TDA4780 datasheet(8/44 Pages) PHILIPS

8 / 44 page

1997 Feb 06

Philips Semiconductors

Preliminary speciﬁcation

RGB video processor with automatic

cut-off control and gamma adjust

TDA4780

Automatic cut-off control

During leakage measurement time the leakage current is

compensated in order to get a reference voltage at the

cut-off measurement info pin. This compensation value is

stored in an external capacitor. During cut-off current

measurement times for the R, G and B channels, the

voltage at this pin is compared with the reference voltage,

which is individually adjustable via I2C-bus for each colour

channel. The control voltages that are derived in this way

are stored in the external feedback capacitors. Shift stages

add these voltages to the corresponding output signals.

The automatic cut-off control may be disabled via the

I2C-bus. In this mode the output voltage is clamped to

2.5 V. Clamping periods are the same as the cut-off

measurement periods.

Signal limiting

The TDA4780 provides two kinds of signal limiting.

First, an average beam limiting, that reduces signal level if

a certain average is exceeded. Second, a peak drive

limiting, that is activated if one of the RGB signals even

shortly exceeds a via I2C-bus adjusted threshold.

The latter can be either referred to the cut-off

measurement level of the outputs or to ground.

When signal limiting occurs, contrast is reduced, and at

minimum contrast brightness is reduced additionally.

Sandcastle decoder and timer

A 3-level detector separates the sandcastle pulse into

combined line and field pulses, line pulses, and clamping

pulses. The timer contains a line counter and controls the

cut-off control measurement.

Application with a 2-level 5 V sandcastle pulse is possible.

Switch on delay circuit

After switch on all signals are blanked and a warm up test

pulse is fed to the outputs during the cut-off measurement

lines. If the voltage at the cut-off measurement input

exceeds an internal level the cut-off control is enabled but

the signal remains still blanked. In the event of output

clamping, the cut-off control is disabled and the switch on

procedure will be skipped.

Y output and hue adjust

The TDA4780 contains a D/A converter for hue adjust.

The analog information can be fed, e.g. to the

multistandard decoder TDA4650 or TDA4655. This output

pin may be switched to a Y output signal, which can be

used for scan velocity modulation (SCAVEM). The Y

output is the Y input signal or the matrixed (RGB) input

signal according to the switch position of the fast switch.

I2C-bus

The TDA4780 contains an I2C-bus receiver for control

function.

ESD protection

The Pins are provided with protection diodes against

ground and supply voltage (see Chapter “Internal pin

configurations”). I2C-bus input pins do not shunt the

I2C-bus signals in the event of missing supply voltage.

EMC

The pins are protected against electromagnetic radiation.

TDA4780 Datasheet(PDF) 8 Page - NXP Semiconductors

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