FSQ0365RL datasheet(12/24 Pages) FAIRCHILD

Part #	FSQ0365RL

Description	Green Mode Fairchild Power Switch (FPS?? for Valley Switching Converter

Download	24 Pages

Scroll/Zoom	100%

Manufacturer	FAIRCHILD [Fairchild Semiconductor]

Direct Link	http://www.fairchildsemi.com

Logo

12 / 24 page

www.fairchildsemi.com

FSQ0365, FSQ0265, FSQ0165, FSQ321, FSQ311 Rev. 1.0.4

12

Functional Description

1. Startup: At startup, an internal high-voltage current

source supplies the internal bias and charges the

external capacitor (Ca) connected to the Vcc pin, as

illustrated in Figure 20. When VCC reaches 12V, the FPS

begins switching and the internal high-voltage current

source is disabled. The FPS continues its normal

switching operation and the power is supplied from the

auxiliary transformer winding unless VCC goes below the

stop voltage of 8V.

Figure 20. Start-up Circuit

2. Feedback Control: FPS employs current mode

control, as shown in Figure 21. An opto-coupler (such as

the FOD817A) and shunt regulator (such as the KA431)

are typically used to implement the feedback network.

Comparing the feedback voltage with the voltage across

the RSENSE resistor makes it possible to control the

switching duty cycle. When the reference pin voltage of

the shunt regulator exceeds the internal reference

voltage of 2.5V, the opto-coupler LED current increases,

thus pulling down the feedback voltage and reducing the

duty cycle. This event typically happens when the input

voltage is increased or the output load is decreased.

2.1 Pulse-by-Pulse Current Limit: Because current

mode control is employed, the peak current through the

SenseFET is limited by the inverting input of PWM

comparator (VFB*), as shown in Figure 21. Assuming

that the 0.9mA current source flows only through the

internal resistor (3R + R = 2.8k), the cathode voltage of

diode D2 is about 2.5V. Since D1 is blocked when the

feedback voltage (VFB) exceeds 2.5V, the maximum

voltage of the cathode of D2 is clamped at this voltage,

thus clamping VFB*. Therefore, the peak value of the

current through the SenseFET is limited.

2.2 Leading Edge Blanking (LEB): At the instant the

internal SenseFET is turned on, a high-current spike

usually occurs through the SenseFET, caused by

primary-side capacitance and secondary-side rectifier

reverse recovery. Excessive voltage across the Rsense

resistor would lead to incorrect feedback operation in the

current mode PWM control. To counter this effect, the

FPS employs a leading edge blanking (LEB) circuit. This

circuit inhibits the PWM comparator for a short time

(tLEB) after the SenseFET is turned on.

Figure 21. Pulse-Width-Modulation (PWM) Circuit

3. Synchronization: The FSQ-series employs a valley

switching technique to minimize the switching noise and

loss. The basic waveforms of the valley switching

converter are shown in Figure 22. To minimize the

MOSFET's switching loss, the MOSFET should be

turned on when the drain voltage reaches its minimum

value, as shown in Figure 22. The minimum drain

voltage is indirectly detected by monitoring the VCC

winding voltage, as shown in Figure 22.

Figure 22. Valley Resonant Switching Waveforms

8V/12V

V

ref

Internal

Bias

V

CC

V

str

I

CH

V

CC good

V

DC

C

a

FSQ0365RN Rev.00

2

5

3

OSC

V

CC

V

ref

I

delay

I

FB

V

SD

R

3R

Gate

driver

OLP

D1

D2

+

V

FB*

-

V

FB

KA431

C

B

V

O

FOD817A

R

sense

SenseFET

FSQ0365RN Rev. 00

V

DC

V

RO

V

RO

V

ds

t

F

0.7V

V

sync

300ns Delay

0.2V

ON

V

ovp (6V)

FSQ0365RN Rev.00

MOSFET Gate

Similar Part No. - FSQ0365RL

Manufacturer	Part #	Datasheet	Description
Fairchild Semiconductor	FSQ0365RL	1Mb / 24P	Green Mode Fairchild Power Switch (FPS?? for Valley Switching Converter - Low EMI and High Efficiency
Fairchild Semiconductor	FSQ0365RL	892Kb / 21P	Green Mode Fairchild Power Switch (FPS)

More results

Similar Description - FSQ0365RL

Manufacturer	Part #	Datasheet	Description
Fairchild Semiconductor	FSQ0365_0709	1Mb / 24P	Green Mode Fairchild Power Switch (FPS?? for Valley Switching Converter - Low EMI and High Efficiency
	FSQ510MX	1Mb / 14P	Green Mode Fairchild Power Switch (FPS) for Valley Switching Converter - Low EMI and High Efficiency
	FSQ510	534Kb / 15P	Green Mode Fairchild Power Switch (FPS) for Valley Switching Converter - Low EMI and High Efficiency
	FSCQ0765RT	726Kb / 24P	Green Mode Fairchild Power Switch (FPS) for Quasi-Resonant Switching Converter
	FSCQ1565RP	1Mb / 24P	Green Mode Fairchild Power Switch (FPS) for Quasi-Resonant Switching Converter
	FSDM0265RNB	904Kb / 20P	Green Mode Fairchild Power Switch (FPS)
	FSDM1265RB	380Kb / 20P	Green Mode Fairchild Power Switch (FPS)
	FSDM0465RE	405Kb / 20P	Green Mode Fairchild Power Switch (FPS??
	FSL106HR	942Kb / 13P	Green Mode Fairchild Power Switch (FPS??
	FSL116LR	934Kb / 13P	Green Mode Fairchild Power Switch (FPS??

More results

FSQ0365RL Datasheet(PDF) 12 Page - Fairchild Semiconductor

FSQ0365RL Datasheet(HTML) 12 Page - Fairchild Semiconductor

Similar Part No. - FSQ0365RL

Similar Description - FSQ0365RL

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Datasheet Download

Link URL