General Description
Critical loads often employ parallel-connected power
supplies with redundancy in order to enhance system
reliability. The MAX8535/MAX8536/MAX8585 are highly
integrated but inexpensive MOSFET controllers that pro-
vide isolation and redundant power capability in high-reli-
ability systems. The MAX8535/MAX8585 are used in 12V
systems, and have an internal charge pump to drive the
gates of the n-channel pass elements to VCC + 10V. The
MAX8536 is used in 3.3V and 5V systems, with a charge-
pump output of VCC + 5V.
During startup, the MAX8535/MAX8536/MAX8585 mo ni -
tor the voltage drop across external MOSFETs. Once
VCC approaches or exceeds the bus voltage, the
MOSFETs are turned on. The MAX8535/MAX8536/
MAX8585 feature a dual-purpose TIMER input. A single
external resistor from TIMER to ground sets the turn-on
speed of the external MOSFETs. Optionally, the TIMER
input can be used as a logic-enable pin. Once the
device is turned on, the MAX8535/MAX8536/MAX8585
monitor the load, protecting against overvoltage, under-
voltage, and reverse-current conditions.
Overvoltage and undervoltage fault thresholds are
adjustable and can be disabled. The current-limit trip
points are set by the external MOSFETs’ RDS(ON),
reducing component count. An open-drain logic-low
fault output indicates if an overvoltage, undervoltage, or
reverse-current fault occurs.
All devices come in a space-saving 8-pin µMAX®
package and are specified over the extended -40°C to
+85°C temperature range.
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Applications
Silver Box Supplies for Servers
On-Board Redundant Power Supplies in Blade
Servers
Network/Telecom Power Supplies
Rectifiers
Redundant Power Supplies in High-Availability
Systems
Features
♦Simple, Integrated, and Inexpensive ORing
MOSFET Controller
♦ORing MOSFET Drive for 12V
(MAX8535/MAX8585) and 3.3V or 5V
(MAX8536) Bus
♦Eliminates ORing Diode Power Dissipation and
Reverse Leakage Current
♦Provides N + 1 Redundant Supply Capability for
Highly Reliable Systems
♦Isolates Failed Supply from Output Bus in <1µs
♦Reverse-Current Flow Detection
♦Programmable Soft-Start
♦Logic-Enable Input
♦Adjustable Overvoltage and Undervoltage Trip
Points
♦Fault-Indicator Output
♦Space-Saving 8-Pin µMAX Package
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
________________________________________________________________ Maxim Integrated Products 1
MAX8535
MAX8536
MAX8585
GATE CS
FAULT
UVP
OVP
GND
TIMER
VCC
SILVER BOX
OR
RECTIFIERS
OUT+
OUT-
REDUNDANT OUTPUT BUS
+VO-VO
N.C.
OUTPUT:
3.3V/5V
(MAX8536),
12V
(MAX8535)
Typical Operating Circuit
Ordering Information
19-2735; Rev 1; 3/04
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
PART TEMP RANGE PIN-PACKAGE
MAX8535EUA -40°C to +85°C 8 µMAX
MAX8535AEUA -40°C to +85°C 8 µMAX
MAX8536EUA -40°C to +85°C 8 µMAX
MAX8585EUA -40°C to +85°C 8 µMAX
Pin Configuration, Functional Diagrams, and Typical
Application Circuits appear at end of data sheet.
EVALUATION KIT
AVAILABLE
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VCC = 12V (MAX8535/MAX8535A/MAX8585), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE
= 0.01µF, TA= 0°C to +85°C, unless otherwise noted.)
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.
GATE to GND (MAX8535/MAX8535A/MAX8585)...-0.3V to +28V
VCC to GND (MAX8535/MAX8535A/MAX8585) .....-0.3V to +18V
CS, FAULT to GND
(MAX8535/MAX8535A/MAX8585)......................-0.3V to +15V
GATE to GND (MAX8536) ............................ -0.3V to (VCC + 6V)
VCC, CS, FAULT to GND (MAX8536).......................-0.3V to +6V
OVP, UVP, TIMER to GND........................................-0.3V to +6V
Continuous Power Dissipation (TA= +70°C)
8-Pin µMAX (derate 4.5mW/°C above +70°C).............362mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Junction Temperature.........................................………..+150°C
Lead Temperature (soldering, 10s).................................+300°C
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
VCC SUPPLY
VCC = 14V (MAX8535/
MAX8535A/MAX8585) 2 4.5
VCC Supply Current
TIMER = 2.5V
VCC = 6V (MAX8536) 2 3 mA
VCC = 14V (MAX8535/
MAX8535A/MAX8585) 4.5
VCC Shutdown Current TIMER = 0V VCC = 6V (MAX8536) 3 mA
MAX8535/MAX8535A/
MAX8585, charge pump on
814
MAX8536, charge pump on
3.0 5.5VCC Input Voltage
TIMER = 2.5V
MAX8535/MAX8535A/
MAX8585, charge pump off
17
V
CS = 14V (MAX8535/
MAX8535A/MAX8585)
100
CS Input Current
TIMER = 2.5V
CS = 5.5V (MAX8536) 50 µA
CS Isolation
C S = m ax op er ati ng vol tag e, V
C C = 0V , I( V
C C
) -0.05
-1 µA
MAX8535/MAX8535A/MAX8585, rising
threshold 6 6.5 7
VCC Undervoltage Lockout VCCOK MAX8536, rising threshold 2.5 2.7 2.9 V
Rising threshold 14
14.5
15
VCC Overvoltage Internal
Threshold
MAX8535/
MAX8535A/
MAX8585 Falling threshold
13.3 13.9 14.5
V
CHARGE-PUMP VOLTAGE
Measured from VGATE to VCC, VCC = 3.3V
(MAX8536) 5 5.5 6
VCC = 5V (MAX8536) 5 5.5 6
Gate Voltage VGATE
V
C C
= 12V ( M AX 853 5/M AX 85 35A /M AX 8585)
91112
V
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 12V (MAX8535/MAX8535A/MAX8585), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE
= 0.01µF, TA= 0°C to +85°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
RTIMER = 20kΩ
187
RTIMER = 125kΩ
450
RTIMER = open
500
Charge-Pump Switching
Frequency
VTIMER = 1.5V
550
kHz
TIMER
TIMER Voltage
1.219 1.25 1.281
V
TIMER Maximum Source Current
VTIMER = 1V 80
100 120
µA
TIMER High-Input Current VTIMER = 1.5V 10 20 µA
MAX8535/MAX8535A/MAX8585 1.5 3.4
TIMER Maximum Frequency
Select Voltage Input Range MAX8536 1.5
VCC - 0.6
V
TIMER Logic High VIH Charge pump enabled 1.0 V
TIMER Logic Low VIL Charge pump disabled 0.5 V
FAULT
Fault Output Low Voltage IFAULT = 0.5mA 0.8 V
Fault Sink Current FAULT = 0.8V 0.5 mA
FAULT = 18V ( MAX 8535 /MAX 8535A/MAX 8585)
5
Fault Leakage Current FAULT = 6V (MAX8536) 5 µA
GATE
Gate On Threshold Measured from VCC to CS 0.3 0.4 0.5 V
ITIMER = 0µA (MAX8535/
MAX8535A/MAX8585) 35 50 65
VGATE =
VCC = 12V ITIMER = 50µA (MAX8535/
MAX8535A/MAX8585) 15 25 36
ITIMER = 0µA (MAX8536) 17 25 33
Gate Drive Current
VGATE =
VCC = 5V ITIMER = 50µA (MAX8536) 8 12 16
µA
Gate Shutdown Delay From fault sense to the start of gate voltage
falling, or from TIMER to the start of gate
voltage falling
200 300
ns
GATE = VCC + 5V (MAX8535/MAX8536)
100 200 300
Gate Discharge Current GATE = VCC + 5V (MAX8535A/MAX8585)
200 300 400
mA
G ate vol tag e fal l fr om faul t to V
GAT E
= V
C C
,
C
GAT E
= 0.01µF ( 200ns + C V /I = 700n s , ty p )
(MAX8535/MAX8536) 0.7
Gate Fall Time
MAX8535A/MAX8585
0.55
µs
CURRENT SENSE
Measured from CS to VCC
(MAX8535/MAX8535A/MAX8536) 20 30 40
Reverse-Current Threshold MAX8585 -3 0 +3 mV
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS
(VCC = 12V (MAX8535/MAX8535A/MAX8585), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE
= 0.01µF, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
VCC SUPPLY
VCC = 14V (MAX8535/
MAX8535A/MAX8585) 4.5
VCC Supply Current
TIMER = 2.5V
VCC = 6V (MAX8536) 3 mA
VCC = 14V (MAX8535/
MAX8535A/MAX8585) 4.5
VCC Shutdown Current TIMER = 0V VCC = 6V (MAX8536) 3 mA
MAX8535/MAX8535A/
MAX8585, charge pump on
814
MAX8536, charge pump on
3.0 5.5VCC Input Voltage
TIMER = 2.5V
MAX8535/MAX8535A/
MAX8585, charge pump off
17
V
CS Isolation
C S = m ax op er ati ng vol tag e, V
C C
= 0V , I( V
C C
)
-1 µA
(MAX8535/MAX8535A/MAX8585) rising
threshold 6.0 7.0
VCC Undervoltage Lockout VCCOK (MAX8536) rising threshold 2.5 2.9 V
Rising threshold 14 15
VCC Overvoltage Internal
Threshold
(MAX8535/
MAX8535A/
MAX8585) Falling threshold
13.3 14.5
V
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 12V (MAX8535/MAX8535A/MAX8585), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE
= 0.01µF, TA= 0°C to +85°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
TIMER = open (MAX8535/MAX8535A/
MAX8536)
524
Startup Reverse-Current Blank
Time MAX8585 32 ms
Forward-Current Threshold Measured from VCC to CS 5 10 15 mV
OVERVOLTAGE PROTECTION OVP rising
1.219 1.25 1.281
OVP Fault Threshold VOVP OVP falling
1.2
V
OVP Bias Current 0.2 µA
UNDERVOLTAGE PROTECTION UVP rising threshold
1.219 1.25 1.281
UVP Fault Voltage VUVP UVP falling threshold
1.119 1.15 1.181
V
UVP Bias Current 0.4 µA
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 12V (MAX8535/MAX8535A/MAX8585), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE
= 0.01µF, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CHARGE-PUMP VOLTAGE
Measured from VGATE to VCC, VCC = 3.3V
(MAX8536) 56
VCC = 5V (MAX8536) 5 6
Gate Voltage VGATE
V
C C
= 12V ( M AX 8535/M AX 8535A/M AX 8585) 9 12
V
TIMER
TIMER Voltage
1.200 1.281
V
TIMER Maximum Source Current
VTIMER = 1.0V 80
120
µA
TIMER High-Input Current VTIMER = 1.5V 20 µA
MAX8535/MAX8535A/MAX8585 1.5 3.4
TIMER Maximum Frequency
Select Voltage Input Range MAX8536 1.5
VCC - 0.6
V
TIMER Logic High VIH Charge pump enabled 1.1 V
TIMER Logic Low VIL Charge pump disabled 0.5 V
FAULT
Fault Output Low Voltage IFAULT = 0.5mA 0.8 V
Fault Sink Current FAULT = 0.8V 0.5 mA
FAULT = 18V (MAX8535/
MAX8535A/MAX8585) 5
Fault Leakage Current
FAULT = 6V (MAX8536) 5 µA
GATE
Gate On Threshold Measured from VCC to CS 0.3 0.5 V
ITIMER = 0µA (MAX8535/
MAX8535A/MAX8585) 35 65
VGATE =
VCC = 12V ITIMER = 50µA (MAX8535/
MAX8535A/MAX8585) 15 36
ITIMER = 0µA (MAX8536) 17 33
Gate-Drive Current
VGATE =
VCC = 5V ITIMER = 50µA (MAX8536) 8 16
µA
Gate Shutdown Delay From fault sense to the start of gate voltage
falling, or from TIMER to the start of gate
voltage falling
300
ns
GATE = VCC + 5V (MAX8535/MAX8536)
100 300
Gate Discharge Current MAX8535A/MAX8585
200 400
mA
CURRENT SENSE
Measured from CS to VCC
(MAX8535/MAX8535A/MAX8586) 20 40
Reverse-Current Threshold MAX8585 -5 +5 mV
Forward-Current Threshold Measured from VCC to CS 5 15 mV
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
6 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 12V (MAX8535/MAX8535A/MAX8585), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE
= 0.01µF, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
Note 1: Specifications to -40°C are guaranteed by design and not production tested.
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
OVERVOLTAGE PROTECTION
OVP Fault Threshold VOVP OVP rising
1.20 1.281
V
OVP Bias Current 0.2 µA
UNDERVOLTAGE PROTECTION UVP rising threshold
1.200 1.281
UVP Fault Voltage VUVP UVP falling threshold
1.10 1.19
V
UVP Bias Current 0.4 µA
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
_______________________________________________________________________________________ 7
STANDBY:
CPMP: OFF
GATE: LOW
WAIT
FOR
VSHARE
CS - VCC < 0.4V
VSHARE = (CS - VCC) < 0.4V
IFORWARD = (VCC - CS) > 0.01V
IREVERSE = (CS - VCC) > 0.03V CS - VCC > 0.4V
VCC > VCCOK
ON:
SET
VSHARE LATCH,
CHARGE PUMP
ON
UVP FAULT
UVP = OK
CS
VCC
CS - 0.4V
CS + 0.01V
VSHARE LATCH
IREVERSE BLANKING
FAULT
SHUTDOWN GATE:
FAULT LATCHED
FAULT
SHUTDOWN GATE:
FAULT LATCHED
UVP FAULT
SHUTDOWN GATE:
FAULT NOT LATCHED
IREVERSE CONDITION DETECTED AFTER
500ms BLANK TIME
(MAX8535/MAX8535A/MAX8536)
(MAX8585)
IREVERSE AFTER
32ms BLANK TIME
CS - 0.03V
IFORWARD
AND OVP FAULT
IFORWARD
IREVERSE
TIMER >1V
ALL TRANSITIONS ARE ASYNCHRONOUS
VCC OR
TIMER
CYCLED
VCC OR
TIMER
CYCLED
500ms
FAULT
SHUTDOWN GATE:
NOT LATCHED
OVP OK AND
IREVERSE DURING
FIRST 500ms
UVP = OK
State Diagram
MAX8535 Typical Operating Characteristics
(VCC = 12V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE = 0.01µF, BUS = 100µF, TA= +25°C, unless otherwise specified.)
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
8 _______________________________________________________________________________________
GATE-CHARGE CURRENT
vs. TIMER RESISTANCE (RTIMER)
MAX8535/MAX8536 toc01
RESISTANCE (kΩ)
GATE-CHARGE CURRENT (µA)
100
10
20
30
40
50
60
010 1000
TA = -40°C
TA = +25°C
TA = +85°C
SUPPLY CURRENT
vs. TEMPERATURE
MAX8535/MAX8536 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
806040200-20
2.2
2.4
2.6
2.8
3.0
3.2
3.4
2.0 -40
TIMER = GND
TIMER IS UNCONNECTED
MAX8535
REVERSE-CURRENT THRESHOLD
vs. TEMPERATURE
MAX8535/MAX8536 toc03
TEMPERATURE (°C)
REVERSE-CURRENT THRESHOLD (mV)
603510-15
27
29
31
33
35
34
32
30
28
26
25 -40 85
UVP AND OVP LEAKAGE CURRENT
vs. TEMPERATURE
MAX8535/MAX8536 toc04
TEMPERATURE (°C)
LEAKAGE CURRENT (nA)
806040200-20
20
40
60
80
100
120
140
0-40
UVP
OVP
POWER-UP WAVEFORM (VBUS = 0V)
MAX8535/MAX8536 toc05
IMOSFET
10A/div
VCS
10V/div
VGATE
20V/div
VCC
10V/div
4ms/div
POWER-UP WAVEFORM (VBUS = 12V)
MAX8535/MAX8536 toc06
IMOSFET
2A/div
VCS
10V/div
VGATE
20V/div
VCC
10V/div
4ms/div
MAX8535 Typical Operating Characteristics (continued)
(VCC = 12V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE = 0.01µF, BUS = 100µF, TA= +25°C, unless otherwise specified.)
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
_______________________________________________________________________________________ 9
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 12V, VBUS = 12V)
MAX8535/MAX8536 toc07
IMOSFET
50mA/div
VCS
10V/div
VGATE
20V/div
VTIMER
2V/div
4ms/div
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 12V, VBUS = 0V)
MAX8535/MAX8536 toc08
IMOSFET
10A/div
VCS
10V/div
VGATE
20V/div
VTIMER
1V/div
4ms/div
REVERSE-CURRENT FAULT WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc09
IMOSFET
5A/div
VFAULT
10V/div
VGATE
20V/div
VCS
1V/div
12V
400ns/div
UVP FAULT WAVEFORM
(R1 = 100Ω)
MAX8535/MAX8536 toc10
VFAULT
10V/div
VUVP
1V/div
1µs/div
1.25V
VCS
10V/div
VGATE
20V/div
SELECTIVE OVP SHUTDOWN WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc11
VFAULT
10V/div
VGATE1
(OVP UNIT)
20V/div
VGATE2
(GOOD UNIT)
20V/div
VCS
1V/div
12V
1µs/div
MAX8536 Typical Operating Characteristics
(VCC = 12V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE = 0.01µF, BUS = 100µF, TA= +25°C, unless otherwise specified.)
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
10 ______________________________________________________________________________________
GATE-CHARGE CURRENT
vs. TIMER RESISTANCE (RTIMER)
MAX8535/MAX8536 toc12
RESISTANCE (kΩ)
GATE-CHARGE CURRENT (µA)
100
5
10
15
20
25
30
010 1000
TA = +85°C
TA = +25°C
TA = -40°C
SUPPLY CURRENT
vs. TEMPERATURE
MAX8535/MAX8536 toc13
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
806040200-20
1.2
1.4
1.6
1.8
2.0
2.2
1.0 -40
TIMER IS UNCONNECTED
TIMER = GND
MAX8536
REVERSE-CURRENT THRESHOLD
vs. TEMPERATURE
MAX8535/MAX8536 toc14
TEMPERATURE (°C)
REVERSE-CURRENT THRESHOLD (mV)
603510-15-40 85
26
27
28
29
30
31
32
33
34
35
25
UVP AND OVP LEAKAGE CURRENT
vs. TEMPERATURE
MAX8535/MAX8536 toc15
TEMPERATURE (°C)
LEAKAGE CURRENT (nA)
806040200-20
20
40
60
80
100
120
140
0-40
UVP
OVP
POWER-UP WAVEFORM (VBUS = 0V)
MAX8535/MAX8536 toc16
IMOSFET
2A/div
VCS
5V/div
VGATE
10V/div
VCC
5V/div
4ms/div
POWER-UP WAVEFORM (VBUS = 5V)
MAX8535/MAX8536 toc17
IMOSFET
1A/div
VCS
5V/div
VGATE
10V/div
VCC
5V/div
4ms/div
MAX8536 Typical Operating Characteristics (continued)
(VCC = 12V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE = 0.01µF, BUS = 100µF, TA= +25°C, unless otherwise specified.)
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
______________________________________________________________________________________ 11
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 5V, VBUS = 5V)
MAX8535/MAX8536 toc18
IMOSFET
50mA/div
VCS
5V/div
VGATE
10V/div
VTIMER
2V/div
4ms/div
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 5V, VBUS = 0V)
MAX8535/MAX8536 toc19
IMOSFET
1A/div
VCS
5V/div
VGATE
10V/div
VTIMER
2V/div
10ms/div
REVERSE-CURRENT FAULT WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc20
IMOSFET
5A/div
VFAULT
5V/div
VGATE
10V/div
VCS
1V/div
5V
400ns/div
UVP FAULT WAVEFORM
(R1 = 100Ω)
MAX8535/MAX8536 toc21
VCS
1V/div
VFAULT
5V/div
VGATE
VUVP
2V/div
1µs/div
1.25V
SELECTIVE OVP SHUTDOWN WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc22
VFAULT
5V/div
VGATE2
(GOOD UNIT)
10V/div
VGATE1
(OVP UNIT)
10V/div
VCS
1V/div
5V
1µs/div
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
12 ______________________________________________________________________________________
Detailed Description
Critical loads often employ parallel-connected power
supplies with redundancy to enhance system reliability.
The MAX8535/MAX8536/MAX8585 are highly integrated
but inexpensive MOSFET controllers that provide isolation
and redundant power capability in high-reliability sys-
tems. The MAX8535/MAX8585 is used in 12V systems
and has an internal charge pump to drive the gates of the
n-channel pass elements to VCC + 10V. The MAX8536 is
used in 3.3V and 5V systems, with a charge pump output
of VCC + 5V.
During startup, the MAX8535/MAX8536/MAX8585 moni-
tor the voltage drop across external MOSFETs. Once
VCC approaches or exceeds the bus voltage, the
MOSFETs are turned on. The MAX8535/MAX8536/
MAX8585 feature a dual-purpose TIMER input. A single
external resistor from TIMER to ground sets the turn-on
speed of the external MOSFETs. Optionally, the TIMER
input can be used as a logic-enable pin. Once the
device is turned on, the MAX8535/MAX8536/MAX8585
monitor the load, protecting against overvoltage, under-
voltage, and reverse-current conditions.
Overvoltage and undervoltage fault thresholds are
adjustable and can be disabled. The current-limit trip
points are set by the external MOSFETs’ RDS(ON),
reducing component count. An open-drain logic-low
fault output indicates if an overvoltage, undervoltage, or
reverse-current fault occurs.
VCC
VCC is the power-supply input for the MAX8535/
MAX8536/MAX8585 and the input to the internal charge
pump that drives the gate of the external MOSFETs. The
MAX8535/MAX8536/MAX8585 monitor VCC at all times.
VCC connects directly to the power supply (Silver Box or
DC-DC power modules). During startup, the device
turns on when VCC rises above the undervoltage thresh-
old VCCOK. After VCC exceeds VCCOK and VCC is
greater than (CS - 0.4V), the charge pump turns on, dri-
ving GATE high and turning on the external MOSFETs .
TIMER
The MAX8535/MAX8536/MAX8585 provide a program-
mable-frequency charge pump and shutdown function
through TIMER. Slowing down the charge-pump fre-
quency allows a user to program soft-start. Connecting
a resistor from TIMER to GND sets the charge-pump fre-
quency from 100kHz to 500kHz. Connecting TIMER to a
logic high sets charge-pump operation to a maximum
frequency of 550kHz. Pulling TIMER to GND shuts down
the charge pump and turns off the external MOSFET.
Reducing the charge-pump frequency increases the
IREVERSE startup blank time (see the Reverse-Current
Fault section).
GATE
GATE is the output of the internal charge pump that
drives the external MOSFETS. During startup, the GATE
voltage ramps up according to the charge-pump fre-
quency. At 250kHz, the GATE drive current for the
MAX8535/MAX8585 is 2 5µA and the GATE drive current
Pin Description
PIN NAME FUNCTION
1 GATE Gate Drive Output. Bypass GATE with a 0.01µF capacitor to ground.
2 GND Ground
3V
CC Power-Supply Input. Bypass VCC with a 0.1µF capacitor to ground.
4 UVP Undervoltage Input. Connect a resistor-divider from the VCC to GND with the center point connected
to UVP. Leave high impedance if not used. UVP fault threshold must be set above VCCOK threshold.
5 TIMER
Timer Input. Connect a resistor from TIMER to ground to select the charge-pump operating
frequency. The charge-pump frequency is proportional to the TIMER output current. TIMER can
source up to 100µA. If pulled low (<0.5V), the gate drive is disabled. If pulled high (above 1.25V), the
charge pump operates at 550kHz.
6 OVP Overvoltage Input. Connect a resistor-divider from the CS to GND with the center point connected to
OVP. Connect to GND if not used.
7FAULT Open-Drain Fault Output. FAULT is low during a fault, high impedance during normal operation.
Connect a pullup resistor of 50kΩ or higher value to a voltage rail.
8CS
Current-Sensing Input. Connect CS to the positive side of the system bus. Bypass with 1nF capacitor
to GND.
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
______________________________________________________________________________________ 13
for the MAX8536 is 12µA. Increasing the charge-pump
frequency increases the GATE drive current. Adding a
resistor from GATE to the gate of the external MOSFETs
further increases turn-on and turn-off times.
CS
The voltage drop across the external MOSFETs is mea-
sured between the VCC and CS inputs. CS connects to
the positive side of the system bus. The voltage drop
across the CS and VCC determines operation modes.
IFORWARD is defined as VCC - CS > 0.01V. IREVERSE is
defined as CS - VCC > 0.03V in all except the
MAX8585. In the MAX8585, IREVERSE = 0V.
FAULT Conditions
The MAX8535/MAX8536/MAX8585 contain a versatile
FAULT output that signals overvoltage, undervoltage,
or reverse-current conditions. During a FAULT condi-
tion, the charge pump shuts down and the GATE dis-
charges to ground.
Undervoltage Fault
The MAX8535/MAX8536/MAX8585 turn off the external
MOSFET if the input voltage falls below the UVP thresh-
old. If UVP is left unconnected, the undervoltage input
is disabled. Set the undervoltage threshold to any value
above VCCOK. When the input voltage rises above the
UVP threshold, FAULT clears and the MOSFET turns
back on.
Overvoltage Fault
The MAX8535/MAX8536/MAX8585 contain an
adjustable OVP feature. A resistor-divider from the CS
system bus to the OVP input pin sets the overvoltage
threshold. When the OVP level is exceeded and the
part is in the IFORWARD condition (defined as VCC >
CS + 0.01V), the MAX8535/MAX8536/MAX8585 turn off
the external MOSFET and a fault is latched. If there is
no IFORWARD condition, an OVP detection has no
effect. In this way, only the input supply, which is caus -
ing the overvoltage condition, is turned off in a redun-
dant power system application. An overvoltage fault is
a latching fault condition, and requires VCC or TIMER
to be cycled to reset the part.
Reverse-Current Fault
The MAX8535/MAX8536 contain a reverse-current pro-
tection feature. If, after the 500ms (typ) startup blank
time, an IREVERSE condition is detected, the MAX8535/
MAX8536 turn off the external MOSFET and a fault is
latched. A reverse-current fault forces the MAX8535/
MAX8536 to latch off. Cycle VCC or TIMER to exit a
latched fault condition. Startup blanking time allows the
incoming power supply to connect to the system bus at
VBUS - 0.4V. Reducing charge-pump frequency
increases the startup blanking time. The MAX8585
does not latch this fault.
Applications Information
Selecting the Timer Resistor
To set the frequency of the internal charge-pump oper-
ation, connect a resistor from TIMER to GND.
Determine the frequency by using the equation:
Pull TIMER above 1.5V for maximum charge-pump fre-
quency. Pull TIMER below 0.5V to disable the charge
pump. Leave TIMER unconnected for a 500kHz
charge-pump frequency.
Selecting the Gate Capacitor
and Gate Resistor
The charge pump uses an internal monolithic transfer
capacitor to charge the external MOSFET gates.
Frequency A V
RkHz A
TIMER
=×
⎛
⎝
⎜⎞
⎠
⎟
5 100 125
µµ-./
Table 1. MAX8535/MAX8536/MAX8585 Fault Modes
FAULT MODE PIN CONDITIONS GATE PIN FAULT PIN LATCHING
VCC UVLO VCC < VCCOK Low
High impedance
No
UVP pin undervoltage protection UVP < 1.25V Low Low No
OVP pin overvoltage protection OVP > 1.25V
VCC > CS + 0.01V Low Low Yes
Reverse-current protection
( M AX 8535/M AX 8536) VCC < CS - 0.03V
Gate ON for t > 0.5s Low Low Yes
Reverse-current protection
( M AX 8585) VCC < CS
Gate ON for t > 0.032s Low Low No
V
C C
i nter nal ( M AX 85 35/M AX 8585 )
over vol tag e p r otec ti on VCC > 14.5V Low Low No
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
14 ______________________________________________________________________________________
Normally, the external MOSFET’s gate capacitance is
sufficient to serve as a reservoir capacitor. If the
MOSFETs are located at a significant distance from the
MAX8535/MAX8536/MAX8585, place a local bypass
capacitor (0.01µF, typ) across GATE and GND. For
slower turn-on times, add a small capacitor between
GATE and GND and a series resistor between GATE
and the gate of the MOSFETs.
Set the UVP Fault Threshold
To set the undervoltage lockout threshold, use a resistor-
divider connected between VCC and GND, with the
center node of the divider connected to UVP. For
example, use a 10kΩresistor (R4 in Figure 4) from UVP
to GND and calculate the other resistor (R3) using:
where VUVLO is the desired undervoltage lockout volt-
age and VUVP is the UVP reference threshold specified
in the Electrical Characteristics (1.25V, typ). To defeat
the UVP, leave UVP unconnected.
Set the OVP Fault Threshold
To set the OVP threshold, use a resistor-divider con-
nected between CS and GND, with the center node of
the divider connected to OVP. For example, use a
10kΩresistor (R6 in Figure 4) from OVP to GND and
calculate the other resistor, R5, using:
where VOVLO is the desired overvoltage lockout voltage
and VOVP is the OVP reference threshold specified in
the Electrical Characteristics (1.25V, typ). To defeat the
OVP, connect the OVP input to GND.
MOSFET Selection
The MAX8535/MAX8536/MAX8585 drive n-channel
MOSFETs. The most important feature of the MOSFETs
is RDS(ON). As load current flows through the external
MOSFET, a voltage (VDS) is generated from drain-to-
source due to the MOSFET’s on-resistance, RDS(ON).
The MAX8535/MAX8536/MAX8585 monitor VDS of the
MOSFETs at all times. The MAX8535/MAX8536/
MAX8585 determine the state of the monitored power
supply by measuring the voltage drop across the exter-
nal MOSFETs. With two external MOSFETs, the equa-
tion becomes:
VDSTOTAL = RDS(ON)1 x ILOAD + RDS(ON)2 x ILOAD
Selecting a MOSFET with a low RDS(ON) allows more
current to flow through the MOSFETs before the
MAX8535/MAX8536/MAX8585 detect reverse-current
(IREVERSE) and forward-current (IFORWARD) conditions.
Using a Single MOSFET
Single MOSFETs can be used if the OVP function is not
needed. Connect the source of the MOSFET to VCC
and the drain of the MOSFET to CS.
Layout Guidelines
Keep all traces as short as possible and maximize the
high-current trace width to reduce the effect of undesir-
able parasitic inductance. The MOSFET generates a
fair amount of heat because of the high currents
involved. In order to dissipate the heat generated by
the MOSFET, make the power traces very wide with a
large amount of copper area, and place the MAX8535/
MAX8536/MAX8585 as close as possible to the drain of
the external MOSFET. A more efficient way to achieve
good power dissipation on a surface-mount package is
to lay out two copper pads directly under the MOSFET
package on both sides of the board. Connect the two
pads to the ground plane through vias and use
enlarged copper mounting pads on the topside of the
board. Use a ground plane to minimize impedance and
inductance. Refer to the MAX8535 Evaluation Kit data
sheet for an example of a PC board layout.
In addition to the usual high-power considerations,
bypassing prevent false faults by:
1) Bypass VCC with a 0.1µF capacitor to ground and
bypassing CS with a 1nF capacitor to ground.
2) Making the traces connecting UVP and OVP as
short as possible.
3) Kelvin connecting VCC and CS to the external
MOSFET.
RR
V
V
OVLO
OVP
56 1=⎛
⎝
⎜⎞
⎠
⎟
-
RR
V
V
UVLO
UVP
34 1=⎛
⎝
⎜⎞
⎠
⎟
-
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
______________________________________________________________________________________ 15
Functional Diagrams
CONTROL
LOGIC
VOLTAGE
SHARE
REVERSE CURRENT
FORWARD CURRENT
OVERVOLTAGE INTERNAL
OVERVOLTAGE EXTERNAL
UNDERVOLTAGE
SHUTDOWN
CHARGE
PUMP
VCC
CLK
VCC
1.25V REF
IOSC ENABLE
GND
MAX8535
MAX8585
14.5V
1.25V
1.25V
10mV *0mV OFFSET
IN THE MAX8585
30mV*400mV
FAULT
TIMER
GATE VCC CS
OVP
UVP
Figure 1. MAX8535/MAX8585 Functional Diagram
CONTROL
LOGIC
VOLTAGE
SHARE
REVERSE CURRENT
FORWARD CURRENT
OVERVOLTAGE EXTERNAL
UNDERVOLTAGE
SHUTDOWN
CHARGE
PUMP
VCC
CLK
VCC
1.25V REF
IOSC ENABLE
MAX8536
1.25V
1.25V
10mV30mV400mV
FAULT
TIMER
GATE VCC CS
OVP
UVP
GND
Figure 2. MAX8536 Functional Diagram
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
16 ______________________________________________________________________________________
Typical Application Circuits
MAX8535
MAX8585
GATE CS
FAULT
OVP
ENABLE
GND
TIMER
UVP
VCC
SILVER BOX
OR
RECTIFIERS
OUT+
OUT-
OUTPUT BUS
+VO-VO
OUTPUT:
12V/20A
Q1 AND Q2
2XSUB75N03-04
30V/4mΩ
C3
1nF
R5
100kΩR2
51kΩ
R6
10kΩ
R7
24.9kΩ
R1
10Ω
C1
0.01µF,
50V
C2
0.1µF,
16V
R3
53.6kΩ
R4
10kΩ
Figure 3. Typical Application Circuit for 12V/20A Output with OVP and UVP
MAX8536
GATE CS
FAULT
OVP
GNDTIMER
UVP
VCC
SILVER BOX
OR
RECTIFIERS
OUT+
OUT-
OUTPUT BUS
+VO-VO
OUTPUT:
3.3V OR 5V/20A
Q1 AND Q2
2XSUB75N03-04
30V/4mΩ
C3
1nF
R5
35.7kΩR2
51kΩ
R6
10kΩ
R7
24.9kΩ
R1
10Ω
C1
0.01µF,
50V
C2
0.1µF,
16V
R3
13.3kΩ
R4
10kΩ
Figure 4. Typical Application Circuit for 3.3V or 5V/20A Output with OVP and UVP
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
______________________________________________________________________________________ 17
MAX8535
MAX8585
GATE CS
FAULT
UVP
OVP
GND
TIMER
ON
OFF
ENABLE
VCC
SILVER BOX
OR
RECTIFIERS
OUT+
OUT-
OUTPUT BUS
+VO-VO
N.C.
OUTPUT:
12V/20A
C1
0.01µF,
50V
C2
0.1µF,
16V R3
7.5kΩ
R4
7.5kΩ
Q1
SUB75N03-04
30V/4mΩ
R1
10ΩC3
1nF
R2
51kΩ
Figure 5. Typical Application Circuit for 12V/20A Output without OVP and UVP
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
18 ______________________________________________________________________________________
MAX8535
MAX8585
GATE CS
FAULT
OVP
GND
TIMER
TIMER
UVP
VCC
SILVER BOX
A
OUT+
OUT-
OUTPUT BUS
+VO-VO
Q1A AND Q2A
2XSUB75N03-04
30V/4mΩ
C3A
1nF
R5A
100kΩR2A
51kΩ
R6A
10kΩ
R7A
24.9kΩ
R1A
10Ω
C1A
0.01µF,
50V
C2A
0.1µF,
16V
R3A
53.6kΩ
R4A
10kΩ
MAX8535
MAX8585
GATE CS
FAULT
OVP
GND
UVP
VCC
SILVER BOX
B
OUT+
OUT-
OUTPUT BUS
Q1B AND Q2B
2XSUB75N03-04
30V/4mΩ
C3B
1nF
R2B
51kΩ
R7B
24.9kΩ
R1B
10Ω
C1B
0.01µF,
50V
C2B
0.1µF,
16V
R3B
53.6kΩ
R4B
10kΩ
V+
VCCA = 12V/20A
VCCB = 12V/20A
N + 1
U1
U2
Figure 6. N + 1 Redundant Power System Connections
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
______________________________________________________________________________________ 19
Chip Information
TRANSISTOR COUNT: 3011
PROCESS: BiCMOS
1
2
3
4
8
7
6
5
CS
FAULT
OVP
TIMERUVP
VCC
GND
GATE
MAX8535
MAX8536
MAX8585
µMAX
TOP VIEW
Pin Configuration
MAX8535/MAX8536/MAX8585
ORing MOSFET Contr ollers with Fastest
Fault Isolation for Redundant Power Supplies
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
8LUMAXD.EPS
PACKAGE OUTLINE, 8L uMAX/uSOP
1
1
21-0036 J
REV.DOCUMENT CONTROL NO.APPROVAL
PROPRIETARY INFORMATION
TITLE:
MAX
0.043
0.006
0.014
0.120
0.120
0.198
0.026
0.007
0.037
0.0207 BSC
0.0256 BSC
A2 A1
c
eb
A
L
FRONT VIEW SIDE VIEW
E H
0.6±0.1
0.6±0.1
ÿ 0.50±0.1
1
TOP VIEW
D
8
A2 0.030
BOTTOM VIEW
16∞
S
b
L
H
E
D
e
c
0∞
0.010
0.116
0.116
0.188
0.016
0.005
8
4X S
INCHES
-
A1
A
MIN
0.002
0.950.75
0.5250 BSC
0.25 0.36
2.95 3.05
2.95 3.05
4.78
0.41
0.65 BSC
5.03
0.66
6∞0∞
0.13 0.18
MAX
MIN
MILLIMETERS
- 1.10
0.05 0.15
α
α
DIM
