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PDF LTC4352 Data sheet ( Hoja de datos )
| Número de pieza | LTC4352 | |
| Descripción | Low Voltage Ideal Diode Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Features
n Low Loss Replacement for Power Diode
n Controls N-Channel MOSFET
n 0V to 18V Supply ORing or Holdup
n 0.5μs Turn-On and Turn-Off Time
n Undervoltage and Overvoltage Protection
n Open MOSFET Detect
n Status and Fault Outputs
n Hot Swappable
n Reverse Current Enable Input
n 12-Pin MSOP and DFN (3mm × 3mm) Packages
Applications
n Redundant Power Supplies
n Supply Holdup
n Telecom Infrastructure
n Computer Systems and Servers
LTC4352
Low Voltage Ideal Diode
Controller with Monitoring
Description
The LTC®4352 creates a near-ideal diode using an external
N-channel MOSFET. It replaces a high power Schottky diode
and the associated heat sink, saving power and board area.
The ideal diode function permits low loss power ORing
and supply holdup applications.
The LTC4352 regulates the forward voltage drop across
the MOSFET to ensure smooth current transfer in diode-
OR applications. A fast turn-on reduces the load voltage
droop during supply switch-over. If the input supply fails
or is shorted, a fast turn-off minimizes reverse currents.
The controller operates with supplies from 2.9V to 18V.
For lower voltages, an external supply is needed at the
VCC pin. Power passage is disabled during undervoltage
or overvoltage conditions. The controller also features an
open MOSFET detect circuit that flags excessive voltage
drop across the pass transistor in the on state. A REV pin
enables reverse current, overriding the diode behavior
when desired.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT and PowerPath are trademarks of Linear Technology Corporation. All other trademarks
are the property of their respective owners.
Typical Application
2.9V TO 18V
2.9V to 18V Ideal Diode
0.1µF*
Si7336ADP
TO LOAD
0.1µF
CPO SOURCE VIN GATE OUT
VCC STATUS
UV LTC4352
OV FAULT
REV GND
4352 TA01
*OPTIONAL
MOSFET ON
STATUS
FAULT
Power Dissipation vs Load Current
4.0
3.5
3.0
DIODE (SBG1025L)
2.5
2.0
1.5
POWER
SAVED
1.0
0.5
0
0
MOSFET (Si7336ADP)
2 4 6 8 10
LOAD CURRENT (A)
4352 TA01b
4352fa
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1 page  
LTC4352
Pin Functions
VIN (Pin 1): Voltage Sense and Supply Input. Connect this
pin to the power input side of the MOSFET. The low voltage
supply VCC is generated from VIN. The voltage sensed at
this pin is used to control the MOSFET gate.
VCC (Pin 2): Low Voltage Supply. Connect a 0.1μF capacitor
from this pin to ground. When VIN ≥ 2.9V, this pin provides
decoupling for an internal regulator that generates a 4.1V
supply. For applications where VIN < 2.9V, connect an
external supply voltage in the range 2.9V to 6V to this pin.
UV (Pin 3): Undervoltage Comparator Input. Connect this
pin to an external resistive divider from VIN. If the volt-
age at this pin falls below 0.5V, an undervoltage fault is
detected and the MOSFET is turned off. The comparator
has a built-in hysteresis of 5mV. Tie to VCC if unused.
OV (Pin 4): Overvoltage Comparator Input. Connect this
pin to an external resistive divider from VIN. If the volt-
age at this pin rises above 0.5V, an overvoltage fault is
detected and the MOSFET is turned off. The comparator
has a built-in hysteresis of 5mV. Tie to GND if unused.
STATUS (Pin 5): MOSFET Status Output. This pin is pulled
low by an open-drain output when the external MOSFET
is on. An internal 10µA current source pulls this pin up
to a diode below VCC. It may be pulled above VCC using
an external pull-up. Tie to GND or leave open if unused.
FAULT (Pin 6): Fault Output. This pin is pulled low by an
open-drain output when a fault occurs. This fault could
either be an undervoltage fault, an overvoltage fault, or
an open MOSFET fault. The external MOSFET is turned off
for undervoltage and overvoltage faults, while it is left on
for open MOSFET fault. An internal 10µA current source
pulls this pin up to a diode below VCC. It may be pulled
above VCC using an external pull-up. Tie to GND or leave
open if unused.
REV (Pin 7): Reverse Current Enable Input. Connect this
pin to GND for normal diode operation that blocks reverse
current. Driving this pin above 1V fully turns on the MOSFET
gate to allow reverse current. An internal 10µA current
source pulls this pin to GND.
OUT (Pin 8): Output Voltage Sense Input. Connect this
pin to the output side of the MOSFET. The voltage sensed
at this pin is used to control the MOSFET gate.
GND (Pin 9): Device Ground.
CPO (Pin 10): Charge Pump Output. Connect a capacitor
from this pin to the SOURCE pin. The value of this capaci-
tor is approximately 10x the gate capacitance (CISS) of the
MOSFET switch. The charge stored on this capacitor is
used to pull-up the gate during a fast turn-on. Leave this
pin open if fast turn-on is not needed.
GATE (Pin 11): MOSFET Gate Drive Output. Connect this
pin to the gate of the external N-channel MOSFET switch.
An internal clamp limits the gate voltage to 6.1V above,
and a diode below SOURCE. During fast turn-on a 1.5A
pull-up charges GATE to CPO. During fast turn-off a 1.5A
pull-down discharges GATE to SOURCE.
SOURCE (Pin 12): MOSFET Gate Drive Return. Connect
this pin to the source of the external N-channel MOSFET
switch.
EXPOSED PAD (Pin 13, DD Package Only): Exposed pad
may be left open or connected to device ground.
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LTC4352
Applications INFORMATION
External CPO Supply
The internal charge pump takes milliseconds to charge
up the CPO pin capacitor especially during device power
up. This time can be shortened by connecting an external
supply to the CPO pin. A series resistor is needed to limit
the current into the internal clamp between the CPO and
SOURCE pins. The CPO supply should also be higher than
the main input supply to meet the gate drive requirements
of the MOSFET. Figure 7 shows such a 5V ideal diode ap-
plication, where a 12V supply is connected to the CPO pin
through a 1k resistor. The 1k limits the current into the
CPO pin to 5.3mA, when the SOURCE pin is grounded.
Input Transient Protection
When the capacitances at the input and output are very
small, rapid changes in current can cause transients that
exceed the 24V Absolute Maximum Rating of the VIN and
OUT pins. In ORing applications using a single MOSFET, one
surge suppressor connected from OUT to ground clamps
all the inputs. In the absence of a surge suppressor, an
output capacitance of 10μF is sufficient in most applications
to prevent the transient from exceeding 24V. Back-to-back
MOSFET applications, depending on voltage levels, may
require a surge suppressor on each supply input.
Design Example
The following design example demonstrates the calcula-
tions involved for selecting components in a 12V system
with 10A maximum load current (see Figure 1).
First, calculate the RDS(ON) of the MOSFET to achieve the
desired forward drop at full load. Assuming a VFWD of
50mV (which is comfortably below the 200mV minimum
open MOSFET fault threshold):
RDS(ON)
≤
VFWD
ILOAD
=
50mV
10A
=
5mΩ
The Si7336ADP offers a good solution, in a SO-8 sized
package, with a maximum RDS(ON) of 4mΩ and BVDSS of
30V. The maximum power dissipation in the MOSFET is:
P = I2LOAD • RDS(ON) = (10A)2 • 4mΩ = 0.4W
With a maximum steady-state thermal resistance, θJA,
of 65°C/W, 0.4W causes a modest 26°C rise in junction
temperature of the Si7336ADP above the ambient.
The input capacitance, CISS, of the Si7336ADP is about
6500pF. Slightly exceeding the 10x recommendation, a
0.1µF capacitor is selected for C2.
Q1
Si7336ADP
5V TO LOAD
12V
R7 C2
1k 0.1µF
VIN GATE
SOURCE
LTC4352
OUT
CPO
GND
4352 F07
Figure 7. 5V Ideal Diode with External 12V Powering CPO for
Faster Start-up and Refresh
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC4352.PDF ] | |
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