SG6742HR_HL Fairchild Semiconductor, SG6742HR_HL Datasheet - Page 10

• Manufacturer Part Number: SG6742HR_HL
• Description: The highly integrated SG6742HL/HR PWM controller provides several features to enhance the performance of flyback converters
• Manufacturer: Fairchild Semiconductor

© 2008 Fairchild Semiconductor Corporation
SG6742HL/HR • Rev. 1.0.4
Functional Description
Thermal Protection
An NTC thermistor, R
can be connected from the RT pin to ground. A
constant current I
voltage on the RT pin can be expressed as V
(R
temperatures, R
When V
off after 20ms (t
PWM turns off immediately after 130µs (t
Limited Power Control
The FB voltage increases every time the output of the
power supply is shorted or overloaded. If the FB voltage
remains higher than a built-in threshold for longer than
t
turned off, V
When V
controller is totally shut down. V
turn-on threshold voltage of 15.5V through the startup
resistor until PWM output is restarted. This protection
feature continues as long as the overloading condition
persists.
overheating due to overloading conditions. When V
less than 1.05V (V
20ms (t
turned off immediately after 130µs (t
D-OLP
NTC
, PWM output is turned off. As PWM output is
+ R
D-OTP1
DD
RT
This
goes below the turn-off threshold (~9.5V) the
A
is less than 1.05V (V
), where I
DD
). If V
begins decreasing.
D-OTP1
NTC
prevents
RT
RT
RTTH1
is smaller, such that V
is less than 0.7V (V
). If V
is output from the RT pin. The
NTC
RT
), the PWM is turned off after
, in series with a resistor R
is 100µA. At high ambient
RT
the
is less than 0.7V (V
DD
(Continued)
RTTH1
power
is charged up to the
D-OTP2
), the PWM turns
D-OTP2
RTTH2
).
RT
supply
decreases.
), PWM is
).
RT
= I
RTTH2
from
RT
RT
A
is
),
•
,
10
Noise Immunity
Noise on the current sense or control signal may cause
significant pulse-width jitter, particularly in continuous-
conduction mode. Slope compensation helps alleviate
this problem. Good placement and layout practices
should be followed. Avoiding long PCB traces and
component leads, locating compensation and filter
components near the SG6742HL/HR, and increasing
the power MOS gate resistance improve performance.
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