Datasheet

LTC4360-1/LTC4360-2
11
436012fa
APPLICATIONS INFORMATION
Figure 10. Recommended Layout for N-Channel MOSFET and P-/N-Channel MOSFET Configurations
LTC4360 to shut off the MOSFET before V
OUT
overshoots
to a dangerous voltage. A larger C
OUT
also helps to lower
the ∆V
OUT
due to the discharge of the energy in L
IN
if the
MOSFET BV
DSS
is used as an input clamp.
Layout Considerations
Figure 10 shows example PCB layouts for the single
N-channel MOSFET (SC70 package) configuration and the
P-channel MOSFET/N-channel MOSFET (Complementary
P, N MOSFET in TSOP-6 package) configuration. Keep the
traces to the MOSFETs wide and short. The PCB traces
associated with the power path through the MOSFETs
should have low resistance.
Si3590DV
436012 F09
Si1470DH
SUPPLY/IN
SUPPLY
IN
OUT
OUT
GND
GND
6 5 4
1 2 3
1
2
3
4
8
7
6
5
LTC4360-2
1
2
3
4
8
7
6
5
1 2 3
6 5 4
LTC4360-1
Figure 9. Overvoltage Protection Waveforms When 20V Plugged into 5V System
V
IN
20V/DIV
V
GATE
10V/DIV
V
OUT
5V/DIV
I
CABLE
10A/DIV
1µs/DIV
436012 F08
FIGURE 8 CIRCUIT
R
IN
= 150mΩ, L
IN
= 2µH
LOAD = 10Ω, C
OUT
= 10µF (16V, SIZE 1210)
with the USB input already live. As shown in Figure 9, a
large current can build up in L
IN
to charge up C
OUT
. When
the N-channel MOSFET shuts off, the energy stored in L
IN
is dumped into C
OUT
, causing a large 40V input transient .
The LTC4360 limits this to a 1V rise in the output voltage.
If the voltage rise at V
OUT
due to the discharge of the
energy in L
IN
into C
OUT
is not acceptable or the avalanche
capability of the MOSFET is exceeded, an additional exter-
nal clamp such as the SMAJ24A can be placed between
IN and GND. C
OUT
is the decoupling capacitor of the
protected circuits and its value will largely be determined
by their requirements. Using a larger C
OUT
will work with
L
IN
to slow down the dV/dt at OUT, allowing time for the