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PDF LTC4354 Data sheet ( Hoja de datos )
| Número de pieza | LTC4354 | |
| Descripción | Negative Voltage Diode-OR Controller and Monitor | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n Controls N-Channel MOSFETs
n Replaces Power Schottky Diodes
n Less Than 1µs Turn-off Time Limits Peak
Fault Current
n 80V Operation
n Smooth Switchover without Oscillation
n No Reverse DC Current
n Fault Output
n Selectable Fault Thresholds
n Available in 8-Lead (3mm × 2mm) DFN and
8-Lead SO Packages
Applications
n AdvancedTCA Systems
n –48V Distributed Power Systems
n Computer Systems/Servers
n Telecom Infrastructure
n 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.
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.
Typical Application
–48V_RTN
–48V Diode-OR
12k
VA = –48V
VB = –48V
VCC
LTC4354
FAULT
DA DB
2k 2k
GA
GB VSS
IRF3710
IRF3710
33k
LOAD
LED
1µF
4354 TA01
Power Dissipation vs Load Current
6
5
DIODE (MBR10100)
4
3 POWER
SAVED
2
1
FET (IRF3710)
0
0 2 4 6 8 10
CURRENT (A)
4354 TA01b
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1
1 page  
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
VSS if unused.
VCC (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 VCC at 11V. Bypass this pin with a 1µF
capacitor to VSS.
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 VSS in less than 1µs. Quickly turning off the pass
transistors prevents excessive reverse currents. Leave the
pins open if unused.
VSS (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 VSS 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 VSS if unused.
EXPOSED PAD (Pin 9): Exposed pad is common to VSS
and may be left open or connected to Pins 2 and 5.
Functional Diagram
VCC
3
BV = 11V
–+ 30mV
–+ 30mV
+
AMP A
–
55k
5 VSS
4 GA
1 DA
FAULT 7
VSS +
AMP B
–
55k
VSS
FAULT DETECTION
6 GB
8 DB
2 VSS
VSS
4354 FD
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5 Page 
Package Description
Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings.
LTC4354
DDB Package
8-Lead Plastic DFN (3mm × 2mm)
(Reference LTC DWG # 05-08-1702 Rev B)
0.61 ±0.05
(2 SIDES)
2.55 ±0.05
1.15 ±0.05
0.70 ±0.05
0.25 ±0.05
0.50 BSC
2.20 ±0.05
(2 SIDES)
PACKAGE
OUTLINE
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
3.00 ±0.10
(2 SIDES)
R = 0.05
TYP
R = 0.115
TYP
5
0.40 ±0.10
8
PIN 1 BAR
TOP MARK
(SEE NOTE 6)
0.200 REF
2.00 ±0.10
(2 SIDES)
0.75 ±0.05
0.56 ±0.05
(2 SIDES)
4
0.25 ±0.05
PIN 1
R = 0.20 OR
0.25 × 45°
1 CHAMFER(DDB8) DFN 0905 REV B
0.50 BSC
0 – 0.05
2.15 ±0.05
(2 SIDES)
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING CONFORMS TO VERSION (WECD-1) IN JEDEC PACKAGE OUTLINE M0-229
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
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11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LTC4354.PDF ] | |
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