FSFR1800L Fairchild Semiconductor, FSFR1800L Datasheet - Page 10

• Manufacturer Part Number: FSFR1800L
• Description: IC FPS POWER SWITCH 9-SIP
• Manufacturer: Fairchild Semiconductor
• Series: FPS™r

Specifications of FSFR1800L

• Output Isolation: Isolated
• Frequency Range: 94kHz ~ 106kHz
• Voltage - Input: 9.6 V ~ 25 V
• Voltage - Output: 500V
• Power (watts): 260W
• Operating Temperature: -40°C ~ 130°C
• Package / Case: 9-SIP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

© 2007 Fairchild Semiconductor Corporation
FSFR series Rev.1.0.9
Functional Description
1. Basic Operation: FSFR-series is designed to drive
high-side and low-side MOSFETs complementarily with
50% duty cycle. A fixed dead time of 350ns is introduced
between consecutive transitions, as shown in Figure 16.
2. Internal Oscillator: FSFR-series employs a current-
controlled oscillator, as shown in Figure 17. Internally,
the voltage of R
charging/discharging current for the oscillator capacitor,
C
pin (I
frequency increases as I
3. Frequency Setting: Figure 18 shows the typical
voltage gain curve of a resonant converter, where the
gain is inversely proportional to the switching frequency
in the ZVS region. The output voltage can be regulated
by modulating the switching frequency. Figure 19 shows
the typical circuit configuration for R
coupler transistor is connected to the R
the switching frequency.
T
, is obtained by copying the current flowing out of R
gate drive
High side
MOSFET
gate drive
MOSFET
Low side
CTC
Figure 17. Current Controlled Oscillator
Figure 16. MOSFETs Gate Drive Signal
) using a current mirror. Therefore, the switching
T
pin is regulated at 2V and the
CTC
increases.
Dead time
T
pin, where the opto-
T
pin to modulate
time
T
10
The minimum switching frequency is determined as:
Assuming
transistor is 0.2V, the maximum switching frequency is
determined as:
To prevent excessive inrush current and overshoot of
output voltage during startup, increase the voltage gain
of the resonant converter progressively. Since the
voltage gain of the resonant converter is inversely
proportional to the switching frequency, the soft-start is
implemented by sweeping down the switching frequency
from an initial high frequency (f
voltage is established. The soft-start circuit is made by
connecting R-C series network on the R
f
f
Figure 18. Resonant Converter Typical Gain Curve
min
max
=
=
Gain
1.8
1.6
1.4
1.2
1.0
0.8
0.6
(
5.2
5.2
R
60
Figure 19. Frequency Control Circuit
R
R
min
k
min
k
max
Ω
Ω
the
70
×
+
100(
4.68
80
saturation
f
R
R
min
max
kHz
min
k
C
Ω
90
ss
)
) 100(
×
f
CON
R
100
normal
RT
ss
freq (kHz)
voltage
110
kHz
Control
f
)
I S S
120
max
LVcc
Soft-start
IC
SG
) until the output
130
of
T
pin, as shown
www.fairchildsemi.com
VDL
f
140
opto-coupler
ISS
PG
150
(1)
(2)