ld7577gs Leadtrend Technology, ld7577gs Datasheet - Page 13

• Manufacturer Part Number: ld7577gs
• Description: High Voltage Green-mode Pwm Controller With Brown-out Protection
• Manufacturer: Leadtrend Technology

Leadtrend Technology Corporation
LD7577-DS-01 January 2009
UVLO- OFF
UVLO - ON
Voltage
4.00V
3.80V
1.05V
Line
V
Vcc
OUT
BNO
AC OK area
Switching
Fig. 19
Fig.20
Non- Switching
www.leadtrend.com.tw
AC OK area
Switching
t
t
t
t
13
In order to protect BNO pin from being damaged during the
dividing resistors floating, an internal zener diode is
implemented in BNO pin. Fig. 19 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. 21.
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. However, such
design won’t cover the conditions of disconnection of gate
resistor R
resistor connected at the MOSFET gate terminal (as shown
in figure 22) to provide extra protection for fault conditions.
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 23, the resistor R8 can provide a
discharge path to avoid the MOSFET from being
false-triggered by the coupling through the gate-to-drain
capacitor C
pulled low to maintain MOSFET in a off-state no matter the
gate resistor is disconnected or opened in any case.
0
6
5
4
3
2
1
3.0
G
GD
. It is still strongly recommended to have a
3.5
. Therefore, the gate of MOSFET should be
4. 0
Fig. 21 V
4.5
V
125°C
BNO
BNO
5.0
vs. I
LD7577
BNO
5.5
25°C
6
-40°C