ld7577ja Leadtrend Technology, ld7577ja Datasheet - Page 9

• Manufacturer Part Number: ld7577ja
• Description: High Voltage Green-mode Pwm Controller With Brown-out Protection
• Manufacturer: Leadtrend Technology

Application Information
Operation Overview
As long as the green power requirement becomes a trend
and the power saving is becoming more and more
important for switching power supplies and switching
adaptors, the traditional PWM controllers are not able to
support such new requirements. Furthermore, the cost
and size limitation forces the PWM controllers to
powerfully integrate more functions, thereby reducing the
external part count.
applications to provide an easy and cost effective solution;
and its detailed features are described as below.
Internal High-Voltage Startup Circuit and
Under Voltage Lockout (UVLO)
Leadtrend Technology Corporation
LD7577JA-DS-00b November 2009
0.2
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0
0
Vin
Cbulk
1
Comp
Fig. 13 V
The LD7577JA is ideal for these
2
LD7577JA
HV
Fig. 14
R1
V
GND
BNO
VCC
3
BNO
(V)
OUT
CS
vs. I
BNO
C1
D1
4
www.leadtrend.com.tw
Rs
25°C
5
6
9
Traditional circuits’ power on the PWM controller through
a startup resistor to constantly provide current from a
rectified voltage to the capacitor connected to Vcc pin.
Nevertheless, this startup resistor was usually of larger
resistance, and it therefore required more power and
more time to start up.
To achieve the optimized topology, as shown in figure 14,
The LD7577JA is built in with high voltage startup circuit
to optimize the power saving. During the startup sequence,
a high-voltage current source sinks current from C
capacitor to provide the startup current as well as to
charge the Vcc capacitor C1. During the initialization of
the startup, Vcc voltage is lower than the UVLO(off)
threshold thus the current source is on to supply a current
of 1mA. Meanwhile, the Vcc current consumed by the
LD7577JA is as low as 320μA thus most of the HV current
is utilized to charge the Vcc capacitor. By using such
configuration, the turn-on delay time will be almost the
same no matter whether operation condition is under
low-line or high-line.
When Vcc voltage reaches UVLO(on) threshold, the
LD7577JA is powered on to start issuing the gate drive
signal, the high-voltage current source is then disabled,
and the Vcc supply current will be only provided from the
LD7577JA
BULK