TDA9103 datasheet(12/27 Pages) STMICROELECTRONICS

12 / 27 page

The dynamic behaviour of the PLL is fixed by an

external filter which integrates the current of the

charge pump. A ”CRC” filter is generally used.

PLL1 is inhibited by applying a high level on Pin 35

(PLLinhib) which is a TTL compatible input. The inhibi-

tion results from the opening of 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 charge and dis-

charge of the capacitor, by a current proportionnal

to the current in the resistor. typical thresholds of

sawtooth are 1.6V and 6.4V.

PLL1F

Figure 9

C Lockdet

LOCKDET

COMP1

INPUT

INTERFACE

CHARGE

PUMP

PLL

INHIBITION

VCO

PHASE

ADJUST

Eini

Horizontal

Adjust

R0 C0

Filter

Horizontal

Input

High

Low

3.2V

OSC

11 10

Figure 8 : Principle Diagram

The control voltage of the VCO is typically com-

prised between 1.6V and 6V. The theoretical fre-

quency range of this VCO is in the ratio 1

→ 3.75,

but due to spread and thermal drift of external

components and the circuit itself, the effective fre-

quency range has to be smaller (e.g. 30kHz

→

82kHz). In the absenceof synchronisationsignal the

control voltage is equal to 1.6V typ. and the VCO

oscillates on its lowest frequency (free frequency).

The synchro frequencyhas to be always higher than

the free frequency and a margin has to be taken. As

an example for a synchro range from 30kHz to

82kHz, the suggested free frequency is 27kHz. To

compensate for the spread of external components

and of the circuit itself, the free frequency may be

adjusted by a DC voltage on Pin 14 (Fmin adjust)

(see Figure10 for details).

The PLL1 ensures the coincidence between the

leading edge of the synchro signal and a phase

reference obtained by comparison between the

sawtooth of the VCO and an internal DC voltage

adjustable between 2.4V and 4V (by Pin 15). So a

±45° phase adjustment is possible.

Loop

Fil ter

(0.8V < a < 1.2V)

FHMINADJ

1.6V

6.4V

1.6V

0.75T T

FLIP FLOP

(1.6V < V

< 6V)

4I0

Figure 10 : Details of VCO and Fhmin Adjustment

TDA9103

12/27

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