Datasheet

LT1934/LT1934-1
14
1934fe
APPLICATIONS INFORMATION
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 fi rst plot is the response with
a 2.2μF 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
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 fi ltering and can
slightly improve the effi ciency of the circuit, though it is
likely to be the largest component in the circuit. An alterna-
tive solution is shown in Figure 7c. A 1Ω resistor is added
+
LT1934
2.2μF
V
IN
10V/DIV
I
IN
10A/DIV
10μs/DIV
V
IN
CLOSING SWITCH
SIMULATES HOT PLUG
I
IN
(7a)
(7b)
(7c)
(7d)
(7e)
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
+
LT1934
2.2μF
10μF
35V
AI.EI.
LT1934
2.2μF0.1μF
1Ω
LT1934-1
1μF
LT1934-1
1μF
1934 F07
0.1μF
4.7Ω
Figure 7. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation When the LT1934 is Connected to a Live Supply