MC44605_06 ONSEMI [ON Semiconductor], MC44605_06 Datasheet - Page 16

• Manufacturer Part Number: MC44605_06
• Description: High Safety, Latched Mode, GreenLine TM PWM Controller for (Multi) Synchronized Applications
• Manufacturer: ONSEMI [ON Semiconductor]

and:
So:
of which, Dis
latch” of the disabling block. So, when the calculated power
is higher than the threshold, the circuit is definitively
disabled (the system considers that there is an overload
condition).
the R
Overheating Detection Section (O.H.D.)
In the O.H.D. block, that is the power MOSFET heating
which is calculated, using the following equation:
where: p
A comparator is used to compare V
Finally, replacing V
In the MPL block, the converter input power is calculated.
V
MPL
MPL
R
d is the duty cycle
R
on
dson
value to be used, can be deducted:
MPL
+
are the power switch on−time losses
V
MPL
is the conduction MOSFET resistor
p on + 1
MPL
2
+
Figure 14. OHD and MPL
, is connected to the “definitive inhibition
Γ
R
T
MPL
k
2.5 V
2.5 V
MPL
Vcs + R
OHD
OHD
3
MPL
Output
Vcs
R
Vcs
by 2.5 V (the threshold value),
x
dson
C
Dis
2
Dis
Γ
Disabling
1.25
L
T
S
MPL
V
Block
P
OHD
MPL
MPL
MC44605
R 2
Ipk
Ipk 2
S
L
MPL
C
P
T
k
T
MPL
MPL
(Pin) max
to V
Sf
d
Vcs
R 2
ref
S
2
, the output
Pin
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MC44605
16
by building a current source proportional to Vcs
on this current source of a “chopper” controlled by the
circuit output. By this means, the pin 6 average current is
proportional to the squared peak current multiplied to the
duty cycle (refer to Figure 14).
(R
the conduction losses can be obtained.
2.5 V. If V
block is activated by Dis
calculated V
are equal to their maximum value.
In effect,
where: k
source I
where: k2 is a constant
So:
Finally:
where: Γ
Now, as:
So, replacing Vcs and using the p
corresponding to V
dissipation is such that the heating is higher than this
threshold, the “definitive inhibition latch” of the Disabling
Block is activated and so, the output gets definitively
disabled.
As in the MPL section, the squared Ipk term is estimated
The duty cycle is taken into account thanks to the action
So, using an external resistor and capacitor network
Like in the MPL block, this voltage V
The external resistor R
Now, as k
So, by choosing the value of R
OHD
, C
specification. This is a constant equal to k2.
ref
OHD
OHD
OHD
V
OHD
, is proportional to 1/R
V
OHD
V
V
OHD
OHD
OHD
OHD
OHD
is the multiplier gain
) on this pin, a voltage V
is the OHD parameter as defined in the
gets higher than this threshold, the disabling
+ R
that is depending on the reference current
equal to 2.5 V when the conduction losses
+
+ R
+
k
OHD
3
Vcs + R
ref
OHD
R
OHD
OHD
is determined. If the MOSFET
OHD
R
OHD
+ k2
OHD
R
ref
(output of the comparator).
k
S
OHD
choice enables to obtain a
k2
Γ
ref
OHD
on
R
Ipk
R
R
Γ
:
ref
1
ref
equation:
OHD
dson
Vcs 2
R
OHD
OHD
Vcs 2
ref
OHD
Vcs 2
, proportional to
, is compared to
, the heating
R 2
d
S
d
2
.
d
p on