ld7577j Leadtrend Technology, ld7577j Datasheet - Page 11

• Manufacturer Part Number: ld7577j
• Description: High Voltage Green-mode Pwm Controller With Brown-out Protection
• Manufacturer: Leadtrend Technology

Oscillator and Switching Frequency
The switching frequency of the LD7577J is fixed as
65KHz internally to provide the optimized operations by
Leadtrend Technology Corporation
LD7577J-DS-00b July 2009
LD7577J
VCC
GND
OUT
CS
Fig. 16
Fig. 17
Can be removed if the negative
spike is not over spec. (-0.3V).
www.leadtrend.com.tw
250ns
blanking
time
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considering the EMI performance, thermal treatment,
component sizes and transformer design.
Frequency Trembling
The LD7577J is implemented an adjustable frequency
Trembling function which provides the power supply
designers to choose the optimized EMI performance and
lowest system cost. The Trembling frequency is fixed
internally ±4KHz which is incorporated with the 65KHz
switching frequency.
Internal Slope Compensation
Stability is crucial for current mode control when it
operates at more than 50% of duty-cycle. To stabilize the
control loop, the slope compensation is required in the
traditional UC384X design by injecting the ramp signal
from the RT/CT pin through a coupling capacitor. In the
LD7577J, the internal slope compensation circuit has
been implemented to simplify the external circuit design.
On/Off Control
Pulling COMP pin below 1.2V will turn off the LD7577J
and disable the gate output pin of the LD7577J. The
off-mode will be released when the pull-low signal at
COMP pin is removed.
Dual-Oscillator Green-Mode Operation
Lots of topologies have been implemented in different
chips for the green-mode or power saving requirements
such as “burst-mode control”, “skipping-cycle mode”,
“variable off-time control “…etc. The basic operation
theory of all these approaches intends to reduce the
switching cycles under light-load or no-load condition
either by skipping some switching pulses or by reducing
the switching frequency.
What the LD7577J uses to implement the power-saving
operation is Leadtrend Technology’s own IP. By using this
dual-oscillator control, the burst -mode frequency can be
LD7577J