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

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SSL21084T/1,118

GreenChip drivers for LED lighting

NXP Semiconductors. 

NXP Semiconductors

SSL2108X

Drivers for LED lighting

Rinrush

Vsec

LEDs

DVDT

5

HV 1

SSL2108X

VCC

3

6, 7

4

GND NTC

NTC

DRAIN

8

2

SOURCE

Rsense

001aan693

Fig 4. Basic application diagram SSL2108X (SO8 variant)

8.3 Conversion frequency

The maximum conversion frequency is 200 kHz. Therefore, select an inductance value

that with the given supply voltage, LED voltage and component spread the conversion

frequency is always within limits.

8.4 Valley detection

A new cycle is started when the primary switch is switched on see Figure 5. Following

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

and the secondary stroke starts t3. When the secondary stroke is completed with the coil

current at t3 equaling zero, the drain voltage starts to oscillate at approximately VIN  VOUT

level. The amplitude equals VOUT. A special feature, called valley detection is an

integrated part of the SSL2108X circuitry. Dedicated built-in circuitry connected to the

DRAIN pin, senses when the voltage on the drain of the switch has reached its lowest

value. The next cycle is then started and as a result the capacitive switching losses are

reduced. A valley is detected and accepted if both the frequency of the oscillations and

the voltage swing are within the range specified (fring and ∆Vvrec(min)) for detection. 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.

SSL2108X

Preliminary data sheet

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

Rev. 1 — 9 September 2011

© NXP B.V. 2011. All rights reserved.

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