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LM4874
2.1W Differential Input, BTL Output Stereo Audio
Amplifier with Selectable Gain and Shutdown
General Description
The LM4874 features differential stereo inputs, BTL (bridge-
tied load) outputs, and four externally selectable fixed gains.
Operating on a single 5V supply, the LM4874 delivers 1.2W,
1.9W, or 2.1W (typ) of output power to an 8
, 4, or 3 BTL
load (Note 1), respectively, with less than 1% THD+N. The
LM4874's gain is selected using two digital inputs. The nomi-
nal gain values are 6dB, 10dB, 15.6dB, and 21.6dB.
The LM4874 is designed for notebook and other handheld
portable applications. It delivers high quality output power
from a surface-mount package and requires few external
components.
Other features include an active-low micropower shutdown
mode input and thermal shutdown protection.
Key Specifications
j
BTL output power
R
L
= 3
, V
DD
= 5.0V, and THD+N = 1%
2.1W (typ)
j
BTL output power
R
L
= 4
, V
DD
= 5.0V, and THD+N = 1%
1.9W (typ)
j
BTL output power
R
L
= 8
, V
DD
= 5.0V, and THD+N = 1%
1.2W (typ)
j
Micropower shutdown current
0.1A (typ)
j
PSRR (
@
1kHz, V
DD
= 5V, (Fig.1))
62dB (typ)
Features
n
Fully differential input and output
n
Internal gain set: 6dB, 10dB, 15.6dB, and 21.6dB
n
Improved 'click and pop' suppression
n
Thermal shutdown protection circuit
n
Ultra low current micropower shutdown mode
n
3.0V to 5.5V operation
n
Available in space-saving exposed-DAP TSSOP
package
Applications
n
Notebook computers
n
PDAs
n
Portable electronic devices
Connection Diagram
Top View
20046902
Order Number LM4874MH
See NS Package Number MXA20A for Exposed-DAP TSSOP
Boomer
is a registered trademark of National Semiconductor Corporation.
August 2002
LM4874
Boomer
2.1W
Differential
Input,
BTL
Output
Stereo
Audio
Amplifier
with
Selectable
Gain
and
Shutdown
2002 National Semiconductor Corporation
DS200469
www.national.com
Typical Application
20046901
FIGURE 1. Typical Audio Amplifier Application Circuit
LM4874
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2
Absolute Maximum Ratings
(Notes 2,
3)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage
6.0V
Storage Temperature
-65C to + 150C
Input Voltage
-0.3V to V
DD
+ 0.3V
Power Dissipation (Note 4)
Internally Limited
ESD Susceptibility (Note 5)
2000V
ESD Susceptibility (Note 6)
200V
Junction Temperature
150C
Soldering Information
Small Outline Package
Vapor Phase (60 sec.)
215C
Infrared (15 sec.)
220C
See AN-450 "Surface Mounting and their Effects on
Product Reliability" for other methods of soldering surface
mount devices.
Thermal Resistance
JC
(typ) MXA20A
2C/W
JA
(typ) MXA20A
41C/W (Note 7)
Operating Ratings
Temperature Range
T
MIN
T
A
T
MAX
-40C
TA 85C
Supply Voltage
3.0 V
V
DD
5.5V
Electrical Characteristics for LM4874
(Notes 2, 8)
The following specifications applies to the LM4874 when used in the circuit shown in Figure 1 and operating with V
DD
= 5V and
A
V
= 6dB, unless otherwise specified. Limits apply for T
A
= 25C.
Symbol
Parameter
Conditions
LM4874
Units
(Limits)
Typical
(Note 8)
Limit
(Notes 9,
10)
V
DD
Supply Voltage
3.0
5.5
V (min)
V (max)
I
DD
Quiescent Power Supply Current
V
IN
= 0V, I
O
= 0A, R
L
=
9.0
12.0
mA (max)
I
SD
Shutdown Current
V
shutdown
= GND
0.1
1.0
A (max)
V
OS
Output Offset Voltage
7
50
mV (max)
PSRR
Output Supply Rejection Ratio
V
DD
= 5V, V
RIPPLE
= 200mV
P-P
sinewave, C
BYPASS
= 0.47F,
R
L
= 8
62
dB
P
O
Output Power (Note 11)
THD+N = 1% (max), f = 1kHz (Note12)
R
L
= 3
R
L
= 4
R
L
= 8
2.1
1.9
1.2
1.0
W
W
W (min)
THD+N = 10% (max), f = 1kHz
(Note12)
R
L
= 3
R
L
= 4
R
L
= 8
2.6
2.6
1.5
W
W
W
THD+N
Total Harmonic Distortion + Noise
20Hz
f 20kHz
R
L
= 4
, P
O
= 2W
R
L
= 8
, P
O
= 1W
0.3
0.3
%
%
S/N
Signal-to-Noise Ratio
f = 1kHz, C
BYPASS
= 0.47F,
P
O
= 1.1W, R
L
= 8
97
dB
R
IN
Input Resistance
Pins 5, 7, 9, and 17
See Table 1.
Note 1: An LM4874MH that has been properly mounted to a circuit board with a copper heatsink area of at least 2in
2
will deliver 1.9W into 4
or 2.1W into 3.
Note 2: All voltages are measured with respect to the GND pin unless other wise specified.
Note 3: 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 guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions that
guarantee specific performance limits. This assumes that the device is within the Operating Ratings. Specifications are not guaranteed for parameters where no limit
is given, however, the typical value is a good indication of device performance.
Note 4: The maximum power dissipation must be derated at elevated temperatures and is dictated by TJMAX,
JA
, and the ambient temperature, T
A
. The maximum
allowable power dissipation is P
DMAX
= (T
JMAX
- T
A
/
JA
or the number given in Absolute Maximum Ratings, whichever is lower. For the LM4874, see power derating
currents for more information.
Note 5: Human body model, 100 pF discharged through a 1.5 k
resistor.
LM4874
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3
Electrical Characteristics for LM4874
(Notes 2, 8) (Continued)
Note 6: Machine Model, 220pF-240pF discharged through all pins.
Note 7: The given
JA
is for an LM4874 packaged in an MXA20A with the exposed-DAP soldered to an exposed 2in
2
area of 1oz printed circuit board copper. When
driving 4
loads from a 5V supply, the LM4874MH must be mounted to the circuit board and its exposed-DAP soldered to an exposed 2in
2
area of 1oz PCB copper.
Note 8: Typicals are measured at 25C and represent the parametric norm.
Note 9: Limits are guaranteed to National's AOQL (Average Outgoing Quality Level).
Note 10: Datasheet minimum and maximum specification limits are guaranteed by design, test, or statistical analysis.
Note 11: Output power is measured at the amplifier's package pins.
Note 12: When driving 3
or 4 loads and operating on a 5V supply, the LM4874MH must be mounted to a circuit board that has a minimum of 2in
2
of exposed,
uninterrupted copper area connected to the MH package's exposed DAP.
External Components Description
See Figure 1.
Components
Functional Description
1.
C
i
The input coupling capacitor blocks DC voltage at the amplifier's inverting input terminals. C
i
, along with the
LM4874's variable input resistance R
1
(See Table 1), creates a highpass filter with f
C
= 1/(2
R
i
C
i
). Both
inverting and noninverting inputs require a C
i
. Refer to the Application Information section, SELECTING
EXTERNAL COMPONENTS, for an explanation of determining the value of C
i
.
2.
C
S
The supply bypass capacitor. Refer to the POWER SUPPLY BYPASSING section for information about
properly placing, and selecting the value of, this capacitor.
3.
C
B
The capacitor, C
B
, filters the half-supply voltage present on the BYPASS pin. Refer to the Application
Information section, SELECTING EXTERNAL COMPONENTS, for information concerning proper placement
and selecting C
B
's value.
Typical Performance Characteristics
MH Specific Characteristics
THD vs Frequency
THD vs Frequency
20046998
V
DD
= 5V, R
L
= 4
, P
OUT
= 1000mW,
at (from top to bottom at 1kHz):
A
V
= 21.6dB, A
V
= 15.6dB,
A
V
= 10dB, A
V
= 6dB
20046997
V
DD
= 5V, R
L
= 8
, P
OUT
= 400mW,
at (from top to bottom at 1kHz):
A
V
= 21.6dB, A
V
= 15.6dB,
A
V
= 10dB, A
V
= 6dB
LM4874
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4
Typical Performance Characteristics
MH Specific Characteristics
(Continued)
THD vs Frequency
THD vs Frequency
20046999
V
DD
= 5V, R
L
= 8
, P
OUT
= 400mW,
at (from top to bottom at 1kHz):
A
V
= 21.6dB, A
V
= 15.6dB,
A
V
= 10dB, A
V
= 6dB
20046943
V
DD
= 5V, R
L
= 3
, f
IN
= 20Hz,
at (from top to bottom at 50mW):
A
V
= 21.6dB, A
V
= 15.6dB,
A
V
= 10dB, A
V
= 6dB
THD vs Frequency
THD vs Frequency
20046944
V
DD
= 5V, R
L
= 3
, f
IN
= 1kHz,
at (from top to bottom at 50mW):
A
V
= 21.6dB, A
V
= 15.6dB,
A
V
= 10dB, A
V
= 6dB
20046945
V
DD
= 5V, R
L
= 3
, f
IN
= 20kHz,
at (from top to bottom at 50mW):
A
V
= 21.6dB, A
V
= 15.6dB,
A
V
= 10dB, A
V
= 6dB
LM4874
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5
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