MC44608P100 ON Semiconductor, MC44608P100 Datasheet - Page 5

• 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

Regulation
Opto coupler. During the switching phase the switch S2 is
closed and the shunt regulator is accessible by the pin 3. The
shunt regulator voltage is typically 5.0 V. The dynamic
resistance of the shunt regulator represented by the zener
diode is 20 W. The gain of the Control input is given on
Figure 11 which shows the duty cycle as a function of the
current injected into the pin 3.
regulator and the PWM comparator to cancel the high
frequency residual noise.
The pin 3 senses the feedback current provided by the
A 4.0 kHz filter network is inserted between the shunt
Pin
1
2
3
4
5
6
7
8
V CC
Control Input
Control
Input
Demag
Ground
Name
Driver
I
sense
V
V
CC
i
3
5 V
Figure 2. Regulator
V LP−stby
S3
S2
1
1
20 W
The Demag pin offers 3 different functions: Zero voltage crossing detection (50 mV), 24 mA current detection
and 120 mA current detection. The 24 mA level is used to detect the secondary reconfiguration status and the
120 mA level to detect an Over Voltage status called Quick OVP.
The Current Sense pin senses the voltage developed on the series resistor inserted in the source of the
power MOSFET. When I
Current Protection function. A 200 mA current source is flowing out of the pin 3 during the start−up phase and
during the switching phase in case of the Pulsed Mode of operation. A resistor can be inserted between the
sense resistor and the pin 2, thus a programmable peak current detection can be performed during the SMPS
stand−by mode.
A feedback current from the secondary side of the SMPS via the Opto−coupler is injected into this pin. A
resistor can be connected between this pin and GND to allow the programming of the Burst duty cycle during
the Stand−by mode.
This pin is the ground of the primary side of the SMPS.
The current and slew rate capability of this pin are suited to drive Power MOSFETs.
This pin is the positive supply of the IC. The driver output gets disabled when the voltage becomes higher
than 15 V and the operating range is between 6.6 V and 13 V. An intermediate voltage level of 10 V creates a
disabling condition called Latched Off phase.
This pin is to provide isolation between the V
This pin can be directly connected to a 500 V voltage source for start−up function of the IC. During the
Start−up phase a 9.0 mA current source is internally delivered to the V
V
0
0
CC
capacitor. As soon as the IC starts−up, this current source is disabled.
V dd
4 kHz
Filter
&
Regulation
Output
Switching Phase
Stand−by
Latched off Phase
PIN FUNCTION DESCRIPTION
OPERATING DESCRIPTION
sense
Comparator
PWM
reaches 1.0 V, the Driver output (pin 5) is disabled. This is known as the Over
http://onsemi.com
1.6 V
MC44608
5
i
Latched Off Phase while the switch S2 remains open. (See
section PULSED MODE DUTY CYCLE CONTROL).
the regulation process. This resistor is used to determine the
burst duty cycle described in the chapter “Pulsed Duty Cycle
Control” on page 8.
PWM Latch
controlled by the PWM comparator that compares the
oscillator sawtooth with the regulation block output (refer to
the block diagram on page 2).
by the PWM comparator or by the current sense comparator
in case of an over current. This configuration ensures that
only a single pulse appears at the circuit output during an
oscillator cycle.
Current Sense
inserting a ground reference sense resistor R
with the power switch.
The peak current is given by the following equation:
pin 8 and the V
The switch S3 is closed in Stand−by mode during the
The resistor Rdpulsed (Rduty cycle burst) has no effect on
The MC44608 works in voltage mode. The on−time is
The PWM latch is initialized by the oscillator and is reset
The inductor current is converted to a positive voltage by
The maximum current sense threshold is fixed at 1.0 V.
Description
Ipk max +
CC
pin 6.
R sense (W)
CC
1
pin 6 allowing a rapid charge of the
(A)
Sense
in series