LM4950TSBD National Semiconductor, LM4950TSBD Datasheet - Page 15

• Manufacturer Part Number: LM4950TSBD
• Description: BOARD EVALUATION LM4950TS
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4950TSBD

• Amplifier Type: Class AB
• Output Type: 1-Channel (Mono) or 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 7.5W x 1 @ 8 Ohm; 3.1W x 2 @ 4 Ohm
• Voltage - Supply: 9.6 V ~ 16 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4950
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

Application Information
HIGH VOLTAGE BOOMER WITH INCREASED OUTPUT
POWER
Unlike previous 5V Boomer
signed to operate over a power supply voltages range of
9.6V to 16V. Operating on a 12V power supply, the LM4950
will deliver 7.5W into an 8Ω BTL load with no more than 10%
THD+N.
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 3, the LM4950 consists of two opera-
tional amplifiers that drive a speaker connected between
their outputs. The value of external input and feedback re-
sistors determine the gain of each amplifier. Resistors RIN
and RF
20kΩ resistors set AMP
load, such as a speaker, connected between the two ampli-
fier outputs, VOUT
AMP
amplifiers producing signals identical in magnitude, but 180˚
out of phase. Taking advantage of this phase difference, a
load is placed between AMP
entially (commonly referred to as "bridge mode"). This re-
sults in a differential, or BTL, 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
A
’s output serves as AMP
A
set the closed-loop gain of AMP
A
A
and VOUT
VD
B
’s gain to -1. The LM4950 drives a
= 2(R
®
A
amplifiers, the LM4950 is de-
B
and AMP
’s input. This results in both
f
/ R
B
. Figure 3 shows that
FIGURE 3. Typical LM4950 BTL Application Circuit
i
)
B
and driven differ-
A
, whereas two
(1)
A
15
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.
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 am-
plifiers require. Eliminating an output coupling capacitor in a
typical single-ended configuration forces a single-supply am-
plifier’s half-supply bias voltage across the load. This in-
creases internal IC power dissipation and may permanently
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.
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