LTC4359
Ideal Diode Controller with
Reverse Input Protection
FEATURES
DESCRIPTION
Reduces Power Dissipation by Replacing a Power
Schottky Diode
n Wide Operating Voltage Range: 4V to 80V
n Reverse Input Protection to – 40V
n Low 9µA Shutdown Current
n Low 150μA Operating Current
n Smooth Switchover without Oscillation
n Controls Single or Back-to-Back N-Channel MOSFETs
n Available in 6-Pin (2mm × 3mm) DFN, 8-Lead MSOP
and 8-Lead SO Packages
n AEC-Q100 Qualified for Automotive Applications
The LTC®4359 is a positive high voltage ideal diode controller that drives an external N-channel MOSFET to replace
a Schottky diode. It controls the forward-voltage drop
across the MOSFET to ensure smooth current delivery
without oscillation even at light loads. If a power source
fails or is shorted, a fast turn-off minimizes reverse current transients. A shutdown mode is available to reduce
the quiescent current to 9μA for load switch and 14µA for
ideal diode applications.
n
APPLICATIONS
n
n
n
n
n
n
Automotive Battery Protection
Redundant Power Supplies
Supply Holdup
Telecom Infrastructure
Computer Systems/Servers
Solar Systems
When used in high current diode applications, the LTC4359
reduces power consumption, heat dissipation, voltage loss
and PC board area. With its wide operating voltage range,
the ability to withstand reverse input voltage, and high
temperature rating, the LTC4359 satisfies the demanding
requirements of both automotive and telecom applications.
The LTC4359 also easily ORs power sources in systems
with redundant supplies.
All registered trademarks and trademarks are the property of their respective owners.
TYPICAL APPLICATION
Power Dissipation vs Load Current
12V, 20A Automotive Reverse-Battery Protection
BSC028N06NS
VOUT TO LOAD
SMAT70A
70V
SMAJ24A
24V
IN
SOURCE
GATE
OUT
47nF
SHDN
LTC4359
VSS
POWER DISSIPATION (W)
VIN
12V
10
8
SCHOTTKY DIODE (SBG2040CT)
6
POWER
SAVED
4
2
4359 TA01
MOSFET (BSC028N06NS)
1k
0
0
5
10
CURRENT (A)
15
20
4359 TA01a
Rev. F
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1
LTC4359
ABSOLUTE MAXIMUM RATINGS
(Notes 1, 2)
IN, SOURCE, SHDN.................................... –40V to 100V
OUT (Note 3).................................................–2V to 100V
IN – OUT...................................................–100V to 100V
IN – SOURCE..................................................–1V to 80V
GATE – SOURCE (Note 4)..........................–0.3V to +10V
Operating Ambient Temperature Range
LTC4359C................................................. 0°C to 70°C
LTC4359I.............................................. −40°C to 85°C
LTC4359H........................................... −40°C to 125°C
Storage Temperature Range................... −65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MS, SO Packages.............................................. 300°C
PIN CONFIGURATION
TOP VIEW
6 VSS
OUT 1
GATE 2
7
SOURCE 3
TOP VIEW
TOP VIEW
5 SHDN
4 IN
GATE
SOURCE
NC
IN
1
2
3
4
8
7
6
5
OUT
NC
VSS
SHDN
MS8 PACKAGE
8-LEAD PLASTIC MSOP
TJMAX = 150°C, θJA = 163°C/W
DCB PACKAGE
6-LEAD (2mm × 3mm) PLASTIC DFN
TJMAX = 150°C, θJA = 64°C/W
EXPOSED PAD (PIN 7) PCB VSS CONNECTION OPTIONAL
GATE 1
8
OUT
SOURCE 2
7
NC
NC 3
6
VSS
IN 4
5
SHDN
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 150°C, θJA = 130°C/W
ORDER INFORMATION
TAPE AND REEL (MINI)
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4359CDCB#TRMPBF
LTC4359CDCB#TRPBF
LFKF
6-Lead (2mm × 3mm) Plastic DFN
0°C to 70°C
LTC4359IDCB#TRMPBF
LTC4359IDCB#TRPBF
LFKF
6-Lead (2mm × 3mm) Plastic DFN
–40°C to 85°C
LTC4359HDCB#TRMPBF
LTC4359HDCB#TRPBF
LFKF
6-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
TUBE
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC4359CMS8#PBF
LTC4359CMS8#TRPBF
LTFKD
8-Lead Plastic MSOP
0°C to 70°C
LTC4359IMS8#PBF
LTC4359IMS8#TRPBF
LTFKD
8-Lead Plastic MSOP
–40°C to 85°C
LTC4359HMS8#PBF
LTC4359HMS8#TRPBF
LTFKD
8-Lead Plastic MSOP
–40°C to 125°C
LTC4359CS8#PBF
LTC4359CS8#TRPBF
4359
8-Lead Plastic SO
0°C to 70°C
LTC4359IS8#PBF
LTC4359IS8#TRPBF
4359
8-Lead Plastic SO
–40°C to 85°C
LTC4359HS8#PBF
LTC4359HS8#TRPBF
4359
8-Lead Plastic SO
–40°C to 125°C
LTC4359IMS8#WPBF
LTC4359IMS8#WTRPBF
LTFKD
8-Lead Plastic MSOP
–40°C to 85°C
LTC4359HMS8#WPBF
LTC4359HMS8#WTRPBF
LTFKD
8-Lead Plastic MSOP
–40°C to 125°C
LTC4359IDCB#WTRPBF
LTC4359IDCB#WTRPBF
LFKF
6-Lead (2mm × 3mm) Plastic DFN
–40°C to 85°C
AUTOMOTIVE PRODUCTS**
LTC4359HDCB#WTRPBF LTC4359HDCB#WTRPBF LFKF
6-Lead (2mm × 3mm) Plastic DFN
–40°C to 125°C
Contact the factory for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Tape and reel specifications. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix.
**Versions of this part are available with controlled manufacturing to support the quality and reliability requirements of automotive applications. These
models are designated with a #W suffix. Only the automotive grade products shown are available for use in automotive applications. Contact your
local Analog Devices account representative for specific product ordering information and to obtain the specific Automotive Reliability reports for
these models.
2
Rev. F
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LTC4359
ELECTRICAL
CHARACTERISTICS
The
l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, IN = 12V, SOURCE = IN, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
80
V
150
9
15
–15
200
20
30
–40
µA
µA
µA
µA
5
120
0.8
0.8
6
7.5
220
3
3
12
µA
µA
µA
µA
µA
µA
µA
mA
VIN
Operating Supply Range
IN Current
IN = 12V
IN = OUT = 12V, SHDN = 0V
IN = OUT = 24V, SHDN = 0V
IN = −40V
l
l
l
l
IOUT
OUT Current
IN = 12V, In Regulation
IN = 12V, ∆VSD = −1V
IN = OUT = 12V, SHDN = 0V
IN = OUT = 24V, SHDN = 0V
OUT = 12V, IN = SHDN = 0V
l
l
l
l
l
ISOURCE
SOURCE Current
IN = 12V, ∆VSD = −1V
IN = SOURCE = 12V, SHDN = 0V
SOURCE = –40V
l
l
l
1
–0.4
150
4
–0.8
200
15
–1.5
∆VGATE
Gate Drive (GATE–SOURCE)
IN = 4V, IGATE = 0, −1µA
IN = 8V to 80V; IGATE = 0, –1µA
l
l
4.5
10
5.5
12
15
15
V
V
∆VSD
Source-Drain Regulation Voltage (IN –OUT) ∆VGATE = 2.5V
l
20
30
45
mV
IGATE(UP)
Gate Pull-Up Current
GATE = IN, ∆VSD = 0.1V
l
–6
–10
–14
µA
Fault Condition, ∆VGATE = 5V, ∆VSD = −1V
Shutdown Mode, ∆VGATE = 5V, ∆VSD = 0.7V
l
l
70
0.6
130
180
mA
mA
l
0.3
0.5
µs
IGATE(DOWN) Gate Pull-Down Current
4
UNITS
IIN
l
0
3
tOFF
Gate Turn-Off Delay Time
∆VSD = 0.1V to −1V, ∆VGATE < 2V,
CGATE = 0pF
tON
Gate Turn-On Delay Time
IN = 12V, SOURCE = OUT = 0V, SHDN = 0V to 2V
∆VGATE > 4.5V, CGATE = 0pF
VSHDN(TH)
SHDN Pin Input Threshold
IN = 4V to 80V
l
0.6
1.2
2
VSHDN(FLT)
SHDN Pin Float Voltage
IN = 4V to 80V
l
0.6
1.75
2.5
V
ISHDN
SHDN Pin Current
SHDN = 0.5V, LTC4359I, LTC4359C
SHDN = 0.5V, LTC4359H
SHDN = −40V
Maximum Allowable Leakage, VIN = 4V
l
l
l
–1
–0.5
–0.4
–3
–3
–0.8
100
–5
–5
–1.5
µA
µA
mA
nA
GATE = 0V, IGATE(DOWN) = 1mA
l
–0.9
–1.8
–2.7
V
VSOURCE(TH) Reverse SOURCE Threshold for GATE Off
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: All currents into pins are positive; all voltages are referenced to
VSS unless otherwise specified.
200
µs
V
Note 3: An internal clamp limits the OUT pin to a minimum of 100V above
VSS. Driving this pin with more current than 1mA may damage the device.
Note 4: An internal clamp limits the GATE pin to a minimum of 10V above
IN or 100V above VSS. Driving this pin to voltages beyond the clamp may
damage the device.
Rev. F
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3
LTC4359
TYPICAL PERFORMANCE CHARACTERISTICS
IN Current in Regulation
IN Current in Shutdown
200
50
100
50
30
20
TA = 125°C
TA = 85°C
TA = 25°C
TA = –40°C
10
40
20
60
VIN (V)
0
80
0
160
200
VIN = 48V
VIN = 12V
VIN = 4V
IOUT (µA)
ISOURCE (µA)
0.5
∆VSD (V)
50
–1
4359 G04
0.5
–1
–0.5
0
1
0
800
–40
4359 G06
VIN = 12V
∆VSD = 0.1V
–1V
600
VIN = 8V
tOFF (ns)
∆VGATE (V)
20
–30
Gate Turn-Off Time
vs GATE Capacitance
VIN > 12V
10
–20
–10
VOLTAGE (V)
IN = SOURCE
10
80
4359 G03
IN = SOURCE= SHDN
4359 G05
15
VIN = VSOURCE = 12V
VGATE = VIN +2.5V
60
–1.5
Gate Drive vs Gate Current
0
IGATE (µA)
0
–0.5
∆VSD (V)
Gate Current
vs Forward Voltage Drop
–10
–2
100
–50
1
40
20
VSOURCE (V)
IN = SOURCE
0
0
0
Total Negative Current
vs Negative Input Voltage
VSOURCE = 4V
40
TA = 125°C
TA = 85°C
TA = 25°C
TA = –40°C
4359 G02
150
80
–0.5
0
80
VSOURCE > 12V
–1
4
SOURCE Current
vs Forward Voltage Drop
120
–20
60
VIN (V)
4359 G01
OUT Current
vs Forward Voltage Drop
0
40
20
6
2
IIN + ISOURCE + ISHDN (mA)
0
IN = SOURCE = OUT
SHDN = 0V
8
ISOURCE (µA)
IIN (µA)
IIN (µA)
IN = SOURCE = OUT
SHDN = 0V
40
150
0
SOURCE Current in Shutdown
10
400
5
VIN = 4V
200
30
40
–50
0
50
100
150
∆VSD (mV)
0
0
–5
–10
IGATE (µA)
4359 G07
4
–15
4359 G08
0
0
2
6
4
CGATE (nF)
8
10
4359 G09
Rev. F
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LTC4359
TYPICAL PERFORMANCE CHARACTERISTICS
Gate Turn-Off Time
vs Initial Overdrive
200
Gate Turn-Off Time
vs Final Overdrive
1500
VIN = 12V
∆VSD = VINITIAL –1V
Load Current
vs Forward Voltage Drop
VIN = 12V
∆VSD = 45mV
10
VFINAL
FDB3632
CURRENT (A)
tPD (ns)
tPD (ns)
1000
100
500
6
4
FDS3732
50
0
FDMS86101
8
150
2
0
0.25
0.5
VINITIAL (V)
0.75
1
0
0
–0.25
–0.5
–0.75
VFINAL (V)
4359 G10
–1
4359 G11
0
0
25
50
∆VSD (mV)
75
100
4359 G12
PIN FUNCTIONS
Exposed Pad (DCB Package Only): Exposed pad may be
left open or connected to VSS.
GATE: Gate Drive Output. The GATE pin pulls high, enhancing the N-channel MOSFET when the load current creates
more than 30mV of voltage drop across the MOSFET.
When the load current is small, the gate is actively driven
to maintain 30mV across the MOSFET. If reverse current
flows, a fast pull-down circuit connects the GATE to the
SOURCE pin within 0.3μs, turning off the MOSFET.
IN: Voltage Sense and Supply Voltage. IN is the anode of
the ideal diode. The voltage sensed at this pin is used to
control the MOSFET gate.
NC (MS8 and S8 Packages): No Connection. Not internally
connected.
OUT: Drain Voltage Sense. OUT is the cathode of the ideal
diode and the common output when multiple LTC4359s
are configured as an ideal diode-OR. It connects either directly or through a 2k resistor to the drain of the N-channel
MOSFET. The voltage sensed at this pin is used to control
the MOSFET gate.
SHDN: Shutdown Control Input. The LTC4359 can be
shut down to a low current mode by pulling the SHDN
pin below 0.6V. Pulling this pin above 2V or disconnecting it allows an internal 2.6μA current source to turn the
part on. Maintain board leakage to less than 100nA for
proper operation. The SHDN pin can be pulled up to 100V
or down to – 40V with respect to VSS without damage. If
the shutdown feature is not used, connect SHDN to IN.
SOURCE: Source Connection. SOURCE is the return path
of the gate fast pull-down. Connect this pin as close as
possible to the source of the external N-channel MOSFET.
VSS: Supply Voltage Return and Device Ground.
Rev. F
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5
LTC4359
BLOCK DIAGRAM
Q1
VIN
IN
SOURCE
VOUT
GATE
OUT
2.6µA
SHDN
SHUTDOWN
–
+
CHARGE PUMP
f = 500kHz
–
+
–
FPD
COMP
+
+
–1.7V
NEGATIVE
COMP
GATE
AMP
–
+
–
30mV
VSS
IN
30mV
4359 BD
OPERATION
The LTC4359 controls an external N-channel MOSFET to
form an ideal diode. The GATE amplifier (see Block Diagram) senses across IN and OUT and drives the gate of the
MOSFET to regulate the forward voltage to 30mV. As the
load current increases, GATE is driven higher until a point
is reached where the MOSFET is fully on. Further increases
in load current result in a forward drop of RDS(ON)• ILOAD.
If the load current is reduced, the GATE amplifier drives
the MOSFET gate lower to maintain a 30mV drop. If the
input voltage is reduced to a point where a forward drop
of 30mV cannot be supported, the GATE amplifier drives
the MOSFET off.
In the event of a rapid drop in input voltage, such as an
input short-circuit fault or negative-going voltage spike,
reverse current temporarily flows through the MOSFET.
This current is provided by any load capacitance and by
other supplies or batteries that feed the output in diode-OR
applications. The FPD COMP (Fast Pull-Down Comparator)
6
quickly responds to this condition by turning the MOSFET
off in 300ns, thus minimizing the disturbance to the
output bus.
The IN, SOURCE, GATE and SHDN pins are protected
against reverse inputs of up to –40V. The NEGATIVE COMP
detects negative input potentials at the SOURCE pin and
quickly pulls GATE to SOURCE, turning off the MOSFET
and isolating the load from the negative input.
When pulled low the SHDN pin turns off most of the
internal circuitry, reducing the quiescent current to 9µA
and holding the MOSFET off. The SHDN pin may be either
driven high or left open to enable the LTC4359. If left
open, an internal 2.6µA current source pulls SHDN high.
In applications where Q1 is replaced with back-to-back
MOSFETs, the SHDN pin serves as an on/off control for
the forward path, as well as enabling the diode function.
Rev. F
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LTC4359
APPLICATIONS INFORMATION
The LTC4359 operates from 4V to 80V and withstands
an absolute maximum range of –40V to 100V without
damage. In automotive applications the LTC4359 operates
through load dump, cold crank and two-battery jumps,
and it survives reverse battery connections while also
protecting the load.
A 12V/20A ideal diode application is shown in Figure 1.
Several external components are included in addition to
the MOSFET, Q1. Ideal diodes, like their nonideal counterparts, exhibit a behavior known as reverse recovery.
In combination with parasitic or intentionally introduced
inductances, reverse recovery spikes may be generated by
an ideal diode during commutation. D1, D2 and R1 protect
against these spikes which might otherwise exceed the
LTC4359’s –40V to 100V survival rating. COUT also plays
a role in absorbing reverse recovery energy. Spikes and
protection schemes are discussed in detail in the Input
Short-Circuit Faults section.
Q1
BSC028N06NS
VIN
12V
VOUT
12V
20A
D1
SMAT70A
70V
D2
SMAJ24A
24V
IN
GATE
SOURCE
OUT
COUT
47nF
LTC4359
SHDN
VSS
R1
1k
4359 F01
Figure 1. 12V/20A Ideal Diode with Reverse Input Protection
20
MOSFET
(BSC028N06NS)
15
CURRENT (A)
Blocking diodes are commonly placed in series with supply
inputs for the purpose of ORing redundant power sources
and protecting against supply reversal. The LTC4359
replaces diodes in these applications with a MOSFET to
reduce both the voltage drop and power loss associated
with a passive solution. The curve shown on page 1 illustrates the dramatic improvement in power loss achieved in
a practical application. This represents significant savings
in board area by greatly reducing power dissipation in the
pass device. At low input voltages, the improvement in
forward voltage loss is readily appreciated where headroom is tight, as shown in Figure 2.
10
SCHOTTKY DIODE
(SBG2040CT)
5
0
0
0.1
0.3
0.2
VOLTAGE (V)
0.4
0.5
4359 F02
Figure 2. Forward Voltage Drop Comparison
Between MOSFET and Schottky Diode
It is important to note that the SHDN pin, while disabling
the LTC4359 and reducing its current consumption to
9µA, does not disconnect the load from the input since
Q1’s body diode is ever-present. A second MOSFET is
required for load switching applications.
MOSFET Selection
All load current passes through an external MOSFET, Q1.
The important characteristics of the MOSFET are onresistance, RDS(ON), the maximum drain-source voltage,
BVDSS, and the gate threshold voltage VGS(TH).
Gate drive is compatible with 4.5V logic-level MOSFETs
over the entire operating range of 4V to 80V. In applications
above 8V, standard 10V threshold MOSFETs may be used.
An internal clamp limits the gate drive to 15V maximum
between the GATE and SOURCE pins. For 24V and higher
applications, an external Zener clamp (D4) must be added
between GATE and SOURCE to not exceed the MOSFET’s
VGS(MAX) during input shorts.
The maximum allowable drain-source voltage, BVDSS, must
be higher than the power supply voltage. If the input is
grounded, the full supply voltage will appear across the
MOSFET. If the input is reversed, and the output is held
up by a charged capacitor, battery or power supply, the
sum of the input and output voltages will appear across
the MOSFET and BVDSS > OUT + |VIN |.
Rev. F
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7
LTC4359
APPLICATIONS INFORMATION
The MOSFET’s on-resistance, RDS(ON), directly affects
the forward voltage drop and power dissipation. Desired
forward voltage drop should be less than that of a diode
for reduced power dissipation; 100mV is a good starting
point. Choose a MOSFET which has:
RDS(ON) <
LTC4359
SHDN
Q4
VN2222LL
ON OFF
Forward Voltage Drop
ILOAD
4359 F03a
R1
1k
Figure 3a. SHDN Control
The resulting power dissipation is
48V
Pd = (ILOAD)2 • RDS(ON)
R8
240k
Shutdown Mode
In shutdown, the LTC4359 pulls GATE low to SOURCE,
turning off the MOSFET and reducing its current consumption to 9µA. Shutdown does not interrupt forward current
flow, a path is still present through Q1’s body diode, as
shown in Figure 1. A second MOSFET is needed to block
the forward path; see the section Load Switching and
Inrush Control. When enabled the LTC4359 operates as
an ideal diode. If shutdown is not needed, connect SHDN
to IN. SHDN may be driven with a 3.3V or 5V logic signal, or with an open drain or collector. To assert SHDN
low, the pull down must sink at least 5µA at 500mV. To
enable the part, SHDN must be pulled up to at least 2V.
If SHDN is driven with an open drain, open collector or
switch contact, an internal pull-up current of 2.6µA (1µA
minimum) asserts SHDN high and enables the LTC4359.
If leakage from SHDN to ground cannot be maintained at
less than 100nA, add a pull-up resistor to >2V to assure
turn on. The self-driven open circuit voltage is limited
internally to 2.5V. When floating, the impedance is high
and SHDN is subject to capacitive coupling from nearby
clock lines or traces exhibiting high dV/dt. Bypass SHDN
to VSS with 10nF to eliminate injection. Figure 3a is the
simplest way to control the shutdown pin. Since the control
signal ground is different from the SHDN pin reference,
VSS, there could be momentary glitches on SHDN during
transients. Figures 3b and 3c are alternative solutions
that level-shift the control signal and eliminate glitches.
8
VSS
R6
100k
IN
Q5
2N5401
Q4
2N5551
OFF ON
R7
240k
LTC4359
SHDN
VSS
R5
100k
4359 F03b
R1
1k
Figure 3b. Transistor SHDN Control
48V
ON OFF
R7
2k
Q4
MOC
207M
R6
1MΩ
SHDN
R5
2MΩ
IN
LTC4359
VSS
4359 F03c
R1
1k
Figure 4c. Opto-Isolator SHDN Control
Input Short-Circuit Faults
The dynamic behavior of an active, ideal diode entering
reverse bias is most accurately characterized by a delay
followed by a period of reverse recovery. During the delay
phase some reverse current is built up, limited by parasitic
resistances and inductances. During the reverse recovery
Rev. F
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LTC4359
APPLICATIONS INFORMATION
phase, energy stored in the parasitic inductances is transferred to other elements in the circuit. Current slew rates
during reverse recovery may reach 100A/µs or higher.
High slew rates coupled with parasitic inductances in
series with the input and output paths may cause potentially destructive transients to appear at the IN, SOURCE
and OUT pins of the LTC4359 during reverse recovery.
A zero impedance short-circuit directly across the input
and ground is especially troublesome because it permits
the highest possible reverse current to build up during
the delay phase. When the MOSFET finally interrupts the
reverse current, the LTC4359 IN and SOURCE pins experience a negative voltage spike, while the OUT pin spikes in
the positive direction.
To prevent damage to the LTC4359 under conditions
of input short-circuit, protect the IN, SOURCE and OUT
pins as shown in Figure 4. The IN and SOURCE pins are
protected by clamping to the VSS pin with two TransZorbs
or TVS. For input voltages 24V and greater, D4 is needed
to protect the MOSFET’s gate oxide during input shortcircuit conditions. Negative spikes, seen after the MOSFET
turns off during an input short, are clamped by D2, a 24V
TVS. D2 allows reverse inputs to 24V while keeping the
MOSFET off and is not required if reverse-input protection
is not needed. D1, a 70V TVS, protects IN and SOURCE in
VIN
INPUT PARASITIC
INDUCTANCE
+
–
the positive direction during load steps and overvoltage
conditions. OUT can be protected by an output capacitor,
COUT of at least 1.5µF, a TVS across the MOSFET or by
the MOSFET’s avalanche breakdown. Care must be taken
if the MOSFET’s avalanche breakdown is used to protect
the OUT pin. The MOSFET’s BVDSS must be sufficiently
lower than 100V, and the MOSFET’s avalanche energy rating must be ample enough to absorb the inductive energy.
If a TVS across the MOSFET or the MOSFET avalanche
is used to protect the OUT pin, COUT can be reduced to
47nF. COUT and R1 preserve the fast turn off time when
output parasitic inductance causes the IN and OUT voltages to drop quickly.
Reverse Input Protection
In the case of a reverse input where negative voltage is
present on the input, the components D1, D2 and R1
protect the LTC4359. With reverse inputs more negative
than D2’s breakdown voltage (24V), current flows from
system ground through R1. For applications that must
withstand reverse inputs much greater than –24V such
that R1’s power dissipation is unacceptable, it may be
replaced by a diode. If reverse input protection and fast
turn off time are not required, R1 can be removed and VSS
connected to system ground.
REVERSE RECOVERY CURRENT
Q1
FDMS86101
INPUT
SHORT
D1
SMAT70A
70V
OUTPUT PARASITIC
INDUCTANCE
+
–
D4
DDZ9699T
12V
IN SOURCE
GATE
SHDN
D2
LTC4359
SMAJ24A
VSS
24V
VOUT
CLOAD
OUT
R1
1k
COUT
≥1.5µF
4359 F04
Figure 4. Reverse Recovery Produces Inductive Spikes at the IN, SOURCE and OUT Pins.
The Polarity of Step Recovery Is Shown Across Parasitic Inductances
Rev. F
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9
LTC4359
APPLICATIONS INFORMATION
Figure 10 shows a +48V application with reverse input
protection where D5 is used instead of R1 to eliminate
the power dissipation and system ground current when the
input reverses to –48V. With –48V input and OUT powered
by another supply or held up by output capacitance, D2
(5.1V) and D3 (75V) prevent the LTC4359’s OUT–IN pins
from exceeding the 100V absolute maximum rating. R2
limits the current into D1, D2 and D3 during a reverse input.
Paralleling Supplies
Multiple LTC4359s can be used to combine the outputs of
two or more supplies for redundancy or for droop sharing,
as shown in Figure 5. For redundant supplies, the supply
with the highest output voltage sources most or all of the
load current. If this supply’s output is quickly shorted to
ground while delivering load current, the flow of current
temporarily reverses and flows backwards through the
LTC4359’s MOSFET. The LTC4359 senses this reverse
current and activates a fast pull-down to quickly turn off
the MOSFET.
VINA = 12V
PSA
Q1A
FDMS86101
D2A
SMAJ24CA
24V
RTNA
IN SOURCE
GATE
OUT
COUTA
1.5µF
VSS
PSB
RTNB
Q1B
FDMS86101
D2B
SMAJ24CA
24V
Load Switching and Inrush Control
By adding a second MOSFET as shown in Figure 6, the
LTC4359 can be used to control power flow in the forward direction while retaining ideal diode behavior in the
reverse direction. The body diodes of Q1 and Q2 prohibit
Q2
FQA140N10
VIN
28V
ON OFF
Q1
FDMS86101
VOUT
28V
10A
D1
SMAJ58A
58V
D2
SMAJ24A
24V
R1A
1k
VINB = 12V
Droop sharing can be accomplished if both power supply
output voltages and output impedances are nearly equal.
The 30mV regulation technique ensures smooth load
sharing between outputs without oscillation. The degree
of sharing is a function of MOSFET RDS(ON), the output
impedance of the supplies and their initial output voltages.
12V
10A
BUS
LTC4359
SHDN
If the other, initially lower, supply was not delivering any
load current at the time of the fault, the output falls until
the body diode of its ORing MOSFET conducts. Meanwhile,
the LTC4359 charges the MOSFET gate with 10µA until
the forward drop is reduced to 30mV. If this supply was
sharing load current at the time of the fault, its associated
ORing MOSFET was already driven partially on. In this case,
the LTC4359 will simply drive the MOSFET gate harder in
an effort to maintain a drop of 30mV.
R3
10Ω
C1
10nF
R4
10k
CLOAD
D4
DDZ9699T
12V
IN
SOURCE
SHDN
LTC4359
COUT
1.5µF
GATE OUT
VSS
IN SOURCE
GATE
OUT
COUTB
1.5µF
LTC4359
SHDN
R1
1k
4359 F06
VSS
R1B
1k
4359 F05
Figure 6. 28V Load Switch and Ideal
Diode with Reverse Input Protection
Figure 5. Redundant Power Supplies
10
Rev. F
For more information www.analog.com
LTC4359
APPLICATIONS INFORMATION
current flow when the MOSFETs are off. Q1 serves as the
ideal diode, while Q2 acts as a switch to control forward
power flow. On/off control is provided by the SHDN pin,
and C1 and R4 may be added if inrush control is desired.
1 S
VIN
4 G
When SHDN is driven high and provided VIN >VOUT + 30mV,
GATE sources 10µA and gradually charges C1, pulling up
both MOSFET gates. Q2 operates as a source follower and
VOUT
D 5
GATE
OUT
1
3
2
SOURCE
LTC4359
7
5
4
IN
6
10µA • CLOAD
C1
If VIN –100V Operation
LTC4355
Positive Voltage Diode-OR Controller and
Monitor
Controls Two N-Channel MOSFETs, 0.4µs Turn-Off, 80V Operation
LTC4357
Positive High Voltage Ideal Diode Controller
Controls Single N-Channel MOSFET, 0.5µs Turn-Off, 80V Operation
LTC4358
5A Ideal Diode
Internal N Channel MOSFET, 9V to 26.5V Operation
LT4363-1/LT4363-2
High Voltage Surge Stopper
Stops High Voltage Surges, 4V to 80V, –60V Reverse Input Protection
LTC4380
Low Quiescent Current Surge Stopper
8µA IQ, 4V to 72V Operation, –60V Reverse Input Protection
LT4256-1/LT4256-2
Positive High Voltage Hot Swap Controllers
Active Current Limiting, Supplies from 10.8V to 80V
Latch-Off and Automatic Retry Option
LTC4260
Positive High Voltage Hot Swap Controller
With I2C and ADC, Supplies from 8.5V to 80V
LTC4364
Surge Stopper with Ideal Diode
4V to 80V Operation, –40V Reverse Input, –20V Reverse Output
20
Rev. F
12/21
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For more information www.analog.com
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