Datasheet

LT3493
14
3493fb
APPLICATIONS INFORMATION
RUN
V
SW
10V/DIV
V
IN
= 12V
V
OUT
= 3.3V
L = 10μH
C
OUT
= 10μF
V
OUT
2V/DIV
20μs/DIV
I
L
0.5A/DIV
V
SW
10V/DIV
V
IN
= 12V
V
OUT
= 3.3V
L = 10μH
C
OUT
= 10μF
V
OUT
2V/DIV
20μs/DIV
I
L
0.5A/DIV
SHDN
GND
3493 F07a
RUN
15k
0.1μF
SHDN
GND
3493 F07b
Figure 7. To Soft-Start the LT3493, Add a Resistor and Capacitor to the SHDN Pin. V
IN
= 12V, V
OUT
= 3.3V, C
OUT
= 10μF, R
LOAD
= 5Ω
V
IN
BOOST
GND FB
SHDN SW
D4
V
IN
LT3493
3493 F08
V
OUT
BACKUP
D4: MBR0540
Figure 8. Diode D4 Prevents a Shorted Input from Discharging
a Backup Battery Tied to the Output; It Also Protects the Circuit
from a Reversed Input. The LT3493 Runs Only When the Input
is Present
a complete discussion). The low loss ceramic capacitor
combined with stray inductance in series with the power
source forms an underdamped tank circuit, and the voltage
at the V
IN
pin of the LT3493 can ring to twice the nominal
input voltage, possibly exceeding the LT3493’s rating and
damaging the part. If the input supply is poorly controlled
or the user will be plugging the LT3493 into an energized
supply, the input network should be designed to prevent
this overshoot.
Figure 9 shows the waveforms that result when an LT3493
circuit is connected to a 24V supply through six feet of
24-gauge twisted pair. The fi rst plot is the response with
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