TDA9105A datasheet(18/31 Pages) STMICROELECTRONICS

18 / 31 page

H-DRIVE

VCC

H-DRIVE

VCC

Figure 19 : Output stage simplified diagram,

showing the two possibilities of

connection

OPERATING DESCRIPTION (continued)

Output Section

The H-drive signal is transmitted to the output

through a shaping block ensuring a duty cycle

adjustable from 30% to 50%. In order to ensure a

reliable operation of the scanning power part, the

output is inhibited in the following circumstances :

-VCC too low,

- Xray protection activated,

- During the horizontal flyback,

- Output voluntarily inhibited through Pin 4.

The output stage is composed of a Darlington NPN

bipolar transistor. Both the collector and the emitter

are accessible (see Figure 16).

The output Darlington is in off-statewhen the power

scanning transistor is also in off-state.

The maximum output current is 20mA, and the

correspondingvoltagedrop of theoutput darlington

is 1.1V typically.

It is evident that the power scanning transistor

cannot be directly driven by the integrated circuit.

An interface has to be designed between the circuit

and the power transistor which can be of bipolar or

MOS type.

Outputs inhibition

The application of a voltage lower than 1V (typ.) on

Pin 4 (duty cycle adjust) inhibits the horizontal and

vertical outputs. This is not memorised.

LOGIC

BLOCK

V-fly

Vsync

V sawtooth

retrace time

H-fly

to 2ND PLL

H OUTPUT

INHIBITION

V OUTPUT

INHIBITION

COMPOSITE

BLANKING

H-Duty cycle

Flyback

0.7V

XRAY

REF

CC off

XRAY Protection

Inhibition

Checking

Figure 20 : Safety Functions Block Diagram

X-RAY PROTECTION : the activation of the X-ray

protectionis obtained by application of a high level

on the X-ray input (>8V). Consequences of X-ray

protection are :

- Inhibition of H drive output,

- Activation of composite blanking output.

The reset of this protection is obtained by VCC

switch off (see Figure 17).

TDA9105A

18/31

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