Texas Instruments TPA3008D2 User manual

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FEATURES DESCRIPTION
APPLICATIONS
10 µF
220 nF 220 nF
PVCC PVCC
220 nF 220 nF
PVCC PVCC
220 pF
Left Differential
Inputs
Right Differential
Inputs
Shutdown/Mute
Gain
Control
BSLP
PVCCL PVCCL
LOUTP LOUTP
PGNDL
PGNDL LOUTN
LOUTN PVCCL
PVCCL BSLN
TPA3008D2
VCLAMPR
SHUTDOWN
V2P5
RINP
LINN
LINP
AVDDREF
NC
GAIN0
GAIN1
NC
NC
AVDD
AGND
COSC
ROSC
AVCC
VCLAMPL
BSRP
PVCCR PVCCR
ROUTP ROUTP
PGNDR PGNDR
ROUTN ROUTN PVCCR PVCCR
BSRN
RINN
AVCC
AGND
10 µF
0.1 µF0.1 µF
0.47 µF
0.47 µF
0.47 µF
0.47 µF
0.47 µF
0.1 µF0.1 µF
10 µF10 µF
1 µF
120 kΩ
1 µF
NC
NC
NC
FAULT
0.1 µF10 µF
1 µF
Control
†Optional output filter for EMI suppression
†
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
10-W STEREO CLASS-D AUDIO POWER AMPLIFIER
•10-W/Channel Into an 16-ΩLoad From a
The TPA3008D2 is a 10-W (per channel) efficient,17-V Supply
class-D audio amplifier for driving bridged-tied stereospeakers. The TPA3008D2 can drive stereo speakers•Up to 92% Efficient, Class-D Operation
as low as 8 Ω. The high efficiency of the TPA3008D2Eliminates Need For Heatsinks
eliminates the need for external heatsinks when•8.5-V to 18-V Single-Supply Operation
playing music.•Four Selectable, Fixed Gain Settings
The gain of the amplifier is controlled by two gain•Differential Inputs Minimizes Common-Mode
select pins. The gain selections are 15.3, 21.2, 27.2,Noise
and 31.8 dB.•Space-Saving, Thermally Enhanced
The outputs are fully protected against shorts toPowerPAD™ Packaging
GND, VCC, and output-to-output shorts. A fault ter-•Thermal and Short-Circuit Protection
minal allows short-circuit fault reporting and automaticWith Auto Recovery Option
recovery. Thermal protection ensures that the maxi-mum junction temperature is not exceeded.•Pinout Similar to TPA3000D Family
•LCD Monitors and TVs•All-In-One PCs
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of TexasInstruments 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.
Copyright © 2004, Texas Instruments IncorporatedProducts conform to specifications per the terms of the TexasInstruments standard warranty. Production processing does notnecessarily include testing of all parameters.

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ABSOLUTE MAXIMUM RATINGS
DISSIPATION RATING TABLE
RECOMMENDED OPERATING CONDITIONS
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
These devices have limited built-in ESD protection. The leads should be shorted together or the deviceplaced in conductive foam during storage or handling to prevent electrostatic damage to the MOS gates.
over operating free-air temperature range (unless otherwise noted)
(1)
TPA3008D2
Supply voltage range AV
CC
, PV
CC
-0.3 V to 20 VLoad Impedance, R
L
≥6ΩSHUTDOWN -0.3 V to VCC + 0.3 VInput voltage range, V
I
GAIN0, GAIN1, RINN, RINP, LINN, LINP -0.3 V to 6 VContinuous total power dissipation See Dissipation Rating TableOperating free–air temperature range, T
A
- 40°C to 85°COperating junction temperature range, T
J
- 40°C to 150°CStorage temperature range, T
stg
- 65°C to 150°CLead temperature 1,6 mm (1/16 inch) from case for 10 seconds 260°C
(1) Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratingsonly, and functional operation of the device at these or any other conditions beyond those indicated under “recommended operatingconditions” is not implied. Exposure to absolute–maximum–rated conditions for extended periods may affect device reliability.
DERATINGPACKAGE T
A
≤25°Cθ
JC
FACTOR T
A
= 70°C T
A
= 85°C(1/θ
JA
)
PHP 4.3 W 1.14 °C/W
(1)
34.7 mW/°C
(1)
2.7 W 2.2 W
(1) Based on a JEDEC high-K PCB with the PowerPAD™ soldered to a thermal land on theprinted-circuit board. See the PowerPAD Thermally Enhanced Package application note (SLMA002).The PowerPAD must be soldered to the PCB.
T
A
= 25°C (unless otherwise noted)
MIN MAX UNIT
Supply voltage, V
CC
PV
CC
, AV
CC
8.5 18 VHigh-level input voltage, V
IH
SHUTDOWN, GAIN0, GAIN1 2 VLow-level input voltage, V
IL
SHUTDOWN, GAIN0, GAIN1 0.8 VSHUTDOWN, V
I
= V
CC
= 18 V 10 µAHigh-level input current, I
IH
GAIN0, GAIN1, V
I
= 5.5 V, V
CC
= 18 V 1 µASHUTDOWN, V
I
= 0 V, V
CC
= 18 V 1 µALow-level input current, I
IL
GAIN0, GAIN1, V
I
= 5.5 V, V
CC
= 18 V 1 µAHigh-level output voltage, V
OH
FAULT, I
OH
= 100 µA AV
DD
- 0.8 V VLow-level output voltage, V
OL
FAULT, I
OL
= -100 µA AGND + 0.8 V VFrequency is set by selection of ROSC and COSCOscillator frequency, f
OSC
200 300 kHz(see the Application Information Section).Operating free–air temperature, T
A
-40 85 °C
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AVAILABLE OPTIONS
DC ELECTRICAL CHARACTERISTICS
AC ELECTRICAL CHARACTERISTICS
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
T
A
PACKAGED DEVICE48-PIN HTQFP (PHP)
(1)
-40°C to 85°C TPA3008D2PHP
(1) The PHP package is available taped and reeled. To order a tapedand reeled part, add the suffix R to the part number (e.g.,TPA3008D2PHPR).
T
A
= 25°C, V
CC
= 12 V, R
L
= 8 Ω(unless otherwise noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Class-D output offset voltage INN and INP connected together,|V
OO
| 2 5 55 mV(measured differentially) Gain = 31.8 dBV2P5 2.5-V Bias voltage No load 2.5 VI
L
= 10 mA, SHUTDOWN = 2 V,AV
DD
+5-V internal supply voltage 4.5 5 5.5 VV
CC
= 8.5 V to 18 VPSRR Power supply rejection ratio V
CC
= 11.5 V to 12.5 V -76 dBI
CC
Quiescent supply current SHUTDOWN = 2 V, no load 11 22 mAQuiescent supply current in shut-I
CC(SD)
SHUTDOWN = 0 V 1.6 25 µAdown mode
High side 600V
CC
= 12 V,r
DS(on)
Drain-source on-state resistance I
O
= 1 A, Low side 500 mΩT
J
= 25°C
Total 1100 1300GAIN0 = 0.8 V 14.6 15.3 16.2GAIN1 = 0.8 V
GAIN0 = 2 V 20.5 21.2 21.8G Gain dBGAIN0 = 0.8 V 26.4 27.2 27.8GAIN1 = 2 V
GAIN0 = 2 V 31.1 31.8 32.5t
on
Turnon time C
(V2P5)
= 1 µF, SHUTDOWN = 2 V 16 mst
off
Turnoff time C
(V2P5)
= 1 µF, SHUTDOWN = 0.8 V 60 µs
T
A
= 25°C, V
CC
= 12 V, R
L
= 8 Ω, (unless otherwise noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
200 mV
PP
ripple from 20 Hz to 1 kHz,k
SVR
Supply voltage rejection ratio -70 dBGain = 15.6 dB, Inputs ac-coupled to GNDTHD+N = 0.13%, f = 1 kHz, R
L
= 8 Ω5THD+N = 10%, f = 1 kHz, R
L
= 8 Ω8.5THD+N = 0.16%, f = 1 kHz, R
L
= 16 Ω,P
O
Continuous output power W5V
CC
= 17 VTHD+N = 10%, f = 1 kHz, R
L
= 16 Ω,
10V
CC
= 17 VTotal harmonic distortion plusTHD+N P
O
= 1 W, f = 1 kHz, R
L
= 8 Ω0.1%noise
20 Hz to 22 kHz, A-weighted filter,V
n
Output integrated noise floor -80 dBGain = 15.6 dBCrosstalk P
O
= 1 W, R
L
= 8 Ω, Gain = 15.6 dB, -93 dBf = 1 kHzMaximum output at THD+N < 0.5%,SNR Signal-to-noise ratio 97 dBf = 1 kHz, Gain = 15.6 dBThermal trip point 150 °CThermal hystersis 20 °C
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Biases
and
References
TTL Input
Buffer
(VCC Compl)
Start-up and
Protection
Logic
SC
Detect
Thermal
VDDok
RINP
RINN
Ramp
Generator
COSC
ROSC
VCCok
5-V LDO
AVCC
AVDD
AVDD
VDD
and
PWM
Mode
Logic
Gain
Adj.
Gain
Control
Deglitch
and
PWM
Mode
Logic
Gain
Adj.
LINP
LINN
Gate
Drive
VClamp
Gen
Gate
Drive
PVCC
BSRP
PVCCR(2)
ROUTP(2)
PGNDR
PGNDR
ROUTN(2)
PVCCR(2)
BSRN
Gate
Drive
VClamp
Gen
Gate
Drive
PVCC
BSLP
PVCCL(2)
LOUTP(2)
PGNDL
PGNDL
LOUTN(2)
PVCCL(2)
BSLN
VCLAMPL
VCLAMPR
GAIN0 4To Gain Adj.
Blocks and
Start-up Logic
SHUTDOWN
V2P5
V2P5 V2P5
AVCC
AGND(2)
V2P5
V2P5
Deglitch
GAIN1
AVDDREF
FAULT
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
FUNCTIONAL BLOCK DIAGRAM
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13 14 15 16 17 18 19 20 21 22 23 24
25
26
27
28
29
30
31
32
33
34
35
36
48 47 46 45 44 43 42 41 40 39 38 37
1
2
3
4
5
6
7
8
9
10
11
12
BSRN PVCCR PVCCR ROUTN ROUTN PGNDR PGNDR ROUTP ROUTP PVCCR PVCCR BSRP
VCLAMPR
NC
NC
NC
NC
AGND
COSC
ROSC
AGND
VCLAMPL
SHUTDOWN
RINN
RINP
V2P5
LINP
LINN
NC
GAIN0
GAIN1
FAULT
NC
BSLN
PVCCL PVCCL
LOUTN LOUTN
PGNDL PGNDL
LOUTP LOUTP PVCCL PVCCL
BSLP
TPA3008D2
AVCC
AVDD
AVDDREF
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
PHP PACKAGE
(TOP VIEW)
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TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
TERMINAL FUNCTIONS
PIN NAME PIN NUMBER I/O DESCRIPTION
AGND 26, 30 - Analog ground for digital/analog cells in coreAV
CC
33 - High-voltage analog power supply, not connected internally to PVCCR or PVCCL5-V Regulated output for use by internal cells and GAIN0, GAIN1 pins only. NotAV
DD
29 O
specified for driving other external circuitry.AV
DD
REF 7 O 5-V Reference output—connect to gain setting resistor or directly to GAIN0, GAIN1.BSLN 13 - Bootstrap I/O for left channel, negative high-side FETBSLP 24 - Bootstrap I/O for left channel, positive high-side FETBSRN 48 - Bootstrap I/O for right channel, negative high-side FETBSRP 37 - Bootstrap I/O for right channel, positive high-side FETCOSC 28 I/O I/O for charge/discharging currents onto capacitor for ramp generator.Short-circuit detect fault output.FAULT = high, short-circuit detected.FAULT 11 O
FAULT = low, normal operation.Status is reset when power is cycled or SHUTDOWN is cycled.GAIN0 9 I Gain select least significant bit. TTL logic levels with compliance to AV
DD
.GAIN1 10 I Gain select most significant bit. TTL logic levels with compliance to AV
DD
.LINN 6 I Negative audio input for left channelLINP 5 I Positive audio input for left channelLOUTN 16, 17 O Class-D 1/2-H-bridge negative output for left channelLOUTP 20, 21 O Class-D 1/2-H-bridge positive output for left channel8, 12, 31, 32,NC - No internal connection34, 35PGNDL 18, 19 - Power ground for left channel H-bridgePGNDR 42, 43 - Power ground for right channel H-bridgePower supply for left channel H-bridge (internally connected to pins 22 and 23), notPVCCL 14, 15 -
connected to PVCCR or AV
CC
.Power supply for left channel H-bridge (internally connected to pins 14 and 15), notPVCCL 22, 23 -
connected to PVCCR or AV
CC
.Power supply for right channel H-bridge (internally connected to pins 46 and 47),PVCCR 38, 39 -
not connected to PVCCL or AV
CC
.Power supply for right channel H-bridge (internally connected to pins 38 and 39),PVCCR 46, 47 -
not connected to PVCCL or AV
CC
.RINP 3 I Positive audio input for right channelRINN 2 I Negative audio input for right channelROSC 27 I/O I/O current setting resistor for ramp generator.ROUTN 44, 45 O Class-D 1/2-H-bridge negative output for right channelROUTP 40, 41 O Class-D 1/2-H-bridge positive output for right channelShutdown signal for IC (low = shutdown, high = operational). TTL logic levels withSHUTDOWN 1 I
compliance to V
CC
.VCLAMPL 25 - Internally generated voltage supply for left channel bootstrap capacitors.VCLAMPR 36 - Internally generated voltage supply for right channel bootstrap capacitors.V2P5 4 O 2.5-V Reference for analog cells.Connect to AGND and PGND—should be the center point for both grounds. InternalThermal Pad - -
resistive connection to AGND.
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TYPICAL CHARACTERISTICS
0.01 20 20 k
100 1 k 10 k
THD+N −Total Harmonic Distortion + Noise − %
VCC = 18 V,
RL= 16 
Gain = 21.6 dB
f − Frequency − Hz
10
0.1
PO= 2.5 W
PO= 0.5 W
PO= 1 W
1
0.005
10
0.01
0.1
20 20 k 100 1 k 10 k
PO= 2.5 W
THD+N −Total Harmonic Distortion + Noise − %
VCC = 12 V,
RL= 16 ,
Gain = 21.6 dB
f − Frequency − Hz
PO= 1 W
1
PO= 0.5 W
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
TABLE OF GRAPHS
FIGURE
THD+N Total harmonic distortion + noise vs Frequency 1, 2, 3, 4THD+N Total harmonic distortion + noise vs Output power 5, 6Closed-loop response 7Output power vs Supply voltage 8, 9Efficiency vs Output power 10Efficiency vs Total output power 11V
CC
Supply current vs Total output power 12Crosstalk vs Frequency 13k
SVR
Supply ripple rejection ratio vs Frequency 14CMRR Commom-mode rejection ratio vs Frequency 15
TOTAL HARMONIC DISTORTION + NOISE TOTAL HARMONIC DISTORTION + NOISEvs vsFREQUENCY FREQUENCY
Figure 1. Figure 2.
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0.005
10
0.01
0.1
20 20 k 100 1 k 10 k
PO= 5 W
THD+N −Total Harmonic Distortion + Noise − %
VCC = 18 V,
RL= 8 ,
Gain = 21.6 dB
f − Frequency − Hz
PO= 1 W
PO= 2.5 W
1
0.01
0.1
10
20 20 k 100 1 k 10 k
THD+N −Total Harmonic Distortion + Noise − %
VCC = 12 V,
RL= 8 
Gain = 21.6 dB
f − Frequency − Hz
PO= 1 W
PO= 2.5 W
PO= 0.5 W
1
0.01
10
0.1
1
20m 10100 m 1
THD+N −Total Harmonic Distortion + Noise − %
PO− Output Power − W
VCC = 12 V,
RL= 8 ,
Gain = 21.6 dB
20200 m 2
1 kHz
20
20 Hz
20 kHz
0.01
10
0.1
1
20m 10100 m 1
THD+N −Total Harmonic Distortion + Noise − %
PO− Output Power − W
VCC = 18 V,
RL= 16 ,
Gain = 21.6 dB
20 Hz
20200 m 2
20 kHz
1 kHz
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
TOTAL HARMONIC DISTORTION + NOISE TOTAL HARMONIC DISTORTION + NOISEvs vsFREQUENCY FREQUENCY
Figure 3. Figure 4.
TOTAL HARMONIC DISTORTION + NOISE TOTAL HARMONIC DISTORTION + NOISEvs vsOUTPUT POWER OUTPUT POWER
Figure 5. Figure 6.
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28
24
20
16
10 100 1k
Gain − dB
32
36
f − Frequency − Hz
40
10k
12
8
4
080k
VCC = 12 V,
RL= 8 Ω,
Gain = 32 dB
33 kHz, RC LPF
Gain
Phase
Phase −
50
0
100
−150

−100
−50
150
0
1
2
3
4
5
6
7
8
9
10
11
12
8 9 10 11 12 13 14 15 16 17 18
PO− Output Power − W
THD+N = 10%
THD+N = 1%
RL= 16 
VCC − Supply Voltage − V
2
3
4
5
6
7
8
9
8 9 10 11 12 13 14
THD+N = 1%
THD+N = 10%
RL= 8 
VCC − Supply Voltage − V
PO− Output Power − W
10
11
12
Power represented by dashed line
may require external heatsinking
0
10
20
30
40
50
60
70
0 1 2 3 4 5 6
PO− Output Power (Per Channel) − W
Efficiency − %
80
90
100
7 8 9 10
VCC = 18 V,
RL= 16 
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
OUTPUT POWER
vsCLOSED-LOOP RESPONSE SUPPLY VOLTAGE
Figure 7. Figure 8.
OUTPUT POWER EFFICIENCYvs vsSUPPLY VOLTAGE OUTPUT POWER
Figure 9. Figure 10.
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0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8 9 10
Efficiency − %
16 
8 
PO− Total Output Power − W
11 12
VCC = 12 V,
LC Filter,
Resistive Load,
Stereo Operation
0
0.2
0.4
0.6
0.8
1
1.2
1.4
0 2 4 6 8 10 12
PO− Total Output Power − W
1.6
1.8
2.0
14 16 18 20
LC Filter,
Resistive Load,
Stereo Operation
− Supply Current − AVCC
VCC = 18 V,
RL= 16 
VCC = 12 V,
RL= 16 
VCC = 12 V,
RL= 8 
−100
−90
−80
−70
−60
−50
−40
−30
−20
−10
0
20 100 1 k 10 k
Crosstalk − dB
f − Frequency − Hz
VCC = 12 V,
PO= 2.5 W,
Gain = 21.6 dB
RL= 8
20 k
−100
−90
−80
−70
−60
−50
−40
20 100 1 k 10 k
f − Frequency − Hz
kSVR − Supply Ripple Rejection Ratio − dB
VCC = 12 V,
V(RIPPLE) = 200 mVPP,
RL= 8 ,
Gain = 15.6 dB
20 k
−30
−20
−10
0
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
EFFICIENCY SUPPLY CURRENTvs vsTOTAL OUTPUT POWER TOTAL OUTPUT POWER
Figure 11. Figure 12.
CROSSTALK SUPPLY RIPPLE REJECTION RATIOvs vsFREQUENCY FREQUENCY
Figure 13. Figure 14.
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−70
−60
−50
−40
−30
−20
−10
0
100 1 k 10 k20
VCC = 12 V,
Gain = 15.6 dB,
RL= 8 
Output Referred
f − Frequency − Hz
CMRR − Common-Mode Rejection Ratio − dB
20 k
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
COMMON-MODE REJECTION RATIOvsFREQUENCY
Figure 15.
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APPLICATION INFORMATION
220 nF 220 nF
PVCC PVCC
220 nF 220 nF
PVCC PVCC
220 pF
Right Differential
Inputs
Shutdown/Mute
BSLP PVCCL PVCCL LOUTP LOUTP PGNDL PGNDL LOUTN LOUTN
PVCCL PVCCL BSLN
TPA3008D2
VCLAMPR
SHUTDOWN
V2P5
RINP
LINN
LINP
AVDDREF
NC
GAIN0
GAIN1
NC
NC
AVDD
AGND
COSC
ROSC
AVCC
VCLAMPL
BSRP
PVCCR PVCCR
ROUTP ROUTP
PGNDR PGNDR
ROUTN ROUTN
PVCCR PVCCR
BSRN
RINN
AVCC
AGND
10 F10 F
0.1 F0.1 F
0.47 F
0.47 F
0.47 F
0.47 F
0.47 F
0.1 F 0.1 F
10 F 10 F
1 F
120 k
1 F
NC
NC
NC
FAULT
0.1 F10 F
1 F
Control
Left Differential
Inputs
Gain
Control
1 nF1 nF
 
Chip ferrite bead (example: Fair-Rite 251206700743) shown for EMI suppression.
1 nF
1 nF

Fault Reporting
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
Figure 16. Stereo Class-D With Differential Inputs
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CLASS-D OPERATION
Traditional Class-D Modulation Scheme
0 V
−12 V
+12 V
Current
OUTP
Differential Voltage
Across Load
OUTN
TPA3008D2 Modulation Scheme
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
APPLICATION INFORMATION (continued)
This section focuses on the class-D operation of the TPA3008D2.
The traditional class-D modulation scheme, which is used in the TPA032D0x family, has a differential outputwhere each output is 180 degrees out of phase and changes from ground to the supply voltage, V
CC
. Therefore,the differential prefiltered output varies between positive and negative V
CC
, where filtered 50% duty cycle yields0 V across the load. The traditional class-D modulation scheme with voltage and current waveforms is shown inFigure 17 . Note that even at an average of 0 V across the load (50% duty cycle), the current to the load is high,causing high loss and thus causing a high supply current.
Figure 17. Traditional Class-D Modulation Scheme's Output Voltage and Current Waveforms Into anInductive Load With No Input
The TPA3008D2 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 greaterthan 50% and OUTN is less than 50% for positive output voltages. The duty cycle of OUTP is less than 50% andOUTN is greater than 50% for negative output voltages. The voltage across the load sits at 0 V throughout mostof the switching period, greatly reducing the switching current, which reduces any I
2
R losses in the load.
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0 V
−12 V
+12 V
Current
OUTP
OUTN
Differential
Voltage
Across
Load
0 V
−12 V
+12 V
Current
OUTP
OUTN
Differential
Voltage
Across
Load
Output = 0 V
Output > 0 V
Efficiency: LC Filter Required With the Traditional Class-D Modulation Scheme
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
APPLICATION INFORMATION (continued)
Figure 18. The TPA3008D2 Output Voltage and Current Waveforms Into an Inductive Load
The main reason that the traditional class-D amplifier needs an output filter is that the switching waveform resultsin maximum current flow. This causes more loss in the load, which causes lower efficiency. The ripple current islarge for the traditional modulation scheme, because the ripple current is proportional to voltage multiplied by thetime at that voltage. The differential voltage swing is 2 x V
CC
, and the time at each voltage is half the period forthe traditional modulation scheme. An ideal LC filter is needed to store the ripple current from each half cycle forthe 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 TPA3008D2 modulation scheme has little loss in the load without a filter because the pulses are short andthe change in voltage is V
CC
instead of 2 x V
CC
. As the output power increases, the pulses widen, making theripple current larger. Ripple current could be filtered with an LC filter for increased efficiency, but for mostapplications the filter is not needed.
An LC filter with a cutoff frequency less than the class-D switching frequency allows the switching current to flowthrough the filter instead of the load. The filter has less resistance than the speaker, which results in less powerdissipation, therefore increasing efficiency.
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Effects of Applying a Square Wave Into a Speaker
Efficiency (theoretical, %) RL
RLrds(on)100% 8
(8 1.3) 100% 86%
(1)
P(total) PO
Efficiency 8.5 W
0.86 9.88 W
(2)
Other losses P(total)(measured) P(total) (theoretical) 10.49 9.88 0.61 W
(3)
P(dis) 0.61 W (12 V 22 mA) 0.35 W
(4)
When to Use an Output Filter for EMI Suppression
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
APPLICATION INFORMATION (continued)
Audio specialists have advised for years not to apply a square wave to speakers. If the amplitude of thewaveform is high enough and the frequency of the square wave is within the bandwidth of the speaker, thesquare wave could cause the voice coil to jump out of the air gap and/or scar the voice coil. A 250-kHz switchingfrequency, however, does not significantly move the voice coil, as the cone movement is proportional to 1/f
2
forfrequencies beyond the audio band.
Damage may occur if the voice coil cannot handle the additional heat generated from the high-frequencyswitching current. The amount of power dissipated in the speaker may be estimated by first considering theoverall efficiency of the system. If the on-resistance (rds(on)) of the output transistors is considered to cause thedominant loss in the system, then the maximum theoretical efficiency for the TPA3008D2 with an 8-Ωload is asfollows:
The maximum measured output power is approximately 8.5 W with an 12-V power supply. The total theoreticalpower supplied (P(total)) for this worst-case condition would therefore be as follows:
The efficiency measured in the lab using an 8-Ωspeaker was 81%. The power not accounted for as dissipatedacross the r
DS(on)
may be calculated by simply subtracting the theoretical power from the measured power:
The quiescent supply current at 12 V is measured to be 22 mA. It can be assumed that the quiescent currentencapsulates all remaining losses in the device, i.e., biasing and switching losses. It may be assumed that anyremaining power is dissipated in the speaker and is calculated as follows:
Note that these calculations are for the worst-case condition of 8.5 W delivered to the speaker. Because the 0.35W is only 4% of the power delivered to the speaker, it may be concluded that the amount of power actuallydissipated in the speaker is relatively insignificant. Furthermore, this power dissipated is well within thespecifications of most loudspeaker drivers in a system, as the power rating is typically selected to handle thepower generated from a clipping waveform.
Design the TPA3008D2 without the filter if the traces from amplifier to speaker are short (< 50 cm). Poweredspeakers, where the speaker is in the same enclosure as the amplifier, is a typical application for class-D withouta filter.
Most applications require a ferrite bead filter. The ferrite filter reduces EMI around 1 MHz and higher (FCC andCE only test radiated emissions greater than 30 MHz). When selecting a ferrite bead, choose one with highimpedance at high frequencies, but low impedance at low frequencies.
Use a LC output filter if there are low frequency (<1 MHz) EMI-sensitive circuits and/or there are long wires fromthe amplifier to the speaker.
When both an LC filter and a ferrite bead filter are used, the LC filter should be placed as close as possible tothe IC followed by the ferrite bead filter.
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0.1 µF
0.1 µF
0.47 µF
33 µH
33 µH
OUTP
OUTN
L1
L2
C1C2
C3
1 nF
Ferrite
Chip Bead
OUTP
OUTN
Ferrite
Chip Bead
1 nF
Gain setting via GAIN0 and GAIN1 inputs
INPUT RESISTANCE
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
APPLICATION INFORMATION (continued)
Figure 19. Typical LC Output Filter, Cutoff Frequency of 27 kHz, Speaker Impedance = 8 Ω
Figure 20. Typical Ferrite Chip Bead Filter (Chip bead example: Fair-Rite 2512067007Y3)
The gain of the TPA3008D2 is set by two input terminals, GAIN0 and GAIN1.
The gains listed in Table 1 are realized by changing the taps on the input resistors inside the amplifier. Thiscauses the input impedance (Z
i
) to be dependent on the gain setting. The actual gain settings are controlled byratios of resistors, so the gain variation from part-to-part is small. However, the input impedance may shift by20% due to shifts in the actual resistance of the input resistors.
For design purposes, the input network (discussed in the next section) should be designed assuming an inputimpedance of 26 kΩ, which is the absolute minimum input impedance of the TPA3008D2. At the lower gainsettings, the input impedance could increase as high as 165 kΩ
Table 1. Gain Setting
INPUT IMPEDANCEAMPLIFIER GAIN (dB)
(kΩ)GAIN1 GAIN0
TYP TYP
0 0 15.3 1370 1 21.2 881 0 27.2 521 1 31.8 33
Each gain setting is achieved by varying the input resistance of the amplifier that can range from its smallestvalue, 33 kΩ, to the largest value, 137 kΩ. As a result, if a single capacitor is used in the input high-pass filter,the -3 dB or cutoff frequency changes when changing gain steps.
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CiIN Zi
Zf
Input
Signal
f1
2ZiCi
(5)
INPUT CAPACITOR, C
I
fc1
2ZiCi
−3 dB
fc
(6)
Ci1
2Zifc
(7)
Power Supply Decoupling,C
S
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
The -3-dB frequency can be calculated using Equation 5. Use Table 1 for Z
i
values.
In the typical application, an input capacitor (C
i
) is required to allow the amplifier to bias the input signal to theproper dc level for optimum operation. In this case, C
i
and the input impedance of the amplifier (Z
i
) form ahigh-pass filter with the corner frequency determined in Equation 6 .
The value of C
i
is important, as it directly affects the bass (low-frequency) performance of the circuit. Considerthe example where Z
i
is 137 kΩand the specification calls for a flat bass response down to 20 Hz. Equation 6 isreconfigured as Equation 7 .
In this example, C
i
is 58 nF; so, one would likely choose a value of 0.1 µF as this value is commonly used. If thegain is known and is constant, use Z
i
from Table 1 to calculate C
i
. A further consideration for this capacitor is theleakage path from the input source through the input network (C
i
) and the feedback network to the load. Thisleakage current creates a dc offset voltage at the input to the amplifier that reduces useful headroom, especiallyin high gain applications. For this reason, a low-leakage tantalum or ceramic capacitor is the best choice. Whenpolarized capacitors are used, the positive side of the capacitor should face the amplifier input in mostapplications as the dc level there is held at 2.5 V, which is likely higher than the source dc level. Note that it isimportant to confirm the capacitor polarity in the application.
For the best pop performance, C
I
should be less than or equal to 1µF.
The TPA3008D2 is a high-performance CMOS audio amplifier that requires adequate power supply decouplingto ensure that the output total harmonic distortion (THD) is as low as possible. Power supply decoupling alsoprevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling isachieved 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 V
CC
lead works best. For filteringlower frequency noise signals, a larger aluminum electrolytic capacitor of 10 µF or greater placed near the audiopower amplifier is recommended. The 10-µF capacitor also serves as local storage capacitor for supplyingcurrent during large signal transients on the amplifier outputs.
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BSN and BSP Capacitors
VCLAMP Capacitors
Internal Regulated 5-V Supply (AV
DD
)
Differential Input
SHUTDOWN OPERATION
USING LOW-ESR CAPACITORS
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
The full H-bridge output stages use only NMOS transistors. Therefore, they require bootstrap capacitors for thehigh side of each output to turn on correctly. A 220-nF ceramic capacitor, rated for at least 25 V, must beconnected from each output to its corresponding bootstrap input. Specifically, one 220-nF capacitor must beconnected from xOUTP to xBSP, and one 220-nF capacitor must be connected from xOUTN to xBSN. (See theapplication circuit diagram in Figure 16 .)
The bootstrap capacitors connected between the BSxx pins and corresponding output function as a floatingpower supply for the high-side N-channel power MOSFET gate drive circuitry. During each high-side switchingcycle, the bootstrap capacitors hold the gate-to-source voltage high enough to keep the high-side MOSFETsturned on.
To ensure that the maximum gate-to-source voltage for the NMOS output transistors is not exceeded, twointernal regulators clamp the gate voltage. Two 1-µF capacitors must be connected from VCLAMPL (pin 25) andVCLAMPR (pin 36) to ground and must be rated for at least 25 V. The voltages at the VCLAMP terminals varywith V
CC
and may not be used for powering any other circuitry.
The AV
DD
terminal (pin 29) is the output of an internally generated 5-V supply, used for the oscillator,preamplifier, and volume control circuitry. It requires a 1-µF capacitor, placed close to the pin, to keep theregulator stable.
This regulated voltage can be used to control GAIN0 and GAIN1 terminals, but should not be used to driveexternal circuitry.
The differential input stage of the amplifier cancels any noise that appears on both input lines of the channel. Touse the TPA3008D2 with a differential source, connect the positive lead of the audio source to the INP input andthe negative lead from the audio source to the INN input. To use the TPA3008D2 with a single-ended source, acground the INP or INN input through a capacitor equal in value to the input capacitor on INN or INP and applythe audio source to either input. In a single-ended input application, the unused input should be ac grounded atthe audio source instead of at the device input for best noise performance.
The TPA3008D2 employs a shutdown mode of operation designed to reduce supply current (I
CC
) to the absoluteminimum level during periods of nonuse for power conservation. The SHUTDOWN input terminal should be heldhigh (see specification table for trip point) during normal operation when the amplifier is in use. PullingSHUTDOWN low causes the outputs to mute and the amplifier to enter a low-current state. Never leaveSHUTDOWN unconnected, because amplifier operation would be unpredictable.
For the best power-off pop performance, place the amplifier in the shutdown mode prior to removing the powersupply voltage.
Low-ESR capacitors are recommended throughout this application section. A real (as opposed to ideal) capacitorcan be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this resistorminimizes 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.
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SHORT-CIRCUIT PROTECTION AND AUTOMATIC RECOVERY FEATURE
THERMAL PROTECTION
PRINTED-CIRCUIT BOARD (PCB) LAYOUT
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
The TPA3008D2 has short-circuit protection circuitry on the outputs that prevents damage to the device duringoutput-to-output shorts, output-to-GND shorts, and output-to-V
CC
shorts. When a short circuit is detected on theoutputs, the part immediately disables the output drive. This is a latched fault and must be reset by cycling thevoltage on the SHUTDOWN pin to a logic low and back to the logic high state for normal operation. This clearsthe short-circuit flag and allows for normal operation if the short was removed. If the short was not removed, theprotection circuitry again activates.
The fault terminal can be used for automatic recovery from a short-circuit event, or used to monitor the statuswith an external GPIO.
Thermal protection on the TPA3008D2 prevents damage to the device when the internal die temperatureexceeds 150°C. There is a ±15 degree tolerance on this trip point from device to device. Once the dietemperature exceeds the thermal set point, the device enters into the shutdown state and the outputs aredisabled. This is not a latched fault. The thermal fault is cleared once the temperature of the die is reduced by20°C. The device begins normal operation at this point with no external system interaction.
Because the TPA3008D2 is a class-D amplifier that switches at a high frequency, the layout of the printed-circuitboard (PCB) should be optimized according to the following guidelines for the best possible performance.•Decoupling capacitors—The high-frequency 0.1-µF decoupling capacitors should be placed as close to thePVCC (pins 14, 15, 22, 23, 38, 39, 46, and 47) and AV
CC
(pin 33) terminals as possible. The V2P5 (pin 4)capacitor, AV
DD
(pin 29) capacitor, and VCLAMP (pins 25 and 36) capacitor should also be placed as closeto the device as possible. Large (10 µF or greater) bulk power supply decoupling capacitors should beplaced near the TPA3008D2 on the PVCCL, PVCCR, and AV
CC
terminals.•Grounding—The AV
CC
(pin 33) decoupling capacitor, AV
DD
(pin 29) capacitor, V2P5 (pin 4) capacitor, COSC(pin 28) capacitor, and ROSC (pin 27) resistor should each be grounded to analog ground (AGND, pins 26and 30). The PVCC decoupling capacitors should each be grounded to power ground (PGND, pins 18, 19,42, and 43). Analog ground and power ground may be connected at the PowerPAD, which should be usedas a central ground connection or star ground for the TPA3008D2. Basically, an island should be createdwith a single connection to PGND at the PowerPAD.•Output filter—The ferrite EMI filter (Figure 20 ) should be placed as close to the output terminals as possiblefor the best EMI performance. The LC filter (Figure 19 ) should be placed close to the outputs. The capacitorsused in both the ferrite and LC filters should be grounded to power ground. If both filters are used, the LCfilter should be placed first, following the outputs.•PowerPAD—The PowerPAD must be soldered to the PCB for proper thermal performance and optimalreliability. The dimensions of the PowerPAD thermal land should be 5 mm by 5 mm (197 mils by 197 mils).The PowerPAD size measures 4,55 x 4,55 mm. Four rows of solid vias (four vias per row, 0,3302 mm or 13mils diameter) should be equally spaced underneath the thermal land. The vias should connect to a solidcopper plane, either on an internal layer or on the bottom layer of the PCB. The vias must be solid vias, notthermal relief or webbed vias. For additional information, see the PowerPAD Thermally Enhanced Packageapplication note, (SLMA002).
For an example layout, see the TPA3008D2 Evaluation Module (TPA3008D2EVM) User Manual, (SLOU165).Both the EVM user manual and the PowerPAD application note are available on the TI Web site athttp://www.ti.com.
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BASIC MEASUREMENT SYSTEM
TPA3008D2
SLOS435A – MAY 2004 – REVISED JULY 2004
This application note focuses on methods that use the basic equipment listed below:•Audio analyzer or spectrum analyzer•Digital multimeter (DMM)•Oscilloscope
•Twisted-pair wires•Signal generator•Power resistor(s)•Linear regulated power supply•Filter components
•EVM or other complete audio circuit
Figure 21 shows the block diagrams of basic measurement systems for class-AB and class-D amplifiers. A sinewave is normally used as the input signal because it consists of the fundamental frequency only (no otherharmonics are present). An analyzer is then connected to the APA output to measure the voltage output. Theanalyzer must be capable of measuring the entire audio bandwidth. A regulated dc power supply is used toreduce the noise and distortion injected into the APA through the power pins. A System Two audio measurementsystem (AP-II) (Reference 1) by Audio Precision includes the signal generator and analyzer in one package.
The generator output and amplifier input must be ac-coupled. However, the EVMs already have the ac-couplingcapacitors, (C
IN
), so no additional coupling is required. The generator output impedance should be low to avoidattenuating the test signal, and is important because the input resistance of APAs is not high. Conversely, theanalyzer-input impedance should be high. The output impedance, R
OUT
, of the APA is normally in the hundredsof milliohms and can be ignored for all but the power-related calculations.
Figure 21 (a) shows a class-AB amplifier system. It takes an analog signal input and produces an analog signaloutput. This amplifier circuit can be directly connected to the AP-II or other analyzer input.
This is not true of the class-D amplifier system shown in Figure 21 (b), which requires low-pass filters in mostcases in order to measure the audio output waveforms. This is because it takes an analog input signal andconverts it into a pulse-width modulated (PWM) output signal that is not accurately processed by someanalyzers.
20