SSL1750 datasheet(12/29 Pages) NXP

12 / 29 page

SSL1750_1

Product data sheet

Rev. 01 — 15 September 2008

12 of 29

NXP Semiconductors

SSL1750

SMPS control IC for LED drivers

7.2.7 Overcurrent protection (pin PFCSENSE)

The maximum peak current is limited cycle-by-cycle by sensing the voltage across an

external sense resistor (RSENSE1) on the source of the external MOSFET. The voltage is

measured via the pin PFCSENSE.

7.2.8 Mains undervoltage lockout / brownout protection (pin VINSENSE)

To prevent the PFC from operating at very low mains input voltages, the voltage on pin

VINSENSE is sensed continuously. As soon as the voltage on this pin drops below the

Vstop(VINSENSE) level, switching of the PFC is stopped. If the low mains situation continues,

the PFC bus voltage eventually drops. The voltage on pin VOSENSE then drops below the

Vstart(fb) level and the ﬂyback converter is also disabled.

The voltage on pin VINSENSE is clamped to a minimum value,

(Vstart(VINSENSE) −∆Vpu(VINSENSE), for a fast restart as soon as the mains input voltage is

restored after a mains dropout.

7.2.9 Overvoltage protection (pin VOSENSE)

An overvoltage protection circuit has been built in to prevent output overvoltage during

load steps and mains transients.

As soon as the voltage on pin VOSENSE exceeds the Vovp(VOSENSE) level, switching of the

power factor correction circuit is inhibited. Switching of the PFC recommences as soon as

the voltage on VOSENSE voltage drops below the Vovp(VOSENSE) level again.

When the resistor between pin VOSENSE and ground is open, the overvoltage protection

is also triggered.

7.2.10 PFC open loop protection (pin VOSENSE)

The power factor correction circuit does not start switching until the voltage on pin

VOSENSE is above the Vth(ol)(VOSENSE) level. This protects the circuit from open loop and

VOSENSE short situations. As pin VOSENSE draws a small input current, switching is

also inhibited when the pin is left open.

Fig 7.

Burst mode control

Vburst(H)

Vburst(L)

soft-stop

ton control

soft-start

VVOSENSE

envelop of

peak current

014aaa019

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