NCP1234 ONSEMI [ON Semiconductor], NCP1234 Datasheet - Page 28

• Manufacturer Part Number: NCP1234
• Description: Fixed Frequency Current Mode Controller for Flyback Converters
• Manufacturer: ONSEMI [ON Semiconductor]

and the DRV switching starts only if it is allowed; whereas
the Low latch (typically sensing an overtemperature) is
taken into account only after the soft−start is finished. In
addition, the NTC current is doubled to I
the soft−start period, to speed up the charging of the Latch
pin capacitor. The maximum value of Latch pin capacitor is
given by the following formula (The standard start−up
condition is considered and the NTC current is neglected) :
Temperature Shutdown
a trip point guaranteed above 135C and below 165C, and
a typical hysteresis of 30C. When the temperature rises
above the high threshold, the controller stops switching
Internal Latch Signal
The die includes a temperature shutdown protection with
V
V
CC(min)
CC(on)
V
CC
DRV
latch event)
allowed (no
Switching
pre-start phase
Latch signal
Figure 47. Latch−off Function Timing Diagram
high during
NTC(SSTART)
http://onsemi.com
during
28
instantaneously, and the HV current source is turned off.
Internal logic state is reset. When the temperature falls
below the low threshold, the HV start−up current source is
enabled, and a regular start−up sequence takes place.
C
initiated by
LATCHmax
Start-up
V
CC(on)
(t
Latch
Noise spike
+
+
ignored
t
2.8 @ 10
SSTARTmin
blanking)
−3
V
1.0
clamp0min
@ 130 @ 10
@ I
NTC(SSTART)min
−6
F + 364 nF
Latch-off
time
time
time
(eq. 2)