LA1136N Datasheet, PDF (18/28 Pages) Sanyo Semicon Device – AM Tuners for Car Radios and Home Stereos

LA1136N, 1136NM, 1137N, 1137NM
14. Stop Detector Adjustment
Although this explanation is for the LA1137N, it is identical for the LA1136N, except that the pin numbers are different.
The LA1137N is designed for use with the following microcontrollers.
Stop detection method: LM7001 (Sanyo) (SD output only)
IF count method:
LM7000 (Sanyo)
LC7230 (Sanyo)
(1) Support for the LM7001
The search stop detector uses the active HIGH signal of pin18.
Ω
S-meter load
Unit (capacitance: F)
Ω
Ω
Antenna input – dBµ
The IF signal from the IF amplifier is detected, on pin 16 the signal that determined the bandwidth characteristics through the
narrowband filter BFU450CN (BFU450CN is equivalent to the amplifier emitter load) is detected, and the S-meter output is
output by the S-meter drive circuit by driving with current the load on pin 17. Therefore, the S-meter output V_SM on pin 17
has the following relationship with the S-meter load R17.
V_SM ∞ R17
In the above example, 3 kΩ is changed to 4.5 kΩ, but the R ratio of the output is 1.5x. However, the meter output has an upper
limit; as a guide, saturation occurs when the upper limit is at about V_CC – 1.4 V. The pin 18 SD output is generated by
comparing the S-meter output described above with the reference voltage Vref on pin 9 (400 µ × R9). Using the
recommended constants, Vref = 400 µ × 2.4 k = 1.0 (V).
The comparator compares the electric potential of pin 17 with that of pin 9 and detects when the electric potential of pin 17
is greater than that of pin 9, in which event the transistor is turned off and the SD output changes from LOW to HIGH (GND
to V_DD).
Note that, in consideration of differences in circuit configurations, Vref should be at least 0.7 V.
No. 3507-18/28