TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 D D D OR DGN PACKAGE (TOP VIEW) 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 Ω – 700 mW at VDD = 5 V, BTL – 250 mW at VDD = 3.3 V, BTL Integrated Depop Circuitry Thermal and Short-Circuit Protection Surface-Mount Packaging – SOIC – PowerPAD MSOP D D D D SHUTDOWN BYPASS IN+ IN– 1 8 2 7 3 6 4 5 VO – GND VDD VO + description The TPA721 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 TPA721 can deliver 250-mW of continuous power into a BTL 8-Ω load at less than 0.6% 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 wireless 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 supply current of 7 µA during shutdown. The TPA721 is available in an 8-pin SOIC surface-mount package and the surface-mount PowerPAD MSOP, which reduces board space by 50% and height by 40%. VDD 6 VDD RF VDD/2 Audio Input RI CI 4 IN – 3 IN+ 2 BYPASS CS – VO+ 5 + CB – VO– 8 + 700 mW 7 GND 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. Copyright 2000, Texas Instruments Incorporated 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. POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 1 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 AVAILABLE OPTIONS PACKAGED DEVICES TA SMALL OUTLINE† (D) MSOP Symbolization MSOP‡ (DGN) – 40°C to 85°C TPA721D TPA721DGN ABC † In the D package, the maximum output power is thermally limited to 350 mW; 700 mW peaks can be driven, as long as the RMS value is less than 350 mW. ‡ 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., TPA301DR). Terminal Functions TERMINAL NAME NO. I/O DESCRIPTION I BYPASS is the tap to the voltage divider for internal mid-supply bias. This terminal should be connected to a 0.1-µF to 2.2-µF capacitor when used as an audio amplifier. BYPASS 2 GND 7 IN – 4 I IN – is the inverting input. IN – is typically used as the audio input terminal. IN+ 3 I IN + is the noninverting input. IN + is typically tied to the BYPASS terminal. SHUTDOWN 1 I SHUTDOWN places the entire device in shutdown mode when held high (IDD < 7 µA). VDD VO+ 6 5 O VDD is the supply voltage terminal. VO+ is the positive BTL output. VO– 8 O VO– is the negative BTL output. GND is the ground connection. 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . – 40°C to 85°C Operating junction temperature range, TJ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . – 40°C to 150°C Storage temperature range, Tstg . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –65°C to 150°C Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 260°C § 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 ≤ 25°C 725 mW DERATING FACTOR 5.8 mW/°C TA = 70°C 464 mW TA = 85°C 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 PowerPAD 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 ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Supply voltage, VDD Operating free-air temperature, TA 2 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 MIN MAX UNIT 2.5 5.5 V – 40 85 °C TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 electrical characteristics at specified free-air temperature, VDD = 3.3 V, TA = 25°C (unless otherwise noted) ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Á ÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Á ÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ PARAMETER TEST CONDITIONS VOO PSRR Output offset voltage (measured differentially) See Note 1 Power supply rejection ratio IDD IDD(SD) Supply current VDD = 3.2 V to 3.4 V BTL mode MIN TYP MAX mV 1.25 2.5 mA 7 50 µA 85 Supply current, shutdown mode (see Figure 4) UNIT 20 dB NOTE 1: At 3 V < VDD < 5 V the dc output voltage is approximately VDD/2. operating characteristics, VDD = 3.3 V, TA = 25°C, RL = 8 Ω ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ PARAMETER TEST CONDITIONS MIN TYP MAX 250 UNIT PO THD + N Output power, see Note 2 THD = 0.5%, See Figure 9 Total harmonic distortion plus noise f = 200 Hz to 4 kHz, See Figure 7 BOM B1 Maximum output power bandwidth PO = 250 mW, Gain = 2, Unity-gain bandwidth Open Loop, See Figure 15 kSVR Supply ripple rejection ratio f = 1 kHz, CB = 1 µF, See Figure 2 79 dB Vn Noise output voltage Gain = 1, CB = 0.1 µF, See Figure 19 17 µV(rms) THD = 2%, mW 0.55% See Figure 7 20 kHz 1.4 MHz NOTE 2: 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 = 25°C (unless otherwise noted) ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ Á ÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁÁ ÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ ÁÁÁ PARAMETER TEST CONDITIONS VOO PSRR Output offset voltage (measured differentially) IDD IDD(SD) Supply current Power supply rejection ratio MIN VDD = 4.9 V to 5.1 V TYP MAX mV 1.25 2.5 mA 50 100 µA 78 Supply current, shutdown mode (see Figure 4) UNIT 20 dB operating characteristics, VDD = 5 V, TA = 25°C, RL = 8 Ω PARAMETER TEST CONDITIONS MIN PO THD + N Output power THD = 0.5%, See Figure 13 Total harmonic distortion plus noise Maximum output power bandwidth PO = 250 mW, Gain = 2, f = 200 Hz to 4 kHz, See Figure 11 BOM B1 Unity-gain bandwidth Open Loop, See Figure 16 THD = 2%, See Figure 11 TYP 700† MAX UNIT mW 0.5% 20 kHz 1.4 MHz Supply ripple rejection ratio f = 1 kHz, CB = 1 µF, See Figure 2 80 dB Vn Noise output voltage Gain = 1, CB = 0.1 µF, See Figure 20 17 µV(rms) † The DGN package, properly mounted, can conduct 700 mW RMS power continuously. The D package can only conduct 350 mW RMS power continuously wtih peaks to 700 mW. kSVR POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 3 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 PARAMETER MEASUREMENT INFORMATION VDD 6 RF VDD/2 Audio Input RI CI VDD CS 4 IN – 3 IN+ 2 BYPASS VO+ 5 – + RL = 8 Ω CB – VO– 8 + 7 GND 1 SHUTDOWN Bias Control Figure 1. BTL Mode Test Circuit TYPICAL CHARACTERISTICS Table of Graphs FIGURE kSVR Supply ripple rejection ratio vs Frequency IDD Supply current vs Supply voltage 3, 4 vs Supply voltage 5 PO THD + N Vn PD 4 Output power vs Load resistance Total harmonic distortion plus noise vs Frequency vs Output power 2 6 7, 8, 11, 12 9, 10, 13, 14 Open loop gain and phase vs Frequency 15, 16 Closed loop gain and phase vs Frequency 17, 18 Output noise voltage vs Frequency 19, 20 Power dissipation vs Output power 21, 22 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 TYPICAL CHARACTERISTICS SUPPLY RIPPLE REJECTION RATIO vs FREQUENCY SUPPLY CURRENT vs SUPPLY VOLTAGE 1.8 RL = 8 Ω CB = 1 µF BTL –20 BTL 1.6 I DD – Supply Current – mA –10 –30 –40 –50 –60 –70 VDD = 3.3 V –80 –100 20 100 1.4 1.2 1 0.8 VDD = 5 V –90 10k 1k 0.6 2.5 20k 3 f – Frequency – Hz 3.5 4 4.5 5 5.5 VDD – Supply Voltage – V Figure 2 Figure 3 SUPPLY CURRENT vs SUPPLY VOLTAGE 90 SHUTDOWN = High 80 70 I DD – Supply Current – µ A k SVR –Supply Ripple Rejection Ratio – dB 0 60 50 40 30 20 10 0 2.5 3 3.5 4 4.5 5 5.5 VDD – Supply Voltage – V Figure 4 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 5 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 TYPICAL CHARACTERISTICS OUTPUT POWER vs SUPPLY VOLTAGE 1000 THD+N 1% f = 1 kHz BTL PO – Output Power – mW 800 600 RL = 8 Ω RL = 32 Ω 400 200 0 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% f = 1 kHz BTL PO – Output Power – mW 700 600 VDD = 5 V 500 400 300 VDD = 3.3 V 200 100 0 8 16 24 32 40 48 56 RL – Load Resistance – Ω Figure 6 6 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 64 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 TYPICAL CHARACTERISTICS TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY 10 THD+N –Total Harmonic Distortion + Noise – % THD+N –Total Harmonic Distortion + Noise – % 10 VDD = 3.3 V PO = 250 mW RL = 8 Ω BTL AV = –20 V/V 1 AV = –10 V/V AV = –2 V/V 0.1 0.01 20 100 1k 10k VDD = 3.3 V RL = 8 Ω AV = –2 V/V BTL PO = 50 mW 1 0.1 PO = 125 mW PO = 250 mW 0.01 20 20k 100 1k f – Frequency – Hz Figure 7 TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER 10 VDD = 3.3 V f = 1 kHz AV = –2 V/V BTL THD+N –Total Harmonic Distortion + Noise – % THD+N –Total Harmonic Distortion + Noise – % 10 1 RL = 8 Ω 0.1 0.01 0.05 0.1 20k Figure 8 TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER 0 10k f – Frequency – Hz 0.15 0.2 0.25 0.3 0.35 0.4 f = 20 kHz 1 f = 10 kHz f = 1 kHz 0.1 f = 20 Hz 0.01 0.01 PO – Output Power – W VDD = 3.3 V RL = 8 Ω CB = 1 µF AV = –2 V/V BTL 0.1 1 PO – Output Power – W Figure 9 Figure 10 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 7 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 TYPICAL CHARACTERISTICS TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY TOTAL HARMONIC DISTORTION PLUS NOISE vs FREQUENCY 10 VDD = 5 V PO = 700 mW RL = 8 Ω BTL THD+N –Total Harmonic Distortion + Noise – % THD+N –Total Harmonic Distortion + Noise – % 10 AV = –20 V/V 1 AV = –10 V/V AV =– 2 V/V 0.1 0.01 20 100 1k 10k 20k VDD = 5 V RL = 8 Ω AV = –2 V/V BTL 1 PO = 700 mW 0.1 PO = 350 mW 0.01 20 100 f – Frequency – Hz 20k TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER 10 10 THD+N –Total Harmonic Distortion + Noise – % THD+N –Total Harmonic Distortion + Noise – % 10k Figure 12 TOTAL HARMONIC DISTORTION PLUS NOISE vs OUTPUT POWER VDD = 5 V f = 1 kHz AV = –2 V/V BTL 1 RL = 8 Ω 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 f = 20 kHz 1 f = 10 kHz f = 1 kHz f = 20 Hz 0.1 0.01 0.01 VDD = 5 V RL = 8 Ω CB = 1 µF AV = –2 V/V BTL PO – Output Power – W 0.1 PO – Output Power – W Figure 13 8 1k f – Frequency – Hz Figure 11 0.01 0.1 PO = 50 mW Figure 14 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 1 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 TYPICAL CHARACTERISTICS OPEN-LOOP GAIN AND PHASE vs FREQUENCY 80 180° VDD = 3.3 V RL = Open BTL 70 140° Phase 100° 50 60° 40 20° 30 Gain 20 – 20° 10 Phase Open-Loop Gain – dB 60 –60° 0 –100° –10 –140° –20 –30 1 101 102 103 104 –180° f – Frequency – kHz Figure 15 OPEN-LOOP GAIN AND PHASE vs FREQUENCY 80 180° VDD = 5 V RL = Open BTL 70 60 140° 100° 60° 40 20° 30 Gain 20 – 20° 10 Phase Open-Loop Gain – dB Phase 50 –60° 0 –100° –10 –140° –20 –30 1 101 102 f – Frequency – kHz 103 104 –180° Figure 16 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 9 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 TYPICAL CHARACTERISTICS CLOSED-LOOP GAIN AND PHASE vs FREQUENCY 1 180° Phase 0.75 170° 0.25 0 160° Gain –0.25 150° –0.5 –0.75 140° –1 –1.25 –1.5 –1.75 –2 101 Phase Closed-Loop Gain – dB 0.5 VDD = 3.3 V RL = 8 Ω PO = 250 mW BTL 102 130° 103 104 105 106 120° f – Frequency – Hz Figure 17 CLOSED-LOOP GAIN AND PHASE vs FREQUENCY 1 180° Phase 0.75 170° 0.25 0 160° Gain –0.25 150° –0.5 –0.75 140° –1 –1.25 –1.5 –1.75 –2 101 VDD = 5 V RL = 8 Ω PO = 700 mW BTL 102 130° 103 104 105 f – Frequency – Hz Figure 18 10 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 120° 106 Phase Closed-Loop Gain – dB 0.5 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 TYPICAL CHARACTERISTICS OUTPUT NOISE VOLTAGE vs FREQUENCY 100 VDD = 3.3 V BW = 22 Hz to 22 kHz RL = 8 Ω or 32 Ω AV = –1 V/V Vn – Output Noise Voltage – µV Vn – Output Noise Voltage – µV 100 OUTPUT NOISE VOLTAGE vs FREQUENCY VO BTL Vo+ 10 1 20 100 1k 10k VDD = 5 V BW = 22 Hz to 22 kHz RL = 8 Ω or 32 Ω AV = –1 V/V VO BTL Vo+ 10 1 20 20k 100 f – Frequency – Hz Figure 19 800 BTL Mode VDD = 3.3 V RL = 8 Ω BTL Mode VDD = 5 V 700 PD – Power Dissipation – mW PD – Power Dissipation – mW 20k POWER DISSIPATION vs OUTPUT POWER 350 250 200 150 100 10k Figure 20 POWER DISSIPATION vs OUTPUT POWER 300 1k f – Frequency – Hz RL = 32 Ω 50 RL = 8 Ω 600 500 400 300 200 RL = 32 Ω 100 0 0 200 400 600 0 0 PD – Output Power – mW 200 400 600 800 1000 PD – Output Power – mW Figure 21 Figure 22 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 11 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 APPLICATION INFORMATION bridged-tied load Figure 23 shows a linear audio power amplifier (APA) in a BTL configuration. The TPA721 BTL amplifier consists of two linear amplifiers driving both ends of the load. There are several potential benefits to this differential drive configuration but initially consider power to the load. 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 × VO(PP) into the power equation, where voltage is squared, yields 4× the output power from the same supply rail and load impedance (see equation 1). + O(PP) (rms) 2 Ǹ2 V V Power + V (1) 2 (rms) R L VDD VO(PP) RL 2x VO(PP) VDD –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-Ω speaker from a singled-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 µF to 1000 µF) 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. f 12 (corner) + 2 p R1 C (2) L C POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 APPLICATION INFORMATION bridged-tied load (continued) For example, a 68-µF capacitor with an 8-Ω speaker would attenuate low frequencies below 293 Hz. The BTL configuration cancels the dc offsets, which eliminates 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 4× 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 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). IDD VO IDD(RMS) V(LRMS) Figure 25. Voltage and Current Waveforms for BTL Amplifiers POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 13 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 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. + P PL Efficiency (3) SUP Where: P L V Lrms + V rms 2 L R L 2 + 2R Vp L + VǸ2P + VDD IDDrms + VDDp R2VP L 2V P I DDrms + pR P SUP L Efficiency of a BTL Configuration p VP + 2V DD + p ǒ Ǔ P LR L 2 ń 1 2 (4) 2V DD 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-Ω BTL Systems OUTPUT POWER (W) EFFICIENCY (%) PEAK-to-PEAK VOLTAGE (V) INTERNAL DISSIPATION (W) 0.125 33.6 1.41 0.26 0.25 47.6 0.29 0.375 58.3 2.00 2.45† 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. 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 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 APPLICATION INFORMATION application schematic Figure 26 is a schematic diagram of a typical handheld audio application circuit, configured for a gain of –10 V/V. VDD 6 RF 50 kΩ Audio Input RI 10 kΩ CI VDD/2 4 IN – 3 IN+ 2 BYPASS VDD CS 1 µF – VO+ 5 + CB 2.2 µF – VO– 8 + 700 mW 7 GND From System Control SHUTDOWN 1 Bias Control Figure 26. TPA721 Application Circuit The following sections discuss the selection of the components used in Figure 26. component selection gain setting resistors, RF and RI ǒǓ The gain for each audio input of the TPA721 is set by resistors RF and RI according to equation 5 for BTL mode. BTL Gain + *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 TPA721 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 is required for proper startup 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 kΩ and 20 kΩ. The effective impedance is calculated in equation 6. Effective Impedance + RRF)RRI F (6) I POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 15 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 APPLICATION INFORMATION gain setting resistors, RF and RI (continued) As an example consider an input resistance of 10 kΩ and a feedback resistor of 50 kΩ. The BTL gain of the amplifier would be –10 V/V and the effective impedance at the inverting terminal would be 8.3 kΩ, 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 kΩ, 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 of approximately 5 pF should be placed in parallel with RF when RF is greater than 50 kΩ. This, in effect, creates a low pass filter network with the cutoff frequency defined in equation 7. –3 dB f co(lowpass) + 2 p R1 C F F (7) fc For example, if RF is 100 kΩ and CF is 5 pF, then fco is 318 kHz, which is well outside of the audio range. 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 f co(highpass) + 2 p R1 C I I (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 kΩ and the specification calls for a flat bass response down to 40 Hz. Equation 8 is reconfigured as equation 9. C 16 I + 2 p R1 fco (9) I POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 APPLICATION INFORMATION input capacitor, CI (continued) In this example, CI is 0.40 µF, so one would likely choose a value in the range of 0.47 µF to 1 µF. 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 TPA721 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 µF 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 µF or greater placed near the audio power amplifier is recommended. midrail bypass capacitor, CB The midrail bypass capacitor, CB, is the most critical capacitor and serves several important functions. During startup 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-kΩ source inside the amplifier. To keep the start-up pop as low as possible, the relationship shown in equation 10 should be maintained. This insures the input capacitor is fully charged before the bypass capacitor is fully charged and the amplifier starts up. ǒ C 10 B 250 kΩ Ǔ ǒ v R 1 F Ǔ ) RI C (10) I As an example, consider a circuit where CB is 2.2 µF, CI is 0.47 µF, RF is 50 kΩ, and RI is 10 kΩ. Inserting these values into the equation 10 we get: 18.2 v 35.5 which satisfies the rule. Bypass capacitor, CB, values of 0.1 µF to 2.2 µF 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 applications section. 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. POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 17 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 APPLICATION INFORMATION 5-V versus 3.3-V operation The TPA721 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 TPA721 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-Ω 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 than operation from 5-V supplies for a given output-power level. 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 TPA721 data sheet, one can see that when the TPA721 is operating from a 5-V supply into a 8-Ω speaker that 700 mW peaks are available. Converting watts to dB: P dB + 10 Log PW + 10Log 700 mW + –1.5 dB Subtracting the headroom restriction to obtain the average listening level without distortion yields: –1.5 dB – 15 dB = –16.5 (15 dB headroom) –1.5 dB – 12 dB = –13.5 (12 dB headroom) –1.5 dB – 9 dB = –10.5 (9 dB headroom) –1.5 dB – 6 dB = –7.5 (6 dB headroom) –1.5 dB – 3 dB = –4.5 (3 dB headroom) Converting dB back into watts: P 18 W + 10PdBń10 + 22 mW (15 dB headroom) + 44 mW (12 dB headroom) + 88 mW (9 dB headroom) + 175 mW (6 dB headroom) + 350 mW (3 dB headroom) POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 APPLICATION INFORMATION headroom and thermal considerations (continued) 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 700 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-Ω system, the internal dissipation in the TPA721 and maximum ambient temperatures is shown in Table 2. Table 2. TPA721 Power Rating, 5-V, 8-Ω, BTL PEAK OUTPUT POWER (mW) D PACKAGE (SOIC) DGN PACKAGE (MSOP) MAXIMUM AMBIENT TEMPERATURE (0 CFM) MAXIMUM AMBIENT TEMPERATURE (0 CFM) 110°C AVERAGE OUTPUT POWER POWER DISSIPATION (mW) 700 700 mW 675 34°C 700 350 mW (3 dB) 595 47°C 115°C 700 176 mW (6 dB) 475 68°C 122°C 700 88 mW (9 dB) 350 89°C 125°C 700 44 mW (12 dB) 225 111°C 125°C Table 2 shows that the TPA721 can be used to its full 700-mW rating without any heat sinking in still air up to 110°C and 34°C for the DGN package (MSOP) and D pacakge (SOIC) respectively. POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 19 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 MECHANICAL DATA D (R-PDSO-G**) PLASTIC SMALL-OUTLINE PACKAGE 14 PINS SHOWN 0.050 (1,27) 0.020 (0,51) 0.014 (0,35) 14 0.010 (0,25) M 8 0.008 (0,20) NOM 0.244 (6,20) 0.228 (5,80) 0.157 (4,00) 0.150 (3,81) Gage Plane 0.010 (0,25) 1 7 0°– 8° A 0.044 (1,12) 0.016 (0,40) Seating Plane 0.069 (1,75) MAX 0.010 (0,25) 0.004 (0,10) PINS ** 0.004 (0,10) 8 14 16 A MAX 0.197 (5,00) 0.344 (8,75) 0.394 (10,00) A MIN 0.189 (4,80) 0.337 (8,55) 0.386 (9,80) DIM 4040047 / D 10/96 NOTES: A. B. C. D. 20 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 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 TPA721 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER SLOS231B – NOVEMBER 1998 – REVISED MARCH 2000 MECHANICAL DATA DGN (S-PDSO-G8) PowerPAD PLASTIC SMALL-OUTLINE PACKAGE 0,38 0,25 0,65 8 0,25 M 5 Thermal Pad (See Note D) 0,15 NOM 3,05 2,95 4,98 4,78 Gage Plane 0,25 1 0°– 6° 4 3,05 2,95 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. 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