LM1868.PDF
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LM1868 AM/FM Radio System
February 1995
LM1868 AM/FM Radio System
General Description
The combination of the LM1868 and an FM tuner will pro-
vide all the necessary functions for a 0.5 watt AM/FM radio.
Included in the LM 1868 are the audio power amplifier, FM
IF and detector, and the AM converter, IF, and detector.
The device is suitable for both line operated and 9V battery
applications.
Features
Y
DC selection of AM/FM mode
Y
Regulated supply
Y
Audio amplifier bandwidth decreased in AM mode,
reducing amplifier noise in the AM band
Y
AM converter AGC for excellent overload
characteristics
Y
Low current internal AM detector for low tweet radiation
Block Diagram
TL/H/7909±1
Order Number LM1868N
See NS Package Number N20A
Note: See table for coil data
C
1995 National Semiconductor Corporation
TL/H/7909
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.
Supply Voltage (Pin 19)
Storage Temperature Range
b
55
§
Cto
a
150
§
C
Operating Temperature Range
0
§
Cto
a
70
§
C
15V
Lead Temperature (Soldering, 10 sec.)
260
§
C
Package Dissipation
2.0W
Above T
A
e
25
§
C, Derate Based on
T
J(MAX)
e
150
§
C and
i
JA
e
60
§
C/W
Electrical Characteristics
Test Circuit, T
A
e
25
§
C, V
S
e
9V, R
L
e
8
X
(unless otherwise noted)
Parameter
Conditions
Min
Typ Max
Units
STATIC CHARACTERISTICS e
AM
e
0, e
FM
e
0
Supply Current
AM Mode, S1 in Position 1
22
30
mA
Regulator Output Voltage (Pin 16)
3.5
3.9
4.8
V
Operating Voltage Range
4.5
15
DYNAMIC CHARACTERISTICSÐAM MODE
f
AM
e
1 MHz, f
mod
e
1 kHz, 30% Modulation, S1 in Position 1, P
O
e
50 mW unless noted
Maximum Sensitivity
Measure e
AM
for P
O
e
50 mW,
8
16
m
V
Maximum Volume
Signal-to-Noise
e
AM
e
10 mV
40
50
dB
Detector Output
e
AM
e
1mV
40
60
85
mV
Measure at Top of Volume Control
Overload Distortion
e
AM
e
50 mV, 80% Modulation
2
10 %
Total Harmonic Distortion (THD)
e
AM
e
10 mV
1.1
2
%
DYNAMIC CHARACTERISTICSÐFM MODE f
FM
e
10.7 MHz, f
mod
e
400 Hz,
D
f
e
g
75 kHz, P
O
e
50 mW, S1 in Position 1
b
3 dB Limiting Sensitivity
15
45
m
V
Signal-to-Noise Ratio
e
FM
e
10 mV
50
64
dB
Detector Output
e
FM
e
10 mV,
D
f
e
g
22.5 kHz
40
60
85
mV
Measure at Top of Volume Control
AM Rejection
e
FM
e
10 mV, 30% AM Modulation
40
50
dB
Total Harmonic Distortion (THD)
e
FM
e
10 mV
1.1
2
%
DYNAMIC CHARACTERISTICSÐAUDIO AMPLIFIER ONLY f
e
1 kHz, e
AM
e
0, e
FM
e
0, S1 in Position 2
Power Output
THD
e
10%, R
L
8
X
V
S
e
6V
250
325
mW
V
S
e
9V
500
700
mW
Bandwidth
AM Mode, P
O
e
50 mW
11
kHz
FM Mode, P
O
e
50 mW
22
kHz
Total Harmonic Distortion (THD)
P
O
e
50 mW, FM Mode
0.2
%
Voltage Gain
41
dB
Typical Performance Characteristics
(Test Circuit) All curves are measured at audio output
Quiescent Supply Current
vs Voltage
FM Limiting Characteristics
FM IF AM Rejection
TL/H/7909±2
2
Typical Performance Characteristics
(Continued)
All curves are measured at audio output (Test Circuit)
Gain vs Frequency Audio
AM Characteristics
Recovered Audio vs Supply
Amplifier Only
Power Dissipation vs Power
Power Dissipation vs Power
Distortion vs Frequency
Output, R
L
e
8
X
Out, R
L
e
16
X
Audio Amplifier Only
TL/H/7909±3
Test Circuit
Note: See table for coil data
TL/H/7909±4
3
FM Performance (88 MHz±108 MHz) AM Performance (525 kHz±1650 kHz)
#
30 dB quieting sensitivity: 3.5
m
V
#
Maximum sensitivity: 100
m
V/m
#
b
3 dB limiting sensitivity: 7
m
V
#
20 dB quieting sensitivity: 250
m
V/m
#
Tweet* worst case: 5%
100 mV/m: 1.5%
*Tweet is an audio tone produced by the 2nd and 3rd harmonic of the IF
beating against the received signal. It is measured as an equivalent modu-
lation level: i.e., a 30% tweet has the same amplitude at the detector as a
desired signal with 30% modulation.
TL/H/7909±5
PC Board Layout
TL/H/7909±6
Component Side
Typical Performance Characteristics
Typical Application
All curves are measured at audio output
TL/H/7909±7
TL/H/7909±8
5
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