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OPERATING DESCRIPTION (continued)

2.5 X-RAY Protection

X-Ray protection is activated when the ABL input (1 V on Pin 20) is at a low level. It inhibits both H-Drive,

and Vout while Video goes into off-mode.

This activation is internally delayed by 2 lines to avoid erratic detection (short parasitics).

Figure 12. Safety Functions Block Diagram

3. VERTICAL PART

3.1 Function

When the synchronization pulse is not present, an

internal current source sets the free running fre-

the typical free running frequency is 100Hz.

The typical free running frequency can be calculat-

ed according to:

fo(Hz) = 1.5

A positive TTL level pulse applied on Pin 1(Vin) is

used to synchronize the ramp in the range [fmin,

fmax] (see Figure 13). This frequency range de-

pends on the external capacitor connected on Pin

5. A 150nF (

50 Hz to 165 Hz applications.

The typical maximum and minimum frequency, at

can be calculated as follows:

When an S correction is applied, these values are

slightly modified.

With a synchronization pulse, the internal oscilla-

tor is synchonized immediately but its amplitude

changes. An internal correction then adjusts it in

less than half a second. The ramp top value (Pin 5)

is sampled on the AGC capacitor (Pin 3) at each

clock pulse. A transconductance amplifier modi-

fies the charge current of the capacitor so as to

make the amplitude constant again. We recom-

mend using an AGC capacitor with a low leakage

current. A value lower than 100nA is mandatory.

A good level of stability for the internal closed loop

is obtained by a 470nF

Pin 3 (VAGC).

VRB (Pin 8) is used for decoupling the internal 2V

reference voltage by a capacitor.

HORIZONTAL

OUTPUT

INHIBITION

VERTICAL

OUTPUT

INHIBITION

S

R

Q

Horizontal Flyback

0.7V

XRAY Protection

V

V

CC

V

2

C Reset

VSCinh

+

20

ABL

+1V

Video-off

1

COSC

6