TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
D
1-W BTL Output (5 V, 0.11 % THD+N)
D
3.3-V and 5-V Operation
D
No Output Coupling Capacitors Required
D
Shutdown Control (IDD = 0.6 µA)
D
Uncompensated Gains of 2 to 20 (BTL
Mode)
D
Surface-Mount Packaging
D
Thermal and Short-Circuit Protection
D
High Supply Ripple Rejection Ratio
(56 dB at 1 kHz)
D
LM4861 Drop-In Compatible
description
The TP A4861 is a bridge-tied load (BTL) audio power amplifier capable of delivering 1 W of continuous average
power into an 8-Ω load at 0.2% THD+N from a 5-V power supply in voiceband frequencies (f < 5 kHz). A BTL
configuration eliminates the need for external coupling capacitors on the output in most applications. Gain is
externally configured by means of two resistors and does not require compensation for settings of 2 to 20.
Features of the amplifier are a shutdown function for power-sensitive applications as well as internal thermal
and short-circuit protection. The TPA4861 works seamlessly with TI’s TPA4860 in stereo applications. The
amplifier is available in an 8-pin SOIC surface-mount package that reduces board space and facilitates
automated assembly .
Audio
Input
Bias
Control
V
DD
1 W
6
5
8
7
VO1
VO2
V
DD
1
2
34IN+
IN–
BYPASS
SHUTDOWN
VDD/2
C
I
R
I
R
F
C
S
C
B
–
+
–
+
GND
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
2
GND
V
DD
VO1
D PACKAGE
(TOP VIEW)
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
AVAILABLE OPTIONS
PACKAGED DEVICE
T
A
SMALL OUTLINE
†
(D)
–40°C to 85°C TPA4861D
†
The D package is available tape and reeled. To order a tape and
reeled part, add the suffix R to the part number (e.g., TP A4861DR).
Terminal Functions
TERMINAL
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 µF – 1.0 µF capacitor when used as an audio power 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 ≤ 0.6 µA).
VO1 5 O VO1 is the positive BTL output.
VO2 8 O VO2 is the negative BTL output.
V
DD
6 VDD is the supply voltage terminal.
absolute maximum ratings over operating free-air temperature range (unless otherwise noted)
‡
Supply voltage, VDD 6 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Input voltage, VI –0.3 V to VDD +0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Continuous total power dissipation Internally Limited (see Dissipation Rating Table). . . . . . . . . . . . . . . . . . . . .
Operating free-air temperature range, T
A
–40°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating junction temperature range, TJ –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
recommended operating conditions
MIN MAX UNIT
Supply voltage, V
DD
2.7
5.5
V
p
VDD = 3 V
1.25
2.7
V
Common-mode input voltage, V
IC
VDD = 5 V
1.25
4.5
V
Operating free-air temperature, T
A
–40
85
°C
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
3
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
electrical characteristics at specified free-air temperature, VDD = 3.3 V (unless otherwise noted)
TPA4861
PARAMETER
TEST CONDITIONS
MIN TYP MAX
UNIT
V
OO
Output offset voltage
See Note 1
20
mV
PSRR
Power supply rejection ratio (∆VDD/∆VOO)
VDD = 3.2 V to 3.4 V
75
dB
I
DD
Supply current
2.5
mA
I
DD(SD)
Supply current, shutdown
0.6
µA
NOTE 1: At 3 V < VDD < 5 V the dc output voltage is approximately VDD/2.
operating characteristics, VDD = 3.3 V, T
A
= 25°C, RL = 8 Ω
TPA4861
PARAMETER
TEST CONDITIONS
MIN TYP MAX
UNIT
p
p
THD = 0.2%, f = 1 kHz,
AV = –2 V/V
400
mW
POOutput power, see Note 2
THD = 2%, f = 1 kHz,
AV = –2 V/V
500
mW
B
OM
Maximum output power bandwidth
Gain = –10 V/V ,
THD = 2%
20
kHz
B
1
Unity-gain bandwidth
Open Loop
1.5
MHz
pp
pp
BTL
f = 1 kHz,
CB = 0.1 µF
56
dB
Supply ripple rejection ratio
SE
f = 1 kHz,
CB = 0.1 µF
30
dB
V
n
Noise output voltage, see Note 3
Gain = –2 V/V
20
µV
NOTES: 2. Output power is measured at the output terminals of the device.
3. Noise voltage is measured in a bandwidth of 20 Hz to 20 kHz.
electrical characteristics at specified free-air temperature range, VDD = 5 V (unless otherwise
noted)
TPA4861
PARAMETER
TEST CONDITION
MIN TYP MAX
UNIT
V
OO
Output offset voltage
See Note 1
20
mV
PSRR
Power supply rejection ratio (∆VDD/∆VOO)
VDD = 4.9 V to 5.1 V
70
dB
I
DD
Supply current
3.5
mA
I
DD(SD)
Supply current, shutdown
0.6
µA
NOTE 1: At 3 V < VDD < 5 V the dc output voltage is approximately VDD/2.
operating characteristic, VDD = 5 V, T
A
= 25°C, RL = 8 Ω
TPA4861
PARAMETER
TEST CONDITIONS
MIN TYP MAX
UNIT
p
p
THD = 0.2%, f = 1 kHz,
AV = –2 V/V
1000
mW
POOutput power, see Note 2
THD = 2%, f = 1 kHz,
AV = –2 V/V
1100
mW
B
OM
Maximum output power bandwidth
Gain = –10 V/V ,
THD = 2%
20
kHz
B
1
Unity-gain bandwidth
Open Loop
1.5
MHz
pp
pp
BTL
f = 1 kHz,
CB = 0.1 µF
56
dB
Supply ripple rejection ratio
SE
f = 1 kHz,
CB = 0.1 µF
30
dB
V
n
Noise output voltage, see Note 3
Gain = –2 V/V
20
µV
NOTES: 2. Output power is measured at the output terminals of the device.
3. Noise voltage is measured in a bandwidth of 20 Hz to 20 kHz.
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
4
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Table of Graphs
FIGURE
V
OO
Output offset voltage
Distribution
1,2
I
DD
Supply current distribution
vs Free-air temperature
3,4
ÁÁ
Á
THD+N
БББББББББ
Á
Total harmonic distortion plus noise
БББББББ
Á
vs Frequency
ÁÁ
Á
5,6,7,8,9,
10,11,15,
16,17,18
ÁÁÁБББББББББÁБББББББ
Á
vs Output power
ÁÁ
Á
12,13,14,
19,20,21
I
DD
Supply current
vs Supply voltage
22
V
n
Output noise voltage
vs Frequency
23,24
Maximum package power dissipation
vs Free-air temperature
25
Power dissipation
vs Output power
26,27
Maximum power output
vs Free-air temperature
28
p
p
vs Load resistance
29
Output power
vs Supply voltage
30
Open-loop gain
vs Frequency
31
k
SVR
Supply ripple rejection ratio
vs Frequency
32,33
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 1
Number of Amplifiers
DISTRIBUTION OF TPA4861
OUTPUT OFFSET VOLTAGE
20
10
0
VOO – Output Offset Voltage – mV
25
15
5
VDD = 5 V
–4 –3 –2 –1 0 1 2 3 4 5 6
Figure 2
Number of Amplifiers
DISTRIBUTION OF TPA4861
OUTPUT OFFSET VOLTAGE
20
10
0
VOO – Output Offset Voltage – mV
25
15
5
–4 –3 –2 –1 0 1 2 3 4 5 6
VDD = 3.3 V
30
Figure 3
– Supply Current – mA
SUPPLY CURRENT DISTRIBUTION
vs
FREE-AIR TEMPERATURE
4
2.5
1.5
0.5
TA – Free-Air Temperature –°C
–40 25
3
2
1
VDD = 5 V
I
DD
3.5
85
5
4.5
Typical
Figure 4
– Supply Current – mA
SUPPLY CURRENT DISTRIBUTION
vs
FREE-AIR TEMPERATURE
3.5
2
1
0
TA – Free-Air Temperature –°C
–40 25
2.5
1.5
0.5
VDD = 3.3 V
I
DD
3
85
Typical
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
6
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 5
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
VDD = 5 V
PO = 1 W
AV = –2 V/V
RL = 8 Ω
CB = 0.1 µF
CB = 1 µF
THD+N – Total Harmonic Distortion Plus Noise – %
Figure 6
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
VDD = 5 V
PO = 1 W
AV = –10 V/V
RL = 8 Ω
CB = 0.1 µF
CB = 1 µF
THD+N – Total Harmonic Distortion Plus Noise – %
Figure 7
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
VDD = 5 V
PO = 1 W
AV = –20 V/V
RL = 8 Ω
CB = 0.1 µF
CB = 1 µF
THD+N – Total Harmonic Distortion Plus Noise – %
Figure 8
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
VDD = 5 V
PO = 0.5 W
AV = –2 V/V
RL = 8 Ω
CB = 0.1 µF
CB = 1 µF
THD+N – Total Harmonic Distortion Plus Noise – %
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
7
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 9
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
VDD = 5 V
PO = 0.5 W
AV = –10 V/V
RL = 8 Ω
CB = 0.1 µF
CB = 1 µF
THD+N – Total Harmonic Distortion Plus Noise – %
Figure 10
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 5 V
PO = 0.5 W
AV = –20 V/V
RL = 8 Ω
CB = 0.1 µF
CB = 1 µF
Figure 11
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 5 V
AV = –10 V/V
Single Ended
RL = 8 Ω
PO = 250 mW
RL = 32 Ω
PO = 60 mW
Figure 12
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
0.02
10
1
0.1
0.01
0.1 1
PO – Output Power – W
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 5 V
AV = –2 V/V
RL = 8 Ω
f = 20 Hz
CB = 0.1 µF
2
CB = 1 µF
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
8
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 13
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
0.02
10
1
0.1
0.01
0.1 1
PO – Output Power – W
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 5 V
AV = –2 V/V
RL = 8 Ω
f = 1 kHz
2
CB = 0.1 µF
CB = 1 µF
Figure 14
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
0.02
10
1
0.1
0.01
0.1 1
PO – Output Power – W
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 5 V
AV = –2 V/V
RL = 8 Ω
f = 20 kHz
CB = 0.1 µF
2
CB = 1 µF
Figure 15
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 3.3 V
PO = 350 mW
RL = 8 Ω
AV = –2 V/V
CB = 0.1 µF
CB = 1 µF
Figure 16
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 3.3 V
PO = 350 mW
RL = 8 Ω
AV = –10 V/V
CB = 1 µF
CB = 0.1 µF
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 17
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 3.3 V
PO = 350 mW
RL = 8 Ω
AV = –20 V/V
CB = 1 µF
CB = 0.1 µF
Figure 18
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
20
10
1
0.1
0.01
100 1 k 10 k 20 k
f – Frequency – Hz
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 3.3 V
AV = –10 V/V
Single Ended
RL = 32 Ω
PO = 60 mW
RL = 8 Ω
PO = 250 mW
Figure 19
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
0.02
10
1
0.1
0.01
0.1 1
PO – Output Power – W
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 3.3 V
AV = –2 V/V
RL = 8 Ω
f = 20 Hz
CB = 0.1 µF
2
CB = 1.0 µF
Figure 20
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
0.02
10
1
0.1
0.01
0.1 1
PO – Output Power – W
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 3.3 V
AV = –2 V/V
RL = 8 Ω
f = 1 kHz
CB = 0.1 µF
2
CB = 1 µF
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
10
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 21
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
20 m
10
1
0.1
0.01
0.1 1
PO – Output Power – W
THD+N – Total Harmonic Distortion Plus Noise – %
VDD = 3.3 V
AV = –2 V/V
RL = 8 Ω
f = 20 kHz
CB = 1 µF
2
CB = 0.1 µF
Figure 22
– Supply Current – mAI
DD
SUPPLY CURRENT
vs
SUPPLY VOLTAGE
2.5
5
2
1
0
3 3.5
VDD – Supply Voltage – V
4 4.5 5 5.5
4
3
TA = 0°C
TA = 85°C
TA = 25°C
TA = –40°C
Figure 23
OUTPUT NOISE VOLTAGE
vs
FREQUENCY
20
10
3
10
2
10
1
1
100 1 k 10 k 20 k
f – Frequency – Hz
VDD = 5 V
V01 +V02
V01
V02
– Output Noise Voltage – V
n
Vµ
Figure 24
OUTPUT NOISE VOLTAGE
vs
FREQUENCY
20
10
3
10
2
10
1
1
100 1 k 10 k 20 k
f – Frequency – Hz
VDD = 3.3 V
V02
V01
V01 +V02
– Output Noise Voltage – V
n
Vµ
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
11
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 25
0.4
0.2
0
–25 0 25 50 75
0.6
0.8
100
TA – Free-Air Temperature – °C
Maximum Package Power Dissipation – W
MAXIMUM PACKAGE POWER DISSIPATION
vs
FREE-AIR TEMPERATURE
–50
Figure 26
POWER DISSIPATION
vs
OUTPUT POWER
1
0.75
0.5
0
0 0.75
PO – Output Power – W
0.25 0.5 1 1.25
VDD = 5 V
0.25
RL = 8 Ω
RL = 16 Ω
P
D
– Power Dissipation – W
Figure 27
POWER DISSIPATION
vs
OUTPUT POWER
0.5
0.3
0.2
0
0 0.5
PO – Output Power – W
0.1 0.4
VDD = 3.3 V
0.4
RL = 8 Ω
RL = 16 Ω
0.1
0.2 0.3
P
D
– Power Dissipation – W
Figure 28
160
40
20
0
0 0.25 1.50.5 0.75 1
– Free-Air Temperature –
PO – Maximum Output Power – W
1.25
C
°
T
A
80
60
120
100
140
MAXIMUM OUTPUT POWER
vs
FREE-AIR TEMPERATURE
RL = 16 Ω
RL = 8 Ω
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
12
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 29
– Power Output – W
OUTPUT POWER
vs
LOAD RESISTANCE
4
1.4
0.8
0.4
0
820 36
Load Resistance – Ω
12 16 24 28 32
1
0.6
0.2
VDD = 5 V
VDD = 3.3 V
P
O
AV = –2 V/V
f = 1 kHz
CB = 0.1 µF
THD+N ≤ 1%
1.2
4840 44
Figure 30
– Power Output – W
OUTPUT POWER
vs
SUPPLY VOLTAGE
3
1.75
1
0.5
0
3.5 5
Supply Voltage – V
4 4.5 5.5
1.25
0.75
0.25
P
O
1.5
AV = –2 V/V
f = 1 kHz
CB = 0.1 µF
THD+N ≤ 1%
2.5
2
RL = 8 Ω
RL = 4 Ω
RL = 16 Ω
Figure 31
Open-Loop Gain – dB
OPEN-LOOP GAIN
vs
FREQUENCY
10
100
60
20
–20
100 100 k
f – Frequency – Hz
VDD = 5 V
RL = 8 Ω
CB = 0.1 µF
1 k 10 k 1 M 10 M
80
40
0
45°
–45°
–135°
–225°
0°
–90°
–180°
Phase
Gain
Phase
Figure 32
SUPPLY RIPPLE REJECTION RATIO
vs
FREQUENCY
100
0
–90
–100
1 k 10 k 20 k
f – Frequency – Hz
CB = 0.1 µF
CB = 1 µF
–80
–70
–60
–50
–40
–30
–20
–10
VDD = 5 V
RL = 8 Ω
Bridge-Tied Load
k
SVR
– Supply Ripple Rejection Ratio – dB
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
13
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
SUPPLY RIPPLE REJECTION RATIO
vs
FREQUENCY
100
0
–90
–100
1 k 10 k 20 k
f – Frequency – Hz
CB = 0.1 µF
CB = 1 µF
–80
–70
–60
–50
–40
–30
–20
–10
VDD = 5 V
RL = 8 Ω
Single Ended
k
SVR
– Supply Ripple Rejection Ratio – dB
Figure 33
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
14
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
bridged-tied load versus single-ended mode
Figure 34 shows a linear audio power amplifier (AP A) in a bridge-tied load (BTL) configuration. A BTL amplifier
actually consists of two linear amplifiers driving both ends of the load. There are several potential benefits to
this differential drive configuration, but initially, let us consider power to the load. The differential drive to the
speaker means that as one side is slewing up the other side is slewing down and vice versa. This, in effect,
doubles the voltage swing on the load as compared to a ground-referenced load. Plugging twice the voltage
into the power equation, where voltage is squared, yields 4 times 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)
22
Ǹ
R
L
2x V
O(PP)
V
O(PP)
–V
O(PP)
V
DD
V
DD
Figure 34. Bridge-Tied Load Configuration
In a typical computer sound channel operating at 5 V, bridging raises the power into an 8-Ω speaker from a
singled-ended (SE) limit of 250 mW to 1 W. In sound power that is a 6-dB improvement, which is loudness that
can be heard. In addition to increased power, frequency response is a concern; consider the single-supply SE
configuration shown in Figure 35. A coupling capacitor is required to block the dc offset voltage from reaching
the load. These capacitors can be quite large (approximately 40 µF to 1000 µF) so they tend to be expensive,
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.
TPA4861
1-W AUDIO POWER AMPLIFIER
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APPLICATION INFORMATION
bridged-tied load versus single-ended mode (continued)
f
(corner)
+
1
2pR
L
C
C
(2)
For example, a 68-µF capacitor with an 8-Ω speaker would attenuate low frequencies below 293 Hz. The BTL
configuration cancels the dc offsets, which eliminates the need for the blocking capacitors. Low-frequency
performance is then limited only by the input network and speaker response. Cost and PCB space are also
minimized by eliminating the bulky coupling capacitor.
R
L
C
C
V
O(PP)
V
O(PP)
V
DD
Figure 35. Single-Ended Configuration
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 times the output power of the
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, IDDrms, 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 36).
V
(LRMS)
V
O
I
DD
I
DD(RMS)
Figure 36. Voltage and Current Waveforms for BTL Amplifiers
TPA4861
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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 transistor 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.
VLrms
+
V
P
2
Ǹ
IDDrms
+
2V
P
p
R
L
P
SUP
+
VDDIDDrms
+
V
DD2VP
p
R
L
Efficiency
+
P
L
P
SUP
Efficiency of a BTL Configuration
+
p
V
P
2V
DD
+
p
ǒ
PLR
L
2
Ǔ
1ń2
2V
DD
(3)
P
L
+
VLrms
2
R
L
+
V
p
2
2R
L
Where:
(4)
T able 1 employs equation 4 to calculate efficiencies for four different output power levels. Note that 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. Note that 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. For a stereo 1-W audio system with 8-Ω loads and a 5-V supply , the maximum
draw on the power supply is almost 3.25 W.
Table 1. Efficiency Vs Output Power in 5-V 8-Ω BTL Systems
Output Power
(W)
Efficiency
(%)
Peak-to-Peak
Voltage
(V)
Internal
Dissipation
(W)
0.25 31.4 2.00 0.55
0.50 44.4 2.83 0.62
1.00 62.8 4.00 0.59
1.25 70.2 4.47
†
0.53
†
High peak voltages cause the THD to increase.
TPA4861
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APPLICATION INFORMATION
BTL amplifier efficiency (continued)
A final point to remember about linear amplifiers, whether they are SE or BTL configured, is how to manipulate
the terms in the efficiency equation to utmost advantage when possible. Note that in equation 4, VDD is in the
denominator. This indicates that as VDD goes down, efficiency goes up.
For example, if the 5-V supply is replaced with a 10-V supply (TPA4861 has a maximum recommended V
DD
of 5.5 V) in the calculations of Table 1 then efficiency at 1 W would fall to 31% and internal power dissipation
would rise to 2.18 W from 0.59 W at 5 V . Then for a stereo 1-W system from a 10-V supply , the maximum draw
would be almost 6.5 W. Choose the correct supply voltage and speaker impedance for the application.
selection of components
Figure 37 is a schematic diagram of a typical notebook computer application circuit.
Audio
Input
Bias
Control
VDD = 5 V
1 W
Internal
Speaker
6
5
8
7
VO1
VO2
V
DD
1
2
34IN+
IN–
BYPASS
SHUTDOWN (see Note A)
VDD/2
C
I
R
I
R
F
C
F
50 kΩ 50 kΩ
46 kΩ
46 kΩ
C
B
C
S
NOTE A: SHUTDOWN must be held low for normal operation and asserted high for shutdown mode.
–
+
–
+
Figure 37. TPA4861 Typical Notebook Computer Application Circuit
TPA4861
1-W AUDIO POWER AMPLIFIER
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POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
gain setting resistors, RF and R
I
The gain for the TPA4861 is set by resistors RF and RI according to equation 5.
(5)
Gain+*
2
ǒ
R
F
R
I
Ǔ
BTL mode operation brings about the factor of 2 in the gain equation due to the inverting amplifier mirroring the
voltage swing across the load. Given that the TPA4861 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 RF values are required for proper startup operation of the
amplifier. Taken together it is recommended that the effective impedance seen by the inverting node of the
amplifier be set between 5 kΩ and 20 kΩ. The effective impedance is calculated in equation 6.
(6)
Effective Impedance
+
RFR
I
RF)
R
I
As an example consider an input resistance of 10 kΩ and a feedback resistor of 50 kΩ. The gain of the amplifier
would be –10 V/V and the effective impedance at the inverting terminal would be 8.3 kΩ, which is well within
the recommended range.
For high performance applications metal film resistors are recommended because they tend to have lower noise
levels than carbon resistors. For values of R
F
above 50 kΩ the amplifier tends to become unstable due to a pole
formed from RF and the inherent input capacitance of the MOS input structure. For this reason, a small
compensation capacitor of approximately 5 pF should be placed in parallel with RF. This, in effect, creates a low
pass filter network with the cutoff frequency defined in equation 7.
(7)
f
co(lowpass)
+
1
2pRFC
F
For example if RF is 100 kΩ and Cf is 5 pF then fco is 318 kHz, which is well outside of the audio range.
input capacitor, C
I
In the typical application, an input capacitor, CI, is required to allow the amplifier to bias the input signal to the
proper dc level for optimum operation. In this case, CI and RI form a high-pass filter with the corner frequency
determined in equation 8.
(8)
f
co(highpass)
+
1
2pR
I
C
I
The value of CI is important to consider, as it directly af fects the bass (low frequency) performance of the circuit.
Consider the example where RI is 10 kΩ and the specification calls for a flat bass response down to 40 Hz.
Equation 8 is reconfigured as equation 9.
(9)
C
I
+
1
2pRIf
co
In this example, CI is 0.40 µF, so one would likely choose a value in the range of 0.47 µF to 1 µF. A further
consideration for this capacitor is the leakage path from the input source through the input network (RI, CI) and
the feedback resistor (RF) to the load. This leakage current creates a dc offset voltage at the input to the amplifier
that reduces useful headroom, especially in high gain applications. For this reason a low-leakage tantalum or
ceramic capacitor is the best choice. When polarized capacitors are used, the positive side of the capacitor
should face the amplifier input in most applications as the dc level there is held at V
DD
/2, which is likely higher
than the source dc level. Please note that it is important to confirm the capacitor polarity in the application.
TPA4861
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APPLICATION INFORMATION
power supply decoupling, C
S
The TPA4861 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling
to ensure that the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also
prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is
achieved by using two capacitors of different types that target different types of noise on the power supply leads.
For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance
(ESR) ceramic capacitor, typically 0.1 µF placed as close as possible to the device V
DD
lead, works best. For
filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10 µF or greater placed near
the power amplifier is recommended.
midrail bypass capacitor, C
B
The midrail bypass capacitor, CB, serves several important functions. During start-up or recovery from
shutdown mode, CB determines the rate at which the amplifier starts up. This helps to push the start-up pop
noise into the subaudible range (so slow it can not be heard). 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. The capacitor is fed from a 25-kΩ source inside the amplifier . T o keep the start-up
pop as low as possible, the relationship shown in equation 10 should be maintained.
(10)
1
ǒ
CB
25 kΩ
Ǔ
v
1
ǒ
CIR
I
Ǔ
As an example, consider a circuit where CB is 0.1 µF, CI is 0.22 µF and RI is 10 kΩ. Inserting these values into
the equation 9 we get:
400v454
which satisfies the rule. Bypass capacitor, CB, values of 0.1 µF to 1 µF ceramic or tantalum low-ESR capacitors
are recommended for the best THD and noise performance.
TPA4861
1-W AUDIO POWER AMPLIFIER
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APPLICATION INFORMATION
single-ended operation
Figure 38 is a schematic diagram of the recommended SE configuration. In SE mode configurations, the load
should be driven from the primary amplifier output (VO1, terminal 5).
Audio
Input
V
DD
6
5
8
VO1
VO2
V
DD
2
34IN+
IN–
BYPASS
VDD/2
C
I
R
I
R
F
C
S
C
B
250-mW
External
Speaker
CSE = 0.1 µF
RSE = 50 Ω
C
C
–
+
–
+
Figure 38. Singled-Ended Mode
Gain is set by the RF and RI resistors and is shown in equation 1 1. Since the inverting amplifier is not used to
mirror the voltage swing on the load, the factor of 2 is not included.
(11)
Gain+*
ǒ
R
F
R
I
Ǔ
The phase margin of the inverting amplifier into an open circuit is not adequate to ensure stability, so a
termination load should be connected to V
O
2. This consists of a 50-Ω resistor in series with a 0.1-µF capacitor
to ground. It is important to avoid oscillation of the inverting output to minimize noise and power dissipation.
The output coupling capacitor required in single-supply SE mode also places additional constraints on the
selection of other components in the amplifier circuit. The rules described earlier still hold with the addition of
the following relationship:
(12)
1
ǒ
CB
25 kΩ
Ǔ
v
1
ǒ
CIR
I
Ǔ
Ơ
1
R
L
C
C
TPA4861
1-W AUDIO POWER AMPLIFIER
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POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
output coupling capacitor, C
C
In the typical single-supply SE configuration, an output coupling capacitor (C
C
) is required to block the dc bias
at the output of the amplifier thus preventing dc currents in the load. As with the input coupling capacitor, the
output coupling capacitor and impedance of the load form a high-pass filter governed by equation 13.
(13)
f
out high
+
1
2pR
L
C
C
The main disadvantage, from a performance standpoint, is that the load impedances are typically small, which
drives the low-frequency corner higher. Large values of C
C
are required to pass low frequencies into the load.
Consider the example where a CC of 68 µF is chosen and loads vary from 8 Ω, 32 Ω, and 47 kΩ. Table 2
summarizes the frequency response characteristics of each configuration.
Table 2. Common Load Impedances vs Low Frequency Output Characteristics in SE Mode
R
L
C
C
Lowest Frequency
8 Ω 68 µF 293 Hz
32 Ω 68 µF
73 Hz
47,000 Ω 68 µF 0.05 Hz
As Table 2 indicates, most of the bass response is attenuated into 8-Ω loads, while headphone response is
adequate and drive into line level inputs (a home stereo for example) is very good.
shutdown mode
The TP A4861 employs a shutdown mode of operation designed to reduce supply current, I
DD(q)
, to the absolute
minimum level during periods of nonuse for battery-power conservation. For example, during device sleep
modes or when other audio-drive currents are used (i.e., headphone mode), the speaker drive is not required.
The SHUTDOWN input terminal should be held low during normal operation when the amplifier is in use. Pulling
SHUTDOWN high causes the outputs to mute and the amplifier to enter a low-current state,
I
DD(SD)
= 0.6 µA. SHUTDOWN should never be left unconnected because amplifier operation would be
unpredictable.
using low-ESR capacitors
Low-ESR capacitors are recommended throughout this applications section. A real 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.
TPA4861
1-W AUDIO POWER AMPLIFIER
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POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
thermal considerations
A prime consideration when designing an audio amplifier circuit is internal power dissipation in the device. The
curve in Figure 39 provides an easy way to determine what output power can be expected out of the TP A4861
for a given system ambient temperature in designs using 5-V supplies. This curve assumes no forced airflow
or additional heat sinking.
160
40
20
0
0 0.25 1.50.5 0.75 1
– Free-Air Temperature –
PO – Maximum Output Power – W
1.25
C
°
T
A
80
60
120
100
140
RL = 16 Ω
RL = 8 Ω
VDD = 5 V
Figure 39. Free-Air Temperature vs Maximum Continuous Output Power
5-V versus 3.3-V operation
The TPA4861 was designed for operation over a supply range of 2.7 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 as far as supply bypassing, gain
setting, or stability. Supply current is slightly reduced from 3.5 mA (typical) to 2.5 mA (typical). The most
important consideration is that of output power. Each amplifier in TPA4861 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 when V
O(PP)
= 4 V while operating at 5 V . The reduced voltage swing subsequently reduces maximum output
power into an 8-Ω load to less than 0.33 W before distortion begins to become significant.
Operation at 3.3-V supplies, as can be shown from the efficiency formula in equation 4, consumes
approximately two-thirds of the supply power for a given output-power level than operation from 5-V supplies.
When the application demands less than 500 mW, 3.3-V operation should be strongly considered, especially
in battery-powered applications.
TPA4861
1-W AUDIO POWER AMPLIFIER
SLOS163B – SEPTEMBER 1996 – REVISED MARCH 2000
23
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
IMPORTANT NOTICE
T exas Instruments and its subsidiaries (TI) reserve the right to make changes to their products or to discontinue
any product or service without notice, and advise customers to obtain the latest version of relevant information
to verify, before placing orders, that information being relied on is current and complete. All products are sold
subject to the terms and conditions of sale supplied at the time of order acknowledgment, including those
pertaining to warranty, patent infringement, and limitation of liability.
TI warrants performance of its semiconductor products to the specifications applicable at the time of sale in
accordance with TI’s standard warranty. Testing and other quality control techniques are utilized to the extent
TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily
performed, except those mandated by government requirements.
Customers are responsible for their applications using TI components.
In order to minimize risks associated with the customer’s applications, adequate design and operating
safeguards must be provided by the customer to minimize inherent or procedural hazards.
TI assumes no liability for applications assistance or customer product design. TI does not warrant or represent
that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other
intellectual property right of TI covering or relating to any combination, machine, or process in which such
semiconductor products or services might be or are used. TI’s publication of information regarding any third
party’s products or services does not constitute TI’s approval, warranty or endorsement thereof.
Copyright 2000, Texas Instruments Incorporated
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