IL44608 Datasheet, PDF (7/13 Pages) IK Semicon Co., Ltd – External Components Reliable and Flexible SMPS Controller

Overvoltage Protection
The IL44608 offers two OVP functions:
– a fixed function that detects when V_CC is higher than
15.4 V
– a programmable function that uses the demag pin.
The current flowing into the demag pin is mirrored and
compared to the reference current Iovp (120 μA). Thus this
OVP is quicker as it is not impacted by the V_CC inertia and
is called QOVP.
In both cases, once an OVP condition is detected, the
output is latched off until a new circuit START–UP.
IL44608N
Mode Transition
The LW latch Figure 8 is the memory of the working
status at the end of every switching sequence.
Two different cases must be considered for the logic at
the termination of the SWITCHING PHASE:
1. No Over Current was observed
2. An Over Current was observed
These 2 cases are corresponding to the signal labeled
NOC in case of “No Over Current” and “OC” in case of
Over Current. So the effective working status at the end of
the ON time memorized in LW corresponds to Q=1 for no
over current and Q=0 for over current.
This sequence is repeated during the Switching phase.
Several events can occur:
1. SMPS switch OFF
2. SMPS output overload
3. Transition from Normal to Pulsed Mode
4. Transition from Pulsed Mode to Normal Mode
Start–up Management
The V_i pin 8 is directly connected to the HV DC rail
V_in. This high voltage current source is internally con-
nected to the V_CC pin and thus is used to charge the V_CC
capacitor. The V_CC capacitor charge period corresponds to
the Start–up phase. When the V_CC voltage reaches 13 V,
the high voltage 9.0 mA current source is disabled and the
device starts working. The device enters into the switching
phase.
It is to be noticed that the maximum rating of the Vi pin
8 is 500 V. ESD protection circuitry is not currently added
to this pin due to size limitations and technology con-
straints. Protection is limited by the drain–substrate junc-
tion in avalanche breakdown. To help increase the applica-
tion safety against high voltage spike on that pin it is poss-
ible to insert a small wattage 1.0 k Ω series resistor be-
tween the V_in rail and pin 8.
The Figure 7 shows the V_CC voltage evolution in case
of no external current source providing current into the
V_CC pin during the switching phase. This case can be en-
countered in SMPS when the self supply through an aux-
iliary winding is not present (strong overload on the SMPS
output for example). The Figure 17 also depicts this work-
ing configuration. In case of the hiccup mode, the duty
cycle of the switching phase is in the range of 10%.
1. SMPS Switch off
When the mains is switched OFF, so long as the bulk
electrolithic bulk capacitor provides energy to the SMPS,
the controller remains in the switching phase. Then the
peak current reaches its maximum peak value, the switch-
ing frequency decreases and all the secondary voltages are
reduced. The V_CC voltage is also reduced. When V_CC is
equal to 10 V, the SMPS stops working.
2011, February, Rev. 01