ld7578h Leadtrend Technology, ld7578h Datasheet - Page 14

• Manufacturer Part Number: ld7578h
• Description: High Voltage Green-mode Pwm Controller With Over Temperature Protection
• Manufacturer: Leadtrend Technology

(-)LATCH
Protection
Protection
Under
temperature may be increased significantly and cause
some damage on the components or further inhibits the
dangerous. To prevent damage due to system’s
malfunction, the OTP is required for the power circuit. The
OTP circuit is implemented by sensing the hot-spot of
power circuit like power MOSFET or output rectifier. It
can be easily achieved by connecting a NTC on the
(-)LATCH pin of LD7578H. As the device temperature or
ambient temperature rises high enough, the resistance of
NTC will decrease, so that the voltage on the (-)LATCH
pin will be
When the V
0.95V), LD7578H will shutdown the gate output and then
latch-off the power supply. The controller will be kept
latched unless Vcc drops below 8V (power down reset)
and the fault condition is removed. So the gate output
will remain off even the abnormal condition is released.
It requires 2 terms to successfully re-start the circuit. One
is to cool down the circuit till NTC resistance increases
Leadtrend Technology Corporation
LD7578H-DS-00 February 2010
OVP Level
UVLO(off)
UVLO(on)
V
(
PDR
−
)
Latch
VCC
OUT
some
Switching
=
(-)LATCH
100
Pin
μ
abnormal
(OTP)
A
OVP Tripped
⋅
falls below threshold voltage (typical
R
NTC
and
Non-Switching
Fig. 18
---
conditions,
Over
AC power Off
De-latch
Latched
AC power On
www.leadtrend.com.tw
Temperature
the
Switching
ambient
Mode
t
t
14
and V
unplug AC power and start a new cycle of AC power-on.
The detailed operation is depicted as figure 19.
Pull-Low Resistor on the Gate Pin of
MOSFET
An anti-floating resistor is implemented in the OUT pin to
prevent any uncertain output, which may cause MOSFET
working abnormally or false triggering-on.
such design won’t cover the conditions of disconnection of
gate resistor R
a resistor connected on the MOSFET gate terminal (as
shown in figure 20) to provide extra protection for fault
condition.
This external pull-low resistor is to prevent the MOSFET
from being damaged during power-on when the gate
resistor is disconnected. In such a single-fault condition,
as shown in figure 21, the resistor R8 can provide a
UVLO(off)
UVLO(on)
PDR (8V)
AC input Voltage
1.05V
0.95V
V
(-)LATCH
(-)Latch
OUT
VCC
Switching
OTP
rises above 1.05V. The alternative is to
G
. It is still strongly recommended to have
OTP Release
Non-Switching
Fig. 19
AC Off
LD7578H
Latch Released
AC On (Recycle)
However,
Switching
t
t
t
t