STV2001 datasheet(28/46 Pages) STMICROELECTRONICS

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STV2001

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14.2.5 - 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).

This protection is latched; it may be reset either by switching VCC off or by I

2C (see Figure 13).

Figure 13. Safety Functions Block Diagram

14.3 - VERTICAL PART

14.3.1 - 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 calculat-

ed according to:

fo(Hz) = 1.5 . 10-5 .

A positive TTL level pulse applied on Pin 2 (Vin) is

used to synchronize the ramp in the range [fmin,

fmax] (see Figure 14). This frequency range de-

pends on the external capacitor connected on

Pin 6 (VCAP). A 150nF (

± 5%) capacitor is recom-

mended for 50 Hz to 165 Hz applications.

The typical maximum and minimum frequency, at

25oC and without any correction (S correction),

can be calculated as follows:

f(Max.) = 3.5 x fo and f(Min.) = 0.33 x fo

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 6)

is sampled on the AGC capacitor (Pin 4) 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

± 5% capacitor value on

Pin 4 (VAGC).

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

reference voltage by a capacitor.

14.3.2 - I2C Control Adjustments

S correction shapes can then be added to this

ramp. This frequency-independent S correction is

generated internally. Its amplitudes is adjustable

via the I2C. S correction can be inhibited by apply-

ing the selected bits.

Finally, the amplitude of the S corrected ramp is

adjustable via the vertical ramp amplitude control

(VOUT) to drive an external power stage.

HORIZONTA L

OUTPUT

INHIBITION

VERTICAL

OUTPUT

INHIBITION

Horizontal Flyback

0.7V

XRAY Protection

CC Checking

CC off or I

C Reset

VSCinh

I2C Drive on/off

I2C Ramp on/off

ABL

+1V

Video-off

COSC

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