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PDF LD7577GS Data sheet ( Hoja de datos )
| Número de pieza | LD7577GS | |
| Descripción | High Voltage Green-Mode PWM Controller | |
| Fabricantes | Leadtrend | |
| Logotipo |  |
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LD7577
1/15/2009
High Voltage Green-Mode PWM Controller with
Brown-Out Protection
Rev. 01
General Description
The LD7577 integrates several functions of protections, and
EMI-improved solution in SOP-8 package. It minimizes the
component counts and the circuit space.
The device provides functions of low startup current,
green-mode power-saving operation, leading-edge blanking
of the current sensing and internal slope compensation.
Also, it features more protections like OLP (Over Load
Protection), OVP (Over Voltage Protection), and brownout
protection to prevent the circuit from being damaged under
abnormal conditions.
Features
z High-Voltage (500V) Startup Circuit
z Current Mode Control
z Non-Audible-Noise Green Mode Control
z UVLO (Under Voltage Lockout)
z LEB (Leading-Edge Blanking) on CS Pin
z Internal Slope Compensation
z OVP (Over Voltage Protection) on Vcc Pin
z AC Input OVP (Over Voltage Protection)
z OLP (Over Load Protection)
z Precision Brownout Protection
z 500mA Driving Capability
Applications
z Switching AC/DC Adaptor and Battery Charger
z Open Frame Switching Power Supply
z LCD Monitor/TV Power
Typical Application
AC EMI
input Filter
*
HV VCC OUT
BNO
LD7577
CS
GND COMP
*
*See Application Information
Leadtrend Technology Corporation
LD7577-DS-01 January 2009
1
www.leadtrend.com.tw
photocoupler
TL431
1 page  
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=15.0V)
PARAMETER
CONDITIONS
High-Voltage Supply (HV Pin)
High-Voltage Current Source
Vcc< UVLO(on), HV=500V
Off-State Leakage Current
Vcc> UVLO(off), HV=500V
Supply Voltage (Vcc Pin)
Startup Current
Vcc< UVLO(on)
Operating Current
(with 1nF load on OUT pin)
VCOMP=0V
VCOMP=3V
OLP tripped
OVP tripped
UVLO (off)
UVLO (on)
OVP Level
Voltage Feedback (Comp Pin)
Short Circuit Current
Open Loop Voltage
VCOMP=0V
COMP pin open
Green Mode Threshold VCOMP
Burst Mode Threshold VCOMP
Current Sensing (CS Pin)
Maximum Input Voltage
Leading Edge Blanking Time
Input impedance
VCOMP>1.9V
Delay to Output
Oscillator for Switching Frequency
Frequency
Green Mode Frequency
Temp. Stability
(-40°C ~105°C)
Voltage Stability
(VCC=11V-25V)
LD7577
MIN
TYP
MAX UNITS
0.5 1.0 1.5 mA
8.9 35 μA
320 μA
2.85
mA
3.2 mA
0.68
mA
0.78
mA
9.0
10.0
11.0
V
15.0
16.0
17.0
V
26.5
28.0
29.5
V
1.5
6.0
2.35
1.4
2.2 mA
V
V
V
0.80
0.85
0.90
V
250 nS
1 MΩ
100 nS
60 65 70 KHz
22 KHz
5%
1%
Leadtrend Technology Corporation
LD7577-DS-01 January 2009
5
www.leadtrend.com.tw
5 Page 
LD7577
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 LD7577 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
well controlled and further to avoid the generation of audible
noise.
Fig. 16
Oscillator and Switching Frequency
The switching frequency of the LD7577 is fixed as 65KHz
internally to provide the optimized operations by considering
the EMI performance, thermal treatment, component sizes
and transformer design.
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 LD7577, 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 LD7577 and
disable the gate output pin of the LD7577. The off-mode will
be released when the pull-low signal at COMP pin is
removed.
Over Load Protection (OLP)
To protect the circuit from being damaged under over load
condition or short condition, a smart OLP function is built in
with the LD7577, as shown in Figure 17 shows the
waveforms of the OLP operation. If output voltage drops,
the feedback system tends to force the voltage loop toward
the saturation (6V) and then pulls the voltage of COMP pin
to high. Whenever the VCOMP trips to the OLP threshold
5.0V and continues over 30mS, OLP is activated and then
turns off the gate output to stop the switching of power
circuit. The 30mS delay time is to prevent the false trigger
from the power-on and turn-off transient.
A divide-2 counter is implemented to reduce the input
average power under OLP behavior. Whenever OLP is
activated, the output is latched off and the divide-2 counter
starts to count the number of UVLO(off). The latch is
released if the 2nd UVLO(off) point is counted then the
power circuit is recovered to switch again.
By using such protection mechanism, the average input
power can be reduced to a very low level so that the
component temperature and stress can be controlled within
the safe operating area.
Leadtrend Technology Corporation
LD7577-DS-01 January 2009
11
www.leadtrend.com.tw
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LD7577GS.PDF ] | |
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