TDA9112A View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'TDA9112A' PDF : 60 Pages View PDF
TDA9112A
9.8 Miscellaneous
9.8.1 Safety functions
The safety functions comprise supply voltage
monitoring with appropriate actions, soft start and
soft stop features on H-drive and B-drive signals
on HOut and BOut outputs, B-drive cut-off at unlock
condition and X-ray protection.
For supply voltage supervision, refer to subsection
9.1.1 and Figure 1. A schematic diagram putting to-
gether all safety functions and composite PLL1
lock and V-blanking indication is in Figure 19.
9.8.1.1 Soft start and soft stop function
For soft start and soft stop features for H-drive and
B-drive signal, refer to subsection 9.3.7 and subsec-
tion 9.7 , respectively. See also the Figure 10 and
Figure 11. Regardless why the H-drive or B-drive
signal are switched on or off (I²C-bus command,
power up or down, X-ray protection), the signals
always phase-in and phase-out in the way drawn
in the figures, the first to phase-in and last to
phase-out being the H-drive signal, which is to bet-
ter protect the power stages at abrupt changes like
switch-on and off. The timing of phase-in and
phase-out depends on the capacitance connected
to HPosF pin which is virtually unlimited for this
function. However, as it has a dual function (see
subsection 9.3.2 ), a compromise thereof is to be
found.
The soft stop at power down condition can be con-
sidered as a special case. As at this condition the
thresholds VHOn, VBOn and VHBNorm depend on
the momentary level of supply voltage (marked
VHOn’, VBOn’, VHBNorm’ in Figure 11), the timing of
soft stop mechanism depends, apart from the ca-
pacitance on HPosF, also on the falling speed of
supply voltage. The device is capable of perform-
ing a correct soft stop sequence providing that, at
the moment the supply voltage reaches VCCStop,
the voltage on HPosF has already fallen below
VHOn (Section 9.8).
9.8.1.2 B-drive cut-off at unlock condition
This function is described in subsection 9.7.2 .
9.8.1.3 X-ray protection
The X-ray protection is activated if the voltage lev-
el on XRay input exceeds VThrXRay threshold and if
the VCC is higher than the voltage level VCCXRay-
En. As a consequence, the H-drive and B-drive
signals on HOut and BOut outputs are inhibited
(switched off) after a 2-horizontal deflection line
delay provided to avoid erratic excessive X-ray
condition detection at short parasitic spikes. The
XRayAlarm I²C-bus flag is set to 1 to inform the
MCU.
This protection is latched; it may be reset either by
VCC drop or by I²C-bus bit XRayReset
(see Chapter 8 - page 27).
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