MC44604_05 ONSEMI [ON Semiconductor], MC44604_05 Datasheet - Page 15

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

The Sawtooth Generation
about 1.6 V and 3.6 V.
discharging an external capacitor C
distinct current sources = I
is permanently connected to the charging current source
(0.4 I
higher than the charge one to be able to decrease the C
voltage. This condition is performed, its value being
(2 I
compare the C
values. The comparison to the low value enables to detect the
end of the discharge phase while the comparison to the high
value determines when the charge cycle must be stopped. A
latch (L
third state can exist. This phase can be produced when at the
end of the discharge phase, the oscillator has to wait for a
demagnetization pulse before re−starting. During this
delay, the C
valley value (X1.6 V). So, a third regulated current source
I
C
REGUL
T
In the steady state, the oscillator voltage varies between
Indeed, the sawtooth is obtained by charging and
Two comparators are used to generate the sawtooth. They
Now, in addition to the charge and discharge cycles, a
ref
10
ref
).
1.6 V
DISCH
) and so, the discharge current source has to be
3.6 V
1 V
controlled by C
T
1
V
) memorizes the oscillator state.
voltage must remain equal to the oscillator
ref
T
0
voltage to the oscillator valley and peak
C
C
I
0.4 I
C
C
REGUL
Figure 30. Oscillator
VOS PROT
OSC LOW
OSC HIGH
OSC REGUL
REF
OSC REGUL
MC44604
DISCHARGE
charge
C
T
DISCH
R
S
< 1.6 V
and I
, is connected to C
Q
T
V
discharge
osc prot
(Pin 10), using two
I
DISCHARGE
S
R
L
OSC
V
. In fact, C
demag out
Q
0
http://onsemi.com
V
osc
T
1
MC44604
in
T
T
15
order to perfectly compensate the (0.4 I
that permanently supplies C
charge. So, the maximum duty cycle is 80%. (Note 1)
second latch (L
details.)
Oscillator Frequency
following equations:
where:
and
So, as:
arrangement is not activated, the following equation can
be obtained:
Demagnetization Block (Note 2)
must be low. Now, this latch reset is activated by the L
output during the discharge phase. So, to restart, the L
to be set (refer to Figure 30). To perform this, the
demagnetization signal must be low.
consists in using the V
voltage is:
− negative during the on−time,
− positive during the off−time,
− equal to zero for the dead−time with generally a
consists of a comparator that can compare the V
voltage to a reference that is typically equal to 65 mV.
Note 1. The output is disabled by the signal V
Note 2. The demagnetization detection can be inhibited by
On−time is only allowed during the oscillator capacitor
The demagnetization condition is taken into account by a
The oscillator frequency can be deducted using the
T
DV is the oscillator peak to peak value
I
T
I
f
To enable the output, the L
In a fly−back, a good means to detect the demagnetization
That is why, the MC44604 demagnetization detection
charge
discharge
osc
charge
discharge
ringing (refer to Figure 31).
connecting pin 8 to the ground.
is lower than 1 V. (Refer to Figure 29 and Figure 30.)
= 1 /(T
is the oscillator charge current
is the oscillator charge time
is the oscillator discharge current
is the oscillator discharge time
T
discharge
osc
T
charge
charge
). (Refer to demagnetization § for further
f osc X
+ C
+ C
CC
+ T
osc
R
T
T
winding voltage. Indeed this
T
0 · 395
ref
.
discharge
•
•
.
latch complementary output
DV
DV I
•
C
T
I
charge
discharge
) if the REGUL
ref
osc prot
) current source
CC
when V
winding
osc
DISCH
has
CT