SSL4120T datasheet(29/47 Pages) NXP

29 / 47 page

SSL4120T

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Objective data sheet

Rev. 1 — 21 June 2012

29 of 47

NXP Semiconductors

SSL4120T

Resonant power supply control IC with PFC

7.8.10.2

Overcurrent regulation, OCR-HBC

The lowest comparator levels at the SNSCURHBC pin, Vocr(HBC) (typ.

−0.5 V and +0.5 V),

relate to the overcurrent regulation voltage. There are comparators for both the positive

and negative polarities. The positive comparator is active during the high-side on-time and

the following high-side to low-side non-overlap time. The negative comparator is active

during the remaining time. If either level is exceeded, the frequency will be slowly

increased. This is accomplished by discharging the soft start capacitor. Each time the

OCR level is exceeded, the event is latched until the next stroke and the soft start

discharge current is enabled. When both the positive and negative OCR levels are

exceeded, the soft start discharge current will flow continuously.

Overcurrent regulation is very effective at limiting the output current during start-up. A

smaller soft start capacitor can be used to achieve a faster start-up. Using a smaller

capacitor may result in an output current that is too high at times, but the OCR function will

slow down the frequency sweep when needed to keep the output current within the

specified limits. Figure 18 shows the operation of the OCR during output voltage start-up.

Fig 17. Boost voltage compensation

VCur(HBC) = Rcur(HBC) × ICur(HBC)

Iocr(high)

Iocp(high)

Iocp(nom)

Iocr(nom)

−Iocr(nom)

−Iocp(nom)

−Iocr(high)

−Iocp(high)

ICur(HBC)

ISNSCURHBC

Vreg

Vuvp

VBoost

GATELS

GATEHS

sink current only with positive VSNSCURHBC

sink

source

low VBoost

strong compensation

high OCP

low VBoost

strong compensation

high OCR

nominal VBoost

no compensation

nominal OCP

nominal VBoost

no compensation

nominal OCR

VSNSCURHBC

014aaa865

VSNSCURHBC

Vocr(HBC)

−Vocr(HBC)

Vocp(HBC)

−Vocp(HBC)

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