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PDF LD7575B Data sheet ( Hoja de datos )
| Número de pieza | LD7575B | |
| Descripción | Green-Mode PWM Controller | |
| Fabricantes | Leadtrend | |
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Hay una vista previa y un enlace de descarga de LD7575B (archivo pdf) en la parte inferior de esta página. Total 17 Páginas | ||
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LD7575B
5/26/2008
Green-Mode PWM Controller with High-Voltage
Rev. 00
Start-Up Circuit
General Description
The LD7575B is a current-mode PWM controller with
excellent power-saving operation. It features a high-
voltage current source to directly supply the startup current
from bulk capacitor and further to provide a lossless startup
circuit. The integrated functions such as the leading-edge
blanking of the current sensing, internal slope compensation,
and the small package provide the users a high efficiency,
minimum external component counts, and low cost solution
for AC/DC power applications.
Furthermore, the embedded over voltage protection, over
load protection and the special green-mode control provide
the solution for users to design a high performance power
circuit easily. The LD7575B is offered in both SOP-8 and
DIP-8 package.
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 Programmable Switching Frequency
z Internal Slope Compensation
z OVP (Over Voltage Protection) on Vcc
z OLP (Over Load Protection)
z 500mA Driving Capability
Applications
z Switching AC/DC Adapter and Battery Charger
z Open Frame Switching Power Supply
z LCD Monitor/TV Power
Typical Application
Leadtrend Technology Corporation
LD7575B-DS-00 May 2008
1
1 page  
LD7575B
Electrical Characteristics
(TA = +25oC unless otherwise stated, VCC=15.0V)
PARAMETER
CONDITIONS
MIN
TYP
MAX UNITS
High-Voltage Supply (HV Pin)
High-Voltage Current Source
Vcc< UVLO(on), HV=500V
0.5 1.0 1.5 mA
Off-State Leakage Current
Vcc> UVLO(off), HV=500V
35 μA
Supply Voltage (Vcc Pin)
Startup Current
0.5 mA
Operating Current
(with 1nF load on OUT pin)
VCOMP=0V
VCOMP=3V
Protection tripped (OVP)
2.4 3.4 mA
2.9 4.4 mA
0.5 mA
Protection tripped (OLP)
0.43
mA
UVLO (off)
9.0
10.0
11.0
V
UVLO (on)
15.0
16.0
17.0
V
OVP Level
25.0
27.5
30.0
V
Voltage Feedback (Comp Pin)
Short Circuit Current
Open Loop Voltage
VCOMP=0V
COMP pin open
1.5 2.2 mA
6.3 V
Green Mode Threshold VCOMP
2.35 V
Current Sensing (CS Pin)
Maximum Input Voltage
0.80
0.85
0.90
V
Leading Edge Blanking Time
220 nS
Input impedance
1 MΩ
Delay to Output
100 nS
Oscillator (RT pin)
Frequency
RT=100KΩ
60.0
65.0
70.0 KHz
Green Mode Frequency
Fs=65.0KHz
21 KHz
Temp. Stability
(-40°C ~105°C)
5%
Voltage Stability
(VCC=11V-25V)
1%
Gate Drive Output (OUT Pin)
Output Low Level
VCC=15V, Io=20mA
1V
Output High Level
VCC=15V, Io=20mA
9
V
Rising Time
Load Capacitance=1000pF
50 160 nS
Falling Time
Load Capacitance=1000pF
30 60 nS
OLP (Over Load Protection)
OLP Trip Level
5.0 V
OLP Delay Time (note)
Fs=65KHz
33 mS
Note: The OLP delay time is proportional to the period of switching cycle. So that, the lower RT value will set the higher
switching frequency and the shorter OLP delay time.
Leadtrend Technology Corporation
LD7575B-DS-00 May 2008
5
5 Page 
LD7575B
VCC
UVLO(on)
UVLO(off)
COMP
5.0V
OUT
OLP
2nd UVLO(off)
OLP Counter Reset
30mS
OLP trip Level
t
t
Fig. 18
Switching
Non-Switching
Fig. 17
Switching
t
OVP (Over Voltage Protection) on Vcc
The Vgs ratings of the nowadays power MOSFETs are most
with maximum 30V. To prevent the Vgs from the fault
condition, LD7575B is implemented an OVP function on Vcc.
Whenever the Vcc voltage is higher than the OVP threshold
voltage, the output gate drive circuit will be shutdown
simultaneous thus to stop the switching of the power
MOSFET until the next UVLO(on).
The Vcc OVP function in LD7575B is an auto-recovery type
protection. If the OVP condition, usually caused by the
feedback loop opened, is not released, the Vcc will tripped
the OVP level again and re-shutdown the output. The Vcc
is working as a hiccup mode. Figure 18 shows its
operation.
On the other hand, if the OVP condition is removed, the Vcc
level will get back to normal level and the output is
automatically returned to the normal operation.
Fault Protection
A lot of protection features have been implemented in the
LD7575B to prevent the power supply or adapter from being
damaged caused by single fault condition on the open or
short condition on the pin of LD7575B. Under the conditions
listed below, the gate output will be off immediately to
protect the power circuit ---
y RT pin short to ground
y RT pin floating
y CS pin floating
Pull-Low Resistor on the Gate Pin of MOSFET
In LD7575B, an anti-floating resistor is implemented on the
OUT pin to prevent the output from any uncertain state
which may causes the MOSFET working abnormally or false
triggered-on. However, such design won’t cover the
condition of disconnection of gate resistor Rg thus it is still
strongly recommended to have a resistor connected on the
MOSFET gate terminal (as shown in figure 19) to provide
extra protection for fault condition.
This external pull-low resistor is to prevent the MOSFET
from damage during power-on under the gate resistor is
disconnected. In such single-fault condition, as show in
figure 20, the resistor R8 can provide a discharge path to
avoid the MOSFET from being false-triggered by the current
through the gate-to-drain capacitor Cgd. Therefore, the
MOSFET is always pull-low and kept in the off-state
whenever the gate resistor is disconnected or opened in any
case.
Leadtrend Technology Corporation
LD7575B-DS-00 May 2008
11
11 Page | ||
| Páginas | Total 17 Páginas | |
| PDF Descargar | [ Datasheet LD7575B.PDF ] | |
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