TDA9109 datasheet(18/30 Pages) STMICROELECTRONICS

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PLL1F

(Loop Filter)

1.6V

6.4V

1.6V

0 0.875T

H TH

FLIP FLOP

(1.3V < V

< 6V)

4 I0

(0.80 < a < 1.30)

I2C Free Running

Adjustment

Figure 9 : Details of VCO

LOCKDET

COMP1

INPUT

INTERFACE

H/HVIN

High

CHARGE

PUMP

Low

PLL

INHIBITION

VCO

PLL1F

PHASE

ADJUST

I2C

HPOS

Adj.

OSC

Tramext

I2C

Forced

Frequency

Lock/Unlock

Status

HPOSITION

Figure 8 : Block Diagram

OPERATING DESCRIPTION (continued)

PLL1F

m F

4.7

m F

1.8k

Figure 7

II.2 - PLL1

The PLL1 consists of a phase comparator, an exter-

nal filter and a voltage-controlled oscillator (VCO).

The phase comparator is a "phase frequency" type

designed in CMOS technology. This kind of phase

detector avoids locking on wrong frequencies. It is

followed by a "charge pump", composed of two

current sources : sunk and sourced (typically I = 1mA

when locked and I = 140

µA when unlocked). This

difference between lock/unlock allows smooth catch-

ing of the horizontal frequency by PLL1. This effect

is reinforced by an internal original slow down system

when PLL1 is locked, avoiding the horizontal fre-

quency changing too quickly.

The dynamic behaviour of PLL1 is fixed by an exter-

nal filter which integrates the current of the charge

pump. A "CRC" filter is generally used (see Figure 7).

The PLL1 is internally inhibited during extracted

vertical sync (if any) to avoid taking in account

missing pulses or wrong pulses on phase compara-

tor.The inhibition is done by a switch located be-

tween the charge pump and the filter (see Figure 8).

The VCO uses an external RC network. It delivers

a linear sawtooth obtained by the charge and the

discharge of the capacitor, with a current propor-

tional to the current in the resistor. The typical

thresholds of the sawtooth are 1.6V and 6.4V.

The control voltage of the VCO is between 1.33V

and 6V (see Figure 9). The theorical frequency

range of this VCO is in the ratio of 1 to 4.5. The

effective frequency range has to be smaller (1 to

4.2) due to clamp intervention on the filter lowest

value. To remove the device and external compo-

nents spread, it is possible to adjust the free run-

ning frequency through I

2C. This adjustment can

be done automatically on the manufacturing line

without manual operation by using Hlock/unlock

information. The adjustment range is 0.8 to 1.3 f0

(where 1.3 f0 is the free running frequency at power

on reset).

TDA9109/S

18/30

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