TDA4886A Datasheet, PDF (8/52 Pages) NXP Semiconductors – 140 MHz video controller with I2C-bus

Philips Semiconductors
140 MHz video controller with I²C-bus
Product specification
TDA4886A
1. Control bit FPOL = 0
The cathode voltage (DC-coupled) is divided by a
voltage divider and fed back to the IC. During the
output clamping pulse it is compared with an
adjustable feedback reference voltage with a range of
approximately 5.77 to 4.05 V. Any difference will lead
to a reference black level correction (control bit
PEDST = 0) or pedestal black level correction (control
bit PEDST = 1) by charging or discharging the
integrated capacitor which stores the black level
information between the output clamping pulses.
The DC voltages of the output stages should be
designed in such a way that the reference black
level/pedestal black level is within the range of
0.5 to 2.5 V.
For correct operation it is necessary that there is
enough headroom for ultra black signals (negative
brightness setting, pedestal black level if control bit
PEDST = 1). Any clipping with the video supply
voltage at the cathode can disturb the signal rise/fall
times or the black level stabilization.
2. Control bit FPOL = 1
For applications with AC-coupled cathodes the signal
outputs are fed back internally. During the output
clamping pulse they are compared with a feedback
reference voltage of approximately 0.75, 1.0, 1.25 or
1.5 V (depending on the values of control bits BLH2
and BLH1). These values ensure a good adaptability
to discrete and integrated post amplifiers as well.
For black level restoration the DAC outputs (FB/R₁,
FB/R₂ and FB/R₃) with a range of approximately
5.77 to 4.05 V can be used.
The use of pedestal blanking allows a very simple
black level restoration with a DC diode clamp instead
of a complicated pulse restoration circuit because the
pedestal black level is the most negative output signal.
7.6 Clamping and blanking pulses
The pin CLI of TDA4886A can be directly connected to
pin CLBL of e.g. TDA4855 sync processor for input
clamping pulses and vertical blanking pulses.
The threshold for the input clamping pulse (typical 3 V) is
higher than the threshold for the vertical blanking pulse
(typical 1.4 V) but there must be no blanking during input
clamping. Thus vertical blanking only is enabled if no input
clamping is detected. For this reason the input clamping
pulse must have rise/fall times faster than 75 ns/V during
the transition from 1.2 to 3.5 V and vice versa. The internal
vertical blanking pulse will be delayed by typical 270 ns.
During the vertical blanking pulse at pin CLI signal
blanking, brightness blanking and with control bit
PEDST = 1 pedestal blanking will be activated. Input
clamping pulses during vertical blanking will not switch off
blanking.
For proper input clamping the input signals have to be at
black level during the input clamping pulse.
An input pulse at pin HFB (e.g. horizontal flyback pulse)
will be scanned with two thresholds. If the input pulse
exceeds the first one (typical 1.4 V) signal blanking,
brightness blanking and if control bit PEDST = 1
pedestal blanking will be activated. If the input pulse
exceeds the second one (typical 3 V) additionally output
clamping will be activated. The vertical blanking pulse can
also be mixed with the horizontal flyback pulse at pin HFB.
7.7 On Screen Display (OSD)
If the fast blanking input signal at pin FBL exceeds the
threshold (typical 1.4 V) the input signals are blanked
(signal blanking) and OSD signals are enabled. Then any
signal at pins OSD₁, OSD₂ or OSD₃ exceeding the same
threshold will create an insertion signal with an amplitude
of 120% of the nominal colour signal (approximately 74%
of the maximum colour signal). The amplitude can be
controlled by OSD contrast (driven by the I²C-bus) with a
range of 12 dB. The OSD signals are inserted at the same
point as the contrast controlled input signals and will be
treated with brightness and gain control like normal input
signals.
With control bit DISO = 1 the OSD signal insertion and fast
blanking (pin FBL) are disabled.
7.8 Subcontrast adjustment, contrast modulation
and beam current limiting
The pin LIM is a linear contrast control pin which allows
subcontrast setting, contrast modulation and beam current
limiting. The maximum contrast is defined by the actual
I²C-bus setting. Input signals at pin LIM act on video and
OSD signals and do not affect the contrast bit resolution.
To achieve brightness uniformity over the screen, scan
dependent contrast modulation is possible.
1998 Dec 04
8