STV9118 datasheet(36/46 Pages) STMICROELECTRONICS

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STV9118

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10.8 - MISCELLANEOUS

10.8.1 - 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 and X-ray protection.

For supply voltage supervision, refer to paragraph

Power supply and voltage references on page 25

and Figure 1. A schematic diagram putting togeth-

er all safety functions and composite PLL1 lock

and V-blanking indication is in Figure 15.

10.8.2 - Soft start and soft stop functions

For soft start and soft stop features for H-drive and

B-drive signal, refer to paragraph Soft-start and

soft-stop on H-drive on page 29 and sub chapter-

DC/DC CONTROLLER SECTION on page 34, re-

spectively. See also the Figure 10. 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 figure, the first

to phase-in and last to phase-out being the H-drive

signal, which is to better protect the power stages

at abrupt changes like switch-on and off. The tim-

ing of phase-in and phase-out only depends on

the capacitance connected to HPosF pin which is

virtually unlimited for this function. Yet it has a dual

function (see paragraph PLL1 on page 26), so a

compromise thereof is to be found.

10.8.3 - X-ray protection

The X-ray protection is activated if the voltage lev-

el on XRay input exceeds VThrXRay threshold. 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 detec-

tion 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 I

2C bus bit XRayReset (see chap-

ter I2C BUS CONTROL REGISTER MAP on

page 21).

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