LT3493 LINER [Linear Technology], LT3493 Datasheet - Page 14

• Manufacturer Part Number: LT3493
• Manufacturer: LINER [Linear Technology]

LT3493
APPLICATIONS INFORMATION
14
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
Figure 7. To Soft-Start the LT3493, Add a Resistor and Capacitor to the SHDN Pin. V
V
IN
D4: MBR0540
D4
0.1μF
RUN
V
SHDN
IN
GND
15k
RUN
LT3493
BOOST
FB
SHDN
SHDN
SW
GND
GND
3493 F07b
3493 F07a
3493 F08
V
BACKUP
OUT
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
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
0.5A/DIV
0.5A/DIV
10V/DIV
10V/DIV
2V/DIV
2V/DIV
V
V
V
V
OUT
OUT
SW
SW
I
I
L
L
IN
V
V
L = 10μH
C
V
V
L = 10μH
C
IN
OUT
OUT
IN
OUT
OUT
pin of the LT3493 can ring to twice the nominal
= 12V
= 12V
= 3.3V
= 10μF
= 3.3V
= 10μF
IN
= 12V, V
20μs/DIV
20μs/DIV
OUT
= 3.3V, C
OUT
= 10μF , R
LOAD
= 5Ω
3493fb