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TPA6120A2
www.ti.com
SLOS431 - MARCH 2004
HIGH FIDELITY HEADPHONE AMPLIFIER
FEATURES
* * * * * * * * * * * * * * * 80 mW into 600 From a 12-V Supply at 0.00014% THD + N Current-Feedback Architecture Greater than 120 dB of Dynamic Range SNR of 120 dB Output Voltage Noise of 5 Vrms at Gain = 2 V/V Power Supply Range: 5 V to 15 V 1300 V/s Slew Rate Differential Inputs Independent Power Supplies for Low Crosstalk Short Circuit and Thermal Protection
DESCRIPTION
The TPA6120A2 is a high fidelity audio amplifier built on a current-feedback architecture. This high bandwidth, extremely low noise device is ideal for high performance equipment. The better than 120 dB of dynamic range exceeds the capabilities of the human ear, ensuring that nothing audible is lost due to the amplifier. The solid design and performance of the TPA6120A2 ensures that music, not the amplifier, is heard. Three key features make current-feedback amplifiers outstanding for audio. The first feature is the high slew rate that prevents odd order distortion anomalies. The second feature is current-on-demand at the output that enables the amplifier to respond quickly and linearly when necessary without risk of output distortion. When large amounts of output power are suddenly needed, the amplifier can respond extremely quickly without raising the noise floor of the system and degrading the signal-to-noise ratio. The third feature is the gain-independent frequency response that allows the full bandwidth of the amplifier to be used over a wide range of gain settings. The excess loop gain does not deteriorate at a rate of 20 dB/decade.
2.7 nF
APPLICATIONS
Professional Audio Equipment Mixing Boards Headphone Distribution Amplifiers Headphone Drivers Microphone Preamplifiers
Filter and I/V Gain Stage 1/2 OPA4134
CF
Stereo Hi-Fi Headphone Driver TPA6120A2
RF
AUDIO DAC
RF LRCK PCM Audio Data Source BCK DATA SCK IOUT L+ +IN B -IN B RF 1 k 2.7 nF 2.7 nF RF 1 k OUT C RI 1 k +IN D IOUT R- -IN D RF CF 1 k 2.7 nF OUT D RI 1 k RIN+ RIN- OUT B IOUT L- -IN A +IN A 1 k OUT A RI 1 k RI 1 k LIN- LIN+ RF 1 k
1 k RO 10
LOUT
PCM1792 or DSD1792
ZEROL ZEROR
CF CF RF
1/2 OPA4134
1 k
MS Controller MDI MC MDO RST
IOUT R+
+IN C -IN C
RO 10
ROUT DYR > 120 dB for Whole System!
RF 1 k
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 (c) 2004, Texas Instruments Incorporated
TPA6120A2
SLOS431 - MARCH 2004
www.ti.com
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam during storage or handling to prevent electrostatic damage.
ABSOLUTE MAXIMUM RATINGS
over operating free-air temperature range (unless otherwise noted)
Supply voltage, VCC+ to VCCInput voltage, VI (2) Differential input voltage, VID Minimum load impedance Continuous total power dissipation Operating free-air temperature range, TA Operating junction temperature range, TJ Storage temperature range, Tstg Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds (1) (2) (3)
(3) (1)
TPA6120A2 33 V VCC 6V 8 See Dissipation Rating Table - 40C to 85C - 40C to 150C - 40C to 125C 235C
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. When the TPA6120A2 is powered down, the input source voltage must be kept below 600-mV peak. The TPA6120A2 incorporates an exposed PowerPAD on the underside of the chip. This acts as a heatsink and must be connected to a thermally dissipating plane for proper power dissipation. Failure to do so may result in exceeding the maximum junction temperature that could permanently damage the device. See TI Technical Brief SLMA002 for more information about utilizing the PowerPAD thermally enhanced package.
DISSIPATION RATING TABLE
PACKAGE DWP (1) JA (1) (C/W) 44.4 JC (C/W) 33.8 TA = 25C POWER RATING 2.8 W
The PowerPAD must be soldered to a thermal land on the printed-circuit board. See the PowerPAD Thermally Enhanced Package application note (SLMA002)
AVAILABLE OPTIONS
TA -40C to 85C (1) PACKAGE DWP (1) PART NUMBER TPA6120A2DWP SYMBOL 6120A2
The DWP package is available taped and reeled. To order a taped and reeled part, add the suffix R to the part number (e.g., TPA6120A2DWPR).
RECOMMENDED OPERATING CONDITIONS
MIN Supply voltage, VCC+ and VCCLoad impedance Operating free-air temperature, TA Split Supply Single Supply VCC = 5 V or 15 V 5 10 16 -40 85 MAX 15 30 UNIT V C
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ELECTRICAL CHARACTERISTICS
over operating free-air temperature range (unless otherwise noted)
PARAMETER |VIO| PSRR VIC ICC IO ri ro VO Input offset voltage (measured differentially) Power supply rejection ratio Common mode input voltage Supply current (each channel) Output current (per channel) Input offset voltage drift Input resistance Output resistance Output voltage swing Open Loop VCC = 15 V, RL = 25 11.8 to -11.5 TEST CONDITIONS VCC = 5 V or 15 V VCC = 2.5 V to 5.5 V VCC = 5 V VCC = 15 V VCC = 5 V VCC= 15 V VCC= 5 V to 15 V VCC = 5 V or 15 V 700 20 300 13 12.5 to -12.2 3.6 13.4 MIN TYP 2 75 3.7 13.5 11.5 13 15 MAX 5 UNIT mV dB V mA mA V/C k V
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OPERATING CHARACTERISTICS (1)
TA = 25C, RL = 25 , Gain = 2 V/V (unless otherwise noted)
PARAMETER TEST CONDITIONS SMTPE ratio = 4:1, Gain = 2 V/V, IM frequency = 60 Hz High frequency = 7 kHz PO = 100 mW, RL = 32 f = 1 kHz PO = 100 mW, RL = 64 f = 1 kHz VCC = 12 V, Gain = 3 V/V RL = 600 , f = 1 kHz THD+N Total harmonic distortion plus noise VCC = 15 V, Gain = 3 V/V RL = 600 , f = 1 kHz VCC = 12 V, Gain = 3 V/V VCC = 15 V, Gain = 3 V/V RL = 32 f = 10 Hz to 22 kHz V(RIPPLE) = 1 VPP RL = 64 f = 10 Hz to 22 kHz V(RIPPLE) = 1 VPP VCC = 5 V or 15 V VCC = 15 V, Gain = 5 V/V, VO = 20 VPP VCC = 5 V, Gain = 2 V/V, VO = 5 VPP VCC = 12 V to 15 V RL = 32 to 64 f = 1 kHz VCC = 12 V to 15 V RL = 32 to 64 f = 1 kHz RL = 32 , f = 1 kHz Dynamic range RL = 64 , f = 1 kHz Crosstalk (1) VCC = 12 V to 15 V RL = 32 to 64 f = 1 kHz Gain = 2 V/V Gain = 100 V/V Gain = 2 V/V Gain = 100 V/V VCC = 12 V VCC = 15 V VCC = 12 V VCC = 15 V VI = 1 VRMS RF = 1 k VCC = 12 V to 15 V, RL = 32 , VI = 1 VPP VCC = 12 V to 15 V, RL = 64 , VI = 1 VPP VCC = 12 V VCC = 15 V VCC = 12 V VCC = 15 V PO = 80 mW PO = 40 mW PO = 125 mW PO = 62.5 mW VO = 15 VPP, RL = 10 k f = 1 kHz VO = 15 VPP, RL = 10 k f = 1 kHz VCC= 12 V VCC= 15 V VCC= 12 V VCC= 15 V MIN TYP 0.00014% MAX UNIT
IMD
Intermodulation distortion (SMPTE)
0.000095% 0.00055% 0.00060% 0.00038% 0.00029% 0.00014% 0.000065% 0.00012% 0.000061% 0.000024%
0.000021% -80 -83 -76 -79 100 1300 900 5 50 125 104 123 125 124 126 -90 dB dB dB dB V/s Vrms dB
kSVR
Supply voltage rejection ratio
CMRR SR
Common mode rejection ratio (differential) Slew rate
Vn
Output noise voltage
SNR
Signal-to-noise ratio
For IMD, THD+N, kSVR, and crosstalk, the bandwidth of the measurement instruments was set to 80 kHz.
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DEVICE INFORMATION
Thermally Enhansed SOIC (DWP) PowerPADTM Package Top View
LVCC- LOUT LVCC+ LIN+ LIN- NC NC NC NC NC
1 2 3 4 5 6 7 8 9 10
20 19 18 17 16 15 14 13 12 11
RVCC- ROUT RVCC+ RIN+ RIN- NC NC NC NC NC
NC - No internal connection
TERMINAL FUNCTIONS
PIN NAME LVCCLOUT LVCC+ LIN+ LINNC RINRIN+ RVCC+ ROUT RVCCThermal Pad PIN NUMBER 1 2 3 4 5 6,7,8,9,10,11,12,13,14,15 16 17 18 19 20 I/O I O I I I I I I O I DESCRIPTION Left channel negative power supply - must be kept at the same potential as RVCC-. Left channel output Left channel positive power supply Left channel positive input Left channel negative input Not internally connected Right channel negative input Right channel positive input Right channel positive power supply Right channel output Right channel negative power supply - must be kept at the same potential as LVCC-. Connect to ground. The thermal pad must be soldered down in all applications to properly secure device on the PCB.
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TYPICAL CHARACTERISTICS Table of Graphs
FIGURE vs Frequency Total harmonic distortion + noise Power dissipation Supply voltage rejection ratio Intermodulation distortion Crosstalk Signal-to-noise ratio Slew rate Small and large signal frequency response 400-mV step response 10-V step response 20-V step response vs Output voltage vs Output power vs Output power vs Frequency vs High frequency vs IM Amplitude vs Frequency vs Gain vs Output step 1, 2, 3, 4 5 6, 7, 8 9 10, 11 12 13 14 15, 16 17, 18 19, 20 21 22 23
TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY
0.01 THD+N -Total Harmonic Distortion + Noise - % THD+N -Total Harmonic Distortion + Noise - % RL = 10 kW, Gain = 3 V/V, RF = 2 kW, RI = 1 kW, BW = 80 kHz 0.01
TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY
RL = 600 W, Gain = 3 V/V, RF = 2 kW, RI = 1 kW, BW = 80 kHz
0.001
VCC = +15 VO = 15 VPP VCC = +12 VO = 15 VPP 0.0001 VCC = +12 VO = 12 VPP
0.001
VCC = +15 V, PO = 125 mW
VCC = +12 V, PO = 80 mW
0.00001 10
VCC = +15 VO = 23 VPP 100 1k f - Frequency - Hz 10 k 50 k
0.0001 10 100 1k f - Frequency - Hz 10 k 50 k
Figure 1.
Figure 2.
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TYPICAL CHARACTERISTICS (continued)
TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY
0.1 THD+N -Total Harmonic Distortion + Noise - % THD+N -Total Harmonic Distortion + Noise - % RL = 64 W, Gain = 2 V/V, RF = 1 kW, RI = 1 kW, BW = 80 kHz 1 RL = 32 W, Gain = 2 V/V, RF = 1 kW, RI = 1 kW, BW = 80 kHz
TOTAL HARMONIC DISTORTION + NOISE vs FREQUENCY
0.1
0.01 VCC = +15 V, PO = 700 mW VCC = +15 V, PO = 1.35 W 0.001 VCC = +12 V, PO = 425 mW
VCC = +15 V, PO = 1.5 W 0.01 VCC = +15 V, PO = 1.25 W VCC = +12 V, PO = 950 mW VCC = +12 V, PO = 800 mW 0.001
0.0001 10
VCC = +12 V, PO = 500 mW 100 1k f - Frequency - Hz 10 k 50 k
0.0001 10
100
1k f - Frequency - Hz
10 k
50 k
Figure 3. TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT VOLTAGE
10 THD+N -Total Harmonic Distortion + Noise - % THD+N -Total Harmonic Distortion + Noise - % RL = 10 kW, Gain = 3 V/V, f = 1 kHz, RF = 2 kW, RI = 1 kW, BW = 80 kHz 10 RL = 600 W, Gain = 3 V/V, f = 1 kHz, RF = 2 kW, RI = 1 kW, BW = 80 kHz
Figure 4. TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT POWER
1
1
0.1
0.1 VCC = +12 V 0.01 VCC = +15 V 0.001
0.01
0.001
VCC = +12 V
0.0001 VCC = +15 V 0.00001 35 10 15 20 25 30 35 VO - Output Voltage - VPP
0.0001 0.00001 0.01
0.1 PO - Output Power - W
0.2
Figure 5.
Figure 6.
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TYPICAL CHARACTERISTICS (continued)
TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT POWER
10 THD+N -Total Harmonic Distortion + Noise - % THD+N -Total Harmonic Distortion + Noise - % RL = 64 W, Gain = 2 V/V, f = 1 kHz, RF = 1 kW, RI = 1 kW, BW = 80 kHz VCC = +12 V 0.1 VCC = +15 V 0.01 10 RL = 32 W, Gain = 2 V/V, f = 1 kHz, RF = 1 kW, RI = 1 kW, BW = 80 kHz VCC = +12 V 0.1 VCC = +15 V 0.01
TOTAL HARMONIC DISTORTION + NOISE vs OUTPUT POWER
1
1
0.001
0.001
0.0001 0.01
0.1 PO - Output Power - W
1
2
0.0001 0.01
0.1
1
2
34
PO - Output Power - W
Figure 7. POWER DISSIPATION vs OUTPUT POWER
Mono Operation VCC = +15 V, RL = 32 W k SVR - Supply Voltage Rejection Ratio - dB 2 1.8 PD - Power Dissipation - W 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 0.5 1 1.5 2 2.5 3 3.5 VCC = +12 V, RL = 64 W VCC = +15 V, RL = 64 W VCC = +12 V, RL = 32 W 0 -10 -20 -30 -40 -50 -60 -70 -80 -90 10 100 PO - Output Power - W VCC = +12 V, V(ripple) = 1 VPP, Gain = 2 V/V BW = 80 kHz
Figure 8. SUPPLY VOLTAGE REJECTION RATIO vs FREQUENCY
Representative of both positive and negative supplies.
64 W 32 W
1k f - Frequency - Hz
10 k
50 k
Figure 9.
Figure 10.
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TYPICAL CHARACTERISTICS (continued)
SUPPLY VOLTAGE REJECTION RATIO vs FREQUENCY
-0 k SVR - Supply Voltage Rejection Ratio - dB -10 -20 -30 -40 -50 -60 -70 -80 -90 10 0.00001 100 1k f - Frequency - Hz 10 k 50 k 2k 32 W 64 W VCC = +15 V, V(ripple) = 1 VPP, Gain = 2 V/V BW = 80 kHz 0.1
INTERMODULATION DISTORTION vs HIGH FREQUENCY
4:1 SMPTE Ratio VI = 1 VPP, Gain = 2 V/V, IM Frequency = 60 Hz
Intermodulation Distortion - %
0.01
Representative of both positive and negative supplies.
0.001
VCC = +12 V, RL = 32 W
VCC = +15 V, RL = 32 W
0.0001 VCC = +15 V, RL = 64 W 50 k
VCC = +12 V, RL = 64 W
10 k f - High Frequency - Hz
Figure 11. INTERMODULATION DISTORTION vs IM AMPLITUDE (AT INPUT)
10 4:1 SMPTE Ratio Gain = 3 V/V, High Frequency = 7 kHz IM Frequency = 60 Hz VCC = +12 V, RL = 32 W 0.1 VCC = +12 V, RL = 64 W 0.01 VCC = +15 V, RL = 32 W -60 RF = 1 kW, Gain = 2 V/V, BW = 80 kHz
Figure 12. CROSSTALK vs FREQUENCY
Intermodulation Distortion - %
1
-70
VCC = +15 V, RL = 64 W VCC = +12 V, RL = 64 W
Crosstalk - dB
-80
-90
VCC = +15 V, RL = 32 W
-100 0.001 -110 0.0001 0.00001 0 VCC = +15 V, RL = 64 W 1 2 3 4 5 6 7 8 9 10 -120 10 100
VCC = +12 V, RL = 32 W
1k f - Frequency - Hz
10 k
50 k
IM Amplitude (At Input) - VPP
Figure 13.
Figure 14.
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SLOS431 - MARCH 2004
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TYPICAL CHARACTERISTICS (continued)
SIGNAL-TO-NOISE RATIO vs GAIN
130 RI = 64 W Signal-To-Noise Ratio - dB 125 VCC = +12 V Signal-To-Noise Ratio - dB 125 130 THD+N, RI = 64 W VCC = +15 V
SIGNAL-TO-NOISE RATIO vs GAIN
120
120
115
115
110 RI = 32 W 105
110 THD+N, RI = 32 W
105
100
1
10
20
30
40
50
60
70
80
90 100
100
1
10
20
30
40
50
60
70
80
90 100
Gain - V/V
Gain - V/V
Figure 15. SLEW RATE vs OUTPUT STEP
1500 1300 1100 Slew Rate - V/ s 900 700 VCC = 15 V Gain = 5 V/V RF = 1 k RL = 25 1000 900 +SR -SR Slew Rate - V/ s 700 800 VCC = 5 V Gain = 2 V/V RF = 1 k RL = 25
Figure 16. SLEW RATE vs OUTPUT STEP
+SR -SR 600 500 400 300
500 300
200 100 0 5 10 15 Output Step (Peak-To-Peak) - V 20 0 1 2 3 4 Output Step (Peak-To-Peak) - V 5
100
Figure 17.
Figure 18.
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TYPICAL CHARACTERISTICS (continued)
SMALL AND LARGE SIGNAL FREQUENCY RESPONSE
-3 -6 -9 Output Level - dBV -12 -15 -18 -21 VI = 62.5 mV -24 -27 -30 10 Gain = 1 V/V VCC = 15 V RF = 820 RL = 25 100 1k 10k 100k 1M 10M 100M 500M f - Frequency - Hz -18 -21 -24 10 VI = 125 mV VI = 250 mV Output Level - dBV VI = 500 mV 3 0 -3 -6 -9 -12 -15 VI = 62.5 mV Gain = 2 V/V VCC = 15 V RF = 680 RL = 25 100 1k 10k 100k 1M 10M 100M 500M f - Frequency - Hz VI = 125 mV VI = 250 mV VI = 500 mV
SMALL AND LARGE SIGNAL FREQUENCY RESPONSE
Figure 19. 400-mV STEP RESPONSE
400 300 VO - Output Voltage - mV 200 100 0 -100 -200 -300 -400 0 50 100 150 200 250 300 350 400 450 500 t - Time - ns 8 6 4 2 0 -2 -4 -6 -8 0 50
Figure 20. 10-V STEP RESPONSE
VO - Output Voltage - V
VCC = 15 V Gain = 2 V/V RL = 25 RF = 1 k tr/tf= 300 ps See Figure 3
VCC = 15 V Gain = 2 V/V RL = 25 RF = 1 k tr/tf= 5 ns See Figure 3 100 150 200 250 300 350 400 450 500 t - Time - ns
Figure 21.
Figure 22.
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TYPICAL CHARACTERISTICS (continued)
20-V STEP RESPONSE
16 12 8 4 0 -4 -8 -12 -16 0 50 100 150 200 250 300 350 400 450 500 t - Time - ns VCC = 15 V Gain = 5 V/V RL = 25 RF = 2 k tr/tf= 5 ns See Figure 3
VO - Output Voltage - V
Figure 23.
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APPLICATION INFORMATION
Current-Feedback Amplifiers The TPA6120A2 is a current-feedback amplifier with differential inputs and single-ended outputs. Current-feedback results in low voltage noise, high open-loop gain throughout a large frequency range, and low distortion. It can be used in a similar fashion as voltage-feedback amplifiers. The low distortion of the TPA6120A2 results in a signal-to-noise ratio of 120 dB as well as a dynamic range of 120 dB. Independent Power Supplies The TPA6120A2 consists of two independent high-fidelity amplifiers. Each amplifier has its own voltage supply. This allows the user to leave one of the amplifiers off, saving power, and reducing the heat generated. It also reduces crosstalk. Although the power supplies are independent, there are some limitations. When both amplifiers are used, the same voltage must be applied to each amplifier. For example, if the left channel amplifier is connected to a 12-V supply, the right channel amplifier must also be connected to a 12-V supply. If it is connected to a different supply voltage, the device may not operate properly and consistently. When the use of only one amplifier is preferred, it must be the left amplifier. The voltage supply to the left amplifier is also responsible for internal start-up and bias circuitry of the device. Regardless of whether one or both amplifiers are used, the VCC- pins of both amplifiers must always be at the same potential. To power down the right channel amplifier, disconnect the VCC+ pin from the power source. The two independent power supplies can be tied together on the board to receive their power from the same source. Power Supply Decoupling As with any design, proper power supply decoupling is essential. It prevents noise from entering the device via the power traces and provides the extra power the device can sometimes require in a rapid fashion. This prevents the device from being momentarily current starved. Both of these functions serve to reduce distortion, leaving a clean, uninterrupted signal at the output. Bulk decoupling capacitors should be used where the main power is brought to the board. Smaller capacitors should be placed as close as possible to the actual power pins of the device. Because the TPA6120A2 has four power pins, use four surface mount capacitors. Both types of capacitors should be low ESR. Resistor Values
RF = 1 kW VCC- RI = 1 kW - VI RS = 50 W VCC+ + RO = 10 W RL
Figure 24. Single-Ended Input With a Noninverting Gain of 2 V/V In the most basic configuration (see Figure 24), four resistors must be considered, not including the load impedance. The feedback and input resistors, RF and RI, respectively, determine the closed-loop gain of the amplifier. RO is a series output resistor designed to protect the amplifier from any capacitance on the output path, including board and load capacitance. RS is a series input resistor. Because the TPA6120A2 is a current-feedback amplifier, take care when choosing the feedback resistor.
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APPLICATION INFORMATION (continued)
The value of the feedback resistor should be chosen by using Figure 27 through Figure 32 as guidelines. The gain can then be set by adjusting the input resistor. The smaller the feedback resistor, the less noise is introduced into the system. However, smaller values move the dominant pole to higher and higher frequencies, making the device more susceptible to oscillations. Higher feedback resistor values add more noise to the system, but pull the dominant pole down to lower frequencies, making the device more stable. Higher impedance loads tend to make the device more unstable. One way to combat this problem is to increase the value of the feedback resistor. It is not recommended that the feedback resistor exceed a value of 10 k. The typical value for the feedback resistor for the TPA6120A2 is 1 k. In some cases, where a high-impedance load is used along with a relatively large gain and a capacitive load, it may be necessary to increase the value of the feedback resistor from 1 k to 2 k, thus adding more stability to the system. Another method to deal with oscillations is to increase the size of RO.
CAUTION:
Do not place a capacitor in the feedback path. Doing so can cause oscillations. Capacitance at the outputs can cause oscillations. Capacitance from some sources, such as layout, can be minimized. Other sources, such as those from the load (e.g., the inherent capacitance in a pair of headphones), cannot be easily minimized. In this case, adjustments to RO and/or RF may be necessary. The series output resistor should be kept at a minimum of 10 . It is small enough so that the effect on the load is minimal, but large enough to provide the protection necessary such that the output of the amplifier sees little capacitance. The value can be increased to provide further isolation, up to 100 . The series resistor, RS, should be used for two reasons: 1. It prevents the positive input pin from being exposed to capacitance from the line and source. 2. It prevents the source from seeing the input capacitance of the TPA6120A2. The 50- resistor was chosen because it provides ample protection without interfering in any noticeable way with the signal. Not shown is another 50- resistor that can be placed on the source side of RS to ground. In that capacity, it serves as an impedance match to any 50- source.
RF = 1 kW VCC- RI = 1 kW VI - + VCC+ RO = 10 W RL
Figure 25. Single-Ended Input With a Noninverting Gain of -1 V/V
RF = 1 kW VCC- RI= 1 kW VI- VI+ RI = 1 kW VCC+ RF = 1 kW - + RO = 10 W RL
Figure 26. Differential Input With a Noninverting Gain of 2 V/V Figure 26 shows the TPA6120A2 connected with differential inputs. Differential inputs are useful because they take the greatest advantage of the device's high CMRR. The two feedback resistor values must be kept the same, as do the input resistor values.
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APPLICATION INFORMATION (continued)
Special note regarding mono operation: * If both amplifiers are powered on, but only one channel is to be used, the unused amplifier MUST have a feedback resistor from the output to the negative input. Additionally, the positive input should be grounded as close to the pin as possible. Terminate the output as close to the output pin as possible with a 25- load to ground. * These measures should be followed to prevent the unused amplifier from oscillating. If it oscillates, and the power pins of both amplifiers are tied together, the performance of the amplifier could be seriously degraded. Checking for Oscillations and Instability Checking the stability of the amplifier setup is recommended. High frequency oscillations in the megahertz region can cause undesirable effects in the audio band. Sometimes, the oscillations can be quite clear. An unexpectedly large draw from the power supply may be an indication of oscillations. These oscillations can be seen with an oscilloscope. However, if the oscillations are not obvious, or there is a chance that the system is stable but close to the edge, placing a scope probe with 10 pF of capacitance can make the oscillations worse, or actually cause them to start. A network analyzer can be used to determine the inherent stability of a system. An output vs frequency curve generated by a network analyzer can be a good indicator of stability. At high frequencies, the curve shows whether a system is oscillating, close to oscillation, or stable. Looking at Figure 27 through Figure 32, several different phenomena occur. In one scenario, the system is stable because the high frequency rolloff is smooth and has no peaking. Increasing RF decreases the frequency at which this rolloff occurs (see the Resistor Values section). Another scenario shows some peaking at high frequency. If the peaking is 2 dB, the amplifier is stable as there is still 45 degrees of phase margin. As the peaking increases, the phase margin shrinks, the amplifier and the system, move closer to instability. The same system that has a 2-dB peak has an increased peak when a capacitor is added to the output. This indicates the system is either on the verge of oscillation or is oscillating, and corrective action is required.
3 2 Normalized Output Response - dB 1 0 -1 -2 -3 -4 -5 -6 -7 10 VCC = 15 V RL = 100 Gain = 1 V/V VI = 200 mV 100 1k 10k 100k 1M 10M 100M 500M RF = 1 k RF = 620 Normalized Output Response - dB RF = 820 3 2 RF = 430 1 0 -1 -2 -3 -4 -5 -6 10 VCC = 15 V RL = 100 Gain = 2 V/V VI = 200 mV 100 1k 10k RF = 1 k RF = 620
100k
1M
10M 100M 500M
f - Frequency - Hz
f - Frequency - Hz
Figure 27. Normalized Output Response vs Frequency
Figure 28. Normalized Output Response vs Frequency
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APPLICATION INFORMATION (continued)
1 0 Normalized Output Response - dB Normalized Output Response - dB -1 -2 -3 -4 -5 -6 -7 -8 -9 10 VCC = 15 V RF = 1 k Gain = 1 V/V VI = 200 mV 100 1k 10k 100k 1M 10M 100M 500M RL = 25 RL = 100 RL = 200 1 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 10 VCC = 15 V RF = 1 k Gain = 2 V/V VI = 200 mV 100 1k 10k 100k RL = 25 RL = 200 RL = 100
RL = 50
RL = 50
1M
10M 100M 500M
f - Frequency - Hz
f - Frequency - Hz
Figure 29. Normalized Output Response vs Frequency
3 2 RF = 620 Output Amplitude - dB Output Amplitude - dB 1 0 -1 -2 -3 -4 -5 -6 10 VCC = 5 V Gain = 1 V/V RL = 25 VI = 200 mV 100 1k 10k 100k 1M 10M 100M 500M f - Frequency - Hz RF = 1.5 k RF = 1 k
Figure 30. Normalized Output Response vs Frequency
9 8 7 6 5 4 3 2 1 0 10 VCC = 5 V Gain = 2 V/V RL = 25 VI = 200 mV 100 1k 10k 100k 1M 10M 100M 500M f - Frequency - Hz RF = 1.2 k RF = 820 RF = 510
Figure 31. Output Amplitude vs Frequency
Figure 32. Output Amplitude vs Frequency
PCB Layout Proper board layout is crucial to getting the maximum performance out of the TPA6120A2. A ground plane should be used on the board to provide a low inductive ground connection. Having a ground plane underneath traces adds capacitance, so care must be taken when laying out the ground plane on the underside of the board (assuming a 2-layer board). The ground plane is necessary on the bottom for thermal reasons. However, certain areas of the ground plane should be left unfilled. The area underneath the device where the PowerPAD is soldered down should remain, but there should be no ground plane underneath any of the input and output pins. This places capacitance directly on those pins and leads to oscillation problems. The underside ground plane should remain unfilled until it crosses the device side of the input resistors and the output series resistor. Thermal reliefs should be avoided if possible because of the inductance they introduce.
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TPA6120A2
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SLOS431 - MARCH 2004
APPLICATION INFORMATION (continued)
Despite the removal of the ground plane in critical areas, stray capacitance can still make its way onto the sensitive outputs and inputs. Place components as close as possible to the pins and reduce trace lengths. See Figure 33 and Figure 34. It is important for the feedback resistor to be extremely close to the pins, as well as the series output resistor. The input resistor should also be placed close to the pin. If the amplifier is to be driven in a noninverting configuration, ground the input close to the device so the current has a short, straight path to the PowerPAD (gnd).
Too Long RI VI - + TPA6120A2 Too Long Too Long RO RL Too Long RF
Figure 33. Layout That Can Cause Oscillation
Minimized Length of Feedback Path Short Trace Before Resistors VI
RF - RO
RI + RL TPA6120A2 Minimized Length of the Trace Between Output Node and RO
Ground as Close to the Pin as Possible
Figure 34. Layout Designed To Reduce Capacitance On Critical Nodes
Thermal Considerations
Amplifiers can generate quite a bit of heat. Linear amplifiers, as opposed to Class-D amplifiers, are extremely inefficient, and heat dissipation can be a problem. There is no one to one relationship between output power and heat dissipation, so the following equations must be used: PL Efficiency of an amplifier + P SUP (1) Where
PL + P SUP I CCavg VLRMS V V , and VLRMS + P , therefore, P L + P per channel RL 2RL 2 + VCC I CCavg ) VCC I CC(q) p VP V 1 +p sin(t) dt + * [cos(t)] 2 + P RL pR L p RL 0 0
p 2 VP
2 2
(2) (3)
(4)
Where
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TPA6120A2
SLOS431 - MARCH 2004
www.ti.com
APPLICATION INFORMATION (continued)
VP + 2 PL R L
(5)
Therefore, VV P SUP + CC P ) V CC I CC(q) p RL
PL = Power delivered to load (per channel) PSUP = Power drawn from power supply VLRMS = RMS voltage on the load RL = Load resistance VP = Peak voltage on the load ICCavg = Average current drawn from the power supply ICC(q) = Quiescent current (per channel) VCC = Power supply voltage (total supply voltage = 30 V if running on a 15-V power supply = Efficiency of a SE amplifier
(6)
For stereo operation, the efficiency does not change because both PL and PSUP are doubled. This effects the amount of power dissipated by the package in the form of heat. A simple formula for calculating the power dissipated, PDISS, is shown in Equation 7: P DISS + (1 * h) P SUP In stereo operation, PSUP is twice the quantity that is present in mono operation. The maximum ambient temperature, TA, depends on the heat-sinking ability of the system. JA for a 20-pin DWP, whose thermal pad is properly soldered down, is shown in the dissipation rating table. T A Max + T J Max * JA P Diss
2 1.8 PD - Power Dissipation - W 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0 0 0.5 1 1.5 2 2.5 3 3.5 VCC = +12 V, RL = 64 W VCC = +15 V, RL = 64 W VCC = +12 V, RL = 32 W Mono Operation VCC = +15 V, RL = 32 W
(7)
(8)
PO - Output Power - W
Figure 35. Power Dissipation vs Output Power
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TPA6120A2
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SLOS431 - MARCH 2004
Application Circuit
OPA4134 V+ + 5V 10 F 0.1 F V- + 0.1 F 10 F + -5 V + 12 V 100 F
CF 2.7 nF
TPA6120A2 VCC+ 10 F VCC- -12 V 10 F 100 F +
RF 1 kW 1 4 V+ VCC- RI 1 kW 4 5 - 2 3 0.1 mF RF 1 kW VCC+ 0.1 mF
RF 1 kW V-
-INA
2 3
- +
11
OUTA
5V 0.1 F + 1 2 3 4 PCM Audio Data Source 5 6 7 0.1 F 8 9 ZEROL ZEROR MSEL LRCK DATA BCK SCK DGND VDD PCM1792 VCC2L AGND3L 28 27 10 F
+
0.1 mF 19 0.1 mF
CF 2.7 nF RI 1 kW
LIN- LIN+
4
LOUT
RO 10 W
+
RF 1 kW
IOUTL- 26 IOUTL+ AGND2 VCC1 VCOML VCOMR IREF AGND1 IOUTR- IOUTR+ AGND3R VCC2R 25 24 23 22 21 20 10 k + + 47 F -INB 5V
6 5 - +
V- 11 7
OUTB
4 V+
47 F 10 F +
CF 2.7 nF
RF 1 kW V- 9 - + 4 V+ CF 2.7 nF 11 8 RF 1 kW VCC- RI 1 kW 20 16 -
10 MS 11 MDI Controller 12 MC 13 MDO 14 RST 3.3 V +
19 18 17 16 15 + 10 F 0.1 F -INC 5V
OUTC
10
RIN- RIN+
RI 1 kW 17 RF 1 kW 11 14 + 18
ROUT
RO 10 W
RF 1 kW V- 13 - + 4 V+
VCC+
10 F
-IND
12
OUTD
Figure 36. Typical Application Circuit In many applications, the audio source is digital. It must go through a digital-to-analog converter (DAC) so that traditional analog amplifiers can drive the speakers or headphones. Figure 36 shows a complete circuit schematic for such a system. The digital audio is fed into a high performance DAC. The PCM1792, a Burr-Brown product from TI, is a 24-bit, stereo DAC. The output of the PCM1792 is current, not voltage, so the OPA4134 is used to convert the current input to a voltage output. The OPA4134, a Burr-Brown product from TI, is a low-noise, high-speed, high-performance operational amplifier. CF and RF are used to set the cutoff frequency of the filter. The RC combination in Figure 36 has a cutoff frequency of 59 kHz. All four amplifiers of the OPA4134 are used so the TPA6120A2 can be driven differentially.
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TPA6120A2
SLOS431 - MARCH 2004
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The output of the OPA4134 goes into the TPA6120A2. The TPA6120A2 is configured for use with differential inputs, stereo use, and a gain of 2V/V. Note that the 0.1-uF capacitors are placed at every supply pin of the TPA6120A2, as well as the 10- series output resistor. Each output goes to one channel of a pair of stereo headphones, where the listener enjoys crisp, clean, virtually noise free music with a dynamic range greater than the human ear is capable of detecting.
20
THERMAL PAD DATA
DWP (R-PDSO-G20)
PowerPADTM PLASTIC SMALL-OUTLINE PACKAGE
www.ti.com
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