FSL518APG datasheet(14/27 Pages) ONSEMI

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FSL518H, FSL538H, FSL518A, FSL538A

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APPLICATION INFORMATION

HV Current Source for VCC Start up and

VCC Regulation

The HV current source utilizes voltage on DRAIN pin to

charge capacitor on VCC pin. This current source is

activated during start-up and provides operating current

when VCC is lower than VCC-HVREG. Thanks to VCC

start-up function, no external start-up circuitry is needed.

The HV current source is disabled when VCC voltage is

charged to VCC-START.

VCC regulation also helps avoiding start-up failure during

soft-start and keeps FSL5x8 operating to count auto-restart

delay time (tAR) in protection mode, as illustrated in Figure

34. It also enables the use of smaller capacitance for VCC

biasing. The VCC regulation is not functional when the

external bias is higher than VCC-HVREG.

Figure 34. VCC Start Up and VCC Regulation

HV Current

Source

DRAIN

VCC

VCC−START/STOP

tAR

VCC

Regulation

Initial Setting for Line Detection and Adjusting

Burst-mode Operation

LINE pin is used for both input-voltage detection and

burst-mode setting. When a voltage divider is connected

between bulk capacitor and LINE pin, a Zener diode

connected to LINE pin will allow to set level of burst-mode

operation. If there is no voltage divider, the line-detection

function is disabled and burst-mode operation level is set

linearly by simply connecting a resistor between LINE pin

and GND pin. In order to avoid interference from switching

noise, connecting a ceramic capacitor to LINE pin is

recommended.

When line detection is enabled, voltage on LINE pin is

monitored to offer brown-in (BI), brown-out (BO) and line

over-voltage protections (LOVP).

With IBURST, VLINE reflects resistance of the external

resistor. FSL5x8 adjusts burst-mode operation threshold

based on real-time VLINE level. Please refer to burst

threshold setting table for LINE pin configuration and

settings.

Figure 35. Architecture of LINE-pin Setting

FALSE

• Input Voltage Detection

• Brown−in/out Function

• Setting Burst Threshold by

Zener

• Setting Burst Threshold by

Resistance

VBULK

LINE

RBURST

IBURST

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