TDA9112A datasheet(49/60 Pages) STMICROELECTRONICS

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TDA9112A

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internal reference and so the output voltage is I²C-

bus adjustable by means of

BREF I²C-bus control.

Both step-up (DC/DC converter output voltage

higher than its input voltage) and step-down (out-

put voltage lower than input) can be built.

9.7.1

Synchronization of DC/DC controller

For sake of application flexibility, the output drive

signal on BOut pin can be synchronized with one of

four events in Table 9. For the first line case, the

synchronization instant is every second top of hor-

izontal VCO saw tooth. See Figure 7.

9.7.2

Soft-start and soft-stop on B-drive

The soft-start and soft-stop procedure is carried

out at each switch-on or switch-off of the B-drive

signal, either via HBOutEn I²C-bus bit or after re-

set of XRayAlarm I²C-bus flag, to protect external

power component. See Figure 10 and sub chapter

Safety functions

on page 50.

The drive signal on BOut pin can be switched off

alone by means of BMute I²C-bus bit, without

switching off the drive signal on pin HOut. The

switch-off is quasi-immediate, without the soft-stop

procedure. At switching back on, the soft-start of

the DC/DC controller is performed, timed by an in-

ternal timing circuit, see Figure 18.

When BSafeEn I²C-bus bit is enabled, the drive

signal on BOut pin will go off as soon as the hori-

zontal PLL1 indicates unlocked state, without the

soft-stop. Resuming of locked state will initiate the

soft-start mechanism of the DC/DC controller,

timed by an internal timing circuit.

Table 9. IDC/DC controller Off-to-On edge timing

Figure 18. DC/DC converter controller block diagram

BOutPh

(Sad07h/D7)

BOHEdge

(Sad17h/D3)

Timing of Off-to-On transition on BOut output

VCO ramp top at Horizontal frequency divided by two

Middle of H-flyback plus tBTrigDel

Falling edge of H-drive signal

Rising edge of H-drive signal

N type

Soft start

H-drive edge

H-fly-back

~500ns

Monostable

P type

Feedback

(I²C)

B-drive inhibition

(I²C)

(+delay)

(I²C)

VBReg

VC2

÷2

BOut

BISense

HPosF

BComp

BRegIn

BOutPol

BOutPh

BOHEdge

VThrBIsCurr

VCO

VCC

(safety functions)

timing

B-drive protection at H-unlock

(safety functions)

Safety block

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