MC44608P100 ON Semiconductor, MC44608P100 Datasheet - Page 6

• Manufacturer Part Number: MC44608P100
• Description: IC PWM FLYBCK ISO VM 8DIP
• Manufacturer: ON Semiconductor

Specifications of MC44608P100

• Pwm Type: Voltage Mode
• Number Of Outputs: 1
• Frequency - Max: 110kHz
• Duty Cycle: 86%
• Voltage - Supply: 6.6 V ~ 13 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -25°C ~ 85°C
• Package / Case: 8-DIP (0.300", 7.62mm)
• Frequency-max: 110kHz
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: MC44608P100OS

activation of a 200 mA current source:
and of a leading edge blanking. Thanks to that, this pin is not
sensitive to the power switch turn on noise and spikes and
practically in most applications, no filtering network is
required to sense the current.
switching phase.
producing a sharp output turn off (high slew rate). This
results in an abrupt output turn off in the event of an over
current and in the majority of the pulsed mode switching
sequence.
Demagnetization Section
comparator designed to compare the V
to a reference that is typically equal to 50 mV.
the demagnetization detection even during start−up.
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.
also directly connected to the output, which is disabled
during the demagnetization phase.
programmable 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 mA.
Rsense
In stand−by mode, this current can be lowered as due to the
The current sense input consists of a filter (6.0 kW, 4.0 pF)
Finally, this pin is used:
− as a protection against over currents (Isense > I)
− as a reduction of the peak current during a Pulsed Mode
The overcurrent propagation delay is reduced by
The MC44608 demagnetization detection consists of a
This reference is chosen low to increase effectiveness of
A latch is incorporated to turn the demagnetization block
For a higher safety, the demagnetization block output is
The demagnetization pin is also used for the quick,
Ipk
Isense
max *stby
Rcs
Figure 3. Current Sense
2
1
+
200 A
0
1 * (R cs (kW)
m
R sense (W)
Switching Phase
&
L.E.B.
CC
winding voltage
0, 2)
Overcurrent
Comparator
STAND−BY
START−UP
(A)
1 V
+
−
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OC
MC44608
6
case, the quick and programmable OVP is also disabled.
Oscillator
built around a fixed value capacitor CT successively
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.
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
oscillator 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
working conditions (Refer to DMG signal in the Figure 6).
from Demag
Oscillator Buffer
logic block
This function can be inhibited by grounding it but in this
The MC44608 contains a fixed frequency oscillator. It is
The complete demagnetization status DMG is used to
DMG
DMG
Figure 4. Demagnetization Block
&
Output
>120 A
> 24 A
IDCH
Figure 5. Oscillator Block
&
m
m
SDCH
ICH
DMG
R Q
S
50/20 mV
SCH
Idemag
CT
+
−
2.4 V
4 V
Current Mirror
+
−
Window
comp
1
Clock
Demag
OSC