LM1896N-1 National Semiconductor, LM1896N-1 Datasheet - Page 6

• Manufacturer Part Number: LM1896N-1
• Description: IC AMP AUDIO PWR 2.1W STER 14DIP
• Manufacturer: National Semiconductor
• Type: Class ABr

Specifications of LM1896N-1

• Output Type: 1-Channel (Mono) or 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 2.1W x 1 @ 8 Ohm; 1.3W x 2 @ 8 Ohm
• Voltage - Supply: 3 V ~ 10 V
• Features: Depop
• Mounting Type: Through Hole
• Package / Case: 14-DIP (0.300", 7.62mm)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *LM1896N-1; LM1896-1

Figure 2 the gain is
Figure 3 shows a plot of recovered audio as a function of
Application Hints
AM Radios
The LM1896 LM2896 has been designed fo fill a wide
range of audio power applications A common problem with
IC audio power amplifiers has been poor signal-to-noise per-
formance when used in AM radio applications In a typical
radio application the loopstick antenna is in close proximity
to the audio amplifer Current flowing in the speaker and
power supply leads can cause electromagnetic coupling to
the loopstick resulting in system oscillation In addition
most audio power amplifiers are not optimized for lowest
noise because of compensation requirements If noise from
the audio amplifier radiates into the AM section the sensitiv-
ity and signal-to-noise ratio will be degraded
The LM1896 exhibits extremely low wideband noise due in
part to an external capacitor C5 which is used to tailor the
bandwidth The circuit shown in Figure 2 is capable of a
signal-to-noise ratio in excess of 60 dB referred to 50 mW
Capacitor C5 not only limits the closed loop bandwidth it
also provides overall loop compensation Neglecting C2 in
A curve of
Performance Curves
field strength in V M The receiver section in this example
is an LM3820 The power amplifier is located about two
inches from the loopstick antenna Speaker leads run paral-
lel to the loopstick and are 1 8 inch from it Referenced to a
20 dB S N ratio the improvement in noise performance
over conventional designs is about 10 dB This corresponds
to an increase in usable sensitivity of about 8 5 dB
Bridge Amplifiers
The LM1896 LM2896 can be used in the bridge mode as a
monaural power amplifier In addition to much higher power
output the bridge configuration does not require output cou-
pling capacitors The load is connected directly between the
amplifier outputs as shown in Figure 4
where A
b
3 dB BW (
V
A
V
e
(S)
R2
e
o
R2
) vs A
a
S
S
R5
FIGURE 3 Improved AM Sensitivity over Conventional Design
a
a
A
V
V
is shown in the Typical
o
o
o
e
R5C5
1
6
Amp 1 has a voltage gain set by 1
amp 1 drives amp 2 which is configured as an inverting
amplifier with unity gain Because of this phase inversion in
amp 2 there is a 6 dB increase in voltage gain referenced to
V
C
from causing offset in amp 2 Low frequency response is
influenced by
Several precautions should be observed when using the
LM1896 LM2896 in bridge configuration Because the am-
plifiers are driving the load out of phase an 8
appear as a 4
load Power dissipation is twice as severe in this situation
For example if V
maximum dissipation is
This amount of dissipation is equivalent to driving two 4
loads in the stereo configuration
When adjusting the frequency response in the bridge config-
uration R5C5 and R10C10 form a 2 pole cascade and the
b
To measure the output voltage a floating or differential me-
ter should be used because a prolonged output short will
over dissipate the package Figure 1 shows the complete
bridge amplifier
i
B
3 dB bandwidth is actually shifted to a lower frequency
where R
The voltage gain in bridge is
is used to prevent DC voltage on the output of amp 1
C
e
e
P
feedback capacitor
feedback resistor
D
load and a 4
e
S
e
V
20 R
TL H 7920 – 9
V
o
V
P
i
f
L
6V and R
BW
2
S
D
e
e
L
e
2 1
c
e
2 R
0 9 Watts
2
2 RC
0 707
e
1
speaker will appear as a 2
a
B
L
R5
R2
C
20
a
e
B
6
c
2
R5 R2 The output of
8
4
c
bridged then the
2
speaker will