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參數資料

型號：	FAN6921MLMY
廠商：	Fairchild Semiconductor
文件頁數：	20/23頁
文件大小：	1764K
描述：	IC CTLR PFC/FLYBACK 16-SOICN
標準包裝：	2,500
模式：	臨界傳導（CRM）
電流 - 啟動：	10µA
電源電壓：	8.5 V ~ 25 V
工作溫度：	-40°C ~ 105°C
安裝類型：	表面貼裝
封裝/外殼：	16-SOIC（0.154"，3.90mm 寬）
供應商設備封裝：	16-SOIC N
包裝：	帶卷 (TR)

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?2010 Fairchild Semiconductor Corporation

www.fairchildsemi.com

FAN6921ML " Rev. 1.0.3

Protection for PWM Stage

VDD Pin Over-Voltage Protection (OVP)

over-voltage protection is used to prevent device

damage once V

voltage is higher than device stress

rating voltage. In case of V

OVP, the controller stops

all switching operation immediately and enters latch-off

mode until the AC plug is removed.

Adjustable Over-Temperature Protection and

Externally Latch Triggering (RT Pin)

Figure 43 is a typical application circuit with an internal

block of RT pin. As shown, a constant current I

flows

out from the RT pin, so the voltage V

on RT pin can

be obtained as I

current multiplied by the resistor,

which consists of NTC resistor and R

resistor. If the RT

pin voltage is lower than 0.8 V and lasts for a debounce

time, latch mode is activated and stops all PFC and

PWM switching.

The RT pin is usually used to achieve over-temperature

protection with a NTC resistor and provides external

latch triggering for additional protection. Engineers can

use an external triggering circuit (e.g. transistor) to pull

low the RT pin and activate controller latch mode.

Generally, the external latch triggering needs to activate

rapidly since it is usually used to protect power system

from abnormal conditions. Therefore, the protection

debounce time of the RT pin is set to around 100 祍

once RT pin voltage is lower than 0.5 V.

For over-temperature protection, because the

temperature would not change immediately; the RT pin

voltage is reduced slowly as well. The debounce time

for adjustable OTP should not need a fast reaction. To

prevent improper latch triggering on the RT pin due to

exacting test conditions (e.g. lightning test); when the

RT pin triggering voltage is higher than 0.5 V, the

protection debounce time is set to around 10ms. To

avoid improper triggering on the RT pin, it is

recommended to add a small value capacitor (e.g.

1000 pF) paralleled with NTC and R

resistor.

Latched

0.8V

=100礎

FAN6921

Adjustable Over-

Temperature protection&

External Latch triggering

NTC

0.5V

Debounce

time

110祍

10ms

Figure 43. Adjustable Over-Temperature Protection

Output Over-Voltage Protection (DET Pin)

Referring to Figure 44, during the discharge time of

PWM transformer inductor; the voltage across on

auxiliary winding is reflected from secondary winding

and therefore the flat voltage on the DET pin is

proportional to the output voltage. FAN6921ML can

sample this flat voltage level after a t

OFF

blanking time to

perform output over-voltage protection. This t

OFF

blanking time is used to ignore the voltage ringing from

leakage inductance of PWM transformer. The sampled

flat voltage level is compared with internal threshold

voltage 2.5 V and, once the protection is activated,

FAN6921ML enters latch mode.

The controller can protect rapidly by this kind of cycle-

by-cycle sampling method in the case of output over

voltage. The protection voltage level can be determined

by the ratio of external resistor divider R

and R

DET

. The

flat voltage on DET pin can be expressed by the

following equation:

(

)

DET

N N V

?nbsp ?/DIV>

(2)

?/DIV>

D E T

P W M

G a t e

A U X

?/DIV>

0 . 3 V

O F F

b l a n k i n g

s a m p l i n g

h e r e

?/DIV>

Figure 44. Operation Waveform of Output

Over-Voltage Detection

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相關代理商/技術參數	參數描述
FAN6921MR	制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Integrated Critical-Mode PFC / Quasi-Resonant Current-Mode PWM Controller
FAN6921MRMY	功能描述:電流型 PWM 控制器 Crtcl Md PFC & Quasi Res Cur Md PWM Cntlr RoHS:否制造商:Texas Instruments 開關頻率:27 KHz 上升時間: 下降時間: 工作電源電壓:6 V to 15 V 工作電源電流:1.5 mA 輸出端數量:1 最大工作溫度:+ 105 C 安裝風格:SMD/SMT 封裝 / 箱體:TSSOP-14
FAN6961	制造商:FAIRCHILD 制造商全稱:Fairchild Semiconductor 功能描述:Interleaved Dual BCM PFC Controllers
FAN6961BMY	制造商:Fairchild Semiconductor Corporation 功能描述:
FAN6961DY	功能描述:功率因數校正 IC Green mode PFC Fwd PWM Controller RoHS:否制造商:Fairchild Semiconductor 開關頻率:300 KHz 最大功率耗散: 最大工作溫度:+ 125 C 安裝風格:SMD/SMT 封裝 / 箱體:SOIC-8 封裝:Reel

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