ML4828 Micro Linear, ML4828 Datasheet - Page 8

• Manufacturer Part Number: ML4828
• Description: BiCMOS Phase Modulation/Soft Switching Controller
• Manufacturer: Micro Linear

ML4828
If the current limit condition persists, then I
reactivated, thus charging C
in Figure 7. Eventually, the voltage at RST will exceed
2.5V, and the soft start comparator will trip, shutting down
all power drivers and inhibiting any further delivery of
power. At the same time, the soft start capacitor C
discharged to prepare for the next start up cycle.
During the I
discharged through R
When the condition causing the current limit is removed,
R
When the voltage at RST (pin 12) drops to 1.25V, the soft
start comparator and the converter will undergo a start up
cycle. The restart delay (t
8
RST
V(PIN 20)
V(PIN 12)
2.5V
will discharge C
1V
Figure 7. I
LIM
Waveforms During Short Circuit.
shutdown, I
t
t
D RST
RST
RST
RST
(
LIM
with a time constant of:
with a time constant of t
D(RST)
)
and Resulting RC
R
RST
RST
RST
t
RST
) is given by:
is turned off, and C
to a higher level as shown
C
. 1 39
RST
RST
RST
will be
RST.
SS
RST
is
(12)
(13)
is
For example, with C
and
Since the threshold for shutdown is 2.5V, the controller
will shut down after approximately 125ms. After the
converter recovers form the current limit condition, the
controller will reactivate after 8.3s.
UNDERVOLTAGE LOCKOUT
During start-up, the ML4828 draws very little current
(typically 150 A) and V
above 6.0V, the internal circuitry and V
and will stay enabled until V
lockout threshold.
SHUTDOWN FUNCTION
The ML4828 can be externally shut down by bringing
SDN (pin 19) low. The shutdown threshold (V
by
For example, if V
2.4V < V
CC
t
D RST
< 6.0V, the SDN pin will be TTL compatible.
(
)
CC
dv
= 5V, then V
(
dt
RST
240
V
SD
REF
= 25 F and R
k
500
25
0 33
is disabled. When V
.
CC
25
F
A
falls below the 4.5V UV
SD
F
V
)
20
CC
= 1.67V. As long as
1 39 8 3
V
RST
s
.
REF
= 240k :
are enabled,
.
SD
s
CC
) is given
rises
(14)
(15)
(16)