LM2896 [ETC]
;
| 型号： | LM2896 |
| 厂家： | 
ETC |
| 描述： |
|
| 文件： | 总10页 (文件大小：268K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
February 1995
LM1896/LM2896 Dual Audio Power Amplifier
General Description
Features
Y
Low AM radiation
The LM1896 is a high performance 6V stereo power amplifi-
er designed to deliver 1 watt/channel into 4X or 2 watts
bridged monaural into 8X. Utilizing a unique patented com-
pensation scheme, the LM1896 is ideal for sensitive AM
radio applications. This new circuit technique exhibits lower
wideband noise, lower distortion, and less AM radiation than
conventional designs. The amplifier’s wide supply range
(3V–9V) is ideal for battery operation. For higher supplies
Y
Low noise
Y
e
3V, 4X, stereo P
250 mW
o
Y
Y
Y
Y
Y
Y
Wide supply operation 3V–15V (LM2896)
Low distortion
No turn on ‘‘pop’’
Adjustable voltage gain and bandwidth
Smooth waveform clipping
l
(V
S
9V) the LM2896 is available in an 11-lead single-in-
e
P
o
9W bridged, LM2896
line package. The LM2896 package has been redesigned,
resulting in the slightly degraded thermal characteristics
shown in the figure Device Dissipation vs Ambient Tempera- Applications
Y
ture.
Compact AM-FM radios
Y
Y
Stereo tape recorders and players
High power portable stereos
Typical Applications
TL/H/7920–1
e
e
20 kHz)
FIGURE 1. LM2896 in Bridge Configuration (A
400, BW
Order Number LM2896P
See NS Package Number P11A
V
Order Number LM1896N
See NS Package Number N14A
C
1995 National Semiconductor Corporation
TL/H/7920
RRD-B30M115/Printed in U. S. A.
Absolute Maximum Ratings
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales
Office/Distributors for availability and specifications.
Junction Temperature
150 C
§
260 C
§
Lead Temperature (Soldering, 10 sec.)
Thermal Resistance
Supply Voltage
LM1896
LM2896
i
i
i
i
(DIP)
(DIP)
(SIP)
(SIP)
30 C/W
§
JC
JA
JC
JA
e
e
V
V
12V
18V
S
S
137 C/W
§
10 C/W
§
a
0 C to 70 C
Operating Temperature (Note 1)
Storage Temperature
55 C/W
§
§
65 C to 150 C
§
§
b
a
§
Electrical Characteristics
Unless otherwise specified, T
e
e
e
e
4X. For LM2896,
L
25 C, A
§
200 (46 dB). For the LM1896; V
6V and R
A
V
S
e
e
e
12V and R 8X. Test circuit shown in Figure 2.
L
T
25 C, V
§
TAB
S
LM1896
LM2896
Parameter
Conditions
Units
Min Typ Max Min Typ Max
e
Supply Current
P
o
0W, Dual Mode
15
25
10
25
40
15
mA
V
Operating Supply Voltage
3
3
e
e
1 kHz
Output Power
LM1896N-1
LM1896N-2
THD
10%, f
e
e
e
e
V
S
V
S
V
S
V
S
V
S
V
S
V
S
6V, R
4X Dual Mode
8X Bridge Mode
8X Dual Mode
0.9
1.1
1.8
1.3
W/ch
W
L
L
L
e
e
25 C
A
6V, R
9V, R
T
2.1
§
e
e
e
e
e
(
W/ch
W/ch
W
e
LM2896P-1
LM2896P-2
12V, R
12V, R
8X Dual Mode
2.0
7.2
2.5
9.0
7.8
2.5
L
e
8X Bridge Mode
L
e
T
25 C
§
TAB
e
e
9V, R
9V, R
4X Bridge Mode
4X Dual Mode
W
L
*
W/ch
L
e
1 kHz
Distortion
f
e
e
e
P
o
P
o
P
o
50 mW
0.5W
1W
0.09
0.11
0.09
0.11
0.14
%
%
%
e
Output Referred, V
e
e
IN
Power Supply Rejection
Ratio (PSRR)
C
BY
100 mF, f
1 kHz, C
e
0.1 mF
b
b
b
b
b
b
40
50
54
64
40
50
54
64
dB
dB
250 mV
RIPPLE
e
Output Referred
e
e
Channel Separation
C
BY
100 mF, f
1 kHz, C
IN
0.1 mF
b
b
e
Noise
Equivalent Input Noise R
e
0,
S
e
b
20 20 kHz
C
0.1 mF, BW
1.4
1.4
mV
mV
mV
IN
CCIR/ARM
Wideband
1.4
2.0
1.4
2.0
DC Output Level
Input Impedance
Input Offset Voltage
2.8
50
3
3.2
5.6
50
6
6.4
V
100 350
5
100 350
5
kX
mV
Voltage Difference
between Outputs
LM1896N-2, LM2896P-2
10
20
10
20
mV
Input Bias Current
120
120
nA
Note 1: For operation at ambient temperature greater than 25 C, the LM1896/LM2896 must be derated based on a maximum 150 C junction temperature using a
§ §
thermal resistance which depends upon mounting techniques.
2
Typical Performance Curves
LM1896 Maximum Device
Dissipation vs Ambient
Temperature
b
3 dB Bandwidth vs Voltage
Gain for Stable Operation
LM2896 Device Dissipation
vs Ambient Temperature
TL/H/7920–2
3
Typical Performance Curves (Continued)
Total Harmonic Distortion
vs Power Output
Power Dissipation vs
e
Power Dissipation vs
Power Output R
e
8X
Power Output R
4X
L
L
TL/H/7920–3
Equivalent Schematic
6, 9 No connection on LM1896
TL/H/7920–4
( ) indicates pin number for LM2896
Connection Diagrams
Single-In-Line Package
Dual-In-Line Package
TL/H/7920–5
Top View
TL/H/7920–6
Top View
4
Typical Applications (Continued)
TL/H/7920–8
TL/H/7920–7
6, 9 No connection on LM1896
( ) Indicates pin number for LM2896
e
e
30 kHz
FIGURE 2. Stereo Amplifier with A
200, BW
V
External Components (Figure 2)
Components
Comments
R5/R2 for one channel and A
e
a
e
V
a
1 R10/R13
1. R2, R5, R10, R13
Sets voltage gain, A
1
V
for the other channel.
Bootstrap resistor sets drive current for output stage and allows pins 3 and 12 to
go above V .
2. R3, R12
S
3. R
Works with C to stabilize output stage.
o
o
4. C1, C14
Input coupling capacitor. Pins 1 and 14 are at a DC potential of V /2. Low
S
frequency pole set by:
1
e
f
L
2q R C1
IN
Feedback capacitors. Ensure unity gain at DC. Also a low frequency pole at:
5. C2, C13
6. C3, C12
1
e
f
L
2qR2C2
Bootstrap capacitors, used to increase drive to output stage. A low frequency
pole is set by:
1
e
f
L
2qR3C3
7. C5, C10
8. C7
Compensation capacitor. These stabilize the amplifiers and adjust their
bandwidth. See curve of bandwidth vs allowable gain.
Improves power supply rejection (See Typical Performance Curves). Increasing
C7 increases turn-on delay.
9. C
Output coupling capacitor. Isolates pins 5 and 10 from the load. Low frequency
pole set by:
1
c
e
f
L
2q C R
c
L
10. C
11. C
Works with R to stabilize output stage.
o
o
Provides power supply filtering.
S
5
Application Hints
AM Radios
a
Amp 1 has a voltage gain set by 1
R5/R2. The output of
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
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.
V . The voltage gain in bridge is:
i
V
R5
R2
o
e
a
1
2
V
#
J
i
C
B
is used to prevent DC voltage on the output of amp 1
from causing offset in amp 2. Low frequency response is
influenced by:
1
e
f
L
2q R C
B
B
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 8X speaker will
appear as a 4X load, and a 4X speaker will appear as a 2X
load. Power dissipation is twice as severe in this situation.
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
Figure 2, the gain is:
e
e
8X bridged, then the
For example, if V
6V and R
S
L
maximum dissipation is:
V2S
2
6
a
S
A
0
V
o
e
c
e
c
2
P
2
e
D
A (S)
V
c
4
20 R
20
0.9 Watts
a
L
S
0
o
e
P
D
a
R2
R5
1
e
e
, 0
o
where A
V
This amount of dissipation is equivalent to driving two 4X
loads in the stereo configuration.
R2
R5C5
b
A curve of 3 dB BW (0 ) vs A is shown in the Typical
o
V
When adjusting the frequency response in the bridge config-
uration, R5C5 and R10C10 form a 2 pole cascade and the
Performance Curves.
Figure 3 shows a plot of recovered audio as a function of
field strength in mV/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.
b
3 dB bandwidth is actually shifted to a lower frequency:
0.707
e
BW
2qRC
e
e
where R
C
feedback resistor
feedback capacitor
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.
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.
TL/H/7920–9
FIGURE 3. Improved AM Sensitivity over Conventional Design
6
Application Hints (Continued)
TL/H/7920–10
Figure 4. Bridge Amplifier Connection
Printed Circuit Layout
Printed Circuit Board Layout
less than 50 kX to prevent an input-output oscillation. This
oscillation is dependent on the gain and the proximity of the
Figure 5 and Figure 6 show printed circuit board layouts for
the LM1896 and LM2896. The circuits are wired as stereo
amplifiers. The signal source ground should return to the
input ground shown on the boards. Returning the loads to
power supply ground through a separate wire will keep the
THD at its lowest value. The inputs should be terminated in
a
bridge elements R and C to the ( ) input. If the bridge
mode is not used, do not insert R , C into the PCB.
B
B
B
B
To wire the amplifer into the bridge configuration, short the
capacitor on pin 7 (pin 1 of the LM1896) to ground. Connect
together the nodes labeled BRIDGE and drive the capacitor
connected to pin 5 (pin 14 of the LM1896).
TL/H/7920–11
FIGURE 5. Printed Circuit Board Layout for the LM1896
7
Printed Circuit Layout (Continued)
TL/H/7920–12
FIGURE 6. Printed Circuit Board Layout for the LM2896
8
Physical Dimensions inches (millimeters)
Molded Dual-In-Line Package (N)
Order Number LM1896N
See NS Package Number N14A
9
Physical Dimensions inches (millimeters) (Continued)
Single-In-Line Package (P)
Order Number LM2896P
NS Package Number P11A
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