SSL4120 datasheet(28/48 Pages) NXP

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SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

28 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

The fast charge and discharge is used for the upper frequency range where

VSSHBC/EN <Vss(hf-lf)(SSHBC) = 5.6 V. In the upper frequency range, the currents in the

converter do not react strongly to frequency variations.

The slow charge and discharge speed is used for the lower frequency range where

VSSHBC/EN >Vss(hf-lf)(SSHBC) = 5.6 V. In the lower frequency range, the currents in the

converter react strongly to frequency variations.

Section 7.8.10.2 describes how the two-speed soft-start function is used for overcurrent

regulation.

The soft-start capacitor is not charged or discharged during non-operation time in burst

mode. The soft-start voltage does not change during this time.

7.8.8.3

Soft-start reset

Some protection functions, such as overcurrent protection, require fast correction of the

operating frequency set point, but do not require switching to stop. See the protection

overview in Section 7.9 for details on which protection functions use this step to the

maximum frequency. The SSL4120 has a special fast soft-start reset feature for the HBC

controller that forces Vfmax(ss)(RFMAX) on the RFMAX pin. Soft-start reset is also used when

the HBC controller is enabled using the SSHBC/EN pin or after a restart to ensure a

safe-start at maximum frequency. Soft-start reset is not used when the operation was

stopped in burst mode.

When a protection function is activated, the oscillator control input is disconnected from

the soft-start capacitor Css(HBC) which is connected between the SSHBC/EN pin and

ground. The switching frequency is immediately set to a maximum. Setting the switching

frequency to a maximum restores safe switching operation in most cases. At the same

time, the capacitor is discharged to the maximum frequency level Vfmax(SSHBC). Once

VSSHBC/EN has reached this level, the oscillator control input is connected to the pin again

and the normal soft-start sweep follows. Figure 16 shows the soft-start reset and the

two-speed frequency sweep downwards.

Fig 16. Soft-start reset and two-speed soft-start

Protection

Vfmax(SSHBC)

VSSHBC/EN

Vfmin(SSHBC)

fmin

fHB

fmax

off

fmax

forced

fast

sweep

slow sweep

regulation

Vss(hf-lf)(SSHBC)

014aaa864

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