TDA9111 datasheet(27/43 Pages) STMICROELECTRONICS

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TDA9111

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2.3 PLL2

PLL2 ensures a constant position of the shaped

flyback signal in comparison with the sawtooth of

the VCO, taking into account the saturation time

Ts (see Figure 11)

Figure 11. PLL2 Timing Diagram

The phase comparator of PLL2 is followed by a

charge pump (typical output current: 0.5 mA).

The flyback input consists of an NPN transistor.

The input current must be limited to less than 5 mA

(see Figure 12).

Figure 12. Flyback Input Electrical Diagram

The duty cycle is adjustable through I2C from 30 %

to 65 %. For a safe start-up operation, the initial

duty cycle (after power-on reset) is 65% in order to

avoid having too long a conduction period of the

horizontal scanning transistor.

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

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

maximum frequency, which means that Ts max is

around 34 % of TH.

2.4 Output Section

The H-drive signal is sent to the output through a

shaping stage which also controls the H-drive duty

cycle (I

2C adjustable) (see Figure 11). In order to

secure the scanning power part operation, the out-

put is inhibited in the following cases:

– when VCC or VDD are too low

– when the XRAY protection is activated

– during the Horizontal flyback

– when the HDrive I2C bit control is off.

The output stage consists of a NPN bipolar tran-

sistor. Only the collector is accessible (see

Figure 13).

Figure 13.

This output stage is intended for “reverse” base

control, where setting the output NPN in off-state

will control the power scanning transistor in off-

state.

The maximum output current is 30mA, and the

corresponding voltage drop of the output VCEsat is

0.4V Max.

Obviously the power scanning transistor cannot be

directly driven by the integrated circuit. An inter-

face has to be added between the circuit and the

power transistor either of bipolar or MOS type.

2.5 X-RAY Protection

The X-Ray protection is activated by application of

a high level on the X-Ray input (more than 8.2V on

Pin 25). It inhibits the H-Drive and B+ outputs.

This activation is internally delayed by 2 lines to

avoid erratic detection when short parasitics are

present .

HOsc

Sawtooth

7/8TH

1/8 TH

Flyback

Internally

shaped Flyback

HDrive

Duty Cycle

1.6V

4.0V

6.4V

500

Ω

HFLY

GND 0V

20k

Ω

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