SSL21081AT datasheet(10/22 Pages) PHILIPS

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SSL21081AT

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Product data sheet

Rev. 6 — 3 October 2013

10 of 21

NXP Semiconductors

SSL21081AT

Compact non-dimmable LED driver IC

8.5 DVDT pin supply (dV/dt)

The DVDT pin is connected to an internal single-sided rectification stage. When a different

voltage with sufficient amplitude is supplied to the pin, the IC can be powered without any

other external power connection. This provides an effective method to prevent additional

high power losses, which are the result if a regulator were used for continuously powering

the IC. Unlike an auxiliary supply, additional inductor windings are not required.

8.6 VCC regulator

During supply dips, the input voltage can drop so much that it can no longer supply the

required IC current through the DVDT pin. Under these conditions, if the VCC voltage

drops to below the VCC(swon)reg level, another regulator with a current capability of up to

Isup(high)HV is started. The job of the regulator is to fill in the required supply current, which

the dV/dt supply does not deliver, thus preventing that the IC enters UVLO. When the

VCC voltage exceeds the VCC(swon)reg level, the regulator is turned off.

8.7 NTC functionality and PWM regulation

The NTC pin can be used as a control method for LED thermal protection. Alternatively,

the pin can be used as an input to disable/enable light output using a digital signal

(PWM regulation). The pin has an internal current source that generates the current of

Ioffset(NTC). An NTC resistor to monitor the LED temperature can be connected directly to

the NTC pin. Depending on the resistance value and the corresponding voltage on the

NTC pin, the converter reacts as shown in Figure 6.

During start-up, before VCC reaches VCC(startup) the voltage on the NTC pin must be less

than the minimum value of Vact(tmr)NTC. This is valid when the voltage on the NTC pin is

derived from the VCC using a resistive divider and a PTC in series with the resistor

between pins VCC and NTC.

If an NTC resistor is connected between the NTC pin and ground, the voltage on the NTC

pin is 0 V when VCC reaches VCC(startup).

Fig 6.

NTC control curve

SSL21081AT Datasheet(PDF) 10 Page - NXP Semiconductors