LM4925 2 Cell, Single Ended Output, 40mW Stereo Headphone Audio Amplifier General Description Key Specifications The unity gain stable LM4925 is both a mono differential output (for BTL operation) audio amplifier and a Single Ended (SE) stereo headphone amplifier. Operating on a single 3V supply, the mono-BTL mode delivers 410mW into an 8Ω load at 1% THD+N. In Single Ended stereo headphone mode, the amplifier delivers 40mW per channel into a 16Ω load at 1% THD+N. n n n n n n n With the LM4925 packaged in the MM and LLP packages, the customer benefits include low profile and small size. This package minimizes PCB area and maximizes output power. The LM4925 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 = 8Ω, VDD = 3.0V, THD+N = 1%) 410mW (typ) Single Ended Output Power Per Channel (RL = 16Ω, VDD = 3.0V, THD+N = 1%) 40mW (typ) Micropower shutdown current 0.1µA (typ) Supply voltage operating range 1.5V < VDD < 3.6V PSRR 100Hz, VDD = 3V, BTL 70dB (typ) Features n BTL mode for mono speaker n 2-cell 1.5V to 3.6V battery operation n Single ended headphone operation with output coupling capacitors n Unity-gain stable n “Click and pop” suppression circuitry for both Shutdown and Mute n Active low micro-power shutdown n Active-low mute mode n Thermal shutdown protection circuitry Applications n Portable two-cell audio products n Portable two-cell electronic devices Typical Application 20121157 FIGURE 1. Block Diagram Boomer ® is a registered trademark of National Semiconductor Corporation. © 2005 National Semiconductor Corporation DS201211 www.national.com LM4925 2 Cell, Single Ended Output, 40mW Stereo Headphone Audio Amplifier February 2005 LM4925 Connection Diagrams MSOP Package 20121158 Top View Order Number LM4925MM See NS Package Number MUB10A for MSOP LD Package 20121152 Top View Order Number LM4925SD See NS Package Number SDA10A www.national.com 2 LM4925 Typical Connections 20121159 FIGURE 2. Typical Capacitive Couple (SE) Output Configuration Circuit 20121167 FIGURE 3. Typical BTL Speaker Configuration Circuit 3 www.national.com LM4925 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. 3.8V Thermal Resistance −65˚C to +150˚C θJA (typ) MUB10A 175˚C/W −0.3V to VDD +0.3V θJA (typ) LDA10A 73˚C/W Supply Voltage Storage Temperature Input Voltage 220˚C Power Dissipation (Note 2) Internally limited ESD Susceptibility(Note 3) 2000V ESD Susceptibility (Note 4) 200V Junction Temperature Operating Ratings Temperature Range 150˚C TMIN ≤ TA ≤ TMAX Solder Information Small Outline Package Vapor Phase (60sec) −40˚C ≤ TA ≤ +85˚C 1.5V ≤ VDD ≤ 3.6V Supply Voltage 215˚C Electrical Characteristics VDD = 3.0V (Notes 1, 5) The following specifications apply for the circuit shown in Figure 2 for Single Ended Outputs (AV = 2.5V) and Figure 3 for BTL Outputs (AV-BTL = 2), unless otherwise specified. Limits apply for TA = 25˚C. Symbol Parameter Conditions LM4925 Typical Limit Units (Limits) (Note 6) (Note 7) IDD Quiescent Power Supply Current VIN = 0V, IO = 0A, RL = ∞ (Note 8) 1.0 1.6 mA (max) ISD Shutdown Current VSHUTDOWN = GND 0.1 1 µA (max) VOS Output Offset Voltage PO Output Power (Note 9) THD+N Total Harmonic Distortion + Noise VNO Output Voltage Noise Crosstalk PSRR Power Supply Rejection Ratio 2 10 mV (max) RL = 8Ω, BTL, Fig. 3, THD+N = 1%, f = 1kHz 410 350 mW (min) RL = 16Ω, Fig. 2, SE per Channel, THD+N = 1%, f = 1kHz 40 30 mW (min) 0.5 % (max) RL = 8Ω, BTL, PO = 300mW, Fig. 3, f = 1kHz 0.1 RL = 16Ω, SE, PO = 20mW per channel, Fig.2, f = 1kHz 0.05 20Hz to 20kHz, A-weighted, Input Referred, Single Ended Output, Fig. 2 10 µVRMS RL = 16Ω, Fig. 2 58 dB VRIPPLE = 200mVP-P sine wave CBYPASS = 4.7µF, RL = 8Ω f = 100Hz, BTL, Fig. 3 70 dB VRIPPLE = 200mVP-P sine wave CBYPASS = 4.7µF, RL = 16Ω f = 100Hz, SE, Fig. 2 68 dB VIH Control Logic High 1.5V ≤ VDD ≤ 3.6V 0.7VDD V (min) VIL Control Logic Low 1.5V ≤ VDD ≤ 3.6V 0.3VDD V (max) 1VPP Reference, Ri = 20k, Rf = 50k 70 dB (min) Mute Attenuation www.national.com 4 Symbol Parameter Conditions LM4925 Typical Limit (Note 6) (Note 7) 1.6 Units (Limits) IDD Quiescent Power Supply Current VIN = 0V, IO = 0A, RL = ∞ (Note 8) 0.9 ISD Shutdown Current VSHUTDOWN = GND 0.05 1 µA (max) VOS Output Offset Voltage 2 10 mV (max) RL = 8Ω, BTL, Fig. 3, THD+N = 1%, f = 1kHz 120 90 mW (min) RL = 16Ω, Fig. 2, SE per Channel, THD+N = 1%, f = 1kHz 10 7 mW (min) 0.5 % (max) PO Output Power (Note 9) THD+N Total Harmonic Distortion + Noise VNO Output Voltage Noise Crosstalk PSRR Power Supply Rejection Ratio mA (max) RL = 8Ω, BTL, PO = 50mW, Fig. 3, f = 1kHz 0.15 RL = 16Ω, SE, PO = 5mW per channel, Fig.2, f = 1kHz 0.1 20Hz to 20kHz, A-weighted, Input Referred, Single Ended Output, Fig. 2 10 µVRMS RL = 16Ω, Fig. 2 58 dB VRIPPLE = 200mVP-P sine wave CBYPASS = 4.7µF, RL = 8Ω f = 100Hz, BTL, Fig. 3 70 dB VRIPPLE = 200mVP-P sine wave CBYPASS = 4.7µF, RL = 16Ω f = 100Hz, SE, Fig. 2 68 dB VIH Control Logic High 1.5V ≤ VDD ≤ 3.6V 0.7VDD V (min) VIL Control Logic Low 1.5V ≤ VDD ≤ 3.6V 0.3VDD V (max) 1VPP Reference, Ri = 20k, Rf = 50k 70 dB (min) Mute Attenuation 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. Note 2: The maximum power dissipation is dictated by TJMAX, θJA, and the ambient temperature TA and must be derated at elevated temperatures. The maximum allowable power dissipation is PDMAX = (TJMAX − TA)/θJA. For the LM4925, TJMAX = 150˚C. For the θJAs, please see the Application Information section or the Absolute Maximum Ratings section. Note 3: Human body model, 100pF discharged through a 1.5kΩ 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 25˚C 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. 5 www.national.com LM4925 Electrical Characteristics VDD = 1.8V (Notes 1, 5) The following specifications apply for the circuit shown in Figure 2 for Single Ended Outputs (AV = 2.5V) and Figure 3 for BTL Outputs (AV-BTL = 2), unless otherwise specified. Limits apply for TA = 25˚C. LM4925 Typical Performance Characteristics THD+N vs Frequency VDD = 3V, SE, RL = 16Ω PO = 20mW per channel THD+N vs Frequency VDD = 1.8V, SE, RL = 16Ω PO = 5mW per channel 20121108 20121110 THD+N vs Frequency VDD = 3V, BTL, RL = 8Ω PO = 300mW THD+N vs Frequency VDD = 1.8V, BTL, RL = 8Ω PO = 50mW 20121107 20121109 THD+N vs Output Power VDD = 3V, SE, RL = 16Ω f = 1kHz, Both channels THD+N vs Output Power VDD = 1.8V, SE, RL = 16Ω f = 1kHz, Both channels 20121112 www.national.com 20121114 6 LM4925 Typical Performance Characteristics (Continued) THD+N vs Output Power VDD = 1.8V, BTL, RL = 8Ω f = 1kHz THD+N vs Output Power VDD = 3V, BTL, RL = 8Ω f = 1kHz 20121111 20121133 Output Power vs Supply Voltage RL = 8Ω, BTL, f = 1kHz Output Noise vs Frequency 20121106 20121115 Output Power vs Load Resistance VDD = 1.8V, BTL, f = 1kHz Output Power vs Supply Voltage RL = 16Ω, SE, f = 1kHz 20121117 20121116 7 www.national.com LM4925 Typical Performance Characteristics (Continued) Output Power vs Load Resistance VDD = 1.8V, SE, f = 1kHz Output Power vs Load Resistance VDD = 3V, BTL, f = 1kHz 20121134 20121119 Output Power vs Supply Voltage RL = 8Ω, BTL, f = 1kHz Output Power vs Load Resistance VDD = 3V, SE, f = 1kHz 20121120 20121121 Power Dissipation vs Output Power VDD = 1.8V, RL = 8Ω, BTL, f = 1kHz Power Dissipation vs Output Power VDD = 1.8V, RL = 16Ω, SE, f = 1kHz 20121123 20121124 www.national.com 8 LM4925 Typical Performance Characteristics (Continued) Power Dissipation vs Output Power VDD = 3V, RL = 8Ω, BTL, f = 1kHz Power Dissipation vs Output Power VDD = 3V, RL = 16Ω, SE, f = 1kHz 20121125 20121126 Power Supply Rejection vs Frequency VDD = 1.8V, RL = 16Ω, SE VRIPPLE = 200mVp-p, AV = 2.5V/V Power Supply Rejection vs Frequency VDD = 1.8V, RL = 8Ω, BTL VRIPPLE = 200mVp-p, AV-BTL = 2V/V 20121130 20121129 Power Supply Rejection vs Frequency VDD = 3V, RL = 16Ω, SE VRIPPLE = 200mVp-p, AV = 2.5V/V Power Supply Rejection vs Frequency VDD = 3V, RL = 8Ω, BTL VRIPPLE = 200mVp-p, AV-BTL = 2V/V 20121131 20121132 9 www.national.com LM4925 A bridge configuration, such as the one used in LM4925, also creates a second advantage over single-ended amplifiers. Since the differential outputs, VoA and VoB, 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. Application Information BRIDGE (BTL) CONFIGURATION EXPLANATION The LM4925 is a stereo audio power amplifier capable of operating in bridged (BTL) mode. As shown in Figure 3, the LM4925 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 Ri while the second amplifier’s gain is fixed by the two external 20kΩ 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 MODE SELECT DETAIL The LM4925 can be configured for either single ended (see Figure 2 ) or BTL mode (see Figure 3). When the SE/BTL pin has a logic high (VDD) applied to it, the LM4925 is in BTL mode. If a logic low (GND) is applied to SE/BTL, the LM4925 operates in single-ended mode. The slew rate of VDD must be greater than 2.5V/ms to ensure reliable Power on reset (POR). 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 LM4925. This circuit shows the LM4925 with a 25-50kΩ. Pull-up resistor connected from the shutdown pin to VDD. The shutdown pin of the LM4925 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 LM4925 by either allowing shutdown to be high before the LM4925 powers on (the microcontroller powers up first) or allows shutdown to ramp up with VDD (the LM4925 powers up first). This will ensure the LM4925 powers up properly and enters the correct mode of operation (BTL or SE). Please note that the SE/BTL pin should be tied to GND for single-ended (SE) mode, and to Vdd for BTL mode. AVD = 2 * (Rf / Ri) By driving the load differentially through outputs VoA and VoB, an amplifier configuration commonly referred to as “bridged mode” is established. Bridged mode operation is different from the classical single-ended amplifier configuration where one side of the load is connected to ground. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage. Four times the output power is possible as compared to a single-ended amplifier under the same conditions. This increase in attainable output power assumes that the amplifier is not current limited or clipped. In order to choose an amplifier’s closed-loop gain without causing excessive clipping, please refer to the Audio Power Amplifier Design section. 20121161 FIGURE 4. Recommended Circuit for Different Supply Turn-On Timing www.national.com 10 MICRO POWER SHUTDOWN (Continued) The voltage applied to the SHUTDOWN pin controls the LM4925’s shutdown function. Activate micro-power shutdown by applying a logic-low voltage to the SHUTDOWN pin. When active, the LM4925’s micro-power shutdown feature turns off the amplifier’s bias circuitry, reducing the supply current. 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 100kΩ 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. Shutdown enable/disable times are controlled by a combination of Cbypass and VDD. Larger values of Cbypass results in longer turn on/off times from Shutdown. Longer shutdown times also improve the LM4925’s resistance to click and pop upon entering or returning from shutdown. For a 3.0V supply and Cbypass = 4.7µF, the LM4925 requires about 2 seconds to enter or return from shutdown. This longer shutdown time enables the LM4925 to have virtually zero pop and click transients upon entering or release from shutdown. Smaller values of Cbypass will decrease turn-on time, but at the cost of increased pop and click and reduced PSRR. When the LM4925 is in shutdown, the outputs become very low impedance (less than 5Ω to GND). POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged (BTL) 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 LM4925 has two operational amplifiers in one package, the maximum internal power dissipation in BTL mode is 4 times that of a single-ended amplifier. The maximum power dissipation for a given application can be derived from the power dissipation graphs or from Equation 1. PDMAX = 4 * (VDD) 2 / (2π2RL) (1) 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 / (2π2RL) (2) Since the LM4925 has two operational amplifiers in one package, the maximum internal power dissipation point is twice that of the number that results from Equation 2. The maximum power dissipation point obtained from either Equations 1, 2 must not be greater than the power dissipation that results from Equation 3: PDMAX = (TJMAX - TA) / θJA (3) For package MUB10A, θJA = 175˚C/W. TJMAX = 150˚C for the LM4925. 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 3.0V power supply, with an 16Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 129˚C 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. MUTE The LM4925 also features a mute function that enables extremely fast turn-on/turn-off with a minimum of output pop and click. 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 activation techniques match those given for the shutdown function as well. 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 LM4925 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. The LM4925 is unity-gain stable that gives the designer maximum system flexibility. The LM4925 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 1MΩ. 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 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 3.0V regulator) with 10µF 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 LM4925. A bypass capacitor value in the range of 0.1µF to 4.7µF is recommended. 11 www.national.com LM4925 Application Information LM4925 Application Information that allows the LM4925to 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. (Continued) filter that limits low frequency response. This value should be chosen based on needed frequency response and turn-on time. 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 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 0.1µF to 0.47µF), is recommended. (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. fL = 100Hz/5 = 20Hz AUDIO POWER AMPLIFIER DESIGN fH = 20kHz * 5 = 100kHz A 25mW/32Ω Audio Amplifier Given: Power Output Load Impedance Input Level Input Impedance As stated in the External Components section, Ri in conjunction with Ci creates a 10mWrms 16Ω 0.4Vrms Ci ≥ 1 / (2π * 20kΩ * 20Hz) = 0.397µF; use 0.39µF. 20kΩ 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 LM4925GBWP of 3MHz. This example displays that if a designer has a need to design an amplifier with higher differential gain, the LM4925can still be used without running into bandwidth limitations. 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. 3.0V is a standard voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom www.national.com 12 LM4925 Application Information (Continued) LM4925 BOARD ARTWORK Composite View Silk Screen 20121164 20121165 Top Layer Bottom Layer 20121163 20121166 13 www.national.com LM4925 Physical Dimensions inches (millimeters) unless otherwise noted MSOP Package Order Number LM4925MM NS Package Number MUB10A LD Package Order Number LM4925LD NS Package Number LDA10A www.national.com 14 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. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. National Semiconductor Americas Customer Support Center Email: [email protected] Tel: 1-800-272-9959 www.national.com National Semiconductor Europe Customer Support Center Fax: +49 (0) 180-530 85 86 Email: [email protected] Deutsch Tel: +49 (0) 69 9508 6208 English Tel: +44 (0) 870 24 0 2171 Français Tel: +33 (0) 1 41 91 8790 National Semiconductor Asia Pacific Customer Support Center Email: [email protected] National Semiconductor Japan Customer Support Center Fax: 81-3-5639-7507 Email: [email protected] Tel: 81-3-5639-7560 LM4925 2 Cell, Single Ended Output, 40mW Stereo Headphone Audio Amplifier Notes