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PDF LD7576A Data sheet ( Hoja de datos )

Número de pieza LD7576A
Descripción Green-Mode PWM Controller
Fabricantes Leadtrend 
Logotipo Leadtrend Logotipo



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No Preview Available ! LD7576A Hoja de datos, Descripción, Manual

LD7576A
1 1/29/2009
Green-Mode PWM Controller with High-Voltage
Start-Up Circuit and Adjustable OLP Delay Time
REV. 00b
General Description
The LD7576A brings hi gh performance, and com bines
highly inte grated functions, protections an d EMI-improve
solution. It’s an id eal so lution for those cost-sensitive
systems, redu cing comp onent count and overa ll s ystem
cost.
The LD7576A features near-lossless high v oltage startup
circuit, green-mode power-saving operation, leading-edge
blanking of the curre nt sensi ng an d i nternal slop e
compensation. They are also equipped with protections,
such as OLP (Over Load Pro tection), OVP (Over Voltage
Protection) and OT P (Over T emperature Protection), to
prevent circuit damage 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
z On-Chip OTP (Over Temperature Protection)
z OLP (Over Load Protection)
z 500mA Driving Capability
z Adjustable OLP delay time
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
LD7576A-DS-00b November , 2009
1
www.leadtrend.com.tw
http://www.Datasheet4U.com

1 page




LD7576A pdf
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 0.5
Off-State Leakage Current
Vcc> UVLO(off),HV=500V
Supply Voltage (VCC Pin)
Startup Current
VCOMP=0V
Operating Current
(with 1nF load on OUT pin)
VCOMP=3V
OLP tripped
OVP tripped
OTP tripped
UVLO (off)
UVLO (on)
OVP Level
Voltage Feedback (COMP Pin)
Short Circuit Current
VCOMP=0V
Open Loop Voltage
COMP pin open
Green Mode Threshold VCOMP
Current Sensing (CS Pin)
Maximum Input Voltage
Leading Edge Blanking Time
Input impedance
Delay to Output
Oscillator for Switching Frequency
Frequency
Temp. Stability
(-40°C ~105°C)
Voltage Stability
(VCC=11V-25V)
Low Frequency Timer (CT Pin)
Low Frequency Period
CT=0.047μF
Temp. Stability
(-40°C ~105°C)
Voltage Stability
(VCC=11V-25V)
LD7576A
MIN TYP MAX UNITS
1.0 1.5 mA
35 μA
100
2.7 3.5
3.1 4.0
0.5
0.6
0.5
9.0 10.0 11.0
15.0 16.0 17.0
26.5 28.0 29.5
μA
mA
mA
mA
mA
mA
V
V
V
1.3 2.2
5.6
2.35
mA
V
V
0.80 0.85 0.90
V
230 nS
1 MΩ
100 nS
61.0 65.0 69.0 KHz
5%
1%
4.7 mS
5%
1%
Leadtrend Technology Corporation
LD7576A-DS-00b November , 2009
5
www.leadtrend.com.tw

5 Page





LD7576A arduino
LD7576A
Dual-Oscillator Green-Mode Operation
There are many different topolo gies has bee n
implemented i n different ch ips for the green-m ode or
power saving requirements such as “burst- mode control”,
“skipping-cycle mode”, “variable off-time control “…etc.
The basic operatio n theor y of all these approac hes
intended to reduce the switching cycles under light-load or
no-load condition either by skipping some switching pulses
or reduce the switching frequency.
By usi ng LD proprietar y d ual-oscillator techn ique, the
green-mode frequency can be well controlled to avo id the
generation of audible noise.
Fig. 16
Oscillator and Switching Frequency
The s witching frequency of L D7576A is fi xed at 6 5KHz
internally to provide th e optimize d operatio ns in
consideration of the EMI per formance, thermal treatment,
component sizes and transformer design.
Internal Slope Compensation
A fundamental issue of current mode control is the stability
problem when its duty-cycle is more than 50%. To stabilize
the control lo op, slope com pensation is need ed in the
traditional UC 384X desi gn b y in jecting the ramp signal
from the RT /CT pin throu gh a c oupling capac itor. In
LD7576A, the internal slo pe compens ation circuit has
been implemented to simplify the external circuit design.
On/Off Control
By pulling COMP pin lower than 1.2V will disable the gate
output pin of LD7576A immediately. The off mode c an be
released when the pull-low signal is removed.
Over Load Protection (OLP) - Auto Recovery
To protect the circuit from being damaged during over load
condition and short or open loop condition, the LD7576A is
implemented with smart OL P function. LD7576A features
auto recover y function, the waveform of which is
exemplified in figure 17. In the e xample of the fau lt
condition, the feedback system tends to f orce the v oltage
loop to ward th e saturation a nd then pu ll the voltage hi gh
on COMP pin (VCOMP). When the V COMP ramps up to
the OLP threshold of 5V and stays for longer than the OLP
delay time, the protection will be activated to turn off the
gate output and to stop the s witching of power circuit. The
OLP delay time, set by the capacitor connected to CT pin,
is to prevent the false trig gering from the power-on a nd
turn-off transient. The higher capacitance of the capacitor
in CT pin, the long er OLP del ay time. T he recommended
capacitance w ill be 0.1μF for a OLP de lay time arou nd
110mS and 0.047μF for around 45mS.
A divi de-by-2 counter is i mplemented t o red uce th e
average p ower und er OLP b ehavior. Whenever OLP is
activated, the output is la tched off and the divid e-by-2
counter starts to count the number Vcc reaches UVLO(off).
The latch will be released when Vcc reaches the 2nd time
and then the output is recovered to switching again.
With the prote ction mech anism, the averag e inp ut po wer
will be minimized, so that the component temperature and
stress can be controlled within a safe operating area.
Leadtrend Technology Corporation
LD7576A-DS-00b November , 2009
11
www.leadtrend.com.tw

11 Page







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