LT1934 LINER [Linear Technology], LT1934 Datasheet - Page 13

• Manufacturer Part Number: LT1934
• Description: Micropower Step-Down Switching Regulators in ThinSOT
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
Figure 7 shows the waveforms that result when an LT1934
circuit is connected to a 24V supply through six feet of
24-gauge twisted pair. The first plot is the response with
a 2.2 F ceramic capacitor at the input. The input voltage
rings as high as 35V and the input current peaks at 20A.
One method of damping the tank circuit is to add another
capacitor with a series resistor to the circuit. In Figure 7b
24V SUPPLY
IMPEDANCE
U
ENERGIZED
LOW
+
U
Figure 7. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation When the LT1934 is Connected to a Live Supply
SIMULATES HOT PLUG
CLOSING SWITCH
AI.EI.
0.1 F
0.1 F
10 F
35V
W
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
+
I
4.7
IN
1
V
IN
U
2.2 F
2.2 F
2.2 F
1 F
1 F
LT1934-1
LT1934-1
LT1934
LT1934
LT1934
(7a)
(7b)
(7c)
(7d)
(7e)
an aluminum electrolytic capacitor has been added. This
capacitor’s high equivalent series resistance damps the
circuit and eliminates the voltage overshoot. The extra
capacitor improves low frequency ripple filtering and can
slightly improve the efficiency of the circuit, though it is
likely to be the largest component in the circuit. An
alternative solution is shown in Figure 7c. A 1 resistor is
10V/DIV
10A/DIV
V
I
IN
IN
10 s/DIV
LT1934/LT1934-1
1934 F07
13
1934f