LC72131 View Datasheet(PDF) - SANYO -> Panasonic

Part Name

Description

View to exact match

LC72131

AM/FM PLL Frequency Synthesizer

SANYO -> Panasonic 

LC72131, 72131M

Clock Time Base Usage Notes

The pull-up resistor used on the clock time base output pin (BO1) should be at least 100 kΩ. This is to prevent degrading

the VCO C/N characteristics when a loop filter is formed using the built-in low-pass filter transistor. Since the clock time

base output pin and the low-pass filter have a common ground internal to the IC, it is necessary to minimize the time

base output pin current fluctuations and to suppress their influence on the low-pass filter. Also, to prevent chattering we

recommend using a Schmitt input at the controller (microprocessor) that receives this signal.

Other Items

DZ1

DZ0

Dead zone mode

0

0

DZA

0

1

DZB

1

0

DZC

1

1

DZD

Charge pump

ON/ON

ON/ON

OFF/OFF

OFF/OFF

1. Notes on the Phase Comparator Dead Zone

Dead zone

– –0 s

–0 s

+0 s

+ +0 s

Since correction pulses are output from the charge pump even if the PLL is locked when the charge pump is in the

ON/ON state, the loop can easily become unstable. This point requires special care when designing application

circuits.

The following problems may occur in the ON/ON state.

• Side band generation due to reference frequency leakage

• Side band generation due to both the correction pulse envelope and low frequency leakage

Schemes in which a dead zone is present (OFF/OFF) have good loop stability, but have the problem that acquiring a

high C/N ratio can be difficult. On the other hand, although it is easy to acquire a high C/N ratio with schemes in

which there is no dead zone, it is difficult to achieve high loop stability. Therefore, it can be effective to select DZA

or DZB, which have no dead zone, in applications which require an FM S/N ratio in excess of 90 to 100 dB, or in

which an increased AM stereo pilot margin is desired. On the other hand, we recommend selecting DZC or DZD,

which provide a dead zone, for applications which do not require such a high FM signal-to-noise ratio and in which

either AM stereo is not used or an adequate AM stereo pilot margin can be achieved.

No. 4921-20/23

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