NCP1396B ON Semiconductor, NCP1396B Datasheet - Page 22

• Manufacturer Part Number: NCP1396B
• Description: High Performance Resonant Mode Controller featuring High-voltage Drivers
• Manufacturer: ON Semiconductor

Fast input
As soon as its voltage exceeds 1V typical, all pulses are
off and maintained off as long as the fault is present.
When the pin is released, pulses come back and the soft-
start is activated.
can observe the feedback pin via a resistive divided and
thus implement skip cycle operation. The resonant
converter can be designed to lose regulation in light load
conditions, forcing the FB level to increase. When it
reaches the programmed level, it triggers the fast fault
input and stops pulses. Then Vout slowly drops, the loop
reacts by decreasing the feedback level which, in turn,
unlocks the pulses, Vout goes up again and so on: we are
in skip cycle mode.
Figure 47. A resistor can easily program the capacitor discharge time
The fast input is not affected by a delayed action.
Thanks to the low activation level of 1V, this pin
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Startup behaviour
current consumption is kept to Istrup, allowing to crank-
up the converter via a resistor connected to the bulk
capacitor. When Vcc reaches the VccON level, output
Mlower goes high first and then output Mupper. This
sequence will always be the same whatever triggers the
pulse delivery: fault, OFF to ON etc… Pulsing the output
Mlower high first gives an immediate charge of the
bootstrap capacitor. Then, the rest of pulses follow,
delivered at the highest switching value, set by the resistor
on pin 2. The soft-start capacitor ensures a smooth
frequency decrease to either the programmed minimum
value (in case of fault) or to a value corresponding to the
operating point if the feedback loop closes first. Figure 49
shows typical signals evolution at power on.
When the Vcc voltage grows-up, the internal
Figure 48. Skip cycle can be
implemented via two resistors on
the FB pin to the Fast fault input.
Vcc
2
3
FB
Fast fault