NCP1360 Datasheet, PDF (18/29 Pages) ON Semiconductor – Low Power Offline Constant Current & Constant Voltage PWM Current-Mode Controller

NCP1360, NCP1365
• V_out Over Voltage Protection: if the internally−built
output voltage becomes higher than V_OVP level
(V_{ref_CV1} + 26%) a fault is detected.
♦ A & C version: This fault is latched and operations
are resumed like in the V_CC Over Voltage Protection
case.
♦ B version: the part enters in double hiccup mode
before resuming operations.
• V_out Under Voltage Protection: After each circuit
power on sequence, V_out UVP detection is enabled only
after the startup timer T_{EN_UVP}. This timer ensures that
the power supply is able to fuel the output capacitor
before checking the output voltage in on target. After
this startup blanking time, UVP detection is enabled
and monitors the Output voltage level. When the power
supply is running in constant−current mode and when
the output voltage falls below V_UVP level, the controller
stops sending drive pulses and enters a double hiccup
mode before resuming operations (A & B version), or
latches off (C version).
• V_s/ZCD Pin Short Protection: at the beginning of
each off−time period, the V_s/ZCD pin is tested to check
whether it is shorted or left open. In case a fault is
detected, the controller enters in a double hiccup mode
before resuming operations.
• Temperature Shutdown: if the junction temperature
reaches the T_SHTDN level, the controller stop driving the
V_bulk
power mosfet until the junction temperature decreases
by T_SHTDN(HYS), then the operation is resumed after a
double hiccup mode.
Startup Operation
The high−voltage startup current source is connected to
the bulk capacitor via the HV pin, it charges the V_CC
capacitor. During startup phase, it delivers 100 mA to fuel the
V_CC capacitor. When V_CC pin reaches V_CC(on) level, the
NCP1360/65 is enabled. Before sending the first drive pulse
to the power MOSFET, the CS pin has been tested for an
open or shorted situation. If CS pin is properly wired, then
the controller sends the first drive pulse to the power
MOSFET. After sending these first pulses, the controller
checks the correct Vs/ZCD pin wiring. Considering the
Vs/ZCD pin properly wired, the controller engages a
softstart sequence. The softstart sequence controls the max
peak current from the minimal frozen primary peak current
(V_CS(VCO)= 120 mV: 15% of V_ILIM) to the nominal pulse
width by smoothly increasing the level.
Figure 44 illustrates a standard connection of the HV pin
to the bulk capacitor. If the controller is in a latched fault
mode (ex V_{CC_OVP} has been detected), the power supply will
resume the operation after unplugging the converter from
the ac line outlet. Due the extremely low controller
consumption in latched mode, the release of the latch could
be very long. The unplug duration for releasing the latch will
be dependent on the bulk capacitor size.
R_HV
L
1 Vs/ZCD HV 8
N
2 COMP
2 CS
Vcc 6
4 DRV GND 5
C_Vcc
V_aux
Figure 44. HV Startup Connection to the Bulk Capacitor
The following calculation illustrates the time needed for
releasing the latch state:
C_bulkV_{in_ac} ^Ǹ2
t_unplug u
I_HV
(eq. 1)
For the following typical application with a 10 mF bulk
capacitor and a wide mains input range, in the worst case the
power supply needs to be unplug at least for 38 seconds @
265 V ac and 12 seconds @ 85 Vac. It is important to note
that the previous recommendation is no longer valid with the
B version, as all the faults are set to autorecovery mode only.
Protecting the Controller Against Negative Spikes
As with any controller built upon a CMOS technology, it
is the designer’s duty to avoid the presence of negative
spikes on sensitive pins. Negative injection has the bad habit
to forward−bias the controller substrate and can induce
erratic behaviors. Sometimes, the injection can be so strong
that internal parasitic SCRs are triggered and latch the
controller. The HV pin can be the problem in certain
circumstances. During the turn−off sequence, e.g. when the
user unplugs the power supply, the controller is still fed by
its V_CC capacitor and keeps activating the MOSFET ON and
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