ld7578j Leadtrend Technology, ld7578j Datasheet - Page 12

• Manufacturer Part Number: ld7578j
• Description: High Voltage Green-mode Pwm Controller With Over Temperature Protection
• Manufacturer: Leadtrend Technology

OVP (Over Voltage Protection) on Vcc- Auto
Recovery
The V
mostly with 30V maximum. To protect the V
condition, LD7578J is implemented with OVP function on
Vcc. Whenever the Vcc voltage is larger than the OVP
threshold voltage, the output gate drive circuit will be shut
down simultaneously and stop switching of the power
MOSFET until the next UVLO(
The Vcc OVP function in LD7578J is an auto-recovery type
protection. If the OVP condition, usually caused by open
feedback loop, is not released, the Vcc will trip the OVP
level again and shutdown the output. The Vcc is working in
hiccup mode. Fig. 18 shows its operation.
Once the OVP condition is removed, the Vcc and the output
will resume to normal operation.
Leadtrend Technology Corporation
LD7578J-DS-00 March 2009
GS
ratings of the nowadays power MOSFETs are
Fig. 17
ON
).
www.leadtrend.com.tw
GS
from the fault
12
To protect the power circuit from damage due to system
failure, over temperature protection (OTP) is required. The
OTP circuit is implemented to sense a hot-spot of power
circuit like power MOSFET or output rectifier. It can be
easily achieved by connecting a NTC with (-)LATCH pin of
LD7578J.
temperature rises, the resistance of NTC decreases. So, the
voltage on the (-)LATCH pin could be written as below.
When the V
(typical 0.95V), LD7578J will shutdown the gate output and
then latch the power supply off. The controller will remain
latched unless the Vcc drops below 8V (power down reset)
and the fault condition is removed at the same time. There
are 2 conditions required to restart it successfully. First, cool
down the circuit so that NTC resistance will increase and
raise V
cord and restart AC power-on recycling. The detailed
operation is depicted in Fig. 19.
Pull-Low Resistor on the Gate Pin of MOSFET
An anti-floating resistor is built in with the OUT pin to
prevent the output from any uncertain state. Otherwise, it
may cause the MOSFET to work abnormally or mis-trigger.
However, such design won’t cover the condition of
disconnection between the OUT pin and the gate terminal
for the MOSFET. Thus it is still strongly recommended to
(-)LATCH Pin --- Latched Mode Protection
V
(-)LATCH
(
−
)
Latch
(-)LATCH
As the device temperature or ambient
=
above 1.05V. Then, remove the AC power
100
is less than the defined threshold voltage
μ
A
⋅
R
Fig. 18
NTC
LD7578J