TDA9109 datasheet(19/30 Pages) STMICROELECTRONICS

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OPERATING DESCRIPTION (continued)

H Osc

Sawtooth

H Drive

1.6V

4.0V

6.4V

7/8T

1/8T

Duty Cycle

Internally

Shaped Flyback

Flyback

The duty cycle of H-drive is fixed (48%).

Figure 11 : PLL2 Timing Diagram

H Osc

Sawtooth

Phase REF1

H Synchro

1.6V

6.4V

2.8V < Vb < 4.0V

7/8T

1/8T

Phase REF1 is obtained by comparison between the sawtooth and

a DC voltage adjustable between 2.8V and 4.0V. The PLL1 en-

sures the exact coincidence between the signal phase REF and

HSYNC. A

± TH/10 phase adjustment is possible.

Figure 10 : PLL1 Timing Diagram

The sync frequencymust always be higher than the

free running frequency. For example, when using

a sync range between 24kHz and 100kHz, the

suggested free running frequency is 23kHz.

This can be obtainedonly byadjustingf0 (for instance,

making R0 adjustable). If no adjustment is possible,

more margin must be provided to cope with the

components spread :

±8% for the IC, ±1% for R0,

±2 or 5% for C0, leading to ±11%or 14% on f0. The

same percentage of frequency range will lost at

upper end of the range.

Another feature is the capability for the MCU to

force the horizontal frequency through I

2C to 2xf0

or 3xf0 (for burn-in mode or safety requirements).

In this case, the inhibition switch is opened, leaving

PLL1 free, but the voltage on PLL1 filter is forced

to 2.66V (for 2xf0) or 4.0V (for 3xf0).

PLL1 ensuresthe coincidencebetween the leading

edge of the sync signal and a phase reference

obtained by comparison between the sawtooth of

the VCO and an internal DC voltage which is I

adjustable between 2.8V and 4.0V (corresponding

± 10%) (see Figure 10).

The TDA9109/SN also includes a Lock/Unlock

identification block which senses in real time

whether PLL1 is locked or not on the incoming

horizontal sync signal. The resulting information is

available on HLOCKOUT (see Sync Processor).

When PLL1 is unlocked, it forces HLOCKOUT to

high level.

The lock/unlock information is also available

through the I

2C read.

II.3 - PLL2

PLL2 ensures a constant position of the shaped

flyback signal in comparison with the sawtooth of

the VCO, taking into accountthe saturation time Ts

(see Figure 11).

The phase comparator of PLL2 (phase type com-

parator) is followed by a charge pump (typical

output current : 0.5mA).

The flyback input consists of an NPN transistor.

This input must be current driven. The maximum

recommended input current is 5mA (see Fig-

ure 12).

The duty cycle is fixed (48%).

The maximum storage time (Ts Max.) is (0.44TH -

TFLY/2). Typically, TFLY/TH is around 20% which

means that Ts max is around 34% of TH.

TDA9109/SN

19/30

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