FSFR1700 データシートの表示（PDF） - Fairchild Semiconductor

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FSFR1700

Fairchild Power Switch (FPS™) for Half-Bridge Resonant Converters

Fairchild Semiconductor 

connecting R-C series network on the RT pin, as shown

in Figure 19. FSFR-series also has an internal soft-start

for 3ms to reduce the current overshoot during the initial

cycles, which adds 40kHz to the initial frequency of the

external soft-start circuit, as shown in Figure 20. The

initial frequency of the soft-start is given as:

f ISS = (5.2kΩ + 5.2kΩ ) ×100 + 40 (kHz) (3)

Rmin

RSS

It is typical to set the initial frequency of soft-start two ~

three times the resonant frequency (fO) of the resonant

network.

The soft-start time is three to four times of the RC time

constant. The RC time constant is as follows:

TSS = RSS ⋅ CSS

(4)

fs

f ISS

40kHz

Control loop

take over

Figure 22. Control Pin Configuration for Pulse

Skipping

Remote On / Off: When an auxiliary power supply is

used for standby, the main power stage using FSFR-

series can be shut down by pulling down the control pin

voltage, as shown in Figure 23. R1 and C1 are used to

ensure soft-start when switching resumes.

time

Figure 20. Frequency Sweeping of Soft-start

4. Control Pin: The FSFR-series has a control pin for

protection, cycle skipping, and remote on/off. Figure 21

shows the internal block diagram for control pin.

Figure 23. Remote On / Off Circuit

Figure 21. Internal Block of Control Pin

Protection: When the control pin voltage exceeds 5V,

protection is triggered. Detailed applications are

described in the protection section.

Pulse Skipping: FSFR-series stops switching when the

control pin voltage drops below 0.4V and resumes

switching when the control pin voltage rises above 0.6V.

To use pulse-skipping, the control pin should be

connected to the opto-coupler collector pin. The

frequency that causes pulse skipping is given as:

SKIP = 5.2k + 4.16k x100(kHz) (5)

R min R max

5. Protection Circuits: The FSFR-series has several

self-protective functions, such as Overload Protection

(OLP), Over-Current Protection (OCP), Abnormal Over-

Current Protection (AOCP), Over-Voltage Protection

(OVP), and Thermal Shutdown (TSD). OLP, OCP, and

OVP are auto-restart mode protections; while AOCP and

TSD are latch-mode protections, as shown in Figure 24.

Auto-restart Mode Protection: Once a fault condition is

detected, switching is terminated and the MOSFETs

remain off. When LVCC falls to the LVCC stop voltage of

11.3V, the protection is reset. The FPS resumes normal

operation when LVCC reaches the start voltage of 14.5V.

© 2007 Fairchild Semiconductor Corporation

FSFR series • 1.0.3

11

www.fairchildsemi.com

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