Philips Semiconductors
Product specification
Economy Autosync Deflection Controller
(EASDC)
TDA4858
CLSEL (pin 10) is the selection input for the position of the
video clamping pulse. If CLSEL is connected to ground,
the clamping pulse is triggered with the trailing edge of
horizontal sync. For a clamping pulse which starts with the
leading edge of horizontal sync, pin 10 must be connected
FUNCTIONAL DESCRIPTION
Horizontal sync separator and polarity correction
HSYNC (pin 15) is the input for horizontal synchronization
signals, which can be DC-coupled TTL signals (horizontal
to VCC
.
or composite sync) and AC-coupled negative-going video
sync signals. Video syncs are clamped to 1.28 V and
sliced at 1.4 V. This results in a fixed absolute slicing level
of 120 mV related to sync top.
The lower level of the sandcastle pulse is the vertical
blanking pulse, which is derived directly from the internal
oscillator waveform. It is started by the vertical sync and
stopped with the start of the vertical scan. This results in
optimum vertical blanking.
For DC-coupled TTL signals the input clamping current is
limited. The slicing level for TTL signals is 1.4 V.
Blanking will be activated continuously, if one of the
following conditions is true:
The separated sync signal (either video or TTL) is
integrated on an internal capacitor to detect and normalize
the sync polarity.
No horizontal flyback pulses at HFLB (pin 1)
X-ray protection is activated
Normalized horizontal sync pulses are used as input
signals for the vertical sync integrator, the PLL1 phase
detector and the frequency-locked loop.
Soft start of horizontal drive [voltage at HPLL2 (pin 31)
is LOW]
Supply voltage at VCC (pin 9) is low (see Fig.14)
Vertical sync integrator
PLL1 is unlocked while frequency-locked loop is in
search mode.
Normalized composite sync signals from HSYNC are
integrated on an internal capacitor in order to extract
vertical sync pulses. The integration time is dependent on
the horizontal oscillator reference current at HREF
(pin 28). The integrator output directly triggers the vertical
oscillator. This signal is available at VSYNC (normally
vertical sync input; pin 14), which is used as an output in
this mode.
Blanking will not be activated if the horizontal sync
frequency is below the valid range or there are no sync
pulses available.
Frequency-locked loop
The frequency-locked loop can lock the horizontal
oscillator over a wide frequency range. This is achieved by
a combined search and PLL operation. The frequency
range is preset by two external resistors and the
Vertical sync slicer and polarity correction
Vertical sync signals (TTL) applied to VSYNC (pin 14) are
sliced at 1.4 V. The output signal of the sync slicer is
integrated on an internal capacitor to detect and normalize
the sync polarity.
fmin
1
recommended ratio is
=
----------
fmax
-------
3.5
Larger ranges are possible by extended applications.
If a composite sync signal is detected at HSYNC, VSYNC
is used as output for the integrated vertical sync (e.g. for
power saving applications).
Without a horizontal sync signal the oscillator will be
free-running at fmin. Any change of sync conditions is
detected by the internal coincidence detector. A deviation
of more than 4% between horizontal sync and oscillator
frequency switches the horizontal section into search
mode. This means that PLL1 control currents are switched
off immediately. Then the internal frequency detector
starts tuning the oscillator. Very small DC currents at
HPLL1 (pin 26) are used to perform this tuning with a well
defined change rate. When coincidence between
Video clamping/vertical blanking generator
The video clamping/vertical blanking signal at CLBL
(pin 16) is a two-level sandcastle pulse which is especially
suitable for video ICs such as the TDA488x family, but also
for direct applications in video output stages.
The upper level is the video clamping pulse, which is
triggered by the trailing edge of the horizontal sync pulse.
The width of the video clamping pulse is determined by an
internal single-shot multivibrator.
horizontal sync and oscillator frequency is detected,
the search mode is replaced by a normal PLL operation.
1997 Oct 27
6
NXP [ NXP ]
