LM4916 LM4916 1.5V, Mono 85mW BTL Output, 14mW Stereo Headphone Audio Amplifier Literature Number: SNAS179D LM4916 1.5V, Mono 85mW BTL Output, 14mW Stereo Headphone Audio Amplifier General Description Key Specifications The unity gain stable LM4916 is both a mono differential output (for bridge-tied loads or BTL) audio power amplifier and a Single Ended (SE) stereo headphone amplifier. Operating on a single 1.5V supply, the mono BTL mode delivers 85mW into an 8 load at 1% THD+N. In Single Ended stereo headphone mode, the amplifier delivers 14mW per channel into a 16 load at 1% THD+N. n n n n n n n With the LM4916 packaged in the MM and LLP packages, the customer benefits include low profile and small size. These packages minimize PCB area and maximizes output power. The LM4916 features circuitry that reduces output transients ("clicks" and "pops") during device turn-on and turn-off, an externally controlled, low-power consumption, active-low shutdown mode, and thermal shutdown. Boomer audio power amplifiers are designed specifically to use few external components and provide high quality output power in a surface mount package. Mono-BTL output power (RL = 8, VDD = 1.5V, THD+N = 1%) 85mW (typ) Stereo Headphone output power (RL = 16, VDD = 1.5V, THD+N = 1%) 14mW (typ) Micropower shutdown current 0.02A (typ) Supply voltage operating range 0.9V < VDD < 2.5V PSRR 1kHz, VDD = 1.5V 66dB (typ) Features n Single-cell 0.9V to 2.5V battery operation n BTL mode for mono speaker n Single ended headphone operation with coupling capacitors n Unity-gain stable n "Click and pop" suppression circuitry n Active low micropower shutdown n Low current, active-low mute mode n Thermal shutdown protection circuitry Applications n Portable one-cell audio products n Portable one-cell electronic devices Typical Application 20048701 FIGURE 1. Block Diagram Boomer (R) is a registered trademark of National Semiconductor Corporation. (c) 2006 National Semiconductor Corporation DS200487 www.national.com LM4916 1.5V, Mono 85mW BTL Output, 14mW Stereo Headphone Audio Amplifier July 2006 LM4916 Connection Diagrams MSOP Package MSOP Marking 200487F9 Z - Plant Code X - Date Code T - Die Traceability G - Boomer Family A9 - LM4916MM 20048702 Top View Order Number LM4916MM See NS Package Number MUB10A for MSOP LD Package LLP Marking 200487G0 Z - Plant Code XY - Date Code T - Die Traceability Bottom Line - Part Number 20048752 Top View Order Number LM4916LD See NS Package Number LDA10A www.national.com 2 LM4916 Typical Connections 20048703 FIGURE 2. Typical Single Ended Output Configuration Circuit 20048705 FIGURE 3. Typical BTL Speaker Configuration Circuit 3 www.national.com LM4916 Absolute Maximum Ratings (Note 1) Infrared (15 sec) See AN-450 "Surface Mounting and their Effects on Product Reliablilty" for other methods of soldering surface mount devices. If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. 3.6V Thermal Resistance -65C to +150C JA (typ) MUB10A 175C/W -0.3V to VDD +0.3V JA (typ) LDA10A 73C/W Supply Voltage Storage Temperature Input Voltage 220C Power Dissipation (Note 2) Internally limited ESD Susceptibility(Note 3) 2000V ESD Susceptibility (Note 4) 200V Junction Temperature Operating Ratings Temperature Range 150C TMIN TA TMAX Solder Information -40C TA 85C 0.9V VDD 2.5V Supply Voltage (Note 10) Small Outline Package Vapor Phase (60sec) 215C Electrical Characteristics for the LM4916 (Notes 1, 5) The following specifications apply for the circuit shown in Figure 4 operating with VDD = 1. 5V, unless otherwise specified. Limits apply for TA = 25C. Symbol VDD Parameter Conditions LM4916 Typical Limit (Note 6) (Note 7) Supply Voltage (Notes 10, 11) IDD Quiescent Power Supply Current VIN = 0V, IO = 0A, RL = (Note 8) 1.0 ISD Shutdown Current VSHUTDOWN = GND 0.02 VOS Output Offset Voltage BTL Units (Limits) 0.9 V (min) 2.5 V (max) 1.4 mA (max) A (max) 5 50 70 mV (max) f = 1kHz PO Output Power (Note 9) RL = 8 BTL, THD+N = 1% 85 RL = 16 SE, THD+N = 1% 14 RL = 8, BTL, PO = 25mW, f = 1kHz 0.1 RL = 16, SE, PO = 5mW, f = 1kHz 0.2 mW (min) mW THD+N Total Harmonic Distortion + Noise VNO Output Voltage Noise 20Hz to 20kHz, A-weighted 10 IMUTE Mute Current VMUTE = 0, SE 15 A RL = 16, SE 55 dB (min) VRIPPLE = 200mVP-P CBYPASS = 4.7F, RL = 8 f = 1kHz, BTL 62 dB VRIPPLE = 200mVP-P sine wave CBYPASS = 4.7F, RL = 16 f = 1kHz, SE 66 dB (min) Crosstalk PSRR Power Supply Rejection Ratio 0.5 % VRMS VIH Control Logic High 0.7 V (min) VIL Control Logic Low 0.3 V (max) www.national.com 4 Note 2: The maximum power dissipation is dictated by TJMAX, JA, and the ambient temperature TA and must be derated at elevated temperatures. The maximum allowable power dissipation is PDMAX = (TJMAX - TA)/JA. For the LM4916, TJMAX = 150C. For the JAs, please see the Application Information section or the Absolute Maximum Ratings section. Note 3: Human body model, 100pF discharged through a 1.5k resistor. Note 4: Machine model, 220pF-240pF discharged through all pins. Note 5: All voltages are measured with respect to the ground (GND) pins unless otherwise specified. Note 6: Typicals are measured at 25C and represent the parametric norm. Note 7: Datasheet min/max specification limits are guaranteed by design, test, or statistical analysis. Note 8: The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier. Note 9: Output power is measured at the device terminals. Note 10: When operating on a power supply voltage of 0.9V, the LM4916 willl not function below 0C. At a power supply voltage of 1V or greater, the LM4916 will operate down to -40C. Note 11: Ripple on power supply line should not exceed 400mVpp. 5 www.national.com LM4916 Note 1: 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. LM4916 Typical Performance Characteristics THD+N vs Frequency VDD = 1.5V, PO = 5mW, RL = 16 BW < 80kHz, Single Ended Output VDD THD+N vs Frequency = 1.5V, RL = 8, PO = 25mW BTL Output, AV = -1 200487D5 200487C2 THD+N vs Frequency VDD = 1.2V, PO = 5mW RL = 16, Single Ended Output, AV = -1 VDD THD+N vs Frequency = 1.2V, RL = 8, PO = 25mW BTL Output, AV = -1 200487D0 200487D6 THD+N vs Output Power VDD = 1.5V, RL = 16, f = 1kHz Single Ended Output, AV = -1 VDD 200487D7 www.national.com THD+N vs Output Power = 1.5V, RL = 8, f = 1kHz BTL Output, AV = -1 200487D8 6 LM4916 Typical Performance Characteristics (Continued) THD+N vs Output Power VDD = 1.2V, RL = 16, f = 1kHz Single Ended Output, AV = -1 VDD THD+N vs Output Power = 1.2V, RL = 8, f = 1kHz BTL Output, AV = -1 200487D9 200487E0 Output Power vs Supply Voltage f = 1kHz, RL = 8, BTL Output, AV = -1 Output Power vs Supply Voltage f = 1kHz, RL = 16, Single Ended Output, AV = -1 200487G1 200487G2 Output Power vs Load Resistance VDD = 1.5V, f = 1kHz BTL Output, AV = -1 Output Power vs Load Resistance VDD = 1.5V, f = 1kHz Single Ended Output, AV = -1 200487E6 200487E5 7 www.national.com LM4916 Typical Performance Characteristics (Continued) Output Power vs Load Resistance VDD = 1.2V, f = 1kHz BTL Output, AV = -1 Output Power vs Load Resistance VDD = 1.2V, f = 1kHz Single Ended Output, AV = -1 200487E4 200487E3 Power Dissipation vs Output Power f = 1kHz, THD+N < 1% BTL Output, AV = -1 Power Dissipation vs Output Power f = 1kHz, THD+N < 1%, AV = -1 Single Ended Output, Both Channels 200487F5 200487F6 Power Supply Rejection Ratio VDD = 1.5V, VRIPPLE = 200mVPP RL = 16, Single Ended Output Input Terminated into 10 Channel Separation RL = 16, PO = 5mW Single Ended Output, AV = -1 200487D4 www.national.com 200487C6 8 LM4916 Typical Performance Characteristics (Continued) Power Supply Rejection Ratio VDD = 1.2V, VRIPPLE = 200mVPP RL = 16, Single Ended Output Input Terminated into 10 Power Supply Rejection Ratio VDD = 1.5V, VRIPPLE = 200mVPP RL = 8, BTL Input Terminated into 10 200487C5 200487C8 Frequency Response vs Input Capacitor Size VDD = 1.5V, RL = 16 AV = -1, BW < 80kHz, Single Ended Output Power Supply Rejection Ratio VDD = 1.2V, VRIPPLE = 200mVPP RL = 8, BTL Input Terminated into 10 200487F8 200487C7 Frequency Response vs Input Capacitor Size VDD = 1.5V, RL = 8 AV = -1, BW < 80kHz, BTL Output Open Loop Frequency Response VDD = 1.5V, No load 200487B8 200487C4 9 www.national.com LM4916 Typical Performance Characteristics (Continued) Supply Voltage vs Supply Current Clipping Voltage vs Supply Voltage 200487E2 200487F1 Noise Floor VDD = 1.5V, Single Ended Output 16, 80kHz Bandwith Noise Floor VDD = 1.5V, BTL Output 8, 80kHz Bandwith 200487C3 200487B7 Power Derating Curve VDD = 1.5V Shutdown Hystresis Voltage VDD = 1.5V 200487F4 200487E1 www.national.com 10 LM4916 Typical Performance Characteristics (Continued) Mute Attenuation vs Load Resistance Shutdown Current Distribution 200487F2 200487F7 bridge amplifier design has a few distinct advantages over the single-ended configuration. It provides a 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. Application Information SINGLE ENDED (SE) CONFIGURATION EXPLANATION As shown in Figure 2, the LM4916 has two operational amplifiers internally, which have externally configurable gain. The closed loop gain of the two configurable amplifiers is set by selecting the ratio of Rf to Ri. Consequently, the gain for each channel of the IC is AVD = -(Rf / Ri) A bridge configuration, such as the one used in LM4916, 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. When the LM4916 operates in Single Ended mode, coupling capacitors are used on each output (VoA and VoB) and the SE/BTL pin (Pin 8) is connected to ground. These output coupling capacitors blocks the half supply voltage to which the output amplifiers are typically biased and couples the audio signal to the headphones or other single-ended (SE) loads. The signal return to circuit ground is through the headphone jack's sleeve. MODE SELECT DETAIL The LM4916 can be configured in either Single Ended or BTL mode (see Figure 2 and Figure 3). The default state of the LM4916 at power up is single ended. During initial power up or return from shutdown, the LM4916 must detect the correct mode of operation by sensing the status of the SE/BTL pin. When the bias voltage of the part ramps up to 60mV (as seen on the Bypass pin), an internal comparator detects the status of SE/BTL; and at 10mV, latches that value in place. Ramp up of the bias voltage will proceed at a different rate from this point on depending upon operating mode. BTL mode will ramp up about 11 times faster than Single Ended mode. Shutdown is not a valid command during this time period (TWU) and should not enabled to ensure a proper power on reset (POR) signal. In addition, the slew rate of VDD must be greater than 2.5V/ms to ensure reliable POR. Recommended power up timing is shown in Figure 5 along with proper usage of Shutdown and Mute. The mode-select circuit is suspended during CB discharge time. The circuit shown in Figure 4 presents an applications solution to the problem of using different supply voltages with different turn-on times in a system with the LM4916. This circuit shows the LM4916 with a 25-50k. Pull-up resistor connected from the shutdown pin to VDD. The shut- BRIDGED (BTL) CONFIGURATION EXPLANATION As shown in Figure 3, the LM4916 has two internal operational amplifiers. The first amplifier's gain is externally configurable, while the second amplifier should be externally fixed in a unity-gain, inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Riwhile the second amplifier's gain should be fixed by the two external 20k resistors. Figure 3 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 11 www.national.com LM4916 Application Information ers up first) or allows shutdown to ramp up with VDD (the LM4916 powers up first). This will ensure the LM4916 powers up properly and enters the correct mode of operation. Please note that the SE/BTL pin (Pin 8) should be tied to GND for Single Ended mode, and to VDD for BTL mode. (Continued) down pin of the LM4916 is also being driven by an open drain output of an external microcontroller on a separate supply. This circuit ensures that shutdown is disabled when powering up the LM4916 by either allowing shutdown to be high before the LM4916 powers on (the microcontroller pow- 20048753 FIGURE 4. Recommended Circuit for Different Supply Turn-On Timing www.national.com 12 LM4916 Application Information (Continued) 20048754 FIGURE 5. Turn-On, Shutdown, and Mute Timing for Cap-Coupled Mode The maximum power dissipation point obtained from either Equations 1, 2 must not be greater than the power dissipation that results from Equation 3: 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 LM4916 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 BTL application can be derived from the power dissipation graphs or from Equation 1. PDMAX = 4*(VDD) 2 / (22RL) PDMAX = (TJMAX - TA) / JA For package MUB10A, JA = 175C/W. TJMAX = 150C for the LM4916. Depending on the ambient temperature, TA, of the system surroundings, Equation 3 can be used to find the maximum internal power dissipation supported by the IC packaging. If the result of Equation 1 or 2 is greater than that of Equation 3, then either the supply voltage must be decreased, the load impedance increased or TA reduced. For the typical application of a 1.5V power supply, with a 16 load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 146C provided that device operation is around the maximum power dissipation point. Thus, for typical applications, power dissipation is not an issue. Power dissipation is a function of output power and thus, if typical operation is not around the maximum power dissipation point, the ambient temperature may be increased accordingly. Refer to the Typical Performance Characteristics curves for power dissipation information for lower output powers. (1) When operating in Single Ended mode, 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 / (22RL) (3) (2) Since the LM4916 has two operational amplifiers in one package, the maximum internal power dissipation point is twice that of the number that results from Equation 2. From Equation 2, assuming a 1.5V power supply and a 16 load, the maximum power dissipation point is 7mW per amplifier. Thus the maximum package dissipation point is 14mW. 13 www.national.com LM4916 Application Information tivation techniques match those given for the shutdown function as well. Mute may not appear to function when the LM4916 is used to drive high impedance loads. This is because the LM4916 relies on a typical headphone load (16-32) to reduce input signal feed-through through the input and feedback resistors. Mute attenuation can thus be calculated by the following formula: (Continued) EXPOSED-DAP PACKAGE PCB MOUNTING CONSIDERATIONS The LM4916's exposed-DAP (die attach paddle) package (LD) provides 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 surrounding air. The LD package should have its DAP soldered to a copper pad on the PCB. The DAP's PCB copper pad may be connected to a large plane of continuous unbroken copper. This plane forms a thermal mass, heat sink, and radiation area. Further detailed and specific information concerning PCB layout, fabrication, and mounting an LD (LLP) package is available from National Semiconductor's Package Engineering Group under application note AN1187. Mute Attenuation (dB) = 20Log[RL / (Ri+RF)] Parallel load resistance may be necessary to achieve satisfactory mute levels when the application load is known to be high impedance. The mute function, described above, is not necessary when the LM4916 is operating in BTL mode since the shutdown function operates quickly in BTL mode with less power consumption than mute. In these modes, the Mute signal is equivalent to the Shutdown signal. Mute may be enabled during shutdown transitions, but should not be toggled for a brief period immediately after exiting or entering shutdown. These brief time periods are labeled X1 (time after returning from shutdown) and X2 (time after entering shutdown) and are shown in the timing diagram given in Figure 5. X1 occurs immediately following a return from shutdown (TWU) and lasts 40ms 25%. X2 occurs after the part is placed in shutdown and the decay of the bias voltage has occurred (2.2*250k*CB) and lasts for 100ms 25%. The timing of these transition periods relative to X1 and X2 is also shown in Figure 5. While in single ended mode, mute should not be toggled during these time periods, but may be toggled during the shutdown transitions or any other time the part is in normal operation. Failure to operate mute correctly may result in much higher click and pop values or failure of the device to mute at all. POWER SUPPLY BYPASSING As with any amplifier, proper supply bypassing is important for low noise performance and high power supply rejection. The capacitor location on the power supply pins should be as close to the device as possible. Typical applications employ a battery (or 1.5V regulator) with 10F tantalum or electrolytic capacitor and a ceramic bypass capacitor that aid in supply stability. This does not eliminate the need for bypassing the supply nodes of the LM4916. A bypass capacitor value in the range of 0.1F to 1F is recommended. MICRO POWER SHUTDOWN The voltage applied to the SHUTDOWN pin controls the LM4916's shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHUTDOWN pin. When active, the LM4916's micro-power shutdown feature turns off the amplifier's bias circuitry, reducing the supply current. The trigger point varies depending on supply voltage and is shown in the Shutdown Hysteresis Voltage graphs in the Typical Performance Characteristics section. The low 0.02A (typ) shutdown current is achieved by applying a voltage that is as near as ground as possible to the SHUTDOWN pin. A voltage that is higher than ground may increase the shutdown current. 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 100k pull-up resistor between the SHUTDOWN pin and VDD. Connect the switch between the SHUTDOWN pin and ground. Select normal amplifier operation by opening the switch. Closing the switch connects the SHUTDOWN pin to ground, 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 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. 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 LM4916 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The LM4916 is unity-gain stable that gives the designer maximum system flexibility. The LM4916 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 1Vrms are available from sources such as audio codecs. Very large values should not be used for the gain-setting resistors. Values for Ri and Rf should be less than 1M. 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 closed-loop bandwidth of the amplifier. To a large extent, the bandwidth is dictated by the choice of external components shown in Figures 2 and 3. The input coupling capacitor, Ci, forms a first order high pass filter that limits low frequency response. This value should be chosen based on needed frequency response and turn-on time. MUTE When in single ended mode, the LM4916 also features a mute function that enables extremely fast turn-on/turn-off with a minimum of output pop and click with a low current consumption (20A, typical). The mute function leaves the outputs at their bias level, thus resulting in higher power consumption than shutdown mode, but also provides much faster turn on/off times. Providing a logic low signal on the MUTE pin enables mute mode. Threshold voltages and acwww.national.com SELECTION OF INPUT CAPACITOR SIZE Amplifying the lowest audio frequencies requires a high value input coupling capacitor, Ci. A high value capacitor can be expensive and may compromise space efficiency in portable designs. In many cases, however, the headphones used in portable systems have little ability to reproduce signals below 60Hz. Applications using headphones with this 14 LM4916 Application Information Single-Ended (Continued) limited frequency response reap little improvement by using a high value input capacitor. In addition to system cost and size, turn on time is affected by the size of the input coupling capacitor Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage. This charge comes from the output via the feedback. Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on time can be minimized. A small value of Ci (in the range of 0.1F to 0.47F), is recommended. CB(F) TON 0.1 117ms 0.22 179ms 0.47 310ms 1.0 552ms 2.2 1.14s 4.7 2.4s Bypass Capacitor Value Selection BTL Besides minimizing the input capacitor size, careful consideration should be paid to value of CB, the capacitor connected to the BYPASS pin. Since CB determines how fast the LM4916 settles to quiescent operation, its value is critical when minimizing turn-on pops. The slower the LM4916's outputs ramp to their quiescent DC voltage (nominally VDD/ 2), the smaller the turn-on pop. Choosing CB equal to 4.7F along with a small value of Ci (in the range of 0.1F to 0.47F), produces a click-less and pop-less shutdown function. As discussed above, choosing Ci no larger than necessary for the desired bandwidth helps minimize clicks and pops. This ensures that output transients are eliminated when power is first applied or the LM4916 resumes operation after shutdown. CB(F) TON (ms) 0.1 72 0.22 79 0.47 89 1.0 112 2.2 163 4.7 283 In order to 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". AUDIO POWER AMPLIFIER DESIGN Minimizing External Components Operating the LM4916 at higher gain settings can minimize the use of external components. For instance, a BTL configuration with a gain setting greater than 8V/V (AV > 8) makes the output capacitor CO unnecessary. For the Single Ended configuration, a gain setting greater than 4V/V (AV > 4) eliminates the need for output capacitor CO2 and output resistor RO, on each output channel. If the LM4916 is operating with a lower gain setting (AV < 4), external components can be further minimized only in Single Ended mode. For each channel, output capacitor (CO2 ) and output resistor (RO) can be eliminated. These components need to be compensated for by adding a 7.5k resistor (RC) between the input pin and ground pin on each channel (between Pin 1 and GND, and between Pin 5 and GND). A 25mW/32 Audio Amplifier Given: Power Output Load Impedance Input Level 10mWrms 16 0.4Vrms Input Impedance 20k A designer must first choose a mode of operation (SE or BTL) and 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. 1.5V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the LM4916 to reproduce peak in excess of 10mW 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 gain can be determined from Equation 2. OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE The LM4916 contains circuitry that eliminates turn-on and shutdown transients ("clicks and pops"). For this discussion, turn-on refers to either applying the power supply voltage or when the micro-power shutdown mode is deactivated. As the VDD/2 voltage present at the BYPASS pin ramps to its final value, the LM4916's internal amplifiers are configured as unity gain buffers. An internal current source charges the capacitor connected between the BYPASS pin and GND 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 VDD/2. As soon as the voltage on the bypass pin is stable, the device becomes fully operational and the amplifier outputs are reconnected to their respective output pins. Although the BYPASS pin current cannot be modified, changing the size of CB alters the device's turn-on time. 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: (4) From Equation 4, the minimum AV is 1; use AV = 1. Since the desired input impedance is 20k, and with a AV gain of 1, a ratio of 1:1 results from Equation 1 for Rf to R. The values are chosen with Ri = 20k and Rf = 20k. The final design step is to address the bandwidth requirements which must be stated as a pair of -3dB frequency points. Five times away from a -3dB point is 0.17dB down from passband response which is better than the required 0.25dB specified. 15 www.national.com LM4916 Application Information Ci 1 / (2 * 20k * 20Hz) = 0.397F; use 0.39F. (Continued) fL = 100Hz/5 = 20Hz The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain, AV. With an AVV = 1 and fH = 100kHz, the resulting GBWP = 100kHz which is much smaller than the LM4916 GBWP of 3MHz. This example displays that if a designer has a need to design an amplifier with higher differential gain, the LM4916 can still be used without running into bandwidth limitations. fH = 20kHz * 5 = 100kHz As stated in the External Components section, Ri in conjunction with Ci creates a www.national.com 16 LM4916 Revision History Rev Date Description 1.0 7/11/03 Re-released the D/S to the WEB. 1.1 7/25/06 Deleted the RL labels on curves E5, E6, E3, and E4, per Allan S., then re-released the D/S to the WEB. 17 www.national.com LM4916 Physical Dimensions inches (millimeters) unless otherwise noted MSOP Package Order Number LM4916MM NS Package Number MUB10A LD Package Order Number LM4916LD NS Package Number LDA10A www.national.com 18 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. 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