IL44608 Datasheet, PDF (6/13 Pages) IK Semicon Co., Ltd – External Components Reliable and Flexible SMPS Controller

Demagnetization Section
The IL44608N demagnetization detection consists of a
comparator designed to compare the V_CC winding voltage
to a reference that is typically equal to 50 mV.
This reference is chosen low to increase effectiveness
of the demagnetization detection even during start–up.
A latch is incorporated to turn the demagnetization
block output into a low level as soon as a voltage less than
50 mV is detected, and to keep it in this state until a new
pulse is generated on the output. This avoids any ringing
on the input signal which may alter the demagnetization
detection.
For a higher safety, the demagnetization block output is
also directly connected to the output, which is disabled
during the demagnetization phase.
The demagnetization pin is also used for the quick, pro-
grammable OVP. In fact, the demagnetization input current
is sensed so that the circuit output is latched off when this
current is detected as higher than 120 μA.
IL44608N
The complete demagnetization status DMG is used to
inhibit the recharge of the CT capacitor. Thus in case of
incomplete transformer demagnetization the next switching
cycle is postpone until the DMG signal appears. The oscil-
lator remains at 2.4 V corresponding to the sawtooth valley
voltage. In this way the SMPS is working in the so called
SOPS mode (Self Oscillating Power Supply). In that case
the effective switching frequency is variable and no longer
depends on the oscillator timing but on the external work-
ing conditions (Refer to DMG signal in the Figure 6)
This function can be inhibited by grounding it but in
this case, the quick and programmable OVP is also dis-
abled.
Oscillator
The IL44608 contains a fixed frequency oscillator. It
is built around a fixed value capacitor CT successive-
ly charged and discharged by two distinct current
sources ICH and IDCH. The window comparator
senses the CT voltage value and activates the sources
when the voltage is reaching the 2.4 V/4.0 V levels.
The OSC and Clock signals are provided according to
the Figure 6. The Clock signals correspond to the CT ca-
pacitor discharge. The bottom curve represents the current
flowing in the sense resistor Rcs. It starts from zero and
stops when the sawtooth value is equal to the control vol-
tage Vcont. In this way the SMPS is regulated with a vol-
tage mode control.
2011, February, Rev. 01