FAN7585 Ver la hoja de datos (PDF) - Fairchild Semiconductor
Número de pieza
componentes Descripción
Fabricante
FAN7585 Datasheet PDF : 16 Pages
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1. OVP Block
FAN7585
Vo
3.3V 5V 12V
14 16 18
R101
R1
R3
R5
PT
Vref=5V
D
19
A
B
C
SET of
R/S Latch
R102
R2
R4
OVP COMP
R6 1.25V
R102, R102
: External Components
The OVP function is simply realized by connecting Pin14, Pin16, Pin18 to each secondary outputs. R1, R2, R3, R4, R5, R6 are
internal resistors of the IC. Each OVP level is determined by resistor ratio and the typical values are 4.1V/6.4V/14.2V respec-
tively.
• OVP detecting voltage for +3.3V
V O V P 1 ( + 3.3 V )
=
R-----1-----+-----R----2--
R2
× VA
=
R-----1-----+-----R----2--
R2
×
V
ref
=
4.1V
• OVP detecting voltage for +5V
VOVP2(+5V)
=
R-----3-----+-----R----4--
R4
×
VB
=
R-----3-----+-----R----4--
R4
× Vref
=
6.4V
• OVP detecting voltage for +12V
VO V P 3 ( + 12 V )
=
R-----5-----+-----R----6--
R6
×
VC
=
R-----5-----+-----R----6--
R6
×
Vref
=
14.2V
Especially, Pin19(PT) is prepared for extra OVP input or another protection signal. That is, if you want over voltage protection
of extra output voltage, then you can make a function with two external resistors.
• OVP detecting voltage for PT
PT
=
R-----1---0----1-----+----R-----1---0----2-
R102
× VD
=
R-----1---0---R-1----1-+--0--R-2----1---0----2-
× Vref
In the case of OVP, a system designer should know a fact that the main power can be dropped after a little time because of
system delay, even if PWM is triggered by OVP. So when the OVP level is tested with a set, you should check the secondary
outputs(+3.3V/+5V/+12V) and PG(Pin11) simultaneously. Then you can know the each OVP level as checking each output
voltage in just time that PG(Pin11) is triggered from high to low.
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