SG5842JA Fairchild Semiconductor, SG5842JA Datasheet - Page 11

• Manufacturer Part Number: SG5842JA
• Description: The highly integrated SG5842A/JA series of PWM controllers provides several features to enhance the performance of flyback converters
• Manufacturer: Fairchild Semiconductor

© 2007 Fairchild Semiconductor Corporation
SG5842A/SG582JA • Rev. 1.4.3
Functional Description
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 longer than t
OLP
off, the supply voltage V
When V
10.5V), the controller is totally shut down. V
charged up to the turn-on threshold voltage of 16.5V
through the startup resistor until PWM output is
restarted. This protection feature remains activated as
long as the overloading condition persists. This
prevents the power supply from overheating due to
overloading conditions.
Protection Latch Circuit
The built-in latch function provides a versatile protection
feature that does not require external components (see
ordering information for a detailed description). To reset
the latch circuit, disconnect the AC line voltage of the
power supply.
t
D
, PWM output is turned off. As PWM output is turned
-
OLP
(ms)
DD
goes below the turn-off threshold (eg.
=
. 2
154
DD
×
R
begins decreasing.
I
(K
Ω
)
(Continued)
DD
(2)
D-
is
11
Thermal Protection
An external NTC thermistor can be connected from the
RT pin to ground. A fixed current, I
the RT pin. Because the impedance of the NTC
decreases at high temperatures, when the voltage of
the RT pin drops below 1.05V, PWM output is latched
off. The RT pin output current is related to the PWM
frequency programming resistor R
Noise Immunity
Noise from the current sense or the control signal may
cause significant pulse width jitter, particularly in
continuous-conduction
helps alleviate this problem. Good placement and
layout practices should be followed. Avoid long PCB
traces and component leads. Compensation and filter
components should be located near the SG5842A/JA.
Increasing the power-MOS gate resistance is advised.
mode.
Slope
I
.
RT
, is sourced from
compensation
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