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PDF LD7578J Data sheet ( Hoja de datos )

Número de pieza LD7578J
Descripción High Voltage Green-Mode PWM Controller
Fabricantes Leadtrend 
Logotipo Leadtrend Logotipo



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No Preview Available ! LD7578J Hoja de datos, Descripción, Manual

LD7578J
03/03/2009
High Voltage Green-Mode PWM Controller with
Over Temperature Protection
Rev. 00
General Description
The LD7578J integrates several functions of protections,
and EMI-improved solution in a SOP-8/or DIP-8 package to
minimize 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 LD7578J features more protections like OLP (Over
Load Protection), OVP (Over Voltage Protection), and OTP
(Over Temperature Protection) to prevent the circuit being
damaged under the abnormal conditions. The LD7578J
features built-in auto-recovery function for OVP on Vcc pin
and OLP.
Furthermore, the LD7578J features frequency trembling to
depress radiation noise and is an excellent solution for EMI
filter design.
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 Frequency Trembling
z Internal Slope Compensation
z Internal Over Current Protection
z OVP (Over Voltage Protection) on Vcc
z OLP (Over Load Protection)
z External OTP through a NTC
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
Leadtrend Technology Corporation
LD7578J-DS-00 March 2009
1
www.leadtrend.com.tw

1 page




LD7578J pdf
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=15.0V)
PARAMETER
CONDITIONS
High-Voltage Supply (HV Pin)
High-Voltage Current Source
Off-State Leakage Current
Supply Voltage (Vcc Pin)
Startup Current
VCC< UVLO(on), HV=500V
VCC> UVLO(off), HV=500V
Operating Current
(with 1nF load on OUT pin)
VCOMP=0V, LD7578J
VCOMP=3V, LD7578J
OLP tripped, LD7578J
OVP tripped, LD7578J
(-)Latch Pin Tripped
LD7578J
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
Current Sensing (CS Pin)
Maximum Input Voltage,Vcs_off
Leading Edge Blanking Time
Input impedance
VCOMP > 1.9
VCOMP <1.9
Delay to Output
LD7578J
MIN
TYP
MAX UNITS
0.5 1.0 1.5 mA
35 μA
320
3.3
3.6
0.78
0.88
μA
mA
mA
mA
mA
0.68
mA
9.0
10.0
11.0
V
15.0
16.0
17.0
V
26.5
28.0
29.5
V
1.45
5.6
2.35
2.0 mA
V
V
0.80
0.85
0.90
V
250 nS
1700
nS
1 MΩ
100 nS
Leadtrend Technology Corporation
LD7578J-DS-00 March 2009
5
www.leadtrend.com.tw

5 Page





LD7578J arduino
LD7578J
disabled immediately under such condition. The off-mode
can be released when the pull-low signal 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 LD7578J 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 to avoid the generation of audible noise.
Fig. 16
Frequency Trembling
The LD7578J is implemented with a frequency trembling
function which helps the power supply designers to optimize
EMI performance with lower system cost. The Trembling
frequencies is fixed internally at ±4KHz, and incorporates
with the 65KHz switching frequencies respectively.
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 LD7578J, the
internal slope compensation circuit has been implemented
to simplify the external circuit design.
On/Off Control
The LD7578J can be turned off by pulling COMP pin to
lower than 1.2V. The gate output pin of LD7578J will be
Over Load Protection (OLP) - Auto Recovery
To protect the circuit from the damage caused by overload
condition or output short condition, a smart OLP function is
implemented in the LD7578J for it. The OLP function in
LD7578J is an auto-recovery type protection. Fig. 17 shows
the waveforms of the OLP operation. Under such fault
condition, the feedback system will force the voltage loop
toward saturation and thus pull the voltage on COMP pin
(VCOMP) to high. Whenever the VCOMP trips the OLP
threshold of 5.0V and stays for over 30mS (if switching
frequency is 65KHz), the protection will be activated to turn
off the gate output and to shutdown the switching of power
circuit. The 30mS delay time is to prevent the false-trigger
during the power-on and turn-off transient.
A divided-by-2 counter is implemented to reduce the
average power under OLP behavior. Whenever OLP is
activated, the output is latched off and the divided-by-2
counter starts to count the number of UVLO(off). The
latch is released if the 2nd UVLO(off) point is counted, and
then the output recovers switching 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
a safe operating area.
Leadtrend Technology Corporation
LD7578J-DS-00 March 2009
11
www.leadtrend.com.tw

11 Page







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