LTC4360ISC8-2TRMPBF datasheet(10/12 Pages) LINER

10 / 12 page

LTC4360-1/LTC4360-2

436012f

APPLICATIONS INFORMATION

Figure 10. Recommended Layout for N-Channel MOSFET

and P-/N-Channel MOSFET Conﬁgurations

If the voltage rise at VOUT due to the discharge of the

energy in LIN into COUT 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. COUT is the decoupling capacitor of the

protected circuits and its value will largely be determined

by their requirements. Using a larger COUT will work with

LIN to slow down the dV/dt at OUT, allowing time for the

LTC4360 to shut off the MOSFET before VOUT overshoots

to a dangerous voltage. A larger COUT also helps to lower

the

ΔVOUT due to the discharge of the energy in LIN if the

MOSFET BVDSS 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

OUT

GND

LTC4360-2

LTC4360-1

Figure 8. Setup for Testing 20V Plugged into 5V System

LOAD

436012 F07

OUT

COUT

Si1470DH

LIN

RIN

20V

WALL

ADAPTER

USB

LTC4360

100k

B160

OUT

GND

GATE

–

ICABLE

Figure 9. Overvoltage Protection Waveforms

When 20V Plugged into 5V System

VIN

20V/DIV

VGATE

10V/DIV

VOUT

5V/DIV

ICABLE

10A/DIV

1μs/DIV

436012 F08

FIGURE 8 CIRCUIT

RIN = 150mΩ, LIN = 2μH

LOAD = 10Ω, COUT = 10μF (16V, SIZE 1210)

Figure 8 shows a particularly severe situation which can

occur in a mobile device with dual power inputs. A 20V wall

adaptor is mistakenly hot-plugged into the 5V device with

the USB input already live. As shown in Figure 9, a large

current can build up in LIN to charge up COUT. When the

N-channel MOSFET shuts off, the energy stored in LIN is

dumped into COUT, causing a large 40V input transient. The

LTC4360 limits this to a 1V rise in the output voltage.

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