FSFR2100U_10 FAIRCHILD [Fairchild Semiconductor], FSFR2100U_10 Datasheet - Page 12

• Manufacturer Part Number: FSFR2100U_10
• Description: Fairchild Power Switch (FPS) for Half-Bridge Resonant Converters
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

© 2007 Fairchild Semiconductor Corporation
FSFR series Rev.1.0.9
Current Sensing Using Resonant Capacitor Voltage:
For high-power applications, current sensing using a
resistor may not be available due to the severe power
dissipation in the resistor. In that case, indirect current
sensing using the resonant capacitor voltage can be a
good alternative because the amplitude of the resonant
capacitor voltage (V
current in the primary side (I
To minimize power dissipation, a capacitive voltage
divider is generally used for capacitor voltage sensing, as
shown in Figure 26.
V
Cr
p p
−
=
2
I
π
V
V
p
CS
CS
Figure 24. Half-Wave Sensing
Figure 25. Full-Wave Sensing
p p
f C
R
s
−
sense
CS
CS
r
Control
Control
SG
SG
IC
IC
cr
Ids
p-p
Ids
PG
) is proportional to the resonant
PG
R
p
Cr
sense
p-p
Cr
Np
) as:
I
V
V
I
Np
ds
ds
CS
CS
Ns
Ns
Ns
Ns
(6)
12
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 27.
Auto-restart Mode Protection: Once a fault condition is
detected, switching is terminated and the MOSFETs
remain off. When LV
11.3V, the protection is reset. The FPS resumes normal
operation when LV
V
CON
V
I
sense
p
V
Figure 26. Current Sensing Using Resonant
Cr
V
V
sense
Cr
p p
−
pk
CC
Capacitor Voltage
=
C
CC
reaches the start voltage of 14.5V.
sense
C
T
falls to the LV
B
delay
+
C
B
=
R C
d
d
V
sense
2
pk
=
CC
V
CON
stop voltage of
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V
V
V
sense
sense
Cr
p-p
pk
pk