FEATURES
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LT4351
MOSFET Diode-OR
Controller
DESCRIPTION
The LT
®
4351 creates a near ideal diode using external
single or back-to-back N-channel MOSFETs. This ideal
diode function permits low loss ORing of multiple power
sources. Power sources can easily be ORed together to
increase total system power and reliability with minimal
effect on supply voltage or efficiency. Disparate power
supplies can be efficiently ORed together.
The IC monitors the input supply with respect to the load
and turns on the MOSFET(s) when the input supply is
higher. If the MOSFET’s R
DS(ON)
is sufficiently small, the
LT4351 will regulate the voltage across the MOSFET(s)
to 15mV. A STATUS pin indicates the MOSFET on-state.
An internal boost regulator generates the MOSFET gate
drive voltage. Low operating voltage allows for ORing of
supplies as low as 1.2V.
The LT4351 will disable power passage during undervolt-
age or overvoltage conditions. These voltages are set by
resistive dividers on the UV and OV pins. The undervoltage
threshold has user programmable hysteresis. Overvoltage
detection is filtered to reduce false triggering.
The LT4351 is available in a 10-pin MSOP package.
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Low Loss Replacement for ORing Diode in Multiple
Sourced Power Supplies
External N-Channel MOSFETs for High Current
Capability
Internal Boost Regulator Supply for MOSFET
Gate Drive
Wide Input Range: 1.2V to 18V
Fast Switching MOSFET Gate Control
Input Under and Overvoltage Detection
STATUS and
FAULT
Outputs for Monitoring
Internal MOSFET Gate Clamp
Available in a 10-pin MSOP Package
APPLICATIONS
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Paralleled Power Supplies
Uninterrupted Supplies
High Availability Systems
N + 1 Redundant Power Supplies
L,
LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
Dual 5V Redundant Supply
Si4862DY
POWER
SUPPLY
1
4.7µH
5V
10µF
1µF
V
IN
MBR0530
MBR0530
24.9k
1%
232
1%
1.47k
1%
SW
UV
OV
GND
V
DD
LT4351
STATUS
FAULT
STATUS
FAULT
GND
LT4351
GATE
OUT
1×
5V COMMON
C
LOAD
LOAD
1×
1µF
OUT
GATE
V
IN
V
DD
SW
UV
MBR0530
MBR0530
24.9k
1%
232
1%
1.47k
1%
Si4862DY
5V
10µF
4.7µH
POWER
SUPPLY
2
OV
4351 TA01
4351fd
1
LT4351
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
GATE
V
DD
V
IN
SW
GND
1
2
3
4
5
10
9
8
7
6
OUT
STATUS
FAULT
UV
OV
V
IN
Voltage ................................................ –0.3V to 19V
OUT Voltage ............................................. –0.3V to 19V
V
DD
Voltage .............................................. –0.3V to 30V
FAULT,
STATUS Voltages.......................... –0.3V to 30V
FAULT,
STATUS Current .......................................... 8mA
UV, OV Voltages ......................................... –0.3V to 9V
SW Voltage .............................................. –0.3V to 32V
Operating Temperature Range
LT4351C .................................................. 0°C to 70°C
LT4351I ............................................... –40°C to 85°C
Junction Temperature (Note 2) ............................ 125°C
Storage Temperature Range.................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
MS PACKAGE
10-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 120°C/W
ORDER INFORMATION
LEAD FREE FINISH
LT4351CMS#PBF
LT4351IMS#PBF
TAPE AND REEL
LT4351CMS#TRPBF
LT4351IMS#TRPBF
PART MARKING
LTZZ
LTA1
PACKAGE DESCRIPTION
10-Lead Plastic MSOP
10-Lead Plastic MSOP
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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
SYMBOL
V
IN
I
VIN
V
UV(TH)
I
UV(HYST)
I
UV
V
OV(TH)
PARAMETER
Operating Range
V
IN
Supply Current
Undervoltage Turn-Off Voltage
Threshold
I
UV
Hysteresis
UV Input Bias Current
Overvoltage Threshold
Supply and Protection
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
OUT
= 5V, V
DD
= 16.1V, V
UV
= 0.4V, V
OV
= 0.2V, GATE Open, unless
otherwise specified.
CONDITIONS
l
MIN
1.2
TYP
MAX
18
UNITS
V
mA
mA
mV
µA
nA
mV
V
IN
= 1.2V, V
OUT
= 1.1V, V
DD
= 12.3V
V
IN
= 18V, V
OUT
= 17.9V, V
DD
= 29.1V
UV Falling
Difference Between I
UV
at V
UV(TH)
+ 10mV and
V
UV(TH)
– 10mV
V
UV
= V
UV(TH)
+ 10mV
OV Rising
l
l
l
l
l
l
1.41
1.71
290
7
300
10
–100
290
300
2
2.1
310
13
–400
310
4351fd
2
LT4351
ELECTRICAL CHARACTERISTICS
SYMBOL
I
OV
V
F(ON)
I
F(OFF)
Boost Supply
V
BR
t
OFF
I
SWLIM
Gate Drive
V
IOR
∆V
GL
∆V
G(MAX)
V
G(OFF)
I
GSO
I
GSK
V
DD
I
VDD
Input-to-Output Regulated Voltage
Gate Voltage Limit
Maximum Gate Voltage
Gate Off-Voltage
Gate Source Current
Gate Sink Current
Operating Range
V
DD
Supply Current
V
IN
= 1.2V, V
OUT
= 1.1V, V
DD
= 12.3V, GATE Open
V
IN
= 18V, V
OUT
= 17.9V, V
DD
= 29.1V, GATE Open
V
IN
= 5V, V
OUT
= 4.9V, V
DD
= 13V Measured with
Respect to V
DD
V
IN
= 5V, V
OUT
= 4.9V, V
DD
= 16.1V Measured with
Respect to V
OUT
V
OUT
= 5.1V
V
OUT
= 4.9V, V
GATE
= 9V
V
OUT
= 5.1V, V
GATE
= 9V
l
l
l
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
OUT
= 5V, V
DD
= 16.1V, V
UV
= 0.4V, V
OV
= 0.2V, GATE Open, unless
otherwise specified.
PARAMETER
OV Input Bias Current
FAULT
Pin On-Voltage
FAULT
Pin Leakage Current
Boost Regulation Trip Voltage
Boost Supply Off-Time
Boost Supply Switch Current Limit
l
CONDITIONS
V
OV
= V
OV(TH)
– 10mV
I
F
= 5mA in Fault Condition
V
F
= 30V, V
IN
= 4.9V
Measured as V
DD
to V
IN
, Rising Edge
l
l
l
MIN
TYP
–100
0.14
0.04
MAX
–400
0.25
1
11.4
650
25
–3
7.8
0.30
UNITS
V
V
µA
V
ns
mA
mV
V
V
V
A
A
l
10.2
350
4
10.7
600
450
15
–2.3
7
7.4
0.16
0.670
0.670
30
3
3.6
0.75
185
210
0.13
0.04
4
5.6
1
230
0.25
1
V
mA
mA
V
mV
V
µA
Status Functions
∆V
GIS
V
IOGF
V
ST(ON)
I
ST(OFF)
Minimum Gate Voltage for Turning V
OUT
= 4.9V, I
STATUS
= 1mA
On Status
V
IN
to V
OUT
Fault Voltage with
Open Gate
Status Pin On-Voltage
Status Pin Leakage Current
V
OUT
Falling, Measured with Respect to V
IN
I
ST
= 5mA, V
OUT
= 4.9V, Status On
V
ST
= 30V, Status Off, V
IN
= 4.9V
l
l
l
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.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formula:
T
J
= T
A
+ (P
D
• 120°C/W)
4351fd
3
LT4351
TYPICAL PERFORMANCE CHARACTERISTICS
Undervoltage Threshold
vs Temperature
310
308
306
304
V
UV(TH)
(mV)
V
OV(TH)
(mV)
302
300
298
296
294
292
290
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
V
IN
= 1.2V
V
IN
= 5V
V
IN
= 12V
V
IN
= 20V
305
303
301
299
297
295
293
–50
T
A
= 25°C, unless otherwise noted.
Overvoltage Threshold
vs Temperature
V
IN
= 1.2V
V
IN
= 5V
V
IN
= 12V
V
IN
= 20V
V
UV(TH)
(mV)
–25
50
25
0
75
TEMPERATURE (°C)
100
125
310
308
306
304
302
300
298
296
294
292
290
Undervoltage Threshold vs V
IN
0
2
4
6
8
10 12 14 16 18 20
V
IN
(V)
4351 G03
4351 G01
4351 G02
Overvoltage Threshold vs V
IN
310
308
306
OV HYSTERESIS (mV)
304
V
UV(TH)
(mV)
302
300
298
296
294
292
290
0
2
4
6
8
10 12 14 16 18 20
V
IN
(V)
4351 G04
Overvoltage Hysteresis
vs Temperature
25
V
IN
= 5V
20
18
16
TURN-OFF DELAY (µs)
14
12
10
8
6
4
2
0
–50
–25
50
0
75
25
TEMPERATURE (°C)
100
125
0
Overvoltage Turn-Off Delay
vs Overvoltage Overdrive
V
IN
= 5V
20
15
10
5
0
35
20
15
10
25
30
5
OV VOLTAGE ABOVE THRESHOLD (mV)
3451 G06
4351 G05
2.0
1.9
1.8
1.7
I
VIN
vs Temperature
V
IN
= 1.2V
V
IN
= 5V
V
IN
= 12V
V
IN
= 20V
I
VDD
(mA)
4.5
I
VDD
vs Temperature
V
IN
= 1.2V
V
IN
= 5V
V
IN
= 12V
V
IN
= 20V
0.50
0.45
0.40
0.35
V
GOFF
(V)
Gate Off-Voltage vs Temperature
4.0
V
IN
= 5V
V
OUT
= 5V
I
VIN
(mA)
1.6
1.5
1.4
1.3
1.2
1.1
1.0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
3.5
0.30
0.25
0.20
0.15
V
IN
= 5V
V
OUT
= 5.1V
3.0
2.5
0.10
0.05
2.0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
0
–50
–25
50
25
0
75
TEMPERATURE (°C)
100
125
4351 G07
4351 G08
4351 G09
4351fd
4
LT4351
TYPICAL PERFORMANCE CHARACTERISTICS
GATE Pin Turn On and Off Waveform
with 10nF Capacitor Load
TURN ON
T
A
= 25°C, unless otherwise noted.
Typical SW Pin Waveform
V
GATE
2V/DIV
V
SW
5V/DIV
TURN OFF
4351 G10
4351 G11
V
IN
= 5V
V
OUT
= 4.9V TO 5.1V SQUARE WAVE
50ns/DIV
V
IN
= 5V
L = 4.7µH
500ns/DIV
Typical SW Pin Waveform
SW Pin Waveform at Maximum
Boost Regulator Output
V
SW
5V/DIV
V
SW
5V/DIV
V
IN
= 5V
4.7µH INDUCTOR
10µs/DIV
4351 G12
V
IN
= 5V
4.7µH INDUCTOR
10µs/DIV
4351 G13
4351fd
5
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