SSL4120 datasheet(24/48 Pages) NXP

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SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

24 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

Two external components determine the frequency range:

• Capacitor Cfmin connected between the CFMIN pin and ground sets the minimum

frequency in combination with an internally trimmed current source Iosc(min).

• Resistor Rfmax connected between the RFMAX pin and ground sets the frequency

range and thus the maximum frequency.

The oscillator frequency depends on the charge and discharge currents of Cfmin. The

charge and discharge current contains a fixed component, Iosc(min), which determines the

minimum frequency. In addition, a variable component that is 4.9 times greater than the

current in the RFMAX pin. The value of Rfmax and the RFMAX voltage pin determine

IRFMAX:

• The voltage on the RFMAX pin is Vfmin(RFMAX) = 0 V at the minimum frequency.

• The voltage on the RFMAX pin is Vfmax(fb)(RFMAX) = 1.5 V at the maximum feedback

frequency.

• The voltage on the RFMAX pin is Vfmax(ss)(RFMAX) = 2.5 V at the maximum soft-start

frequency.

The maximum frequency of the oscillator is internally limited. The HB frequency is limited

to flimit(HB) (minimum. 500 kHz). Figure 13 shows the relationship between VRFMAX, Rfmax,

Cfmin and fHB.

Fig 12. Determination of frequency

VOLTAGE PIN SSHBC

POLARITY INVERSION

(max 2.5 V)

VOLTAGE PIN RFMAX

CONVERSION TO CURRENT

via Rfmax

FEEDBACK CURRENT

PIN SNSFB

FIXED fmin CURRENT

CONVERSION TO

VOLTAGE (max 1.5 V)

(DIS-)CHARGE CURRENT

PIN CFMIN

CONVERSION TO

FRQUENCY via Cfmin

014aaa860

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