TDA9109N datasheet(21/32 Pages) STMICROELECTRONICS

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OPERATING DESCRIPTION (continued)

Horizontal Flyback

Internal Trigged

Horizontal Flyback

Horizontal Focus

Cap Sawtooth

Horizontal Dynamic

Focus Parabola

Output

4.7V

400ns

Figure 15

III - VERTICAL PART

III.1 - Function

When the synchronization pulse is not present, an

internal current source sets the free running fre-

quency. For an external capacitor, COSC = 150nF,

the typical free running frequency is 100Hz.

The typical free running frequency can be calcu-

lated by :

f0 (Hz)= 1.5 ⋅ 10

−5 ⋅ 1

COSC

A negative or positive TTL level pulse applied on

Pin 2 (VSYNC)as well as a TTLcomposite sync on

Pin 1 can synchronize the ramp in the range

[fmin , fmax]. This frequencyrange depends on the

ext e rn al capa c it or con nect ed on Pin 2 2.

A 150nF (

±5%) capacitor is recommended for

50Hz to 165Hz applications.

The typical maximum and minimum frequency, at

oC and without any correction (S correction or

C correction), can be calculated by :

f(Max.) = 2.5 x f0 and f(Min.) = 0.33 x f0

If S or C corrections are applied, these values are

slighty affected.

If a synchronization pulse is applied, the internal

oscillator is synchonized immediately but its am-

plitude changes. An internal correction then ad-

justs it in less than half a second. The top value of

the ramp (Pin 22) is sampled on the AGC capacitor

(Pin 20) at each clock pulse and a transconduc-

tance amplifier modifies the charge current of the

capacitor in such a way to make the amplitude

again constant.

The read status register provides the vertical Lock-

Unlock and the vertical sync polarity information.

We recommend the use of an AGC capacitor with

low leakage current. A value lower than 100nA is

mandatory.

A good stability of the internal closed loop is

reached by a 470nF

± 5% capacitor value on

Pin 20 (VAGC).

III.2 - I

2C Control Adjustments

S and C correction shapes can then be added

to this ramp. These frequency independent S

and C corrections are generated internally.

Their amplitudes are adjustable by their respec-

tive I

2C registers. They can also be inhibited by

the ir select bits.

Finally, the amplitude of this S and C corrected

ramp can be adjusted by the vertical ramp ampli-

tude control register.

The adjusted ramp is available on Pin 23 (VOUT)to

drive an external power stage.

The gain of this stage can be adjusted (

±25%)

depending on its register value.

The mean value of this ramp is driven by its own

2C register (vertical position). Its value is

VPOS = 7/16

⋅ VREF-V ± 300mV.

Usually VOUT is sent through a resistive divider to

the inverting input of the booster. Since VPOS

derives from VREF-V, the bias voltage sent to the

non-inverting input of the booster should also de-

rive from VREF-V to optimize the accuracy (see Ap-

plication Diagram).

III.3 - Vertical Moiré

By using the vertical moiré, VPOS can be modu-

lated from frame to frame. This function is intended

to cancel the fringes which appear when line to line

interval is very close to the CRT vertical pitch.

The amplitude of the modulation is controlled by

switched-off via the control bit D7.

TDA9109/N

21/32

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