LM4862M

LM4862 www.ti.com SNAS102F – MAY 1997 – REVISED MAY 2013 LM4862 675 mW Audio Power Amplifier with Shutdown Mode Check for Samples: LM4862 FEATURES DESCRIPTION • The LM4862 is a bridge-connected audio power amplifier capable of delivering typically 675mW of continuous average power to an 8Ω load with 1% THD+N from a 5V power supply. 1 2 • • • • No Output Coupling Capacitors, Bootstrap Capacitors or Snubber Circuits are Necessary Small Outline or PDIP Packaging Unity-Gain Stable External Gain Configuration Capability Pin Compatible with LM4861 APPLICATIONS • • • Portable Computers Cellular Phones Toys and Games KEY SPECIFICATIONS • • • Boomer audio power amplifiers were designed specifically to provide high quality output power with a minimal amount of external components. Since the LM4862 does not require output coupling capacitors, bootstrap capacitors, or snubber networks, it is optimally suited for low-power portable systems. The LM4862 features an externally controlled, lowpower consumption shutdown mode, as well as an internal thermal shutdown protection mechanism. The unity-gain stable LM4862 can be configured by external gain-setting resistors. THD+N for 500mW Continuous Average Output Power at 1kHz into 8Ω 1% (max) Output Power at 10% THD+N at 1kHz into 8Ω 825 mW (typ) Shutdown Current 0.7μA (typ) Typical Application Connection Diagram *Refer to Application Information for information concerning proper selection of the input coupling capacitor. Figure 1. Typical Audio Amplifier Application Circuit Figure 2. Small Outline and PDIP Package-Top View See Package Number D0008A or P0008E 1 2 Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet. All trademarks are the property of their respective owners. PRODUCTION DATA information is current as of publication date. Products conform to specifications per the terms of the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 1997–2013, Texas Instruments Incorporated LM4862 SNAS102F – MAY 1997 – REVISED MAY 2013 www.ti.com These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates. Absolute Maximum Ratings (1) (2) Supply Voltage 6.0V −65°C to +150°C Storage Temperature −0.3V to VDD + 0.3V Input Voltage (3) Internally limited ESD Susceptibility (4) 2000V ESD Susceptibility (5) 200V Power Dissipation Junction Temperature Soldering Information Thermal Resistance (1) (2) (3) (4) (5) 150°C Small Outline Package Vapor Phase (60 sec.) 215°C Infrared (15 sec.) 220°C θJC (typ)—D0008A 35°C/W θJA (typ)—D0008A 170°C/W θJC (typ)—P0008E 37°C/W θJA (typ)—P0008E 107°C/W 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication of device performance. If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and specifications The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TMAX − TA)/θJA. For the LM4862, TJMAX = 150°C. The typical junction-toambient thermal resistance, when board mounted, is 170°C/W for package number D0008A and is 107°C/W for package number P0008E. Human body model, 100 pF discharged through a 1.5 kΩ resistor. Machine Model, 200 pF–240 pF discharged through all pins. Operating Ratings Temperature Range TMIN ≤ TA ≤ TMAX 2 −40°C ≤ TA ≤ 85°C 2.7V ≤ VDD ≤ 5.5V Supply Voltage Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 LM4862 www.ti.com SNAS102F – MAY 1997 – REVISED MAY 2013 Electrical Characteristics (1) (2) The following specifications apply for VDD = 5V unless otherwise specified. Limits apply for TA = 25°C. Symbol Parameter Conditions LM4862 Typical VDD Supply Voltage (3) Limit (4) Units (Limits) 2.7 V (min) 5.5 V (max) 6.0 mA (max) IDD Quiescent Power Supply Current VIN = 0V, IO = 0A (5) 3.6 ISD Shutdown Current VPIN1 = VDD 0.7 5 μA (max) VOS Output Offset Voltage VIN = 0V 5 50 mV (max) PO Output Power THD = 1% (max); f = 1 kHz; RL = 8Ω 675 500 mW (min) THD + N = 10%; f = 1 kHz; RL = 8Ω 825 mW THD + N Total Harmonic Distortion + Noise PO = 500 mWrms; RL = 8Ω AVD = 2; 20 Hz ≤ f ≤ 20 kHz 0.55 % PSRR Power Supply Rejection Ratio VDD = 4.9V to 5.1V 50 dB (1) (2) (3) (4) (5) All voltages are measured with respect to the ground pin, unless otherwise specified. 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 ensure specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not ensured for parameters where no limit is given, however, the typical value is a good indication of device performance. Typicals are measured at 25°C and represent the parametric norm. Limits are ensured to TI's AOQL (Average Outgoing Quality Level). The quiescent power supply current depends on the offset voltage when a practical load is connected to the amplifier. Automatic Switching Circuit Figure 3. Automatic Switching Circuit Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 3 LM4862 SNAS102F – MAY 1997 – REVISED MAY 2013 www.ti.com External Components Description (Figure 1) Components Functional Description 1. Ri Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also forms a high pass filter with Ci at fc = 1/(2πRiCI). 2. Ci Input coupling capacitor which blocks the DC voltage at the amplifier's input terminals. Also creates a highpass filter with Ri at fc = 1/(2πRiCi). Refer to PROPER SELECTION OF EXTERNAL COMPONENTS for an explanation of how to determine the value of Ci. 3. RF Feedback resistance which sets the closed-loop gain in conjunction with Ri. 4. CS Supply bypass capacitor which provides power supply filtering. Refer to POWER SUPPLY BYPASSING for proper placement and selection of the supply bypass capacitor. 5. CB Bypass pin capacitor which provides half-supply filtering. Refer to PROPER SELECTION OF EXTERNAL COMPONENTS for proper placement and selection of the half-supply bypass capacitor. 4 Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 LM4862 www.ti.com SNAS102F – MAY 1997 – REVISED MAY 2013 Typical Performance Characteristics THD+N vs Frequency THD+N vs Frequency Figure 4. Figure 5. THD+N vs Frequency THD+N vs Output Power Figure 6. Figure 7. THD+N vs Output Power THD+N vs Output Power Figure 8. Figure 9. Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 5 LM4862 SNAS102F – MAY 1997 – REVISED MAY 2013 www.ti.com Typical Performance Characteristics (continued) 6 Output Power vs Supply Voltage Output Power vs Supply Voltage Figure 10. Figure 11. Output Power vs Supply Voltage Output Power vs Load Resistance Figure 12. Figure 13. Power Dissipation vs Output Power Power Derating Curve Figure 14. Figure 15. Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 LM4862 www.ti.com SNAS102F – MAY 1997 – REVISED MAY 2013 Typical Performance Characteristics (continued) Dropout Voltage vs Power Supply Noise Floor Figure 16. Figure 17. Frequency Response vs Input Capacitor Size Power Supply Rejection Ratio Figure 18. Figure 19. Open Loop Frequency Response Supply Current vs Supply Voltage Figure 20. Figure 21. Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 7 LM4862 SNAS102F – MAY 1997 – REVISED MAY 2013 www.ti.com APPLICATION INFORMATION BRIDGE CONFIGURATION EXPLANATION As shown in Figure 1, the LM4862 has two operational amplifiers internally, allowing for a few different amplifier configurations. The first amplifier's gain is externally configurable, while the second amplifier is internally fixed in a unity-gain, inverting configuration. The closed-loop gain of the first amplifier is set by selecting the ratio of Rf to Ri while the second amplifier's gain is fixed by the two internal 10 kΩ resistors. Figure 1 shows that the output of amplifier one serves as the input to amplifier two which results in both amplifiers producing signals identical in magnitude, but out of phase 180°. Consequently, the differential gain for the IC is AVD = 2*(Rf/Ri) (1) By driving the load differentially through outputs Vo1 and Vo2, an amplifier configuration commonly referred to as “bridged mode” is established. Bridged mode operation is different from the classical single-ended amplifier configuration where one side of the load is connected to ground. A bridge amplifier design has a few distinct advantages over the single-ended configuration, as it provides differential drive to the load, thus doubling output swing for a specified supply voltage. Consequently, 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 which will damage high frequency transducers used in loudspeaker systems, please refer to AUDIO POWER AMPLIFIER DESIGN. A bridge configuration, such as the one used in LM4862, 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, singleended amplifier configuration. Without an output coupling capacitor, the half-supply bias across the load would result in both increased internal lC power dissipation and also permanent loudspeaker damage. POWER DISSIPATION Power dissipation is a major concern when designing a successful amplifier, whether the amplifier is bridged or single-ended. A direct consequence of the increased power delivered to the load by a bridge amplifier is an increase in internal power dissipation. Equation 2 states the maximum power dissipation point for a bridge amplifier operating at a given supply voltage and driving a specified output load. PDMAX = 4*(VDD)2/(2π2RL) (2) Since the LM4862 has two operational amplifiers in one package, the maximum internal power dissipation is 4 times that of a single-ended amplifier. Even with this substantial increase in power dissipation, the LM4862 does not require heatsinking. From Equation 2, assuming a 5V power supply and an 8Ω load, the maximum power dissipation point is 625 mW. The maximum power dissipation point obtained from Equation 2 must not be greater than the power dissipation that results from Equation 3: PDMAX = (TJMAX–TA)/θJA (3) For package D0008A, θJA = 170°C/W and for package P0008E, θJA = 107°C/W. TJMAX = 150°C for the LM4862. 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 2 is greater than that of Equation 3, then either the supply voltage must be decreased, the load impedance increased, or the ambient temperature reduced. For the typical application of a 5V power supply, with an 8Ω load, the maximum ambient temperature possible without violating the maximum junction temperature is approximately 44°C provided that device operation is around the maximum power dissipation point. Power dissipation is a function of output power and thus, if typical operation is not around the maximum power dissipation point, the ambient temperature can be increased. Refer to Typical Performance Characteristics for power dissipation information for lower output powers. 8 Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 LM4862 www.ti.com SNAS102F – MAY 1997 – REVISED MAY 2013 POWER SUPPLY BYPASSING As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply rejection. The capacitor location on both the bypass and power supply pins should be as close to the device as possible. As displayed in Typical Performance Characteristics, the effect of a larger half supply bypass capacitor is improved PSSR due to increased half-supply stability. Typical applications employ a 5V regulator with 10 μF and a 0.1 μF bypass capacitors which aid in supply stability, but do not eliminate the need for bypassing the supply nodes of the LM4862. The selection of bypass capacitors, especially CB, is thus dependant upon desired PSSR requirements, click and pop performance as explained in PROPER SELECTION OF EXTERNAL COMPONENTS, system cost, and size constraints. SHUTDOWN FUNCTION In order to reduce power consumption while not in use, the LM4862 contains a shutdown pin to externally turn off the amplifier's bias circuitry. The shutdown feature turns the amplifier off when a logic high is placed on the shutdown pin. The trigger point between a logic low and logic high level is typically half supply. It is best to switch between ground and supply to provide maximum device performance. By switching the shutdown pin to VDD, the LM4862 supply current draw will be minimized in idle mode. While the device will be disabled with shutdown pin voltages less than VDD, the idle current may be greater than the typical value of 0.7 μA. In either case, the shutdown pin should be tied to a definite voltage because leaving the pin floating may result in an unwanted shutdown condition. In many applications, a microcontroller or microprocessor output is used to control the shutdown circuitry which provides a quick, smooth transition into shutdown. Another solution is to use a single-pole, single-throw switch that when closed, is connected to ground and enables the amplifier. If the switch is open, then a soft pull-up resistor of 47 kΩ will disable the LM4862. There are no soft pull-down resistors inside the LM4862, so a definite shutdown pin voltage must be applied externally, or the internal logic gate will be left floating which could disable the amplifier unexpectedly. AUTOMATIC SWITCHING CIRCUIT As shown in Figure 3, the LM4862 and the LM4880 can be set up to automatically switch on and off depending on whether headphones are plugged in. The LM4880 is used to drive a stereo single ended load, while the LM4862 drives a bridged internal speaker. The Automatic Switching Circuit is based upon a single control pin common in many headphone jacks which forms a normally closed switch with one of the output pins. The output of this circuit (the voltage on pin 5 of the LM4880) has two states based on the position of the switch. When the switch inside the headphone jack is open, the LM4880 is enabled and the LM4862 is disabled since the NMOS inverter is on. If a headphone jack is not present, it is assumed that the internal speakers should be on and the external speakers should be off. Thus the voltage on the LM4862 shutdown pin is low and the voltage on the LM4880 shutdown pin is high. The operation of this circuit is rather simple. With the switch closed, RP and RO form a resistor divider which produces a gate voltage of less than 50 mV. The gate voltage keeps the NMOS inverter off and RSD pulls the shutdown pin of the LM4880 to the supply voltage. This shuts down the LM4880 and places the LM4862 in its normal mode of operation. When the switch is open, the opposite condition is produced. Resistor RP pulls the gate of the NMOS high which turns on the inverter and produces a logic low signal on the shutdown pin of the LM4880. This state enables the LM4880 and places the LM4862 in shutdown mode. Only one channel of this circuit is shown in Figure 3 to keep the drawing simple but a typical application would be a LM4880 driving a stereo headphone jack and two LM4862's driving a pair of internal speakers. If a single internal speaker is required, one LM4862 can be used as a summer to mix the left and right inputs into a mono channel. 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 LM4862 is tolerant of external component combinations, consideration to component values must be used to maximize overall system quality. Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 9 LM4862 SNAS102F – MAY 1997 – REVISED MAY 2013 www.ti.com The LM4862 is unity-gain stable which gives a designer maximum system flexibility. The LM4862 should be used in low gain configurations to minimize THD+N values, and maximize the signal to noise ratio. Low gain configurations require large input signals to obtain a given output power. Input signals equal to or greater than 1 Vrms are available from sources such as audio codecs. Please refer to 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 band-width is dictated by the choice of external components shown in Figure 1. The input coupling capacitor, Ci, forms a first order high pass filter which limits low frequency response. This value should be chosen based on needed frequency response for a few distinct reasons. Selection of Input Capacitor Size Large input capacitors are both expensive and space hungry for portable designs. Clearly, a certain sized capacitor is needed to couple in low frequencies without severe attenuation. But in many cases the speakers used in portable systems, whether internal or external, have little ability to reproduce signals below 100–150 Hz. Thus using a large input capacitor may not increase system performance. In addition to system cost and size, click and pop performance is effected by the size of the input coupling capacitor, Ci. A larger input coupling capacitor requires more charge to reach its quiescent DC voltage (nominally ½ VDD). This charge comes from the output via the feedback and is apt to create pops upon device enable. Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be minimized. Besides minimizing the input capacitor size, careful consideration should be paid to the bypass capacitor value. Bypass capacitor, CB, is the most critical component to minimize turn-on pops since it determines how fast the LM4862 turns on. The slower the LM4862's outputs ramp to their quiescent DC voltage (nominally ½ VDD), the smaller the turn-on pop. Choosing CB equal to 1.0 μF along with a small value of Ci (in the range of 0.1 μF to 0.39 μF), should produce a virtually clickless and popless shutdown function. While the device will function properly, (no oscillations or motorboating), with CB equal to 0.1 μF, the device will be much more susceptible to turn-on clicks and pops. Thus, a value of CB equal to 1.0 μF or larger is recommended in all but the most cost sensitive designs. AUDIO POWER AMPLIFIER DESIGN Design a 500 mW/8Ω Audio Amplifier Given: Power Output 500 mWrms Load Impedance 8Ω Input Level 1 Vrms Input Impedance 20 kΩ Bandwidth 100 Hz–20 kHz ± 0.25 dB A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating from Figure 10, Figure 11, and Figure 12 in Typical Performance Characteristics, the supply rail can be easily found. A second way to determine the minimum supply rail is to calculate the required Vopeak using Equation 4 and add the dropout voltage. Using this method, the minimum supply voltage would be (Vopeak + (2*VOD)), where VOD is extrapolated from the Figure 16 in Typical Performance Characteristics. (4) Using the Output Power vs Supply Voltage graph for an 8Ω load, the minimum supply rail is 4.3V. But since 5V is a standard supply voltage in most applications, it is chosen for the supply rail. Extra supply voltage creates headroom that allows the LM4862 to reproduce peaks in excess of 500 mW without clipping the signal. 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 POWER DISSIPATION. Once the power dissipation equations have been addressed, the required differential gain can be determined from Equation 5. (5) (6) Rf/Ri = AVD/2 10 Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 LM4862 www.ti.com SNAS102F – MAY 1997 – REVISED MAY 2013 From Equation 5, the minimum AVD is 2; use AVD = 2. Since the desired input impedance was 20 kΩ, and with a AVD of 2, a ratio of 1:1 of Rf to Ri results in an allocation of Ri = Rf = 20 kΩ. The final design step is to address the bandwidth requirements which must be stated as a pair of −3 dB frequency points. Five times away from a –3 dB point is 0.17 dB down from passband response which is better than the required ±0.25 dB specified. This fact results in a low and high frequency pole of 20 Hz and 100 kHz respectively. As stated in External Components Description , Ri in conjunction with Ci create a highpass filter. Ci ≥ 1/(2π*20 kΩ*20 Hz) = 0.397 μF; use 0.39 μF. (7) The high frequency pole is determined by the product of the desired high frequency pole, fH, and the differential gain, AVD. With an AVD = 2 and fH = 100 kHz, the resulting GBWP = 100 kHz which is much smaller than the LM4862 GBWP of 12.5 MHz. This figure displays that if a designer has a need to design an amplifier with a higher differential gain, the LM4862 can still be used without running into bandwidth problems. Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 11 LM4862 SNAS102F – MAY 1997 – REVISED MAY 2013 www.ti.com REVISION HISTORY Changes from Revision E (May 2013) to Revision F • 12 Page Changed layout of National Data Sheet to TI format .......................................................................................................... 11 Submit Documentation Feedback Copyright © 1997–2013, Texas Instruments Incorporated Product Folder Links: LM4862 PACKAGE OPTION ADDENDUM www.ti.com 30-Sep-2021 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan (2) Lead finish/ Ball material MSL Peak Temp Op Temp (°C) Device Marking (3) (4/5) (6) LM4862M ACTIVE SOIC D 8 95 Non-RoHS & Green Call TI Level-1-235C-UNLIM -40 to 85 LM 4862M LM4862M/NOPB ACTIVE SOIC D 8 95 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 LM 4862M LM4862MX/NOPB ACTIVE SOIC D 8 2500 RoHS & Green SN Level-1-260C-UNLIM -40 to 85 LM 4862M (1) The marketing status values are defined as follows: ACTIVE: Product device recommended for new designs. LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect. NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design. PREVIEW: Device has been announced but is not in production. Samples may or may not be available. OBSOLETE: TI has discontinued the production of the device. (2) RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may reference these types of products as "Pb-Free". RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption. Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of