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LM4870 Datasheet(PDF) 4 Page - National Semiconductor (TI)

[Old version datasheet] Texas Instruments acquired National semiconductor.
Part No. LM4870
Description  1.1W Audio Power Amplifier with Shutdown Mode
Download  8 Pages
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Manufacturer  NSC [National Semiconductor (TI)]
Direct Link  http://www.national.com
Logo NSC - National Semiconductor (TI)

LM4870 Datasheet(HTML) 4 Page - National Semiconductor (TI)

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Typical Performance Characteristics (Continued)
Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in
Figure 1, the LM4870 has two operational am-
plifiers internally, allowing for a few different amplifier con-
figurations. The first amplifier’s gain is externally config-
urable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of
the first amplifier is set by selecting the ratio of R
f to R i while
the second amplifier’s gain is fixed by the two internal 40 k
resistors.
Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both am-
plifiers producing signals identical in magnitude, but out of
phase 180˚. Consequently, the differential gain for the IC is:
A
vd = 2 * (Rf/Ri)
By driving the load differentially through outputs V
O1 and
V
O2, an amplifier configuration commonly referred to as
“bridged mode” is established. Bridged mode operation is
different from the classical single-ended amplifier configura-
tion where one side of its load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration, as it provides differential
drive to the load, thus doubling output swing for a specified
supply voltage. Consequently, four times the output power is
possible as compared to a single-ended amplifier under the
same conditions. This increase in attainable output power
assumes that the amplifier is not current limited or clipped. In
order to choose an amplifier’s closed-loop gain without caus-
Supply Current Distribution
vs Temperature
DS100094-19
Power Dissipation
vs Output Power
DS100094-20
Output Power vs
Load Resistance
DS100094-21
Output Power vs
Supply Voltage
DS100094-22
Output Power vs
Supply Voltage
DS100094-27
Open Loop
Frequency Response
DS100094-23
Power Supply
Rejection Ratio
DS100094-24
www.national.com
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