TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
1
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
D
Compatible With PC 99 Desktop Line-Out
Into 10-kΩ Load
D
Compatible With PC 99 Portable Into 8-Ω
Load
D
Internal Gain Control, Which Eliminates
External Gain-Setting Resistors
D
DC Volume Control From 20 dB to –40 dB
D
2-W/Ch Output Power Into 3-Ω Load
D
Input MUX Select Terminal
D
PC-Beep Input
D
Depop Circuitry
D
Stereo Input MUX
D
Fully Differential Input
D
Low Supply Current and Shutdown Current
D
Surface-Mount Power Packaging
24-Pin TSSOP PowerPAD
description
The TPA0242 is a stereo audio power amplifier in a 24-pin TSSOP thermally enhanced package capable of
delivering 2 W of continuous RMS power per channel into 3-Ω loads. This device minimizes the number of
external components needed, which simplifies the design and frees up board space for other features. When
driving 1 W into 8-Ω speakers, the TP A0242 has less than 0.22% THD+N across its specified frequency range.
Included within this device is integrated depop circuitry that virtually eliminates transients that cause noise in
the speakers.
Amplifier gain is controlled by a dc voltage input on the VOLUME terminal. There are 31 discrete steps covering
the range of 20 dB (maximum volume setting) to –40 dB (minimum volume setting) in 2 dB steps. When the
VOLUME terminal exceeds 3.54 V, the device is muted. An internal input MUX allows two sets of stereo inputs
to the amplifier . The HP/LINE terminal allows the user to select which MUX input is active regardless of whether
the amplifier is in SE or BTL mode. In notebook applications, where internal speakers are driven as BTL and
the line outputs (often headphone drive) are required to be SE, the TPA0242 automatically switches into SE
mode when the SE/BTL input is activated, and this effectively reduces the gain by 6 dB.
The TPA0242 consumes only 20 mA of supply current during normal operation. A miserly shutdown mode
reduces the supply current to less than 150 µA.
The PowerPAD package (PWP) delivers a level of thermal performance that was previously achievable only
in TO-220-type packages. Thermal impedances of approximately 35°C/W are truly realized in multilayer PCB
applications. This allows the TP A0242 to operate at full power into 8-Ω loads at ambient temperatures of 85°C.
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 1999, 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
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
GND
HP/LINE
VOLUME
LOUT+
LLINEIN
LHPIN
PVDD
RIN
LOUT–
LIN
BYPASS
GND
GND
RLINEIN
SHUTDOWN
ROUT+
RHPIN
VDD
PVDD
CLK
ROUT–
SE/BTL
PC-BEEP
GND
PWP PACKAGE
(TOP VIEW)
PowerPAD is a trademark of Texas Instruments Incorporated.
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
2POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
functional block diagram
ROUT+
–
+
–
+
R
MUX
32-Step
Volume
Control
PC
Beep
MUX
Control
Depop
Circuitry Power
Management
–
+
–
+
L
MUX
32-Step
Volume
Control
RHPIN
RLINEIN
VOLUME
RIN
PC-BEEP
SE/BTL
LHPIN
LLINEIN
LIN
ROUT–
PVDD
VDD
BYPASS
SHUTDOWN
GND
LOUT+
LOUT–
HP/LINE
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
3
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
AVAILABLE OPTIONS
PACKAGED DEVICE
TATSSOP†
(PWP)
–40°C to 85°C TPA0242PWP
†The PWP package is available taped and reeled. T o order a taped and reeled part,
add the suffix R to the part number (e.g., TPA0242PWPR).
Terminal Functions
TERMINAL
I/O
DESCRIPTION
NAME NO.
I/O
DESCRIPTION
BYPASS 11 Tap to voltage divider for internal mid-supply bias generator
CLK 17 IIf a 47-nF capacitor is attached, the TPA0242 generates an internal clock. An external clock can override
the internal clock input to this terminal.
GND 1, 12
13, 24 Ground connection for circuitry. Connected to thermal pad
LHPIN 6 I Left channel headphone input, selected when SE/BTL is held high
LIN 10 ICommon left input for fully differential input. AC ground for single-ended inputs
LLINEIN 5 I Left channel line negative input, selected when SE/BTL is held low
LOUT+ 4 O Left channel positive output in BTL mode and positive output in SE mode
LOUT– 9 O Left channel negative output in BTL mode and high-impedance in SE mode
HP/LINE 2 I HP/LINE is the input MUX control input. When the HP/LINE terminal is held high, the headphone inputs
(LHPIN or RHPIN [6, 20]) are active. When the HP/LINE terminal is held low , the line BTL inputs (LLINEIN
or RLINEIN [5, 23]) are active.
PC-BEEP 14 IThe input for PC Beep mode. PC-BEEP is enabled when a > 1-V (peak-to-peak) square wave is input to
PC-BEEP.
PVDD 7, 18 IPower supply for output stage
RHPIN 20 IRight channel headphone input, selected when SE/BTL is held high
RIN 8 I Common right input for fully differential input. AC ground for single-ended inputs
RLINEIN 23 IRight channel line input, selected when SE/BTL is held low
ROUT+ 21 ORight channel positive output in BTL mode and positive output in SE mode
ROUT– 16 ORight channel negative output in BTL mode and high-impedance in SE mode
SE/BTL 15 IHold SE/BTL low for BTL mode and hold high for SE mode.
SHUTDOWN 22 IWhen held low , this terminal places the entire device, except PC-BEEP detect circuitry , in shutdown mode.
VDD 19 I Analog VDD input supply. This terminal needs to be isolated from PVDD to achieve highest performance.
VOLUME 3 I VOLUME detects the dc level at the terminal and sets the gain for 31 discrete steps covering a range of
20 dB to –40 dB for dc levels of 0.15 V to 3.54. When the dc level is over 3.54 V, the device is muted.
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
4POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
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, TA –40°C to 85°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating junction temperature range, TJ –40°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range, Tstg –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 af fect device reliability.
DISSIPATION RATING TABLE
PACKAGE TA ≤ 25°CDERATING F ACTOR TA = 70°C TA = 85°C
PWP 2.7 W‡21.8 mW/°C1.7 W 1.4 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
T exas Instruments Recommended
Board for PowerPAD
on page 33 of the before mentioned document.
recommended operating conditions
MIN MAX UNIT
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Supply voltage, VDD
ÁÁÁ
ÁÁÁ
4.5
ÁÁÁ
ÁÁÁ
5.5
ÁÁÁ
ÁÁÁ
V
High level in
p
ut voltage VIH
SE/BTL, HP/LINE 4
V
High
-
le
v
el
inp
u
t
v
oltage
,
V
IH SHUTDOWN 2
V
Low level in
p
ut voltage VIL
SE/BTL, HP/LINE 3
V
Lo
w-
le
v
el
inp
u
t
v
oltage
,
V
IL SHUTDOWN 0.8
V
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ
Operating free-air temperature, TA
ÁÁÁ
ÁÁÁ
–40
ÁÁÁ
ÁÁÁ
85
ÁÁÁ
ÁÁÁ
°C
electrical characteristics at specified free-air temperature, VDD = 5 V, T A = 25°C (unless otherwise
noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
ÁÁÁÁ
ÁÁÁÁ
|VOS|
Output offset voltage (measured dif ferentially)
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
VI = 0, Av = 2 V/V
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
25
ÁÁÁ
ÁÁÁ
mV
ÁÁÁÁ
ÁÁÁÁ
Supply ripple rejection ratio
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
VDD = 4.9 V to 5.1 V
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
67
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
dB
|IIH|High-level input current VDD = 5.5 V, VI = VDD
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
900
ÁÁÁ
ÁÁÁ
nA
|IIL|Low-level input current VDD = 5.5 V, VI = 0 V
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
900
ÁÁÁ
ÁÁÁ
nA
ÁÁÁÁ
ÁÁÁÁ
IDD
Su
pp
ly current
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
BTL mode
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
20
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
mA
ÁÁÁÁ
ÁÁÁÁ
I
DD
S
u
ppl
y
c
u
rrent
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
SE mode
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
10
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
mA
ÁÁÁÁ
ÁÁÁÁ
IDD(SD)
Supply current, shutdown mode
ÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
150
ÁÁÁ
ÁÁÁ
300
ÁÁÁ
ÁÁÁ
µA
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
5
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
operating characteristics, VDD = 5 V , T A = 25°C, RL = 4 Ω, Gain = 2 V/V , BTL mode (unless otherwise
noted)
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
ÁÁÁÁ
ÁÁÁÁ
PO
ÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
Output power
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
THD = 1%,
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
f = 1 kHz
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
2
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
W
ÁÁÁÁ
ÁÁÁÁ
THD + N
ÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
Total harmonic distortion plus noise
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
PO = 1 W,
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
f = 20 Hz to 15 kHz
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
0.22%
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁÁ
ÁÁÁÁ
BOM
ÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
Maximum output power bandwidth
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
THD = 5%
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
>15
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
kHz
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
Su
pp
ly ri
pp
le rejection ratio
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
f = 1 kHz CB=047µF
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
BTL mode
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
65
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
dB
ÁÁÁÁ
ÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
S
u
ppl
y
ripple
rejection
ratio
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
f
=
1
kH
z,
C
B =
0
.
47
µ
F
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
SE mode
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
60
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
dB
ÁÁÁÁ
V
ÁÁÁÁÁÁÁÁÁÁ
Noise out
p
ut voltage
ÁÁÁÁÁÁÁ
CB = 0.47 µF,
ÁÁÁÁÁÁÁ
BTL mode
ÁÁÁ
ÁÁÁ
34
ÁÁÁ
ÁÁÁ
µVRMS
ÁÁÁÁ
ÁÁÁÁ
V
n
ÁÁÁÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁÁÁÁ
Noise
o
u
tp
u
t
v
oltage
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
Bµ
f = 20 Hz to 20 kHz
ÁÁÁÁÁÁÁ
ÁÁÁÁÁÁÁ
SE mode
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
44
ÁÁÁ
ÁÁÁ
ÁÁÁ
ÁÁÁ
µ
V
RMS
TYPICAL CHARACTERISTICS
Table of Graphs
FIGURE
vs Output power 1, 4, 6, 8, 10
THD+N
Total harmonic distortion
p
lus noise
vs Voltage gain 2
THD
+
N
Total
harmonic
distortion
pl
u
s
noise
vs Frequency 3, 5, 7, 9, 11
vs Output voltage 12
VnOutput noise voltage vs Bandwidth 13
Supply ripple rejection ratio vs Frequency 14, 15
Crosstalk vs Frequency 16, 17, 18
Shutdown attenuation vs Frequency 19
SNR Signal-to-noise ratio vs Bandwidth 20
Closed loop response 21, 22
POOutput power vs Load resistance 23, 24
PD
Power dissi
p
ation
vs Output power 25, 26
P
D
Po
w
er
dissipation
vs Ambient temperature 27
ZIInput impedance vs Gain 28
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
6POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 1
0.1%
0.01%0.5 0.75 1 1.25 1.5 1.75 2
1%
10%
2.25 2.5 2.75 3
PO – Output Power – W
AV = +20 to 4 dB
f = 1 kHz
BTL
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
RL = 8 ΩRL = 3 Ω
RL = 4 Ω
Figure 2
0.01%
–40 –30 –20 –10 0
THD+N –Total Harmonic Distortion + Noise
A - Voltage Gain - dB
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
VOLTAGE GAIN
1%
0.1%
10 20
V
PO = 1 W for AV≥6dB
VO= 1 VRMS for AV≤4 dB
RL = 8 Ω
BTL
Figure 3
0.01%
10%
20 100 1k 10k 20k
THD+N –Total Harmonic Distortion + Noise
f – Frequency – Hz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
1%
0.1%
RL = 3 Ω
AV = +20 to 0 dB
BTL
PO = 1.75 W
PO = 0.5 W
PO = 1 W
Figure 4
0.1%
0.01%
0.01 0.1
1%
10%
110
f = 20 Hz
f = 1 kHz
PO – Output Power – W
RL = 3 Ω
AV = +20 to +4 dB
BTL
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
f = 20 kHz
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
7
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 5
0.1%
0.01%20 100
1%
10%
1k 10k
f – Frequency – Hz
RL = 4 Ω
AV = +20 to +4 dB
BTL
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
PO= 0.25 W
20k
PO= 1 W
PO=1.5 W
Figure 6
0.1%
0.01%
0.01 0.1
1%
10%
110
f = 20 Hz
f = 1 kHz
PO – Output Power – W
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
f = 20 kHz
RL = 4 Ω
AV = +20 to +4 dB
BTL
Figure 7
0.01%
10%
20 100 1k 10k 20k
THD+N –Total Harmonic Distortion + Noise
f – Frequency – Hz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
1%
0.1%
PO = 0.25 W
PO = 0.5 W
PO = 1 W
RL = 8 Ω
AV = +20 to +4 dB
BTL
Figure 8
0.1%
0.01%
0.01 0.1
1%
10%
110
f = 20 Hz
f = 1 kHz
PO – Output Power – W
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
f = 20 kHz
RL = 8 Ω
AV = +20 to +4 dB
BTL
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
8POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 9
0.1%
0.01%
20
1%
10%
10k
f – Frequency – Hz
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
PO = 25 mW
20k
RL = 32 Ω
AV = +14 to +4 dB
SE
PO = 50 mW PO = 75 mW
100 1k
0.001%
Figure 10
0.1%
0.01%
0.01 0.1
1%
10%
1
f = 20 Hz
f = 1 kHz
PO – Output Power – W
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT POWER
f = 20 kHz
RL = 32 Ω
AV = +14 to +4 dB
SE
Figure 11
0.001%
10%
20 100 1k 10k 20k
THD+N –Total Harmonic Distortion + Noise
f – Frequency – Hz
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
FREQUENCY
1%
0.1%
VO = 1 VRMS
0.01%
RL = 10 kΩ
AV = +14 to 0 dB
SE
Figure 12
THD+N –Total Harmonic Distortion + Noise
TOTAL HARMONIC DISTORTION PLUS NOISE
vs
OUTPUT VOLTAGE
f = 20 kHz
VO – Output Voltage – VRMS
0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2
0.001%
0.01%
0.1%
1%
10%
RL = 10 kΩ
AV = +14 to +4 dB
SE
f = 1 kHz
f = 20 Hz
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
9
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 13
120
00 100
140
160
1k 10k
BW – Bandwidth – Hz
VDD = 5 V
RL = 4 Ω
OUTPUT NOISE VOLTAGE
vs
BANDWIDTH
AV = +20 dB
20k
AV = +6 dB
– Output Noise Voltage – VµVnRMS
20
40
60
80
100
Figure 14
–100
–12020 100
–80
1k 10k
RL = 8 Ω
CB = 0.47 µF
BTL
SUPPLY RIPPLE REJECTION RATIO
vs
FREQUENCY
AV = +6 dB
–60
–40
–20
0
f – Frequency – Hz 20k
AV = +20 dB
Supply Ripple Rejection Ratio – dB
Figure 15
–100
–12020 100
–80
1k 10k
RL = 32 Ω
CB = 0.47 µF
SE
SUPPLY RIPPLE REJECTION RATIO
vs
FREQUENCY
AV = 0 dB
–60
–40
–20
0
f – Frequency – Hz 20k
AV = +14 dB
Supply Ripple Rejection Ratio – dB
Figure 16
–120
–80
20 100 1k 10k 20k
Crosstalk – dB
f – Frequency – Hz
CROSSTALK
vs
FREQUENCY
–90
–100
–110
PO = 1 W
RL = 8 Ω
AV = +20 dB
BTL
–70
–60
LEFT TO RIGHT
RIGHT TO LEFT
–50
–40
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
10 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 17
–120
–80
20 100 1k 10k 20k
Crosstalk – dB
f – Frequency – Hz
CROSSTALK
vs
FREQUENCY
–90
–100
–110
PO = 1 W
RL = 8 Ω
AV = +6 dB
BTL
–70
–60
LEFT TO RIGHT
RIGHT TO LEFT
–50
–40
Figure 18
–120
–40
20 100 1k 10k 20k
Crosstalk – dB
f – Frequency – Hz
CROSSTALK
vs
FREQUENCY
–60
–80
–100
VO = 1 VRMS
RL = 10 kΩ
AV = +6 dB
SE
LEFT TO RIGHT
RIGHT TO LEFT
–110
–90
–70
–50
Figure 19
–120
–40
20 100 1k 10k 20k
Shutdown Attenuation – dB
f – Frequency – Hz
SHUTDOWN ATTENUATION
vs
FREQUENCY
–60
–80
–100
–20
0VI = 1 VRMS
RL = 8 Ω, BTL
RL = 32 Ω, SE
RL = 10 kΩ, SE
Figure 20
80
110
0 100 1k 10k 20k
SNR – Signal-To-Noise Ratio – dB
BW – Bandwidth – Hz
SIGNAL-TO-NOISE RATIO
vs
BANDWIDTH
105
100
95
115
120
85
90
PO = 1 W
RL = 8 Ω
BTL
AV = +20 dB
AV = +6 dB
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
11
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
–10
20
10 100 1k 10k 100k
Gain – dB
f – Frequency – Hz
CLOSED LOOP RESPONSE
15
10
5
25
30
–5
0
180°
90°
0°
–90°
–180°
1M
Phase Margin
m
φ–
RL = 8 Ω
AV = +20 dB
BTL Gain
Phase
Figure 21
–10
20
10 100 1k 10k 100k
Gain – dB
f – Frequency – Hz
CLOSED LOOP RESPONSE
15
10
5
25
30
–5
0
180°
90°
0°
–90°
–180°
1M
RL = 8 Ω
AV = +6 dB
BTL
Gain
Phase
Phase Margin
m
φ–
Figure 22
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
12 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
Figure 23
2
1.5
00 8 16 24 32 40
2.5
3
3.5
48 56 64
RL – Load Resistance – Ω
AV = +20 to 0 dB
BTL
– Output Power – WPO
OUTPUT POWER
vs
LOAD RESISTANCE
1% THD+N
10% THD+N
1
0.5
Figure 24
750
00816
1000
1250
1500
24 32
RL – Load Resistance – Ω
AV = +14 to 0 dB
SE
– Output Power – mWPO
OUTPUT POWER
vs
LOAD RESISTANCE
1% THD+N
10% THD+N
500
250
40 48 56 64
Figure 25
0.6
0.4
0.2
001
– Power Dissipation – W
1
1.2
POWER DISSIPATION
vs
OUTPUT POWER
1.4
1.5 2.5
0.8
PO – Output Power – W
PD
4 Ω
8 Ω
f = 1 kHz
BTL
Each Channel
3 Ω
1.6
1.8
0.5 2
Figure 26
0.1
0.05
00 0.2
– Power Dissipation – W
0.2
0.25
POWER DISSIPATION
vs
OUTPUT POWER
0.3
0.3 0.8
0.15
PO – Output Power – W
PD
8 Ω
32 Ωf = 1 kHz
BTL
Each Channel
4 Ω
0.35
0.4
0.1 0.70.4 0.5 0.6
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
13
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
TYPICAL CHARACTERISTICS
1
0
–40 0
– Power Dissipation – W
3
4
POWER DISSIPATION
vs
AMBIENT TEMPERATURE
5
20 160
2
TA – Ambient Temperature – °C
PD
6
7
–20 10040 60 80 120 140
ΘJA3
ΘJA1,2
ΘJA4 ΘJA1 = 45.9°C/W
ΘJA2 = 45.2°C/W
ΘJA3 = 31.2°C/W
ΘJA4 = 18.6°C/W
Figure 27
40
30
20
10
–40 –20
60
70
INPUT IMPEDANCE
vs
GAIN
80
–10 10
50
AV – Gain – dB
90
–30 0 20
– Input Impedance – kZIΩ
Figure 28
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
14 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
THERMAL INFORMATION
The thermally enhanced PWP package is based on the 24-pin TSSOP, but includes a thermal pad (see Figure 29)
to provide an effective thermal contact between the IC and the PWB.
T raditionally, surface mount and power have been mutually exclusive terms. A variety of scaled-down TO-220-type
packages have leads formed as gull wings to make them applicable for surface-mount applications. These packages,
however, have only two shortcomings: they do not address the very low profile requirements (<2 mm) of many of
today’s advanced systems, and they do not offer a terminal-count high enough to accommodate increasing
integration. On the other hand, traditional low-power surface-mount packages require power-dissipation derating that
severely limits the usable range of many high-performance analog circuits.
The PowerPAD package (thermally enhanced TSSOP) combines fine-pitch surface-mount technology with thermal
performance comparable to much larger power packages.
The PowerPAD package is designed to optimize the heat transfer to the PWB. Because of the very small size and
limited mass of a TSSOP package, thermal enhancement is achieved by improving the thermal conduction paths that
remove heat from the component. The thermal pad is formed using a patented lead-frame design and manufacturing
technique to provide a direct connection to the heat-generating IC. When this pad is soldered or otherwise thermally
coupled to an external heat dissipator, high power dissipation in the ultra-thin, fine-pitch, surface-mount package can
be reliably achieved.
DIE
Side View (a)
End View (b)
Bottom View (c)
DIE
Thermal
Pad
Figure 29. Views of Thermally Enhanced PWP Package
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
15
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
Table 1. DC Volume Control
VOLUME (Terminal 3)
GAIN of AMPLIFIER
FROM
(V) TO
(V)
GAIN
of
AMPLIFIER
(dB)
0 0.15 20
0.15 0.28 18
0.28 0.39 16
0.39 0.5 14
0.5 0.61 12
0.61 0.73 10
0.73 0.84 8
0.84 0.95 6
0.95 1.06 4
1.06 1.17 2
1.17 1.28 0
1.28 1.39 –2
1.39 1.5 –4
1.5 1.62 –6
1.62 1.73 –8
1.73 1.84 –10
1.84 1.95 –12
1.95 2.07 –14
2.07 2.18 –16
2.18 2.29 –18
2.29 2.41 –20
2.41 2.52 –22
2.52 2.63 –24
2.63 2.74 –26
2.74 2.86 –28
2.86 2.97 –30
2.97 3.08 –32
3.08 3.2 –34
3.2 3.31 –36
3.31 3.42 –38
3.42 3.54 –40
3.54 5 –85
selection of components
Figure 30 and Figure 31 are schematic diagrams of typical notebook computer application circuits.
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
16 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
ROUT+ 21
R
MUX
RHPIN
RLINEIN
+
–
23
20
CIRHP
0.47 µF
Right
Head–
phone
Input
Signal
CIRLINE
0.47 µF
Right
Line
Input
Signal
CRIN
0.47 µF
8 RIN
ROUT– 16
+
–1 kΩ
COUTR
330 µF
100 kΩ
L
MUX
LHPIN
LLINEIN5
6
CILHP
0.47 µF
Left
Head–
phone
Input
Signal CILLINE
0.47 µF
Left
Line
Input
Signal
CLIN
0.47 µF
10 LIN
1 kΩ
COUTL
330 µF
VDD
100 kΩ
Depop
Circuitry
Power
Management
PVDD 18
VDD 19
BYPASS 11
SHUT–
DOWN 22
GND
LOUT+ 4
+
–
LOUT– 9
+
–
CBYP
0.47 µF
1,12,
13,24
To
System
Control
CSR
0.1 µF
VDD
CSR
0.1 µF
VDD
See Note A
PC–
Beep
PC–BEEP
HP/LINE
14
CPCB
0.47 µF
PC BEEP
Input
Signal
2
Gain/
MUX
Control
VOLUME
CLK
3
17 SE/BTL
15
CCLK
47 nF
VDD
50 kΩ
NOTE A: A 0.1 µF ceramic capacitor should be placed as close as possible to the IC. For filtering lower–frequency noise signals, a larger
electrolytic capacitor of 10 µF or greater should be placed near the audio power amplifier.
Figure 30. Typical TPA0242 Application Circuit Using Single-Ended Inputs and Input MUX
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
17
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
ROUT+ 21
R
MUX
RHPIN
RLINEIN
+
–
23
20
CIRIN–
0.47 µF
8 RIN
ROUT– 16
+
–1 kΩ
COUTR
330 µF
100 kΩ
L
MUX
LHPIN
LLINEIN5
6
CILIN–
0.47 µF
10 LIN
1 kΩ
COUTL
330 µF
VDD
100 kΩ
Depop
Circuitry
Power
Management
PVDD 18
VDD 19
BYPASS 11
SHUT–
DOWN 22
GND
LOUT+ 4
+
–
LOUT– 9
+
–
CBYP
0.47 µF
1,12,
13,24
To
System
Control
CSR
0.1 µF
VDD
CSR
0.1 µF
VDD
See Note A
PC–
Beep
PC–BEEP
14
CPCB
0.47 µF
PC BEEP
Input
Signal
Gain/
MUX
Control
VOLUME
CLK
3
1717 SE/BTL
15
N/C
CIRIN+
0.47 µF
Right
Positive
Differential
Input
Signal
Right
Negative
Differential
Input
Signal
CCLK
47 nF
VDD
50 kΩ
HP/LINE
2
Left
Negative
Differential
Input
Signal
CILIN+
0.47 µF
Left
Positive
Differential
Input
Signal
N/C
NOTE A: A 0.1 µF ceramic capacitor should be placed as close as possible to the IC. For filtering lower–frequency noise signals, a larger
electrolytic capacitor of 10 µF or greater should be placed near the audio power amplifier.
Figure 31. Typical TPA0242 Application Circuit Using Differential Inputs
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
18 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
input resistance
Each gain setting is achieved by varying the input resistance of the amplifier , which can range from its smallest
value to over 6 times that value. As a result, if a single capacitor is used in the input high pass filter, the –3 dB
or cut-off frequency will also change by over 6 times. If an additional resistor is connected from the input pin
of the amplifier to ground, as shown in the figure below, the variation of the cut-off frequency will be much
reduced.
C
R
IN RI
Rf
Input Signal
Figure 32. Resistor on Input for Cut-Off Frequency
The input resistance at each gain setting is given in Figure 28:
The –3 dB frequency can be calculated using the following formula:
(1)
ƒ–3 dB
+
1
2
p
C
ǒ
R
ø
RI
Ǔ
If the filter must be more accurate, the value of the capacitor should be increased while the value of the resistor
to ground should be decreased. In addition, the order of the filter could be increased.
input capacitor, CI
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 the input impedance of the amplifier, ZI, form a
high-pass filter with the corner frequency determined in equation 2.
fc(highpass)
+
1
2
p
ZINCI
–3 dB
fc
(2)
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
19
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
The value of CI is important to consider as it directly affects the bass (low frequency) performance of the circuit.
Consider the example where ZI is 710 kΩ and the specification calls for a flat bass response down to 40 Hz.
Equation 2 is reconfigured as equation 3.
CI
+
1
2
p
ZIfc(3)
In this example, CI is 5.6 nF so one would likely choose a value in the range of 5.6 nF to 1 µF. A further
consideration for this capacitor is the leakage path from the input source through the input network (CI) and the
feedback network to the load. This leakage current creates a dc offset voltage at the input to the amplifier that
reduces useful headroom, especially in high gain applications. For this reason a low-leakage tantalum or
ceramic capacitor is the best choice. When polarized capacitors are used, the positive side of the capacitor
should face the amplifier input in most applications as the dc level there is held at VDD/2, which is likely higher
than the source dc level. Note that it is important to confirm the capacitor polarity in the application.
power supply decoupling, CS
The TPA0242 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 µF placed as close as possible to the device VDD lead, works best. For
filtering lower-frequency noise signals, a larger aluminum electrolytic capacitor of 10 µF or greater placed near
the audio power amplifier is recommended.
midrail bypass capacitor, CBYP
The midrail bypass capacitor, CBYP, is the most critical capacitor and serves several important functions. During
startup or recovery from shutdown mode, CBYP determines the rate at which the amplifier starts up. The second
function is to reduce noise produced by the power supply caused by coupling into the output drive signal. This
noise is from the midrail generation circuit internal to the amplifier, which appears as degraded PSRR and
THD+N.
Bypass capacitor , CBYP, values of 0.47 µF to 1 µF ceramic or tantalum low-ESR capacitors are recommended
for the best THD and noise performance.
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
20 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
output coupling capacitor, CC
In the typical single-supply SE configuration, an output coupling capacitor (CC) 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 4.
(4)
fc(high)
+
1
2
p
RLCC
–3 dB
fc
The main disadvantage, from a performance standpoint, is the load impedances are typically small, which drives
the low-frequency corner higher, degrading the bass response. Large values of CC are required to pass low
frequencies into the load. Consider the example where a CC of 330 µF is chosen and loads vary from 3 Ω,
4 Ω, 8 Ω, 32 Ω, 10 kΩ, 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
RLCCLowest Frequency
3 Ω330 µF161 Hz
4 Ω330 µF120 Hz
8 Ω330 µF60 Hz
32 Ω330 µF15 Hz
10,000 Ω330 µF0.05 Hz
47,000 Ω330 µF0.01 Hz
As Table 2 indicates, most of the bass response is attenuated into a 4-Ω load, an 8-Ω load is adequate,
headphone response is good, and drive into line level inputs (a home stereo for example) is exceptional.
using low-ESR capacitors
Low-ESR capacitors are recommended throughout this applications section. A real (as opposed to ideal)
capacitor can be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this
resistor minimizes the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this
resistance the more the real capacitor behaves like an ideal capacitor.
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
21
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
bridged-tied load versus single-ended mode
Figure 33 shows a Class-AB audio power amplifier (APA) in a BTL configuration. The TPA0242 BTL amplifier
consists of two Class-AB amplifiers driving both ends of the load. There are several potential benefits to this
differential drive configuration, but, initially 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 2 × VO(PP) into the power
equation, where voltage is squared, yields 4× the output power from the same supply rail and load impedance
(see equation 5).
Power
+
V(rms)2
RL
(5)
V(rms)
+
VO(PP)
22
Ǹ
RL2x VO(PP)
VO(PP)
–VO(PP)
VDD
VDD
Figure 33. 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, ground reference) 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 there are frequency response concerns.
Consider the single-supply SE configuration shown in Figure 34. A coupling capacitor is required to block the
dc offset voltage from reaching the load. These capacitors can be quite large (approximately 33 µF to 1000 µF)
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 6.
f(c)
+
1
2
p
RLCC(6)
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
22 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
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.
RL
CCVO(PP)
VO(PP)
VDD
–3 dB
fc
Figure 34. 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 the SE
configuration. Internal dissipation versus output power is discussed further in the
crest factor and thermal
considerations
section.
single-ended operation
In SE mode (see Figure 33 and Figure 34), the load is driven from the primary amplifier output for each channel
(OUT+, terminals 21 and 4).
The amplifier switches single-ended operation when the SE/BTL terminal is held high. This puts the negative
outputs in a high-impedance state, and reduces the amplifier’s gain by 6 dB.
input MUX operation
The input MUX allows two separate inputs to be applied to the amplifier. This allows the designer to choose
which input is active independent of the state of the SE/BTL terminal. When the HP/LINE terminal is held high,
the headphone inputs are active. When the HP/LINE terminal is held low, the line BTL inputs are active.
BTL amplifier efficiency
Class-AB 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
VDD. 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 and average values of power in the
load and in the amplifier, the current and voltage waveform shapes must first be understood (see Figure 35).
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
23
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
V(LRMS)
VOIDD
IDD(avg)
Figure 35. Voltage and Current Waveforms for BTL Amplifiers
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.
Efficiency of a BTL amplifier
+
PL
PSUP (7)
Where:
(8)
PL
+
VLrms2
RL, andVLRMS
+
VP
2
Ǹ
, therefore, PL
+
VP2
2RL
PL = Power delivered to load
PSUP = Power drawn from power supply
VLRMS = RMS voltage on BTL load
RL = Load resistance
VP = Peak voltage on BTL load
IDDavg = Average current drawn from
the power supply
VDD = Power supply voltage
ηBTL = Efficiency of a BTL amplifier
and PSUP
+
VDD IDDavg and IDDavg
+
1
p
ŕ
p
0
VP
RLsin(t) dt
+
1
p
VP
RL[cos(t)]
p
0
+
2VP
p
RL
Therefore,
PSUP
+
2V
DD VP
p
RL
substituting PL and PSUP into equation 7,
Efficiency of a BTL amplifier
+
VP2
2R
L
2V
DD VP
p
RL
+
p
VP
4V
DD
VP
+
2P
LRL
Ǹ
h
BTL
+
p
2P
LRL
Ǹ
4V
DD
Where:
Therefore,
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
24 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
T able 3 employs equation 8 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 3. Efficiency Vs Output Power in 5-V 8-Ω BTL Systems
Output Power
(W) Efficiency
(%) 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.
A final point to remember about Class-AB amplifiers (either SE or BTL) is how to manipulate the terms in the
efficiency equation to utmost advantage when possible. Note that in equation 8, VDD is in the denominator. This
indicates that as VDD goes down, efficiency goes up.
crest factor and thermal considerations
Class-AB 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 range, or headroom above the average power
output, to pass the loudest portions of the signal without distortion. In other words, music typically has a crest
factor between 12 dB and 15 dB. When determining the optimal ambient operating temperature, the internal
dissipated power at the average output power level must be used. From the TPA0242 data sheet, one can see
that when the TPA0242 is operating from a 5-V supply into a 3-Ω speaker that 4 W peaks are available.
Converting watts to dB:
PdB
+
10Log PW
Pref
+
10Log 4W
1W
+
6dB (9)
Subtracting the headroom restriction to obtain the average listening level without distortion yields:
6 dB – 15 dB = –9 dB (15 dB crest factor)
6 dB – 12 dB = –6 dB (12 dB crest factor)
6 dB – 9 dB = –3 dB (9 dB crest factor)
6 dB – 6 dB = 0 dB (6 dB crest factor)
6 dB – 3 dB = 3 dB (3 dB crest factor)
Converting dB back into watts:
PW
+
10PdB
ń
10
Pref
+
63 mW (18 dB crest factor)
+
125 mW (15 dB crest factor)
+
250 mW (9 dB crest factor)
+
500 mW (6 dB crest factor)
+
1000 mW (3 dB crest factor)
(10)
+
2000 mW (15 dB crest factor)
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
25
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
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 2 W of continuous power output with a 3 dB crest
factor, 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, 3-Ω system, the internal dissipation in the TPA0242 and
maximum ambient temperatures is shown in Table 4.
Table 4. TPA0242 Power Rating, 5-V, 3-Ω, Stereo
PEAK OUTPUT POWER
(W) AVERAGE OUTPUT POWER POWER DISSIPATION
(W/Channel) MAXIMUM AMBIENT
TEMPERATURE
42 W (3 dB) 1.7 –3°C
41000 mW (6 dB) 1.6 6°C
4500 mW (9 dB) 1.4 24°C
4250 mW (12 dB) 1.1 51°C
4125 mW (15 dB) 0.8 78°C
463 mW (18 dB) 0.6 96°C
Table 5. TPA0242 Power Rating, 5-V, 8-Ω, Stereo
PEAK OUTPUT POWER AVERAGE OUTPUT POWER POWER DISSIPATION
(W/Channel) MAXIMUM AMBIENT
TEMPERATURE
2.5 W 1250 mW (3 dB crest factor) 0.55 100°C
2.5 W 1000 mW (4 dB crest factor) 0.62 94°C
2.5 W 500 mW (7 dB crest factor) 0.59 97°C
2.5 W 250 mW (10 dB crest factor) 0.53 102°C
The maximum dissipated power , PDmax, is reached at a much lower output power level for an 8 Ω load than for
a 3 Ω load. As a result, this simple formula for calculating PDmax may be used for an 8 Ω application:
PDmax
+
2V2
DD
p
2RL
(11)
However, in the case of a 3 Ω load, the PDmax occurs at a point well above the normal operating power level.
The amplifier may therefore be operated at a higher ambient temperature than required by the PDmax formula
for a 3 Ω load.
The maximum ambient temperature depends on the heat sinking ability of the PCB system. The derating factor
for the PWP package is shown in the dissipation rating table (see page 4). Converting this to ΘJA:
ΘJA
+
1
Derating Factor
+
1
0.022
+
45°C
ń
W(12)
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
26 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
To calculate maximum ambient temperatures, first consider that the numbers from the dissipation graphs are
per channel so the dissipated heat needs to be doubled for two channel operation. Given ΘJA, the maximum
allowable junction temperature, and the total internal dissipation, the maximum ambient temperature can be
calculated with the following equation. The maximum recommended junction temperature for the TPA0242 is
150°C. The internal dissipation figures are taken from the Power Dissipation vs Output Power graphs.
TAMax
+
TJMax
*
ΘJA PD
+
150
*
45(0.6
2)
+
96°C(15 dB crest factor)
(13)
NOTE:
Internal dissipation of 0.6 W is estimated for a 2-W system with 15 dB crest factor per channel.
Tables 4 and 5 show that for some applications no airflow is required to keep junction temperatures in the
specified range. The TPA0242 is designed with thermal protection that turns the device off when the junction
temperature surpasses 150°C to prevent damage to the IC. Tables 4 and 5 were calculated for maximum
listening volume without distortion. When the output level is reduced the numbers in the table change
significantly. Also, using 8-Ω speakers dramatically increases the thermal performance by increasing amplifier
efficiency.
SE/BTL operation
The ability of the TP A0242 to easily switch between BTL and SE modes is one of its most important cost saving
features. This feature eliminates the requirement for an additional headphone amplifier in applications where
internal stereo speakers are driven in BTL mode but external headphone or speakers must be accommodated.
Internal to the TPA0242, two separate amplifiers drive OUT+ and OUT–. The SE/BTL input (terminal 15)
controls the operation of the follower amplifier that drives LOUT– and ROUT– (terminals 9 and 16). When
SE/BTL is held low, the amplifier is on and the TPA0242 is in the BTL mode. When SE/BTL is held high, the OUT–
amplifiers are in a high output impedance state, which configures the TPA0242 as an SE driver from LOUT+
and ROUT+ (terminals 4 and 21). IDD is reduced by approximately one-half in SE mode. Control of the SE/BTL
input can be from a logic-level CMOS source or, more typically, from a resistor divider network as shown in
Figure 36.
ROUT+ 21
R
MUX
RHPIN
RLINEIN
+
–
23
20
8 RIN
ROUT– 16
+
–1 kΩ
COUTR
330 µF
100 kΩ
SE/BTL 15
100 kΩ
VDD
Figure 36. TPA0242 Resistor Divider Network Circuit
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
27
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
Using a readily available 1/8-in. (3.5 mm) stereo headphone jack, the control switch is closed when no plug is
inserted. When closed the 100-kΩ/1-kΩ divider pulls the SE/BTL input low. When a plug is inserted, the 1-kΩ
resistor is disconnected and the SE/BTL input is pulled high. When the input goes high, the OUT– amplifier is
shut down causing the speaker to mute (virtually open-circuits the speaker). The OUT+ amplifier then drives
through the output capacitor (CO) into the headphone jack.
PC BEEP operation
The PC BEEP input allows a system beep to be sent directly from a computer through the amplifier to the
speakers with few external components. The input is activated automatically. When the PC BEEP input is active,
both of the LINEIN and HPIN inputs are deselected and both the left and right channels are driven in BTL mode
with the signal from PC BEEP. The gain from the PC BEEP input to the speakers is fixed at 0.3 V/V and is
independent of the volume setting. When the PC BEEP input is deselected, the amplifier will return to the
previous operating mode and volume setting. Furthermore, if the amplifier is in shutdown mode, activating PC
BEEP will take the device out of shutdown and output the PC BEEP signal, then return the amplifier to shutdown
mode.
When PCB ENABLE is held low , the amplifier will automatically switch to PC BEEP mode after detecting a valid
signal at the PC BEEP input. The preferred input signal is a square wave or pulse train with an amplitude of 1
Vpp or greater. T o be accurately detected, the signal must have a minimum of 1 Vpp amplitude, rise and fall times
of less than 0.1 µs and a minimum of 8 rising edges. When the signal is no longer detected, the amplifier will
return to its previous operating mode and volume setting.
If it is desired to ac-couple the PC BEEP input, the value of the coupling capacitor should be chosen to satisfy
the following equation:
CPCB
w
1
2
p
ƒPCB (100 k
W
)(14)
The PC BEEP input can also be dc-coupled to avoid using this coupling capacitor. The pin normally sits at midrail
when no signal is present.
shutdown modes
The TPA0242 employs a shutdown mode of operation designed to reduce supply current, IDD, to the absolute
minimum level during periods of nonuse for battery-power conservation. The SHUTDOWN input terminal
should be held high during normal operation when the amplifier is in use. Pulling SHUTDOWN low causes the
outputs to mute and the amplifier to enter a low-current state, IDD = 150 µA. SHUTDOWN should never be left
unconnected because amplifier operation would be unpredictable.
Table 6. HP/LINE, SE/BTL, and Shutdown Functions
INPUTS†AMPLIFIER STATE
HP/LINE SE/BTL SHUTDOWN INPUT OUTPUT
X X Low X Mute
Low Low High Line BTL
Low High High Line SE
High Low High HP BTL
High High High HP SE
†Inputs should never be left unconnected.
X = do not care
TPA0242
STEREO 2-W AUDIO POWER AMPLIFIER
WITH DC VOLUME CONTROL AND MUX CONTROL
SLOS287 – NOVEMBER 1999
28 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
MECHANICAL DATA
PWP (R-PDSO-G**) PowerPAD PLASTIC SMALL-OUTLINE PACKAGE
4073225/E 03/97
0,50
0,75
0,25
0,15 NOM
Thermal Pad
(See Note D)
Gage Plane
2824
7,70
7,90
20
6,40
6,60
9,60
9,80
6,60
6,20
11
0,19
4,50
4,30
10
0,15
20
A
1
0,30
1,20 MAX
1614
5,10
4,90
PINS **
4,90
5,10
DIM
A MIN
A MAX
0,05
Seating Plane
0,65
0,10
M
0,10
0°–8°
20-PIN SHOWN
NOTES: A. All linear dimensions are in millimeters.
B. This drawing is subject to change without notice.
C. Body dimensions do not include mold flash or protrusions.
D. The package thermal performance may be enhanced by bonding the thermal pad to an external thermal plane. This pad is electrically
and thermally connected to the backside of the die and terminals 1, 12, 13, and 24. The dimensions of the thermal pad are
2.40 mm × 4.70 mm (maximum). The pad is centered on the bottom of the package.
E. Falls within JEDEC MO-153
PowerPAD is a trademark of Texas Instruments Incorporated.
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