1999 Nov 10

4

Philips Semiconductors

Preliminary specification

Full bridge vertical deflection output circuit

in LVDMOS

TDA8357J

FUNCTIONAL DESCRIPTION

Vertical output stage

The vertical driver circuit has a bridge configuration.

The deflection coil is connected between the

complimentary driven output amplifiers. The differential

input circuit is voltage driven. The input circuit is specially

designed for direct connection to driver circuits delivering

a differential signal but it is also suitable for single-ended

applications. The output currents of the driver device are

converted to voltages by the conversion resistors

and INB. The differential input voltage is compared with

proportional with the output current. The relationship

between the differential input current and the output

current is defined by:

2

The output current should measure 0.5 to 2.0 A (p-p) and

input voltage range is 100 mV to 1.6 V for each input. The

formula given does not include internal bondwire

internal bondwire resistance (typical value of 50 m

Ω) the

actual value of the current in the deflection coil will be

about 5% lower than calculated.

Flyback supply

The flyback voltage is determined by the flyback supply

very high efficiency is achieved. The available flyback

to the absence of a coupling capacitor which is not

required in a bridge configuration. The very short rise

and fall times of the flyback switch are determined mainly

by the slew-rate value of more than 300 V/

µs.

Protection

The output circuit contains protection circuits for:

• Too high die temperature

• Overvoltage of output A.

Guard circuit

A guard circuit with output pin GUARD is provided.

The guard circuit generates a HIGH-level during the

flyback period. The guard circuit is also activated for one

of the following conditions:

• During an open-loop condition.

The guard signal can be used for blanking the picture tube

and signalling fault conditions. The vertical

synchronization pulses of the guard signal can be used by

an On Screen Display (OSD) microcontroller.

Damping resistor compensation

HF loop stability is achieved by connecting a damping

Both the resistor current and the deflection coil current flow

coil current at the start of the scan.

The difference in the damping resistor current values

during scan and flyback have to be externally

compensated in order to achieve a short settling time.

with a zener diode is connected between pins OUTA

and INA (see Fig.4). The zener diode voltage value should

where:

at flyback

R

CMP

V

FB

V

loss FB

()

–

V

Z

–

() R

D1

×

R

CV1

×

V

FB

V

loss FB

()

–

I

coil peak

()

R

coil

×

–

() R

M

×

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