参数资料
型号: FAN7621SJ
厂商: Fairchild Semiconductor
文件页数: 9/17页
文件大小: 0K
描述: IC OFF-LINE CTRLR PROG PFM 16SOP
标准包装: 47
输出隔离: 隔离
频率范围: 94kHz ~ 106kHz
工作温度: -40°C ~ 130°C
封装/外壳: 16-SOIC(0.209",5.30mm 宽)
供应商设备封装: 16-SOP
包装: 管件
其它名称: FAN7621SJ-ND
FAN7621SJFS
Functional Description
1. Basic Operation
Gain
FAN7621 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
1.8
f min
f normal
f
max
f ISS
transitions, as shown in Figure 16.
Dead t ime
High-side
1.6
1.4
MOSFET
gate drive
1.2
Low-side
MOSFET
gate drve
Figure 16. MOSFETs Gate Drive Signal
time
1.0
0.8
Soft-sta rt
0.6
60
70
80
90
100
110
120
130
140
150
2. Internal Oscillator
FAN7621 employs a current-controlled oscillator, as
Frequency (kHz)
Figure 18. Resonant Converter Typical Gain Curve
shown in Figure 17. Internally, the voltage of R T pin is
regulated at 2V and the charging / discharging current
for the oscillator capacitor, C T , is obtained by copying the
current flowing out of R T pin (I CTC ) using a current mirror.
Therefore, the switching frequency increases as I CTC
increases.
V CC
LV CC
HV CC
RT
V REF
I CTC
+
R max
R min
R SS
HO
I CTC
2I CTC
C T
3V
1V
-
+
-
S Q
R -Q
F/F
C SS
CON
CTR
LO
CS
+
8
R T
-
2V
Counter
(1/4)
Gate drive
SG
PG
R sense
5.2 k Ω
f min =
× 100( kHz )
5.2 k Ω 4.68 k Ω
f max = (
+
) × 100( kHz )
Figure 17. Current Controlled Oscillator
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 T pin, where the opto-
coupler transistor is connected to the R T pin to modulate
the switching frequency.
? 2009 Fairchild Semiconductor Corporation
FAN7621 ? Rev. 1.0.3
9
Figure 19. Frequency Control Circuit
The minimum switching frequency is determined as:
(1)
R min
Assuming the saturation voltage of opto-coupler
transistor is 0.2V, the maximum switching frequency is
determined as:
(2)
R min R max
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
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