SSL21084T/1,118(2013) 데이터 시트보기 (PDF) - NXP Semiconductors.

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SSL21084T/1,118
(Rev.:2013)

Mains driver LED driver IC

NXP Semiconductors. 

NXP Semiconductors

SSL21084T

Mains dimmable LED driver IC

8.3 Valley detection

A new cycle is started when the primary switch is switched on (see Figure 4). In the

following sections, “on” represents the conductive state and off the non-conductive state.

Following time t1, when the peak current is detected on the SOURCE pin, the switch is

turned off and the secondary stroke starts at t2. When the secondary stroke is completed

with the coil current at t3 equaling zero, the drain voltage starts to oscillate at

approximately the Vi  VO level. The peak to peak amplitude equals 2  VO. In a tapped

buck topology, this amplitude is multiplied by the ratio of the windings.

A special feature, called valley detection is an integrated part of the SSL21084T circuitry.

Dedicated built-in circuitry connected to the DRAIN pin, senses when the voltage on the

drain of the switch reaches its lowest value. The next cycle is then started at t00 and as a

result the capacitive switching losses are reduced. If both the frequency of the oscillations

and the voltage swing are within the range specified (fring and Vvrec(min)) for detection, a

valley is detected and accepted. If a valid valley is not detected, the secondary stroke is

continued until the maximum off-time (toff(high)) is reached. Then the next cycle is started.

VGATE

VDRAIN

VIN

0

magnetization

demagnetization

IL

0

1

2

3

t0

t1 t2

t3

T

Fig 4. Waveforms and valley detection

VOUT

valley

4

t00

aaa-001744

SSL21084T

Product data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 6 — 3 October 2013

© NXP B.V. 2013. All rights reserved.

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