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PDF LD7578 Data sheet ( Hoja de datos )
| Número de pieza | LD7578 | |
| Descripción | Green-Mode PWM Controller | |
| Fabricantes | Leadtrend | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LD7578 (archivo pdf) en la parte inferior de esta página. Total 19 Páginas | ||
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LD7578
10/08/2008
Green-Mode PWM Controller with HV Start-Up Circuit
and OTP Protection
Rev.00
General Description
Features
The LD7578 integrates several functions of protections in
a 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, the LD7578 features more
protections like OLP (Over Load Protection), OVP (Over
Voltage Protection), and external OTP (Over Temperature
Protection) to prevent the circuit from being damaged
under abnormal conditions.
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
z OLP (Over Load Protection)
z OTP through a NTC/Latch-Off Mode
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
input
EMI
Filter
*
HV VCC OUT
LD7578
(-)LATCH
CS
GND COMP
*
*See Application Information
photocoupler
TL431
Leadtrend Technology Corporation
LD7578-DS-00 October 2008
1
www.leadtrend.com.tw
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
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
COMP>1.9V
Input impedance
Delay to Output
Oscillator for Switching Frequency
Frequency
Green Mode Frequency
Temp. Stability
(-40°C ~105°C)
Voltage Stability
(VCC=11V-25V)
LD7578
MIN TYP MAX UNITS
0.5 1.0 1.5 mA
8.9 35 μA
320
3.3 3.8
3.3 3.8
0.78
0.88
9.0 10.0 11.0
15.0 16.0 17.0
26.5 28.0 29.5
μA
mA
mA
mA
mA
V
V
V
1.5 2.2
6.0
2.35
1.4
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
LD7578-DS-00 October 2008
5
www.leadtrend.com.tw
5 Page 
LD7578
will be released when the pull-low signal at COMP pin is
removed.
Fig. 16
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 LD7578 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.
Oscillator and Switching Frequency
The switching frequency of the LD7578 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
LD7578, 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 LD7578 and
disable the gate output pin of the LD7578. The off-mode
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 LD7578, 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.
Leadtrend Technology Corporation
LD7578-DS-00 October 2008
11
www.leadtrend.com.tw
11 Page | ||
| Páginas | Total 19 Páginas | |
| PDF Descargar | [ Datasheet LD7578.PDF ] | |
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