FSDL0365 Fairchild Semiconductor, FSDL0365 Datasheet - Page 11

• Manufacturer Part Number: FSDL0365
• Description: Green Mode Fairchild Power Switch (FPSTM)
• Manufacturer: Fairchild Semiconductor

4.2 Thermal Shutdown (TSD) :
trol IC are integrated, making it easier for the control IC to
detect the temperature of the Sense FET. When the tempera-
ture exceeds approximately 140 C, thermal
vated.
4.3 Abnormal Over Current Protection (AOCP) :
Even though the FPS
and current mode PWM feedback, these are not enough to
protect the FPS
transformer pin short occurs. In addition to start-up, soft-
start is also activated at each restart attempt during auto-
restart and when restarting after latch mode is activated. The
FPS
tection) circuit as shown in figure 7. When the gate turn-on
signal is applied to the power Sense FET, the AOCP block is
Vcc
OLP
8V
6V
3V
Vsense
Vfb
TM
t
1 t
t
2
1
COM PARATOR
COMPARATOR
has an internal AOCP (Abnormal Over Current Pro-
V
C
PW M
FPS switching
FPS switching
FPS switching
FPS switching
AOCP
AOCP
fb
RC
(
1
V
Figure 7. AOCP Function & Block
1 (
fb
t
Delay current (5uA) charges the Cfb
Delay current (5uA) charges the Cfb
Delay current (5uA) charges the Cfb
Delay current (5uA) charges the Cfb
Figure 6. Over load protection
In
2 t
LEB
TM
I
1 (
t
delay
) 2
when a secondary side diode short or a
V
V
(
R
(
TM
t
t
) 1
)) 1
);
;
V
has OLP (Over Load Protection)
I
CLK
delay
(
t
) 1
S
R
5
3
uA
V
,
,
3 t
V
Q
R
The Sense FET and the
1 (
t
2
8 .
t
) 2
K
V
,
C
(
t
Following Vcc
Following Vcc
Following Vcc
Following Vcc
) 1
fb
shutdown is acti-
Out Driver
3
4 t
C
V
fb
_
fig
Rsense
2 .
Drain
con-
t
enabled and monitors the current through the sensing resis-
tor. The voltage across the resistor is then compared with a
preset AOCP level. If the sensing resistor voltage is greater
than the AOCP level, pulse by pulse AOCP is triggered
regardless of uncontrollable LEB time. Here, pulse by pulse
AOCP stops Sense FET within 350nS after it is activated.
4.4 Over Voltage Protection (OVP) : In case of malfunc-
tion in the secondary side feedback circuit, or feedback loop
open caused by a defect of solder, the current through the
opto-coupler transistor becomes almost zero. Then, Vfb
climbs up in a similar manner to the over load situation, forc-
ing the preset maximum current to be supplied to the SMPS
until the over load protection is activated. Because excess
energy is provided to the output, the output voltage may
exceed the rated voltage before the over load protection is
activated, resulting in the breakdown of the devices in the
secondary side. In order to prevent this situation, an over
voltage protection (OVP) circuit is employed. In general,
Vcc is proportional to the output voltage and the FPS
Vcc instead of directly monitoring the output voltage. If
V
mination of the switching operation. In order to avoid undes-
ired activation of OVP during normal operation, Vcc should
be properly designed to be below 19V.
5. Soft Start :
increases the feedback voltage together with the Sense FET
current slowly after it starts up. The typical soft start time is
15msec, as shown in figure 8, where progressive increments
of Sense FET current are allowed during the start-up phase.
The pulse width to the power switching device is progres-
sively increased to establish the correct working conditions
for transformers, inductors, and capacitors. The voltage on
the output capacitors is progressively increased with the
intention of smoothly establishing the required output volt-
age. It also helps to prevent transformer saturation and
reduce the stress on the secondary diode.
2.15A
0.98A
CC
Drain current
exceeds 19V, OVP circuit is activated resulting in ter-
[A]
1mS
The FPS
15steps
TM
has an internal soft start circuit
Current limit
FSDL0165RN
TM
that
uses
11
t