NCP1396B ON Semiconductor, NCP1396B Datasheet - Page 13

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

The NCP1396 A/B includes all necessary features to help
building a rugged and safe switch-mode power supply
featuring an extremely low standby power. The below
bullets detail the benefits brought by implementing the
NCP1396 controller:
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Wide frequency range: A high-speed Voltage
Control Oscillator allows an output frequency
excursion from 50 kHz up to 500 kHz on Mlower and
Mupper outputs.
Adjustable dead-time: Thanks to a single resistor
wired to ground, the user has the ability to include
some dead-time, helping to fight cross-conduction
between the upper and the lower transistor.
Adjustable soft-start: Every time the controller starts
to operate (power on), the switching frequency is
pushed to the programmed maximum value and
slowly moves down toward the minimum frequency,
until the feedback loop closes. The soft-start
sequence is activated in the following cases: a)
normal startup b) back to operation from an off state:
during hiccup faulty mode, brown-out or temperature
shutdown (TSD). In the NCP1396A, the soft-start is
not activated back to operation from the fast fault
input, unless the feedback pin voltage is below 0.6 V.
To the opposite, in the B version, the soft-start is
always activated back from the fast fault input
whatever the feedback level is.
Adjustable minimum and maximum frequency
excursion: In resonant applications, it is important to
stay away from the resonating peak to keep operating
the converter in the right region. Thanks to a single
external resistor, the designer can program its lowest
frequency point, obtained in lack of feedback voltage
(during the startup sequence or in short-circuit
conditions). Internally trimmed capacitors offer a
±3% precision on the selection of the minimum
switching frequency. The adjustable upper stop being
less precise to ±15%.
Low startup current: When directly powered from
the high-voltage DC rail, the device only requires 300
µA to start-up. In case of an auxiliary supply, the B
version offers a lower start-up threshold to cope with
a 12 V dc rail.
Brown-Out detection: To avoid operation from a low
input voltage, it is interesting to prevent the controller
from switching if the high-voltage rail is not within
the right boundaries. Also, when teamed with a PFC
front-end circuitry, the brown-out detection can
ensure a clean start-up sequence with soft-start,
ensuring that the PFC is stabilized before energizing
the resonant tank. The A version features a 27 µA
Application information
NCP1396A, NCP1396B
http://onsemi.com
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hysteresis current for the lowest consumption and the
B version slightly increases this current to 100 µA in
order to improve the noise immunity.
Adjustable fault timer duration: When a fault is
detected on the slow fault input or when the FB path
is broken, a timer starts to charge an external
capacitor. If the fault is removed, the timer opens the
charging path and nothing happens. When the timer
reaches its selected duration (via a capacitor on pin
3), all pulses are stopped. The controller now waits
for the discharge via an external resistor of pin 3
capacitor to issue a new clean startup sequence with
soft-start.
Cumulative fault events: In the NCP1396A/B, the
timer capacitor is not reset when the fault disappears.
It actually integrates the information and cumulates
the occurrences. A resistor placed in parallel with the
capacitor will offer a simple way to adjust the
discharge rate and thus the auto-recovery retry rate.
Fast and slow fault detection: In some application,
subject to heavy load transients, it is interesting to
give a certain time to the fault circuit, before
activating the protection. On the other hands, some
critical faults cannot accept any delay before a
corrective action is taken. For this reason, the
NCP1396A/B includes a fast fault and a slow fault
input. Upon assertion, the fast fault immediately
stops all pulses and stays in the position as long as
the driving signal is high. When released low (the
fault has gone), the controller has several choices: in
the A version, pulses are back to a level imposed by
the feedback pin without soft-start, but in the B
version, pulses are back through a regular soft-start
sequence.
Skip cycle possibility: The absence of soft-start on
the NCP1396A fast fault input offers an easy way to
implement skip cycle when power saving features are
necessary. A simple resistive connection from the
feedback pin to the fast fault input, and skip can be
implemented.
Broken feedback loop detection: Upon start-up or
any time during operation, if the FB signal is missing,
the timer starts to charge a capacitor. If the loop is
really broken, the FB level does not grow-up before
the timer ends counting. The controller then stops all
pulses and waits that the timer pin voltage collapses
to 1V typically before a new attempt to re-start, via
the soft-start. If the optocoupler is permanently
broken, a hiccup takes place.
Finally, two circuit versions, A and B: The A and B
versions differ because of the following changes: