MC44BS373CAD datasheet(23/52 Pages) MOTOROLA

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MC44BS373CA Data Sheet

MC44BS373CA Modes of Operation

15.5 Transient Output Inhibit

To minimize the risk of interference to other channels while the UHF PLL is acquiring a lock on the desired

frequency, the sound and video modulators are turned off during a timeout period for the following cases:

•

Power-on from zero (that is, all VCC switched from 0 to 5 V)

•

UHF oscillator power-on from off state (that is, OSC bit switched from 1 to 0)

There is a timeout of 263 ms until the output is enabled. This lets the UHF PLL settle to its programmed

frequency. During the 263-ms timeout, the sound PLL current source is set to 10

µA typical to speed up the

locking time. After the timeout, the current source is switched to 1

µA. Use care when selecting loop filter

components to ensure the loop transient does not exceed this delay.

For test purposes, it is possible to disable the 263-ms delay using test mode1, state1.h. (This is called

speed-up mode.) Table 17 provides settings pertaining to test mode 1.

15.6 UHF Oscillator—VHF range

The UHF oscillator is fully integrated and does not require any external components.

For low-frequency testing or VHF range operation (test mode 1, states 1.b to 1.e) the UHF oscillator can be

internally divided by 2, 4, 8, or 16.

15.7 UHF PLL Section

The reference divider is a fixed divide-by-128, resulting in a reference frequency of 31.25 kHz with a

4.0-MHz crystal.

The prescaler is a fixed divide-by-8 and is permanently engaged.

The programmable divider division ratio is controlled by the state of control bits N0 to N11.

The divider ratio N for a desired frequency F (in MHz) is given by:

with:

NOTE

Programming a division ratio of N = 0 is not allowed.

15.8 Logic Output Port (LOP)

The LOP pin controls any logic function. The primary applications for LOP are to control an external

attenuator or an external switch between the antenna input and TV output. A typical attenuator application

with PIN diode is shown in Figure 6. The LOP pin switches the PIN attenuator depending on the signal

strength of the antenna input. This reduces the risk of intermodulation in certain areas. The LOP can also be

used as an off position bypass switch or for other logic functions in the application.

---

128

----------

2048

N11

1024

N10

×…… 4 N2

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