MC44603
As depicted in Figure 47, an undervoltage lockout has
been incorporated to garantee that the IC is fully functional
before allowing system operation.
Undervoltage Lockout Section
Figure 47. V
Management
CC
This block particularly, produces V (Pin 16 voltage) and
ref
I
that is determined by the resistor R connected between
ref
ref
Pin 16 and the ground:
R
R
ref
F Stby
V
R
ref
ref
I
where V
2.5 V (typically)
ref
ref
Pin 15
Pin 16
V
Another resistor is connected to the Reference Block:
ref enable
startup
1
R
that is used to fix the standby frequency.
F Stby
V
C
CC
In addition to this, V
is compared to a second threshold
). UVLO1 is
CC
level that is nearly equal to 9.0 V (V
1
disable1
generated to reset the maximum duty cycle and soft–start
block disabling the output stage as soon as V becomes
Reference Block:
Voltage and Current
Sources Generator
0
CC
. In this way, the circuit is reset and made
1
0
(V , I , ...)
lower than V
ref ref
disable1
V
Startup
14.5 V
ready for the next startup, before the reference block is
disabled (refer to Figure 29). Finally, the upper limit for the
minimum normal operating voltage is 9.4 V (maximum value
disable2
7.5 V
C
UVLO1
UVLO1
of V
) and so the minimum hysteresis is 4.2 V.
disable1
(to Soft–Start)
((V
)
= 13.6 V).
stup–th min
V
disable1
9.0 V
The large hysteresis and the low startup current of the
MC44603 make it ideally suited for off–line converter
applications where efficient bootstrap startup techniques are
required.
18
MOTOROLA ANALOG IC DEVICE DATA
ONSEMI [ ONSEMI ]
