Datasheet

LTC4361-1/LTC4361-2
10
436112fb
applicaTions inFormaTion
Figure 4. 20V Hot-Plug into a 10µF Capacitor
Figure 5. 20V Hot-Plug into the LTC4361
+
LOAD
436112 F04a
MOBILE
DEVICE
WALL ADAPTOR
AC/DC
C
OUT
IN
L
IN
R
IN
CABLE
I
CABLE
V
IN
10V/DIV
I
CABLE
20A/DIV
5µs/DIV
436112 F04b
R
IN
= 150mΩ,
L
IN
= 0.7µH
LOAD = 10Ω, C
OUT
= 10µF
+
LOAD
LTC4361
M1
Si1470DH
GATE
GND
436112 F05a
MOBILE
DEVICE
WALL ADAPTOR
AC/DC
C
OUT
SENSE OUT
IN
IN OUT
L
IN
R
IN
R
SENSE
CABLE
I
CABLE
V
IN
10V/DIV
V
OUT
1V/DIV
I
CABLE
20A/DIV
5µs/DIV
436112 F05b
R
IN
= 150mΩ,
L
IN
= 0.7µH, R
SENSE
= 25mΩ
LOAD = 10Ω, C
OUT
= 10µF
Input Transients
Figure 4 shows a typical setup when an AC wall adaptor
charges a mobile device. The inductor L
IN
represents the
lumped equivalent inductance of the cable and the EMI filter
found in some wall adaptors. R
IN
is the lumped equivalent
resistance of the cable, adaptor output capacitor ESR and
the connector contact resistance.
L
IN
and R
IN
form an LC tank circuit with any capacitance
at IN. If the wall adaptor is powered up first, plugging the
wall adaptor output to IN does the equivalent of applying
a voltage step to this LC circuit. The resultant voltage
overshoot at IN can rise to twice the DC output voltage
of the wall adaptor as shown in Figure 4. Figure 5 shows
the 20V adaptor output applied to the LTC4361. Due to
the low capacitance at the IN pin, the plug-in transient has
been brought down to a manageable level.