SSL4120 datasheet(22/48 Pages) NXP

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SSL4120

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Product data sheet

Rev. 2 — 1 November 2012

22 of 48

NXP Semiconductors

SSL4120

Resonant power supply controller IC with PFC for LED lighting

The HB transition time depends on the resonant current amplitude when switching starts.

There is a complex relationship between this amplitude, the frequency, Vboost and the

output voltage. Ideally, the IC switches on the MOSFET when the HB transition is

complete. If it waits any longer, VHB can swing back, especially at high output loads. The

advanced adaptive non-overlap time function controls the timing. The adaptive

non-overlap time function makes it unnecessary to choose a fixed dead time (which is

always a compromise). This saves on external components.

Adaptive non-overlap time sensing measures the HB slope after one MOSFET has been

switched off. Normally, the HB slope starts immediately (the voltage starts rising or falling).

Once the transition at the HB node is complete, the slope ends (the voltage stops

rising/falling). This slope end is detected by the ANO time sensor and the other MOSFET

is switched on. In this way, the non-overlap time is automatically optimized even when the

HB transition cannot be completed which minimizes switching losses.

Figure 10 illustrates the adaptive non-overlap time function operation of the inductive

mode.

The non-overlap time depends on the HB slope but it has upper and lower limits.

An integrated minimum non-overlap time, tno(min) prevents cross conduction occurring

under any circumstances.

The maximum non-overlap time is limited to the oscillator charge time. If the HB slope is

longer than the oscillator charge time (1⁄4 of HB switching period), the MOSFET is forced

to switch on. In this case, the MOSFET is not soft switching. This limitation ensures the

MOSFET on-time is at least 1⁄4 of the HB switching period at very high switching

frequencies.

7.8.4.2

Capacitive mode

Section 7.8.4.1 is true for normal operation with a switching frequency higher than the

resonance frequency. When an error condition occurs (for example; output short, load

pulse too high) the switching frequency is lower than the resonance frequency. The

resonant tank then has a capacitive impedance. In capacitive mode, the HB slope does

not start after the MOSFET switches off. Switching on the other MOSFET is not

recommended in this situation. The absence of soft switching increases dissipation in the

Fig 10. Adaptive non-overlap time function (normal inductive operation)

fast HB slope

Vboost

GATELS

GATEHS

slow HB slope

incomplete HB slope

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