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| TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 D D D D D D Fully Specified for 3.3-V and 5-V Operation Wide Power Supply Compatibility 2.5 V - 5.5 V Output Power for RL = 8 - 350 mW at VDD = 5 V - 250 mW at VDD = 3.3 V Ultralow Supply Current in Shutdown Mode . . . 0.15 A Thermal and Short-Circuit Protection Surface-Mount Packaging - SOIC - PowerPADTM MSOP D OR DGN PACKAGE (TOP VIEW) SHUTDOWN BYPASS IN+ IN- 1 2 3 4 8 7 6 5 VO - GND VDD VO + description The TPA321 is a bridge-tied load (BTL) audio power amplifier developed especially for low-voltage applications where internal speakers are required. Operating with a 3.3-V supply, the TPA321 can deliver 250-mW of continuous power into a BTL 8- load at less than 1% THD+N throughout voice band frequencies. Although this device is characterized out to 20 kHz, its operation was optimized for narrower band applications such as cellular communications. The BTL configuration eliminates the need for external coupling capacitors on the output in most applications, which is particularly important for small battery-powered equipment. This device features a shutdown mode for power-sensitive applications with a quiescent current of 0.15 A during shutdown. The TPA321 is available in an 8-pin SOIC surface-mount package and the surface-mount PowerPADTM MSOP, which reduces board space by 50% and height by 40%. VDD 6 RF Audio Input RI CI 4 3 IN - IN+ VDD/2 VO+ 5 CS 1 F - + VDD 2 CB 0.1 F BYPASS - + VO- 8 7 GND 350 mW From System Control 1 SHUTDOWN Bias Control 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. PowerPAD is a trademark of Texas Instruments. PRODUCTION DATA information is 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) 2000, Texas Instruments Incorporated POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 1 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 AVAILABLE OPTIONS PACKAGED DEVICES TA SMALL OUTLINE (D) MSOP (DGN) MSOP SYMBOLIZATION - 40C to 85C TPA321D TPA321DGN AJB The D and DGN packages are available taped and reeled. To order a taped and reeled part, add the suffix R to the part number (e.g., TPA321DR). Terminal Functions TERMINAL NAME BYPASS GND IN - IN+ SHUTDOWN VDD VO+ VO- NO. 2 7 4 3 1 6 5 8 O O I I I I/O I DESCRIPTION BYPASS is the tap to the voltage divider for internal mid-supply bias. This terminal should be connected to a 0.1-F to 1-F capacitor when used as an audio amplifier. GND is the ground connection. IN - is the inverting input. IN - is typically used as the audio input terminal. IN + is the noninverting input. IN + is typically tied to the BYPASS terminal for SE operations. SHUTDOWN places the entire device in shutdown mode when held high (IDD < 1 A). VDD is the supply voltage terminal. VO+ is the positive BTL output. VO- is the negative BTL output. absolute maximum ratings over operating free-air temperature range (unless otherwise noted) Supply voltage, VDD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 V Input voltage, VI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3 V to VDD +0.3 V Continuous total power dissipation . . . . . . . . . . . . . . . . . . . . . internally limited (see Dissipation Rating Table) Operating free-air temperature range, TA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 40C to 85C Operating junction temperature range, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 40C to 150C Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -65C to 150C Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260C Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability. DISSIPATION RATING TABLE PACKAGE D TA 25C 725 mW DERATING FACTOR 5.8 mW/C TA = 70C 464 mW TA = 85C 377 mW DGN 2.14 W 17.1 mW/C 1.37 W 1.11 W Please see the Texas Instruments document, PowerPAD Thermally Enhanced Package Application Report (literature number SLMA002), for more information on the PowerPADTM package. The thermal data was measured on a PCB layout based on the information in the section entitled Texas Instruments Recommended Board for PowerPAD on page 33 of the before mentioned document. recommended operating conditions AAAAA A AA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA AAA A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA A Supply voltage, VDD 2.5 5.5 85 V Operating free-air temperature, TA - 40 C 2 POST OFFICE BOX 655303 MIN MAX UNIT * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 electrical characteristics at specified free-air temperature, VDD = 3.3 V, TA = 25C (unless otherwise noted) AAA A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA A A AAA A A A AA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AAA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A A |VOS| Output offset voltage (measured differentially) Power supply rejection ratio Supply current (see Figure 3) 5 20 mV dB mA A PSRR VDD = 3.2 V to 3.4 V 85 IDD IDD(SD) 0.7 1.5 5 Supply current, shutdown mode (see Figure 4) 0.15 PARAMETER TEST CONDITIONS MIN TYP MAX UNIT operating characteristics, VDD = 3.3 V, TA = 25C, RL = 8 PARAMETER PO Output power, see Note 1 THD = 0.5%, TEST CONDITIONS MIN TYP MAX UNIT mW AAAAAAAAAAAAAA AAAA AA A A AAAAAAAAAAAAAAAAAAAA AA A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A A A AA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AAA AA AA AA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AA A AAA A A A AAAA AA AA AA A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AAA AA AA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A See Figure 9 250 THD + N Total harmonic distortion plus noise Maximum output power bandwidth Unity-gain bandwidth PO = 250 mW, Gain = 2, AV = -2 V/V, See Figure 7 Open Loop, f = 1 kHz, See Figure 2 AV = -1 V/V, RL = 32 , f = 20 Hz to 4 kHz, See Figure 7 THD = 3%, 1.3% 10 kHz B1 See Figure 15 CB = 1 F, 1.4 71 15 MHz dB Supply ripple rejection ratio Noise output voltage Vn CB = 0.1 F, See Figure 19 V(rms) NOTE 1: Output power is measured at the output terminals of the device at f = 1 kHz. electrical characteristics at specified free-air temperature, VDD = 5 V, TA = 25C (unless otherwise noted) PARAMETER |VOS| Output offset voltage (measured differentially) TEST CONDITIONS MIN TYP 5 MAX UNIT mV dB mA A 20 AA A A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AA A AAA A A A AAAA A AA AA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AA A AAAAA AAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A A A AAAA AA AA AA A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AAA AA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AAAAA A A AAAA AA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA AA A AAA A A A A A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AA A A AAA A A A A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAA A A A A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAA AAA A AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA AAAAAAAAAA AA AAA PSRRAAAAAAAAAAAAAAAAAA = 4.9 V to 5.1 V Power supply rejection ratio VDD IDD Supply current (see Figure 3) IDD(SD) Supply current, shutdown mode (see Figure 4) 78 0.7 1.5 5 0.15 operating characteristics, VDD = 5 V, TA = 25C, RL = 8 PARAMETER PO Output power THD = 0.5%, TEST CONDITIONS MIN TYP MAX UNIT mW See Figure 13 700 1% THD + N Total harmonic distortion plus noise Maximum output power bandwidth Unity-gain bandwidth PO = 250 mW, Gain = 2, AV = -2 V/V, See Figure 11 Open Loop, f = 1 kHz, See Figure 2 AV = -1 V/V, RL = 32 , f = 20 Hz to 4 kHz, See Figure 11 THD = 2%, 10 kHz B1 See Figure 16 CB = 1 F, 1.4 65 15 MHz dB Supply ripple rejection ratio Noise output voltage Vn CB = 0.1 F, See Figure 20 V(rms) POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 3 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 PARAMETER MEASUREMENT INFORMATION VDD 6 RF Audio Input RI CI 4 3 IN - - IN+ + VDD/2 VO+ 5 CS 1 F VDD 2 CB 0.1 F BYPASS RL = 8 - + VO- 8 7 GND 1 SHUTDOWN Bias Control Figure 1. Test Circuit TYPICAL CHARACTERISTICS Table of Graphs FIGURE kSVR IDD PO THD + N Supply voltage rejection ratio Supply current Output power Total harmonic distortion plus noise Open loop gain and phase Closed loop gain and phase Vn PD Output noise voltage Power dissipation vs Frequency vs Supply voltage vs Supply voltage vs Load resistance vs Frequency vs Output power vs Frequency vs Frequency vs Frequency vs Output power 2 3, 4 5 6 7, 8, 11, 12 9, 10, 13, 14 15, 16 17, 18 19, 20 21, 22 4 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 TYPICAL CHARACTERISTICS SUPPLY VOLTAGE REJECTION RATIO vs FREQUENCY 0 kSVR - Supply Voltage Rejection Ratio - dB -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 20 100 1k f - Frequency - Hz 10 k 20 k -0.1 2 3 4 5 6 VDD - Supply Voltage - V VDD = 3.3 V VDD = 5 V I DD - Supply Current - mA RL = 8 CB = 1 F 1.1 SUPPLY CURRENT vs SUPPLY VOLTAGE 0.9 0.7 0.5 0.3 0.1 Figure 2 SUPPLY CURRENT (SHUTDOWN) vs SUPPLY VOLTAGE 0.5 SHUTDOWN = High 0.45 I DD(SD)- Supply Current - A 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 2 2.5 3 3.5 4 4.5 5 5.5 VDD - Supply Voltage - V Figure 3 Figure 4 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 5 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 TYPICAL CHARACTERISTICS OUTPUT POWER vs SUPPLY VOLTAGE 1000 THD+N 1% 800 PO - Output Power - mW 600 RL = 8 400 RL = 32 200 0 2 2.5 3 3.5 4 4.5 5 5.5 VDD - Supply Voltage - V Figure 5 OUTPUT POWER vs LOAD RESISTANCE 800 THD+N = 1% 700 PO - Output Power - mW 600 VDD = 5 V 500 400 300 200 100 0 8 16 24 32 40 48 56 64 RL - Load Resistance - VDD = 3.3 V Figure 6 6 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 TYPICAL CHARACTERISTICS TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY 10 THD+N -Total Harmonic Distortion + Noise - % VDD = 3.3 V PO = 250 mW RL = 8 THD+N -Total Harmonic Distortion + Noise - % AV = -20 V/V TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY 10 VDD = 3.3 V RL = 8 AV = -2 V/V PO = 50 mW 1 1 AV =- 10 V/V AV = -2 V/V 0.1 PO = 125 mW 0.1 0.01 20 100 1k f - Frequency - Hz 10k 20k 0.01 20 PO = 250 mW 100 1k f - Frequency - Hz 10k 20k Figure 7 TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER 10 THD+N -Total Harmonic Distortion + Noise - % VDD = 3.3 V f = 1 kHz AV = -2 V/V 1 THD+N -Total Harmonic Distortion + Noise - % Figure 8 TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER 10 f = 20 kHz f = 10 kHz 1 f = 1 kHz RL = 8 0.1 0.1 f = 20 Hz VDD = 3.3 V RL = 8 AV = -2 V/V 0.1 PO - Output Power - W 1 0.01 0.04 0.1 0.16 0.22 0.28 0.34 0.4 0.01 0.01 PO - Output Power - W Figure 9 Figure 10 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 7 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 TYPICAL CHARACTERISTICS TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY 10 THD+N -Total Harmonic Distortion + Noise - % VDD = 5 V PO = 350 mW RL = 8 THD+N -Total Harmonic Distortion + Noise - % AV = -20 V/V TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY 10 VDD = 5 V RL = 8 AV = -2 V/V PO = 50 mW 1 1 AV =- 10 V/V 0.1 AV = -2 V/V PO = 175 mW 0.1 PO = 350 mW 0.01 20 100 1k f - Frequency - Hz 10k 20k 0.01 20 100 1k f - Frequency - Hz 10k 20k Figure 11 TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER 10 THD+N -Total Harmonic Distortion + Noise - % VDD = 5 V f = 1 kHz AV = -2 V/V 1 RL = 8 THD+N -Total Harmonic Distortion + Noise - % Figure 12 TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER 10 f = 20 kHz f = 10 kHz 1 f = 1 kHz 0.1 0.1 f = 20 Hz VDD = 5 V RL = 8 AV = -2 V/V 0.01 0.1 0.25 0.40 0.55 0.70 0.85 1 0.01 0.01 0.1 PO - Output Power - W 1 PO - Output Power - W Figure 13 Figure 14 8 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 TYPICAL CHARACTERISTICS OPEN-LOOP GAIN AND PHASE vs FREQUENCY 40 Phase 30 Gain Open-Loop Gain - dB 20 60 10 0 0 -60 -10 -120 Phase - Phase - VDD = 3.3 V RL = Open 120 180 -20 -30 1 101 102 f - Frequency - kHz 103 104 -180 Figure 15 OPEN-LOOP GAIN AND PHASE vs FREQUENCY 40 Phase 30 Gain Open-Loop Gain - dB 20 60 10 0 0 -60 -10 -120 VDD = 5 V RL = Open 120 180 -20 -30 1 101 102 f - Frequency - kHz 103 104 -180 Figure 16 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 9 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 TYPICAL CHARACTERISTICS CLOSED-LOOP GAIN AND PHASE vs FREQUENCY 1 0.75 0.5 Closed-Loop Gain - dB 0.25 0 -0.25 -0.5 -0.75 -1 -1.25 -1.5 -1.75 -2 101 VDD = 3.3 V RL = 8 PO = 0.25 W CI =1 F 102 103 104 105 106 140 Gain 150 160 Phase - Phase - Phase 170 180 130 120 f - Frequency - Hz Figure 17 CLOSED-LOOP GAIN AND PHASE vs FREQUENCY 1 Phase 0.75 0.5 Closed-Loop Gain - dB 0.25 0 -0.25 -0.5 -0.75 -1 -1.25 -1.5 -1.75 -2 101 VDD = 5 V RL = 8 PO = 0.35 W CI =1 F 102 103 104 105 140 Gain 150 160 170 180 130 120 106 f - Frequency - Hz Figure 18 10 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 TYPICAL CHARACTERISTICS OUTPUT NOISE VOLTAGE vs FREQUENCY 100 Vn - Output Noise Voltage - V(rms) VDD = 3.3 V BW = 22 Hz to 22 kHz RL = 32 CB =0.1 F AV = -1 V/V VO BTL 100 Vn - Output Noise Voltage - V(rms) OUTPUT NOISE VOLTAGE vs FREQUENCY VDD = 5 V BW = 22 Hz to 22 kHz RL = 32 CB =0.1 F AV = -1 V/V VO BTL 10 VO+ 10 VO+ 1 20 100 1k f - Frequency - Hz 10 k 20 k 1 20 100 1k f - Frequency - Hz 10 k 20 k Figure 19 POWER DISSIPATION vs OUTPUT POWER 300 720 Figure 20 POWER DISSIPATION vs OUTPUT POWER 270 PD - Power Dissipation - mW 240 210 180 PD - Power Dissipation - mW 640 560 480 400 150 VDD = 3.3 V RL = 8 320 VDD = 5 V RL = 8 0 200 400 600 800 1000 1200 120 90 0 100 200 240 160 300 400 PO - Output Power - mW PO - Output Power - mW Figure 21 Figure 22 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 11 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION bridge-tied load Figure 23 shows a linear audio power amplifier (APA) in a BTL configuration. The TPA321 BTL amplifier consists of two linear amplifiers driving both ends of the load. There are several potential benefits to this differential drive configuration but power to the load should be initially considered. The differential drive to the speaker means that as one side is slewing up, the other side is slewing down, and vice versa. This in effect doubles the voltage swing on the load as compared to a ground referenced load. Plugging 2 x VO(PP) into the power equation, where voltage is squared, yields 4x the output power from the same supply rail and load impedance (see equation 1). V (rms) Power + + V O(PP) 22 V (rms) RL VDD 2 (1) VO(PP) RL VDD 2x VO(PP) -VO(PP) Figure 23. Bridge-Tied Load Configuration In a typical portable handheld equipment sound channel operating at 3.3 V, bridging raises the power into an 8- speaker from a single-ended (SE, ground reference) limit of 62.5 mW to 250 mW. In sound power that is a 6-dB improvement, which is loudness that can be heard. In addition to increased power, there are frequency response concerns. Consider the single-supply SE configuration shown in Figure 24. A coupling capacitor is required to block the dc offset voltage from reaching the load. These capacitors can be quite large (approximately 33 F to 1000 F) so they tend to be expensive, heavy, occupy valuable PCB area, and have the additional drawback of limiting low-frequency performance of the system. This frequency limiting effect is due to the high pass filter network created with the speaker impedance and the coupling capacitance and is calculated with equation 2. 12 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION bridge-tied load versus single-ended mode (continued) fc + 2 pR1 C (2) LC For example, a 68-F capacitor with an 8- speaker would attenuate low frequencies below 293 Hz. The BTL configuration cancels the dc offsets, eliminating the need for the blocking capacitors. Low-frequency performance is then limited only by the input network and speaker response. Cost and PCB space are also minimized by eliminating the bulky coupling capacitor. VDD -3 dB VO(PP) CC RL VO(PP) fc Figure 24. Single-Ended Configuration and Frequency Response Increasing power to the load does carry a penalty of increased internal power dissipation. The increased dissipation is understandable considering that the BTL configuration produces 4x the output power of a SE configuration. Internal dissipation versus output power is discussed further in the thermal considerations section. BTL amplifier efficiency Linear amplifiers are notoriously inefficient. The primary cause of these inefficiencies is voltage drop across the output stage transistors. There are two components of the internal voltage drop. One is the headroom or dc voltage drop that varies inversely to output power. The second component is due to the sinewave nature of the output. The total voltage drop can be calculated by subtracting the RMS value of the output voltage from VDD. The internal voltage drop multiplied by the RMS value of the supply current, IDDrms, determines the internal power dissipation of the amplifier. An easy-to-use equation to calculate efficiency starts out as being equal to the ratio of power from the power supply to the power delivered to the load. To accurately calculate the RMS values of power in the load and in the amplifier, the current and voltage waveform shapes must first be understood (see Figure 25). VO IDD V(LRMS) IDD(RMS) Figure 25. Voltage and Current Waveforms for BTL Amplifiers POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 13 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION BTL amplifier efficiency (continued) Although the voltages and currents for SE and BTL are sinusoidal in the load, currents from the supply are very different between SE and BTL configurations. In an SE application the current waveform is a half-wave rectified shape whereas in BTL it is a full-wave rectified waveform. This means RMS conversion factors are different. Keep in mind that for most of the waveform both the push and pull transistors are not on at the same time, which supports the fact that each amplifier in the BTL device only draws current from the supply for half the waveform. The following equations are the basis for calculating amplifier efficiency. Efficiency Where: P L + P PL (3) 2 L SUP + V rms 2 L R L + 2R Vp V Lrms P SUP P + V2 + VDD IDDrms + VDDR2VP pL 2V P I DDrms + pR L Efficiency of a BTL Configuration + 2V p VP DD + p P LR L 2 2V DD 12 (4) Table 1 employs equation 4 to calculate efficiencies for three different output power levels. The efficiency of the amplifier is quite low for lower power levels and rises sharply as power to the load is increased resulting in a nearly flat internal power dissipation over the normal operating range. The internal dissipation at full output power is less than in the half power range. Calculating the efficiency for a specific system is the key to proper power supply design. Table 1. Efficiency vs Output Power in 3.3-V 8- BTL Systems OUTPUT POWER (W) 0.125 0.25 0.375 EFFICIENCY (%) 33.6 47.6 58.3 PEAK-to-PEAK VOLTAGE (V) 1.41 2.00 2.45 INTERNAL DISSIPATION (W) 0.26 0.29 0.28 High-peak voltage values cause the THD to increase. A final point to remember about linear amplifiers (either SE or BTL) is how to manipulate the terms in the efficiency equation to utmost advantage when possible. Note that in equation 4, VDD is in the denominator. This indicates that as VDD goes down, efficiency goes up. 14 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION application schematics Figure 26 is a schematic diagram of a typical handheld audio application circuit, configured for a gain of -10 V/V. CF 5 pF Audio Input RF 50 k VDD/2 4 IN - IN+ VDD 6 CS 1 F - + VO+ 5 VDD CI RI 0.47 F 10 k 3 2 CB 2.2 F BYPASS - + VO- 8 7 GND 350 mW From System Control 1 SHUTDOWN Bias Control Figure 26. TPA321 Application Circuit Figure 27 is a schematic diagram of a typical handheld audio application circuit, configured for a gain of -10 V/V with a differential input. RF 50 k Audio Input- RI 10 k CI Audio Input+ RI 10 k VDD 6 VDD/2 4 3 IN - - IN+ + VO+ 5 CS 1 F VDD RF 50 k 2 BYPASS - + GND 1 SHUTDOWN Bias Control VO- 8 7 700 mW CI CB 2.2 F From System Control Figure 27. TPA321 Application Circuit With Differential Input POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 15 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION application schematics (continued) It is important to note that using the additional RF resistor connected between IN+ and BYPASS will cause VDD/2 to shift slightly, which could influence the THD+N performance of the amplifier. Although an additional external op-amp could be used to buffer BYPASS from RF, tests in the lab have shown that the THD+N performance is only minimally affected by operating in the fully differential mode as shown in Figure 27. The following sections discuss the selection of the components used in Figures 26 and 27. component selection gain setting resistors, RF and RI The gain for each audio input of the TPA321 is set by resistors RF and RI according to equation 5 for BTL mode. BTL Gain + AV + * 2 R F R I (5) BTL mode operation brings about the factor 2 in the gain equation due to the inverting amplifier mirroring the voltage swing across the load. Given that the TPA321 is a MOS amplifier, the input impedance is very high, consequently input leakage currents are not generally a concern although noise in the circuit increases as the value of RF increases. In addition, a certain range of RF values are required for proper start-up operation of the amplifier. Taken together it is recommended that the effective impedance seen by the inverting node of the amplifier be set between 5 k and 20 k. The effective impedance is calculated in equation 6. Effective Impedance I + RRFRR ) F (6) I As an example, consider an input resistance of 10 k and a feedback resistor of 50 k. The BTL gain of the amplifier would be -10 V/V, and the effective impedance at the inverting terminal would be 8.3 k, which is well within the recommended range. For high performance applications metal film resistors are recommended because they tend to have lower noise levels than carbon resistors. For values of RF above 50 k, the amplifier tends to become unstable due to a pole formed from RF and the inherent input capacitance of the MOS input structure. For this reason, a small compensation capacitor, CF, of approximately 5 pF should be placed in parallel with RF when RF is greater than 50 k. This, in effect, creates a low-pass filter network with the cutoff frequency defined in equation 7. -3 dB fc + 2 pR1 C (7) FF fc For example, if RF is 100 k and CF is 5 pF then fc is 318 kHz, which is well outside of the audio range. 16 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION input capacitor, CI In the typical application an input capacitor, CI, is required to allow the amplifier to bias the input signal to the proper dc level for optimum operation. In this case, CI and RI form a high-pass filter with the corner frequency determined in equation 8. -3 dB fc 1 + 2 pR C II (8) fc The value of CI is important to consider as it directly affects the bass (low frequency) performance of the circuit. Consider the example where RI is 10 k and the specification calls for a flat bass response down to 40 Hz. Equation 8 is reconfigured as equation 9. C I 1 + 2 pR fc I (9) In this example, CI is 0.40 F, so one would likely choose a value in the range of 0.47 F to 1 F. A further consideration for this capacitor is the leakage path from the input source through the input network (RI, CI) and the feedback resistor (RF) to the load. This leakage current creates a dc offset voltage at the input to the amplifier that reduces useful headroom, especially in high gain applications. For this reason a low-leakage tantalum or ceramic capacitor is the best choice. When polarized capacitors are used, the positive side of the capacitor should face the amplifier input in most applications, as the dc level there is held at VDD/2, which is likely higher than the source dc level. It is important to confirm the capacitor polarity in the application. power supply decoupling, CS The TPA321 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to ensure the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is achieved by using two capacitors of different types that target different types of noise on the power supply leads. For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR) ceramic capacitor, typically 0.1 F, placed as close as possible to the device VDD lead, works best. For filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10 F or greater placed near the audio power amplifier is recommended. POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 17 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION midrail bypass capacitor, CB The midrail bypass capacitor, CB, is the most critical capacitor and serves several important functions. During start-up or recovery from shutdown mode, CB determines the rate at which the amplifier starts up. The second function is to reduce noise produced by the power supply caused by coupling into the output drive signal. This noise is from the midrail generation circuit internal to the amplifier, which appears as degraded PSRR and THD + N. The capacitor is fed from a 250-k source inside the amplifier. To keep the start-up pop as low as possible, the relationship shown in equation 10 should be maintained, which insures the input capacitor is fully charged before the bypass capacitor is fully charged and the amplifier starts up. 10 C B 250 k v R ) RI F 1 C (10) I As an example, consider a circuit where CB is 2.2 F, CI is 0.47 F, RF is 50 k and RI is 10 k. Inserting these values into the equation 10 we get: 18.2 v 35.5 which satisfies the rule. Bypass capacitor, CB, values of 2.2 F to 1 F ceramic or tantalum low-ESR capacitors are recommended for the best THD and noise performance. using low-ESR capacitors Low-ESR capacitors are recommended throughout this application. A real (as opposed to ideal) capacitor can be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this resistance, the more the real capacitor behaves like an ideal capacitor. 5-V versus 3.3-V operation The TPA321 operates over a supply range of 2.5 V to 5.5 V. This data sheet provides full specifications for 5-V and 3.3-V operation, as these are considered to be the two most common standard voltages. There are no special considerations for 3.3-V versus 5-V operation with respect to supply bypassing, gain setting, or stability. The most important consideration is that of output power. Each amplifier in TPA321 can produce a maximum voltage swing of VDD - 1 V. This means, for 3.3-V operation, clipping starts to occur when VO(PP) = 2.3 V as opposed to VO(PP) = 4 V at 5 V. The reduced voltage swing subsequently reduces maximum output power into an 8- load before distortion becomes significant. Operation from 3.3-V supplies, as can be shown from the efficiency formula in equation 4, consumes approximately two-thirds the supply power for a given output-power level than operation from 5-V supplies. 18 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 APPLICATION INFORMATION headroom and thermal considerations Linear power amplifiers dissipate a significant amount of heat in the package under normal operating conditions. A typical music CD requires 12 dB to 15 dB of dynamic headroom to pass the loudest portions without distortion as compared with the average power output. From the TPA321 data sheet, one can see that when the TPA321 is operating from a 5-V supply into a 8- speaker 350 mW peaks are available. Converting watts to dB: P P mW + 10 Log P W + 10Log 350 W + -4.6 dB dB 1 ref Subtracting the headroom restriction to obtain the average listening level without distortion yields: -4.6 dB - 15 dB = -19.6 dB (15 dB headroom) -4.6 dB - 12 dB = -16.6 dB (12 dB headroom) -4.6 dB - 9 dB = -13.6 dB (9 dB headroom) -4.6 dB - 6 dB = -10.6 dB (6 dB headroom) -4.6 dB - 3 dB = -7.6 dB (3 dB headroom) Converting dB back into watts: PW + 10PdB 10 x Pref = 11 mW (15 dB headroom) = 22 mW (12 dB headroom) = 44 mW (9 dB headroom) = 88 mW (6 dB headroom) = 175 mW (3 dB headroom) This is valuable information to consider when attempting to estimate the heat dissipation requirements for the amplifier system. Comparing the absolute worst case, which is 350 mW of continuous power output with 0 dB of headroom, against 12 dB and 15 dB applications drastically affects maximum ambient temperature ratings for the system. Using the power dissipation curves for a 5-V, 8- system, the internal dissipation in the TPA321 and maximum ambient temperatures is shown in Table 2. Table 2. TPA321 Power Rating, 5-V, 8-, BTL PEAK OUTPUT POWER (mW) 350 350 350 350 350 350 AVERAGE OUTPUT POWER 350 mW 175 mW (3 dB) 88 mW (6 dB) 44 mW (9 dB) 22 mW (12 dB) 11 mW (15 dB) POWER DISSIPATION (mW) 600 500 380 300 200 180 MAXIMUM AMBIENT TEMPERATURE 0 CFM 46C 64C 85C 98C 115C 119C Table 2 shows that the TPA321 can be used to its full 350-mW rating without any heat sinking in still air up to 46C. POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 19 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 MECHANICAL DATA D (R-PDSO-G**) 14 PINS SHOWN PLASTIC SMALL-OUTLINE PACKAGE 0.050 (1,27) 0.020 (0,51) 0.014 (0,35) 14 8 0.008 (0,20) NOM 0.244 (6,20) 0.228 (5,80) 0.157 (4,00) 0.150 (3,81) 0.010 (0,25) M Gage Plane 0.010 (0,25) 1 A 7 0- 8 0.044 (1,12) 0.016 (0,40) Seating Plane 0.069 (1,75) MAX 0.010 (0,25) 0.004 (0,10) 0.004 (0,10) PINS ** DIM A MAX 8 0.197 (5,00) 0.189 (4,80) 14 0.344 (8,75) 0.337 (8,55) 16 0.394 (10,00) 0.386 (9,80) 4040047 / D 10/96 A MIN NOTES: A. B. C. D. All linear dimensions are in inches (millimeters). This drawing is subject to change without notice. Body dimensions do not include mold flash or protrusion, not to exceed 0.006 (0,15). Falls within JEDEC MS-012 20 POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 TPA321 350-mW MONO AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS SLOS312A - JUNE 2000 - REVISED JUNE 2000 MECHANICAL DATA DGN (S-PDSO-G8) PowerPADTM PLASTIC SMALL-OUTLINE PACKAGE 0,65 8 5 0,38 0,25 0,25 M Thermal Pad (See Note D) 0,15 NOM 3,05 2,95 4,98 4,78 Gage Plane 0,25 1 3,05 2,95 4 0- 6 0,69 0,41 Seating Plane 1,07 MAX 0,15 0,05 0,10 4073271/A 04/98 NOTES: A. B. C. D. All linear dimensions are in millimeters. This drawing is subject to change without notice. Body dimensions include mold flash or protrusions. The package thermal performance may be enhanced by attaching an external heat sink to the thermal pad. This pad is electrically and thermally connected to the backside of the die and possibly selected leads. E. Falls within JEDEC MO-187 PowerPAD is a trademark of Texas Instruments. POST OFFICE BOX 655303 * DALLAS, TEXAS 75265 21 IMPORTANT NOTICE Texas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue any product or service without notice, and advise customers to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those pertaining to warranty, patent infringement, and limitation of liability. TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with TI's standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. Customers are responsible for their applications using TI components. In order to minimize risks associated with the customer's applications, adequate design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. TI's publication of information regarding any third party's products or services does not constitute TI's approval, warranty or endorsement thereof. Copyright (c) 2000, Texas Instruments Incorporated |
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