SSL4120 datasheet(13/48 Pages) NXP

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SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

13 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

7.5.2 Protection and restart timer

The SSL4120 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 is set independently using the external resistor Rprot

and capacitor Cprot connected to the RCPROT pin.

7.5.2.1

Protection timer

Certain error conditions are allowed to persist for a time period before protective action

must be taken. The protection timer defines the protection period (how long the error can

persist before the protection function is triggered). The protection functions that use the

protection timer are 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) = 100 A flows from the RCPROT pin and charges Cprot.

Rprot causes the voltage to increase exponentially. The protection time elapses when the

RCPROT voltage reaches the upper switching level. When the protection time has

elapsed, the appropriate protective action is taken and Cprot is discharged.

If the error condition is removed before the voltage on the RCPROT pin reaches

Vu(RCPROT), Cprot is discharged using Rprot and no action is taken.

The RCPROT voltage can be forced > Vu(RCPROT) by an external circuit to trigger a restart.

7.5.2.2

Restart timer

The IC must be disabled for a time period on certain error conditions. Particularly when

the error condition can cause components to overheat. In such cases, the IC is disabled to

allow the power supply to cool down. It automatically restarts. The restart timer

determines the restart time. The restart timer is active in the Restart state. The protection

functions which trigger a restart are found in the protection functions 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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