LTC4358
5A Ideal DiodeFEATURESDESCRIPTIONn

The LTC®4358 is a 5A ideal diode that uses an internal
20mΩ N-channel MOSFET to replace a Schottky diodewhen used in diode-OR and high current diode applications. The LTC4358 reduces power consumption, heatdissipation, and PC board area.

Replaces a Power Schottky Dioden Internal 20mΩ N-Channel MOSFET
n 0.5μs Turn-Off Time Limits Peak Fault Current
n Operating Voltage Range: 9V to 26.5V
n Smooth Switchover without Oscillationn No Reverse DC Current
n Available in 14-Pin (4mm × 3mm) DFN and
16-Lead TSSOP Packages

The LTC4358 easily ORs power supplies together to increase total system reliability. In diode-OR applications,the LTC4358 regulates the forward voltage drop acrossthe internal MOSFET to ensure smooth current transferfrom one path to the other without oscillation. If the powersource fails or is shorted, a fast turnoff minimizes reverse
current transients.

APPLICATIONSn

N+1 Redundant Power Supplies
High Availability Systems
n Telecom Infrastructuren Automotive SystemsnL, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.

TYPICAL APPLICATION
12V, 5A Diode-OR

Power Dissipation vs Load Current
3.0

IN

DRAIN

2.5

OUT
LTC4358

VDD
VOUT TO
5A LOADGND

POWER DISSIPATION (W)

VINA = 12V

DIODE (B530C)
2.0
1.5
POWER SAVED
1.0
0.5

VINB = 12V

IN

DRAIN

FET (LTC4358)
0

OUT
LTC4358

VDD

0

2

4
CURRENT (A)684358 TA01b

GND4358 TA01

4358fa1

LTC4358
ABSOLUTE MAXIMUM RATINGS (Notes 1, 2)
Supply Voltages
IN, OUT, VDD, DRAIN Voltage ................. –0.3V to 28V
Output Voltage
GATE (Note 3) .......................... VIN – 0.2V to VIN + 6V
Operating Ambient Temperature Range
LTC4358C ................................................ 0°C to 70°C
LTC4358I.............................................. –40°C to 85°C

Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
FE Package ....................................................... 300°C

PIN CONFIGURATIONTOP VIEWTOP VIEW

IN

1

16 IN

IN

1

14 IN

IN

2

15 IN

IN

2

13 IN

IN

3

14 IN

IN

3

12 IN

IN

4

IN

4

GATE

5

NC

5

GATE

6

11 NC

NC

7

10 OUT

GND

8

9

15
DRAIN

11 IN
10 NC

NC

6

9 OUT

GND

7

8 VDD

DE PACKAGE
14-LEAD (4mm s 3mm) PLASTIC DFN

17
DRAIN

13 IN
12 IN

VDD

FE PACKAGE
16-LEAD PLASTIC TSSOPTJMAX = 125°C, θJC = 4°C/W, θJA = 43°C/W

TJMAX = 125°C, θJC = 10°C/W, θJA = 38°C/W

ORDER INFORMATIONLEAD FREE FINISH

TAPE AND REELPART MARKING*PACKAGE DESCRIPTIONTEMPERATURE RANGE

LTC4358CDE#PBF

LTC4358CDE#TRPBF

4358

14-Lead (4mm × 3mm) Plastic DFN

0°C to 70°C

LTC4358IDE#PBF

LTC4358IDE#TRPBF

4358

14-Lead (4mm × 3mm) Plastic DFN–40°C to 85°C

LTC4358CFE#PBF

LTC4358CFE#TRPBF

4358FE

16-Lead Plastic TSSOP

0°C to 70°C

LTC4358IFE#PBF

LTC4358IFE#TRPBF

4358FE

16-Lead Plastic TSSOP–40°C to 85°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *Temperature grades are 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/

4358fa2

LTC4358
ELECTRICAL CHARACTERISTICS The l denotes the speciﬁcations which apply over the full operating
temperature range, otherwise speciﬁcations are at TA = 25°C. VOUT = VDD, VDD = 9V to 26.5V, unless otherwise noted.
SYMBOLPARAMETERCONDITIONS

MIN

VDD

Operating Supply Rangel

IDD

Operating Supply Currentl

IIN

IN Pin Current

VIN = VOUT ± 1V, No Load

l

IOUT

OUT Pin Current

VIN = VOUT ± 1V, No Loadl

IDRAINDRAIN Pin Current

VIN = 0V, VOUT = VDD = VDRAIN = 26.5V

ΔVGATE

N-Channel Gate Drive (VGATE – VIN)

VDD, VOUT = 9V to 26.5Vl

4.5

IGATE(UP)N-Channel Gate Pull Up Current

VGATE = VIN, VIN – VOUT = 0.1V

l

–14

–20

IGATE(DOWN)

N-Channel Gate Pull Down
Current in Fault Condition

VGATE = VIN + 5V

l

1

2

tON

Turn-On Time

l

200

500

μs

tOFF

Turn-Off Time

VIN – VOUT = –1V –| 0.1V, VDRAIN = VIN,
VOUT = VDD, VGATE – VIN > 4.5V–
VIN – VOUT = 55mV |– –1V, VDRAIN = VIN,
VOUT = VDD, VGATE – VIN < 1V

l

300

500

ns

ΔVSD

Source-Drain Regulation Voltage(VIN – VOUT)

1mA < IIN < 100mA

l

10

25

55

mV

ΔVSD

Body Diode Forward Voltage Drop

IIN = 5A, MOSFET Off

l

0.6

0.8

1

V

RDS(ON)Internal N-Channel MOSFET On
Resistance

IIN = 5A

l

20

40

mΩ

–

Note 1: Stresses 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.

TYP

9
150

MAX

UNITS

26.5

V

0.6

mA

350

450

μA

80

160

μA

5
150

μA
μA

15

V

–26

μA

l

A

Note 2: All currents into pins are positive, all voltages are referenced to
GND unless otherwise speciﬁed.
Note 3: An internal clamp limits the GATE pin to a minimum of 6V above
IN. Driving this pin to voltages beyond this clamp may damage the device.

4358fa3

LTC4358
TYPICAL PERFORMANCE CHARACTERISTICS
VDD Current (IDD vs VDD)

400

500

IN Current (IIN vs VIN)

VIN = VOUT = VDD

VIN = VOUT = VDD

400

VIN = VOUT = VDD
80

300

IOUT (μA)

300

IIN (μA)

IDD (μA)

OUT Current (IOUT vs VOUT)
100

200

200

60

40

100
20

100

0

0
0

20

10

30

0

20

10

0

30

0

VDD (V)30

VOUT (V)4358 G03

4358 G02

4358 G01

FET Turn-Off Timevs Final Overdrive

FET Turn-Off Timevs Initial Overdrive

MOSFET RDS(ON) vs Temperature
30

2000

400
IIN = 5A

VIN = 12V
$VSD = 55mV25
VOUT = VDD = 9V

VFINAL

1500

300

15
VOUT = VDD = 26.5V

tPD (ns)

20
tPD (ns)

RDS(ON) (mΩ)

20

10

VIN (V)200
VIN = 12V
$VSD = VINITIAL

10

1000

-1V
500

100
5
0
-50

-25

0

25

50

75

100

125

TEMPERATURE (˚C)
4358 G04

0

0
0

0.2

0.4

0.6

0.8

1

0

-0.2

-0.4

-0.6

-0.8

-1

VFINAL (V)

VINITIAL (V)4358 G05

4358 G06

4358fa4

LTC4358
PIN FUNCTIONS (DE/FE PACKAGES)DRAIN: The exposed pad is the drain of the internal
N-channel MOSFET. This pin must be connected to OUT(Pin 9/Pin 10).
GATE: Gate Drive Output. If reverse current ﬂows, a fast
pulldown circuit quickly connects the GATE pin to the IN
pin, turning off the MOSFET. Leave open if unused.
GND: Device Ground.
IN: Input Voltage and Fast Pulldown Return. IN is theanode of the ideal diode. The voltage sensed at this pin isused to control the source-drain voltage drop across theinternal MOSFET. If reverse current starts to ﬂow, a fast
pulldown circuit quickly turns off the internal MOSFET. The
fast pulldown current is returned through this pin.

NC: No Connection. Not internally connected.
OUT: Output Voltage. The OUT pin is the cathode of the ideal
diode and the common output when multiple LTC4358s
are conﬁgured as an ideal diode-OR. The voltage sensed
at this pin is used to control the source-drain voltage drop
across the MOSFET. Connect this pin to the drain of theinternal N-channel MOSFET (Pin 15/Pin 17).
VDD: Positive Supply Input. The LTC4358 is powered fromthe VDD pin. Connect this pin to OUT either directly or
through an RC hold-up circuit.

BLOCK DIAGRAM
DRAIN

GATE

IN

OUT
CHARGE PUMP

+

+
–

–

25mV

VDD

GATE
AMP

+

–

FPD
COMP

IN

+
– 25mV

GND
4358 BD

4358fa5

LTC4358
OPERATION
High availability systems often employ parallel-connected
power supplies or battery feeds to achieve redundancy
and enhance system reliability. ORing diodes have been
a popular means of connecting these supplies at the pointof load. The disadvantage of this approach is the forward
voltage drop and resulting efﬁciency loss. This drop reduces
the available supply voltage and dissipates signiﬁcant
power. Using an N-channel MOSFET to replace a Schottky
diode reduces the power dissipation and eliminates theneed for costly heat sinks or large thermal layouts in highpower applications.
The LTC4358 is a single positive voltage ideal diode controller that drives an internal N-channel MOSFET as a passtransistor to replace a Schottky diode. The IN and DRAIN
pins form the anode and cathode of the ideal diode. The
input supply is connected to the IN pins, while the DRAIN
pin serves as the output. The OUT pin is connected directly
to DRAIN and VDD. VDD is the supply for the LTC4358 andis derived from the output either directly or through an
RC hold-up circuit.

At power-up, the load current initially ﬂows through the
body diode of the internal MOSFET. The internal MOSFET
turns on and the ampliﬁer tries to regulate the voltage
drop across the IN and OUT connections to 25mV. If
the load current causes more than 25mV of drop, the
MOSFET is driven fully on and the voltage drop is equal to
RDS(ON) • ILOAD.
If the load current is reduced causing the forward drop to
fall below 25mV, the internal MOSFET is driven lower by
a weak pull-down in an attempt to maintain the drop at
25mV. If the load current reverses the MOSFET is turned
off with a strong pull-down.
In the event of a power supply failure, such as if the supply that is conducting most or all of the current is shorted
to ground, reverse current temporarily ﬂows through the
LTC4358 ideal diode that is on. This current is sourced
from any load capacitance and from the other supplies.
The ideal diode is turned off within 500ns, preventing
reverse current from slewing up to a damaging level andminimizing any disturbance on the output.

4358fa6

LTC4358
APPLICATIONS INFORMATION
ORing Two Supply Outputs
Where LTC4358s are used to combine the outputs of two
supplies, the power supply with the highest output voltage
sources most or all of the current. If this supply’s output
is quickly shorted to ground while delivering load current,
the current temporarily reverses and ﬂows backwards
through the LTC4358. When reverse current ﬂows the
LTC4358 ideal diode is quickly turned off.
If the other initially lower supply was not delivering load
current at the time of the fault, the output falls until the
LTC4358 body diode conducts. Meanwhile, the internal
ampliﬁer turns on the MOSFET until the forward drop is
reduced to 25mV. If instead this supply was deliveringload current at the time of the fault, its ORing MOSFET
was already driven at least partially on, and will be driven
harder in an effort to maintain a drop of 25mV.

VINA = 12V

IN

DRAIN

RTNA

OUT
LTC4358

Figure 1 combines the outputs of multiple, redundant
supplies using a simple technique known as droop sharing.
Load current is ﬁrst taken from the highest output, with the
low outputs contributing as the output voltage falls underincreased loading. The 25mV regulation technique ensuressmooth load sharing between outputs without oscillation.
The degree of sharing depends on the 20mΩ resistanceof the LTC4358 internal MOSFET, the output impedanceof the supplies and their initial output voltages.

VDD

GND

VINB = 12V

IN

DRAIN

PS2

OUT

RTNB
LTC4358

VDD

GND

VINC = 12V

IN

DRAIN

PS3
OUT

RTNC

Load Sharing

12V BUSPS1

LTC4358

VDD

GND
4358 F01

Figure 1. Droop Sharing Redundant Supplies

4358fa7

LTC4358
APPLICATIONS INFORMATIONVDD Hold-Up Circuit
In the event of an input short, parasitic inductance between
the input supply of the LTC4358 and the load bypass
capacitor may cause VDD to glitch below its minimum
operating voltage. This causes the turn-off time (tOFF) to
increase. To preserve the fast turn-off time, local output
bypassing of 39μF or more is sufﬁcient or a 100Ω, 0.1μF
RC hold-up circuit on the VDD pin can be used as shownin Figure 2a and Figure 2b.
Layout Considerations
The following advice should be considered when laying out
a printed circuit board for the LTC4358: The OUT pin should

be connected as closely as possible to the EXPOSED PAD(drain of the MOSFET) for good accuracy. Keep the traces
to the IN and DRAIN wide and short. The PCB traces associated with the power path through the MOSFET shouldhave low resistance. See Figure 4.
The DRAIN acts as a heatsink to remove the heat from thedevice. For a single layer PCB with the DFN package, use
Figure 5 to determine the PCB area needed for a speciﬁed maximum current and ambient temperature. If using
a two sided PCB, the maximum current is increased by
10%. If the FE package is used, the maximum current isincreased by 4%.

(a)
VIN = 12V

IN

DRAIN

VOUT

VIN = 12V

IN

OUT

OUT
LTC4358

VOUT
12V
5A

DRAIN

R1
100Ω

LTC4358

VDD

VDD

CBYPASS
39MF

GND

CLOAD

C1
0.1μF

GND

MMBD1205

4358 F03(b)
VIN = 12V

IN

DRAIN

VOUT

OUT
LTC4358

VDD

GND
4358 F02

R1
1007

Figure 3. –12V Reverse Input Protection

C1
0.1MF

Figure 2. Two Methods of Protecting Against Collapse
of VDD From Input Short and Stray Inductance

4358fa8

LTC4358
APPLICATIONS INFORMATION
VIN

GND

VOUT

Figure 4. DFN Layout Considerations for 1” × 1” Single Sided PCB

10

TA =

AREA (INCH2)

85oC

70oC

50oC

25oC

1

0.1
3.0

3.5

4.0

4.5

5.0

5.5

6.0

6.5

DIODE CURRENT (A)4358 F05

Figure 5. Maximum Diode Current vs PCB Area

4358fa9

LTC4358
PACKAGE DESCRIPTIONDE Package
14-Lead Plastic DFN (4mm × 3mm)
(Reference LTC DWG # 05-08-1708)

0.70 ±0.05
3.30 ±0.05

3.60 ±0.05
2.20 ±0.05

1.70 ± 0.05
PACKAGEOUTLINE
0.25 ± 0.05
0.50 BSC
3.00 REF

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONSAPPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

R = 0.115
TYP

4.00 ±0.10(2 SIDES)
R = 0.05
TYP

3.00 ±0.10(2 SIDES)

80.40 ± 0.10
143.30 ±0.10
1.70 ± 0.10

PIN 1 NOTCH
R = 0.20 OR
0.35 × 45°
CHAMFERPIN 1
TOP MARK(SEE NOTE 6)(DE14) DFN 0806 REV B

70.200 REF

1
0.25 ± 0.05
0.50 BSC

0.75 ±0.05
3.00 REF
0.00 – 0.05

BOTTOM VIEW—EXPOSED PAD

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

4358fa10

LTC4358
PACKAGE DESCRIPTIONFE Package
16-Lead Plastic TSSOP (4.4mm)(Reference LTC DWG # 05-08-1663)

Exposed Pad Variation BC

4.90 – 5.10*(.193 – .201)

3.58(.141)

3.58(.141)
16 1514 13 12 1110

6.60 ±0.1092.94(.116)

4.50 ±0.10

6.40
2.94
(.252)(.116)BSC

SEE NOTE 4

0.45 ±0.05
1.05 ±0.10
0.65 BSC
1 2 3 4 5 6 7 8RECOMMENDED SOLDER PAD LAYOUT

4.30 – 4.50*(.169 – .177)

0.09 – 0.20(.0035 – .0079)

0.50 – 0.75(.020 – .030)

NOTE:
1. CONTROLLING DIMENSION: MILLIMETERSMILLIMETERS
2. DIMENSIONS ARE IN(INCHES)3. DRAWING NOT TO SCALE

0.25
REF

1.10
(.0433)MAX
0° – 8°0.65(.0256)
BSC

0.195 – 0.30(.0077 – .0118)
TYP

0.05 – 0.15(.002 – .006)
FE16 (BC) TSSOP 0204

4. RECOMMENDED MINIMUM PCB METAL SIZEFOR EXPOSED PAD ATTACHMENT*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASHSHALL NOT EXCEED 0.150mm (.006") PER SIDE

4358faInformation 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

11

LTC4358
TYPICAL APPLICATION
Plug-In Card Input Diode for Supply Hold-Up
BACKPLANE PLUG-IN CARDCONNECTORS CONNECTOR 1

IN

12V

OUT

HOT SWAP
CONTROLLER

VOUT1

100Ω

+

LTC4358
GND

CHOLDUP

VDD
0.1μF

GND

IN

OUT

HOT SWAP
CONTROLLER

VOUT2

100Ω
LTC4358
GND+
CHOLDUP

VDD
0.1μF

GND
4358 TA02

PLUG-IN CARDCONNECTOR 2

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LTC4354

Negative Voltage Diode-OR Controller
and Monitor
Positive Voltage Diode-OR Controller
and Monitor
Positive High Voltage Ideal Diode Controller

Controls Two N-Channel MOSFETs, 1μs Turn-Off, 80V Operation

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LTC4357–48V Hot Swap Controller with Sequencer

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Dual Supply Hot Swap Controller for Advanced
Mezzanine Cards and μTCA
Hot Swap is a trademark of Linear Technology Corporation.

Active Current Limiting, Supplies From 9V to 80VControls Two N-Channel MOSFETs, 0.5μs Turn-Off, 80V Operation
Controls Single N-Channel MOSFET, 0.5μs Turn-Off, 80V Operation
Controls 12V Main and 3.3V Auxiliary Supplies

4358fa12 Linear Technology Corporation

LT 0808 REV A • PRINTED IN USA

1630 McCarthy Blvd., Milpitas, CA 95035-7417(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com© LINEAR TECHNOLOGY CORPORATION 2007