LM4951
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LM4951
Wide Voltage Range 1.8 Watt Audio Amplifier
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FEATURES
DESCRIPTION
•
The LM4951 is an audio power amplifier primarily
designed for demanding applications in Portable
Handheld devices. It is capable of delivering 1.8W
mono BTL to an 8Ω load, continuous average power,
with less than 1% distortion (THD+N) from a 7.5VDC
power supply.
1
2
•
•
•
•
•
Click and Pop Circuitry Eliminates Noise
during Turn-On and Turn-Off Transitions
Low Current, Active-Low Shutdown Mode
Low Quiescent Current
Thermal Shutdown Protection
Unity-Gain Stable
External Gain Configuration Capability
APPLICATIONS
•
•
•
Portable Handheld Devices up to 9V
Cell Phone
PDA
KEY SPECIFICATIONS
•
•
•
•
•
Wide Voltage Range: 2.7V to 9 V
Quiescent Power Supply Current (VDD =
7.5V): 2.5mA (typ)
Power Output BTL at 7.5V, 1% THD: 1.8 W (typ)
Shutdown Current: 0.01µA (typ)
Fast Turn on Time: 25ms (typ)
Boomer audio power amplifiers were designed
specifically to provide high quality output power with a
minimal amount of external components. The
LM4951 does not require bootstrap capacitors, or
snubber circuits.
The LM4951 features a low-power consumption
active-low shutdown mode. Additionally, the LM4951
features an internal thermal shutdown protection
mechanism.
The LM4951 contains advanced click and pop
circuitry that eliminates noises which would otherwise
occur during turn-on and turn-off transitions.
The LM4951 is unity-gain stable and can be
configured by external gain-setting resistors.
1
2
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.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004–2013, Texas Instruments Incorporated
LM4951
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Typical Application
Rf
VDD
Cs
1.0 PF
VDD
Ri
20k
Ci
0.39 PF
VIN
-
Vo-
AMPA
1k
Rc
CBYPASS
VIH
1.0 PF
+
CCHG
20k
Control
Bias
Bypass
8:
VIL
Shutdown
control
20k
Shutdown
+
AMPB
Vo+
GND
* RC is needed for over/under voltage protection. If inputs are less than VDD +0.3V and greater than –0.3V, and if
inputs are disabled when in shutdown mode, then RC may be shorted.
Figure 1. Typical Bridge-Tied-Load (BTL) Audio Amplifier Application Circuit
Connection Diagram
+
Bypass
1
10
VO
Shutdown
2
9
VDD
CCHG
3
8
NC
NC
4
7
GND
VIN
5
6
VO
-
Figure 2. DPR Package (Top View)
See Package Number DPR0010A
Vo VIN A
Cchg
GND B
VDD
GND
SHUTDOWN
BYPASS C
1
A.
2
Vo +
3
* DAP can either be soldered to GND or left floating.
Figure 3. 9 Bump DSBGA Package (Top View)
See Package Number YZR0009AAA
2
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings (1) (2) (3)
Supply Voltage
9.5V
−65°C to +150°C
Storage Temperature
−0.3V to VDD + 0.3V
Input Voltage
(4)
Internally limited
ESD Susceptibility (5)
2000V
ESD Susceptibility (6)
200V
Power Dissipation
Junction Temperature
150°C
Thermal Resistance θJA (WSON) (4)
52°C/W
See AN-1187 'Leadless Leadframe Packaging (WSON)' (Literature Number
SNOA401)
(1)
(2)
(3)
(4)
(5)
(6)
All voltages are measured with respect to the GND pin, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not specified for parameters where no limit is given, however, the typical value is a good indication
of device performance.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX, θJA, and the ambient temperature,
TA. The maximum allowable power dissipation is P DMAX = (TJMAX − TA) / θJA or the given in Absolute Maximum Ratings, whichever is
lower. For the LM4951 typical application (shown in Figure 1) with VDD = 7.5V, RL = 8Ω mono-BTL operation the max power dissipation
is 1.42W. θJA = 73°C/W.
Human body model, 100pF discharged through a 1.5kΩ resistor.
Machine Model, 220pF–240pF discharged through all pins.
Operating Ratings
Temperature Range
TMIN ≤ TA ≤ TMAX
−40°C ≤ T A ≤ +85°C
2.7V ≤ VDD ≤ 9V
Supply Voltage
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Electrical Characteristics VDD = 7.5V (1) (2)
The following specifications apply for VDD = 7.5V, AV-BTL = 6dB, RL = 8Ω unless otherwise specified. Limits apply for TA =
25°C.
Symbol
Parameter
Conditions
LM4951
Typical (3)
Limit (4) (5)
Units
(Limits)
IDD
Quiescent Power Supply Current
VIN = 0V, IO = 0A,RL = 8Ω
2.5
4.5
ISD
Shutdown Current
VSHUTDOWN = GND (6)
0.01
5
mA (max)
µA (max)
VOS
Offset Voltage
5
30
mV (max)
VSDIH
Shutdown Voltage Input High
1.2
V (min)
VSDIL
Shutdown Voltage Input Low
Rpulldown
Pulldown Resistor on S/D
TWU
Wake-up Time
CB = 1.0µF
Tsd
Shutdown time
CB = 1.0µF
0.4
V (max)
75
45
kΩ (min)
25
35
ms
10
ms (max)
170
150
190
°C (min)
°C (max)
TSD
Thermal Shutdown Temperature
PO
Output Power
THD = 1% (max); f = 1kHz
RL = 8Ω Mono BTL
1.8
1.5
W (min)
THD+N
Total Harmomic Distortion + Noise
PO = 600mWrms; f = 1kHz
AV-BTL = 6dB
0.07
0.5
% (max)
THD+N
Total Harmomic Distortion + Noise
PO = 600mWrms; f = 1kHz
AV-BTL = 26dB
0.35
%
εOS
Output Noise
A-Weighted Filter, Ri = Rf = 20kΩ
Input Referred, Note 10
10
µV
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mVp-p, f = 217Hz,
CB = 1.0μF, Input Referred
66
(1)
(2)
(3)
(4)
(5)
(6)
4
56
dB (min)
All voltages are measured with respect to the GND pin, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not specified for parameters where no limit is given, however, the typical value is a good indication
of device performance.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to GND for
minimum shutdown current.
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Electrical Characteristics VDD = 3.3V (1) (2)
The following specifications apply for VDD = 3.3V, AV-BTL = 6dB, RL = 8Ω unless otherwise specified. Limits apply for TA =
25°C.
Symbol
Parameter
Conditions
LM4951
Typical (3)
Limit (4) (5)
Units
(Limits)
IDD
Quiescent Power Supply Current
VIN = 0V, IO = 0A,RL = 8Ω
2.5
4.5
ISD
Shutdown Current
VSHUTDOWN = GND (6)
0.01
2
µA (max)
VOS
Offset Voltage
3
30
mV (max)
VSDIH
Shutdown Voltage Input High
1.2
V (min)
VSDIL
Shutdown Voltage Input Low
TWU
Wake-up Time
CB = 1.0µF
Tsd
Shutdown time
CB = 1.0µF
PO
Output Power
THD = 1% (max); f = 1kHz
RL = 8Ω Mono BTL
THD+N
Total Harmomic Distortion + Noise1
THD+N
0.4
25
mA (max)
V (max)
ms (max)
10
ms (max)
280
230
mW (min)
PO = 100mWrms; f = 1kHz
AV-BTL = 6dB
0.07
0.5
% (max)
Total Harmomic Distortion + Noise1
PO = 100mWrms; f = 1kHz
AV-BTL = 26dB
0.35
%
εOS
Output Noise
A-Weighted Filter, Ri = Rf = 20kΩ
Input Referred, Note 10
10
µV
PSRR
Power Supply Rejection Ratio
VRIPPLE = 200mVp-p, f = 217Hz,
CB = 1μF, Input Referred
71
(1)
(2)
(3)
(4)
(5)
(6)
61
dB (min)
All voltages are measured with respect to the GND pin, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. Electrical Characteristics state DC and AC electrical
specifications under particular test conditions which ensure specific performance limits. This assumes that the device is within the
Operating Ratings. Specifications are not specified for parameters where no limit is given, however, the typical value is a good indication
of device performance.
Typicals are measured at 25°C and represent the parametric norm.
Limits are specified to AOQL (Average Outgoing Quality Level).
Datasheet min/max specification limits are specified by design, test, or statistical analysis.
Shutdown current is measured in a normal room environment. The Shutdown pin should be driven as close as possible to GND for
minimum shutdown current.
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Typical Performance Characteristics
10
THD+N vs Frequency
VDD = 3.3V, PO = 100mW, AV = 6dB
10
THD+N vs Frequency
VDD = 3.3V, PO = 100mW, AV = 26dB
5
2
1
THD+N (%)
THD+N (%)
1
0.5
0.2
0.1
0.1
0.05
0.02
0.01
20
200
2k
0.01
20
20k
Figure 5.
THD+N vs Frequency
VDD = 5V, PO = 400mW, AV = 6dB
THD+N vs Frequency
VDD = 5V, PO = 400mW, AV = 26dB
10
5
5
2
2
1
1
0.5
0.2
0.5
0.2
0.1
0.1
0.05
0.05
0.02
0.02
0.01
20
50 100 200 500 1k 2k
0.01
20
5k 10k 20k
FREQUENCY (Hz)
10
5k 10k 20k
Figure 4.
THD+N (%)
THD+N (%)
10
50 100 200 500 1k 2k
FREQUENCY (Hz)
FREQUENCY (Hz)
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
Figure 6.
Figure 7.
THD+N vs Frequency
VDD = 7.5V, PO = 600mW, AV = 6dB
THD+N vs Frequency
VDD = 7.5V, PO = 600mW, AV = 26dB
10
5
5
2
THD+N (%)
THD+N (%)
1
0.5
0.2
0.1
2
1
0.5
0.05
0.2
0.02
0.01
20
0.1
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
200
2k
20k
FREQUENCY (Hz)
Figure 8.
6
20
Figure 9.
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Typical Performance Characteristics (continued)
10
THD+N vs Output Power
VDD = 3.3V, f = 1kHz, AV = 6dB
THD+N vs Output Power
VDD = 3.3V, f = 1kHz, AV = 26dB
10
1
THD+N (%)
THD+N (%)
5
0.1
2
1
0.5
0.2
0.01
30m
10m
0.1
10m
500m
100m
20m
OUTPUT POWER (W)
30m 50m 70m 100m
300m 500m
40m 60m 80m
200m 400m
OUTPUT POWER (W)
10
Figure 10.
Figure 11.
THD+N vs Output Power
VDD = 5V, f = 1kHz, AV = 6dB
THD+N vs Output Power
VDD = 5V, f = 1kHz, AV = 26dB
10
5
5
2
THD+N (%)
THD+N (%)
1
0.5
0.2
0.1
2
1
0.5
0.05
0.2
0.02
0.01
10m
20m
50m 100m 200m
500m
0.1
10m 20m
1
OUTPUT POWER (W)
10
50m 100m 200m
500m
1
OUTPUT POWER (W)
Figure 12.
Figure 13.
THD+N vs Output Power
VDD = 7.5V, f = 1kHz, AV = 6dB
THD+N vs Output Power
VDD = 7.5V, f = 1kHz, AV = 26dB
10
5
5
1
THD+N (%)
THD+N (%)
2
0.5
0.2
0.1
2
1
0.5
0.05
0.2
0.02
0.01
10m 20m 50m 100m 200m 500m 1
2 3
0.1
10m 20m 50m 100m 200m 500m 1
2 3
OUTPUT POWER (W)
OUTPUT POWER (W)
Figure 14.
Figure 15.
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Typical Performance Characteristics (continued)
Power Supply Rejection vs Frequency
VDD = 3.3V, AV = 6dB, VRIPPLE = 200mVP-P
Input Terminated into 10Ω
Power Supply Rejection vs Frequency
VDD = 3.3V, AV = 26dB, VRIPPLE = 200mVP-P
Input Terminated into 10Ω
+0
-10
-20
PSRR (dB)
PSRR (dB)
-30
-40
-50
-60
-70
-80
-90
-100
20
50 100 200 500 1k 2k
+0
-2.5
-5
-7.5
-10
-12.5
-15
-17.5
-20
-22.5
-25
-27.5
-30
-32.5
-35
-37.5
-40
-42.5
-45
-47.5
-50
-52.5
-55
-57.5
-60
20
5k 10k 20k
Figure 16.
Figure 17.
Power Supply Rejection vs Frequency
VDD = 5V, AV = 6dB, VRIPPLE = 200mVP-P
Input Terminated into 10Ω
Power Supply Rejection vs Frequency
VDD = 5V, AV = 26dB, VRIPPLE = 200mVP-P
Input Terminated into 10Ω
+0
-10
-20
PSRR (dB)
PSRR (dB)
-30
-40
-50
-60
-70
-80
-90
-100
20
50 100 200 500 1k 2k
+0
-2.5
-5
-7.5
-10
-12.5
-15
-17.5
-20
-22.5
-25
-27.5
-30
-32.5
-35
-37.5
-40
-42.5
-45
-47.5
-50
-52.5
-55
-57.5
-60
20
5k 10k 20k
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 18.
Figure 19.
Power Supply Rejection vs Frequency
VDD = 7.5V, AV = 6dB, VRIPPLE = 200mVP-P
Input Terminated into 10Ω
Power Supply Rejection vs Frequency
VDD = 7.5V, AV = 26dB, VRIPPLE = 200mVP-P
Input Terminated into 10Ω
+0
-10
-20
PSRR (dB)
-30
PSRR (dB)
5k 10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
-40
-50
-60
-70
-80
-90
-100
20
50 100 200 500 1k 2k
5k 10k 20k
+0
-2.5
-5
-7.5
-10
-12.5
-15
-17.5
-20
-22.5
-25
-27.5
-30
-32.5
-35
-37.5
-40
-42.5
-45
-47.5
-50
-52.5
-55
-57.5
-60
20
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 20.
8
50 100 200 500 1k 2k
Figure 21.
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Typical Performance Characteristics (continued)
Noise Floor
VDD = 3.3V, AV = 6dB, Ri = Rf = 20kΩ
BW < 80kHz, A-weighted
Noise Floor
VDD = 3V, AV = 26dB, Ri = 20kΩ, Rf = 200kΩ
BW < 80kHz, A-weighted
30P
OUTPUT NOISE VOLTAGE (V)
OUTPUT NOISE VOLTAGE (V)
50P
40P
20P
10P
9P
8P
7P
6P
5P
4P
3P
2P
150P
120P
100P
95P
90P
85P
82P
75P
72P
65P
62P
55P
52P
50P
1P
20
50 100 200 500 1k 2k
20
5k 10k 20k
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 22.
Figure 23.
Noise Floor
VDD = 5V, AV = 6dB, Ri = Rf = 20kΩ
BW < 80kHz, A-weighted
Noise Floor
VDD = 5V, AV = 26dB, Ri = 20kΩ, Rf = 200kΩ
BW < 80kHz, A-weighted
30P
OUTPUT NOISE VOLTAGE (V)
OUTPUT NOISE VOLTAGE (V)
50P
40P
20P
10P
9P
8P
7P
6P
5P
4P
3P
2P
120P
100P
95P
90P
85P
82P
75P
72P
65P
62P
55P
52P
50P
1P
20
150P
50 100 200 500 1k 2k
20
5k 10k 20k
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 24.
Figure 25.
Noise Floor
VDD = 7.5V, AV = 6dB, Ri = Rf = 20kΩ
BW < 80kHz, A-weighted
Noise Floor
VDD = 7.5V, AV = 26dB, Ri = 20kΩ, Rf = 200kΩ
BW < 80kHz, A-weighted
30P
OUTPUT NOISE VOLTAGE (V)
OUTPUT NOISE VOLTAGE (V)
50P
40P
20P
10P
9P
8P
7P
6P
5P
4P
3P
2P
120P
100P
95P
90P
85P
82P
75P
72P
65P
62P
55P
52P
50P
1P
20
150P
50 100 200 500 1k 2k
5k 10k 20k
20
50 100 200 500 1k 2k
5k 10k 20k
FREQUENCY (Hz)
FREQUENCY (Hz)
Figure 26.
Figure 27.
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Typical Performance Characteristics (continued)
Power Dissipation vs Output Power
VDD = 3.3V, RL = 8Ω, f = 1kHz
Power Dissipation vs Output Power
VDD = 7.5V, RL = 8Ω, f = 1kHz
1600
300
POWER DISSIPATION (mW)
POWER DISSIPATION (mW)
1400
250
200
150
100
1200
1000
800
600
400
200
50
0
0
0
0
50
100
150
200
250
200
400
600
800 1000 1200 1400
OUTPUT POWER (mW)
300
OUTPUT POWER (mW)
Figure 28.
Figure .
Supply Current vs Supply Voltage
RL = 8Ω, VIN = 0V, Rsource = 50Ω
Clipping Voltage vs Supply Voltage
RL = 8Ω,
from top to bottom: Negative Voltage Swing; Positive
Voltage Swing
1.4
2.5
DROPOUT VOPLTAGE (V)
SUPPLY CURRENT (mA)
1.2
2
1.5
1
0.5
1
0.8
0.6
0.4
0.2
0
0
2
3
4
5
6
7
8
9
0
10
2
SUPPLY VOLTAGE (V)
6
8
10
Figure 30.
Output Power vs Supply Voltage
RL = 8Ω,
from top to bottom: THD+N = 10%, THD+N = 1%
Output Power vs Load Resistance
VDD = 3.3V, f = 1kHz
from top to bottom: THD+N = 10%, THD+N = 1%
4
450
3.5
400
OUTPUT POWER (mW)
OUTPUT POWER (mW)
Figure 29.
3
2.5
2
1.5
1
0.5
350
300
250
200
150
100
50
0
0
2.7 3 3.5 4 4.5 5 5.5 6 6.5 7 7.5 8 8.5 9
0
20
40
60
80
100
LOAD RESISTANCE (W)
SUPPLY VOLTAGE (V)
Figure 31.
10
4
SUPPLY VOLTAGE (V)
Figure 32.
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Typical Performance Characteristics (continued)
Output Power vs Load Resistance
VDD = 7.5V, f = 1kHz
from top to bottom: THD+N = 10%, THD+N = 1%
Frequency Response vs Input Capacitor Size
RL = 8Ω
from top to bottom: Ci = 1.0µF, Ci = 0.39µF, Ci = 0.039µF
3000
20
2500
12
OUTPUT LEVEL (dB)
OUTPUT POWER (mW)
16
2000
1500
1000
8
4
0
-4
-8
-12
-16
-20
500
-24
-28
0
8
16
32
48
64
80
20
96 112
LOAD RESISTANCE (W)
50 100 200 500
1k 2k
5k 10k 20k
FREQUENCY (Hz)
Figure 33.
Figure 34.
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APPLICATION INFORMATION
HIGH VOLTAGE BOOMER
Unlike previous 5V Boomer amplifiers, the LM4951 is designed to operate over a power supply voltages range of
2.7V to 9V. Operating on a 7.5V power supply, the LM4951 will deliver 1.8W into an 8Ω BTL load with no more
than 1% THD+N.
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4951 consists of two operational amplifiers that drive a speaker connected between
their outputs. The value of input and feedback resistors determine the gain of each amplifier. External resistors Ri
and Rf set the closed-loop gain of AMPA, whereas two 20kΩ internal resistors set AMPB's gain to -1. The
LM4951 drives a load, such as a speaker, connected between the two amplifier outputs, VO+ and VO -. Figure 1
shows that AMPA's output serves as AMPB's input. This results in both amplifiers producing signals identical in
magnitude, but 180° out of phase. Taking advantage of this phase difference, a load is placed between AMPA
and AMPB and driven differentially (commonly referred to as "bridge mode"). This results in a differential, or BTL,
gain of
AVD = 2(Rf/ Ri)
(1)
Bridge mode amplifiers are different from single-ended amplifiers that drive loads connected between a single
amplifier's output and ground. For a given supply voltage, bridge mode has a distinct advantage over the singleended configuration: its differential output doubles the voltage swing across the load. Theoretically, this produces
four times the output power when compared to a single-ended amplifier under the same conditions. This increase
in attainable output power assumes that the amplifier is not current limited and that the output signal is not
clipped. To ensure minimum output signal clipping when choosing an amplifier's closed-loop gain, refer to the
AUDIO POWER AMPLIFIER DESIGN section. Under rare conditions, with unique combinations of high power
supply voltage and high closed loop gain settings, the LM4951 may exhibit low frequency oscillations.
Another advantage of the differential bridge output is no net DC voltage across the load. This is accomplished by
biasing AMP1's and AMP2's outputs at half-supply. This eliminates the coupling capacitor that single supply,
single-ended amplifiers require. Eliminating an output coupling capacitor in a typical single-ended configuration
forces a single-supply amplifier's half-supply bias voltage across the load. This increases internal IC power
dissipation and may permanently damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a successful bridged amplifier.
The LM4951's dissipation when driving a BTL load is given by Equation (2). For a 7.5V supply and a single 8Ω
BTL load, the dissipation is 1.42W.
PDMAX-MONOBTL = 4(VDD) 2/ 2π2RL: Bridge Mode
(2)
The maximum power dissipation point given by Equation (2) must not exceed the power dissipation given by
Equation (3):
PDMAX' = (TJMAX - TA) / θJA
(3)
The LM4951's TJMAX = 150°C. In the DPR package, the LM4951's θJA is 73°C/W when the metal tab is soldered
to a copper plane of at least 1in2. This plane can be split between the top and bottom layers of a two-sided PCB.
Connect the two layers together under the tab with an array of vias. At any given ambient temperature TA, use
Equation (3) to find the maximum internal power dissipation supported by the IC packaging. Rearranging
Equation (3) and substituting PDMAX for PDMAX' results in Equation (4). This equation gives the maximum ambient
temperature that still allows maximum stereo power dissipation without violating the LM4951's maximum junction
temperature.
TA = TJMAX - PDMAX-MONOBTLθJA
(4)
For a typical application with a 7.5V power supply and a BTL 8Ω load, the maximum ambient temperature that
allows maximum stereo power dissipation without exceeding the maximum junction temperature is approximately
46°C for the TS package.
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TJMAX = PDMAX-MONOBTLθJA + TA
(5)
Equation (5) gives the maximum junction temperature TJMAX. If the result violates the LM4951's 150°C, reduce
the maximum junction temperature by reducing the power supply voltage or increasing the load resistance.
Further allowance should be made for increased ambient temperatures.
The above examples assume that a device is operating around the maximum power dissipation point. Since
internal power dissipation is a function of output power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If the result of Equation 2 is greater than that of Equation (3), then decrease the supply voltage, increase the
load impedance, or reduce the ambient temperature. Further, ensure that speakers rated at a nominal 8Ω do not
fall below 6Ω. If these measures are insufficient, a heat sink can be added to reduce θJA. The heat sink can be
created using additional copper area around the package, with connections to the ground pins, supply pin and
amplifier output pins. Refer to the Typical Performance Characteristics curves for power dissipation information at
lower output power levels.
POWER SUPPLY VOLTAGE LIMITS
Continuous proper operation is ensured by never exceeding the voltage applied to any pin, with respect to
ground, as listed in the Absolute Maximum Ratings section.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is critical for low noise performance and high power supply
rejection. Applications that employ a voltage regulator typically use a 10µF in parallel with a 0.1µF filter
capacitors to stabilize the regulator's output, reduce noise on the supply line, and improve the supply's transient
response. However, their presence does not eliminate the need for a local 1.0µF tantalum bypass capacitance
connected between the LM4951's supply pins and ground. Do not substitute a ceramic capacitor for the
tantalum. Doing so may cause oscillation. Keep the length of leads and traces that connect capacitors between
the LM4951's power supply pin and ground as short as possible. Connecting a larger capacitor, CBYPASS,
between the BYPASS pin and ground improves the internal bias voltage's stability and improves the amplifier's
PSRR. The PSRR improvements increase as the bypass pin capacitor value increases. Too large, however,
increases turn-on time and can compromise the amplifier's click and pop performance. The selection of bypass
capacitor values, especially CBYPASS, depends on desired PSRR requirements, click and pop performance (as
explained in the section, SELECTING EXTERNAL COMPONENTS), system cost, and size constraints.
MICRO-POWER SHUTDOWN
The LM4951 features an active-low micro-power shutdown mode. When active, the LM4951's micro-power
shutdown feature turns off the amplifier's bias circuitry, reducing the supply current. The low 0.01µA typical
shutdown current is achieved by applying a voltage to the SHUTDOWN pin that is as near to GND as possible. A
voltage that is greater than GND may increase the shutdown current.
There are a few methods to control the micro-power shutdown. These include using a single-pole, single-throw
switch (SPST), a microprocessor, or a microcontroller. When using a switch, connect the SPST switch between
the shutdown pin and VDD. Select normal amplifier operation by closing the switch. Opening the switch applies
GND to the SHUTDOWN pin activating micro-power shutdwon.The switch and internal pull-down resistor
ensures that the SHUTDOWN pin will not float. This prevents unwanted state changes. In a system with a
microprocessor or a microcontroller, use a digital output to apply the active-state voltage to the SHUTDOWN pin.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Two quantities determine the value of the input coupling capacitor: the lowest audio frequency that requires
amplification and desired output transient suppression.
As shown in Figure 1, the input resistor (Ri) and the input capacitor (Ci) produce a high pass filter cutoff
frequency that is found using Equation 6.
fc = 1/2πRiCi
(6)
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As an example when using a speaker with a low frequency limit of 50Hz, Ci, using Equation (6) is 0.159µF. The
0.39µF CINA shown in Figure 1 allows the LM4951 to drive high efficiency, full range speaker whose response
extends below 30Hz.
Selecting Value For RC
The LM4951 is designed for very fast turn on time. The Cchg pin allows the input capacitors (CinA and CinB) to
charge quickly to improve click/pop performance. Rchg1 and Rchg2 protect the Cchg pins from any over/under
voltage conditions caused by excessive input signal or an active input signal when the device is in shutdown.
The recommended value for Rchg1 and Rchg2 is 1kΩ. If the input signal is less than VDD+0.3V and greater than
-0.3V, and if the input signal is disabled when in shutdown mode, Rchg1 and Rchg2 may be shorted out.
OPTIMIZING CLICK AND POP REDUCTION PERFORMANCE
The LM4951 contains circuitry that eliminates turn-on and shutdown transients ("clicks and pops"). For this
discussion, turn-on refers to either applying the power supply voltage or when the micro-power shutdown mode
is deactivated.
As the VDD/2 voltage present at the BYPASS pin ramps to its final value, the LM4951's internal amplifiers are
configured as unity gain buffers. An internal current source charges the capacitor connected between the
BYPASS pin and GND in a controlled manner. Ideally, the input and outputs track the voltage applied to the
BYPASS pin.
The gain of the internal amplifiers remains unity until the voltage on the bypass pin reaches VDD/2. As soon as
the voltage on the bypass pin is stable, there is a delay to prevent undesirable output transients (“click and
pops”). After this delay, the device becomes fully functional.
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1.8W into an 8Ω BTL
The following are the desired operational parameters:
Power Output
1.8WRMS
Load Impedance
8Ω
Input Level
0.3VRMS (max)
Input Impedance
20kΩ
Bandwidth
50Hz–20kHz ± 0.25dB
The design begins by specifying the minimum supply voltage necessary to obtain the specified output power.
One way to find the minimum supply voltage is to use the Equation (7) curve in the Typical Performance
Characteristics section. Another way, using Equation 7, is to calculate the peak output voltage necessary to
achieve the desired output power for a given load impedance. To account for the amplifier's dropout voltage, two
additional voltages, based on the Figure 30 in the Typical Performance Characteristics curves, must be added to
the result obtained by Equation (7). The result is Equation (8).
(7)
(8)
VDD = VOUTPEAK + VODTOP + VODBOT
The commonly used 7.5V supply voltage easily meets this. The additional voltage creates the benefit of
headroom, allowing the LM4951 to produce peak output power in excess of 1.8W without clipping or other
audible distortion. The choice of supply voltage must also not create a situation that violates of maximum power
dissipation as explained above in the POWER DISSIPATION section. After satisfying the LM4951's power
dissipation requirements, the minimum differential gain needed to achieve 1.8W dissipation in an 8Ω BTL load is
found using Equation (9).
(9)
Thus, a minimum gain of 12.6 allows the LM4951's to reach full output swing and maintain low noise and THD+N
performance. For this example, let AV-BTL = 13. The amplifier's overall BTL gain is set using the input (Ri) and
feedback (Rf) resistors of the first amplifier in the series BTL configuration. Additionaly, AV-BTL is twice the gain
set by the first amplifier's Ri and Rf. With the desired input impedance set at 20kΩ, the feedback resistor is found
using Equation (10).
14
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Rf/ Ri = AV-BTL/ 2
(10)
The value of Rf is 130kΩ (choose 191kΩ, the closest value). The nominal output power is 1.8W.
The last step in this design example is setting the amplifier's -3dB frequency bandwidth. To achieve the desired
±0.25dB pass band magnitude variation limit, the low frequency response must extend to at least one-fifth the
lower bandwidth limit and the high frequency response must extend to at least five times the upper bandwidth
limit. The gain variation for both response limits is 0.17dB, well within the ±0.25dB-desired limit. The results are
an
fL = 50Hz / 5 = 10Hz
(11)
and an
fL = 20kHz x 5 = 100kHz
(12)
As mentioned in the SELECTING EXTERNAL COMPONENTS section, Ri and Ci create a highpass filter that
sets the amplifier's lower bandpass frequency limit. Find the coupling capacitor's value using Equation (13).
Ci = 1 / 2πRifL
(13)
The result is
1 / (2πx20kΩx10Hz) = 0.795µF
(14)
Use a 0.82µF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in this example) and the differential gain AVD,
determines the upper passband response limit. With AVD = 7 and fH = 100kHz, the closed-loop gain bandwidth
product (GBWP) is 700kHz. This is less than the LM4951's 3.5MHz GBWP. With this margin, the amplifier can
be used in designs that require more differential gain while avoiding performance restricting bandwidth
limitations.
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figures 6-8 show the recommended two-layer PC board layout that is optimized for the DPR0010A. This circuit is
designed for use with an external 7.5V supply 8Ω (min) speakers.
These circuit boards are easy to use. Apply 7.5V and ground to the board's VDD and GND pads, respectively.
Connect a speaker between the board's OUTA and OUTB outputs.
Demonstration Board Layout
Figure 35. Recommended TS SE PCB Layout:
Top Silkscreen
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LM4951
SNAS244N – AUGUST 2004 – REVISED MAY 2013
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Figure 36. Recommended TS SE PCB Layout:
Top Layer
Figure 37. Recommended TS SE PCB Layout:
Bottom Layer
Revision History
16
Rev
Date
1.0
8/25/04
Initial WEB.
1.1
10/19/05
Added the DSBGA pkg, then WEB.
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Description
Copyright © 2004–2013, Texas Instruments Incorporated
Product Folder Links: LM4951
LM4951
www.ti.com
SNAS244N – AUGUST 2004 – REVISED MAY 2013
Rev
Date
Description
1.2
08/30/06
Added the Limit value (=35) on the Twu
(7.5V Elect Char table), then WEB.
1.3
09/11/06
Added the “Selecting Value For Rc, then
WEB.
1.4
05/21/07
Fixed a typo ( X3 value = 0.600±0.075)
instead of (X3 = 0.600±0.75).
1.5
03/18/09
Text edits.
N
05/03/13
Changed layout of National Data Sheet
to TI format.
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17
PACKAGE OPTION ADDENDUM
www.ti.com
14-Feb-2014
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
LM4951SD/NOPB
ACTIVE
WSON
DPR
10
1000
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
L4951SD
LM4951SDX/NOPB
ACTIVE
WSON
DPR
10
4500
Green (RoHS
& no Sb/Br)
CU SN
Level-1-260C-UNLIM
L4951SD
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
14-Feb-2014
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
11-Oct-2013
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM4951SD/NOPB
WSON
DPR
10
1000
178.0
12.4
4.3
4.3
1.3
8.0
12.0
Q1
LM4951SDX/NOPB
WSON
DPR
10
4500
330.0
12.4
4.3
4.3
1.3
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
11-Oct-2013
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM4951SD/NOPB
WSON
DPR
10
1000
210.0
185.0
35.0
LM4951SDX/NOPB
WSON
DPR
10
4500
367.0
367.0
35.0
Pack Materials-Page 2
MECHANICAL DATA
DPR0010A
SDC10A (Rev A)
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