SSL4120 datasheet(9/48 Pages) NXP

9 / 48 page

SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

9 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

7.2.3 High-side driver floating supply (SUPHS pin)

The high-side driver is supplied by an external bootstrap buffer capacitor, CSUPHS. The

bootstrap capacitor is connected between the high-side reference the HB pin and the

high-side driver supply input the SUPHS pin. CSUPHS is charged from the SUPREG pin

using an external diode DSUPHS.

Careful selection of the appropriate diode minimizes the voltage drop between SUPREG

and SUPHS, especially when large MOSFETs and high switching frequencies are used.

7.2.4 High-voltage supply input (SUPHV pin)

In a stand-alone power supply application, the SUPHV pin is connected to Vboost. CSUPIC

and CSUPREG are charged using the HV start-up source (which delivers a constant current

from SUPHV to SUPIC) using this pin.

Short-circuit protection on the SUPIC pin (SCP-SUPIC; see Section 7.9) limits dissipation

in the HV start-up source when SUPIC is shorted to ground. SCP-SUPIC limits the current

on SUPHV to Ired(SUPHV) when the voltage on SUPIC is less than Vscp(SUPIC).

Under normal operating conditions, the SUPIC pin voltage exceeds Vscp(SUPIC) very

quickly after start-up and the HV start-up source switches to Inom(SUPHV).

During start-up and restart, the HV start-up source charges CSUPIC and regulates the

voltage on SUPIC using hysteretic control. The start level has a small amount of

hysteresis Vstart(hys)(SUPIC). The HV start-up source switches-off when VSUPIC exceeds the

start level Vstart(hvd)(SUPIC). Current consumption through the SUPHV pin is low

(Itko(SUPHV)).

Once start-up is complete and the HBC controller is operating, SUPIC is supplied from the

HBC transformer auxiliary winding. In operational state, the HV start-up source is

disabled.

7.3 Flow diagram

The operation of the SSL4120 can be divided into a number of states (see Figure 3). The

abbreviations used in Figure 3 are explained in Table 8.

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