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Miscellaneous
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STMicroelectronics Confidential
8
Miscellaneous
8.1
Summary of Safety Functions
Vertical, horizontal and B+ output stages will be inhibited (and for Vertical, voltage will be
maintained near mid-range, i.e. 3.5 / 8 of the reference voltage)
●
when the supply voltage is too low;
●
following a proper I²C instruction (Sad17h/d1 and Sad17h/d2).
Horizontal and B+ output stages will be inhibited if the X-ray protection threshold (8V on pin 25) is
exceeded. In such case, the H scanning and B+ are definitively stopped, and will only be reset by
switching the supply OFF or through I²C programming (Sad16h/d7). (Please notice that inhibition
affects only the output stages and not the oscillators. Consequently, I²C instructions will be still
transmitted during V Oscillator discharge).
In addition, the H output stage will be inhibited for the entire duration of H flyback, to prevent early
conduction of the scanning transistor.
for a simplified logic diagram. The following are not represented here, but
are already described in this Note:
●
Disable through X-ray pin will be activated only 2 lines after the threshold has been
exceeded, in order to prevent incorrect triggering on very short parasitic voltages;
●
Soft-start will take place every time when switching ON or enabling again. H Duty factor will
always start with maximum value (85%), and progressively reach its assigned value
(consequently, conduction time will begin with minimum value). Similarly, B+Out will begin with
minimum conduction time and increase progressively towards its assigned value.
Miscellaneous functions available on the TDA9112A only:
●
X-ray detection is not triggerable if the supply voltage is lower than 10.4V, to prevent triggering
on a rapid ON-OFF-ON sequence while its filter maintains X-ray input at high voltage.
Figure 23: Safety Functions (Simplified)
Supply
Ref V
H flyback
0.7V
X-ray
s
Q
H Output
Inhibition
V Output
Inhibition
I²C
H drive OFF
I²C
V ramp OFF
I²C
Reset
Supply
Reset
r
B+ Output
Inhibition