NCP1360, NCP1365
www.onsemi.com
25
This ensures the MOSFET current setpoint remains
limited to V
ILIM
in a fault condition.
FB Reset
Max_Ipk reset
OCP
Timer
Count
Reset Timer
LEB1
CS
V
ILIM
POReset
DbleHiccup
LEB2
V
CS(Stop)
4 clk
Counter
Reset
Counter
OCP
1/K
comp
SCP
Peak current
Freeze
Control Law
For
Primary Peak
Current Control
SoftStart
FB_CV
FB_CC
PWM
Latch
Reset
PWM Comp
OCP
Comp
Short Circuit
Comp
R
sense
R
CS
C
CS
Figure 53. Current Setpoint
A 2nd Over−Current Comparator for Abnormal
Overcurrent Fault Detection
A severe fault like a winding short−circuit can cause the
switch current to increase very rapidly during the on−time.
The current sense signal significantly exceeds V
ILIM
. But,
because the current sense signal is blanked by the LEB
circuit during the switch turn on, the power switch current
can abnormally increase, possibly causing system damages.
The NCP1360/65 protects against this dangerous mode by
adding an additional comparator for abnormal overcurrent
fault detection or short−circuit condition. The current sense
signal is blanked with a shorter LEB duration, t
LEB2
,
typically 120 ns, before applying it to the short−circuit
comparator. The voltage threshold of this extra comparator,
V
CS(stop)
, is typically 1.2 V, set 50% higher than V
ILIM
. This
is to avoid interference with normal operation. Four
consecutive abnormal overcurrent faults cause the
controller to enter in auto−recovery mode. The count to 4
provides noise immunity during surge testing. The counter
is reset each time a DRV pulse occurs without activating the
fault overcurrent comparator or after double hiccup
sequence or if the power supply is unplugged with a new
startup sequence after the initial power on reset.
Standby Power Optimization
Assuming the no−load standby power is a critical
parameter, the NCP1360/65 is optimized to reach an ultra
low standby power. When the controller enters standby
mode, a part of the internal circuitry has been disabled in
order to minimize its supply current. When the STBY mode
is enabled, the consumption is only 200 mA (I
CC4
) with the
200 Hz minimal frequency option.
Cable Drop Compensation
NCP1360/65 integrates an internal cable drop
compensation. This circuitry compensates the drop due to
the cable connected between the PCB output of the charger
and the final equipment. As the drop is linearly varying with
the output current level, this level can be compensated by
accounting for the load output current.
Figure 54 illustrates the practical implementation of the
cable compensation with the NCP1360/65 controller.
CC
Control
CBC
V
ref_CV1
FB_CC
Comp
OTA
Sampled Vout
V
ref_CV2
Figure 54. Cable Compensation Implementation
