MC44604_05 ONSEMI [ON Semiconductor], MC44604_05 Datasheet - Page 16

• Manufacturer Part Number: MC44604_05
• Description: High Safety Pulsed Mode Standby GreenLine TM PWM Controller
• Manufacturer: ONSEMI [ON Semiconductor]

applied voltages while an active clamping system limits the
negative voltages to typically −0.33 V. This negative clamp
level is sufficient to avoid the substrate diode switching on.
incorporated in order to keep the demagnetization block
output level low as soon as a voltage lower than 65 mV is
detected and as long as a new restart is produced (high level
on the output) (refer to Figure 33). This process avoids that
any ringing on the signal used on the pin 8, disrupts the
demagnetization detection. Finally, this method results in a
very accurate demagnetization detection.
also directly connected to the output, disabling it during the
demagnetization phase (refer to Figure 29).
Oscillator
V
A diode D has been incorporated to clamp the positive
In addition to the comparator, a latch system has been
For a higher safety, the demagnetization block output is
Pin 8
V
Buffer
demag out
Figure 31. Demagnetization Detection
Figure 32. Demagnetization Block
On−Time
Output
Off−Time Dead−Time
Demag
R
S
C DEM
Q
Zero Current
Detection
65 mV
Clamping System
Negative Active
V
CC
D
−0.33 V
0.75 V
65 mV
Pin 8
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MC44604
16
Maximum Duty Cycle and Soft−Start Control
cannot be more than 80%. Now, using the D
soft−start control, this duty cycle can be limited to a lower
value. Indeed as depicted in Figure 34, the pin 11 voltage is
compared to the oscillator sawtooth, so that the MC44604
output should be disabled as soon as the pin 11 level
becomes lower than the oscillator voltage (refer to Figure 27
and to Figure 25).
Voltage
voltage can easily be fixed by connecting a resistor to this
pin.
or in parallel to a resistor for instance), the pin 11 voltage
increases from 0 to its maximum value progressively (refer
to Figure 26).
depending on the capacitor value (and the resistor value
when a resistor is connected).
startup phase and thus, to perform a soft−start.
D
As explained in the paragraph “oscillator”, the duty cycle
Now, using the internal current source (0,4 I
If a capacitor is connected to pin 11 (without any resistor
Thus, the allowed maximum duty cycle grows for a delay
So, this pin can be used to limit the duty cycle during the
Soft−Start
Capacitor
max
Figure 33. D
Pin 11
Figure 34. Maximum Duty Cycle Control
D
Z
max
2.4 V
V
ref
and Soft−Start Block Diagram
0.4 I
V
OSC
ref
MC44604
Oscillator
Control
Output
D
max
ref
Output
Buffer
), the pin 11
max
(Pin 10)
Pin 11
V
CT
and