ld7576a Leadtrend Technology, ld7576a Datasheet - Page 14

• Manufacturer Part Number: ld7576a
• Description: Green-mode Pwm Controller With High-voltage Start-up Circuit And Adjustable Olp Delay Time
• Manufacturer: Leadtrend Technology

LD7576A
the other hand, the modulating frequency can be set by
adjusting the capacitance value on the CT pin. The best
value for the CT capacitance is from 0.047μF to 0.1μF,
typically generating modulating frequency of 200Hz
~100Hz. It is a tradeoff to select proper CT value between
the EMI performance and OLP delay time.
In theory,
higher CT value will accompany with longer OLP delay
time.
It is strongly recommended to use higher quality capacitor
(low temperature coefficient and low initial tolerance) like
X7R type ceramic capacitor to avoid the variation on the
EMI performance under different temperature conditions.
As show in figure 23, short layout loop from CT to GND is
prefer to prevent any unexpected parasitic effect or
coupling noises. And beware not to connect any extra
loading to CT pin except of the capacitor to minimize the
affect on modulating frequency.
Fig. 23
On-Chip OTP
An internal OTP circuit is embedded inside the LD7576A
to provide the worst-case protection for this controller.
When the chip temperature rises higher than the trip OTP
level, the output will be disabled until the chip is cooled
down below the hysteresis window.
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Leadtrend Technology Corporation
www.leadtrend.com.tw
LD7576A-DS-00b November, 2009