STV6886 View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'STV6886' PDF : 43 Pages View PDF
STV6886
2.4 Output Section
The H-drive signal is sent to the output through a
shaping stage which also controls the H-drive duty
cycle (I2C adjustable) (see Figure 11). In order to
secure the scanning power part operation, the out-
put is inhibited in the following cases:
– when VCC or VDD are too low
– when the XRAY protection is activated
– during the Horizontal flyback
– when the HDrive I2C bit control is off.
The output stage consists of a NPN bipolar tran-
sistor. Only the collector is accessible (see
Figure 13).
Figure 13.
This output stage is intended for “reverse” base
control, where setting the output NPN in off-state
will control the power scanning transistor in off-
state.
The maximum output current is 30mA, and the
corresponding voltage drop of the output VCEsat is
0.4V Max.
Obviously the power scanning transistor cannot be
directly driven by the integrated circuit. An inter-
face has to be added between the circuit and the
power transistor either of bipolar or MOS type.
2.5 X-RAY Protection
The X-Ray protection is activated by application of
a high level on the X-Ray input (more than 8.2V on
Pin 25). It inhibits the H-Drive and B+ outputs.
This activation is internally delayed by 2 lines to
avoid erratic detection when short parasitics are
present .
This protection is latched; it may be reset either by
VCC switch-off or by I2C (see Figure 14 on
page 28).
2.6 Horizontal and Vertical Dynamic Focus
For dynamic focus adjustment, the STV6886 deliv-
ers the sum of two signals on pin 10:
– a parabolic waveform at horizontal frequency,
– a parabolic waveform at vertical frequency.
The horizontal parabola comes from a sawtooth in
phase advance with flyback pulse middle. The
phase advance versus horizontal flyback middle is
kept constant versus frequency (about 1µs). Sym-
metry and amplitude are I2C adjustable (see
Figure 15 on page 28).
The vertical parabola is tracked with VPOS and
VAMP. Its amplitude can be adjusted. It is also af-
fected by S and C corrections.
This positive signal once amplified is to be sent to
the CRT focusing grids.
Because the DC/DC converter is triggered by the
HFocus sawtooth, it is recommended to connect a
capacitor to pin 9, even if HFocus is not needed.
The capacitor value is critical only if Focus is used.
27/43
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