NCP1360, NCP1365
www.onsemi.com
17
APPLICATION INFORMATION
The NCP1365/60 is a flyback power supply controller
providing a means to implement primary side
constant−voltage and constant−current regulation. This
technique does not need a secondary side feedback circuitry,
associated bias current and an opto−coupler. NCP1365/60
implements a current−mode architecture operating in
quasi−resonant mode. The controller prevents
valley−jumping instability and steadily locks out in a
selected valley as the power demand goes down. As long as
the controller is able to detect a valley, the new cycle or the
following drive remains in a valley. Due to a dedicated
valley detection circuitry operating at any line and load
conditions, the power supply efficiency will always be
optimized. In order to prevent any high switching frequency
two frequency clamp options are available.
•Quasi−Resonance Current−mode operation:
implementing quasi−resonance operation in peak
current−mode control optimizes the efficiency by
switching in the valley of the MOSFET drain−source
voltage. Thanks to a proprietary circuitry, the controller
locks−out in a selected valley and remains locked until
the input voltage significantly changes. Only the four
first valleys could be locked out. When the load current
diminishes, valley switching mode of operation is kept
but without valley lock−out. Valley−switching
operation across the entire input/output conditions
brings efficiency improvement and lets the designer
build higher−density converters.
•Frequency Clamp: As the frequency is not fixed and
dependent on the line, load and transformer
specifications, it is important to prevent switching
frequency runaway for applications requiring maximum
switching frequencies up to 90 kHz or 130 kHz. Two
frequency clamp options at 80 kHz or 110 kHz are
available for this purpose. In case frequency clamp is
not needed, a specific version of the 1365/60 exists in
which the clamp is deactivated.
•Primary Side Constant Current Regulation: Battery
charging applications request constant current
regulation. NCP1360/65 controls and regulates the
output current at a constant level regardless of the input
and output voltage conditions. This function offers tight
over power protection by estimating and limiting the
maximum output current from the primary side, without
any particular sensor.
•Primary Side Constant Voltage Regulation: By
monitoring the auxiliary winding voltage on the
primary side, it is possible to determine the end of the
transformer demagnetization in order to indirectly
measure the output voltage. The end of the auxiliary
winding demagnetization corresponds to that of the
secondary winding affected by the transformer turns
ratio. This auxiliary voltage value captured at this
moment will be used to build the primary−side peak
current setpoint in order to control the output voltage.
Vout
Iout
CV mode
CC mode
0
Vnom
Inom
Figure 43. Constant−Voltage & Constant−Current
Mode
•Soft−Start: 4 ms internal fixed soft start guarantees a
peak current starting from zero to its nominal value
with smooth transition in order to prevent any
overstress on the power components at each startup.
•Cycle−by−Cycle peak current limit: If the max peak
current reaches the VILIM level, the over current
protection timer is enabled and starts counting. If the
overload lasts TOCP delay, then the fault is latched and
the controller stops immediately driving the power
MOSFET. The controller enters in a double hiccup
mode before autorecovering with a new startup cycle.
•VCC Over Voltage Protection: If the VCC voltage
reaches the VCC(OVP) threshold the controller enters in
latch mode. Thus it stops driving pulse on DRV pin:
♦A & C version − (Latched VCC(OVP)): VCC
capacitor is internally discharged to the VCC(Clamp)
level with a very low power consumption: the
controller is completely disabled. Resuming
operation is possible by unplugging the line in order
to releasing the internal VCC thyristor with a VCC
current lower than the ICC(Clamp).
♦B version − (Autorecovery): it enters in double
hiccup mode before resuming operation.
•Winding Short−Circuit Protection: An additional
comparator senses the CS signal and stops the
controller if VCS reaches VILIM+50% (after a reduced
LEB: tLEB2). Short circuit protection is enabled only if
4 consecutive pulses reach SCP level. This small
counter prevents any false triggering of short circuit
protection during surge test for instance. This fault is
latched and operations will be resumed like in a case of
VCC Over Voltage Protection.