AN-9719 데이터 시트보기 (PDF) - Fairchild Semiconductor
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AN-9719 Datasheet PDF : 12 Pages
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AN-9719
2.4 Constant Power Control
To constantly limit the output power of the converter, high /
low line compensation is included. Sensing the converter
input voltage through the VIN pin, the high / low line
compensation function generates a line-voltage-dependent
peak-current-limit threshold voltage for constant power
control, as shown in Figure 6.
APPLICATION NOTE
2.5.3 Overload Protection (OLP)
When the upper branch of the voltage divider for the shunt
regulator (KA431 shown) is open circuit, as shown in
Figure 7, or an output over-current or short occurs; there is
no current flowing through the opto-coupler transistor. VFB
(feedback voltage) pulls up to 6V. When the 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 longer than 56ms due
to the overload condition.
Figure 6. Constant Power Control
2.5 Protection Functions
The FSL-series provides full protection functions to prevent
the power supply and the load from being damaged. The
protection features is shown in Table 1.
Table 1. Protection Functions
OVP
OTP
OLP
VIN-H
VIN-L
FSL127H
Latch
Latch
Auto Restart
Latch
Auto Restart
FSL137H
Latch
Latch
Auto Restart
Latch
Auto Restart
2.5.1 VDD Over-Voltage Protection (OVP)
VDD over-voltage protection prevents IC damage caused by
over voltage on the VDD pin. The OVP is triggered when
VDD reaches 28V. It has debounce time (typically 130µs) to
prevent false trigger by switching noise.
2.5.2 Over-Temperature Protection (OTP)
The SenseFET and the control IC integration make
temperature detection of the SenseFET easier. When the
junction temperature exceeds approximately 142°C, thermal
shutdown is activated.
© 2010 Fairchild Semiconductor Corporation
Rev. 1.0.0 • 11/2/10
3
Figure 7. OLP Operator
www.fairchildsemi.com
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