Datasheet

LTC4362-1/LTC4362-2
9
436212fa
APPLICATIONS INFORMATION
Thermal Shutdown
The internal N-channel MOSFET is protected by a thermal
shutdown circuit. If its temperature reaches 150°C, it will
shut off immediately and the PWRGD pull-down releases.
It will turn on again after its temperature drops below
140°C.
Input Transients
Figure 3 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 fi lter
found in some wall adaptors. R
IN
is the lumped equivalent
resistance of the cable, adaptor output capacitor ESR and
the connector contact resistance.
Figure 3. 20V Hot-Plug Into a 10μF Capacitor
Figure 4. 20V Hot-Plug Into the LTC4362
5µs/DIV
V
IN
10V/DIV
I
CABLE
20A/DIV
R
IN
= 150m, L
IN
= 0.7µH
LOAD = 10, C
OUT
= 10µF
436212 F03b
5µs/DIV
V
IN
10V/DIV
V
OUT
1V/DIV
I
CABLE
1A/DIV
R
IN
= 150m, L
IN
= 0.7µH
LOAD = 10, C
OUT
= 10µF
436212 F04b
R
IN
I
CABLE
L
IN
C
OUT
436212 F03a
WALL ADAPTOR
AC/DC
LOAD
IN
MOBILE DEVICE
CABLE
+
R
IN
I
CABLE
L
IN
C
OUT
436212 F04a
WALL ADAPTOR
AC/DC
LT4362
GND
LOAD
OUTIN
OUTIN
MOBILE DEVICE
CABLE
+
L
IN
and R
IN
form an LC tank circuit with any capacitance
at IN. If the wall adaptor is powered-up fi rst, 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 (or more if ceramic capacitors with large
voltage coeffi cients are used) as shown in Figure 3. Figure 4
shows the 20V adaptor output applied to the LTC4362.
Due to the low capacitance at the IN pin, the plug-in transient
has been brought down to a manageable level.
Input transients also occur when the current through
the cable inductance changes abruptly. This can hap-
pen when the LTC4362 turns off its internal N-channel
MOSFET quickly in an overvoltage or overcurrent event.