LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 LM4702 Audio Power Amplifier Series Stereo High Fidelity 200 Volt Driver with Mute Check for Samples: LM4702 FEATURES DESCRIPTION * * * * * The LM4702 is a high fidelity audio power amplifier driver designed for demanding consumer and proaudio applications. Amplifier output power may be scaled by changing the supply voltage and number of output devices. The LM4702 is capable of delivering in excess of 300 watts per channel single ended into an 8 ohm load in the presence of 10% high line headroom and 20% supply regulation. 1 2 Very High Voltage Operation Scalable Output Power Minimum External Components External Compensation Thermal Shutdown and Mute APPLICATIONS * * * * AV Receivers Audiophile Power Amps Pro Audio High Voltage Industrial Applications KEY SPECIFICATIONS * * * * (1) Wide operating voltage range: - LM4702A (1) (in development): 20V to 100V - LM4702B: 20V to 100V - LM4702C: 20V to 75V Equivalent Noise: 3V PSRR: 110dB (typ) THD+N (A and B Grades): 0.0003% The LM4702 includes thermal shut down circuitry that activates when the die temperature exceeds 150C. The LM4702's mute function, when activated, mutes the input drive signal and forces the amplifier output to a quiescent state. The LM4702 is available in 3 grades that span a wide range of applications and performance levels. The LM4702C is targeted at high volume applications. The LM4702B includes a higher voltage rating along with the tighter specifications. The LM4702A(1) (in development) is the premium part with the highest voltage rating, fully specified with limits over voltage and temperature, and is offered in a military 883 compliant TO-3 package. Tentative Max Operating voltage for the LM4702A (in development). 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. UNLESS OTHERWISE NOTED this document contains PRODUCTION DATA information current as of publication date. Products conform to specifications per the terms of Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright (c) 2005-2013, Texas Instruments Incorporated LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com TYPICAL APPLICATION Figure 1. Typical Audio Amplifier Application Circuit 2 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 CONNECTION DIAGRAM 2 LM 0 47 Figure 2. 15-Lead TO-220 (NDL Package) (for LM4702B and LM4702C) Top View A. The 15-lead NDL is a non-isolated package. The package's metal back and any heat sink to which it is mounted are connected to the Vee potential when using only thermal compound. If a mica washer is used in addition to thermal compound, CS (case to sink) is increased, but the heat sink will be electrically isolated from Vee. Figure 3. 15-Lead TO-220 (NDL Package) (for LM4702B and LM4702C) 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. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 3 LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com ABSOLUTE MAXIMUM RATINGS (1) (2) (3) C Part Supply Voltage |V+| + |V-| 200V A, B Parts 200V Differential Input Voltage +/-6V Common Mode Input Range 0.4 Vee to 0.4 Vcc (4) 4W ESD Susceptibility (5) 1.5kV Power Dissipation ESD Susceptibility (6) Junction Temperature (TJMAX) 200V (7) Soldering Information 150C NDL Package (10 seconds) (8) Storage Temperature Thermal Resistance (1) (2) (3) (4) (5) (6) (7) (8) 260C -40C to +150C JA 30C/W JC 1C/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 condition 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's performance. All voltages are measured with respect to the ground pins, unless otherwise specified. 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 de-rated at elevated temperatures and is dictated by TJMAX, JC, and the ambient temperature TA. The maximum allowable power dissipation is PDMAX = (TJMAX -TA)/JC or the number given in the Absolute Maximum Ratings, whichever is lower. For the LM4702, TJMAX = 150C and the typical JC is 1C/W. Refer to the Thermal Considerations section for more information. Human body model, 100pF discharged through a 1.5k resistor. Machine Model: a 220pF - 240pF discharged through all pins. The maximum operating junction temperature is 150C. The 15-lead NDL is a non-isolated package. The package's metal back and any heat sink to which it is mounted are connected to the Vee potential when using only thermal compound. If a mica washer is used in addition to thermal compound, CS (case to sink) is increased, but the heat sink will be electrically isolated from Vee. OPERATING RATINGS (1) (2) Temperature Range (TMIN TA TMAX) Supply Voltage |V+| + |V-| (1) (2) 4 -20C TA +75C LM4702A (in development) +/-20V VTOTAL +/-100V LM4702B +/-20V VTOTAL +/-100V LM4702C +/-20V VTOTAL +/-75V All voltages are measured with respect to the ground pins, 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 condition 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's performance. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 ELECTRICAL CHARACTERISTICS (LM4702C) Vcc = +75V, Vee = -75V (1) (2) The following specifications apply for IMUTE = 1.5mA, Figure 19, unless otherwise specified. Limits apply for TA = 25C. Symbol Parameter Conditions LM4702 Typical (3) Limit (4) (5) Units (Limits) 30 mA (max) ICC Total Quiescent Power Supply Current VCM = 0V, VO = 0V, IO = 0A THD+N Total Harmonic Distortion + Noise No load, AV = 30dB VOUT = 14VRMS @ 1kHz RS Input Bias Resistor Av Closed Loop Voltage Gain Av open Open Loop Gain Vin = 1mVrms, f = 1KHz, C = 30pF 93 dB Vom Output Voltage Swing THD = 0.05%, Freq = 20Hz to 20KHz 51 Vrms (min) Vnoise Output Noise Rs = 10k, LPF = 30kHz, Av = 30dB A-weighted 150 IOUT Output Current Current from Source to Sink Pins 5.5 3 10 mA(min) mA (max) Imute Current into Mute Pin To put part in "play" mode 1.5 1 2 mA(min) mA (max) XTALK Channel Separation (6) f = 1kHz @ Av = 30dB 85 dB SR Slew Rate VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted 15 V/s VOS Input Offset Voltage VCM = 0V, IO = 0mA 10 IB Input Bias Current VCM = 0V, IO = 0mA 500 Power Supply Rejection Ratio Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 110 PSRR (1) (2) (3) (4) (5) (6) 25 0.005 50 % 100 k (max) 26 dB (min) 300 V (max) V 90 35 mV (max) nA 95 dB (min) All voltages are measured with respect to the ground pins, 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 condition 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's performance. Typical specifications are measured at 25C and represent the parametric norm. Tested limits are specified to AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are specified by design, test, or statistical analysis. PCB layout will affect cross talk. It is recommended that input and output traces be separated by as much distance as possible. Return ground traces from outputs should be independent back to a single ground point and use as wide of traces as possible. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 5 LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com ELECTRICAL CHARACTERISTICS (LM4702C) Vcc = +50V, Vee = -50V (1) (2) The following specifications apply for IMUTE = 1.5mA, Figure 19, unless otherwise specified. Limits apply for TA = 25C. Symbol Parameter Conditions LM4702 Typical (3) Limit (4) (5) Units (Limits) 30 mA (max) ICC Total Quiescent Power Supply Current VCM = 0V, VO = 0V, IO = 0A THD+N Total Harmonic Distortion + Noise No load, AV = 30dB VOUT = 10VRMS @ 1kHz RS Input Bias Resistor Av Closed Loop Voltage Gain Av open Open Loop Gain Vin = 1mVrms, f = 1KHz, C = 30pF 93 dB Vom Output Voltage Swing THD = 0.05%, Freq = 20Hz to 20KHz 33 Vrms (min) Vnoise Output Noise Rs = 10k, LPF = 30kHz, Av = 30dB A-weighted 150 IOUT Output Current Outputs Shorted 5.2 3 10 mA(min) mA (max) Imute Current into Mute Pin To put part in "play" mode 1.5 1 2 mA(min) mA (max) XTALK Channel Separation (6) f = 1kHz at Av = 30dB 85 dB SR Slew Rate VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted 15 V/s VOS Input Offset Voltage VCM = 0V, IO = 0mA 10 IB Input Bias Current VCM = 0V, IO = 0mA 500 Power Supply Rejection Ratio Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 110 PSRR (1) (2) (3) (4) (5) (6) 6 22 0.005 50 % 100 k (max) 26 dB (min) 300 V (max) V 90 35 mV (max) nA 95 dB (min) All voltages are measured with respect to the ground pins, 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 condition 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's performance. Typical specifications are measured at 25C and represent the parametric norm. Tested limits are specified to AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are specified by design, test, or statistical analysis. PCB layout will affect cross talk. It is recommended that input and output traces be separated by as much distance as possible. Return ground traces from outputs should be independent back to a single ground point and use as wide of traces as possible. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 ELECTRICAL CHARACTERISTICS (LM4702B) Vcc = +100V, Vee = -100V (1) (2) The following specifications apply for IMUTE = 1.5mA, Figure 19, unless otherwise specified. Limits apply for TA = 25C. Symbol Parameter Conditions LM4702 Limit (4) (5) Units (Limits) 27 35 mA (max) 0.0003 0.001 % (max) 50 100 k (max) 26 dB (min) Typical (3) ICC Total Quiescent Power Supply Current VCM = 0V, VO = 0V, IO = 0A THD+N Total Harmonic Distortion + Noise No load, AV = 30dB VOUT = 20VRMS @ 1kHz RS Input Bias Resistor Av Closed Loop Voltage Gain Av open Open Loop Gain Vin = 1mVrms, f = 1KHz, C = 30pF 93 dB Vom Output Voltage Swing THD = 0.05%, Freq = 20Hz to 20KHz 67 Vrms (min) Vnoise Output Noise Rs = 10k, LPF = 30kHz, Av = 30dB A-weighted 150 IOUT Output Current Outputs Shorted 5.5 3 8 mA(min) mA (max) Imute Current into Mute Pin To put part in "play" mode 1.5 1 2 mA(min) mA (max) XTALK Channel Separation (6) f = 1kHz at Av = 30dB 87 85 dB (min) SR Slew Rate VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted 17 15 V/s (min) VOS Input Offset Voltage VCM = 0V, IO = 0mA 14 40 mV (max) IB Input Bias Current VCM = 0V, IO = 0mA 200 Power Supply Rejection Ratio Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 110 PSRR (1) (2) (3) (4) (5) (6) 300 90 V (max) nA (max) 100 dB (min) All voltages are measured with respect to the ground pins, 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 condition 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's performance. Typical specifications are measured at 25C and represent the parametric norm. Tested limits are specified to AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are specified by design, test, or statistical analysis. PCB layout will affect cross talk. It is recommended that input and output traces be separated by as much distance as possible. Return ground traces from outputs should be independent back to a single ground point and use as wide of traces as possible. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 7 LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com ELECTRICAL CHARACTERISTICS (LM4702A) Vcc = +100V, Vee = -100V (1) (2) (PRE-RELEASE INFORMATION) The following specifications apply for IMUTE = 1.5mA, Figure 19, unless otherwise specified. Limits apply for TA = 25C. Symbol Total Quiescent Power Supply Current ICC LM4702 Limit (4) (5) Units (Limits) 27 TBD mA (max) f = 1kHz 0.001 TBD f = 10kHz TBD TBD f = 100Hz TBD TBD 50 TBD k (max) TBD dB (min) Parameter Conditions VCM = 0V, VO = 0V, IO = 0A Typical (3) No load, AV = 30dB VOUT = 20VRMS Total Harmonic Distortion + Noise THD+N % (max) RS Input Bias Resistor Av Closed Loop Voltage Gain Av open Open Loop Gain Vin = 1mVrms, f = 1KHz, C = 30pF Vom Output Voltage Swing THD = 0.05%, Freq = 20Hz to 20KHz 57 TBD Vrms (min) Vnoise Output Noise Rs = 10k, LPF = 30kHz, Av = 30dB A-weighted 100 80 TBD TBD V (max) IOUT Output Current Outputs Shorted 5.5 TBD TBD mA(min) mA (max) Imute Current into Mute Pin 1.5 TBD TBD mA(min) mA (max) f = 1kHz 90 TBD f = 10kHz TBD TBD f = 100Hz TBD TBD TBD TBD V/s (min) To put part in "play" mode 93 dB Av = 30dB XTALK Channel Separation (6) dB (min) SR Slew Rate VIN = 1.2VP-P, f = 10kHz square Wave, Outputs shorted VOS Input Offset Voltage VCM = 0V, IO = 0mA 5 TBD mV (max) IB Input Bias Current VCM = 0V, IO = 0mA 150 TBD nA (max) PSRR Power Supply Rejection Ratio Rs = 1k, f = 100Hz, Vripple = 1Vrms, Input Referred 110 TBD dB (min) IMD Intermodulation Distortion at 20kHz / 19kHz at 60Hz / 7kHz TBD TBD dB (1) (2) (3) (4) (5) (6) 8 All voltages are measured with respect to the ground pins, 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 condition 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's performance. Typical specifications are measured at 25C and represent the parametric norm. Tested limits are specified to AOQL (Average Outgoing Quality Level). Datasheet min/max specification limits are specified by design, test, or statistical analysis. PCB layout will affect cross talk. It is recommended that input and output traces be separated by as much distance as possible. Return ground traces from outputs should be independent back to a single ground point and use as wide of traces as possible. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 THD+N vs Output Voltage VDD = 50V, f = 1kHz, outputs shorted THD+N vs Output Voltage VDD = 75V, f = 1kHz, outputs shorted 10 5 10 5 2 1 0.5 2 1 0.5 0.2 0.1 0.05 0.2 0.1 0.05 THD+N (%) THD+N (%) TYPICAL PERFORMANCE CHARACTERISTICS FOR LM4702C 0.02 0.01 0.005 0.02 0.01 0.005 0.002 0.001 0.0005 0.002 0.001 0.0005 0.0002 0.0001 100m 200m 500m 1 0.0002 0.0001 100m 200m 500m 1 2 5 20 10 60 OUTPUT VOLTAGE (V) 2 5 10 20 50 90 OUTPUT VOLTAGE (V) Figure 5. THD+N vs Frequency VDD = 50V, VOUT = 10Vrms, outputs shorted THD+N vs Frequency VDD = 75V, VOUT = 14Vrms, outputs shorted 10 5 10 5 2 1 0.5 2 1 0.5 0.2 0.1 0.05 0.2 0.1 0.05 THD+N (%) THD+N (%) Figure 4. 0.02 0.01 0.005 0.02 0.01 0.005 0.002 0.001 0.0005 0.002 0.001 0.0005 0.0002 0.0001 20 0.0002 0.0001 20 50 100 200 500 1k 2k 5k 10k 20k FREQUENCY (Hz) 50 100 200 500 1k 2k 5k 10k 20k FREQUENCY (Hz) Figure 6. Figure 7. Crosstalk vs Frequency VDD = 50V Crosstalk vs Frequency VDD = 75V Figure 8. Figure 9. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 9 LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS FOR LM4702C (continued) +PSRR vs Frequency VDD = 50V, RS = 1k, Ripple on VCC -PSRR vs Frequency VDD = 50V, RS = 1k, Ripple on Vee Figure 10. Figure 11. +PSRR vs Frequency VDD = 75V, RS = 1k, Ripple on VCC -PSRR vs Frequency VDD = 75V, RS = 1k, Ripple on Vee Figure 12. Figure 13. Open Loop and Phase Upper-Phase, Lower-Gain 203 160 180 140 158 120 135 100 113 80 90 60 68 40 45 20 23 0 0 -20 10 100 1k 10k 100k 1M PHASE () GAIN (dB) 180 -23 10M 100M FREQUENCY (Hz) Figure 14. 10 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 TYPICAL PERFORMANCE CHARACTERISTICS FOR LM4702B THD+N vs Output Voltage VDD = 100V THD+N vs Frequency VDD = 100V, VOUT = 30VRMS Figure 15. Figure 16. PSRR vs Frequency VDD = 100V XTALK vs Frequency B grade Demo Amp @ VDD = 50V Figure 17. Figure 18. Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 11 LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com TEST CIRCUIT Rf 56 k : Vcc + 13,14 Ri 1.8k : 22 PF 1.8k : In1 Cs 0.1 PF Cc 30 pF 4 5 3 - 6 Sink1 + Source1 2 Rs 10 P F 7 56k : 15 + 1 5V Cs 0.1 PF Vcc Mute Circuitry 1.4 k : Vcc + 13,14 1.8k : In2 Cs 0.1 PF 8 12 Source2 + 10 P F Rs 56k : 9 22 PF - Sink2 11 Ri 1.8 k : 7 10 15 + Cs 0.1 PF Cc 30 pF - Vcc Rf 56 k : Figure 19. 12 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 APPLICATION INFORMATION MUTE FUNCTION The mute function of the LM4702 is controlled by the amount of current that flows into the mute pin. If there is less than 1mA of current flowing into the mute pin, the part will be in mute. This can be achieved by shorting the mute pin to ground or by floating the mute pin. If there is between 1mA and 2mA of current flowing into the mute pin, the part will be in "play" mode. This can be done by connecting a power supply (Vmute) to the mute pin through a resistor (Rm). The current into the mute pin can be determined by the equation Imute = (Vmute - 2.9) / Rm. For example, if a 5V power supply is connected through a 1.4k resistor to the mute pin, then the mute current will be 1.5mA, at the center of the specified range. It is also possible to use Vcc as the power supply for the mute pin, though Rm will have to be recalculated accordingly. It is not recommended to flow more than 2mA of current into the mute pin because damage to the LM4702 may occur. It is highly recommended to switch between mute and "play" modes rapidly. This is accomplished most easily through using a toggle switch that alternatively connects the mute pin through a resistor to either ground or the mute pin power supply. Slowly increasing the mute current may result in undesired voltages on the outputs of the LM4702, which can damage an attached speaker. THERMAL PROTECTION The LM4702 has a sophisticated thermal protection scheme to prevent long-term thermal stress of the device. When the temperature on the die exceeds 150C, the LM4702 shuts down. It starts operating again when the die temperature drops to about 145C, but if the temperature again begins to rise, shutdown will occur again above 150C. Therefore, the device is allowed to heat up to a relatively high temperature if the fault condition is temporary, but a sustained fault will cause the device to cycle in a Schmitt Trigger fashion between the thermal shutdown temperature limits of 150C and 145C. This greatly reduces the stress imposed on the IC by thermal cycling, which in turn improves its reliability under sustained fault conditions. Since the die temperature is directly dependent upon the heat sink used, the heat sink should be chosen so that thermal shutdown is not activated during normal operation. Using the best heat sink possible within the cost and space constraints of the system will improve the long-term reliability of any power semiconductor device, as discussed in the DETERMINING THE CORRECT HEAT SINK section. POWER DISSIPATION AND HEAT SINKING When in "play" mode, the LM4702 draws a constant amount of current, regardless of the input signal amplitude. Consequently, the power dissipation is constant for a given supply voltage and can be computed with the equation PDMAX = Icc * (Vcc - Vee). For a quick calculation of PDMAX, approximate the current to be 25mA and multiply it by the total supply voltage (the current varies slightly from this value over the operating range). DETERMINING THE CORRECT HEAT SINK The choice of a heat sink for a high-power audio amplifier is made entirely to keep the die temperature at a level such that the thermal protection circuitry is not activated under normal circumstances. The thermal resistance from the die to the outside air, JA (junction to ambient), is a combination of three thermal resistances, JC (junction to case), CS (case to sink), and SA (sink to ambient). The thermal resistance, JC (junction to case), of the LM4702T is 0.8C/W. Using Thermalloy Thermacote thermal compound, the thermal resistance, CS (case to sink), is about 0.2C/W. Since convection heat flow (power dissipation) is analogous to current flow, thermal resistance is analogous to electrical resistance, and temperature drops are analogous to voltage drops, the power dissipation out of the LM4702 is equal to the following: PDMAX = (TJMAX-TAMB) / JA where * * * TJMAX = 150C TAMB is the system ambient temperature JA = JC + CS + SA (1) Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 13 LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com Figure 20. Once the maximum package power dissipation has been calculated using Equation 2, the maximum thermal resistance, SA, (heat sink to ambient) in C/W for a heat sink can be calculated. This calculation is made using Equation 4 which is derived by solving for SA Equation 3. SA = [(TJMAX-TAMB)-PDMAX(JC +CS)] / PDMAX (2) Again it must be noted that the value of SA is dependent upon the system designer's amplifier requirements. If the ambient temperature that the audio amplifier is to be working under is higher than 25C, then the thermal resistance for the heat sink, given all other things are equal, will need to be smaller. PROPER SELECTION OF EXTERNAL COMPONENTS Proper selection of external components is required to meet the design targets of an application. The choice of external component values that will affect gain and low frequency response are discussed below. The gain of each amplifier is set by resistors Rf and Ri for the non-inverting configuration shown in Figure 1. The gain is found by Equation 3 below: AV = 1 + Rf / Ri (V/V) (3) For best noise performance, lower values of resistors are used. A value of 1k is commonly used for Ri and then setting the value of Rf for the desired gain. For the LM4702 the gain should be set no lower than 26dB. Gain settings below 26dB may experience instability. The combination of Ri with Ci (see Figure 1) creates a high pass filter. The low frequency response is determined by these two components. The -3dB point can be found from Equation 4 shown below: fi = 1 / (2RiCi) (Hz) (4) If an input coupling capacitor is used to block DC from the inputs as shown in Figure 1, there will be another high pass filter created with the combination of CIN and RIN. When using a input coupling capacitor RIN is needed to set the DC bias point on the amplifier's input terminal. The resulting -3dB frequency response due to the combination of CIN and RIN can be found from Equation 5 shown below: fIN = 1 / (2RINCIN) (Hz) (5) With large values of RIN oscillations may be observed on the outputs when the inputs are left floating. Decreasing the value of RIN or not letting the inputs float will remove the oscillations. If the value of RIN is decreased then the value of CIN will need to increase in order to maintain the same -3dB frequency response. AVOIDING THERMAL RUNAWAY WHEN USING BIPOLAR OUTPUT STAGES When using a bipolar output stage with the LM4702 (as in Figure 1), the designer must beware of thermal runaway. Thermal runaway is a result of the temperature dependence of Vbe (an inherent property of the transistor). As temperature increases, Vbe decreases. In practice, current flowing through a bipolar transistor heats up the transistor, which lowers the Vbe. This in turn increases the current again, and the cycle repeats. If the system is not designed properly, this positive feedback mechanism can destroy the bipolar transistors used in the output stage. One of the recommended methods of preventing thermal runaway is to use a heat sink on the bipolar output transistors. This will keep the temperature of the transistors lower. A second recommended method is to use emitter degeneration resistors (see Re1, Re2, Re3, Re4 in Figure 1). As current increases, the voltage across the emitter degeneration resistor also increases, which decreases the voltage across the base and emitter. This mechanism helps to limit the current and counteracts thermal runaway. 14 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 A third recommended method is to use a "Vbe multiplier" to bias the bipolar output stage (see Figure 1). The Vbe multiplier consists of a bipolar transistor (Qmult, see Figure 1) and two resistors, one from the base to the collector (Rb2, Rb4, see Figure 1) and one from the base to the emitter (Rb1, Rb3, see Figure 1). The voltage from the collector to the emitter (also the bias voltage of the output stage) is Vbias = Vbe(1+Rb2/Rb1), which is why this circuit is called the Vbe multiplier. When Vbe multiplier transistor (Qmult, see Figure 1) is mounted to the same heat sink as the bipolar output transistors, its temperature will track that of the output transistors. Its Vbe is dependent upon temperature as well, and so it will draw more current as the output transistors heat it up. This will limit the base current into the output transistors, which counteracts thermal runaway. LM4702 DEMO BOARD ARTWORK Figure 21. Top Overlay Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 15 LM4702 SNAS328I - AUGUST 2005 - REVISED APRIL 2013 www.ti.com Figure 22. Top Layer Figure 23. Bottom Layer 16 Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 LM4702 www.ti.com SNAS328I - AUGUST 2005 - REVISED APRIL 2013 REVISION HISTORY Rev Date Description 1.0 8/31/05 Initial WEB. 1.1 9/09/05 Taken out Limits on Vom (under the +75V and +50V). 1.2 9/14/05 Changed TM to R ( Overture R) in the doc title. 1.3 03/08/06 Text edits. 1.4 04/26/04 Edited Limit values on the LM4702B spec table. 1.5 08/09/06 Released the D/S to the WEB with the LM4702B data. 1.6 09/19/06 Removed the "Overture R" from the document title, then released the D/S to the WEB I 04/04/13 Changed layout of National Data Sheet to TI format Submit Documentation Feedback Copyright (c) 2005-2013, Texas Instruments Incorporated Product Folder Links: LM4702 17 PACKAGE OPTION ADDENDUM www.ti.com 19-Oct-2016 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Pins Package Drawing Qty Eco Plan Lead/Ball Finish MSL Peak Temp (2) (6) (3) Op Temp (C) Device Marking (4/5) LM4702BTA/NOPB OBSOLETE TO-220 NDL 15 TBD Call TI Call TI -20 to 75 LM4702BTA LM4702CTA/NOPB OBSOLETE TO-220 NDL 15 TBD Call TI Call TI -20 to 75 LM4702CTA (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) Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability information and additional product content details. TBD: The Pb-Free/Green conversion plan has not been defined. Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes. Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above. Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight in homogeneous material) (3) MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature. (4) There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device. (5) Multiple Device Markings will be inside parentheses. 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