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PDF LD7523 Data sheet ( Hoja de datos )
| Número de pieza | LD7523 | |
| Descripción | Smart Green-Mode PWM Controller | |
| Fabricantes | Leadtrend | |
| Logotipo |  |
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 1. - Smart Green-Mode PWM Controller  Hay una vista previa y un enlace de descarga de LD7523 (archivo pdf) en la parte inferior de esta página. Total 18 Páginas | ||
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LD7523
6/16/2009
Smart Green-Mode PWM Controller with Multiple Protections
REV: 00
General Description
The LD7523 is a low startup current, current mode PWM
controller with green-mode power-saving operation. The
SOP-8/DIP-8 package integrated functions such as the
leading- edge blanking of the current sensing, internal
slope compensation, line compensation, and several
protection features. The protection functions include
cycle-by-cycle current limit, OVP, OLP, and brownout
protection. It provides the users a high efficiency, low
external component counts solution for AC/DC power
applications.
Furthermore, to satisfy various protection requirements,
both latch-mode protection and auto-recoverable
protection can be easily achieved by configuring LD7523
on different operation modes.
The special green-mode control is not only to achieve the
low power consumption but also to offer a
non-audible-noise operation when the LD7523 is
operating under light load or no load condition.
Features
z High-Voltage CMOS Process with Excellent ESD
protection
z Very Low Startup Current (< 35μA)
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 Programmable Line Compensation
z OVP (Over Voltage Protection)
z OLP (Over Load Protection)
z Brownout Protection
z Built in OLP De-Latch Timer
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
OVP
BNO
VCC
LD7523
OUT
CS
GND COMP
Leadtrend Technology Corporation
LD7523-DS-00 June 2009
1
www.leadtrend.com.tw
photocoupler
TL431
Free Datasheet http://www.datasheet4u.com/
1 page  
LD7523
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=12.0V)
PARAMETER
CONDITIONS
Supply Voltage (VCC Pin)
Startup Current
Operating Current
(with 1nF load on OUT pin)
VCOMP=0V
VCOMP=3V
Protection Mode (note 1)
UVLO (off)
UVLO (on)
Voltage Feedback (Comp Pin)
Short Circuit Current
Green Mode Threshold VCOMP
VCOMP=0V
Current Sensing (CS Pin)
Maximum Input Voltage, VCS(OFF)
VBNO=0V (note 2)
VBNO=1.30V
VBNO=3.75V
Leading Edge Blanking Time
Input impedance
Delay to Output
Gate Drive Output (OUT Pin)
Output Low Level
Output High Level
VCC=15V, Io=20mA
VCC=15V, Io=20mA
Rising Time
Falling Time
VCC=15V,Load Cap.=1000pF
VCC=15V ,Load Cap.=1000pF
Oscillator
Frequency
Green Mode Frequency
Frequency Temp. Stability
(-40°C –85°C)
Frequency Voltage Stability
(VCC=12V-30V)
MIN
9.0
12.0
0.80
0.748
0.650
1
9.0
60
TYP
20
3.5
2.7
0.70
9.75
12.75
2.5
2.35
0.85
0.798
0.700
350
200
50
30
65
20
3
1
MAX UNITS
35 μA
mA
mA
mA
10.7 V
13.5 V
4.0 mA
V
0.90
0.848
0.750
NA
V
V
V
nS
MΩ
nS
1.0 V
V
160 nS
60 nS
70 KHz
KHz
%
%
Leadtrend Technology Corporation
LD7523-DS-00 June 2009
5
www.leadtrend.com.tw
Free Datasheet http://www.datasheet4u.com/
5 Page 
LD7523
MOSFET directly. And the maximum duty-cycle of
LD7523 is limited to 75% to avoid the transformer
saturation.
the LD7523, the internal slope compensation circuit has
been internally implemented to simplify the external circuit
design.
Oscillator and Switching Frequency
The switching frequency of LD7523 is fixed as 65KHz
internally to provide the optimized operations by
considering the EMI performance, thermal treatment,
component sizes and transformer design.
Voltage Feedback Loop
The voltage feedback signal is provided from the TL431 in
the secondary side through the photo-coupler to the
COMP pin of LD7523. The input stage of LD7523, like
the UC384X, has 2 diodes voltage offset before feeding
into the voltage divider with 1/3 ratio, that is,
V+ (PWM COMPARATOR
)
=
1
3
× (VCOMP
−
2VF )
A pulling-high resistor is embedded internally to eliminate
the requirement of another resistor in the external circuit.
Dual-Oscillator Green-Mode Operation
There are many different topologies 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 reduce the switching frequency.
By using this dual-oscillator control, the green-mode
frequency can be well controlled and further to avoid the
generation of audible noise.
Current Sensing, Leading-Edge Blanking
The typical current mode PWM controller feedbacks both
current signal and voltage signal to close the control loop
and achieve regulation. The LD7523 detects the primary
MOSFET current from the CS pin, which is not only for the
peak current mode control but also for the pulse-by-pulse
current limit. The maximum voltage threshold of the
current sensing pin is set as 0.85V. Thus the MOSFET
peak current can be calculated as:
IPEAK(MAX)
=
(0.85
−
VLINE _ COMPENSATION )
RS
A 350nS leading-edge blanking (LEB) time is included in
the input of CS pin to prevent the false-trigger from the
current spike. However, the total pulse width of the
turn-on spike is decided by the output power, circuit
design and PCB layout. It is strongly recommended to
adopt a smaller R-C filter (as shown in figure 21) to avoid
the CS pin being damaged by the negative turn-on spike.
Internal Slope Compensation
A fundamental issue of current mode control is the
stability problem when its duty-cycle is over 50%. To
stabilize the control loop, slope compensation is required
in the traditional UC384X design by injecting the ramp
signal from the RT/CT pin through a coupling capacitor. In
Leadtrend Technology Corporation
LD7523-DS-00 June 2009
11
www.leadtrend.com.tw
Fig. 21
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LD7523.PDF ] | |
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