LTC4364IMS-2#PBF - LINEAR TECHNOLOGY

LTC4364-1/LTC4364-2

436412f

TYPICAL APPLICATION

FEATURES DESCRIPTION

Surge Stopper

with Ideal Diode

The LTC

4364 surge stopper with ideal diode controller

protects loads from high voltage transients. It limits and

regulates the output during an overvoltage event, such

as load dump in automobiles, by controlling the voltage

drop across an external N-channel MOSFET pass device.

The LTC4364 also includes a timed, current limited circuit

breaker. In a fault condition, an adjustable fault timer must

expire before the pass device is turned off. The LTC4364-1

latches off the pass device while the LTC4364-2 automati-

cally restarts after a delay. The LTC4364 precisely monitors

the input supply for overvoltage (OV) and undervoltage

(UV) conditions. The external MOSFET is held off in un-

dervoltage and auto-retry is disabled in overvoltage.

An integrated ideal diode controller drives a second MOS-

FET to replace a Schottky diode for reverse input protec-

tion and output voltage holdup. The LTC4364 controls the

forward voltage drop across the MOSFET and minimizes

reverse current transients upon power source failure,

brownout or input short.

Overvoltage Protector Regulates

Output at 27V During Input Transient

Ideal Diode Holds Up Output

During Input Short

4A, 12V Overvoltage Output Regulator with Ideal Diode

Withstands 200V 1ms Transient at VIN

APPLICATIONS

n Wide Operating Voltage Range: 4V to 80V

n Withstands Surges Over 80V with VCC Clamp

n Adjustable Output Clamp Voltage

n Ideal Diode Controller Holds Up Output Voltage

During Input Brownouts

n Reverse Input Protection to –40V

n Reverse Output Protection to –20V

n Overcurrent Protection

n Low 10μA Shutdown Current at 12V

n Adjustable Fault Timer

n 0.1% Retry Duty Cycle During Faults (LTC4364-2)

n Available in 4mm × 3mm 14-Lead DFN, 16-Lead MSOP,

and 16-Lead SO Packages

n Automotive/Avionic Surge Protection

n Hot Swap/Live Insertion

n Redundant Supply ORing

n Output Port Protection

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

OUTSENSEDGATESOURCEHGATE

TMRGND

0.22µF

60V OV ENOUT ENABLE

FAULT

436412 TA01a

F LT

SHDN FB

10Ω

2.2k

383k

VIN

12V

90.9k

10k

102k

22µF

VOUT

CLAMPED

AT 27V

4.99k

CMZ5945B

68V

FDB33N25 FDB3682 10mΩ

6.8nF

VCC

LTC4364

50ms/DIV

CTMR = 6.8µF

ILOAD = 0.5A

VIN

20V/DIV

12V

VOUT

20V/DIV

92V INPUT SURGE

27V CLAMP (ADJUSTABLE)

4364 TA01b

1ms/DIV

CLOAD = 6300µF

ILOAD = 0.5A

VIN

10V/DIV

12V

VOUT

10V/DIV

4364 TA01c

INPUT SHORTED

TO GND

OUTPUT HELD UP

LTC4364-1/LTC4364-2

436412f

ABSOLUTE MAXIMUM RATINGS

Supply Voltage: VCC ................................. –40V to 100V

SOURCE, OV, UV, SHDN Voltages ............. –40V to 100V

DGATE, HGATE Voltages

(Note 3) ..................... SOURCE – 0.3V to SOURCE + 10V

ENOUT, FLT Voltages ................................ –0.3V to 100V

OUT, SENSE Voltages.................................–20V to 100V

Voltage Difference (SENSE to OUT) ............ –30V to 30V

Voltage Difference (OUT to VCC) ..............–100V to 100V

Voltage Difference (SENSE to SOURCE) ..–100V to 100V

(Notes 1, 2)

TMR

ENOUT

FLT

GND

OUT

SENSE

DGATE

SOURCE

HGATE

VCC

SHDN

TOP VIEW

DE PACKAGE

14-LEAD (4mm × 3mm) PLASTIC DFN

TJMAX = 150°C, θJA = 45°C/W

EXPOSED PAD (PIN 15) PCB GND CONNECTION OPTIONAL

OUT

SENSE

DGATE

SOURCE

HGATE

VCC

TMR

ENOUT

F LT

GND

SHDN

TOP VIEW

MS PACKAGE

16-LEAD PLASTIC MSOP

TJMAX = 150°C, θJA = 120°C/W

TOP VIEW

S PACKAGE

16-LEAD PLASTIC SO

OUT

SENSE

DGATE

SOURCE

HGATE

VCC

TMR

ENOUT

FLT

GND

SHDN

TJMAX = 150°C, θJA = 100°C/W

PIN CONFIGURATION

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC4364CDE-1#PBF LTC4364CDE-1#TRPBF 43641 14-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C

LTC4364IDE-1#PBF LTC4364IDE-1#TRPBF 43641 14-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C

LTC4364HDE-1#PBF LTC4364HDE-1#TRPBF 43641 14-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C

LTC4364CDE-2#PBF LTC4364CDE-2#TRPBF 43642 14-Lead (4mm × 3mm) Plastic DFN 0°C to 70°C

LTC4364IDE-2#PBF LTC4364IDE-2#TRPBF 43642 14-Lead (4mm × 3mm) Plastic DFN –40°C to 85°C

LTC4364HDE-2#PBF LTC4364HDE-2#TRPBF 43642 14-Lead (4mm × 3mm) Plastic DFN –40°C to 125°C

LTC4364CMS-1#PBF LTC4364CMS-1#TRPBF 43641 16-Lead Plastic MSOP 0°C to 70°C

LTC4364IMS-1#PBF LTC4364IMS-1#TRPBF 43641 16-Lead Plastic MSOP –40°C to 85°C

LTC4364HMS-1#PBF LTC4364HMS-1#TRPBF 43641 16-Lead Plastic MSOP –40°C to 125°C

LTC4364CMS-2#PBF LTC4364CMS-2#TRPBF 43642 16-Lead Plastic MSOP 0°C to 70°C

LTC4364IMS-2#PBF LTC4364IMS-2#TRPBF 43642 16-Lead Plastic MSOP –40°C to 85°C

LTC4364HMS-2#PBF LTC4364HMS-2#TRPBF 43642 16-Lead Plastic MSOP –40°C to 125°C

FB, TMR Voltages ..................................... –0.3V to 5.5V

Operating Ambient Temperature Range

LTC4364C ................................................ 0°C to 70°C

LTC4364I ............................................. –40°C to 85°C

LTC4364H .......................................... –40°C to 125°C

Storage Temperature Range .................. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

MS, SO Packages ............................................. 300°C

LTC4364-1/LTC4364-2

436412f

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LTC4364CS-1#PBF LTC4364CS-1#TRPBF LTC4364S-1 16-Lead Plastic SO 0°C to 70°C

LTC4364IS-1#PBF LTC4364IS-1#TRPBF LTC4364S-1 16-Lead Plastic SO –40°C to 85°C

LTC4364HS-1#PBF LTC4364HS-1#TRPBF LTC4364S-1 16-Lead Plastic SO –40°C to 125°C

LTC4364CS-2#PBF LTC4364CS-2#TRPBF LTC4364S-2 16-Lead Plastic SO 0°C to 70°C

LTC4364IS-2#PBF LTC4364IS-2#TRPBF LTC4364S-2 16-Lead Plastic SO –40°C to 85°C

LTC4364HS-2#PBF LTC4364HS-2#TRPBF LTC4364S-2 16-Lead Plastic SO –40°C to 125°C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 12V.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VCC Operating Supply Range l4 80 V

ICC Supply Current VCC = SOURCE = SENSE = OUT = 12V, No Fault l370 750 µA

ICC(SHDN) Supply Current in Shutdown Shutdown l10 50 μA

ICC(REV) Reverse Input Current VCC = −30V l0 –10 μA

Surge Stopper

∆VHGATE HGATE Gate Drive, (VHGATE − VSOURCE) VCC = 4V, DGATE Low, IHGATE = 0µA, −1µA

VCC = 8V to 80V, DGATE Low, IHGATE = 0µA, −1µA

IHGATE(UP) HGATE Pull-Up Current VCC = HGATE = DGATE = SOURCE = 12V l–10 –20 –30 µA

IHGATE(DN) HGATE Pull-Down Current Overvoltage: FB = 1.5V, ∆VHGATE = 5V l60 130 mA

Overcurrent: ∆VSNS = 100mV, ∆VHGATE = 5V l60 130 mA

Shutdown/Fault Turn-Off: ∆VHGATE = 5V l0.4 1 mA

ISRC SOURCE Input Current VCC = SOURCE = SENSE = OUT = 12V

VCC = SOURCE = 12V, Shutdown

VSOURCE = –30V

–2.0

–3.5

µA

VFB FB Servo Voltage VCC = 12V to 80V l1.22 1.25 1.28 V

IFB FB Input Current FB = 1.25V l0 1 µA

∆VSNS Overcurrent Fault Threshold,

(VSENSE – VOUT)

VCC = 4V to 80V, OUT = 2.5V to VCC, 0°C to 125°C

VCC = 4V to 80V, OUT = 2.5V to VCC, –40°C to 125°C

VCC = 4V to 80V, OUT = 0V to 1.5V

ISNS SENSE Input Current SENSE = VCC = SOURCE = OUT = 12V

SENSE = –15V

–2

110

–4

µA

ITMR(UP) TMR Pull-Up Current, Overvoltage TMR = 1V, FB = 1.5V, VCC – OUT = 0.5V

TMR = 1V, FB = 1.5V, VCC – OUT = 75V

–1.3

–40

–2.2

–50

–3

–60

µA

TMR Pull-Up Current, Overcurrent TMR = 1V, ∆VSNS = 60mV, VCC – OUT = 0.5V

TMR = 1V, ∆VSNS = 60mV, VCC – OUT = 75V

–6

–210

–10

–260

–14

–310

µA

TMR Pull-Up Current, Warning TMR = 1.3V, FB = 1.5V, VCC – OUT = 0.5V l–3 –5 –7 µA

TMR Pull-Up Current, Retry TMR = 1V, FB = 1.5V l–1.3 –2 –3 µA

ITMR(DN) TMR Pull-Down Current TMR = 1V, FB = 1.5V, Retry

Shutdown

1.1

0.3

0.75

2.7

1.5

µA

VTMR(F) TMR Fault Threshold F LT Falling, VCC = 4V to 80V l1.22 1.25 1.28 V

VTMR(G) TMR Gate Off Threshold HGATE Falling, VCC = 4V to 80V l1.32 1.35 1.38 V

LTC4364-1/LTC4364-2

436412f

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at TA = 25°C. VCC = 12V.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VTMR(R) TMR Retry Threshold HGATE Rising (After 32 Cycles), VCC = 4V to 80V l0.125 0.15 0.175 V

∆VTMR Early Warning Timer Window VTMR(G) – VTMR(F), VCC = 4V to 80V l75 100 125 mV

VUV UV Input Threshold UV Falling, VCC = 4V to 80V l1.22 1.25 1.28 V

VUV(HYST) UV Input Hysteresis l25 50 80 mV

VUV(RST) UV Reset Threshold UV Falling, VCC = 4V to 80V, LTC4364-1 Only l0.5 0.6 0.7 V

VOV OV Input Threshold OV Rising, VCC = 4V to 80V l1.22 1.25 1.28 V

VOV(HYST) OV Input Hysteresis 12 mV

IIN UV, OV Input Current UV, OV = 1.25V

UV, OV = –30V

–0.3

–0.6

µA

VOL ENOUT, F LT Output Low ISINK = 0.25mA

ISINK = 2mA

0.1

0.5

0.3

1.3

ILEAK ENOUT, F LT Leakage Current ENOUT, F LT = 80V l0 2.5 µA

∆VOUT(TH) Out High Threshold (VCC – VOUT) ENOUT from Low to High l0.4 0.7 1 V

VOUT(RST) Out Reset Threshold ENOUT from High to Low l1.4 2.2 3 V

IOUT OUT Input Current VCC = OUT = 12V, SHDN Open

OUT = –15V

–4

–8

µA

Output Current in Shutdown, ISNS + IOUT VCC = SOURCE = SENSE = OUT = 12V, Shutdown l12 40 µA

VSHDN SHDN Input Threshold VCC = 4V to 80V l0.5 1.6 2.2 V

VSHDN(FLT) SHDN Pin Float Voltage VCC = 12V to 80V l2.3 4 6.5 V

ISHDN SHDN Input Current SHDN = 0.5V

Maximum Allowable Leakage, VCC = 4V

SHDN = –30V

–1 –3.3

–1.5

–120

–300

µA

D Retry Duty Cycle, Overvoltage

Retry Duty Cycle, Output Short

FB = 1.5V, VCC = 80V, OUT = 16V

∆VSNS = 60mV, VCC – OUT = 12V

0.125

0.075

0.2

0.12

tOFF,HGATE(UV) Undervoltage to HGATE Low Propagation

Delay

UV Steps from 1.5V to 1V l1.3 4 μs

tOFF,HGATE(OV) Overvoltage to HGATE Low Propagation

Delay

FB Steps from 1V to 1.5V l0.25 1 μs

tOFF,HGATE(OC) Overcurrent to HGATE Low Propagation

Delay ∆VSNS Steps from 0mV to 150mV, OUT = 0V l0.5 2 μs

Ideal Diode

ΔVDGATE DGATE Gate Drive, (VDGATE − VSOURCE) VCC = 4V, No Fault, IDGATE = 0µA, −1µA

VCC = 8V to 80V, No Fault, IDGATE = 0µA, −1µA

8.5

IDGATE(UP) DGATE Pin Pull-Up Current DGATE = SOURCE = VCC = 12V, ∆VSD = 0.1V l–5 –10 –15 µA

IDGATE(DN) DGATE Pin Pull-Down Current ∆VDGATE = 5V, ∆VSD = –0.2V

∆VDGATE = 5V, Shutdown/Fault Turn-Off

0.4

130

∆VSD Ideal Diode Regulation Voltage,

(VSOURCE − VSENSE)∆VDGATE = 2.5V, VCC = SOURCE = 12V

∆VDGATE = 2.5V, VCC = SOURCE = 4V

tOFF(DGATE) DGATE Turn-Off Propagation Delay ∆VSD Steps from 0.1V to –1V l0.35 1.5 μs

Note 1: Stress beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2: All Currents into device pins are positive and all currents out

of device pins are negative. All voltages are referenced to GND unless

otherwise specified.

Note 3: Internal clamps limit the HGATE and DGATE pins to minimum of

10V above the SOURCE pin. Driving these pins to voltages beyond the

clamp may damage the device.

LTC4364-1/LTC4364-2

436412f

TYPICAL PERFORMANCE CHARACTERISTICS

ISNS + IOUT in Shutdown vs VCC

ICC(SHDN) vs Temperature

GATE Pull-Up Current vs VCC ∆VHGATE vs IHGATE

∆VDGATE vs IDGATE ∆VHGATE vs VIN in Figure 1

Supply Current vs VCC ICC(SHDN) vs VCC

∆VDGATE vs VIN in Figure 1

VCC (V)

SUPPLY CURRENT (µA)

250

300

350

436412 G01

200

100

150

020 40 60

10 30 50 70

450

400

VCC = SOURCE = SENSE = OUT

ICC

ISRC

ISNS + IOUT

VCC (V)

ICC(SHDN) (µA)

20 40 60 80

436412 G02

10 30 50 70

SHDN = 0

OUT = 0

OUT = VCC

TEMPERATURE (°C)

–50

ICC(SHDN) (µA)

436412 G03

–25 0 50

OUT = 0

OUT = 12V

75 100 125

SHDN = 0

VCC = 12V

VCC (V)

ISNS + IOUT IN SHUTDOWN (µA)

100

30 50 80

436412 G04

10 20 40 60 70

SOURCE = VCC

SNS = OUT = 48V

SNS = OUT = 24V

SNS = OUT = 12V

VCC (V)

IGATE(UP) (µA)

–4

–8

–12

–16

8 12 40 80

436412 G05

–20

–24

6 10 20 60

HGATE

DGATE

HGATE = DGATE = SOURCE = VCC

∆VSD = 100mV

IHGATE (µA)

∆VHGATE (V)

–20

436412 G06

6–5 –10 –15

14 VCC = 12V

IDGATE (µA)

∆VDGATE (V)

–10

436412 G07

6–4–2 –6 –8

VCC = 12V

VIN (V)

∆VHGATE (V)

8 12 16 20

436412 G08

0Ω

2.2k

4.7k

10k

R4 IN FIGURE 1

VIN (V)

∆VDGATE (V)

8 12 16 20

436412 G09

0Ω

2.2k

4.7k

10k

R4 IN FIGURE 1

LTC4364-1/LTC4364-2

436412f

TYPICAL PERFORMANCE CHARACTERISTICS

Overcurrent Threshold

vs OUT Voltage

Overvoltage TMR Current

vs VCC – VOUT

Overcurrent TMR Current

vs VCC – VOUT

EN, F LT Output Low vs Current

Retry Duty Cycle vs VCC – VOUT

(LTC4364-2 Only)

HGATE Pull-Down Current

vs Temperature

DGATE Pull-Down Current

vs Temperature

Ideal Diode Regulation Voltage

vs VCC

Ideal Diode Regulation Voltage

vs Temperature

TEMPERATURE (°C)

–50

IHGATE(DN) (mA)

150

175

200

25 75

436412 G10

125

100

–25 0 50 100 125

∆VSNS = 100mV OR FB = 1.5V

∆VHGATE = 5V

VCC = 12V

TEMPERATURE (°C)

–50

IDGATE(DN) (mA)

150

175

200

25 75

436412 G11

125

100

–25 0 50 100 125

VSENSE – VSOURCE = 200mV

VCC = 12V

∆VDGATE = 5V

VOUT (V)

∆VSNS (mV)

1.5 2.5 4.0

436412 G12

0.5 1.0 2.0 3.0 3.5

VCC – VOUT (V)

ITMR(UP) (µA)

–10

–20

–30

–40

20 40 60 80

436412 G13

–50

–60

10 30 50 70

OVERVOLTAGE CONDITION

OUT = 5V

TMR = 1V

VCC – VOUT (V)

ITMR(UP) (µA)

–50

–100

–150

–200

20 40 60 80

436412 G14

–250

–300

10 30 50 70

OVERCURRENT CONDITION

OUT = 5V

TMR = 1V

VCC – VOUT (V)

RETRY DUTY CYCLE (%)

0.4

0.6

436412 G15

0.2

020 40 60

10 30 50 70

0.8

0.3

0.5

0.1

0.7

OVERVOLTAGE CONDITION

OUT = 16V

OVERCURRENT CONDITION

OUT = 0V

CURRENT (mA)

VOL (V)

0.25

0.50

0.75

1.00

1.25

1.50

1 2 3 4

436412 G16

VCC = 12V

VCC (V)

∆VSD (mV)

436412 G17

10 812 40

610 20 60

TEMPERATURE (°C)

–50

∆VSD (mV)

050 75 100

436412 G18

–25 25 125

VCC = 4V

VCC = 12V

LTC4364-1/LTC4364-2

436412f

PIN FUNCTIONS

DGATE: Diode Controller Gate Drive Output. When the load

current creates more than 30mV of drop across the MOSFET,

the DGATE pin is pulled high by an internal charge pump

current source and clamped to 12V above the SOURCE pin.

When the load current is small, the DGATE pin is actively

driven to maintain 30mV across the MOSFET. If reverse

current develops, a 130mA fast pull-down circuit quickly

connects the DGATE pin to the SOURCE pin, turning off

the MOSFET. Connect to SOURCE or leave open if unused.

ENOUT: Enable Output. An open-drain output that goes

high impedance when the voltage at the OUT pin is above

(VCC − 0.7V), indicating the external MOSFETs are fully

on. The state of the pin is latched and resets when the

OUT pin drops below 2.2V. The internal FET is capable of

sinking up to 2mA and can withstand up to 80V. Connect

to GND if unused.

Exposed Pad (DE Package Only): Exposed pad may be

left open or connected to device ground (GND).

FB: Voltage Regulator Feedback Input. Connect this pin to

the resistive divider connected between the OUT pin and

ground. During an overvoltage condition, the HGATE pin

is controlled to maintain 1.25V at the FB pin. Connect to

GND to disable the overvoltage clamp.

F LT : Fault Output. An open-drain output that pulls low

after the TMR pin reaches the warning threshold of 1.25V.

It indicates the pass device controlled by the HGATE pin

is about to turn off because either the supply voltage has

stayed at an elevated level for an extended period of time

(overvoltage fault) or the device is in an overcurrent con-

dition (overcurrent fault). The internal FET is capable of

sinking up to 2mA and can withstand up to 80V. Connect

to GND if unused.

GND: Device Ground.

HGATE: Surge Stopper Gate Drive Output. The HGATE pin

is pulled up by an internal charge pump current source and

clamped to 12V above the SOURCE pin. Both voltage and

current amplifiers control the HGATE pin to regulate the

output voltage and limit the current through the MOSFET.

OUT: Output Voltage Sense Input. This pin senses the

voltage at the drain of the external N-channel MOSFET

connected to the DGATE pin. The voltage difference

between VCC and OUT sets the fault timer current. When

this difference drops below 0.7V, the ENOUT pin goes

high impedance.

OV: Overvoltage Comparator Input. When OV is above

its threshold of 1.25V, the fault retry function is inhibited.

When OV falls below its threshold, the HGATE pin is al-

lowed to turn back on when fault conditions are cleared. At

power-up, an OV voltage higher than its threshold blocks

turn-on of the external N-channel MOSFET controlled by

the HGATE pin (see Applications Information). Connect

to GND if unused.

SENSE: Current Sense Input. Connect this pin to the input

side of the current sense resistor. The current limit circuit

controls the HGATE pin to limit the sense voltage between

the SENSE and OUT pins to 50mV if OUT is above 2.5V.

When OUT drops below 1.5V, the sense voltage is reduced

to 25mV for additional protection during an output short.

The sense amplifier also starts a current source to charge

up the TMR pin. The voltage difference between SENSE

and OUT must be limited to less than 30V. Connect to

OUT if unused.

SHDN: Shutdown Control Input. Pulling the SHDN pin

below 0.5V shuts off the LTC4364 and reduces the VCC pin

current to 10μA. Pull this pin above 2.2V or disconnect it

to allow the internal current source to turn the part back

on. When left open, the SHDN voltage is internally clamped

to 4V. The leakage current to ground at the pin should be

limited to no more than 1μA if no pull-up device is used to

turn the part on. The SHDN pin can be pulled up to 100V

or below GND by 40V without damage.

SOURCE: Common Source Input and Gate Drive Return.

Connect this pin directly to the sources of the external

back-to-back N-channel MOSFETs. SOURCE is the anode

of the ideal diode and the voltage sensed between this pin

and the SENSE pin is used to control the source-drain

voltage across the N-channel MOSFET (forward voltage

of the ideal diode).

LTC4364-1/LTC4364-2

436412f

PIN FUNCTIONS

TMR: Fault Timer Input. Connect a capacitor between this

pin and ground to set the times for fault warning, fault

turn-off, and cool down periods. Either voltage regulation

or current regulation starts pulling up the TMR pin. The

current charging up this pin during the fault conditions

increases with the voltage difference between VCC and OUT

pins (see Applications Information). When TMR reaches

1.25V, the F LT pin pulls low to indicate the detection of a

fault condition. If the condition persists, the pass device

controlled by HGATE turns off when TMR reaches the

threshold of 1.35V. As soon as the fault condition disap-

pears, a cool down interval commences while the TMR

pin cycles 32 times between 0.15V and 1.35V with 2μA

charge and discharge currents. When TMR crosses 0.15V

the 32nd time, the HGATE pin is allowed to pull high turn-

ing the pass device back on if the OV pin voltage is below

its threshold for the LTC4364-2 version. The HGATE pin

latches low after fault time-out for the LTC4364-1.

UV: Undervoltage Comparator Input. When the UV pin

falls below its 1.25V threshold, the HGATE pin is pulled

down with a 1mA current. When the UV pin rises above

1.25V plus the hysteresis, the HGATE pin is pulled up by

the internal charge pump. For LTC4364-1, after HGATE

is latched off, pulling the UV pin below 0.6V resets the

latch and allows HGATE to retry. If unused, connect to

the SHDN pin.

VCC: Positive Supply Voltage Input. The positive supply

input ranges from 4V to 80V for normal operation. It can

also be pulled below ground potential by up to 40V during

a reverse battery condition, without damaging the part.

Shutting down the LTC4364 by pulling the SHDN pin to

ground reduces the VCC current to 10μA.

LTC4364-1/LTC4364-2

436412f

BLOCK DIAGRAM

–

RETRY

1.35V

0.15V

TMR

VCC

1.25V

2µA

UVIN

SHDN

OC ENOUT SET

VCC – 0.7V

2.2V

ENOUT RESET

50mV/

25mV

–30mV +

–30mV

OUT

1.25V

SHDN

1.25V

CONTROL

CIRCUITRY

–

IAVA

–

–+

DAFD

20µA

10µA HGATE OFF DGATE OFF

12V

HGATE SOURCE DGATE

F LT

SENSEVCC

CHARGE

PUMP

f = 620kHz

ENOUT

GND

436412 BD

–

32x

LTC4364-1/LTC4364-2

436412f

OPERATION

The LTC4364 is designed to suppress high voltage surges

and limit the output voltage to protect load circuitry and

ensure normal operation in high availability power systems.

It features an overvoltage protection regulator that drives

an external N-channel MOSFET (M1) as the pass device

and an ideal diode controller that drives a second external

N-channel MOSFET (M2) for reverse input protection and

output voltage holdup.

The LTC4364 operates from a wide range of supply voltage,

from 4V to 80V. With a clamp limiting the VCC supply, the

input voltage may be higher than 80V. The input supply

can also be pulled below ground potential by up to 40V

without damaging the LTC4364. The low power supply

requirement of 4V allows it to operate even during cold

cranking conditions in automotive applications.

Normally, the pass device M1 is fully on, supplying current

to the load with very little power loss. If the input voltage

surges too high, the voltage amplifier (VA) controls the gate

of M1 and regulates the voltage at the OUT pin to a level

that is set by an external resistive divider from the OUT pin

to ground and the internal 1.25V reference. The LTC4364

also detects an overcurrent condition by monitoring the

voltage across an external sense resistor placed between

the SENSE and OUT pins. An active current limit circuit

(IA) controls the gate of M1 to limit the sense voltage to

50mV if OUT is above 2.5V. In the case of a severe output

short that brings OUT below 1.5V, the sense voltage is

reduced to 25mV to reduce the stress on M1.

During an overvoltage or overcurrent event, a current

source starts charging up the capacitor connected at

the TMR pin to ground. The pull-up current source in

overcurrent condition is 5 times of that in overvoltage to

accelerate turn-off. When TMR reaches 1.25V, the F LT pin

pulls low to warn of impending turn-off. The pass device

M1 stays on and the TMR pin is further charged up until it

reaches 1.35V, at which point the HGATE pin pulls low and

turns off M1. The fault timer allows the load to continue

functioning during brief transient events while protecting

the MOSFET from being damaged by a long period of input

overvoltage, such as load dump in vehicles. The fault timer

period decreases with the voltage across the MOSFET,

to help keep the MOSFET within its safe operating area

(SOA). The LTC4364-1 latches off M1 and keeps F LT low

after a fault timeout. The LTC4364-2 allows M1 to turn

back on and F LT to go high impedance after a cool down

timer cycle, provided the OV pin is below its threshold.

After the HGATE pin is latched low following fault, mo-

mentarily pulling the SHDN pin below 0.5V resets the fault

and allows HGATE to pull high for both LTC4364-1 and

LTC4364-2. In addition, momentarily pulling the UV pin

below 0.6V allows HGATE to pull high after the cool down

timer delay for LTC4364-1, but has no effect on LTC4364-2.

The source and drain of MOSFET M2 serve as the anode

and cathode of the ideal diode. The LTC4364 controls the

DGATE pin to maintain a 30mV forward voltage across the

drain and source terminals of M2. It reduces the power

dissipation and increases the available supply voltage to

the load, as compared to using a discrete blocking diode.

If M2 is driven fully on and the load current results in

more than 30mV of forward voltage, the forward voltage

is equal to RDS(ON) • ILOAD.

In the event of an input short or a power supply failure,

reverse current temporarily flows through the MOSFET

M2 that is on. If the reverse voltage exceeds –30mV, the

LTC4364 pulls the DGATE pin low strongly and turns off

M2, minimizing the disturbance at the output.

If the input supply drops below the GND pin voltage, the

DGATE pin is pulled to the SOURCE pin voltage, keeping

M2 off. When the HGATE pin pulls low in any fault condi-

tion, the DGATE pin also pulls low, so both pass devices

are turned off.

If the output (and so the SOURCE pin, through the body

diode of M2) drops below GND, the HGATE pin is pulled

to the SOURCE pin voltage, turning M1 off and shutting

down the forward current path.

An input undervoltage condition is accurately detected

using the UV pin. The HGATE and DGATE pins remain low

if UV is below its 1.25V threshold. The SHDN pin not only

turns off the pass devices but also shuts down the internal

circuitry, reducing the supply current to 10µA.

LTC4364-1/LTC4364-2

436412f

APPLICATIONS INFORMATION

Some power systems must cope with high voltage surges

of short duration such as those in automobiles. Load

circuitry must be protected from these transients, yet

critical systems may need to continue operating during

these events.

The LTC4364 drives an N-channel MOSFET (M1) at the

HGATE pin to limit the voltage and current to the load cir-

cuitry during supply transients or overcurrent events. The

selection of M1 is critical for this application. It must stay

on and provide a low impedance path from the input sup-

ply to the load during normal operation and then dissipate

power during overvoltage or overcurrent conditions. The

LTC4364 also drives a second N-channel MOSFET (M2) at

the DGATE pin as an ideal diode to protect the load from

damage during reverse polarity input conditions, and to

block reverse current flow in the event the input collapses.

A typical application circuit using the LTC4364 to regulate

the output at 27V during input surges with reverse input

protection is shown in Figure 1.

Overvoltage Fault

The LTC4364 limits the voltage at the OUT pin during an

overvoltage situation. An internal voltage amplifier regu-

lates the HGATE pin voltage to maintain 1.25V at the FB

pin. During this period of time, the N-channel MOSFET

M1 remains on and supplies current to the load. This

allows uninterrupted operation during brief overvoltage

transient events.

If the voltage regulation loop is engaged for longer than

the timeout period, set by the timer capacitor, an overvolt-

age fault is detected. The HGATE pin is pulled down to the

SOURCE pin by a 130mA current, turning M1 off. This

prevents M1 from being damaged during a long period

of overvoltage, such as during load dump in automobiles.

After the fault condition has disappeared and a cool down

period has transpired, the HGATE pin starts to pull high

again (LTC4364-2). The LTC4364-1 latches the HGATE pin

low after an overvoltage fault timeout and can be reset

using the SHDN or UV pin (see Resetting Faults).

Overcurrent Fault

The LTC4364 features an adjustable current limit that

protects against short circuits and excessive load current.

During an overcurrent event, the HGATE pin is regulated

to limit the current sense voltage across the SENSE and

OUT pins (∆VSNS) to 50mV when OUT is above 2.5V. The

current limit sense voltage is reduced to 25mV when OUT is

below 1.5V for additional protection during an output short.

A current sense resistor is placed between SENSE and

OUT and its value (RSNS) is determined by:

RSNS =

∆V

SNS

ILIM

where ILIM is the desired current limit.

Figure 1. 4A, 12V Overvoltage Output Regulator with Reverse Current Protection

OUTSENSEDGATESOURCEHGATE

TMRGND

CTMR

47nF

UV = 6V

CMZ5945B

68V

1.5KE200A

MAX DC:

100V/–24V

MAX 1ms

TRANSIENT:

200V

SMAJ24A

0.1µF CHG

0.1µF

2.2k

0.5W

OV = 60V OV ENOUT

FAULT

ENABLE

436412 F01

F LT

SHDN FB

10Ω R6

100Ω

1N4148W

VIN

12V

90.9k

383k

10k

102k

4.99k

COUT

22µF

VOUT

CLAMPED AT 27V

FDB33N25

FDB3682

RSNS

10mΩ

VCC

LTC4364

LTC4364-1/LTC4364-2

436412f

APPLICATIONS INFORMATION

An overcurrent fault occurs when the current limit circuitry

has been engaged for longer than the timeout delay set

by the timer capacitor. The HGATE pin is then immediately

pulled low by 130mA to the SOURCE pin, turning off the

MOSFET M1. After the fault condition has disappeared

and a cool down period has transpired, the HGATE pin

is allowed to pull back up and turn on the pass device

(LTC4364-2). The LTC4364-1 latches the HGATE pin low

after the overcurrent fault timeout and can be reset using

the SHDN or UV pin (see Resetting Faults).

Input Overvoltage Comparator

Input overvoltage is detected with the OV pin and an ex-

ternal resistive divider connected to the input (Figure 1).

At power-up, if the OV pin voltage is higher than its 1.25V

threshold before the 100μs internal power-on-reset expires,

or before the input undervoltage condition is cleared at

the UV pin, the HGATE pin will be held low until the OV

pin voltage drops below its threshold. To prevent start-up

in the event the board is hot swapped into an overvoltage

supply, separate resistive dividers with filtering capacitors

can be used for the OV and UV pins (Figure 2). The RC

constants should be skewed so that τUV/τOV > 50. In Fig-

ure2, If the board is plugged into a supply that is higher

than 60V, the LTC4364 will not turn on the pass devices

until the supply voltage drops below 60V.

Once the HGATE pin begins pulling high, an input overvolt-

age condition detected by OV will not turn off the pass

device. Instead, OV prevents the LTC4364 from restarting

following a fault (see Cool Down Period and Restart). This

prevents the pass device from cycling between ON and OFF

states when the input voltage stays at an elevated level for

a long period of time, reducing the stress on the MOSFET.

Input Undervoltage Comparator

The LTC4364 detects input undervoltage conditions such

as low battery using the UV pin. When the voltage at the

UV pin is below its 1.25V threshold, the HGATE pin pulls

low to keep the pass device off. Once the UV pin voltage

rises above the UV threshold plus the UV hysteresis (50mV

typical), the HGATE pin is allowed to pull up without go-

ing through a timer cycle. In Figure 1 and Figure 2, the

input UV threshold is set by the resistive dividers to 6V.

An undervoltage condition does not produce an output

at the F LT pin.

Fault Timer

The LTC4364 includes an adjustable fault timer. Con-

necting a capacitor from the TMR pin to ground sets the

delay period before the MOSFET M1 is turned off during

an overvoltage or overcurrent fault condition. The same

capacitor also sets the cool down period before M1 is

allowed to turn back on after the fault condition has

disappeared. Once a fault condition is detected, a current

source charges up the TMR pin. The current level varies

depending on the voltage drop across the VCC pin and the

OUT pin, corresponding to the MOSFET VDS. The on time

is inversely proportional to the voltage drop across the

MOSFET. This scheme therefore takes better advantage

of the available safe operating area (SOA) of the MOSFET

than would a fixed timer current.

The timer current starts at around 2μA with 0.5V or less

of VCC – VOUT, increasing linearly to 50μA with 75V of

VCC – VOUT during an overvoltage fault (Figure 3a):

ITMR(UP)OV = 2μA + 0.644[μA/V] • (VCC – VOUT – 0.5V)

During an overcurrent fault, the timer current starts at

10μA with 0.5V or less of VCC – VOUT and increases to

260μA with 75V of VCC – VOUT (Figure 3b):

ITMR(UP)OC = 10μA + 3.36[μA/V] • (VCC – VOUT – 0.5V)

This arrangement allows the pass device to turn off faster

during an overcurrent event, since more power is dissipated

under this condition. Refer to the Typical Performance

Characteristics section for the timer current at different

VCC – VOUT in both overvoltage and overcurrent events.

475k

UV = 6V

0V = 60V

436412 F02

10k

383k

100k

τUV = (383k||100k) • 10nF

τOV = (475k||10k) •1nF

10nF

1nF

LTC4364

Figure 2. External UV and OV Configuration Blocks Start-Up Into

an Overvoltage Condition

LTC4364-1/LTC4364-2

436412f

ITMR = 5µA ITMR = 5µA

1.25

1.35

1.25

TIME

436412 F03

tWARNING

20ms/µF

(3a) Overvoltage Fault Timer Current

(3b) Overcurrent Fault Timer Current

tWARNING

0.38ms/µF

tWARNING

20ms/µF

tF LT

25ms/µF

tF LT

4.8ms/µF

tWARNING

2.38ms/µF

tF LT

29.8ms/µF

tF LT

156ms/µF

1.35

VTMR (V)

VCC – VOUT = 75V

(ITMR = 50µA)

VCC – VOUT

= 75V

=10V

VCC – VOUT

= 75V

=10V

VCC – VOUT = 75V

(ITMR = 260µA)

VCC – VOUT = 10V

(ITMR = 42µA)

VCC – VOUT = 10V

(ITMR = 8µA)

Figure 3. Fault Timer Current of the LTC4364

When the voltage at the TMR pin, VTMR, reaches 1.25V,

the F LT pin pulls low to indicate the detection of a fault

condition and provide warning of the impending power

loss. In the case of an overvoltage fault, the timer current

then switches to a fixed 5μA. The interval between F LT

asserting low and the MOSFET M1 turning off is given by:

tWARNING =CTMR •100mV

5µA

This constant early warning period allows the load to

perform necessary backup or housekeeping functions

before the supply is cut off. After VTMR crosses the 1.35V

threshold, the pass device M1 turns off immediately. Note

that during an overcurrent event, the timer current is not

reduced to 5μA after VTMR has reached 1.25V threshold,

since it would lengthen the overall fault timer period and

cause more stress on the power transistor during an

overcurrent event.

Assuming VCC – VOUT remains constant, the on-time of

HGATE during an overvoltage fault is:

tOV =

TMR

•1.25V

ITMR(UP)OV

TMR

•100mV

5µV

and that during an overcurrent fault is:

tOC =

TMR

•1.35V

ITRM(UP)OC

If the fault condition disappears after TMR reaches 1.25V

but is lower than 1.35V, the TMR pin is discharged by 2μA.

When TMR drops to 0.15V, the F LT pin resets to a high

impedance state.

Cool Down Period and Restart

As soon as TMR reaches 1.35V and HGATE pulls low in

a fault condition, the TMR pin starts discharging with a

2μA current. When the TMR pin voltage drops to 0.15V,

TMR charges with 2μA. When TMR reaches 1.35V, it starts

discharging again with 2μA. This pattern repeats 32 times

to form a long cool down timer period before retry (Fig-

ure4). At the end of the cool down period (when the TMR

pin voltage drops to 0.15V the 32nd time), the voltage at

the OV pin is checked. If the OV voltage is above its 1.25V

threshold, retry is inhibited and the HGATE pin remains

low. If the OV pin voltage is below 1.25V minus the OV

hysteresis, the LTC4364-2 retries, pulling the HGATE pin

up and turning on the pass device M1. The F LT pin will

then go to a high impedance state. The total cool down

timer period is given by:

tCOOL =63 •CTMR •1.2V

2µA

The latch-off version, LTC4364-1, latches the HGATE and

F LT pins low after a fault timeout. It also generates the

cool down TMR pulses as shown in Figure 4, but does

not retry after the cool down period. There are two ways

to restart the part. The first method is to pull the UV pin

below 0.6V momentarily (>10μs) after the cool down timer

APPLICATIONS INFORMATION

LTC4364-1/LTC4364-2

436412f

period. If the UV reset pulse is asserted during the cool

down period, the TMR pulses are unaffected and the part

restarts after the cool down period ends. If OV is higher

than 1.25V while UV reset pulse is applied, the part will

not restart until OV drops below 1.25V even if the cool

down period ends.

The second method of restarting the LTC4364-1 is to

pulse the SHDN pin low for more than 200μs. If this is

applied during the cool down period, the cool down timer

is reset with 1mA quickly discharging the TMR pin, and

the part will restart when TMR drops below 0.15V. If the

SHDN reset pulse is applied after the cool down period,

the part restarts immediately. Sufficient cool down time

should be allowed before toggling the SHDN pin to prevent

overstressing the pass device.

A UV reset pulse has no effect on the operation of the

LTC4364-2. However, if a SHDN reset pulse as described

above is asserted in the middle of the cool down period, the

TMR pin quickly discharges with 1mA and the LTC4364-2

is allowed to restart once TMR drops below 0.15V. The OV

pin gates the restart of either LTC4364-1 or LTC4364-2

with a SHDN reset pulse. The part will not restart until OV

drops below 1.25V.

Reverse Input Protection

The LTC4364 can withstand reverse voltage without dam-

age. The VCC, SHDN, UV, OV, HGATE, SOURCE and DGATE

pins can all withstand up to –40V with respect to GND.

The LTC4364 controls a second N-channel MOSFET (M2)

as an ideal diode to replace an in-line blocking diode for

reverse input protection with minimum voltage drop in

normal operation. In the event of an input short or a power

supply brownout, reverse current may temporarily flow

through M2. The LTC4364 detects this reverse current

and immediately pulls the DGATE pin to the SOURCE pin,

turning off M2. This minimizes discharge of the output

reservoir capacitor and holds up the output voltage. In

the case where the input supply drops below ground, the

SOURCE pin is pulled below ground through the body

diode of M1. The LTC4364 responds to this condition by

shorting the DGATE pin to the SOURCE pin, keeping M2 off.

MOSFET Selection

The LTC4364 drives two N-channel MOSFETs, M1 and M2,

as the pass devices to conduct the load current (Figure1).

The important features are on-resistance, RDS(ON), the

maximum drain-source voltage, V(BR)DSS, the threshold

voltage, and the safe operating area, SOA.

The maximum drain-source voltage rating must be higher

than the maximum input voltage. If the output is shorted to

ground or in an overvoltage event, the full supply voltage

will appear across M1. If the input is shorted to ground,

M2 will be stressed by the voltage held up at the output.

The gate drive for both MOSFETs is guaranteed to be more

than 10V and less than 16V for those applications with VCC

higher than 8V. This allows the use of standard threshold

voltage N-channel MOSFETs. For systems with VCC less

than 8V, a logic-level MOSFET is required since the gate

drive can be as low as 5V. For supplies of 24V or higher, a

15V Zener diode is recommended to be placed between

1.35V

1.25V

TMR

∆VHGATE

F LT

1.25V

<1.25V

1st 2nd 31st

0.15V

32nd

436412 F04

OV < 1.25V CHECKED

COOL DOWN PERIOD

Figure 4. Auto-Retry Cool Down Timer Cycle Following an Overvoltage Fault (LTC4364-2 Only)

APPLICATIONS INFORMATION

LTC4364-1/LTC4364-2

436412f

gate and source of each MOSFET for extra protection

(Figures 8 to 10).

Transient Stress in the MOSFET

The SOA of the MOSFET must encompass all fault condi-

tions. In normal operation the pass devices are fully on,

dissipating very little power. But during either overvoltage or

overcurrent faults, the HGATE pin is controlled to regulate

either the output voltage or the current through MOSFET

M1. Large current and high voltage drop across M1 can

coexist in these cases. The SOA curves of the MOSFET

must be considered carefully along with the selection of

the fault timer capacitor.

During an overvoltage event, the LTC4364 drives the pass

MOSFET M1 to regulate the output voltage at an acceptable

level. The load circuitry may continue operating throughout

this interval, but only at the expense of dissipation in the

MOSFET pass device. MOSFET dissipation or stress is a

function of the input voltage waveform, regulation voltage

and load current. The MOSFET must be sized to survive

this stress.

Most transient event specifications use the model shown

in Figure 5. The idealized waveform comprises a linear

ramp of rise time tr, reaching a peak voltage of VPK and

exponentially decaying back to VIN with a time constant

of τ. A typical automotive transient specification has

constants of tr = 10μs, VPK = 80V and τ = 1ms. A surge

condition known as “load dump” has constants of tr =

5ms, VPK = 60V and τ = 200ms.

MOSFET stress is the result of power dissipated within

the device. For long duration surges of 100ms or more,

stress is increasingly dominated by heat transfer; this is

a matter of device packaging and mounting, and heat sink

thermal mass. This is analyzed by simulation, using the

MOSFET’s thermal model.

For short duration transients of less than 100ms, MOS-

FET survival is increasingly a matter of SOA, an intrinsic

property of the MOSFET. SOA quantifies the time required

at any given condition of VDS and ID to raise the junction

temperature of the MOSFET to its rated maximum. MOSFET

SOA is expressed in units of watt-squared-seconds (P2t),

which is an integral of P(t)2dt over the duration of the

transient. This figure is essentially constant for intervals

of less than 100ms for any given device type, and rises

to infinity under DC operating conditions. Destruction

mechanisms other than bulk die temperature distort the

lines of an accurately drawn SOA graph so that P2t is not

the same for all combinations of ID and VDS. In particular

P2t tends to degrade as VDS approaches the maximum

rating, rendering some devices useless for absorbing

energy above a certain voltage.

Calculating Transient Stress

To select a MOSFET suitable for any given application,

the SOA stress of M1 must be calculated for each input

transient which shall not interrupt operation. It is then

a simple matter to choose a device which has adequate

SOA to survive the maximum calculated stress. P2t for a

prototypical transient waveform is calculated as follows

(Figure 6).

Let:

a = VREG – VIN

b = VPK – VIN

where VIN = Nominal Input Voltage.

VIN

436412 F05

Figure 5. Prototypical Transient Waveform Figure 6. Safe Operating Area Required to Survive Prototypical

Transient Waveform

= 80V

τ = 1ms

VIN = 12V

436412 F06

VREG = 16V

tr = 10µs

APPLICATIONS INFORMATION

LTC4364-1/LTC4364-2

436412f

Then:

P2t=ILOAD21

3tr

b−a

( )

b+1

2τ2a2In b

a+3a2+b2– 4ab























Typically VREG ≈ VIN and τ >> tr simplifying the above to:

P2t=1

ILOAD2VPK −VREG

( )

2τ

For the transient conditions of VPK = 80V, VIN = 12V, VREG

= 16V, tr = 10μs and τ = 1ms, and a load current of 3A,

P2t is 18.4W2s—easily handled by a MOSFET in a D-pak

package. The P2t of other transient waveshapes is evalu-

ated by integrating the square of MOSFET power versus

time. LTSpice™ can be used to simulate timer behavior

for more complex transients and cases where overvoltage

and overcurrent faults coexist.

Short-Circuit Stress

SOA stress of M1 must also be calculated for output short-

circuit conditions. Short-circuit P2t is given by:

P2t=VIN •∆VSNS

RSNS











•tOC

where ∆VSNS is the overcurrent fault threshold and tOC is

the overcurrent timer interval.

For VIN = 15V, OUT = 0V, ∆VSNS = 25mV, RSNS = 12mΩ

and CTMR = 100nF, P2t is 2.2W2s—less than the transient

SOA calculated in the previous example. Nevertheless,

to account for circuit tolerances this figure should be

doubled to 4.4W2s.

Limiting Inrush Current and HGATE Pin Compensation

The LTC4364 limits the inrush current to any load capaci-

tance by controlling the HGATE pin voltage slew rate. An

external capacitor, CHG, can be connected from HGATE

to ground to slow down the inrush current further at the

expense of slower turn-off time. The gate capacitor is set at:

CHG =IHGATE(UP)

IINRUSH

•CL

where IHGATE(UP) is the HGATE pin pull-up current, IINRUSH

is the desired inrush current, CL is total load capacitance

at the output. In typical applications, a CHG of 6.8nF is

recommended for loop compensation during overvoltage

and overcurrent events. With input voltage steps faster

than 5V/μs, a larger gate capacitor helps prevent self

enhancement of the N-channel MOSFET.

The added gate capacitor slows down the turn-off time

during fault conditions and allows higher peak currents to

build up during an output short event. If this is a concern,

an extra resistor, R6, in series with CHG can restore the

turn-off time. A diode, D5, should be placed across R6

with the cathode connected to CHG as shown in Figure 1.

In a fast transient input step, D5 provides a bypass path to

CHG for the benefit of holding HGATE low and preventing

self enhancement.

Shutdown

The LTC4364 can be shut down to a low current mode

by pulling SHDN below 0.5V. The quiescent VCC current

drops to 10μA for both the LTC4364-1 and the LTC4364-2.

The SHDN pin can be pulled up to 100V or below GND by

up to 40V without damage. Leaving the pin open allows

an internal current source to pull it up to about 4V and

turn the part on. The leakage current at the pin should be

limited to no more than 1μA if no pull-up device is used

to help turn it on.

Supply Transient Protection

The LTC4364 is tested to operate to 80V and guaranteed

to be safe from damage between 100V and −40V. Voltage

transients above 100V or below −40V may cause permanent

damage. During a short-circuit condition, the large change

in current flowing through power supply traces coupled

with parasitic inductances from associated wiring can

cause destructive voltage transients in both positive and

negative directions at the VCC, SOURCE, and OUT pins. To

reduce the voltage transients, minimize the power trace

parasitic inductance by using short, wide traces. A small

RC filter (R4 and C1 in Figure 1) at the VCC pin filters high

voltage spikes of short pulse width.

APPLICATIONS INFORMATION

LTC4364-1/LTC4364-2

436412f

Another way to limit supply transients above 100V at the

VCC pin is to use a Zener diode and a resistor, D1 and R4,

as shown in Figure 1. D1 clamps voltage spikes at the VCC

pin while R4 limits the current through D1 to a safe level

during the surge. In the negative direction, D1 along with

R4 clamps the VCC pin near GND. The inclusion of R4 in

series with the VCC pin increases the minimum required

supply voltage due to the extra voltage drop across the

resistor, which is determined by the supply current of the

LTC4364 and the leakage current of D1. 2.2k adds about

1V to the minimum operating voltage.

For sustained, elevated suppy voltages, the power dissipa-

tion of R4 becomes unacceptable. This can be resolved

by using an external NPN transistor (Q1 in Figure 7) as

a buffer. To protect Q1 against supply reversal, block the

collector of Q1 with a series diode or tie it to the cathode

of D3 and D4 in Figure 1.

Transient suppressor D3 in Figure 1 clamps the input

voltage to 200V for voltage transients higher than 200V,

to prevent breakdown of M1. It also blocks forward con-

duction in D4. D4 limits the SOURCE pin voltage to 24V

below GND when the input goes negative. COUT helps

absorb the inductive energy at the output upon a sudden

input short, protecting the OUT and SENSE pins.

Output Port Protection

In applications where the output is on a connector, as

shown in Figure 14, if the output is plugged into a supply

that is higher than the input, the ideal diode MOSFET, M2,

turns off to open the backfeeding path. In the case where

the output port is plugged into a supply that is below GND,

the SOURCE pin is pulled below GND through the body

diode of M2. The LTC4364 responds to this condition by

shorting the HGATE pin to the SOURCE pin, turning M1

off and shutting down the current path from VIN to VOUT.

Design Example

As a design example, consider an application with the

following specifications: VIN = 8V to 14V DC with a peak

transient of 200V and decay time constant τ of 1ms, VOUT

≤ 27V, minimum current limit ILIM(MIN) at 4A, low-battery

detection at 6V, input overvoltage level at 60V, and 1ms

of overvoltage early warning (Figure 1).

Selection of CMZ5945B for D1 will limit the voltage at

the VCC pin to less than 71V during the 200V surge. The

minimum required voltage at the VCC pin is 4V when VIN is

at 6V; the maximum supply current for LTC4364 is 750μA.

The maximum value for R4 to ensure proper operation is:

R4 =

6V – 4V

0.75mA =2.7k

Select 2.2k for R4 to accommodate all conditions.

With the minimum Zener voltage at 64V, the peak current

through R4 into D1 is then calculated as:

ID1(PK) =

200V – 64V

2.2k

=62mA

which can be handled by the CMZ5945B with a peak power

rating of 200W at 10/1000μs.

With a bypass capacitance of 0.1μF (C1), along with R4

of 2.2k, high voltage transients up to 250V with a pulse

width less than 20μs are filtered out at the VCC pin.

Next, calculate the resistive divider value to limit VOUT to

27V during an overvoltage event:

VREG =1.25V •R7 +R8

( )

R8 =27V

APPLICATIONS INFORMATION

VCC

LTC4364

GND

436412 F07

100nF

PZTA42

VIN

200V

CMZ5945B

68V

22k

1/4W

Figure 7. Buffering VCC to Extend Input Supply Range

Output Bypassing

The OUT and SENSE pins can withstand up to 100V above

and 20V below GND. In all applications the output must

be bypassed with at least 22μF low ESR electrolytic (COUT

in Figure 1) to stabilize the voltage and current limiting

loops, and to minimize capacitive feedthrough of input

transients. Total ceramic bypassing of up to one-tenth

the total electrolytic capacitance is permissible without

compromising performance.

LTC4364-1/LTC4364-2

436412f

Choosing 250μA for the resistive divider:

R8 =1.25V

250µA =5k

Select 4.99k for R8.

R7 =27V – 1.25V

( )

•R8

1.25V =102.8k

The closest standard value for R7 is 102k.

Now, calculate the sense resistor, RSNS, value:

RSNS =∆VSNS(MIN)

ILIM

=45mV

4A =11mΩ

Choose 10mΩ for RSNS.

CTMR is then chosen for 1ms of early warning time:

CTMR =

1ms•5µA

100mV =50nF

The closest standard value for CTMR is 47nF.

Finally, calculate R1, R2 and R3 for 6V low battery detec-

tion and 60V input overvoltage level:

R1+R2+R3 =1.25V

R2+R3

60V

R1+R2+R3

=1.25V

Simplify the equations and choose 10k for R3 to get:

R2 =60V

6V –1









•R3 =9•R3 =90k

R1=6V

1.25V – 1









•R2+R3

( )

=3.8 •R1+R2

( )

=380k

Select 90.9kΩ for R2 and 383kΩ for R1.

The pass device, M1, should be chosen to withstand an

output short condition with VCC = 14V. In the case of a

severe output short where VOUT = 0V, ITMR(UP) = 55μA and

the total overcurrent fault time is:

tOC =CTMR •VTMR(G)

ITRM(UP)

=47nF •1.35V

55µA =1.15ms

The maximum power dissipation in M1 is:

∆V

DS(M1)

•∆V

SNS(MAX)

RSNS

=14V •32mV

10mΩ=45W

The corresponding P2t is 2.3W2s.

During an output overload or soft short, the voltage at the

OUT pin could stay at 2V or higher. The total overcurrent

fault time when VOUT = 2V is:

tOC =

47nF •1.35V

49µA =1.3ms

The maximum power dissipation in M1 is:

P=14V – 2V

( )

•55mV

10m

Ω

=66W

The corresponding P2t is 5.7W2s. Both of the above condi-

tions are well within the safe operating area of FDB33N25.

To select the pass device, M2, first calculate RDS(ON) to

achieve the desired forward drop VFW at maximum load

current (5.5A). If VFW = 0.25V:

RDS(ON) ≤VFW

ILOAD(MAX)

=0.25V

5.5A =45.5mΩ

The FDB3682 offers a maximum RDS(ON) of 36mΩ at

VGS = 10V so is a good fit. Its minimum BVDSS of 100V

is also sufficient to handle VOUT transients up to 100V

during an input short-circuit event.

Layout Considerations

To achieve accurate current sensing, use Kelvin connections

to the current sense resistor, RSNS. Limit the resistance

from the SOURCE pin to the sources of the MOSFETs to

below 10Ω. The minimum trace width for 1oz copper foil

is 0.02" per amp to ensure the trace stays at a reason-

able temperature. Note that 1oz copper exhibits a sheet

resistance of about 530μΩ/square. Small resistances can

cause large errors in high current applications. Noise im-

munity will be improved significantly by locating resistive

dividers close to the pins with short VCC and GND traces.

APPLICATIONS INFORMATION

LTC4364-1/LTC4364-2

436412f

TYPICAL APPLICATIONS

Figure 8. 2A Wide Range Hot Swap Controller with Circuit Breaker

Figure 9. 28V Hot Swap with Overvoltage Output Regulation at 27V, Circuit Breaker, and Reverse Current Protection

Figure 10. 48V Hot Swap with Overvoltage Output Regulation at 72V, Circuit Breaker, and Reverse Current Protection

OUTSENSEDGATESOURCEHGATE

TMRGND

CTMR

0.22µF

OV ENOUT

436412 F08

F LT

SHDN FB

10Ω

VIN

5V TO 28V

44.2k

118k

4.2V

36V

SMAT70A

5.9k

CLOAD

100µF

VOUT

SUD50N03-9

RSNS

20mΩ

CHG

47nF

DDZ9702T

VCC

LTC4364

OUTSENSEDGATESOURCEHGATE

TMRGND

CTMR

0.1µF

OV ENOUT

436412 F09

F LT

SHDN FB

10Ω

4.02k

VIN

18V TO 33V

6.04k

45V

15V

100k

3.01k

CLOAD

100µF

VOUT

2.5A

CLAMPED

AT 36V

FDB3632

DDZ9702T

FDMS86101

RSNS

15mΩ

CHG

47nF

VCC

LTC4364

110k

DDZ9702T

OUTSENSEDGATESOURCEHGATE

TMRGND

CTMR

0.1µF

OV ENOUT

436412 F10

F LT

SHDN FB

10Ω

2.2k

VIN

36V TO 72V

205k

36V

76V

3.92k

3.48k

226k

4.02k

CLOAD

330µF

VOUT

CLAMPED

AT 72V

CMZ5945B

68V

FDB33N25

FDB3632

RSNS

10mΩ

CHG

47nF

VCC

LTC4364

DDZ9702T

LTC4364-1/LTC4364-2

436412f

TYPICAL APPLICATIONS

Figure 11. Redundant Supply Diode-OR with Overvoltage Surge Protection

Figure 12. High Side Switch with Ideal Diode for Load Protection

OUTSENSEDGATESOURCEHGATE

TMR

CTMRA

0.22µF

ENOUT

F LT

SHDN FB

R5A

10Ω

VINA

12V

R7A

59k

R8A

4.99k

COUTA

22µF

VOUT

CLAMPED

AT 16V

M1A

FDD16AN08A0

M2A

FDD16AN08A0

RSNSA

10mΩ

CHGA

6.8nF

VCC

LTC4364

OUTSENSEDGATESOURCEHGATE

TMR

CTMRB

0.22µF

ENOUT

F LT

SHDN FB

R5B

10Ω

VINB

12V

R7B

59k

R8B

4.99k

436412 F11

COUTB

22µF

M1B

FDD16AN08A0

M2B

FDD16AN08A0

RSNSB

10mΩ

CHGB

6.8nF

VCC

LTC4364

GND

OUTSENSEDGATESOURCEHGATE

TMR GND

SHDN M3

VN2222

100k

OV ENOUT

436412 F12

F LT

SHDN FB

VIN

12V CLOAD

VOUT

FDB3632

FDMS86101

VCC

LTC4364

LTC4364-1/LTC4364-2

436412f

TYPICAL APPLICATIONS

Figure 13. Overvoltage Regulator with Output Keep Alive During Shutdown

PACKAGE DESCRIPTION

DE Package

14-Lead Plastic DFN (4mm × 3mm)

(Reference LTC DWG # 05-08-1708 Rev B)

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

3.00 ±0.10

(2 SIDES)

4.00 ±0.10

(2 SIDES)

NOTE:

1. DRAWING PROPOSED TO BE MADE VARIATION OF VERSION (WGED-3) IN JEDEC

PACKAGE OUTLINE MO-229

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE

TOP AND BOTTOM OF PACKAGE

0.40 ± 0.10

BOTTOM VIEW—EXPOSED PAD

1.70 ± 0.10

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

3.00 REF

148

PIN 1

TOP MARK

(SEE NOTE 6)

0.200 REF

0.00 – 0.05

(DE14) DFN 0806 REV B

PIN 1 NOTCH

R = 0.20 OR

0.35 × 45°

CHAMFER

0.25 ± 0.05

0.50 BSC

3.30 ±0.10

1.70 ± 0.05

3.00 REF

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

2.20 ±0.05

0.70 ±0.05

3.60 ±0.05

PACKAGE

OUTLINE

0.25 ± 0.05

3.30 ±0.05

0.50 BSC

OUTSENSEDGATESOURCEHGATE

TMRGND

CTMR

0.1µF

OV ENOUT

436412 F13

F LT

SHDN FB

2.2k R5

10Ω

VIN

12V

191k

30V

40.2k

10k

287k

24.9k

COUT

22µF

1N4746A

18V, 1W

VOUT

CLAMPED

AT 16V

CMZ5945B

68V

FDD16AN08A0

RSNS

10mΩ

1k, 1W

CHG

6.8nF

VCC

LTC4364

LTC4364-1/LTC4364-2

436412f

MS Package

16-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1669 Rev Ø)

MSOP (MS16) 1107 REV Ø

0.53 ± 0.152

(.021 ± .006)

SEATING

PLANE

0.18

(.007)

1.10

(.043)

MAX

0.17 –0.27

(.007 – .011)

TYP

0.86

(.034)

REF

0.50

(.0197)

BSC

16151413121110

12345678

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.

MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.

INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

0.254

(.010) 0° – 6° TYP

DETAIL “A”

GAUGE PLANE

5.23

(.206)

MIN

3.20 – 3.45

(.126 – .136)

0.889 ± 0.127

(.035 ± .005)

RECOMMENDED SOLDER PAD LAYOUT

0.305 ± 0.038

(.0120 ± .0015)

TYP

0.50

(.0197)

BSC

4.039 ± 0.102

(.159 ± .004)

(NOTE 3)

0.1016 ± 0.0508

(.004 ± .002)

3.00 ± 0.102

(.118 ± .004)

(NOTE 4)

0.280 ± 0.076

(.011 ± .003)

REF

4.90 ± 0.152

(.193 ± .006)

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

LTC4364-1/LTC4364-2

436412f

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

PACKAGE DESCRIPTION

Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.

.016 – .050

(0.406 – 1.270)

.010 – .020

(0.254 – 0.508)× 45°

0° – 8° TYP

.008 – .010

(0.203 – 0.254)

2345678

N/2

.150 – .157

(3.810 – 3.988)

NOTE 3

16 15 14 13

.386 – .394

(9.804 – 10.008)

NOTE 3

.228 – .244

(5.791 – 6.197)

12 11 10 9

S16 REV G 0212

.053 – .069

(1.346 – 1.752)

.014 – .019

(0.355 – 0.483)

TYP

.004 – .010

(0.101 – 0.254)

.050

(1.270)

BSC

.245

MIN

1 2 3 N/2

.160 ±.005

RECOMMENDED SOLDER PAD LAYOUT

.045 ±.005

.050 BSC

.030 ±.005

TYP

INCHES

(MILLIMETERS)

NOTE:

1. DIMENSIONS IN

2. DRAWING NOT TO SCALE

3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.

MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)

4. PIN 1 CAN BE BEVEL EDGE OR A DIMPLE

S Package

16-Lead Plastic Small Outline (Narrow .150 Inch)

(Reference LTC DWG # 05-08-1610 Rev G)

LTC4364-1/LTC4364-2

436412f

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com

 LINEAR TECHNOLOGY CORPORATION 2012

LT 0712 • PRINTED IN USA

RELATED PARTS

TYPICAL APPLICATION

PART NUMBER DESCRIPTION COMMENTS

4356-1/LT4356-2

LT4356-3

Surge Stopper LT4356-1: 7A Shutdown Mode

LT4356-2: Auxiliary Amplifier Alive in Shutdown Mode

LT4356-3: Fault Latchoff

LTC4363 High Voltage Surge Stopper 4V to 80V, VCC Clamp, Adjustable Output Voltage Clamp, 60V Reverse

Input Protection, Overcurrent Protection

LTC4366 Floating Surge Stopper 9V to >500V Operation, Adjustable Output Voltage Clamp

LTC4357 Positive High Voltage Ideal Diode Controller 0.5µs Turn-Off Time, 9V to 80V

LTC4359 Ideal Diode Controller with Reverse Input Protection 4V to 80V Operation, –40V Reverse-Input Protection, Low 13µA

Shutdown Current

LTC4352 Ideal MOSFET ORing Diode External N-Channel MOSFETs Replace ORing Diodes, 0V to 18V

LTC4354 Negative Voltage Diode-OR Controller Controls Two N-Channel MOSFETs, 1µs Turn-Off, 80V Operation

LTC4355 Positive Voltage Diode-OR Controller Controls Two N-Channel MOSFETs, 0.5µs Turn-Off, 80V Operation

LTC4365 Window Passer - OV, UV and Reverse Supply Protection

Controller

2.5V to 34V Operation, Protects 60V to –40V

Figure 14. 0.25A, 12V Surge Stopper with Output Port Protection

OUTSENSEDGATESOURCEHGATE

0.1µF

ENOUT

436412 F14

F LT

SHDN FB

10Ω

VIN

12V

90.9k

383k

60V R3

10k

*PROTECTED AGAINST BACKFEEDING

OR FORWARD CONDUCTING

FROM –20V TO 50V

VOUT*

CLAMPED

AT 18V

FDB3632

FDMS86101

RSNS

0.2Ω

CHG

6.8nF

CIN

10µF

50V

CER

10µF

50V

CER

VCC

LTC4364

GND TMR

4.99k

16.9k

RESR

100mΩ

DDZ9702T

15V

49.9k