SSL5021BTS datasheet(9/20 Pages) NXP

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SSL5021BTS

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Product data sheet

Rev. 2 — 11 March 2015

9 of 20

NXP Semiconductors

SSL5021BTS

Compact low-ripple buck LED driver IC

8.7 Supply management

The IC starts up when the voltage on the VCC pin increases to exceed Vstartup. The IC

locks out (stops switching) when the voltage on the VCC pin drops to below Vth(UVLO). The

hysteresis between the start and stop levels allows the VCC capacitor to supply the IC

during zero-crossings of the mains.

The SSL5021BTS incorporates an internal clamping circuit to limit the voltage on the VCC

pin. The clamp limits the voltage on the VCC pin to the maximum value, Vclamp(VCC). If the

maximum current of the external resistor minus the current consumption of the IC is lower

than the limiting value of IVCC in Table 4, no external Zener diode is required.

8.8 PTC or NTC function and high-temperature foldback

The PTC function or NTC function can be used as a control method for LED thermal

protection. The PTC resistor which is connected to DEMOVP pin senses the temperature.

When the voltage on DEMOVP pin is higher than the foldback level (Vth(fold)), the on-time

is reduced with the increased DEMOVP pin voltage. Then the average LED current is

reduced.

When the temperature keeps increasing, the Vth(ovp) is exceeded. The converter stops

switching. The IC restarts when OVP is triggered.

This feature is optional as shown in Figure 7 and Figure 8. PTC is normally shorted.

SSL5021BTS датащи(PDF) 9 Page - NXP Semiconductors