19-3584; Rev 1; 3/09
ORing MOSFET Controller with
Ultra-Fast 200ns Turn-Off
General Description
The MAX5079 ORing MOSFET controller replaces
ORing diodes in high-reliability redundant, parallel-con-
nected power supplies. Despite their low forward-volt-
age drop, ORing Schottky diodes cause excessive
power dissipation at high currents. The MAX5079
allows for the use of low-on-resistance n-channel power
MOSFETs to replace the Schottky diodes. This results
in low power dissipation, smaller size, and elimination
of heatsinks in high-power applications.
The MAX5079 operates from 2.75V to 13.2V and includes
a charge pump to drive the high-side n-channel MOSFET.
Operation down to 1V is possible if an auxiliary voltage of
at least 2.75V is available. When the controller detects a
positive voltage difference between IN and BUS, the
n-channel MOSFET is turned on. The MOSFET is turned
off as soon as the MAX5079 sees a negative potential at
IN with respect to the BUS voltage, and is automatically
turned back on when the positive potential is restored.
Under fault conditions, the ORing MOSFET’s gate is
pulled down with a 1A current, providing an ultra-fast
200ns turn-off. The reverse voltage turn-off threshold is
externally adjustable to avoid unintentional turn-off of the
ORing MOSFET due to glitches at IN or BUS caused by
hot plugging the power supply.
Additional features include an OVP flag to facilitate
shutdown of a failed power supply due to an overvolt-
age condition, and a PGOOD signal that indicates if V
IN
is either below the undervoltage lockout or V
BUS
is in
an overvoltage condition. The MAX5079 operates over
the -40°C to +85°C temperature range and is available
in a space-saving 14-pin TSSOP package.
o
2.75V to 13.2V Input ORing Voltage
o
1V to 13.2V Input ORing Voltage with 2.75V Aux
Voltage Present
o
2A MOSFET Gate Pulldown Current During Fault
Condition
o
Ultra-Fast 200ns, MOSFET Turn-Off During Fault
Condition
o
Supply Undervoltage and Bus Overvoltage
Detection
o
Power-Good (PGOOD) and Overvoltage (OVP)
Outputs for Fault Detection
o
Space-Saving 14-Pin TSSOP Package
o
-40°C to +85°C Operating Temperature Range
Features
MAX5079
Ordering Information
PART
MAX5079EUD
TEMP RANGE
-40°C to +85°C
PIN-PACKAGE
14 TSSOP
Typical Operating Circuit
SUB 75N 03-04
1V TO 13.2V
V
OUT1
POWER SUPPLY 1
(PS1)
>2.75V
N1
V
IN
IN
AUXIN
UVLO
STH
R
STH
C
STH
C+
C-
FTH
GATE
U1
MAX5079
BUS
PGOOD
OVI
OVP
GND
V
BUS
BUS
COMMON
Applications
Paralleled DC-DC Converter Modules
N+1 Redundant Power Systems
Servers
Base-Station Line Cards
RAID
Networking Line Cards
V
OUT2
POWER SUPPLY 2
(PS2)
C
EXT
R
FTH
SUB 75N 03-04
1V TO 13.2V
V
IN
IN
>2.75V
AUXIN
UVLO
STH
R
STH
C
STH
C+
C-
FTH
GATE
U2
MAX5079
BUS
PGOOD
OVI
OVP
GND
C
BUS
N2
V
BUS
C
EXT
R
FTH
Pin Configuration appears at end of data sheet.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
ORing MOSFET Controller with
Ultra-Fast 200ns Turn-Off
MAX5079
ABSOLUTE MAXIMUM RATINGS
GATE to GND ..............................................-0.3V to (V
IN
+ 8.5V)
All Other Pins to GND.............................................-0.3V to +15V
Continuous Current Into Any Pin ......................................±50mA
Continuous Power Dissipation (T
A
= +70°C)
14-Pin TSSOP (derate 9.1mW/°C above +70°C) ......727.3mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
((V
IN
= 2.75V to 13.2V and V
AUXIN
= 0V) or (V
IN
= 1V and V
AUXIN
= 2.75V to 13.2V), R
STH
= open, R
FTH
= 0, V
UVLO
= 1V, V
OVI
= 0V,
T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= 12V and T
A
= +25°C. See the
Typical Operating Circuit.)
(Note 1)
PARAMETER
POWER SUPPLIES
IN Input Voltage Range
AUXIN Input Voltage Range
(V
AUXIN
- V
IN
) High Threshold
(When GATE Connects Directly
to AUXIN) (Note 2)
(V
AUXIN
- V
IN
) Hysteresis (When
GATE Connects Directly To
AUXIN)
IN Supply Current
AUXIN Leakage Current
AUXIN Supply Current
BUS Leakage Current
BUS Supply Current
IN TO AUXIN SWITCHOVER
Switchover High Threshold
Switchover Low Threshold
IN UNDERVOLTAGE LOCKOUT
Internal UVLO High Threshold
Internal UVLO Hysteresis
External UVLO Threshold
External UVLO Hysteresis
External UVLO Input Bias
V
INTUVLO_HIGH
V
INTUVLO_HYST
V
UVLO
V
UVLO_HYST
I
UVLO
V
IN
rising, V
AUXIN
= 0 or V
AUXIN
rising,
V
IN
= 1V, V
BUS
= 2.75V
V
IN
falling, V
AUXIN
= 0 or V
AUXIN
falling, V
IN
= 1V
V
UVLO
falling
0.568
2.0
2.25
30
0.6
60
500
0.632
2.5
V
mV
V
mV
nA
V
AUXIN_HIGH
V
AUXIN_LOW
(V
IN
- V
AUXIN
), V
AUXIN
falling
(V
IN
- V
AUXIN
), V
AUXIN
rising
-60
-200
+25
-25
+200
+50
mV
mV
V
IN
V
AUXIN
V
AUXIN_
THRESHOLD
SYMBOL
CONDITIONS
MIN
2.75
TYP
MAX
13.20
13.2
13.2
UNITS
V
V
V
V
V
AUXIN
≥
2.75V
1.0
0
V
AUXIN
rising, I
GATE
= 10µA
4.2
4.9
5.7
V
AUXIN_
HYSTERESIS
40
V
UVLO
= 1V, V
IN
> V
BUS
V
AUXIN
= 0
V
UVLO
= 1V, V
AUXIN
= V
IN
, = 3V;
V
IN
> V
BUS
V
IN
= 13.2V, V
BUS
= 0
V
BUS
= 13.2V, V
BUS
> V
IN
,
V
BUS
> V
AUXIN
4
20
4
1
3
mV
mA
µA
mA
mA
mA
I
IN
I
LEAK_AUX
I
AUXIN
I
LEAK_BUS
I
BUS
2
_______________________________________________________________________________________
ORing MOSFET Controller with
Ultra-Fast 200ns Turn-Off
ELECTRICAL CHARACTERISTICS (continued)
((V
IN
= 2.75V to 13.2V and V
AUXIN
= 0V) or (V
IN
= 1V and V
AUXIN
= 2.75V to 13.2V), R
STH
= open, R
FTH
= 0, V
UVLO
= 1V, V
OVI
= 0V,
T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= 12V and T
A
= +25°C. See the
Typical Operating Circuit.)
(Note 1)
PARAMETER
ORing MOSFET CONTROL
ORing MOSFET Turn-On Time
ORing MOSFET Forward Voltage
Threshold (Fast Comparator)
ORing MOSFET Reverse Voltage
Turn-Off Threshold (Fast
Comparator (V
IN
- V
BUS
))
ORing MOSFET Reverse Voltage
Blanking Time (Fast Comparator)
Slow-Comparator Output Voltage
Threshold on STH
ORing MOSFET Reverse Voltage
Turn-Off Threshold (Slow
Comparator (V
IN
- V
BUS
))
(V
IN
- V
BUS
) to I
STH
Transconductance (Slow
Comparator)
ORing MOSFET Reverse Voltage
Blanking Time (Slow
Comparator)
ORing MOSFET DRIVER
Gate-Charge Current
I
GATE
C
EXT
= 100nF, V
IN
≥
2.75V
V
GATE
= V
IN
, V
IN
= 5.1V, V
BUS
= 5V;
V
OUT
= 1V
V
GATE
≥
V
IN
, V
IN
= 2.75V, V
BUS
= 3.5V
V
GATE
≥
V
IN
, V
IN
= 12V, V
BUS
= 13.2V
Gate Fall Time
Gate Discharge Current Delay
Time (Time from V
IN
Falling from
3.7V to 3V to V
GATE
= V
IN
)
Gate to IN Resistance
Gate to IN Clamp Voltage
Gate-Drive Voltage (Measured
with Respect to V
IN
)
V
IN
Switchover Threshold to
Higher GATE Voltage (Note 4)
t
FGATE
V
BUS
= 3.5V, C
GATE
= 0.1µF
V
BUS
= 3.5V, C
GATE
= 0.01µF
V
BUS
= 3.5V
(V
GATE
- V
IN
) = 100mV; V
IN
≥
2.75V
8.5
3.8
6.5
4.5
7.4
7
5
8
7.7
5.5
8.5
V
V
0.7
0.9
2
2
1.3
3.2
600
200
70
200
900
11
ns
6.8
A
mA
t
ON
V
DTH
C
GATE
= 10nF, C
EXT
= 100nF,
MOSFET gate threshold = 2V
(V
IN
- V
BUS
) rising, V
AUXIN
≥
2.75V
R
FTH
= 0
V
FTH
R
FTH
= 12kΩ
R
FTH
= 27kΩ, V
IN
≥
V
BUS
= 2.8V, R
FTH
= 0,
V
BUS
- V
IN
= 0.3V
V
IN
≥
2.75V
R
STH
open
V
STH
R
STH
= 500kΩ
R
STH
= 64kΩ
G
M_STH
V
STH
= 0V
STH floating
t
SBL
C
STH
= 0.047µF
C
STH
= 0.22µF
0.5
0.95
-0.1
V
AUXIN
≥
2.75V
5
-12
-63
-126
10
12.5
-24
-104
-204
50
1
-12
-25
-100
0.17
0.9
5
14
1.5
ms
mS
1.05
-24.0
mV
25
20
-31
-150
-300
ns
V
mV
µs
mV
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX5079
t
FBL
V
O_STH
Gate Discharge Current (Note 3)
I
GATE.DIS_MIN
t
DIS_GATE
R
GATE_IN
ns
Ω
V
V
GATE_IN_CLAMP
I
GATE
= 10mA, V
IN
≥
V
BUS
2.7V < V
IN
< 13.2V
(V
GATE
- V
IN
)
V
IN
= 13.2V
V
IN
= 2.75V
V
IN_SOTH+
_______________________________________________________________________________________
3
ORing MOSFET Controller with
Ultra-Fast 200ns Turn-Off
MAX5079
ELECTRICAL CHARACTERISTICS (continued)
((V
IN
= 2.75V to 13.2V and V
AUXIN
= 0V) or (V
IN
= 1V and V
AUXIN
= 2.75V to 13.2V), R
STH
= open, R
FTH
= 0, V
UVLO
= 1V, V
OVI
= 0V,
T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= 12V and T
A
= +25°C. See the
Typical Operating Circuit.)
(Note 1)
PARAMETER
V
IN
Switchover Hysteresis
(Note 4)
Charge-Pump Frequency
PROTECTION
OVI Input Bias Current
OVI Threshold
OVP Output Low Voltage
OVP Leakage Current
PGOOD Leakage Current
PGOOD Output Low Voltage
I
OVI
V
OVI_TH
V
OVP_LOW
I
OVP_LEAK
I
PG_LEAK
V
PG_LOW
OVI rising
V
OVI
= 1V, I
SINK
= 10mA
V
IN
= 2.75V, V
OVP
= 13.2V
V
PGOOD
= 13.2V
I
SINK
= 2mA
0.2
0.568
0.6
0.2
500
0.632
0.4
1
1
0.4
nA
V
V
µA
µA
V
SYMBOL
V
IN_SOHYS
f
CP
External
Internal, V
IN
< 5V, V
AUXIN
< 5V
CONDITIONS
MIN
TYP
40
70
1100
MAX
UNITS
mV
kHz
Note 1:
Note 2:
Note 3:
Note 4:
All devices are production tested at +25°C. Limits over temperature are guaranteed by design.
Threshold is reached when charge pump turns off.
Gate discharge current is guaranteed through the testing of gate fall time.
V
IN
switchover threshold is V
IN
at which the gate-drive voltage (V
GATE
- V
IN
) goes from 5V to 7V, V
IN
rising and (V
IN
≥
V
BUS
).
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted. See the
Typical Operating Circuit.)
AUXIN SUPPLY CURRENT
vs. TEMPERATURE (V
IN
= V
BUS
= 1V)
MAX5079 toc01
GATE-CHARGE CURRENT vs. V
IN
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
I
GATE
(mA)
MAX5079 toc02
SLOW-COMPARATOR REVERSE VOLTAGE
THRESHOLD (V
STH
vs. R
STH
)
0.18
0.16
0.14
T
A
= -40°C, T
A
= +25°C,
T
A
= +85°C, T
A
= +125°C
MAX5079 toc03
3
0.20
V
AUXIN
= 10V
2
I
AUXIN
(mA)
V
AUXIN
= 5V
T
A
= +25°C
V
STH
(V)
T
A
= -40°C
T
A
= +85°C
0.12
0.10
0.08
1
V
AUXIN
= 2.7V
T
A
= +125°C
0.06
0.04
0.02
0
0
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
V
IN
(V)
10
100
R
STH
(kΩ)
1000
4
_______________________________________________________________________________________
ORing MOSFET Controller with
Ultra-Fast 200ns Turn-Off
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted. See the
Typical Operating Circuit.)
SLOW-COMPARATOR BLANKING TIME
t
STH
vs. C
STH
(R
STH
= 180kΩ)
MAX5079 toc04
MAX5079
MAX5079 toc05
90
80
70
t
STH
(ms)
75mV OVERDRIVE
72
64
56
t
RESPONSE
(ns)
48
40
32
24
16
8
0
V
IN
= 1V, V
AUXIN
= 5V
V
IN
= 5V, V
AUXIN
= 0V
T
A
= +85°C
T
A
= +125°C
50
40
30
20
10
0
0
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
C
STH
(µF)
V
FTH
(V)
60
V
IN
= 12V,
V
AUXIN
= 0V
V
IN
= 2.75V,
V
AUXIN
= 12V
T
A
= -40°C
0
20
40
60
80
100
120
140
-40 -25 -10 5 20 35 50 65 80 95 110 125
TEMPERATURE (°C)
R
FTH
(kΩ)
CHARGE-PUMP FREQUENCY
vs. INPUT VOLTAGE
MAX5079 toc07
GATE-CHARGE CURRENT vs. C
EXT
MAX5079 toc08
FAULT CURRENT WAVEFORM
(IN SHORTED TO PGND)
80
78
76
74
f
CP
(kHz)
72
70
68
66
64
62
60
T
A
= +25°C
T
A
= -40°C
T
A
= +125°C
T
A
= +85°C
MAX5079 toc09
6.0
5.5
GATE-CHARGE CURRENT (mA)
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
1
10
C
EXT
(nF)
MAX5079 toc06
100
FAST-COMPARATOR REVERSE VOLTAGE
THRESHOLD (V
FTH
vs. R
FTH
)
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
80
FAST-COMPARATOR RESPONSE TIME
V
IN
= 12V
MOSFET REVERSE
CURRENT
5A/div
BUS
5V/div
GATE
10V/div
IN
5V/div
100
400ns/div
V
IN
= 5V, V
BUS
= 5V,
V
AUXIN
= 0V, C
STH
= 0,
R
STH
= OPEN, R
FTH
= 0,
UVLO = IN
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
V
IN
(V)
_______________________________________________________________________________________
5
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