an LQA24A with the exposed-DAP soldered to an exposed 2in 2 area of 1oz printed circuit board copper. Note 8: All voltages are measured with respect to the ground pins, unless otherwise specified. All specifications are tested using the typical application as shown in Figure 1. Note 9: When driving 3 loads and operating on a 5V supply, the LM4835MTE must be mounted to the circuit board and forced-air cooled. Note 10: When driving 4 loads and operating on a 5V supply, the LM4835MTE must be mounted to the circuit board. Note 11: When driving a 3 or 4 loads and operating on a 5V supply, the LM4835LQ must be mounted to the circuit board that has a minimum of 2.5in 2 of exposed, uninterrupted copper area connected to the LLP package's exposed DAP. Note 12: 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 13: 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. For the LM4835LQ and LM4835MT, TJMAX = 150C, and the typical junction-to-ambient thermal resistance, when board mounted, is 80C/W for the MTC28 package and 42C/W for the LM4835LQ package. Note 14: Human body model, 100pF discharged through a 1.5k resistor. Note 15: Machine Model, 220pF-240pF discharged through all pins. Note 16: Typicals are measured at 25C and represent the parametric norm. Note 17: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. www.national.com 4 LM4835 Typical Application 10013903 FIGURE 2. Typical Application Circuit Truth Table for Logic Inputs (Note 18) Mute Mode HP Sense DC Vol. Control Bridged Output 0 0 0 Fixed Level Vol. Fixed Single-Ended Output _ 0 0 1 Fixed Level Muted Vol. Fixed 0 1 0 Adjustable Vol. Changes _ 0 1 1 Adjustable Muted Vol. Changes 1 X X _ Muted Muted Note 18: If system beep is detected on the Beep In pin (pin 11), the system beep will be passed through the bridged amplifier regardless of the logic of the Mute and HP sense pins. 5 www.national.com LM4835 Typical Performance Characteristics MTE Specific Characteristics LM4835MTE THD+N vs Output Power LM4835MTE THD+N vs Frequency 10013971 10013970 LM4835MTE THD+N vs Output Power LM4835MTE THD+N vs Frequency 10013972 10013973 LM4835MTE Power Dissipation vs Output Power LM4835MTE (Note 19) Power Derating Curve 10013965 www.national.com 10013964 6 LM4835 Typical Performance Characteristics MTE Specific Characteristics (Continued) LM4835LQ Power Derating Curve 10013982 Note 19: These curves show the thermal dissipation ability of the LM4835MTE at different ambient temperatures given these conditions: 500LFPM + 2in2: The part is soldered to a 2in2, 1 oz. copper plane with 500 linear feet per minute of forced-air flow across it. 2in2on bottom: The part is soldered to a 2in2, 1oz. copper plane that is on the bottom side of the PC board through 21 8 mil vias. 2in2: The part is soldered to a 2in2, 1oz. copper plane. 1in2: The part is soldered to a 1in2, 1oz. copper plane. Not Attached: The part is not soldered down and is not forced-air cooled. Typical Performance Characteristics Non-MTE Specific Characteristics THD+N vs Frequency THD+N vs Frequency 10013958 10013957 7 www.national.com LM4835 Typical Performance Characteristics Non-MTE Specific Characteristics (Continued) THD+N vs Frequency THD+N vs Frequency 10013914 10013915 THD+N vs Frequency THD+N vs Frequency 10013917 10013916 THD+N vs Frequency THD+N vs Frequency 10013918 www.national.com 10013919 8 LM4835 Typical Performance Characteristics Non-MTE Specific Characteristics (Continued) THD+N vs Frequency THD+N vs Frequency 10013921 10013920 THD+N vs Frequency THD+N vs Output Power 10013924 10013922 THD+N vs Output Power THD+N vs Output Power 10013925 10013926 9 www.national.com LM4835 Typical Performance Characteristics Non-MTE Specific Characteristics (Continued) THD+N vs Output Power THD+N vs Output Power 10013927 10013928 THD+N vs Output Power THD+N vs Output Power 10013930 10013929 THD+N vs Output Power THD+N vs Output Power 10013931 www.national.com 10013932 10 LM4835 Typical Performance Characteristics Non-MTE Specific Characteristics (Continued) THD+N vs Output Power THD+N vs Output Power 10013934 10013933 THD+N vs Output Voltage Docking Station Pins THD+N vs Output Voltage Docking Station Pins 10013960 10013959 11 www.national.com LM4835 Typical Performance Characteristics Output Power vs Load Resistance Output Power vs Load Resistance 10013962 10013906 Output Power vs Load Resistance Power Supply Rejection Ratio 10013938 10013907 Output Power vs Load Resistance Dropout Voltage 10013953 10013908 www.national.com 12 LM4835 Typical Performance Characteristics (Continued) Noise Floor Noise Floor 10013942 10013941 Volume Control Characteristics Power Dissipation vs Output Power 10013951 10013910 External Gain/ Bass Boost Characteristics Power Dissipation vs Output Power 10013952 10013961 13 www.national.com LM4835 Typical Performance Characteristics (Continued) Power Derating Curve Crosstalk 10013963 10013949 Output Power vs Supply voltage Crosstalk 10013950 10013954 Output Power vs Supply Voltage Supply Current vs Supply Voltage 10013956 www.national.com 10013909 14 EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS The LM4835's exposed-DAP (die attach paddle) packages (MTE and LQ) 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 2.1W at 1% THD with a 4 load. This high power is achieved through careful consideration of necessary thermal design. Failing to optimize thermal design may compromise the LM4835's high power performance and activate unwanted, though necessary, thermal shutdown protection. The MTE and LQ packages must have their DAPs 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 32(4x8) (MTE) or 6(3x2) (LQ) vias. The via diameter should be 0.012in-0.013in with a 1.27mm 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 4 load. Heatsink areas not placed on the same PCB layer as the LM4835 should be 5in2 (min) for the same supply voltage and load resistance. The last two area recommendations apply for 25C ambient temperature. Increase the area to compensate for ambient temperatures above 25C. In systems using cooling fans, the LM4835MTE can take advantage of forced air cooling. With an air flow rate of 450 linear-feet per minute and a 2.5in2 exposed copper or 5.0in2 inner layer copper plane heatsink, the LM4835MTE can continuously drive a 3 load to full power. The LM4835LQ achieves the same output power level without forced air cooling. In all circumstances and conditions, the junction temperature must be held below 150C to prevent activating the LM4835's thermal shutdown protection. The LM4835'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 LQ packages are shown in the Demonstration Board Layout section. Further detailed and specific information concerning PCB layout, fabrication, and mounting an LQ (LLP) package is available in National Semiconductor's AN1187. BRIDGE CONFIGURATION EXPLANATION As shown in Figure 2, the LM4835 consists of two pairs of operational amplifiers, forming a two-channel (channel A and channel B) stereo amplifier. (Though the following discusses channel A, it applies equally to channel B.) External resistors Rf and Ri set the closed-loop gain of Amp1A, whereas two internal 20k resistors set Amp2A's gain at -1. The LM4835 drives a load, such as a speaker, connected between the two amplifier outputs, -OUTA and +OUTA. Figure 2 shows that Amp1A's output serves as Amp2A's input. This results in both amplifiers producing signals identical in magnitude, but 180 out of phase. Taking advantage of this phase difference, a load is placed between -OUTA and +OUTA and driven differentially (commonly referred to as "bridge mode"). This results in a differential gain of AVD = 2 * (Rf / Ri) (1) Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected between a single amplifier's output and ground. For a given supply voltage, bridge mode has a distinct advantage over the single-ended configuration: its differential output doubles the voltage swing across the load. This produces four times the output power when 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 that the output signal is not clipped. To ensure minimum output signal clipping when choosing an amplifier's closed-loop gain, refer to the Audio Power Amplifier Design section. Another advantage of the differential bridge output is no net DC voltage across the load. This is accomplished by biasing channel A's and channel B's outputs at half-supply. This eliminates the coupling capacitor that single supply, singleended amplifiers require. Eliminating an output coupling capacitor in a single-ended configuration forces a single-supply amplifier's half-supply bias voltage across the load. This increases internal IC power dissipation and may permanently damage loads such as speakers. PCB LAYOUT AND SUPPLY REGULATION CONSIDERATIONS FOR DRIVING 3 AND 4 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 dependent 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, 0.1 trace resistance reduces the output power dissipated by a 4 load from 2.1W to 2.0W. This problem of decreased load dissipation is exacerbated as load impedance decreases. Therefore, to maintain the POWER DISSIPATION Power dissipation is a major concern when successful single-ended or bridged amplifier. states the maximum power dissipation point ended amplifier operating at a given supply driving a specified output load. PDMAX = (VDD)2 / (22RL) 15 designing a Equation (2) for a singlevoltage and Single-Ended (2) www.national.com LM4835 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 supply regulation. Therefore, making the power supply traces as wide as possible helps maintain full output voltage swing. Application Information LM4835 Application Information 7106D can also improve power dissipation. When adding a heat sink, the JA is the sum of JC, CS, and SA. (JC is the junction-to-case thermal impedance, CS is the case-to-sink thermal impedance, and SA is the sink-to-ambient thermal impedance.) Refer to the Typical Performance Characteristics curves for power dissipation information at lower output power levels. (Continued) However, a direct consequence of the increased power delivered to the load by a bridge amplifier is higher internal power dissipation for the same conditions. The LM4835 has two operational amplifiers per channel. The maximum internal power dissipation per channel operating in the bridge mode is four times that of a single-ended amplifier. From Equation (3), assuming a 5V power supply and a 4 load, the maximum single channel power dissipation is 1.27W or 2.54W for stereo operation. PDMAX = 4 * (VDD)2 / (22RL) Bridge Mode POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. Applications that employ a 5V regulator typically use a 10F in parallel with a 0.1F filter capacitors to stabilize the regulator's output, reduce noise on the supply line, and improve the supply's transient response. However, their presence does not eliminate the need for a local 1.0F tantalum bypass capacitance connected between the LM4835's supply pins and ground. Do not substitute a ceramic capacitor for the tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors between the LM4835's power supply pin and ground as short as possible. Connecting a 1F capacitor, CB, between the BYPASS pin and ground improves the internal bias voltage's stability and improves the amplifier's PSRR. The PSRR improvements increase as the bypass pin capacitor value increases. Too large, however, increases turn-on time and can compromise amplifier's click and pop performance. The selection of bypass capacitor values, especially CB, depends on desired PSRR requirements, click and pop performance (as explained in the section, Proper Selection of External Components), system cost, and size constraints. (3) The LM4835's power dissipation is twice that given by Equation (2) or Equation (3) when operating in the single-ended mode or bridge mode, respectively. Twice the maximum power dissipation point given by Equation (3) must not exceed the power dissipation given by Equation (4): PDMAX' = (TJMAX - TA) / JA (4) The LM4835's TJMAX = 150C. In the LQ package soldered to a DAP pad that expands to a copper area of 5in2 on a PCB, the LM4835's JA is 20C/W. In the MTE package soldered to a DAP pad that expands to a copper area of 2in2 on a PCB, the LM4835's JA is 41C/W. At any given ambient temperature TA, use Equation (4) to find the maximum internal power dissipation supported by the IC packaging. Rearranging Equation (4) and substituting PDMAX for PDMAX' results in Equation (5). This equation gives the maximum ambient temperature that still allows maximum stereo power dissipation without violating the LM4835's maximum junction temperature. TA = TJMAX - 2*PDMAX JA SELECTING PROPER EXTERNAL COMPONENTS Optimizing the LM4835's performance requires properly selecting external components. Though the LM4835 operates well when using external components with wide tolerances, best performance is achieved by optimizing component values. The LM4835 is unity-gain stable, giving a designer maximum design flexibility. The gain should be set to no more than a given application requires. This allows the amplifier to achieve minimum THD+N and maximum signal-to-noise ratio. These parameters are compromised as the closed-loop gain increases. However, low gain demands input signals with greater voltage swings to achieve maximum output power. Fortunately, many signal sources such as audio CODECs have outputs of 1VRMS (2.83VP-P). Please refer to the Audio Power Amplifier Design section for more information on selecting the proper gain. (5) For a typical application with a 5V power supply and an 4 load, the maximum ambient temperature that allows maximum stereo power dissipation without exceeding the maximum junction temperature is approximately 99C for the LQ package and 45C for the MTE package. TJMAX = PDMAX JA + TA (6) Equation (6) gives the maximum junction temperature TJMAX. If the result violates the LM4835's 150C, reduce the maximum junction temperature by reducing the power supply voltage or increasing the load resistance. Further allowance should be made for increased ambient temperatures. The above examples assume that a device is a surface mount part operating around the maximum power dissipation point. Since internal power dissipation is a function of output power, higher ambient temperatures are allowed as output power or duty cycle decreases. If the result of Equation (2) is greater than that of Equation (3), then decrease the supply voltage, increase the load impedance, or reduce the ambient temperature. If these measures are insufficient, a heat sink can be added to reduce JA. The heat sink can be created using additional copper area around the package, with connections to the ground pin(s), supply pin and amplifier output pins. External, solder attached SMT heatsinks such as the Thermalloy www.national.com Input Capacitor Value Selection Amplifying the lowest audio frequencies requires high value input coupling capacitor (0.33F in Figure 2). A high value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases, however, the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 150 Hz. Applications using speakers with this limited frequency response reap little improvement by using large input capacitor. Besides effecting system cost and size, the input coupling capacitor has an affect on the LM4835's click and pop performance. When the supply voltage is first applied, a transient (pop) is created as the charge on the input capacitor changes from zero to a quiescent state. The magnitude of 16 mode, an external 1k-5k resistor can be placed in parallel with the internal 20k resistor. The tradeoff for using this resistor is increased quiescent current. (Continued) the pop is directly proportional to the input capacitor's size. Higher value capacitors need more time to reach a quiescent DC voltage (usually VDD/2) when charged with a fixed current. The amplifier's output charges the input capacitor through the feedback resistor, Rf. Thus, pops can be minimized by selecting an input capacitor value that is no higher than necessary to meet the desired -3dB frequency. A shown in Figure 2, the input resistor (20k) and the input capacitor produce a -3dB high pass filter cutoff frequency that is found using Equation (7). (7) As an example when using a speaker with a low frequency limit of 150Hz, the input coupling capacitor, using Equation (7), is 0.063F. The 0.33F input coupling capacitor shown in Figure 2 allows the LM4835 to drive high efficiency, full range speaker whose response extends below 30Hz. 10013905 FIGURE 3. Resistor for Varying Output Loads OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE The LM4835 contains circuitry that minimizes turn-on and shutdown transients or "clicks and pop". For this discussion, turn-on refers to either applying the power supply voltage or when the shutdown mode is deactivated. While the power supply is ramping to its final value, the LM4835's internal amplifiers are configured as unity gain buffers. An internal current source changes the voltage of the BYPASS pin in a controlled, linear manner. Ideally, the input and outputs track the voltage applied to the BYPASS pin. The gain of the internal amplifiers remains unity until the voltage on the bypass pin reaches 1/2 VDD. As soon as the voltage on the bypass pin is stable, the device becomes fully operational. Although the BYPASS pin current cannot be modified, changing the size of CB alters the device's turn-on time and the magnitude of "clicks and pops". Increasing the value of CB reduces the magnitude of turn-on pops. However, this presents a tradeoff: as the size of CB increases, the turn-on time increases. There is a linear relationship between the size of CB and the turn-on time. Here are some typical turn-on times for various values of CB: CB DOCKING STATION INTERFACE Applications such as notebook computers can take advantage of a docking station to connect to external devices such as monitors or audio/visual equipment that sends or receives line level signals. The LM4835 has two outputs, Pin 9 and Pin 13, which connect to outputs of the internal input amplifiers that drive the volume control inputs. These input amplifiers can drive loads of > 1k (such as powered speakers) with a rail-to-rail signal. Since the output signal present on the RIGHT DOCK and LEFT DOCK pins is biased to VDD/2, coupling capacitors should be connected in series with the load. Typical values for the coupling capacitors are 0.33F to 1.0F. If polarized coupling capacitors are used, connect their "+" terminals to the respective output pin. Since the DOCK outputs precede the internal volume control, the signal amplitude will be equal to the input signal's magnitude and cannot be adjusted. However, the input amplifier's closed-loop gain can be adjusted using external resistors. These resistors are shown in Figure 2 as 20k devices that set each input amplifier's gain to -1. Use Equation 8 to determine the input and feedback resistor values for a desired gain. TON 0.01F 2ms 0.1F 20ms 0.22F 44ms 0.47F 94ms 1.0F 200ms - A v = RF / R i (8) Adjusting the input amplifier's gain sets the minimum gain for that channel. The DOCK outputs adds circuit and functional flexibility because their use supercedes using the inverting outputs of each bridged output amplifier as line-level outputs. In order eliminate "clicks and pops", all capacitors must be discharged before turn-on. Rapidly switching VDD may not allow the capacitors to fully discharge, which may cause "clicks and pops". In a single-ended configuration, the output is coupled to the load by COUT. This capacitor usually has a high value. COUT discharges through internal 20k resistors. Depending on the size of COUT, the discharge time constant can be relatively large. To reduce transients in single-ended BEEP DETECT FUNCTION Computers and notebooks produce a system "beep" signal that drives a small speaker. The speaker's auditory output signifies that the system requires user attention or input. To accommodate this system alert signal, the LM4835's pin 11 is a mono input that accepts the beep signal. Internal level detection circuitry at this input monitors the beep signal's magnitude. When a signal level greater than VDD/2 is de17 www.national.com LM4835 Application Information LM4835 Application Information shutdown current is achieved by applying a voltage that is as near as VDD as possible to the SHUTDOWN pin. A voltage that is less than VDD may increase the shutdown current. Table 1 shows the logic signal levels that activate and deactivate micro-power shutdown and headphone amplifier operation. There are a few ways to control the micro-power shutdown. These include using a single-pole, single-throw switch, a microprocessor, or a microcontroller. When using a switch, connect an external 10k pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select normal amplifier operation by closing the switch. Opening the switch connects the SHUTDOWN pin to VDD through the pull-up resistor, activating micro-power shutdown. The switch and resistor guarantee that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a microprocessor or a microcontroller, use a digital output to apply the control voltage to the SHUTDOWN pin. Driving the SHUTDOWN pin with active circuitry eliminates the pull up resistor. (Continued) tected on pin 11, the bridge output amplifiers are enabled. The beep signal is amplified and applied to the load connected to the output amplifiers. A valid beep signal will be applied to the load even when MUTE is active. Use the input resistors connected between the BEEP IN pin and the stereo input pins to accommodate different beep signal amplitudes. These resistors are shown as 200k devices in Figure 2. Use higher value resistors to reduce the gain applied to the beep signal. The resistors must be used to pass the beep signal to the stereo inputs. The BEEP IN pin is used only to detect the beep signal's magnitude: it does not pass the signal to the output amplifiers. The LM4835's shutdown mode must be deactivated before a system alert signal is applied to BEEP IN pin. MICRO-POWER SHUTDOWN The voltage applied to the SHUTDOWN pin controls the LM4835's shutdown function. Activate micro-power shutdown by applying VDD to the SHUTDOWN pin. When active, the LM4835's micro-power shutdown feature turns off the amplifier's bias circuitry, reducing the supply current. The logic threshold is typically VDD/2. The low 0.7A typical TABLE 1. Logic Level Truth Table for SHUTDOWN, HP-IN, and MUX Operation SHUTDOWN PIN HP-IN PIN MUX CHANNEL SELECT PIN OPERATIONAL MODE (MUX INPUT CHANNEL #) Logic Low Logic Low Logic Low Logic Low Bridged Amplifiers (1) Logic Low Logic High Bridged Amplifiers (2) Logic Low Logic High Logic Low Single-Ended Amplifiers (1) Logic Low Logic High Logic High Single-Ended Amplifiers (2) Logic High X X Micro-Power Shutdown MODE FUNCTION The LM4835's MODE function has two states controlled by the voltage applied to the MODE pin (pin 4). Mode 0, selected by applying 0V to the MODE pin, forces the LM4835 to effectively function as a "line-out," unity-gain amplifier. Mode 1, which uses the internal DC controlled volume control, is selected by applying VDD to the MODE pin. This mode sets the amplifier's gain according to the DC voltage applied to the DC VOL CONTROL pin. Prevent unanticipated gain behavior by connecting the MODE pin to VDD or ground. Do not let pin 4 float. MUTE FUNCTION The LM4835 mutes the amplifier and DOCK outputs when VDD is applied to pin 5, the MUTE pin. Even while muted, the LM4835 will amplify a system alert (beep) signal whose magnitude satisfies the BEEP DETECT circuitry. Applying 0V to the MUTE pin returns the LM4835 to normal, unmated operation. Prevent unanticipated mute behavior by connecting the MUTE pin to VDD or ground. Do not let pin 5 float. www.national.com 10013904 FIGURE 4. Headphone Sensing Circuit 18 LM4835 Application Information (Continued) HP-IN FUNCTION Applying a voltage between 4V and VDD to the LM4835's HP-IN headphone control pin turns off Amp2A and Amp2B, muting a bridged-connected load. Quiescent current consumption is reduced when the IC is in this single-ended mode. Figure 4 shows the implementation of the LM4835's headphone control function. With no headphones connected to the headphone jack, the R1-R2 voltage divider sets the voltage applied to the HP-IN pin (pin 16) at approximately 50mV. This 50mV enables Amp1B and Amp2B, placing the LM4835 in bridged mode operation. The output coupling capacitor blocks the amplifier's half supply DC voltage, protecting the headphones. 10013911 The HP-IN threshold is set at 4V. While the LM4835 operates in bridged mode, the DC potential across the load is essentially 0V. Therefore, even in an ideal situation, the output swing cannot cause a false single-ended trigger. Connecting headphones to the headphone jack disconnects the headphone jack contact pin from -OUTA and allows R1 to pull the HP Sense pin up to VDD. This enables the headphone function, turns off Amp2A and Amp2B, and mutes the bridged speaker. The amplifier then drives the headphones, whose impedance is in parallel with resistor R2 and R3. These resistors have negligible effect on the LM4835's output drive capability since the typical impedance of headphones is 32. Figure 4 also shows the suggested headphone jack electrical connections. The jack is designed to mate with a threewire plug. The plug's tip and ring should each carry one of the two stereo output signals, whereas the sleeve should carry the ground return. A headphone jack with one control pin contact is sufficient to drive the HP-IN pin when connecting headphones. A microprocessor or a switch can replace the headphone jack contact pin. When a microprocessor or switch applies a voltage greater than 4V to the HP-IN pin, a bridge-connected speaker is muted and Amp1A and Amp2A drive a pair of headphones. At low, frequencies CLFE is a virtual open circuit and at high frequencies, its nearly zero ohm impedance shorts RLFE. The result is increased bridge-amplifier gain at low frequencies. The combination of RLFE and CLFE form with a -3dB corner frequency at FIGURE 5. Figure 5. Low Frequency Enhancement fC = 1 / (2RLFEC LFE) (9) The bridged-amplifier low frequency differential gain is: AVD = 2(RF + RLFE) / Ri (10) Using the component values shown in Figure 1 (RF = 20k, RLFE = 20k, and CLFE = 0.068F), a first-order, -3dB pole is created at 120Hz. Assuming R i = 20k, the low frequency differential gain is 4. The input (Ci) and output (CO) capacitor values must be selected for a low frequency response that covers the range of frequencies affected by the desired bass-boost operation. DC VOLUME CONTROL The LM4835 has an internal stereo volume control whose setting is a function of the DC voltage applied to the DC VOL CONTROL pin. The volume control's voltage input range is 0V to VDD. The volume range is from 0dB (DC control voltage = 80% VDD) to -80dB (DC control voltage = 0V). The volume remains at 0dB for DC control voltages greater than 80% VDD. When the MODE input is 0V, the LM4835 operates at unity gain, bypassing the volume control. A graph showing a typical volume response versus DC control voltage is shown in the Typical Performance Characteristics section. Like all volume controls, the LM4835's internal volume control is set while listening to an amplified signal that is applied to an external speaker. The actual voltage applied to the DC VOL CONTROL pin is a result of the volume a listener desires. As such, the volume control is designed for use in a feedback system that includes human ears and preferences. This feedback system operates quite well without the need for accurate gain. The user simply sets the volume to the desired level as determined by their ear, without regard to the actual DC voltage that produces the volume. Therefore, the accuracy of the volume control is not critical, as long as the volume changes monotonically, matches well between GAIN SELECT FUNCTION (Bass Boost) The LM4835 features selectable gain, using either internal and external feedback resistors. Either set of feedback resistors set the gain of the output amplifiers. The voltage applied to pin 3 (GAIN SELECT pin) controls which gain is selected. Applying VDD to the GAIN SELECT pin selects the external gain mode. Applying 0V to the GAIN SELECT pin selects the internally set unity gain. In some cases a designer may want to improve the low frequency response of the bridged amplifier or incorporate a bass boost feature. This bass boost can be useful in systems where speakers are housed in small enclosures. A resistor, RLFE, and a capacitor, CLFE, in parallel, can be placed in series with the feedback resistor of the bridged amplifier as seen in Figure 5. 19 www.national.com LM4835 Application Information The amplifier's overall gain is set using the input (Ri) and feedback (Ri) resistors. With the desired input impedance set at 20k, the feedback resistor is found using Equation (14). (Continued) stereo channels, and the step size is small enough to reach a desired volume that is not too loud or too soft. Since gain accuracy is not critical, there will be volume variation from part-to-part even with the same applied DC control voltage. The gain of a given LM4835 can be set with a fixed external voltage, but another LM4835 may require a different control voltage to achieve the same gain. The typical part-to-part variation can be as large as 8dB for the same control voltage. Rf / Ri = AVD / 2 The value of Rf is 30k. The last step in this design example is setting the amplifier's -3dB frequency bandwidth. To achieve the desired 0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the lower bandwidth limit and the high frequency response must extend to at least five times the upper bandwidth limit. The gain variation for both response limits is 0.17dB, well within the 0.25dB desired limit. The results are an AUDIO POWER AMPLIFIER DESIGN Audio Amplifier Design: Driving 1W into an 8 Load The following are the desired operational parameters: Power Output: 1 WRMS Load Impedance: 8 Input Level: 1 VRMS Input Impedance: Bandwidth: (14) 20 k fL = 100Hz / 5 = 20Hz (15) fH = 20kHz x 5 = 100kHz (16) 100 Hz-20 kHz 0.25 dB and an The design begins by specifying the minimum supply voltage necessary to obtain the specified output power. One way to find the minimum supply voltage is to use the Output Power vs Supply Voltage curve in the Typical Performance Characteristics section. Another way, using Equation (10), is to calculate the peak output voltage necessary to achieve the desired output power for a given load impedance. To account for the amplifier's dropout voltage, two additional voltages, based on the Dropout Voltage vs Supply Voltage in the Typical Performance Characteristics curves, must be added to the result obtained by Equation (11). The result is Equation (12). VDD (VOUTPEAK+ (VODTOP + VODBOT)) As mentioned in the Selecting Proper External Components section, Ri and Ci create a highpass filter that sets the amplifier's lower bandpass frequency limit. Find the input coupling capacitor's value using Equation (17). (17) 1 / (2*20k*20Hz) = 0.397F (18) The result is (11) Use a 0.39F capacitor, the closest standard value. (12) The product of the desired high frequency cutoff (100kHz in this example) and the differential gain AVD, determines the upper passband response limit. With AVD = 3 and fH = 100kHz, the closed-loop gain bandwidth product (GBWP) is 300kHz. This is less than the LM4835's 3.5MHz GBWP. With this margin, the amplifier can be used in designs that require more differential gain while avoiding performance,restricting bandwidth limitations. The Output Power vs Supply Voltage graph for an 8 load indicates a minimum supply voltage of 4.6V. This is easily met by the commonly used 5V supply voltage. The additional voltage creates the benefit of headroom, allowing the LM4835 to produce peak output power in excess of 1W without clipping or other audible distortion. The choice of supply voltage must also not create a situation that violates of maximum power dissipation as explained above in the Power Dissipation section. After satisfying the LM4835's power dissipation requirements, the minimum differential gain needed to achieve 1W dissipation in an 8 load is found using Equation (13). RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT Figure (6) through (10) show the recommended four-layer PC board layout that is optimized for the 24-pin LQpackaged LM4835 and associated external components. This circuit is designed for use with an external 5V supply and 4 speakers. This circuit board is easy to use. Apply 5V and ground to the board's VDD and GND pads, respectively. Connect 4 speakers between the board's -OUTA and +OUTA and OUTB and +OUTB pads. (13) Thus, a minimum gain of 2.83 allows the LM4835's to reach full output swing and maintain low noise and THD+N performance. For this example, let AVD = 3. www.national.com Ci 1 / (2RifL) 20 LM4835 Application Information (Continued) 10013977 FIGURE 6. Recommended LQ PC Board Layout: Component-Side Silkscreen 10013978 FIGURE 7. Recommended LQ PC Board Layout: Component-Side Layout 21 www.national.com LM4835 Application Information (Continued) 10013979 FIGURE 8. Recommended LQ PC Board Layout: Upper Inner-Layer Layout 10013980 FIGURE 9. Recommended LQ PC Board Layout: Lower Inner-Layer Layout www.national.com 22 LM4835 Application Information (Continued) 10013981 FIGURE 10. Recommended LQ PC Board Layout: Bottom-Side Layout 23 www.national.com LM4835 LM4835 MDC MWC Stereo 2W Audio Power Amplifier with DC Volume Control and Selectable Gain 10013983 Die Layout (A - Step) DIE/WAFER CHARACTERISTICS Fabrication Attributes General Die Information Physical Die Identification LM4835A Die Step A Physical Attributes Bond Pad Opening Size (min) 104m x 104m Bond Pad Metalization ALUMINUM Passivation NITRIDE OVER PASSIVATION OXIDE Back Side Metal BARE BACK Wafer Diameter 150mm Dise Size (Drawn) 2578m x 2438m Back Side Connection 101.5mils x 96.0mils Thickness 254m Nominal Min Pitch 145m Nominal Floating Special Assembly Requirements: Note: Actual die size is rounded to the nearest micron. Die Bond Pad Coordinate Locations (A - Step) (Referenced to die center, coordinates in m) NC = No Connection, N.U. = Not Used SIGNAL NAME PAD# NUMBER X/Y COORDINATES PAD SIZE X Y X Right Out + 1 -245 1093 212 x 104 Y GND 2 -505 1093 212 x 104 SHUT DOWN 3 -791 1093 104 x 104 Gain Select 4 -936 1093 104 x 104 Mode 5 -1162 835 104 x 104 Mute 6 -1162 690 104 x 104 VDD 7 -1162 340 104 x 104 DC Vol 8 -1162 101 104 x 104 GND 9 -1162 -186 104 x 212 Right Dock 10 -1162 -385 104 x 104 Right In 11 -1162 -618 104 x 104 Beep In 12 -1162 -850 104 x 104 Left In 13 -936 -1093 104 x 104 Left Dock 14 -791 -1093 104 x 104 www.national.com 24 GND 15 -505 -1093 212 x 104 Left Out + 16 -245 -1093 212 x 104 VDD 17 192 -1093 212 x 104 Left Out - 18 660 -1093 212 x 104 Left Gain 2 19 859 -1093 104 x 104 Left Gain 1 20 1162 -854 104 x 104 GND 21 1162 -654 104 x 212 HP Sense 22 1162 -454 104 x 104 Bypass 23 1162 449 104 x 104 GND 24 1162 649 104 x 212 Right Gain 1 25 1162 849 104 x 104 Right Gain 2 26 859 1093 104 x 104 Right Out - 27 660 1093 212 x 104 VDD 28 192 1093 212 x 104 IN U.S.A Tel #: 1 877 Dial Die 1 877 342 5343 Fax: 1 207 541 6140 IN EUROPE Tel: 49 (0) 8141 351492 / 1495 Fax: 49 (0) 8141 351470 IN ASIA PACIFIC Tel: (852) 27371701 IN JAPAN Tel: 81 043 299 2308 25 www.national.com LM4835 LM4835 MDC MWC Stereo 2W Audio Power Amplifier with DC Volume Control and Selectable Gain (Continued) LM4835 Physical Dimensions inches (millimeters) unless otherwise noted LLP Package Order Number LM4835LQ NS Package Number LQA028A For Exposed-DAP LLP www.national.com 26 LM4835 Physical Dimensions inches (millimeters) unless otherwise noted (Continued) TSSOP Package Order Number LM4835MT NS Package Number MTC28 for TSSOP Exposed-DAP TSSOP Package Order Number LM4835MTE NS Package Number MXA28A for Exposed-DAP TSSOP 27 www.national.com LM4835 Stereo 2W Audio Power Amplifiers with DC Volume Control and Selectable Gain Notes 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. National Semiconductor Americas Customer Support Center Email: new.feedback@nsc.com Tel: 1-800-272-9959 www.national.com 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 Francais Tel: +33 (0) 1 41 91 8790 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. 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