PCA84C646P datasheet(17/72 Pages) PHILIPS

17 / 72 page

1995 Jun 15

Philips Semiconductors

Preliminary speciﬁcation

Microcontrollers for TV tuning

control and OSD applications

PCA84C646; PCA84C846

9.4.1

MOUNTING PRECAUTIONS

To achieve good OSD performance, take the following

precautions for the microcontroller mounting:

• Apply the recommended R, Cs and Cp (PLL loop filter)

values as shown in Fig.12 and place them as close as

possible to pin C (41).

• To guarantee stable PLL operation, apply a noise-free

HSYNC signal (pin 6).

• Avoid heavy loading of the output pins.

• The supply voltage (VDD) must be correctly decoupled.

Connect decoupling capacitors as close as possible to

the VDD and VSS pins.

• Position microcontroller optimal and away from

components bearing high voltage and/or strong current.

• PLL loop filter ground of capacitors C

s and Cp must be

directly connected to the VSS pin (21). Avoid a ground

loop and separate the ground from other digital signals

ground.

• The connection between VSS pin (21) and +5 V regulator

ground/switching power supply secondary ground must

be as short as possible.

Fig.12 On-chip OSD oscillator.

handbook, full pagewidth

MED196

VOLTAGE

CONTROLLED

OSCILLATOR

CHARGE PUMP

AND

LOOP FILTER

PHASE/

FREQUENCY

DETECTOR

ACTIVE

LEVEL

DETECTOR

PROGRAMMABLE

7-BIT COUNTER

fOSD

(OSD clock)

divided by N

STANDBY

HSYNC

OSD disable

fVCO

(2)

(1)

(1) R=10to47k

Ω; typ. 15 kΩ.

Cs = 100 to 470 nF; typ. 220 nF.

Cp = 1⁄10 Cs.

For mounting see Section 9.4.1 “Mounting precautions”.

(2) Example:

If f1 = 15.750 kHz and (decimal value of 7-bit counter) = 32 then fVCO = 8.064 MHz

and the output of the Programmable 7-bit counter is 15.750 kHz.

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