SSL4120T datasheet(12/47 Pages) NXP

12 / 47 page

SSL4120T

All information provided in this document is subject to legal disclaimers.

Objective data sheet

Rev. 1 — 21 June 2012

12 of 47

NXP Semiconductors

SSL4120T

Resonant power supply control IC with PFC

7.5.2 Protection and restart timer

The SSL4120T contains a programmable timer which can be used for timing several

protection functions. The timer can be used in two ways - as a protection timer and as a

restart timer. The timing of the timers can be set independently via an external resistor

Rprot and capacitor Cprot connected to pin RCPROT.

7.5.2.1

Protection timer

Certain error conditions can be allowed to persist for a period of time before protective

action needs to be taken. The protection timer defines the protection period - how long the

error is allowed to persist before the protection function is triggered. The protection

functions that use the protection timer can be found in the protection overview in

Section 7.9.

Figure 5 shows the operation of the protection timer. When an error condition occurs, a

fixed current Ich(slow)(RCPROT) (typ. 100

μA) flows out of the RCPROT pin and charges

Cprot. Rprot will cause the voltage to rise exponentially. The protection time has elapsed

when the voltage on RCPROT reaches the upper switching level Vu(RCPROT) (typ. 4 V). At

this instant, the appropriate protective action is taken and Cprot is discharged.

If the error condition is removed before the voltage on RCPROT reaches Vu(RCPROT), Cprot

is discharged via Rprot and no action is taken.

The voltage on RCPROT may be raised above Vu(RCPROT) by an external circuit to force a

restart.

7.5.2.2

Restart timer

Certain error conditions require the IC to be disabled for a period of time, particularly when

the error condition can cause components to overheat. In such cases, the IC should be

disabled to allow the power supply to cool down, before restarting automatically. The

restart time is determined by the restart timer. The restart timer is active in the Restart

state. The protection functions that trigger a restart can be found in the protection

overview in Section 7.9.

Fig 5.

Operation of the protection timer

passed

none

present

short

error

long

error

repetative

error

Vu(RCPROT)

Ich(slow)(RCPROT)

IRCPROT

Error

VRCPROT

Protection time

014aaa853

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