ld7577j Leadtrend Technology, ld7577j Datasheet - Page 13

• Manufacturer Part Number: ld7577j
• Description: High Voltage Green-mode Pwm Controller With Brown-out Protection
• Manufacturer: Leadtrend Technology

Brownout Protection & Line voltage OVP
(Over voltage protection)
The LD7577J is programmable to set the brownout
protection point and the line voltage OVP point though
BNO pin.
The voltage across the BNO pin is proportional to the bulk
capacitor voltage, referred as the line voltage.
brownout comparator is implemented to detect the
abnormal line condition. As soon as the condition is
detected, it will shut down the controller to prevent the
damage. Figure 20 shows the operation. When V
falls below 0.95V, the gate output will be kept off even Vcc
has already achieved UVLO(
hiccup between UVLO(
line voltage is large enough to pull V
the gate output will not start switching even when the next
UVLO(
prevent the false trigger during turn-on and turn-off.
The comparator built in BNO will disable switching from
Gate-out as soon as it detects excessive high line voltage
and BNO voltage over 4.16V. VCC will then operate in
hiccup mode between UVLO-on and UVLO-off. The
Gate-out will not resume switching until VBNO falls below
3.92V. Therefore, it can prevent excessive high line
Leadtrend Technology Corporation
LD7577J-DS-00b July 2009
OVP Level
UVLO(off)
UVLO(on)
ON
VCC
OUT
) is tripped. A hysteresis is implemented to
Switching
OVP Tripped
ON
Non-Switching
Fig. 19
) and UVLO(
ON
). It therefore makes Vcc
BNO
OFF
larger than 1.05V,
www.leadtrend.com.tw
). Unless the
Switching
BNO
A
t
t
13
voltage from damaging the external components. Fig. 21
shows the operation.
In order to protect BNO pin from being damaged during
the dividing resistors floating, an internal zener diode is
implemented in BNO pin. Fig. 13 shows the sinking
capability of the zener diode. To protect BNO pin, the
current flowing in BNO pin must be below 1.5μA, as
shown in Fig. 13.
UVLO(on)
UVLO(off)
1.25V
1.10V
Line Voltage
Vcc
OUT
V
BNO
Non-Switching
Fig. 20
AC OK area
LD7577J
Switching
Non-
Switching
t
t
t
t