SSL21083AT datasheet(10/23 Pages) PHILIPS

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SSL21083AT

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Product data sheet

Rev. 6 — 4 October 2013

10 of 22

NXP Semiconductors

SSL21083AT

Compact non-dimmable LED driver IC

8.4 VCC supply

The SSL21083AT is supplied using three methods:

• Under normal operation, the voltage swing on the DVDT pin is rectified within the IC

providing current towards the VCC pin

• At start-up, there is an internal current source connected to the HV pin. The current

source provides internal power until either the dV/dt supply or an external current on

the VCC pin provides the supply

• Using an auxiliary winding, the voltage can be rectified and connected to the VCC pin

via a series resistor.

The IC starts up when the voltage at the VCC pin exceeds VCC(startup). The IC locks out

(stops switching) when the voltage at the VCC pin is < VCC(stop). The hysteresis between

the start and stop levels allows the IC to be supplied by a buffer capacitor until the dV/dt

supply is settled. The SSL21083AT has an internal VCC clamp, which is an internal active

Zener (or shunt regulator). This internal active Zener limits the voltage on the supply VCC

pin to the maximum value of VCC. If the maximum current of the dV/dt supply minus the

current consumption of the IC (determined by the load on the gate drivers), is lower than

the maximum value of IDD no external Zener diode is required in the dV/dt supply circuit.

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 that

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 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.

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