FAN6862HR Fairchild Semiconductor, FAN6862HR Datasheet - Page 11

• Manufacturer Part Number: FAN6862HR
• Description: A highly integrated PWM controller, FAN6862H(HR) provides several features to enhance the performance of flyback converters
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN6862H(HR) • Rev. 1.0.0
Protections
Self-protective functions include V
Protection (OVP), Open-Loop / Overload Protection
(OLP), Over-Current Protection (OCP), Short-Circuit
Protection (SCP), and Over-Temperature Protection
(OTP). OLP, OCP, and SCP are Auto-Restart Mode
protections; OVP and OTP are Latch-Mode protections.
In FAN6862HR, all of these protections are applied with
Auto-Restart Mode.
Auto-Restart Mode Protections
Once a fault condition is detected, switching is
terminated and the MOSFET remains off. This causes
V
auxiliary winding. When V
protection is reset and the operating current reduces to
startup
FAN6862H(HR) resumes normal operation when V
reaches V
can alternately enable and disable MOSFET switching
until the fault condition is eliminated (see Figure 26).
Latch-Mode Protections
Once this protection is triggered, switching is terminated
and the MOSFET remains off. The latch is reset only
when V
AC power line.
Over-Current Protection (OCP)
FAN6862H(HR)
thresholds. One is for pulse-by-pulse current limit,
which turns off MOSFET for the remainder of the
DD
to fall because no more power is delivered from the
DD
current,
Figure 26. Auto-Restart Operation
DD-ON
is discharged below 4V by unplugging the
(16V). In this manner, the auto-restart
has
which
two
DD
falls to V
causes
over-current
DD
DD-OFF
V
DD
Over-Voltage
(8.5V), the
protection
to
rise.
DD
11
switching cycle when the sensing voltage of MOSFET
drain current reaches the threshold. The other threshold
is for the over-current protection, which shuts down the
MOSFET gate when the sensing voltage of MOSFET
drain current is above the threshold longer than the
shutdown delay (56ms).
Open-Loop / Overload Protection (OLP)
When the upper branch of the voltage divider for the
shunt regulator (KA431 shown in Figure 27) is broken,
no current flows through the opto-coupler transistor,
which pulls up the feedback voltage to 5.2V.
When feedback voltage is above 4.6V for longer than
56ms, OLP is triggered. This protection is also triggered
when the SMPS output drops below the nominal value
for longer than 56ms due to the overload condition.
V
V
by over voltage on the VDD pin. The OVP is triggered
when V
30µs) prevents false triggering by switching noise.
Over-Temperature Protection (OTP)
The OTP circuit is composed of current source and
voltage comparators. Typically, an NTC thermistor is
connected between the RT and GND pins. If the voltage
of this pin drops below a threshold of 1.0V, PWM output
is disabled after t
below
immediately after t
DD
DD
Over-Voltage Protection (OVP)
over-voltage protection prevents IC damage caused
DD
0.7V,
reaches 25V. A debounce time (typically
Figure 27. OLP Operation
it
DOTP
DOTP2
triggers
debounce time. If this pin drops
debounce time.
the
latch-off
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protection