TDA4855 Datasheet, PDF (9/44 Pages) NXP Semiconductors – Autosync Deflection Controller ASDC

Philips Semiconductors
Autosync Deflection Controller (ASDC)
Preliminary specification
TDA4855
To achieve a stabilized amplitude the free-running
frequency f_osc(V), without adjustment, should be at least
10% lower than the minimum trigger frequency.
The contributions shown in Table 3 can be assumed.
Table 3 Calculation of f_osc(V) total spread
Contributing elements:
Minimum frequency offset between f_osc(V)
and lowest trigger frequency
Spread of IC
Spread of R_VREF
Spread of C_VCAP
Total
±10%
±3%
±1%
±5%
19%
Result for 50 to 110 Hz application:
f_{osc (V)} = ^{5--1--0--.-1--H--9--z--} = 42 Hz
Application hint: VAGC (pin 22) has a high input
impedance during scan, thus the pin must not be loaded
externally. Otherwise non-linearities in the vertical output
currents may occur due to the changing charge current
during scan.
Application hint: The full vertical sync range of 1 : 2.5 can
be made usable by incorporating an adjustment of the
free-running frequency. Also the complete sync range can
be shifted to higher frequencies (e.g. 70 to 160 Hz) by
reducing the value of C_VCAP.
Adjustment of vertical size, vertical shift and
S-correction
VPOS (pin 17) is the input for the DC adjustable vertical
picture shift. This pin provides a phase shift at the
sawtooth output VOUT1 and VOUT2 (pins 13 and 12) and
the EW drive output EWDRV (pin 11) in such a way, that
the whole picture moves vertically while maintaining the
correct geometry.
The amplitude of the differential output currents at VOUT1
and VOUT2 can be adjusted via input VAMP (pin 18).
This can be a combination of a DC adjustment and a
dynamic waveform modulation.
VSCOR (pin 19) is used to adjust the amount of vertical
S-correction in the output signal.
The adjustments for vertical size and vertical shift also
affect the waveforms of the EW parabola and the vertical
S-correction. The result of this interaction is that no
readjustment of these parameters is necessary after an
adjustment of vertical picture size or position.
Application hint: VPOS is a current input, which provides
an internal reference voltage while I_VPOS is in the specified
adjustment current range. By grounding VPOS (pin 17) the
symmetrical control range is forced to its centre value.
Application hint: VSCOR is a current input at 5 V.
Superimposed on this level is a very small positive-going
vertical sawtooth, intended to modulate an external
long-tailed transistor pair. This enables further optional DC
controls of functions which are not directly accessible such
as vertical tilt or vertical linearity (see Fig.17).
EW parabola (including horizontal size and trapezium
correction)
EWDRV (pin 11) provides a complete EW drive waveform.
EW parabola amplitude, DC shift (horizontal size) and
trapezium correction can be controlled via separate DC
inputs.
EWPAR (pin 21) is used to adjust the parabola amplitude.
This can be a combination of a DC adjustment and a
dynamic waveform modulation.
The EW parabola amplitude also tracks with vertical
picture size. The parabola waveform itself tracks with the
adjustment for vertical picture shift (VPOS).
Additional effort has been taken to generate a smooth
waveform at the top of the parabola. This is to avoid ringing
in the horizontal output stage.
EWWID (pin 32) offers two modes of operation:
1. Mode 1
Horizontal size is DC controlled via EWWID (pin 32)
and causes a DC shift at the EWDRV output. Also the
complete waveform is multiplied internally by a signal
proportional to the line frequency (which is detected
via the current at HREF (pin 28). This mode is to be
used for driving EW modulator stages which require a
voltage proportional to the line frequency.
2. Mode 2
EWWID (pin 32) is grounded. Then EWDRV is no
longer multiplied by the line frequency. The DC
adjustment for horizontal size must be added to the
input of the B+ control amplifier BIN (pin 5). This mode
is to be used for driving EW modulators which require
a voltage independent of the line frequency.
EWTRP (pin 20) is used to adjust the amount of trapezium
correction in the EW drive waveform.
1996 Jul 18
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