TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
1
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
D
Fully Specified for 3.3-V and 5-V Operation
D
Wide Power Supply Compatibility
2.5 V 5.5 V
D
Output Power for R
L
= 8
350 mW at V
DD
= 5 V, BTL
250 mW at V
DD
= 3.3 V, BTL
D
Ultra-Low Quiescent Current in Shutdown
Mode . . . 0.15
A
D
Thermal and Short-Circuit Protection
D
Surface-Mount Packaging
SOIC
PowerPAD
TM
MSOP
description
The TPA301 is a bridge-tied load (BTL) audio power amplifier developed especially for low-voltage applications
where internal speakers are required. Operating with a 3.3-V supply, the TPA301 can deliver 250-mW of
continuous power into a BTL 8-
load at less than 1% THD+N throughout voice band frequencies. Although
this device is characterized out to 20 kHz, its operation was optimized for narrower band applications such as
cellular communications. The BTL configuration eliminates the need for external coupling capacitors on the
output in most applications, which is particularly important for small battery-powered equipment. This device
features a shutdown mode for power-sensitive applications with a quiescent current of 0.15
A during shutdown.
The TPA301 is available in an 8-pin SOIC surface-mount package and the surface-mount PowerPAD MSOP,
which reduces board space by 50% and height by 40%.
Audio
Input
Bias
Control
VDD
350 mW
6
5
7
VO+
VDD
1
2
4
BYPASS
IN
VDD/2
CI
RI
CS
1
F
CB
0.1
F
RF
SHUTDOWN
VO 8
GND
From System Control
3
IN+
+
+
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.
Copyright
2000, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
1
2
3
4
8
7
6
5
SHUTDOWN
BYPASS
IN+
IN
V
O
GND
V
DD
V
O
+
D OR DGN PACKAGE
(TOP VIEW)
PowerPAD is a trademark of Texas Instruments.
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
2
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
AVAILABLE OPTIONS
PACKAGED DEVICES
MSOP
TA
SMALL OUTLINE
(D)
MSOP
(DGN)
MSOP
Symbolization
40
C to 85
C
TPA301D
TPA301DGN
AAA
The D and DGN packages are available taped and reeled. To order a taped and reeled part, add
the suffix R to the part number (e.g., TPA301DR).
Terminal Functions
TERMINAL
I/O
DESCRIPTION
NAME
NO.
I/O
DESCRIPTION
BYPASS
2
I
BYPASS is the tap to the voltage divider for internal mid-supply bias. This terminal should be connected
to a 0.1-
F to 1-
F capacitor when used as an audio amplifier.
GND
7
GND is the ground connection.
IN
4
I
IN is the inverting input. IN is typically used as the audio input terminal.
IN+
3
I
IN + is the noninverting input. IN + is typically tied to the BYPASS terminal.
SHUTDOWN
1
I
SHUTDOWN places the entire device in shutdown mode when held high (IDD < 1
A).
VDD
6
VDD is the supply voltage terminal.
VO+
5
O
VO+ is the positive BTL output.
VO
8
O
VO is the negative BTL output.
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)
Supply voltage, V
DD
6 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input voltage, V
I
0.3 V to V
DD
+0.3 V
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Continuous total power dissipation
internally limited (see Dissipation Rating Table)
. . . . . . . . . . . . . . . . . . . . .
Operating free-air temperature range, T
A
40
C to 85
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating junction temperature range, T
J
40
C to 150
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range, T
stg
65
C to 150
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds
260
C
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under "recommended operating conditions" is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
DISSIPATION RATING TABLE
PACKAGE
TA
25
C
DERATING FACTOR
TA = 70
C
TA = 85
C
D
725 mW
5.8 mW/
C
464 mW
377 mW
DGN
2.14 W
17.1 mW/
C
1.37 W
1.11 W
Please see the Texas Instruments document, PowerPAD Thermally Enhanced Package Application Report
(literature number SLMA002), for more information on the PowerPAD package. The thermal data was
measured on a PCB layout based on the information in the section entitled
Texas Instruments Recommended
Board for PowerPAD on page 33 of the before mentioned document.
recommended operating conditions
MIN
MAX
UNIT
Supply voltage, VDD
2.5
5.5
V
Operating free-air temperature, TA
40
85
C
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
3
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
electrical characteristics at specified free-air temperature, V
DD
= 3.3 V, T
A
= 25
C (unless otherwise
noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
VOD
Differential output voltage
See Note 1
5
20
mV
PSRR
Power supply rejection ratio
VDD = 3.2 V to 3.4 V
85
dB
IDD(q)
Supply current (see Figure 3)
BTL mode
0.7
1.5
mA
IDD(sd)
Supply current, shutdown mode (see Figure 4)
0.15
5
A
NOTE 1: At 3 V < VDD < 5 V the dc output voltage is approximately VDD/2.
operating characteristics, V
DD
= 3.3 V, T
A
= 25
C, R
L
= 8
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
PO
Output power, see Note 2
THD = 0.5%,
See Figure 9
250
mW
THD + N
Total harmonic distortion plus noise
PO = 250 mW,
Gain = 2,
f = 20 Hz to 4 kHz,
See Figure 7
1.3%
Maximum output power bandwidth
Gain = 2,
See Figure 7
THD = 3%,
10
kHz
B1
Unity-gain bandwidth
Open Loop,
See Figure 15
1.4
MHz
Supply ripple rejection ratio
f = 1 kHz,
See Figure 2
CB = 1
F,
71
dB
Vn
Noise output voltage
Gain = 1,
RL = 32
,
CB = 0.1
F,
See Figure 19
15
V(rms)
NOTE 2: Output power is measured at the output terminals of the device at f = 1 kHz.
electrical characteristics at specified free-air temperature, V
DD
= 5 V, T
A
= 25
C (unless otherwise
noted)
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
VOD
Differential output voltage
5
20
mV
PSRR
Power supply rejection ratio
VDD = 4.9 V to 5.1 V
78
dB
IDD(q)
Quiescent current (see Figure 3)
0.7
1.5
mA
IDD(sd)
Quiescent current, shutdown mode (see Figure 4)
0.15
5
A
operating characteristics, V
DD
= 5 V, T
A
= 25
C, R
L
= 8
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
PO
Output power
THD = 0.5%,
See Figure 13
700
mW
THD + N
Total harmonic distortion plus noise
PO = 250 mW,
Gain = 2,
f = 20 Hz to 4 kHz,
See Figure 11
1%
Maximum output power bandwidth
Gain = 2,
See Figure 11
THD = 2%,
10
kHz
B1
Unity-gain bandwidth
Open Loop,
See Figure 16
1.4
MHz
Supply ripple rejection ratio
f = 1 kHz,
See Figure 2
CB = 1
F,
65
dB
Vn
Noise output voltage
Gain = 1,
RL = 32
,
CB = 0.1
F,
See Figure 20
15
V(rms)
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
4
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
PARAMETER MEASUREMENT INFORMATION
Audio
Input
Bias
Control
VDD
6
5
7
VO+
VDD
1
2
4
BYPASS
IN
VDD/2
CI
RI
CS
1
F
CB
0.1
F
RF
SHUTDOWN
VO 8
RL = 8
GND
3
IN+
+
+
Figure 1. Test Circuit
TYPICAL CHARACTERISTICS
Table of Graphs
FIGURE
kSVR
Supply voltage rejection ratio
vs Frequency
2
IDD
Supply current
vs Supply voltage
3, 4
PO
Output power
vs Supply voltage
5
PO
Output power
vs Load resistance
6
THD + N
Total harmonic distortion plus noise
vs Frequency
7, 8, 11, 12
THD + N
Total harmonic distortion plus noise
vs Output power
9, 10, 13, 14
Open loop gain and phase
vs Frequency
15, 16
Closed loop gain and phase
vs Frequency
17, 18
Vn
Output noise voltage
vs Frequency
19, 20
PD
Power dissipation
vs Output power
21, 22
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
5
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 2
50
60
80
100
20
100
1 k
30
20
f Frequency Hz
SUPPLY VOLTAGE REJECTION RATIO
vs
FREQUENCY
0
10 k 20 k
10
40
70
90
VDD = 5 V
VDD = 3.3 V
RL = 8
CB = 1
F
k
SVR
Supply V
oltage Rejection Ratio dB
Figure 3
VDD Supply Voltage V
SUPPLY CURRENT
vs
SUPPLY VOLTAGE
1.1
0.7
0.3
0.1
0.9
0.5
0.1
3
4
6
2
5
I DD(q)
Supply Current mA
VDD Supply Voltage V
SUPPLY CURRENT (SHUTDOWN)
vs
SUPPLY VOLTAGE
0.15
0.1
0.05
3
4
3.5
4.5
0.35
2
5
0.2
SHUTDOWN = High
0.25
0.3
5.5
2.5
0.4
0.45
0.5
I DD(SD)
Supply Current
A
Figure 4
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
6
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
VDD Supply Voltage V
OUTPUT POWER
vs
SUPPLY VOLTAGE
600
400
200
0
2.5
3.5
3
4
5.5
1000
2
P
4.5
5
O
Output Power mW
800
THD+N 1%
RL = 32
RL = 8
Figure 5
RL Load Resistance
OUTPUT POWER
vs
LOAD RESISTANCE
300
200
100
0
16
32
24
40
64
800
8
P
48
56
O
Output Power mW
400
THD+N = 1%
VDD = 5 V
500
600
VDD = 3.3 V
700
Figure 6
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
7
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 7
f Frequency Hz
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
AV = 2 V/V
VDD = 3.3 V
PO = 250 mW
RL = 8
20
1k
10k
1
0.01
10
0.1
20k
100
AV = 20 V/V
AV = 10 V/V
Figure 8
f Frequency Hz
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
PO = 125 mW
VDD = 3.3 V
RL = 8
AV = 2 V/V
20
1k
10k
1
0.01
10
0.1
20k
100
PO = 50 mW
PO = 250 mW
Figure 9
PO Output Power W
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
RL = 8
0.04
0.1
0.4
1
0.01
10
0.1
0.16
0.22
0.28
0.34
VDD = 3.3 V
f = 1 kHz
AV = 2 V/V
Figure 10
PO Output Power W
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
f = 20 Hz
VDD = 3.3 V
RL = 8
AV = 2 V/V
0.01
0.1
1
1
0.01
10
0.1
f = 1 kHz
f = 10 kHz
f = 20 kHz
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
8
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 11
f Frequency Hz
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
AV = 2 V/V
VDD = 5 V
PO = 350 mW
RL = 8
20
1k
10k
1
0.01
10
0.1
20k
100
AV = 20 V/V
AV = 10 V/V
Figure 12
f Frequency Hz
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
PO = 175 mW
VDD = 5 V
RL = 8
AV = 2 V/V
20
1k
10k
1
0.01
10
0.1
20k
100
PO = 50 mW
PO = 350 mW
Figure 13
PO Output Power W
0.1
0.25
1
0.40
0.55
0.70
0.85
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
RL = 8
VDD = 5 V
f = 1 kHz
AV = 2 V/V
1
0.01
10
0.1
Figure 14
PO Output Power W
THD+N T
otal Harmonic Distortion + Noise %
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
f = 20 Hz
VDD = 5 V
RL = 8
AV = 2 V/V
0.01
0.1
1
1
0.01
10
0.1
f = 1 kHz
f = 10 kHz
f = 20 kHz
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
9
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
10
0
20
30
20
30
f Frequency kHz
40
10
180
120
0
120
180
VDD = 3.3 V
RL = Open
Gain
Phase
60
60
OPEN-LOOP GAIN AND PHASE
vs
FREQUENCY
Open-Loop Gain dB
Phase
1
101
102
103
104
Figure 15
10
0
20
30
1
20
30
f Frequency kHz
40
10
180
120
0
120
180
VDD = 5 V
RL = Open
Gain
Phase
60
60
OPEN-LOOP GAIN AND PHASE
vs
FREQUENCY
Open-Loop Gain dB
Phase
101
102
103
104
Figure 16
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
10
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
CLOSED-LOOP GAIN AND PHASE
vs
FREQUENCY
0.5
1
1.5
2
f Frequency Hz
0.25
0.75
1.25
1.75
0
0.5
Closed-Loop Gain dB
0.25
0.75
130
120
140
Phase
150
160
VDD = 3.3 V
RL = 8
PO = 0.25 W
CI =1
F
1
170
180
Gain
Phase
101
102
103
104
105
106
Figure 17
CLOSED-LOOP GAIN AND PHASE
vs
FREQUENCY
0.5
1
1.5
2
f Frequency Hz
0.25
0.75
1.25
1.75
0
0.5
Closed-Loop Gain dB
0.25
0.75
130
120
140
Phase
150
160
VDD = 5 V
RL = 8
PO = 0.35 W
CI =1
F
1
170
180
Gain
Phase
101
102
103
104
105
106
Figure 18
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
11
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 19
Output Noise V
oltage
V
n
f Frequency Hz
OUTPUT NOISE VOLTAGE
vs
FREQUENCY
20
1 k
10 k
10
1
100
20 k
100
VO BTL
VDD = 3.3 V
BW = 22 Hz to 22 kHz
RL = 32
CB =0.1
F
AV = 1 V/V
VO+
V(rms)
Figure 20
Output Noise V
oltage
V
n
f Frequency Hz
OUTPUT NOISE VOLTAGE
vs
FREQUENCY
20
1 k
10 k
10
1
100
20 k
100
VDD = 5 V
BW = 22 Hz to 22 kHz
RL = 32
CB =0.1
F
AV = 1 V/V
VO BTL
VO+
V(rms)
Figure 21
PO Output Power mW
POWER DISSIPATION
vs
OUTPUT POWER
200
400
0
180
150
120
90
300
P
D
Power Dissipation mW
210
240
270
VDD = 3.3 V
RL = 8
100
300
Figure 22
PO Output Power mW
POWER DISSIPATION
vs
OUTPUT POWER
200
600
400
800
0
1000
1200
VDD = 5 V
RL = 8
400
320
240
160
720
P
D
Power Dissipation mW
480
560
640
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
12
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
bridge-tied load
Figure 23 shows a linear audio power amplifier (APA) in a BTL configuration. The TPA301 BTL amplifier consists
of two linear amplifiers driving both ends of the load. There are several potential benefits to this differential drive
configuration but power to the load should be initially considered. The differential drive to the speaker means
that as one side is slewing up, the other side is slewing down, and vice versa. This in effect doubles the voltage
swing on the load as compared to a ground referenced load. Plugging 2
V
O(PP)
into the power equation, where
voltage is squared, yields 4
the output power from the same supply rail and load impedance (see equation 1).
Power
+
V
(rms)
2
R
L
(1)
V
(rms)
+
V
O(PP)
2 2
RL
2x VO(PP)
VO(PP)
VO(PP)
VDD
VDD
Figure 23. Bridge-Tied Load Configuration
In a typical portable handheld equipment sound channel operating at 3.3 V, bridging raises the power into an
8-
speaker from a single-ended (SE, ground reference) limit of 62.5 mW to 250 mW. In sound power that is
a 6-dB improvement -- which is loudness that can be heard. In addition to increased power, there are frequency
response concerns. Consider the single-supply SE configuration shown in Figure 24. A coupling capacitor is
required to block the dc offset voltage from reaching the load. These capacitors can be quite large
(approximately 33
F to 1000
F) so they tend to be expensive, heavy, occupy valuable PCB area, and have
the additional drawback of limiting low-frequency performance of the system. This frequency limiting effect is
due to the high pass filter network created with the speaker impedance and the coupling capacitance and is
calculated with equation 2.
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
13
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
bridge-tied load versus single-ended mode (continued)
f
(corner)
+
1
2
p
R
L
C
C
(2)
For example, a 68-
F capacitor with an 8-
speaker would attenuate low frequencies below 293 Hz. The BTL
configuration cancels the dc offsets, eliminating the need for the blocking capacitors. Low-frequency
performance is then limited only by the input network and speaker response. Cost and PCB space are also
minimized by eliminating the bulky coupling capacitor.
RL
CC
VO(PP)
VO(PP)
VDD
3 dB
fc
Figure 24. Single-Ended Configuration and Frequency Response
Increasing power to the load does carry a penalty of increased internal power dissipation. The increased
dissipation is understandable considering that the BTL configuration produces 4
the output power of a SE
configuration. Internal dissipation versus output power is discussed further in the
thermal considerations
section.
BTL amplifier efficiency
Linear amplifiers are notoriously inefficient. The primary cause of these inefficiencies is voltage drop across the
output stage transistors. There are two components of the internal voltage drop. One is the headroom or dc
voltage drop that varies inversely to output power. The second component is due to the sinewave nature of the
output. The total voltage drop can be calculated by subtracting the RMS value of the output voltage from V
DD
.
The internal voltage drop multiplied by the RMS value of the supply current, I
DD
rms, determines the internal
power dissipation of the amplifier.
An easy-to-use equation to calculate efficiency starts out as being equal to the ratio of power from the power
supply to the power delivered to the load. To accurately calculate the RMS values of power in the load and in
the amplifier, the current and voltage waveform shapes must first be understood (see Figure 25).
V(LRMS)
VO
IDD
IDD(RMS)
Figure 25. Voltage and Current Waveforms for BTL Amplifiers
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
14
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
BTL amplifier efficiency (continued)
Although the voltages and currents for SE and BTL are sinusoidal in the load, currents from the supply are very
different between SE and BTL configurations. In an SE application the current waveform is a half-wave rectified
shape whereas in BTL it is a full-wave rectified waveform. This means RMS conversion factors are different.
Keep in mind that for most of the waveform both the push and pull transistors are not on at the same time, which
supports the fact that each amplifier in the BTL device only draws current from the supply for half the waveform.
The following equations are the basis for calculating amplifier efficiency.
I
DD
rms
+
2V
P
p
R
L
P
SUP
+
V
DD
I
DD
rms
+
V
DD
2V
P
p
R
L
Efficiency
+
P
L
P
SUP
Efficiency of a BTL Configuration
+
p
V
P
2V
DD
+
p
P
L
R
L
2
1 2
2V
DD
(3)
Where:
(4)
P
L
+
V
L
rms2
R
L
+
Vp
2
2 R
L
V
L
rms
+
V
P
2
Table 1 employs equation 4 to calculate efficiencies for three different output power levels. The efficiency of the
amplifier is quite low for lower power levels and rises sharply as power to the load is increased resulting in a
nearly flat internal power dissipation over the normal operating range. The internal dissipation at full output
power is less than in the half power range. Calculating the efficiency for a specific system is the key to proper
power supply design.
Table 1. Efficiency vs Output Power in 3.3-V 8-
BTL Systems
OUTPUT POWER
(W)
EFFICIENCY
(%)
PEAK-to-PEAK
VOLTAGE
(V)
INTERNAL
DISSIPATION
(W)
0.125
33.6
1.41
0.26
0.25
47.6
2.00
0.29
0.375
58.3
2.45
0.28
High-peak voltage values cause the THD to increase.
A final point to remember about linear amplifiers (either SE or BTL) is how to manipulate the terms in the
efficiency equation to utmost advantage when possible. Note that in equation 4, V
DD
is in the denominator. This
indicates that as V
DD
goes down, efficiency goes up.
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
15
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
application schematic
Figure 26 is a schematic diagram of a typical handheld audio application circuit, configured for a gain of
10 V/V.
Audio
Input
Bias
Control
VDD
350 mW
6
5
7
VO+
VDD
1
2
4
BYPASS
IN
VDD/2
CS
1
F
CB
2.2
F
SHUTDOWN
VO 8
GND
From System Control
3
IN+
+
+
CI
0.47
F
RI
10 k
RF
50 k
CF
5 pF
Figure 26. TPA301 Application Circuit
The following sections discuss the selection of the components used in Figure 26.
component selection
gain setting resistors, R
F
and R
I
The gain for each audio input of the TPA301 is set by resistors R
F
and R
I
according to equation 5 for BTL mode.
(5)
BTL Gain
+
A
V
+ *
2
R
F
R
I
BTL mode operation brings about the factor 2 in the gain equation due to the inverting amplifier mirroring the
voltage swing across the load. Given that the TPA301 is a MOS amplifier, the input impedance is very high,
consequently input leakage currents are not generally a concern although noise in the circuit increases as the
value of R
F
increases. In addition, a certain range of R
F
values are required for proper start-up operation of the
amplifier. Taken together it is recommended that the effective impedance seen by the inverting node of the
amplifier be set between 5 k
and 20 k
. The effective impedance is calculated in equation 6.
(6)
Effective Impedance
+
R
F
R
I
R
F
)
R
I
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
16
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
component selection (continued)
As an example, consider an input resistance of 10 k
and a feedback resistor of 50 k
. The BTL gain of the
amplifier would be 10 V/V, and the effective impedance at the inverting terminal would be 8.3 k
, which is well
within the recommended range.
For high performance applications metal film resistors are recommended because they tend to have lower noise
levels than carbon resistors. For values of R
F
above 50 k
the amplifier tends to become unstable due to a pole
formed from R
F
and the inherent input capacitance of the MOS input structure. For this reason, a small
compensation capacitor, C
F
, of approximately 5 pF should be placed in parallel with R
F
when R
F
is greater than
50 k
. This, in effect, creates a low-pass filter network with the cutoff frequency defined in equation 7.
(7)
3 dB
fco
f
co(lowpass)
+
1
2
p
R
F
C
F
For example, if R
F
is 100 k
and C
F
is 5 pF then f
co
is 318 kHz, which is well outside of the audio range.
input capacitor, C
I
In the typical application an input capacitor, C
I
, is required to allow the amplifier to bias the input signal to the
proper dc level for optimum operation. In this case, C
I
and R
I
form a high-pass filter with the corner frequency
determined in equation 8.
(8)
3 dB
fco
f
co(highpass)
+
1
2
p
R
I
C
I
The value of C
I
is important to consider as it directly affects the bass (low frequency) performance of the circuit.
Consider the example where R
I
is 10 k
and the specification calls for a flat bass response down to 40 Hz.
Equation 8 is reconfigured as equation 9.
(9)
C
I
+
1
2
p
R
I
fco
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
17
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
component selection (continued)
In this example, C
I
is 0.40
F so one would likely choose a value in the range of 0.47
F to 1
F. A further
consideration for this capacitor is the leakage path from the input source through the input network (R
I
, C
I
) and
the feedback resistor (R
F
) 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 V
DD
/2, which is likely higher
than the source dc level. It is important to confirm the capacitor polarity in the application.
power supply decoupling, C
S
The TPA301 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to
ensure the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also prevents
oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is achieved
by using two capacitors of different types that target different types of noise on the power supply leads. For
higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR)
ceramic capacitor, typically 0.1
F, placed as close as possible to the device V
DD
lead, works best. For filtering
lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10
F or greater placed near the audio
power amplifier is recommended.
midrail bypass capacitor, C
B
The midrail bypass capacitor, C
B
, is the most critical capacitor and serves several important functions. During
start-up or recovery from shutdown mode, C
B
determines the rate at which the amplifier starts up. The second
function is to reduce noise produced by the power supply caused by coupling into the output drive signal. This
noise is from the midrail generation circuit internal to the amplifier, which appears as degraded PSRR and THD
+ N. The capacitor is fed from a 250-k
source inside the amplifier. To keep the start-up pop as low as possible,
the relationship shown in equation 10 should be maintained, which insures the input capacitor is fully charged
before the bypass capacitor is fully charged and the amplifier starts up.
(10)
10
C
B
250 k
v
1
R
F
)
R
I
C
I
As an example, consider a circuit where C
B
is 2.2
F, C
I
is 0.47
F, R
F
is 50 k
and R
I
is 10 k
. Inserting these
values into the equation 10 we get:
18.2
v
35.5
which satisfies the rule. Bypass capacitor, C
B
, values of 2.2
F to 1
F ceramic or tantalum low-ESR capacitors
are recommended for the best THD and noise performance.
using low-ESR capacitors
Low-ESR capacitors are recommended throughout this application. A real (as opposed to ideal) capacitor can
be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this resistor minimizes
the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this resistance, the more
the real capacitor behaves like an ideal capacitor.
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
18
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
5-V versus 3.3-V operation
The TPA301 operates over a supply range of 2.5 V to 5.5 V. This data sheet provides full specifications for 5-V
and 3.3-V operation, as these are considered to be the two most common standard voltages. There are no
special considerations for 3.3-V versus 5-V operation with respect to supply bypassing, gain setting, or stability.
The most important consideration is that of output power. Each amplifier in TPA301 can produce a maximum
voltage swing of V
DD
1 V. This means, for 3.3-V operation, clipping starts to occur when V
O(PP)
= 2.3 V as
opposed to V
O(PP)
= 4 V at 5 V. The reduced voltage swing subsequently reduces maximum output power into
an 8-
load before distortion becomes significant.
Operation from 3.3-V supplies, as can be shown from the efficiency formula in equation 4, consumes
approximately two-thirds the supply power for a given output-power level than operation from 5-V supplies.
headroom and thermal considerations
Linear power amplifiers dissipate a significant amount of heat in the package under normal operating conditions.
A typical music CD requires 12 dB to 15 dB of dynamic headroom to pass the loudest portions without distortion
as compared with the average power output. From the TPA301 data sheet, one can see that when the TPA301
is operating from a 5-V supply into a 8-
speaker 350 mW peaks are available. Converting watts to dB:
P
dB
+
10 Log P
W
+
10Log 3500 mW
+
4.6 dB
Subtracting the headroom restriction to obtain the average listening level without distortion yields:
4.6 dB
*
15 dB
+ *
19.6 dB (15 dB headroom)
4.6 dB
*
12 dB
+ *
16.6 dB (12 dB headroom)
4.6 dB
*
9 dB
+ *
13.6 dB (9 dB headroom)
4.6 dB
*
6 dB
+ *
10.6 dB (6 dB headroom)
4.6 dB
*
3 dB
+ *
7.6 dB (3 dB headroom)
Converting dB back into watts:
P
W
+
10
PdB 10
+
11 mW (15 dB headroom)
+
22 mW (12 dB headroom)
+
44 mW (9 dB headroom)
+
88 mW (6 dB headroom)
+
175 mW (3 dB headroom)
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
19
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
headroom and thermal considerations (continued)
This is valuable information to consider when attempting to estimate the heat dissipation requirements for the
amplifier system. Comparing the absolute worst case, which is 350 mW of continuous power output with 0 dB
of headroom, against 12 dB and 15 dB applications drastically affects maximum ambient temperature ratings
for the system. Using the power dissipation curves for a 5-V, 8-
system, the internal dissipation in the TPA301
and maximum ambient temperatures is shown in Table 2.
Table 2. TPA301 Power Rating, 5-V, 8-
, BTL
PEAK OUTPUT POWER
(mW)
AVERAGE OUTPUT POWER
POWER DISSIPATION
(mW)
MAXIMUM AMBIENT
TEMPERATURE
(mW)
(mW)
0 CFM
350
350 mW
600
46
C
350
175 mW (3 dB)
500
64
C
350
88 mW (6 dB)
380
85
C
350
44 mW (9 dB)
300
98
C
350
22 mW (12 dB)
200
115
C
350
11 mW (15 dB)
180
119
C
Table 2 shows that the TPA301 can be used to its full 350-mW rating without any heat sinking in still air up to
46
C.
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
20
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
MECHANICAL DATA
D (R-PDSO-G**)
PLASTIC SMALL-OUTLINE PACKAGE
14 PINS SHOWN
4040047 / D 10/96
0.228 (5,80)
0.244 (6,20)
0.069 (1,75) MAX
0.010 (0,25)
0.004 (0,10)
1
14
0.014 (0,35)
0.020 (0,51)
A
0.157 (4,00)
0.150 (3,81)
7
8
0.044 (1,12)
0.016 (0,40)
Seating Plane
0.010 (0,25)
PINS **
0.008 (0,20) NOM
A MIN
A MAX
DIM
Gage Plane
0.189
(4,80)
(5,00)
0.197
8
(8,55)
(8,75)
0.337
14
0.344
(9,80)
16
0.394
(10,00)
0.386
0.004 (0,10)
M
0.010 (0,25)
0.050 (1,27)
0
8
NOTES: A. All linear dimensions are in inches (millimeters).
B. This drawing is subject to change without notice.
C. Body dimensions do not include mold flash or protrusion, not to exceed 0.006 (0,15).
D. Falls within JEDEC MS-012
TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C JANUARY1998 REVISED MARCH 2000
21
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
MECHANICAL DATA
DGN (S-PDSO-G8)
PowerPAD
TM
PLASTIC SMALL-OUTLINE PACKAGE
0,69
0,41
0,25
Thermal Pad
(See Note D)
0,15 NOM
Gage Plane
4073271/A 04/98
4,98
0,25
5
3,05
4,78
2,95
8
4
3,05
2,95
1
0,38
0,15
0,05
1,07 MAX
Seating Plane
0,10
0,65
M
0,25
0
6
NOTES: A. All linear dimensions are in millimeters.
B. This drawing is subject to change without notice.
C. Body dimensions include mold flash or protrusions.
D. The package thermal performance may be enhanced by attaching an external heat sink to the thermal pad.
This pad is electrically and thermally connected to the backside of the die and possibly selected leads.
E. Falls within JEDEC MO-187
PowerPAD is a trademark of Texas Instruments.
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pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in
accordance with TI's standard warranty. Testing and other quality control techniques are utilized to the extent
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Customers are responsible for their applications using TI components.
In order to minimize risks associated with the customer's applications, adequate design and operating
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Copyright
2000, Texas Instruments Incorporated
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