LM3820 AM Radio System General Description Features The LM3820 is a 3-stage AM radio IC consisting of an RF amplifier, oscillator, mixer, IF amplifier, AGC detector, and zener regulator. The device was originally designed for use in slug-tuned auto radio applications, but is also suitable for capacitortuned portable radios. The LM3820 is an improved replacement for the LM1820. Y Y Y Y Y Y Y Y Input protection diodes Good control on sensitivity Improved S/N and tweet Versatile building-block approach Gain-controlled RF stage Cascode IF amplifier Regulated supply Pin compatible with LM1820 Connection Diagram Dual-In-Line Package TL/H/7967 – 1 Order Number LM3820N See NS Package Number N14A Circuit Schematic TL/H/7967 – 2 C1995 National Semiconductor Corporation TL/H/7967 RRD-B30M115/Printed in U. S. A. LM3820 AM Radio System February 1989 Absolute Maximum Ratings Current into Supply Terminal (Pin 3) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/Distributors for availability and specifications. Power Dissipation (Note 1) Supply Voltage Operating Temperature Range Storage Temperature Range Lead Temperature (Soldering, 10 sec.) 1200 mW 16V 35 mA b 25§ C to a 85§ C b 65§ C to a 150§ C 260§ C Electrical Characteristics (Figure 1 , TA e 25§ C, VS e 6V unless noted) Symbol Parameter IS Supply Current VZ Internal Zener Voltage Input Sensitivity Signal to Noise Ratio Overload Distortion Conditions Min Typ Max Units 12 18 24 mA 7.0 7.5 8.0 V f e 1 MHz, 30% Mod 400 Hz Measure RF Input Level for 10 mV Audio Output with Tuning Peaked 15 35 70 mV f e 1 MHz, 30% Mod 1 kHz (S a N)/N at Audio Output with 100 mV RF Input 22 28 Ð dB f e 1 MHz, 90% Mod 1 kHz THD at Audio Output with 30 mV RF Input Ð 6 10 % No RF Input Note 1: Above TA e 25§ C, derate based on TJ(Max) e 150§ C and iJA e 100 § C/W. Typical Applications *100 mV RF INPUT is equivalent to approx. 1 mV/meter field strength. See Applications Information for coil specifications. FIGURE 1. Capacitor-Tuned Test Fixture 2 TL/H/7967 – 3 Applications Information The circuit shown in Figure 1 is recommended as a starting point for portable radio designs. Loopstick antenna L1 is used in place of L0, and the RF amplifier is used with a resistor load to drive the mixer. A double tuned circuit at the output of the mixer provides selectivity, while the remainder of the gain is provided by the IF section, which is matched to the diode through a unity turns ratio transformer. RAGC may be used in place of CAGC to bypass the internal AGC detector and provide more recovered audio. An AM automobile radio design is shown in Figure 2 . Tuning of both the input and the output of the RF amplifier and the mixer is accomplished with variable inductors. Better selectivity is obtained through the use of double tuned interstage transformers. Input circuits are inductively tuned to prevent microphonics and provide a linear tuning motion to facilitate push-button operation. Coil specifications for Figure 1 are as follows: TL/H/7967 – 4 PCB Layout for Figure 1 Circuit TL/H/7967 – 5 3 Applications Information (Continued) TRANSFORMERS T1: C e 130 pF primary & secondary primary to secondary tap ratioÐ30:1 Q e 60 couplingÐcritical T2: C e 130 pF primary & secondary primary tap ratioÐ8.5:1 secondary tap ratioÐ8.5:1 Q e 60 couplingÐcritical TL/H/7967 – 6 FIGURE 2. Slug-Tuned Auto Radio Schematic Reference Toko* Part Number L0, L2 RWO-6A6255 T1 RRC-3A6426N T2 RRC-3A6427A T3 RZC-1A6425A *Toko America 1250 Feehanville Drive Mount Prospect, IL 60056 (312) 297-0070 FIGURE 3. Representative Part Numbers for the Coils of Figure 1 4 5 LM3820 AM Radio System Physical Dimensions inches (millimeters) Molded Dual-In-Line Package (N) Order Number LM3820N NS Package Number N14A LIFE SUPPORT POLICY NATIONAL’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. National Semiconductor Corporation 1111 West Bardin Road Arlington, TX 76017 Tel: 1(800) 272-9959 Fax: 1(800) 737-7018 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. National Semiconductor Europe Fax: (a49) 0-180-530 85 86 Email: cnjwge @ tevm2.nsc.com Deutsch Tel: (a49) 0-180-530 85 85 English Tel: (a49) 0-180-532 78 32 Fran3ais Tel: (a49) 0-180-532 93 58 Italiano Tel: (a49) 0-180-534 16 80 National Semiconductor Hong Kong Ltd. 13th Floor, Straight Block, Ocean Centre, 5 Canton Rd. Tsimshatsui, Kowloon Hong Kong Tel: (852) 2737-1600 Fax: (852) 2736-9960 National Semiconductor Japan Ltd. Tel: 81-043-299-2309 Fax: 81-043-299-2408 National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.