TDA9106A datasheet(21/30 Pages) STMICROELECTRONICS

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20k

Ω

220nF

From

Phase

Comparator

NOR1

6.5V

H-Lock CAP

37 HLOCKOUT

Figure 12 : LOCK/UNLOCK Block Diagram

OPERATING DESCRIPTION (continued)

function is described in Figure 12.

The NOR1 gate is receiving the phase comparator

output pulses (which also drive the charge pump).

When PLL1 is locked, on point A there is a very

small negative pulse (about 100ns) at each hori-

zontal cycle, so after RC filter, there is a high level

on Pin 13 which forces Hlockout to low level. Hys-

terisis comparator detects locking when Pin 13 is

reaching 6.5V and unlocking when Pin 13 is de-

creasing to 6.0V.

When PLL1 is unlocked, the 100ns negative pulse

on A becomes much larger and consequently the

average level on Pin 13 decreases. It forces Hlock-

out to go high.

The Pin 13 status is approximately the following :

- near 0V when there is no H-Sync

- between 0 and 4V with H-Sync frequency differ-

ent from VCO

- between 4 to 8 V when VCO frequency reaches

H-Sync one (but not already in phase)

- near 8V when PLL1 is locked.

H Osc

Sawtooth

H Drive

1.6V

4.0V

6.4V

7/8T

1/8T

Duty Cycle 48%

Internally

Shaped Flyback

Flyback

Figure 13 : PLL2 Timing Diagram

20k

Ω

GND 0V

HFLY

400

Ω

Figure 14 : Flyback Input Electrical Diagram

It is important to notice that Pin 13 is not an

output pin but is only used for filtering purpose

(see Figure 12 ).

The lock/unlock information is also available throw

2C read.

II.3 - PLL2

The PLL2 ensures a constant position of the

shaped flyback signal in comparion with the saw-

tooth of the VCO (Figure 13).

The phase comparator of PLL2 (phase type com-

parator) is followed by a charge pump with

± 0.5mA

(typ.) output current.

The flyback input is composed of an NPN transis-

tor. This input must be current driven. The maxi-

mum rec om ma nd ed input current is 2mA

(see Figure 14).

The duty cycle is fixed and equal to 48% of hori-

zontal-period.

Maximum storage time is about 43.75% - (Tfly/2.TH).

Typically, Tfly/TH is around20% thatmeansTs max is

around 33.75%.

II.4 - Output Section

The H-drive signal is transmitted to the output

througha shapingblock ensuringTs and dutycycle.

In order to secure scanning power part operation,

the output is inhibited in the following circum-

stances :

TDA9106A

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