FAN8902 Ver la hoja de datos (PDF) - Fairchild Semiconductor
Número de pieza
componentes Descripción
Fabricante
FAN8902 Datasheet PDF : 14 Pages
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FAN8902(KA3902)
4. Oscillator Component Selection
Vref
RT
V/CT
+
CT
−
ID
VL VH
Logic
VCT [V]
VH=3.0
VL=1.75
T=40.0
Td=1.0
TC=39.0
t [µs]
The oscillator timing components can be calculated as follows:
TC = RT × CT × In[(Vref – VL) ⁄ (Vref – VH)]
TD = CT × [(VH – VL) ⁄ ID]
fosc = 1 ⁄ (TC + TD)
= 1.875 ⁄ (RT × CT)
Duty = TC × fosc × 100
For example, if fosc = 25kHz and duty = 95%
CT = (TD × ID) ⁄ (VH – VL)
= 1000[pF]
RT = 1.875 ⁄ (fosc × CT)
= 1.875 ⁄ (25kHz × 1000pF)
= 75[kΩ]
5. Current Command Input Section
The current command I* selects the lower value between VCMD and VLa.
VCMD
CMD 1
La 14 VLa
+
+
−
I* 4R
R
FAN8902
+
Logic
−
7
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