FAN7621B データシートの表示（PDF） - Fairchild Semiconductor
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FAN7621B Datasheet PDF : 17 Pages
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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
10.0V, the protection is reset. FAN7621B resumes
normal operation when LVCC reaches the start voltage of
12.5V.
Latch-Mode Protection: Once this protection is
triggered, switching is terminated and the gate output
signals remain off. The latch is reset only when LVCC is
discharged below 5V.
LVCC
12
+
1 0 /12.5V
-
LVCC good V REF
Internal
Bias
OCP
OLP
OV P
L VCC good
CON
20k
A u t o- re st a rt
protec tion
SQ
R -Q
F /F
Latch
protec tion
QS
-Q R
F /F
Shutdo wn
AOCP
TSD
LVCC < 5V
Figure 24. Protection Blocks
Current Sensing Using Resistor: FAN7621B senses
drain current as a negative voltage, as shown in Figure
25 and Figure 26. Half-wave sensing allows low power
dissipation in the sensing resistor, while full-wave
sensing has less switching noise in the sensing signal.
Ids
CDL
L VCC
HVCC
RT
HO
CON
CTR
V
LO
CS
CS
SG PG
VCS
Ids
Rsense
Figure 26. Full-Wave Sensing
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 (Vcrp-p) is proportional to the resonant
current in the primary side (Ipp-p) as:
V p−p
Cr
=
I p−p
p
2π fsCr
(6)
CDL
LVCC
HVCC
RT
HO
CON
CTR
VCS
LO
CS
SG PG
Rsense
Ids
Ids
V
CS
Figure 25. Half-Wave Sensing
© 2009 Fairchild Semiconductor Corporation
FAN7621B • Rev. 1.0.1
11
www.fairchildsemi.com
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