LM4863N National Semiconductor, LM4863N Datasheet - Page 12

• Manufacturer Part Number: LM4863N
• Description: IC AMP AUDIO PWR 3.2W STER 16DIP
• Manufacturer: National Semiconductor
• Series: Boomer®r
• Type: Class ABr

Specifications of LM4863N

• Output Type: 2-Channel (Stereo) with Stereo Headphones
• Max Output Power X Channels @ Load: 3.2W x 2 @ 3 Ohm; 440mW x 2 @ 8 Ohm
• Voltage - Supply: 2 V ~ 5.5 V
• Features: Depop, Shutdown, Thermal Protection
• Mounting Type: Through Hole
• Package / Case: 16-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM4863N

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Application Information
* Refer to the section Proper Selection of External Components, for a detailed discussion of C
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4863 consists of two pairs of
operational amplifiers, forming a two-channel (channel A and
channel B) stereo amplifier. (Though the following discusses
channel A, it applies equally to channel B.) External resistors
R
internal 20kΩ resistors set Amp2A’s gain at -1. The LM4863
drives a load, such as a speaker, connected between the two
amplifier outputs, -OUTA and +OUTA.
Figure 1 shows that Amp1A’s output serves as Amp2A’s
input. This results in both amplifiers producing signals iden-
tical in magnitude, but 180˚ out of phase. Taking advantage
of this phase difference, a load is placed between -OUTA
and +OUTA and driven differentially (commonly referred to
as "bridge mode"). This results in a differential gain of
Bridge mode amplifiers are different from single-ended am-
plifiers that drive loads connected between a single amplifi-
er’s output and ground. For a given supply voltage, bridge
mode has a distinct advantage over the single-ended con-
figuration: its differential output doubles the voltage swing
across the load. This produces four times the output power
when compared to a single-ended amplifier under the same
conditions. This increase in attainable output power as-
sumes that the amplifier is not current limited or that the
output signal is not clipped. To ensure minimum output sig-
nal clipping when choosing an amplifier’s closed-loop gain,
refer to the Audio Power Amplifier Design section.
f
Pin out shown for the SO package. Refer to the Connection Diagrams for the pinout of the TSSOP, Exposed-DAP
and R
i
set the closed-loop gain of Amp1A, whereas two
A
VD
= 2 x (R
f
FIGURE 1. Typical Audio Amplifier Application Circuit
/ R
i
)
TSSOP, and Exposed-DAP LLP packages.
(Continued)
(1)
12
Another advantage of the differential bridge output is no net
DC voltage across the load. This is accomplished by biasing
channel A’s and channel B’s outputs at half-supply. This
eliminates the coupling capacitor that single supply, single-
ended amplifiers require. Eliminating an output coupling ca-
pacitor in a single-ended configuration forces a single-supply
amplifier’s half-supply bias voltage across the load. This
increases internal IC power dissipation and may perma-
nently damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful single-ended or bridged amplifier. Equation (2)
states the maximum power dissipation point for a single-
ended amplifier operating at a given supply voltage and
driving a specified output load
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is higher internal
power dissipation for the same conditions.
The LM4863 has two operational amplifiers per channel. The
maximum internal power dissipation per channel operating in
the bridge mode is four times that of a single-ended ampli-
fier. From Equation (3), assuming a 5V power supply and an
4Ω load, the maximum single channel power dissipation is
1.27W or 2.54W for stereo operation.
The LM4973’s power dissipation is twice that given by Equa-
tion (2) or Equation (3) when operating in the single-ended
B
P
size.
DMAX
P
DMAX
= 4 x (V
= (V
DD
DD
)
2
)
/ (2π
2
/ (2π
2
R
2
L
R
) Single-Ended
L
) Bridge Mode
01288101
(2)
(3)