NSC LM4870M Datasheet
LM4870
1.1W Audio Power Amplifier with Shutdown Mode
LM4870 1.1W Audio Power Amplifier with Shutdown Mode
October 1997
General Description
The LM4870 is a bridge-connected audio power amplifier capable of delivering 1.1W of continuous average power to an
8Ω load with less than 0.5%THD+N over the audio spectrum
from a 5V power supply.
Boomer audio power amplifiers were designed specifically to
provide high quality output power with a minimal number of
external components. Since the LM4870 does not require
output coupling capacitors, bootstrap capacitors or snubber
networks, it is optimally suited for low-power portable systems.
The LM4870 features an externally controlled, low-power
consumption shutdown mode, as well as an internal thermal
shutdown protection mechanism. It also includes two headphone control inputs and a headphone sense output for external monitoring. The LM4870 is unity-gain stable and the
gain is set using external resistors.
Key Specifications
n THD+N at 1W into 8Ω 0.5%(max)
n Output power into 8Ω at 1kHz
at 10%THD+N
n Shutdown Current 0.6µA (typ)
Features
n No output coupling capacitors, bootstrap capacitors, or
snubber circuits are necessary
n Small Outline (SOIC) power packaging
n Unity-gain stable
n External gain configuration capability
Applications
n Personal computers
n Desktop computers
n Low voltage audio system
Typical Application Connection Diagram
Small Outline Package
1.5W (typ)
DS100094-2
Top View
Order Number LM4870M
See NS Package Number M16A
DS100094-1
FIGURE 1. Typical Audio Amplifier Application Circuit
Boomer®is a registered trademark of National Semiconductor Corporation.
© 1999 National Semiconductor Corporation DS100094 www.national.com
Absolute Maximum Ratings (Note 2)
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 −65˚C to +150˚C
Input Voltage −0.3V to V
Power Dissipation Internally limited
ESD Susceptibility (Note 4) 3000V
ESD Susceptibility (Note 5) 250V
Junction Temperature 150˚C
Soldering Information
Small Outline Package
Vapor Phase (60 sec.) 215˚C
DD
+ 0.3V
Infrared (15 sec.) 220˚C
Thermal Resistance
(typ) 35˚C/W
φ
JC
(typ) 100˚C/W
φ
JA
See AN-450
“Surface Mounting and their Effects on Product
Reliability” for other methods of soldering surface mount devices.
Operating Ratings
Temperature Range
≤ TA≤ T
T
MIN
MAX
Supply Voltage 2.0V ≤ V
−20˚C ≤ TA≤ +85˚C
≤ 5.5V
DD
Electrical Characteristics
(Notes 1, 2) The following specifications apply for V
=
DD
Symbol Parameter Conditions LM4870 Units
V
I
DD
I
SD
V
P
THD+N Total Harmonic Distortion + Noise P
PSRR Power Supply Rejection Ratio V
V
V
V
V
V
Supply Voltage 2.0 V (min)
DD
Quiescent Power Supply Current V
Shutdown Current V
Output Offset Voltage V
OS
Output Power THD+N=0.5%(max); f=1 kHz 1.1 1.0 W (min)
O
Output Dropout Voltage V
od
HP-IN High Input Voltage HP-SENSE=0V to 4V 2.5 V
IH
HP-IN Low Input Voltage HP-SENSE=4V to 0V 2.5 V
IL
HP-SENSE High Output Voltage I
OH
HP-SENSE Low Output Voltage I
OL
Note 1: All voltages are measured with respect to the ground pins, unless otherwise specified.
Note 2: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for which the device is func-
tional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which 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 3: The maximum power dissipation must be derated at elevated temperatures and is dictated by T
allowable power dissipation is P
+150˚C, and the typical junction-to-ambient thermal resistance, when board mounted, is 100˚C/W.
Note 4: Human body model, 100 pF discharged through a 1.5 kΩ resistor.
Note 5: Machine Model, 200 pF–240 pF discharged through all pins.
Note 6: Typicals are measured at 25˚C and represent the parametric norm.
Note 7: Limits are guaranteed to National’s AOQL (Average Outgoing Quality Level).
DMAX
=
(T
)/θJAor the number given in the Absolute Maximum Ratings, whichever is lower. For the LM4870, T
JMAX−TA
=
O
pin2
=
IN
=
O
=
DD
=
IN
=
500 µA 2.8 2.5 V (min)
O
=
−500 µA 0.2 0.8 V (max)
O
5V, R
=
8Ω unless otherwise specified. Limits apply for T
L
Typical Limit
=
A
(Limits)
25˚C.
(Note 6) (Note 7)
5.5 V (max)
=
0V, I
0A 7.0 15.0 mA (max)
O
=
V
DD
0.4 µA
0V 10 50.0 mV (max)
1 Wrms; 20 Hz ≤ f ≤ 20 kHz 0.25
%
4.9V to 5.1V 60 dB
0V to 5V 0.6 1.0 V (max)
, θJA, and the ambient temperature TA. The maximum
JMAX
JMAX
=
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External Components Description (
Figure 1
)
Components Functional Description
1. R
2. C
3. R
4. C
5. C
i
i
f
S
B
Inverting input resistance which sets the closed-loop gain in conjunction with Rf. This resistor also
forms a high pass filter with C
at f
1/(2π R
i
C
iCi
).
=
Input coupling capacitor which blocks DC voltage at the amplifier’s input terminals. Also creates a
highpass filter with R
at f
1/(2π R
i
C
iCi
).
=
Feedback resistance which sets closed-loop gain in conjunction with Ri.
Supply bypass capacitor which provides power supply filtering. Refer to the Application Information
section for proper placement and selection of supply bypass capacitor.
Bypass pin capacitor which provides half supply filtering. Refer to Application Information section for
proper placement and selection of bypass capacitor.
Typical Performance Characteristics
THD+N vs Frequency
THD+N vs Output Power
Supply Current vs
Supply Voltage
DS100094-9
DS100094-12
THD+N vs Frequency
THD+N vs Output Power
Power Derating Curve
DS100094-10
DS100094-13
THD+N vs Frequency
DS100094-11
THD+N vs Output Power
DS100094-14
LM4870 Noise Floor
vs Frequency
DS100094-16
DS100094-17
DS100094-18
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