FeaTures
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LTC4354
Negative Voltage
Diode-OR Controller
and Monitor
DescripTion
The LTC
®
4354 is a negative voltage diode-OR controller
that drives two external N-channel MOSFETs. It replaces
two Schottky diodes and the associated heat sink, saving
power and area. The power dissipation is greatly reduced
by using N-channel MOSFETs as the pass transistors.
Power sources can easily be ORed together to increase
total system power and reliability.
When first powered up, the MOSFET body diode conducts
the load current until the pass transistor is turned on.
The LTC4354 servos the voltage drop across the pass
transistors to ensure smooth transfer of current from one
transistor to the other without oscillation.
The MOSFETs are turned off in less than 1µs whenever
the corresponding power source fails or is shorted. Fast
turn-off prevents the reverse current from reaching a level
that could damage the pass transistors.
A fault detection circuit with an open-drain output capable
of driving an LED or opto-coupler indicates either MOSFET
short, MOSFET open or supply failed.
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Controls N-Channel MOSFETs
Replaces Power Schottky Diodes
Less Than 1µs Turn-off Time Limits Peak
Fault Current
80V Operation
Smooth Switchover without Oscillation
No Reverse DC Current
Fault Output
Selectable Fault Thresholds
Available in 8-Lead (3mm
×
2mm) DFN and
8-Lead SO Packages
applicaTions
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AdvancedTCA Systems
–48V Distributed Power Systems
Computer Systems/Servers
Telecom Infrastructure
Optical Networks
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
Hot Swap, PowerPath and ThinSOT are trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
Typical applicaTion
–48V Diode-OR
–48V_RTN
12k
5
POWER DISSIPATION (W)
33k
V
CC
LTC4354
DA
2k
V
A
= –48V
V
B
= –48V
DB
2k
IRF3710
IRF3710
GA
GB
FAULT
V
SS
1µF
LED
LOAD
DIODE (MBR10100)
4
3
2
1
4354 TA01
Power Dissipation vs Load Current
6
POWER
SAVED
FET (IRF3710)
0
2
4
6
CURRENT (A)
8
10
4354 TA01b
0
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LTC4354
absoluTe MaxiMuM raTings
(Note 1)
I
CC
(100µs duration) ...............................................50mA
Output Voltages
GA, GB .........................................–0.3V to V
CC
+ 0.3V
FAULT ...................................................... –0.3V to 7V
Input Voltages
DA, DB ................................................... –0.3V to 80V
Input Current
DA, DB Current ................................... –1mA to 20mA
Operating Temperature Range
LTC4354C ................................................ 0°C to 70°C
LTC4354I .............................................–40°C to 85°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
pin conFiguraTion
TOP VIEW
DA
V
SS
V
CC
GA
1
2
3
4
9
8 DB
7 FAULT
6 GB
5 V
SS
DA 1
V
SS
2
V
CC
3
GA 4
TOP VIEW
8
7
6
5
DB
FAULT
GB
V
SS
DDB PACKAGE
8-LEAD (3mm
×
2mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 76°C/W
EXPOSED PAD (PIN 9) IS V
SS
, CONNECTION TO PCB OPTIONAL
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 150°C/W
orDer inForMaTion
Lead Free Finish
TAPE AND REEL (MINI)
LTC4354CDDB#TRMPBF
LTC4354IDDB#TRMPBF
TAPE AND REEL
LTC4354CDDB#TRPBF
LTC4354IDDB#TRPBF
PART MARKING*
LBBK
LBMB
PACKAGE DESCRIPTION
8-Lead (3mm
×
2mm) Plastic DFN
TEMPERATURE RANGE
0°C to 70°C
–40°C to 85°C
8-Lead (3mm
×
2mm) Plastic DFN
TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container.
LEAD FREE FINISH
LTC4354CS8#PBF
LTC4354IS8#PBF
TAPE AND REEL
LTC4354CS8#TRPBF
LTC4354IS8#TRPBF
PART MARKING
4354
4354I
PACKAGE DESCRIPTION
8-Lead Plastic SO
8-Lead Plastic SO
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 nonstandard 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/
4354fc
2
LTC4354
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. I
CC
= 5mA, V
SS
= 0V, unless otherwise noted.
SYMBOL
V
Z
∆V
Z
V
CC
I
CC
V
GATE
I
GATE
∆V
SD
∆V
SD(FLT)
t
OFF
V
FAULT
I
FAULT
I
D
PARAMETER
Internal Shunt Regulator Voltage
Internal Shunt Regulator Load Regulation
Operating Voltage Range
V
CC
Supply Current
GATE Pins Output High Voltage
GATE Pins Pull-Up Current
Source Drain Sense Threshold Voltage
Source Drain Fault Detection Threshold
Gate Turn-Off Time in Fault Condition
FAULT Pin Output Low
FAULT Pin Leakage Current
Drain Pin Input Current
V
CC
= (V
Z
– 0.1V), Note 2
V
CC
= 5V
V
CC
= 10.25V
V
CC
= 5V
V
SD
= 60mV; V
GATE
= 5.5V
V
SD
= 0V; V
GATE
= 5.5V
(V
SS
– V
DX
)
(V
SS
– V
DX
); V
CC
= 7V to V
Z
C
GATE
= 3300pF; V
GATE
≤ 2V; V
SD
= –0.4V
I
FAULT
= 5mA
V
FAULT
= 5V
V
DX
= 0V
V
DX
= 80V
l
l
l
l
elecTrical characTerisTics
CONDITIONS
I
CC
= 5mA
I
CC
= 2mA to 10mA
l
l
l
l
MIN
10.25
4.5
0.5
10
4.75
–15
15
10
200
TYP
11
200
1.2
0.8
MAX
11.75
300
V
Z
2
1.1
10.25
UNITS
V
mV
V
mA
mA
V
V
µA
µA
mV
mV
µs
mV
µA
µA
mA
–30
30
30
260
0.7
200
–60
60
55
320
1.2
400
±1
–1.5
1.9
–3.5
1.1
–2.5
1.5
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:
I
CC
is defined as the current level where the V
CC
voltage is lower
by 100mV from the value with 2mA of current.
Note 3:
An internal shunt regulator limits the V
CC
pin to less than 12V
above V
SS
. Driving this pin to voltages beyond the clamp may damage
the part.
Note 4:
All currents into pins are positive; all voltages are referenced to
V
SS
unless otherwise specified.
4354fc
3
LTC4354
unless otherwise noted.
Typical perForMance characTerisTics
Shunt Regulator Voltage
vs Input Current
12.0
11.4
Specifications are at T
A
= 25°C, I
CC
= 5mA, V
SS
= 0V,
Source Drain Sense Voltage
vs Supply Voltage
40
Shunt Regulator Voltage
vs Input Current at Temperature
11.5
11.2
∆V
SD
(mV)
35
V
Z
(V)
11.0
V
Z
(V)
11.0
I
CC
= 10mA
I
CC
= 5mA
30
10.5
10.8
I
CC
= 2mA
25
10.0
0
5
10
I
CC
(mA)
15
20
4354 G01
10.6
–50 –25
50
75
0
25
TEMPERATURE (°C)
100
125
4354 G02
20
5
6
7
8
9
V
CC
(V)
10
11
12
4354 G03
Source Drain Sense Voltage
vs Temperature
40
100
80
I
GATE(UP)
(µA)
60
40
20
0
I
GATE(UP)
vs ∆V
SD
740
Gate Turn-Off Time vs Temperature
35
V
SD
(mV)
720
t
OFF
(ns)
70
60
∆V
SD
(mV)
80
90
4354 G05
30
700
25
680
20
–50 –25
50
75
0
25
TEMPERATURE (°C)
100
125
4354 G04
30
40
50
660
–50 –25
50
75
0
25
TEMPERATURE (°C)
100
125
4354 G05
Fault Threshold Voltage
vs Temperature
290
–3.2
Drain Pin Current vs Temperature
V
DX
= 0V
–1
Drain Pin Current vs Voltage
270
∆V
SD(FLT)
(mV)
–3.0
–0.75
90°C
I
D
(mA)
I
D
(µA)
250
–2.8
–0.5
25°C
230
–2.6
–0.25
–45°C
210
–50 –25
50
75
0
25
TEMPERATURE (°C)
100
125
4354 G06
–2.4
–50 –25
50
75
0
25
TEMPERATURE (°C)
100
125
4354 G08
0
0.3
0.4
0.5
0.6 0.7
V
DX
(V)
0.8
0.9
1
4354 G09
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LTC4354
pin FuncTions
DA, DB (Pins 1, 8):
Drain Voltage Sense Inputs. These
pins sense source drain voltage drop across the N-channel
MOSFETs. An external resistor is recommended to pro-
tect these pins from transient voltages exceeding 80V in
extreme fault conditions. For Kelvin sensing, connect
these pins as close to the drains as possible. Connect to
V
SS
if unused.
V
CC
(Pin 3):
Positive Supply Voltage Input. Connect this
pin to the positive side of the supply through a resistor.
An internal shunt regulator that can sink up to 20mA
typically clamps V
CC
at 11V. Bypass this pin with a 1µF
capacitor to V
SS
.
GA, GB (Pins 4, 6):
Gate Drive Outputs. Gate pins pull high
to 10V minimum, fully enhancing the N-channel MOSFET,
when the load current creates more than 30mV of drop
across the MOSFET. When the load current is small,
the gates are actively servoed to maintain a 30mV drop
across the MOSFET. If reverse current develops more than
–140mV of voltage drop across the MOSFET, the pins pull
low to V
SS
in less than 1µs. Quickly turning off the pass
transistors prevents excessive reverse currents. Leave the
pins open if unused.
V
SS
(Pins 2, 5):
Negative Supply Voltage Input. This is the
device negative supply input and connects to the common
source connection of the N-channel MOSFETs. It also
connects to the source voltage sense input of the servo
amplifiers. For Kelvin sensing, connect Pin 5 as close to
the common source terminal of the MOSFETs as possible.
FAULT (Pin 7):
Fault Output. Open-drain output that
normally pulls the FAULT pin to V
SS
and shunts current
to turn off an external LED or opto-coupler. In the fault
condition, where the pass transistor is fully on and the
voltage drop across it is higher than the fault threshold,
the FAULT pin goes high impedance, turning on the LED or
opto-coupler. This indicates that one or both of the pass
transistors have failed open or failed short creating a cross
conduction current in between the two power supplies.
Connect to V
SS
if unused.
EXPOSED PAD (Pin 9):
Exposed pad is common to V
SS
and may be left open or connected to Pins 2 and 5.
FuncTional DiagraM
V
CC
3
BV = 11V
V
SS
5
30mV
+
–
+
–
30mV
+
AMP A
4
GA
–
55k
1
DA
V
SS
+
AMP B
6
GB
–
FAULT
55k
7
V
SS
8
DB
FAULT DETECTION
2
V
SS
V
SS
4354 FD
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