NCP1236 Datasheet, PDF (29/34 Pages) ON Semiconductor – Fixed Frequency Current Mode Controller for Flyback Converters

NCP1236
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_NTC(SSTART) during
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) :
V_CC
V_CC(on)
t_SSTARTmin @ I_{NTC(SSTART)min}
C_LATCHmax +
V_clamp0min
(eq. 2)
+ ^{2.8 @ 10−3 @ 130 @ 10−6} F + 364 nF
1.0
V_CC(min)
Start-up
initiated by
V_CC(on)
Internal Latch Signal
Latch signal
high during
pre-start phase
Noise spike
ignored
(t_Latch blanking)
time
DRV
Switching
allowed (no
latch event)
time
Latch-off
Figure 51. Latch−off Function Timing Diagram
time
Temperature Shutdown
The die includes a temperature shutdown protection with
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
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.
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