SSL4120 datasheet(26/48 Pages) NXP

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SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

26 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

Below the minimum frequency level, VSNSFB is clamped at Vclamp(SNSFB) = 3.2 V. This

clamp enables a fast recovery of the output voltage regulation loop after an overshoot of

the output voltage. The maximum current the clamp can deliver is Iclamp(SNSFB) =7.3 mA.

7.8.7 HBC open-loop protection, OLP-HBC (SNSFB pin)

Under normal operating conditions, the optocoupler current is between Ifmin(SNSFB) and

Ifmax(SNSFB) and pulls down the voltage at the SNSFB pin. Due to an error in the feedback

loop, the current could be less than Ifmin(SNSFB) with the HBC controller delivering

maximum output power.

The HBC controller features open-loop protection (OLP-HBC) which monitors the SNSFB

pin voltage. When VSNSFB >Volp(SNSFB), the protection timer is started. The Restart state

is activated if the OLP condition is still present after the protection time has elapsed.

7.8.8 HBC soft start (SSHBC/EN pin)

The relationship between switching frequency and output current is not constant. It

depends strongly on the output voltage VO and Vboost. This relationship can be complex.

The SSL4120 contains a soft-start function to ensure that the resonant converter starts or

restarts with safe currents. This soft-start function forces a start at such a high frequency

that the currents are acceptable under all conditions. The soft-start then slowly decreases

the frequency. Normally, output voltage regulation takes over frequency control before

soft-start reaches its minimum frequency. Limiting the output current during start-up also

limits the rate at which the output voltage rises and prevents an overshoot.

Soft-start utilizes the SSHBC/EN pin voltage. The external capacitor Css(HBC) sets the

timing of the soft-start. The SSHBC/EN pin is also used as an enable input. Soft-start

voltage levels are above the enable voltage thresholds.

Fig 14. Transfer function of feedback input

VSNSFB

ISNSFB

Vpu(SNSFB)

Ifmin(SNSFB)

VRFMAX

Ifmax(SNSFB)

VSSHBC = 8.4 V

Iolp(SNSFB)

Volp(SNSFB)

Vfmin(SNSFB)

Vfmax(SNSFB)

Vclamp(SNSFB)

VSNSFB

Iclamp(SNSFB)

014aaa862

Vfmax(ss)(RFMAX)

Vfmax(fb)(RFMAX)

SSL4120 Datasheet(PDF) 26 Page - NXP Semiconductors

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