LM4866LQBD National Semiconductor, LM4866LQBD Datasheet - Page 11

• Manufacturer Part Number: LM4866LQBD
• Description: BOARD EVALUATION LM4866LQ
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4866LQBD

• Amplifier Type: Class AB
• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 3.2W x 2 @ 3 Ohm
• Voltage - Supply: 2 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4866
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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 LM4866 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 LM4866
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
f
and R
Pin out shown for the LLP package. Refer to the Connection Diagrams for the pinout of the TSSOP package.
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
)
(Continued)
(1)
11
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.
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 LM4866 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-
B
size.
P
DMAX
= (V
DD
)
2
/ (2π
2
R
20018601
L
) Single-Ended
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(2)