TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 3-W STEREO CLASS-D AUDIO POWER AMPLIFIER WITH DC VOLUME CONTROL FEATURES • • • • • • • DESCRIPTION 3 W Per Channel into 3-Ω Speakers (THD+N = 10%) – < 0.045% THD at 1.5 W, 1 kHz, 3-Ω Load DC Volume Control With 2-dB Steps From -38 dB to 20 dB Filter Free Modulation Scheme Operates Without a Large and Expensive LC Output Filter Extremely Efficient Third Generation 5-V Class-D Technology – Low Supply Current, 7 mA – Low Shutdown Control, 1 µA – Low Noise Floor, -80 dBV – Maximum Efficiency into 3 Ω, 78% – Maximum Efficiency into 8 Ω, 88% – PSRR, -70 dB Integrated Depop Circuitry Operating Temperature Range, -40°C to 85°C Space-Saving, Surface Mount PowerPAD™ Package APPLICATIONS • • • • The TPA2008D2 is a third generation 5-V class-D amplifier from Texas Instruments. Improvements to previous generation devices include: dc volume control, lower supply current, lower noise floor, higher efficiency, smaller packaging, and fewer external components. Most notably, a new filter-free class-D modulation technique allows the TPA2008D2 to directly drive the speakers, without needing a low-pass output filter consisting of two inductors and three capacitors per channel. Eliminating this output filter saves approximately 30% in system cost and 75% in PCB area. The improvements and functionality make this device ideal for LCD projectors, LCD monitors, powered speakers, and other applications that demand more battery life, reduced board space, and functionality that surpasses currently available class-D devices. A chip-level shutdown control limits total supply current to 1 µA, making the device ideal for battery-powered applications. Protection circuitry increases device reliability: thermal and short circuit. Undervoltage shutdown saves battery power for more essential devices when battery voltage drops to low levels. The TPA2008D2 is available in a 24-pin TSSOP PowerPAD™package. LCD Projectors LCD Monitors Powered Speakers Battery Operated and Space Constrained Systems EFFICIENCY vs OUTPUT POWER 100 8 Ω Speaker 90 4 Ω Speaker Efficiency − % 80 3 Ω Speaker 70 60 50 40 30 VDD = 5 V No Filter 20 10 0 0 0.5 1 1.5 2 2.5 PO − Output Power − W 3 3.5 THD+N − Total Harmonic Distortion + Noise − % TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT POWER 20 10 VDD = 5 V RL = 3 Ω Gain = 0 dB f = 1 kHz 1 f = 20 kHz 0.1 f = 20 Hz 0.01 0.01 0.1 1 4 PO − Output Power − W 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 the Texas Instruments standard warranty. Production processing does not necessarily include testing of all parameters. Copyright © 2003–2004, Texas Instruments Incorporated TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 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. AVAILABLE OPTIONS TSSOP PowerPAD (PWP) (1) (1) Device TPA2008D2PWP (1) Package Designator PWP (1) The PWP package is available taped and reeled. To order a taped and reeled part, add the suffix R to the part number (e.g., TPA2008D2PWPR). PWP PACKAGE (TOP VIEW) LINN LINP SHUTDOWN PVDDL LOUTP PGNDL PGNDL LOUTN PVDDL COSC ROSC AGND 2 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 RINN RINP BYPASS PVDDR ROUTP PGNDR PGNDR ROUTN PVDDR NC VOLUME VDD TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 TERMINAL FUNCTIONS TERMINAL NO. NAME I/O DESCRIPTION AGND 12 - Analog ground BYPASS 22 I Tap to voltage divider for internal mid-supply bias generator used for internal analog reference. COSC 10 I A capacitor connected to this terminal sets the oscillation frequency in conjunction with ROSC. For proper operation, connect a 220-pF capacitor from COSC to ground. LINN 1 I Negative differential audio input for left channel LINP 2 I Positive differential audio input for left channel LOUTN 8 O Negative audio output for left channel LOUTP 5 O Positive audio output for left channel NC 15 I No connection PGNDL 6, 7 - Power ground for left channel H-bridge PGNDR 18, 19 - Power ground for right channel H-bridge PVDDL 4, 9 PVDDR 16, 21 Power supply for left channel H-bridge Power supply for right channel H-bridge RINN 24 I Positive differential audio input for right channel RINP 23 I Negative differential audio input for right channel ROSC 11 I A resistor connected to the ROSC terminal sets the oscillation frequency in conjunction with COSC. For proper operation, connect a 120-kΩ resistor from ROSC to ground. ROUTN 17 O Negative output for right channel ROUTP 20 O Positive output for right channel SHUTDOWN 3 I Places the amplifer in shutdown mode if a TTL logic low is placed on this terminal; normal operation if a TTL logic high is placed on this terminal. VDD 13 - Analog power supply VOLUME 14 I DC volume control for setting the gain on the internal amplifiers. The dc voltage range is 0 to VDD. - - Connect to analog ground and the power grounds must be soldered down in all applications to properly secure device on the PCB. Thermal Pad 3 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 FUNCTIONAL BLOCK DIAGRAM VDD AGND PVDD VDD Gain Adj. RINN Gate Drive ROUTN PGND PVDD Gate Drive Gain Adj. RINP ROUTP PGND SHUTDOWN Volume Control VOLUME Biases and References Startup Protection Logic Ramp Generator COSC Short Circuit Protection Short Circuit Protection VDD ROSC Thermal BYPASS PVDD LINP Gain Adj. Gate Drive LOUTP PGND PVDD LINN Gain Adj. Gate Drive LOUTN PGND ABSOLUTE MAXIMUM RATINGS over operating free-air temperature range unless otherwise noted (1) UNIT VDD,PVDD Supply voltage range VI (RINN, RINP, LINN, LINP, VOLUME) Input voltage range Continuous total power dissipation -0.3 V to 6 V 0 V to VDD See Dissipation Rating Table TA Operating free-air temperature range -40°C to 85°C TJ Operating junction temperature range -40°C to 150°C Tstg Storage temperature range -65°C to 85°C Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds (1) 4 260°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. TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 DISSIPATION RATINGS TABLE PACKAGE TA≤ 25°C DERATING FACTOR TA = 70°C TA = 85°C PWP 2.18 W 21.8 mW/°C 1.2 W 872 mW RECOMMENDED OPERATING CONDITIONS MIN VDD Supply voltage Volume terminal voltage VIH High-level input voltage SHUTDOWN VIL Low-level input voltage SHUTDOWN MAX UNIT 4.5 5.5 V 0 VDD V 2 V 0.8 V PWM frequency 200 300 kHz TA Operating free-air temperature -40 85 °C TJ Operating junction temperature 125 °C ELECTRICAL CHARACTERISTICS TA= 25°C, VDD = PVDD = 5 V (unless otherwise noted) PARAMETER TEST CONDITIONS | VOS | Output offset voltage (measured differentially) VI = 0 V, AV = 20 dB, RL = 8Ω PSRR Power supply rejection ratio VDD = PVDD = 4.5 V to 5.5 V | IIH | High-level input current VDD = PVDD = 5.5 V, VI= VDD = PVDD | IIL | Low-level input current VDD = PVDD = 5.5 V, VI = 0 V IDD Supply current No filter (no load) IDD(max) RMS supply current at max power RL = 3 Ω, PO = 2.5 W/channel (stereo) IDD(SD) Supply current in shutdown mode SHUTDOWN = 0 V Drain-source on-state resistance VDD = 5 V, IO = 500 mA, TJ= 25°C rds(on) MIN TYP MAX 5 25 mV 1 µA -70 7 UNIT dB 1 µA 15 mA 1.8 A 50 1000 High side 450 600 Low side 450 600 TYP MAX nA mΩ OPERATING CHARACTERISTICS TA= 25°C, VDD = PVDD = 5 V, RL = 3 Ω, Gain = 0 dB (unless otherwise noted) PARAMETER TEST CONDITIONS f = 1 kHz, RL = 3 Ω, Stereo operation THD+N = 1% MIN 2.5 UNITS PO Output power THD+N Total harmonic distortion plus noise BOM Maximum output power bandwidth THD = 5% 20 kHz SNR Signal-to-noise ratio Maximum output at THD+N <0.5% 96 dB 150 °C 20 °C THD+N = 10% PO = 2.2 W, f = 20 Hz to 20 kHz PO = 1.5 W, f = 1 kHz Thermal hysteresis Integrated noise floor 20 Hz to 20 kHz, inputs ac grounded W <0.3% 0.045% Thermal trip point Vn 3 Volume = 0 dB 42 Volume = 20 dB 85 µVrms 5 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 Table 1. TYPICAL DC VOLUME CONTROL VOLTAGE ON VOLUME PIN (V) (INCREASING OR FIXED GAIN) VOLTAGE ON VOLUME PIN (V) (DECREASING GAIN) TYPICAL GAIN OF AMPLIFIER (dB) (1) 0-0.33 0.31-0 -38 (2) 0.34-0.42 0.43-0.32 -37 0.43-0.52 0.54-0.44 -35 0.53-0.63 0.64-0.55 -33 0.64-0.75 0.75-0.65 -31 0.76-0.86 0.86-0.76 -29 0.87-0.97 0.97-0.87 -27 0.98-1.07 1.08-0.98 -25 1.08-1.18 1.19-1.09 -23 1.19-1.30 1.32-1.20 -21 1.31-1.41 1.42-1.33 -19 1.42-1.52 1.53-1.43 -17 1.53-1.63 1.63-1.54 -15 1.64-1.75 1.75-1.64 -13 1.76-1.85 1.84-1.76 -12 1.86-1.96 1.96-1.85 -10 1.97-2.07 2.09-1.97 -8 2.08-2.18 2.19-2.10 -6 2.19-2.30 2.33-2.20 -4 2.31-2.40 2.43-2.34 -2 2.41-2.52 2.49-2.44 0 (2) 2.53-2.63 2.62-2.50 2 2.64-2.75 2.75-2.63 4 2.76-2.87 2.85-2.76 6 2.88-2.98 2.99-2.86 8 2.99-3.10 3.12-3.00 10 3.11-3.22 3.25-3.13 12 3.23-3.33 3.36-3.26 14 3.34-3.47 3.48-3.37 16 3.48-3.69 3.64-3.49 18 3.70-VDD VDD-3.65 20 (2) (1) (2) The typical part-to-part gain variation can be as large as ±2 dB (one gain step). Tested in production. The volume control circuitry of the TPA2008D2 is internally referenced to the VDD and AGND terminals. Any common-mode noise between the VOLUME terminal and these terminals will be sensed by the volume control circuitry. If the noise exceeds the step size voltage, the gain will change. In order to minimize this effect, care must be taken to ensure the signal driving the VOLUME terminal is referenced to the VDD and AGND terminals of the TPA2008D2. See section titled, “Special Layout Considerations” for more details. 6 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 TYPICAL CHARACTERISTICS TABLE OF GRAPHS FIGURE Efficiency vs Output power 1, 2 vs Frequency 3-5 vs Output power 6-8 THD+N Total harmonic distortion + noise kSVR Supply ripple rejection ratio vs Frequency 9 Crosstalk vs Frequency 10 CMRR Common-mode rejection ratio vs Frequency 11 Ri Input resistance vs Gain setting 12 EFFICIENCY vs OUTPUT POWER EFFICIENCY vs OUTPUT POWER 100 100 8-Ω Speaker 90 8-Ω Speaker 90 4-Ω Speaker 4-Ω Speaker 80 80 3-Ω Speaker 60 50 40 30 60 50 40 30 20 20 VDD = 5 V No Filter 10 0 3-Ω Speaker 70 Efficiency − % Efficiency − % 70 VDD = 5 V Ferrite Bead Filter 10 0 0.5 1 1.5 2 2.5 3 3.5 0 0 0.5 1 1.5 2 2.5 PO − Output Power − W PO − Output Power − W Figure 1. Figure 2. 3 3.5 7 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY 1 VDD = 5 V RL = 3 Ω Gain = 0 dB PO = 2.2 W 0.1 PO = 300 mW PO = 1.2 W 0.01 20 100 1k THD+N − Total Harmonic Distortion + Noise − % THD+N − Total Harmonic Distortion + Noise − % 1 10k 20k VDD = 5 V RL = 4 Ω Gain = 0 dB PO = 2 W 0.1 PO = 250 mW PO = 1 W 0.01 20 100 1k f − Frequency − Hz Figure 3. Figure 4. TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT POWER 20 VDD = 5 V RL = 8 Ω Gain = 0 dB PO = 1 W 0.1 PO = 50 mW 0.01 PO = 500 mW 100 1k f − Frequency − Hz Figure 5. 8 THD+N − Total Harmonic Distortion + Noise − % THD+N − Total Harmonic Distortion + Noise − % 1 0.001 20 10k 20k f − Frequency − Hz 10k 20k 10 1 VDD = 5 V RL = 3 Ω Gain = 0 dB f = 1 kHz f = 20 kHz 0.1 f = 20 Hz 0.01 0.01 0.1 PO − Output Power − W Figure 6. 1 4 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT POWER TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT POWER 10 THD+N − Total Harmonic Distortion + Noise − % THD+N − Total Harmonic Distortion + Noise − % 10 VDD = 5 V RL = 4 Ω Gain = 0 dB 1 f = 1 kHz 0.1 f = 20 Hz f = 20 kHz 0.01 0.01 0.1 1 VDD = 5 V RL = 8 Ω Gain = 0 dB 1 f = 1 kHz f = 20 kHz 0.01 0.01 3 0.1 PO − Output Power − W Figure 7. Figure 8. SUPPLY RIPPLE REJECTION RATIO vs FREQUENCY CROSSTALK vs FREQUENCY −40 VDD = 5 V Gain = 20 dB C(BYPASS) = 1 µF −50 −55 Crosstalk − dB kSVR − Supply Ripple Rejection Ratio − dB 2 −30 VDD = 5 V C(BYPASS) = 1 µF −50 −60 −65 1 PO − Output Power − W −40 −45 f = 20 Hz 0.1 RL = 4 Ω RL = 3 Ω −70 −60 −70 PO = 2 W, RL = 4 Ω PO = 1 W, RL = 8 Ω −80 −90 RL = 8 Ω −75 −80 20 −100 100 1k 10k 20k −110 20 100 1k f − Frequency − Hz f − Frequency − Hz Figure 9. Figure 10. 10k 20k 9 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 COMMON-MODE REJECTION RATIO vs FREQUENCY INPUT RESISTANCE vs GAIN SETTING 300 VDD = 5 V RL = 8 Ω C(BYPASS) = 1 µF 250 −55 Ri − Input Resistance − kΩ CMRR − Common-Mode rejection Ratio − dB −50 −60 −65 150 100 50 −70 20 100 1k f − Frequency − Hz Figure 11. 10 200 10k 20k 0 −40 VDD = 5 V BTL Load = 8Ω C(BYPASS) = 1 µF −30 −20 −10 0 Gain Setting − dB Figure 12. 10 20 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 APPLICATION INFORMATION APPLICATION CIRCUIT TPA2008D2 1 LINN LIN− 0.1 µF LIN+ 0.1 µF System Control 2 LINP 3 4 5 6 VDD LOUT+ GND 7 1 µF 10 µF 8 9 LOUT− 10 11 220 pF 120 kΩ 12 SHUTDOWN PVDD LOUTP PGND PGND LOUTN PVDD RINN RINP BYPASS PVDD ROUTP PGND PGND ROUTN PVDD COSC NC ROSC VOLUME AGND VDD 24 RIN− 23 0.1 µF RIN+ 22 0.1 µF 21 1 µF 20 ROUT+ 19 GND 1 µF 18 17 ROUT− 16 VDD 15 14 VOLUME 13 VDD 1 µF GND Figure 13. TPA2008D2 In A Stereo Configuration With Differential Inputs 11 TPA2008D2 SLOS413C – JULY 2003 – REVISED MAY 2004 www.ti.com APPLICATION INFORMATION (continued) TRADITIONAL CLASS-D MODULATION SCHEME The traditional class-D modulation scheme, which is used in the TPA032D0x family, has a differential output where each output is 180 degrees out of phase and changes from ground to the supply voltage, VCC. Therefore, the differential prefiltered output varies between positive and negative VCC, where filtered 50% duty cycle yields 0 V across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown in Figure 14. Note that even at an average of 0 V across the load (50% duty cycle), the current to the load is high, resulting in a high I2R loss, thus causing a high supply current. OUTP OUTN +5 V Differential Voltage Across Load 0V −5 V Current Figure 14. Traditional Class-D Modulation Scheme's Output Voltage and Current Waveforms Into an Inductive Load With No Input 12 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 APPLICATION INFORMATION (continued) TPA2008D2 MODULATION SCHEME The TPA2008D2 uses a modulation scheme that still has each output switching from 0 to the supply voltage. However, OUTP and OUTN are now in phase with each other with no input. The duty cycle of OUTP is greater than 50% and OUTN is less than 50% for positive output voltages. The duty cycle of OUTP is less than 50% and OUTN is greater than 50% for negative output voltages. The voltage across the load sits at 0 V throughout most of the switching period, greatly reducing the switching current, which reduces any I2R losses in the load. OUTP OUTN Differential Voltage Across Load Output = 0 V +5 V 0V −5 V Current OUTP OUTN Differential Voltage Output > 0 V +5 V 0V Across Load −5 V Current Figure 15. The TPA2008D2 Output Voltage and Current Waveforms Into an Inductive Load EFFICIENCY: LC FILTER REQUIRED WITH THE TRADITIONAL CLASS-D MODULATION SCHEME The main reason that the traditional class-D amplifier needs an output filter is that the switching waveform results in maximum current flow. This causes more loss in the load, which causes lower efficiency. The ripple current is large for the traditional modulation scheme, because the ripple current is proportional to voltage multiplied by the time at that voltage. The differential voltage swing is 2 × VDD, and the time at each voltage is half the period for the traditional modulation scheme. An ideal LC filter is needed to store the ripple current from each half cycle for the next half cycle, while any resistance causes power dissipation. The speaker is both resistive and reactive, whereas an LC filter is almost purely reactive. The TPA2008D2 modulation scheme has very little loss in the load without a filter because the pulses are very short and the change in voltage is VDD instead of 2 × VDD. As the output power increases, the pulses widen, making the ripple current larger. Ripple current could be filtered with an LC filter for increased efficiency, but for most applications the filter is not needed. An LC filter with a cutoff frequency less than the class-D switching frequency allows the switching current to flow through the filter instead of the load. The filter has less resistance than the speaker, which results in less power dissipation, therefore increasing efficiency. 13 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 APPLICATION INFORMATION (continued) EFFECTS OF APPLYING A SQUARE WAVE INTO A SPEAKER Audio specialists have advised for years not to apply a square wave to speakers. If the amplitude of the waveform is high enough and the frequency of the square wave is within the bandwidth of the speaker, the square wave could cause the voice coil to jump out of the air gap and/or scar the voice coil. A 250-kHz switching frequency, however, does not significantly move the voice coil, as the cone movement is proportional to 1/f2 for frequencies beyond the audio band. Damage may occur if the voice coil cannot handle the additional heat generated from the high-frequency switching current. The amount of power dissipated in the speaker may be estimated by first considering the overall efficiency of the system. If the on-resistance (rds(on)) of the output transistors is considered to cause the dominant loss in the system, then the maximum theoretical efficiency for the TPA2008D2 with an 4-Ω load is as follows: Efficiency (theoretical, %) R R r 100% 4(4 0.45) 100% 89.9% L L ds(on) (1) The maximum measured output power is approximately 2.5 W with a 5-V power supply. The total theoretical power supplied (P(total)) for this worst-case condition would therefore be as follows: P (total) P Efficiency 2.5 W 0.899 2.781 W O (2) The efficiency measured in the lab using a 4-Ω speaker was 80%. The power not accounted for as dissipated across the rds(on) may be calculated by simply subtracting the theoretical power from the measured power: Other losses P (total) (measured) P (total) (theoretical) 3.025 2.781 0.244 W (3) The quiescent supply current at 5 V is measured to be 7 mA. It can be assumed that the quiescent current encapsulates all remaining losses in the device, i.e., biasing and switching losses. It may be assumed that any remaining power is dissipated in the speaker and is calculated as follows: P (dis) 0.244 W (5 V 7 mA) 0.209 W (4) Note that these calculations are for the worst-case condition of 2.5 W delivered to the speaker. Since the 0.209 W is only 7.4% of the power delivered to the speaker, it may be concluded that the amount of power actually dissipated in the speaker is relatively insignificant. Furthermore, this power dissipated is well within the specifications of most loudspeaker drivers in a system, as the power rating is typically selected to handle the power generated from a clipping waveform. WHEN TO USE AN OUTPUT FILTER Design the TPA2008D2 without the filter if the traces from amplifier to speaker are short (< 1 inch). Powered speakers, where the speaker is in the same enclosure as the amplifier, is a typical application for class-D without a filter. Many applications require a ferrite bead filter. The ferrite filter reduces EMI around 1 MHz and higher (FCC and CE only test radiated emissions greater than 30 MHz). When selecting a ferrite bead, choose one with high impedance at high frequencies, but low impedance at low frequencies. Use an LC output filter if there are low frequency (<1 MHz) EMI sensitive circuits and/or there are long wires from the amplifier to the speaker. 14 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 APPLICATION INFORMATION (continued) 15 µH OUTP L1 15 µH C1 C2 0.22 µF 1 µF OUTN C3 L2 0.22 µF Figure 16. Typical LC Output Filter, Cutoff Frequency of 41 kHz, Speaker Impedance = 4Ω 33 µH OUTP L1 33 µH OUTN L2 C1 C2 0.1 µF 0.47 µF C3 0.1 µF Figure 17. Typical LC Output Filter, Cutoff Frequency of 41 kHz, Speaker Impedance = 8 Ω Ferrite Chip Bead OUTP 1 nF Ferrite Chip Bead OUTN 1 nF Figure 18. Typical Ferrite Chip Bead Filter (Chip bead example: Fair-Rite 2512067007Y3) 15 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 APPLICATION INFORMATION (continued) VOLUME CONTROL OPERATION The VOLUME pin controls the volume of the TPA2008D2. It is controlled with a dc voltage, which should not exceed VDD. Table 1 lists the voltage on the VOLUME pin and the corresponding gain. The trip point, where the gain actually changes, is different depending on whether the voltage on the VOLUME terminal is increasing or decreasing as a result of hysteresis about each trip point. The hysteresis ensures that the gain control is monotonic and does not oscillate from one gain step to another. A pictorial representation of the volume control can be found in Figure 19. The graph focuses on three gain steps with the trip points defined in the first and second columns of Table 1. The dotted lines represent the hysteresis about each gain step. Decreasing Voltage on VOLUME Terminal Gain − dB 2 0 Increasing Voltage on VOLUME Terminal −2 2.44 2.53 2.41 2.50 Voltage on VOLUME Pin − V Figure 19. DC Volume Control Operation SPECIAL LAYOUT CONSIDERATIONS The voltage on the VOLUME pin must closely track that of the supply voltage, VDD. As the output power is increased, the noise on the power supply will increase. The noise seen by the PVDD pin must also be seen by the VOLUME pin. It is for that reason that absolutely no capacitor should be placed on the VOLUME pin. Additional steps should be taken to reduce the line capacitance on the VOLUME pin, such as reducing line length. Any capacitance on the VOLUME pin will act as a filter, thus making the voltage seen by the VOLUME pin and VDD different. If the difference is large enough, the amplifier will change gain steps. A star point should be used for power, where the supply voltage for VDD, PVDD, and the volume circuitry can be taken. This point is typically at the bulk decoupling capacitor. The trace connecting the star point to a potentiometer or a DAC should be short. The trace connecting the potentiometer or DAC to the VOLUME pin should be kept as short and straight as possible. As with the VDD, a star ground should likewise be used. There should exist on the board a point where AGND and PGND converge. This should be the only place where the two grounds are connected. The ground used for the volume control should be AGND. If a potentiometer is to be used to control the volume of the device, it should be connected to AGND. A DAC that has a ground reference should have a short trace to AGND from its ground reference input. For an example of proper board layout, please refer to the TPA2008D2 EVM User's Guide, document number SLOU116. 16 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 APPLICATION INFORMATION (continued) SELECTION OF COSC AND ROSC The switching frequency is determined using the values of the components connected to ROSC (pin 11) and COSC (pin 10) and may be calculated with the following equation: fOSC = 6.6 / (ROSC x COSC) (5) The frequency may be varied from 200 kHz to 300 kHz by adjusting the values chosen for ROSC and COSC. The recommended values are COSC = 220 pF, ROSC= 120 kΩ for a switching frequency of 250 kHz. INPUT RESISTANCE Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest value to over five times that value. As a result, if a single capacitor is used in the input high-pass filter, the -3 dB or cutoff frequency also changes by over five times. Rf Ci IN Input Signal Ri The -3-dB frequency can be calculated using equation Equation 6. See Figure 12. Note that due to process variation, the input resistance, Ri, can change by up to 20%. 1 f 3 dB 2 C R i i (6) INPUT CAPACITOR, Ci In a 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 the input resistance of the amplifier (Ri) form a high-pass filter with the corner frequency determined in equation Equation 7. −3 dB fc 1 2 R C i i fc (7) The value of Ci is important, as it directly affects the bass (low frequency) performance of the circuit. Consider the example where Ri is 50 kΩ and the specification calls for a flat bass response down to 30 Hz. Equation Equation 5 is reconfigured as equation Equation 8. 1 C i 2 R f c i (8) In this example, Ci is 0.1 µF, so one would likely choose a value in the range of 0.1 µF to 1 µF. Figure 12 can be used to determine the input impedance for a given gain and can serve to aid in the calculation of Ci. 17 TPA2008D2 SLOS413C – JULY 2003 – REVISED MAY 2004 www.ti.com APPLICATION INFORMATION (continued) A further consideration for this capacitor is the leakage path from the input source through the input network (Ci) and the feedback network 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. Note that it is important to confirm the capacitor polarity in the application. Ci must be 10 times smaller than the bypass capacitor to reduce clicking and popping noise from power on/off and entering and leaving shutdown. After sizing Ci for a given cutoff frequency, size the bypass capacitor to 10 times that of the input capacitor. Ci ≤ CBYP / 10 (9) POWER SUPPLY DECOUPLING, CS The TPA2008D2 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. 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 terminal 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, CBYP The midrail bypass capacitor (CBYP) is the most critical capacitor and serves several important functions. During start-up or recovery from shutdown mode, CBYP 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. Bypass capacitor (CBYP) values of 0.47-µF to 1-µF ceramic or tantalum low-ESR capacitors are recommended for the best THD and noise performance. Increasing the bypass capacitor reduces clicking and popping noise from power on/off and entering and leaving shutdown. To have minimal pop, CBYP should be 10 times larger than Ci. CBYP ≥ 10 × Ci (10) DIFFERENTIAL INPUT The differential input stage of the amplifier cancels any noise that appears on both input lines of the channel. To use the TPA2008D2 EVM with a differential source, connect the positive lead of the audio source to the INP input and the negative lead from the audio source to the INN input. To use the TPA2008D2 with a single-ended source, ac ground either input through a capacitor and apply the audio signal to the remaining input. In a single-ended input application, the unused input should be ac-grounded at the audio source instead of at the device input for best noise performance. SHUTDOWN MODES The TPA2008D2 employs a shutdown mode of operation designed to reduce supply current (IDD) to the absolute minimum level during periods of nonuse for battery-power conservation. The SHUTDOWN input terminal should be held high during normal operation when the amplifier is in use. Pulling SHUTDOWN low causes the outputs to mute and the amplifier to enter a low-current state, IDD(SD) = 1 µA. SHUTDOWN should never be left unconnected because the amplifier state would be unpredictable. 18 TPA2008D2 www.ti.com SLOS413C – JULY 2003 – REVISED MAY 2004 APPLICATION INFORMATION (continued) USING LOW-ESR CAPACITORS Low-ESR capacitors are recommended throughout this application 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. SHORT-CIRCUIT PROTECTION The TPA2008D2 has short circuit protection circuitry on the outputs that prevents damage to the device during output-to-output shorts, output-to-GND shorts, and output-to-VDD shorts. When a short-circuit is detected on the outputs, the part immediately goes into shutdown. This is a latched fault and must be reset by cycling the voltage on the SHUTDOWN pin to a logic low and back to the logic high, or by cycling the power off and then back on. This clears the short-circuit flag and allows for normal operation if the short was removed. If the short was not removed, the protection circuitry activates again. LOW-SUPPLY VOLTAGE DETECTION The TPA2008D2 incorporates circuitry designed to detect when the supply voltage is low. When the supply voltage reaches 1.8 V or below, the TPA2008D2 goes into a state of shutdown. The current consumption drops from millamperes to microamperes, leaving the remaining battery power for more essential devices such as microprocessors. When the supply voltage level returns to normal, the device comes out of its shutdown state and starts to draw current again. Note that even though the device is drawing several milliamperes of current, it is not operationally functional until VDD≥ 4.5 V. THERMAL PROTECTION Thermal protection on the TPA2008D2 prevents damage to the device when the internal die temperature exceeds 150°C. There is a ±15 degree tolerance on this trip point from device to device. Once the die temperature exceeds the thermal set point, the device enters into the shutdown state and the outputs are disabled. This is not a latched fault. The thermal fault is cleared once the temperature of the die is reduced by 20°C. The device begins normal operation at this point with no external system interaction. THERMAL CONSIDERATIONS: OUTPUT POWER AND MAXIMUM AMBIENT TEMPERATURE To calculate the maximum ambient temperature, the following equation may be used: TAmax = TJ – ΘJAPDissipated where: TJ = 125°C ΘJA = 45.87°C/W (11) (The derating factor for the 24-pin PWP package is given in the dissipation rating table.) To estimate the power dissipation, the following equation may be used: PDissipated = PO(average) x ((1 / Efficiency) – 1) Efficiency = ~85% for an 8-Ω load = ~80% for a 4-Ω load = ~75% for a 3-Ω load (12) Example. What is the maximum ambient temperature for an application that requires the TPA2008D2 to drive 2 W into a 4-Ω speaker (stereo)? PDissipated = 4 W x ((1 / 0.8) - 1) = 1 W (PO = 2 W x 2) TAmax = 125°C - (45.87°C/W x 1 W) = 79.13°C 19 PACKAGE OPTION ADDENDUM www.ti.com 18-Apr-2006 PACKAGING INFORMATION Orderable Device Status (1) Package Type Package Drawing Pins Package Eco Plan (2) Qty TPA2008D2PWP ACTIVE HTSSOP PWP 24 60 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPA2008D2PWPG4 ACTIVE HTSSOP PWP 24 60 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPA2008D2PWPR ACTIVE HTSSOP PWP 24 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR TPA2008D2PWPRG4 ACTIVE HTSSOP PWP 24 2000 Green (RoHS & no Sb/Br) CU NIPDAU Level-2-260C-1 YEAR Lead/Ball Finish MSL Peak Temp (3) (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. Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information provided by third parties, and makes no representation or warranty as to the accuracy of such information. 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