NCP1201 ON Semiconductor, NCP1201 Datasheet - Page 13

• Manufacturer Part Number: NCP1201
• Description: Current Mode Controller Fixed Frequency Operation
• Manufacturer: ON Semiconductor

Brownout Detect Protection
electricity brownout, a Bulk Capacitor Voltage Comparator
with programmable hysteresis is included in this device. The
non−inverting input, pin 1, is connected to the voltage
divider comprised of R
Figure 32, monitoring the bulk capacitor voltage level. The
inverting input is connected to a threshold voltage of 1.92 V
internally. As bulk capacitor voltage drops below the
pre−programmed level, i.e. Pin 1 voltage drops below
1.92 V, a reset signal will be generated via internal
protection logic to the PWM Latch to turn off the Power
Switch immediately. At the same time, an internal current
source controlled by the state of the comparator provides a
mean to setup the voltage hysteresis through injecting
current into R
6) show the relationship between V
voltage divider network resistors.
Equations for resistors selection are:
Assume V
using 4.3 kW for R
R Upper ) R Lower +
R Lower +
In order to avoid output voltage bouncing during
BULK_H
[1.92 V(V BULK_H * V BULK_L )]
Lower
(50 mA
Lower
. The equations below (Equations 5 and
= 90 Vdc and V
(V BULK_H * V BULK_L )
then R
Upper
V BULK_H )
50 mA
Upper
and R
BULK_L
is about 195.7 kW.
BULK
Lower
levels and the
= 80 Vdc, by
as shown in
http://onsemi.com
(eq. 5)
(eq. 6)
NCP1201
13
R
R
Upper
Lower
V
Figure 32. Brown−Out Protection Operation
BULK
BOK
V
REF
50 mA
1.92 V
+
−
UVLO