LTC4352
Low Voltage Ideal Diode
Controller with Monitoring
Features
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Description
Low Loss Replacement for Power Diode
Controls N-Channel MOSFET
0V to 18V Supply ORing or Holdup
0.5μs Turn-On and Turn-Off Time
Undervoltage and Overvoltage Protection
Open MOSFET Detect
Status and Fault Outputs
Hot Swappable
Reverse Current Enable Input
12-Pin MSOP and DFN (3mm × 3mm) Packages
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The LTC4352 regulates the forward voltage drop across
the MOSFET to ensure smooth current transfer in diodeOR 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.
Applications
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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.
Redundant Power Supplies
Supply Holdup
Telecom Infrastructure
Computer Systems and Servers
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 Ideal Diode
Power Dissipation vs Load Current
4.0
Si7336ADP
CPO SOURCE VIN
0.1µF
VCC
UV
GATE
OUT
STATUS
LTC4352
OV
REV
FAULT
GND
4352 TA01
*OPTIONAL
3.5
TO LOAD
0.1µF*
MOSFET ON
STATUS
FAULT
POWER DISSIPATION (W)
2.9V TO 18V
3.0
DIODE (SBG1025L)
2.5
2.0
POWER
SAVED
1.5
1.0
0.5
0
MOSFET (Si7336ADP)
0
2
4
6
LOAD CURRENT (A)
8
10
4352 TA01b
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1
LTC4352
Absolute Maximum Ratings
(Notes 1, 2)
VIN, SOURCE Voltages....................................–2V to 24V
VCC Voltage................................................... –0.3V to 7V
OUT Voltage....................................................–2V to 24V
CPO, GATE Voltages (Note 3)...................... –0.3V to 30V
CPO D.C. Current....................................................10mA
UV, OV, REV Voltages................................. –0.3V to 24V
FAULT, STATUS Voltages............................. –0.3V to 24V
FAULT, STATUS Currents...........................................5mA
Operating Ambient Temperature Range
LTC4352C................................................. 0°C to 70°C
LTC4352I..............................................–40°C to 85°C
LTC4352H........................................... –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MS Package....................................................... 300°C
Pin Configuration
TOP VIEW
TOP VIEW
VIN
1
12 SOURCE
VCC
2
11 GATE
UV
3
OV
4
STATUS
5
8 OUT
FAULT
6
7 REV
13
VIN
VCC
UV
OV
STATUS
FAULT
10 CPO
9 GND
1
2
3
4
5
6
12
11
10
9
8
7
SOURCE
GATE
CPO
GND
OUT
REV
MS PACKAGE
12-LEAD PLASTIC MSOP
DD PACKAGE
12-PIN (3mm × 3mm) PLASTIC DFN
TJMAX = 150°C, θJA = 43°C/W
EXPOSED PAD (PIN 13) PCB GND CONNECTION OPTIONAL
TJMAX = 150°C, θJA = 164°C/W
Order Information
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4352CDD#PBF
LTC4352CDD#TRPBF
LDPJ
12-Pin (3mm × 3mm) Plastic DFN
0°C to 70°C
LTC4352IDD#PBF
LTC4352IDD#TRPBF
LDPJ
12-Pin (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC4352HDD#PBF
LTC4352HDD#TRPBF
LDPJ
12-Pin (3mm × 3mm) Plastic DFN
–40°C to 150°C
LTC4352CMS#PBF
LTC4352CMS#TRPBF
4352
12-Lead Plastic MSOP
0°C to 70°C
LTC4352IMS#PBF
LTC4352IMS#TRPBF
4352
12-Lead Plastic MSOP
–40°C to 85°C
LTC4352HMS#PBF
LTC4352HMS#TRPBF
4352
12-Lead Plastic MSOP
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is 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/
4352fa
2
LTC4352
Electrical
Characteristics
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VSOURCE = VIN, VOUT = VIN, VCC Open, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Supplies
VIN
Input Operating Range
l
l
l
2.9
0
0
18
VCC
18
V
V
V
VCC(EXT)
VCC External Supply Range
l
2.9
6
V
VCC(INT)
VCC Internal Regulator Voltage
l
3.5
4.1
4.7
V
IIN
VIN Supply Current
ICC
With External 2.9V to 4.7V VCC Supply
With External 4.7V to 6V VCC Supply
VIN = 0V, VCC = 5V, VOUT = 18V
VIN = 0V, VCC = 5V, VOUT = 18V (LTC4352H)
l
l
l
1.4
–10
–10
3
–13
–25
mA
µA
µA
External VCC Supply Current
VCC = 5V, VIN = 0V
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1.25
2.5
mA
VCC(UVLO)
VCC Undervoltage Lockout Threshold
VCC Rising
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2.45
2.57
2.7
V
ΔVCC(HYST)
VCC Undervoltage Lockout Hysteresis
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50
70
90
mV
l
10
25
40
mV
5
6.1
7.5
V
Ideal Diode Control
VFWD(REG)
Forward Regulation Voltage (VIN − VOUT)
ΔVGATE
MOSFET Gate Drive (VGATE – VSOURCE)
VFWD = 0.1V, I = 0 and –1μA
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tON(GATE)
GATE Turn-On Delay
CGATE = 10nF, VFWD = 0.2V
l
0.25
0.5
µs
tOFF(GATE)
GATE Turn-Off Delay
CGATE = 10nF, VFWD = −0.2V
l
0.2
0.5
µs
VUV Falling, VOV Rising
l
490
500
510
mV
l
2.5
5
8.5
mV
(LTC4352H)
l
l
0.8
0.8
1.0
1.0
1.2
1.25
V
V
0
±1
µA
10
13
µA
200
µA
Input/Output Pins
VUV,OV(TH)
UV, OV Threshold Voltage
ΔVUV,OV(HYST)
UV, OV Threshold Hysteresis
VREV(TH)
REV Threshold Voltage
IUV,OV
UV, OV Current
V = 0.5V
l
IREV
REV Current
VREV = 1V
l
7
IOUT
OUT Current
VOUT = 0V, 12V
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–13
ISOURCE
SOURCE Current
VSOURCE = 0V
l
ICPO(UP)
CPO Pull-Up Current
VCPO = VIN = 2.9V
VCPO = VIN = 18V
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l
IGATE
GATE Fast Pull-Up Current
GATE Fast Pull-Down Current
GATE Off Pull-Down Current
VFWD = 0.2V, ∆VGATE = 0V, VCPO = 17V
VFWD = –0.2V, ∆VGATE = 5V
VUV = 0V, ∆VGATE = 2.5V
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IFLT,STAT(IN)
STATUS, FAULT Leakage Current
V = 18V
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IFLT,STAT(UP)
STATUS, FAULT Pull-Up Current
V = 0V
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VOL
STATUS, FAULT Output Low Voltage
I = 1.25mA
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–85
–130
µA
–60
–50
–90
–75
–115
–100
µA
µA
60
–1.5
1.5
100
145
A
A
µA
0
±1
µA
–10
–12
µA
0.2
0.4
V
–8
VOH
STATUS, FAULT Output High Voltage
I = –1μA
l
VCC – 1
VCC – 0.5
ΔVGATE(ST)
MOSFET On Detect Threshold
STATUS Pulls Low, VFWD = 50mV
STATUS Pulls Low, VFWD = 50mV (LTC4352H)
l
l
0.3
0.28
0.7
0.7
1.1
1.1
V
V
VFWD(FLT)
Open MOSFET Threshold (VIN – VOUT)
FAULT Pulls Low
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200
250
300
mV
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating for extended periods may affect device reliability and
lifetime.
Note 2: All currents into device pins are positive; all currents out of device
V
pins are negative. All voltages are referenced to GND unless otherwise
specified.
Note 3: Internal clamps limit the GATE and CPO pins to a minimum of 5V
above, and a diode below SOURCE. Driving these pins to voltages beyond
the clamp may damage the device.
4352fa
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LTC4352
Typical Performance Characteristics
TA = 25°C, VIN = 12V, VSOURCE = VIN, VOUT = VIN,
VCC Open, unless otherwise noted.
VIN Current vs Voltage
300
1.6
VIN Current vs Voltage with
External VCC
VCC Current vs Voltage
1.50
VCC = 5V
250
1.25
200
0.8
1.00
150
ICC (mA)
IIN (µA)
IIN (mA)
1.2
100
0.25
0
0
3
6
9
VIN (V)
12
15
–50
18
3
0
5
4
VIN (V)
OUT Current vs Voltage
250
6
VCPO –VSOURCE (V)
100
50
VIN = 18V
4
VIN = 2.9V
3
3
6
9
15
12
VOUT (V)
18
2
–1
4
5
6
4352 G03
VOUT = VIN – 0.1V
6
VIN = 18V
5
4
VIN = 2.9V
3
2
1
0
0
3
VCC (V)
GATE Voltage vs Current
1
0
2
1
7
5
150
0
4352 G02
CPO Voltage vs Current
7
200
IOUT (µA)
2
1
4352 G01
300
–50
0
VGATE –VSOURCE (V)
0
0.75
0.50
50
0.4
VIN = 0V
0
0
–40
–20
4352 G04
–100
–60
–80
ICPO (µA)
–120
–1
0
–40
–20
4352 G05
STATUS, FAULT Output Low
Voltage vs Current
–60
–80
IGATE (µA)
–100
–120
4352 G06
STATUS, FAULT Output High
Voltage vs Current
4.0
1
3.5
3.0
2.5
0.6
VOH (V)
VOL (V)
0.8
0.4
2.0
1.5
1.0
0.2
0.5
0
0
1
2
3
CURRENT (mA)
4
5
4352 G07
0
0
–2
–4
–6
–8
CURRENT (µA)
–10
–12
4352 G08
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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 voltage 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 voltage 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 capacitor 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
Functional Diagram
VCC
VIN
CPO
2
1
10
CHARGE
PUMP
f = 3MHz
VCC
100µA
4.1V
+
LDO
+
GATE OFF
–
–
ENABLE
REVERSE
CURRENT
+
–
VIN
–
25mV
DISABLE
LDO
VCC LOW
+
–
2.57V
CP5
UV FAULT
SOURCE
CP2
–
OV 4
1V
8
OUT
7
REV
5
STATUS
6
FAULT
10µA
VCC
10µA
+
CP6
M1
–
VCC
OPEN
MOSFET
DETECT
0.5V
+
+
–
GATE
–
+
12 SOURCE
CP3
0.7V
UV 3
+
–
+
CP4
11 GATE
AMP
10µA
OV FAULT
M2
CP1
Z
*DD PACKAGE ONLY
9
13
GND
EXPOSED PAD*
4352 FD
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LTC4352
Operation
The LTC4352 controls either single or back-to-back
N-channel MOSFETs in order to emulate an ideal diode.
Dual MOSFETs eliminate current flow from the input to the
output in an input undervoltage or overvoltage condition.
When enabled, an amplifier (AMP) monitors the voltage
between the VIN and OUT pins, and drives the GATE pin.
The amplifier controls the gate of the external MOSFET
to servo its forward voltage drop (VIN – OUT) to 25mV.
The gate voltage rises to enhance the MOSFET if the load
current causes more than 25mV of drop. For large output
currents the MOSFET gate is driven fully on and the voltage
drop is equal to ILOAD • RDS(ON).
In the case of an input supply short-circuit, when the
MOSFET is conducting, a large reverse current starts
flowing from the load towards the input. The AMP detects
this failure condition as soon as it appears, and turns off
the MOSFET by pulling down the GATE pin. The REV pin
can be used to allow reverse current, overriding the diode
behavior.
The AMP quickly pulls-up the GATE pin whenever it senses
a large forward voltage drop. An external capacitor between
the CPO and SOURCE pins is needed for fast gate pull-up.
This capacitor is charged up, at device power-up, by the
internal charge-pump. This stored charge is used for the
fast gate pull-up.
limit the GATE to SOURCE voltage to 6.1V, and the CPO to
SOURCE voltage to 6.7V. The same clamps also limit the CPO
and GATE pins to a diode voltage below the SOURCE pin.
OV, UV, and VCC comparators, CP1 to CP3, control power
passage. The MOSFET is held off whenever the OV pin
is above 0.5V, the UV pin is below 0.5V, or the VCC pin is
below 2.57V. There is a 40µs delay from all three conditions becoming good to GATE being allowed to turn on.
Overvoltage causes a fast turn-off, while undervoltage
activates a 100μA pull-down on GATE after a 7μs delay.
Open-drain pull-down, M1, pulls the STATUS pin low when
the GATE to SOURCE voltage exceeds 0.7V, to indicate that
power is passing through the MOSFET. The FAULT output,
M2, pulls low during an undervoltage or overvoltage fault
condition. It also pulls low when GATE is fully on and
the forward voltage drop exceeds 250mV, indicating the
MOSFET has too much current or has failed open circuit.
Note that this open MOSFET fault does not turn off the
MOSFET unlike the undervoltage and overvoltage faults.
LDO is a low dropout regulator that generates a 4.1V
supply at the VCC pin from the VIN input. When a supply
below 2.9V is being ORed, an external supply in the 2.9V
to 6V range is required at the VCC pin. Comparator CP4
will disable LDO when VIN is below VCC.
The GATE pin sources current from the CPO pin, and sinks
current to the SOURCE and GND pins. Internal clamps
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LTC4352
Applications Information
common supply voltage it turns off the MOSFET, thereby
matching the function and performance of an ideal diode.
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
point of load. Diodes with storage capacitors also hold
up supply voltages when an input voltage sags or has a
brownout. The disadvantage of these approaches is the
diode’s significant forward voltage drop and the resulting
power loss. Additionally, diodes provide no information
concerning the status of the sourcing supply. Separate
control must therefore be added to ensure that a supply
that is out of range is not allowed to affect the load.
Power Supply Configuration
The LTC4352 can operate with supplies down to 0V. This
requires powering the VCC pin with an always present
external supply in the 2.9V to 6V range. If not always
present, a series 470Ω resistor or Schottky diode limits
device power dissipation and backfeeding of low VCC
supply when VIN is high. For a 2.9V to 4.7V VCC supply,
VIN should be lower than VCC. A 0.1µF bypass capacitor
should also be connected between the VCC and GND pins,
close to the device. Figure 2 illustrates this.
The LTC4352 solves these problems by using an external
N-channel MOSFET as the pass element (see Figure 1).
The MOSFET is turned on when power is being passed,
allowing for a low voltage drop from the supply to the load.
When the input source voltage drops below the output
If VIN operates above 2.9V then the external supply at
VCC is not needed. The 0.1µF capacitor is still required
for bypassing.
Q1
Si7336ADP
TO LOAD
12V
C2
R4
2.7k
0.1µF
CPO SOURCE VIN
C1
0.1µF
GATE
OUT
D1
MOSFET
ON
D2
STATUS
VCC
UV
LTC4352
OV
FAULT
FAULT
REV
R5
2.7k
D1: GREEN LED LN1351C
D2: RED LED LN1261CAL
GND
4352 F01
Figure 1. 12V Ideal Diode with Status and Fault Indicators
TO LOAD
2.9V TO 18V
VIN
VCC
0.1µF
GATE
LTC4352
GND
OUT
TO LOAD
0V TO VCC
2.9V TO 4.7V
VIN
VCC
0.1µF
GATE
OUT
LTC4352
GND
TO LOAD
0V TO 18V
4.7V TO 6V
VIN
VCC
0.1µF
GATE
OUT
LTC4352
GND
4352 F02
Figure 2. Power Supply Configurations
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LTC4352
APPLICATIONS INFORMATION
CPO and GATE Start-Up
In single MOSFET applications, CPO is initially pulled up
to a diode below the SOURCE pin (Figure 3). In back-toback MOSFET applications, CPO starts off at 0V, since
SOURCE is near ground (Figure 4). CPO starts ramping
up 10µs after VCC clears its undervoltage lockout level.
Another 40µs later, GATE will also start ramping up with
CPO if UV, OV and VIN – OUT conditions allow it to. The
ramp rate is decided by the CPO pull-up current into the
combined CPO and GATE pin capacitances. An internal
clamp limits the CPO voltage to 6.7V above SOURCE,
while the final GATE voltage is determined by the forward
drop servo amplifier.
MOSFET Selection
The LTC4352 drives N-channel MOSFETs to conduct the
load current. The important features of the MOSFET are
its threshold voltage, the maximum drain-source voltage
BVDSS, and the on-resistance RDS(ON).
The gate drive for the MOSFET is guaranteed to be between
5V and 7.5V. This allows the use of logic level threshold
VIN = 5V
C2 = 0.1µF
N-channel MOSFETs. The maximum allowable drain-source
voltage, BVDSS, must be higher than the supply voltages
as the full supply voltage can appear across the MOSFET
when the input falls to 0V.
The FAULT pin pulls low to signal an open MOSFET fault
whenever the forward voltage drop across the enhanced
MOSFET exceeds 250mV. The RDS(ON) should be small
enough to conduct the maximum load current while not
triggering such a fault (when using FAULT), and to stay
within the MOSFET’s power rating at the maximum load
current.
CPO Capacitor Selection
The recommended value of the capacitor between the
CPO and SOURCE pins is approximately 10x the input
capacitance, CISS, of the MOSFET. A larger capacitor takes
a correspondingly longer time to charge up by the internal
charge pump. A smaller capacitor suffers more voltage
drop during a fast gate turn-on event as it shares charge
with the MOSFET gate capacitance.
VIN = 5V
C2 = 0.1µF
CPO
GATE
CPO
GATE
OUT
VOLTAGE
(5V/DIV)
VOLTAGE
(5V/DIV)
OUT
VIN, SOURCE
VIN
VCC
VCC
TIME (2.5ms/DIV)
4352 FO3
Figure 3. Start-up Waveform for Single MOSFET Application
TIME (2.5ms/DIV)
4352 FO4
Figure 4. Start-up Waveform for Back-to-Back MOSFET Application
4352fa
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LTC4352
Applications Information
Undervoltage and Overvoltage Protection
Inrush Control
Unlike a regular diode, the LTC4352 can prevent out of
range input voltages from affecting the load voltage. This
requires back-to-back MOSFETs, and resistive dividers
from the input to the UV and OV pins. For an example,
see Figure 5.
The LTC4352 can be used for inrush control in applications
where the input supply is hot-plugged. See Figure 6. The
CPO capacitor is omitted, since fast turn-on with stored
charge is not desired here. Undervoltage holds the gate
off till the short pin makes contact. 40µs after the UV level
is satisfied, the MOSFET gate ramps up due to the CPO
pull-up current. A RC network on the gate further slows
down the output dV/dt, while allowing fast turn-off during
reverse current or overvoltage conditions. Resistor RG
prevents high frequency oscillations in Q2. A dedicated
hot swap controller may be needed if overcurrent protection is also desired.
MOSFET Q2 is required to block conduction through the
body diode of Q1 when its gate is held off. The resistive
dividers set up the input voltage range where the ideal
diode control is allowed to operate. Outside this range,
the gate is held off and the FAULT pin pulls low.
When using a CPO capacitor in circuit with back-to-back
MOSFETs, there will be a large inrush current to the load
capacitance due to the fast gate turn-on after UV, OV levels
are met. Without the capacitor, the inrush will depend on
the CPO pull-up current charging up the gate capacitance.
Q2
Si7336ADP
Q1
Si7336ADP
12V
Q2
Si7336ADP
5V
Z1
Q1
Si7336ADP
CG
0.1µF
0.15µF
105k
R3
5.11k
R2
C2
31.6k
1%
R3
1k
1%
R2
VIN CPO
SOURCE
UV
3.09k
1%
OV
R1
GND
VIN
SOURCE GATE OUT
UV
GATE
OUT
FAULT
VCC
CPO
LTC4352
OV
STATUS
LTC4352
RG
10Ω
R6
10k
TO LOAD
TO LOAD
NC
GND
4352 F06
C1
0.1µF
REV
GND
BACKPLANE
Z1: DIODES INC. SMAJ12A
CONNECTORS
PLUG-IN CARD
4352 F05
Figure 5. 5V Ideal Diode with UV and OV Protection
Figure 6. Inrush and Ideal Diode Control on a Hot Swap Card
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10
LTC4352
Applications INFORMATION
External CPO Supply
Design Example
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 application, 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.
The following design example demonstrates the calculations 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):
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.
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
VIN
12V
SOURCE
C2
0.1µF
CPO
VFWD 50mV
=
= 5mΩ
ILOAD 10A
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:
Input Transient Protection
R7
1k
RDS (ON) ≤
GATE
TO LOAD
OUT
LTC4352
GND
4352 F07
Figure 7. 5V Ideal Diode with External 12V Powering CPO for
Faster Start-up and Refresh
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11
LTC4352
Applications INFORMATION
LEDs, D1 and D2, require around 3mA for good luminous
intensity. Accounting for a 2V diode drop and 0.5V VOL,
R1 and R2 are set to 2.7k.
PCB Layout Considerations
Connect the VIN and OUT pin traces as close as possible
to the MOSFET’s terminals. Keep the traces to the MOSFET
wide and short to minimize resistive losses. The PCB traces
D
S
D
S
D
G
D
W
TO LOAD
8
OUT
7
9
GND
10
11
VIA TO GROUND PLANE
GATE
TRACK WIDTH W:
0.03˝ PER AMPERE
ON 1OZ CU FOIL
CURRENT FLOW
S
SOURCE 12
W
It is also important to put C1, the bypass capacitor for the
VCC pin, as close as possible between VCC and GND. Also
place C2 near the CPO and SOURCE pins. Surge suppressors, when used, should be mounted close to the LTC4352
using short lead lengths.
Q1
SO-8
CURRENT FLOW
FROM INPUT
SUPPLY
associated with the power path through the MOSFET should
have low resistance. See Figure 8.
C1
MSOP-12
6
5
4
3
VCC
2
1
VIN
LTC4352
VIA TO GROUND PLANE
4352 F08
DRAWING IS NOT TO SCALE!
Figure 8. Recommended PCB Layout for Power MOSFET
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12
LTC4352
Typical Applications
Plug-in Card Supply Holdup Using Ideal Diode at Input
Q1
Si7336ADP
HOT SWAP
CONTROLLER
12V
SOURCE VIN
GATE
TO LOAD
+
OUT
CHOLDUP
LTC4352
GND
GND
BACKPLANE
GND
CONNECTORS
4352 TA02
PLUG-IN CARD
Ideal Diode with Reverse Input Protection
Q1
Si4438DY
3.5V TO 9V
10A LOAD
0.1µF
D3
1N4148
OR
BAT85
CPO SOURCE VIN
GATE
VCC
C1
0.1µF
UV
D5
SMAJ17A
LTC4352
OV
REV
OUT
STATUS
FAULT
GND
D4
BAT85
4352 TA04
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13
LTC4352
Package Description
DD Package
12-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1725 Rev A)
R = 0.115
TYP
7
0.40 ± 0.10
12
0.70 ±0.05
3.50 ±0.05
2.10 ±0.05
2.38 ±0.05
1.65 ±0.05
2.38 ±0.10
3.00 ±0.10
(4 SIDES)
1.65 ± 0.10
6
1
0.23 ± 0.05
0.45 BSC
0.75 ±0.05
0.200 REF
0.25 ± 0.05
PIN 1 NOTCH
R = 0.20 OR
0.25 × 45°
CHAMFER
PIN 1
TOP MARK
(SEE NOTE 6)
PACKAGE
OUTLINE
0.45 BSC
2.25 REF
2.25 REF
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED
0.00 – 0.05
(DD12) DFN 0106 REV A
BOTTOM VIEW—EXPOSED PAD
NOTE:
1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE
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 AND TIE BARS SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
MS Package
12-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1668 Rev Ø)
4.039 ± 0.102
(.159 ± .004)
(NOTE 3)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
12 11 10 9 8 7
0.254
(.010)
3.20 – 3.45
(.126 – .136)
DETAIL “A”
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
0° – 6° TYP
0.406 ± 0.076
(.016 ± .003)
REF
GAUGE PLANE
0.42 ± 0.038
(.0165 ± .0015)
TYP
0.53 ± 0.152
(.021 ± .006)
0.65
(.0256)
BSC
RECOMMENDED SOLDER PAD LAYOUT
DETAIL “A”
0.18
(.007)
SEATING
PLANE
1.10
(.043)
MAX
0.22 – 0.38
(.009 – .015)
TYP
1 2 3 4 5 6
0.650
(.0256)
BSC
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.86
(.034)
REF
0.1016 ± 0.0508
(.004 ± .002)
MSOP (MS12) 1107 REV Ø
4352fa
14
LTC4352
Revision History
REV
DATE
DESCRIPTION
PAGE NUMBER
A
12/10
Added H-grade information
2,3
Revised FAULT pin description in Pin Functions
5
Revised Functional Diagram
6
Added text to Operation section
7
Revised Figures 2, 5, 6 in Applications Information
8, 10
Added new Typical Application
13
Revised Typical Application and Related Parts list
16
4352fa
Information 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.
15
LTC4352
Typical Application
0V to 18V Ideal Diode-OR
VIN1
0V TO 18V
5V
Si7336ADP
CPO SOURCE VIN
GATE
VCC
0.1µF
LTC4352
OV
FAULT
REV
5V
GND
Si7336ADP
0.1µF
CPO SOURCE VIN
GATE OUT
VCC
0.1µF
OUT
STATUS
UV
VIN2
0V TO 18V
TO LOAD
0.1µF
UV
STATUS
LTC4352
OV
REV
FAULT
GND
4352 TA03
Related Parts
PART NUMBER
DESCRIPTION
COMMENTS
LTC1473/LTC1473L
Dual PowerPath™ Switch Driver
N-Channel, 4.75V to 30V/3.3V to 10V, SSOP-16
LTC1479
PowerPath Controller for Dual Battery Systems
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LTC4350
Hot Swappable Load Share Controller
N-Channel, 1.5V to 12V, Share Bus, SSOP-16
LTC4354
Negative Voltage Diode-OR Controller and Monitor
Dual N-Channel, –4.5V to –80V, SO-8, DFN-8
LTC4355
Positive High Voltage Ideal Diode-OR and Monitor
Dual N-Channel, 9V to 80V, SO-16, DFN-14
LTC4357
Positive High Voltage Ideal Diode Controller
N-Channel, 9V to 80V, MSOP-8, DFN-6
LTC4358
5A Ideal Diode
Internal N-Channel, 9V to 26.5V, TSSOP-16, DFN-14
LTC4411
2.6A Low Loss Ideal Diode in ThinSOT™
Internal P-Channel, 2.6V to 5.5V, 40μA IQ, SOT-23
LTC4412/LTC4412HV
Low Loss PowerPath Controller in ThinSOT
P-Channel, 2.5V to 28V/36V, 11μA IQ, TSOT-23
LTC4413/LTC4413-1
Dual 2.6A, 2.5V to 5.5V, Ideal Diodes in DFN-10
Dual Internal P-Channel, 2.5V to 5.5V, DFN-10
LTC4414
36V Low Loss PowerPath Controller for Large PFETs
P-Channel, 3V to 36V, 30μA IQ, MSOP-8
LTC4416/LTC4416-1
36V Low Loss Dual PowerPath Controller for Large PFETs Dual P-Channel, 3.6V to 36V, 70μA IQ, MSOP-10
4352fa
16 Linear Technology Corporation
LT 1210 REV A • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
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