LTC4360ISC8-2TRMPBF datasheet(6/12 Pages) LINER

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LTC4360-1/LTC4360-2

436012f

OPERATION

Mobile devices like cell phones and MP3/MP4 players have

highly integrated subsystems fabricated from deep submi-

cronCMOSprocesses.Thesmallformfactorisaccompanied

by low absolute maximum voltage ratings. The sensitive

electronics are susceptible to damage from transient or DC

overvoltage conditions from the power supply.

Failures or faults in the power adaptor can cause an over-

voltage event. So can hot-plugging an AC adaptor into the

power input of the mobile device (see LTC Application Note

88). Today’s mobile devices derive their power supply or

recharge their internal batteries from multiple alternative

inputs like AC wall adaptors, car battery adaptors and USB

ports. A user may unknowingly plug in the wrong adaptor,

damaging the device with a high or even a negative power

supply voltage.

The LTC4360 protects low voltage electronics from these

overvoltage conditions by controlling a low cost external

N-channel MOSFET conﬁgured as a pass transistor. At

power-up (VIN > 2.1V), a start-up delay cycle begins. Any

overvoltage condition causes the delay cycle to continue

until a safe voltage is present. When the delay cycle

completes, an internal high side switch driver slowly

ramps up the MOSFET gate, powering up the output at

a controlled rate and limiting the inrush current to the

output capacitor.

If the voltage at the IN pin exceeds 5.8V (VIN(OV)),

GATE is pulled low quickly to protect the load. The

incoming power supply must remain below 5.7V

(VIN(OV) – ΔVOV) for the duration of the start-up delay to

restart the GATE ramp-up.

The LTC4360-1 has a CMOS compatible ON input. When

driven low, the part is enabled. When driven high, the

external N-channel MOSFET is turned off and the supply

current of the LTC4360-1 drops to 1.5μA. The PWRGD

pull-down releases during this low current sleep mode,

UVLO or overvoltage and the subsequent 130ms start-up

delay. After the start-up delay, GATE starts its slow ramp-

up and ramps higher than VGATE(TH) to trigger a 65ms

delay cycle. When that completes, PWRGD pulls low.

The LTC4360-2 has a GATEP pin that drives an optional

external P-channel MOSFET to provide protection against

negative voltages at IN.

The typical LTC4360 application protects 2.5V to 5.5V sys-

tems in portable devices from power supply overvoltage.

The basic application circuit is shown in Figure 1. Device

operation and external component selection is discussed

in detail in the following sections.

Start-Up

When VIN is less than the undervoltage lockout level of

2.1V, the GATE driver is held low and the PWRGD pull-

down is high impedance. When VIN rises above 2.1V and

ON (LTC4360-1) is held low, a 130ms delay cycle starts.

Any undervoltage or overvoltage event at IN (VIN < 2.1V or

VIN > 5.7V) restarts the delay cycle. This delay allows the

N-channel MOSFET to isolate the output from any input

transients that occur at start-up. When the delay cycle

completes, GATE starts its slow ramp-up.

GATE Control

An internal charge pump enhances the external MOSFET

with 6V from GATE to OUT. This allows the use of logic-

level N-channel MOSFETs. An internal 6V clamp between

GATE and OUT protects the MOSFET gate.

APPLICATIONS INFORMATION

GATE

COUT

10μF

Si1470DH

436012 F01

VOUT

1.5A

VIN

LTC4360-1

OUT

PWRGD

GND

Figure 1. Protection from Input Overvoltage

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