viper20sp STMicroelectronics, viper20sp Datasheet - Page 8

• Manufacturer Part Number: viper20sp
• Description: Smps Primary I.c.
• Manufacturer: STMicroelectronics

Figure 9:
Ct
Rt
Oscillator
OSC
VDD
1,000
C t
500
300
200
100
22nF
15nF
50
30
1
Ct = 1.5 nF
Ct = 2.7 nF
Ct = 4.7 nF
Ct = 10 nF
Forbidden area
2
Oscillator frequency vs Rt and Ct
3
FC00050
CLK
Forbidden area
5
Rt (k )
40kHz
10
For R
and
C
VIPer20/SP/DIP - VIPer20A/ASP/ADIP
Ct(nF) =
F
t
SW
15nF if F
t
Fsw(kHz)
>1.2K
880
=
20
----------- -
R
FC00030
FC00030
2.3
t
30
C
SW
t
Fsw
1
50
40KHz
–
--------------------- -
R
t
550
–
150
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