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PDF LD7523A Data sheet ( Hoja de datos )
| Número de pieza | LD7523A | |
| Descripción | Smart Green-Mode PWM Controller | |
| Fabricantes | Leadtrend | |
| Logotipo |  |
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LD7523A
12/3/2008
Smart Green-Mode PWM Controller with Multiple Protections
REV: 01
General Description
The LD7523A is a low startup current, current mode PWM
controller with green-mode power-saving operation. The
SOP-8/DIP-8 package integrates functions such as the
leading- edge blanking of the current sensing, internal
slope compensation, line compensation, and several
protection features including cycle-by-cycle current limit,
OVP, OTP, 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 LD7523A
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 LD7523A is
operating under light load or no load condition.
Typical Application
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 OTP (Over Temperature Protection) through a NTC
z Brownout Protection
z Flexibility on Latch/Auto-Recoverable Protection
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
Leadtrend Technology Corporation
LD7523A-DS-01 December 2008
1
www.leadtrend.com.tw
1 page  
LD7523A
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=12.0V)
PARAMETER
CONDITIONS
MIN
Supply Voltage (VCC Pin)
Startup Current
Operating Current
(with 1nF load on OUT pin)
VCOMP=0V
VCOMP=3V
Protection Mode (note 1)
UVLO (off)
9.0
UVLO (on)
12.0
Voltage Feedback (Comp Pin)
Short Circuit Current
Green Mode Threshold VCOMP
VCOMP=0V
Current Sensing (CS Pin)
Maximum Input Voltage, VCS(OFF)
Leading Edge Blanking Time
VBNO=0V (note 2)
VBNO=1.30V
VBNO=3.75V
0.800
0.748
0.650
Input impedance
1
Delay to Output
Gate Drive Output (OUT Pin)
Output Low Level
VCC=15V, Io=20mA
Output High Level
Rising Time
VCC=15V, Io=20mA
Load Capacitance=1000pF
9.0
Falling Time
Load Capacitance=1000pF
Oscillator
Frequency
60
Green Mode Frequency
Frequency Temp. Stability
(-40°C –85°C)
Frequency Voltage Stability
(VCC=12V-30V)
Latch Protection ((-)LATCH Pin)
(-)LATCH Pin Source Current
92
Turn-On Trip Level
3.3
Turn-Off Trip Level
2.40
(-)LATCH pin de-bounce time
100
De-latch Vcc Level
(PDR, Power Down Reset)
6.8
Note 1: When OVP, OLP, or Latch Protection is tripped.
Note 2: Guaranteed by design because Vcs(off) can’t be measured when VBNO=0V.
Leadtrend Technology Corporation
LD7523A-DS-01 December 2008
5
www.leadtrend.com.tw
TYP
20
3.5
2.7
0.7
9.75
12.75
2.5
2.35
0.850
0.798
0.700
350
150
50
30
65
20
100
3.50
2.50
8.0
MAX UNITS
35 μA
5.0 mA
mA
mA
10.7 V
13.5 V
4.0 mA
V
0.900
0.848
0.750
V
V
V
nS
MΩ
nS
1.0 V
V
160 nS
60 nS
70 KHz
KHz
3%
1%
108 μA
3.7 V
2.60 V
μS
8.7 V
5 Page 
LD7523A
Oscillator and Switching Frequency
The switching frequency of LD7523A is fixed at 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 LD7523A. The input stage of LD7523A,
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 feeds back both
current signal and voltage signal to close the control loop
and achieve regulation. The LD7523A 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 due to 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 higher than 50%.
To stabilize the control loop, slope compensation is
needed in the traditional UC384X design by injecting the
ramp signal from the RT/CT pin through a coupling
capacitor. In the LD7523A, the internal slope
compensation circuit has been internally implemented to
simplify the external circuit design.
Fig. 21
Leadtrend Technology Corporation
LD7523A-DS-01 December 2008
11
www.leadtrend.com.tw
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet LD7523A.PDF ] | |
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