MAXIM MAX8536

19-2735; Rev 0; 1/03
KIT
ATION
EVALU
LE
B
A
IL
A
AV
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
Features
♦ Simple, Integrated, and Inexpensive ORing
MOSFET Controller
♦ ORing MOSFET Drive for 12V (MAX8535) 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
Ordering Information
TEMP RANGE
PIN-PACKAGE
MAX8535EUA
PART
-40°C to +85°C
8 µMAX
MAX8536EUA
-40°C to +85°C
8 µMAX
Applications
Typical Operating Circuit
Silver Box Supplies for Servers
OUTPUT:
3.3V/5V
(MAX8536),
12V
(MAX8535)
On-Board Redundant Power Supplies in Blade
Servers
Network/Telecom Power Supplies
OUT+
+VO -VO
Redundant Power Supplies in High-Availability
Systems
SILVER BOX
OR
RECTIFIERS
GATE
VCC
CS
FAULT
MAX8535
MAX8536
TIMER
REDUNDANT OUTPUT BUS
Rectifiers
GND
UVP
N.C.
OVP
Pin Configuration, Functional Diagrams, and Typical
Application Circuits appear at end of data sheet.
OUT-
________________________________________________________________ Maxim Integrated Products
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.
1
MAX8535/MAX8536
General Description
Critical loads often employ parallel-connected power
supplies with redundancy in order to enhance system
reliability. The MAX8535/MAX8536 are highly integrated
but inexpensive MOSFET controllers that provide isolation
and redundant power capability in high-reliability
systems. The MAX8535 is used in 12V systems, and has
an internal charge pump to drive the gates of the Nchannel 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 monitor the
voltage drop across external MOSFETs. Once V CC
approaches or exceeds the bus voltage, the MOSFETs
are turned on. The MAX8535/MAX8536 feature a dualpurpose 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 monitor the load, protecting
against overvoltage, undervoltage, 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’ R DS(ON) ,
reducing component count. An open-drain logic-low
fault output indicates if an overvoltage, undervoltage, or
reverse-current fault occurs.
Both devices come in a space-saving 8-pin µMAX
package and are specified over the extended -40°C to
+85°C temperature range.
MAX8535/MAX8536
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
ABSOLUTE MAXIMUM RATINGS
GATE to GND (MAX8535) ......................................-0.3V to +28V
VCC to GND (MAX8535) .........................................-0.3V to +18V
CS, FAULT to GND (MAX8535)..............................-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
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
(VCC = 12V (MAX8535), 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
VCC = 14V (MAX8535)
2
4.5
VCC = 6V (MAX8536)
2
3
UNITS
VCC SUPPLY
VCC Supply Current
TIMER = 2.5V
VCC Shutdown Current
TIMER = 0V
VCC Input Voltage
TIMER = 2.5V
VCC = 14V (MAX8535)
4.5
VCC = 6V (MAX8536)
3
MAX8535, charge pump on
8
14
MAX8536, charge pump on
3.0
5.5
MAX8535, charge pump off
CS = 14V (MAX8535)
100
50
TIMER = 2.5V
CS Isolation
CS = max operating voltage, VCC = 0V,
I(VCC)
VCC Undervoltage Lockout
VCCOK
VCC Overvoltage Internal
Threshold
V
-0.05
µA
-1
MAX8535, rising threshold
6
6.5
7
MAX8536, rising threshold
2.5
2.7
2.9
Rising threshold
14
14.5
15
Falling threshold
13.3
13.9
14.5
Measured from VGATE to VCC, VCC = 3.3V
(MAX8536)
5
5.5
6
VCC = 5V (MAX8536)
5
5.5
6
VCC = 12V (MAX8535)
9
11
12
MAX8535
only
mA
17
CS = 5.5V (MAX8536)
CS Input Current
mA
µA
V
V
CHARGE-PUMP VOLTAGE
Gate Voltage
VGATE
RTIMER = 20kΩ
Charge-Pump Switching
Frequency
2
V
187
RTIMER = 125kΩ
450
RTIMER = open
500
VTIMER = 1.5V
550
_______________________________________________________________________________________
kHz
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
(VCC = 12V (MAX8535), 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
1.219
1.25
1.281
V
80
100
120
µA
10
20
µA
TIMER
TIMER Voltage
TIMER Maximum Source Current
VTIMER = 1V
TIMER High-Input Current
VTIMER = 1.5V
TIMER Maximum Frequency
Select Voltage Input Range
MAX8535
1.5
MAX8536
1.5
1.0
TIMER Logic High
VIH
Charge pump enabled
TIMER Logic Low
VIL
Charge pump disabled
3.4
VCC - 0.6
V
V
0.5
V
FAULT
Fault Output Low Voltage
IFAULT = 0.5mA
Fault Sink Current
FAULT = 0.8V
Fault Leakage Current
0.8
0.5
V
mA
FAULT = 18V (MAX8535)
5
FAULT = 6V (MAX8536)
5
µA
GATE
Gate On Threshold
Measured from VCC to CS
Gate Drive Current
0.3
0.4
0.5
V
VGATE =
VCC = 12V
ITIMER = 0µA (MAX8535)
35
50
65
ITIMER = 50µA (MAX8535)
15
25
36
VGATE =
VCC = 5V
ITIMER = 0µA (MAX8536)
17
25
33
ITIMER = 50µA (MAX8536)
8
12
16
200
300
ns
200
400
mA
Gate Shutdown Delay
From fault sense to the start of gate voltage
falling, or from TIMER to the start of gate
voltage falling
Gate Discharge Current
GATE = VCC + 5V
Gate Fall Time
Gate voltage fall from fault to VGATE = VCC,
CGATE = 0.01µF (200ns + CV/I = 700ns, typ)
100
0.7
µA
µs
CURRENT SENSE
Reverse-Current Threshold
Measured from CS to VCC
Startup Reverse-Current Blank
Time
TIMER = open
Forward-Current Threshold
OVERVOLTAGE PROTECTION
OVP Fault Threshold
Measured from VCC to CS
VOVP
OVP rising
20
30
40
524
ms
5
10
15
1.219
1.25
1.281
OVP falling
1.2
OVP Bias Current
mV
0.2
mV
V
µA
UNDERVOLTAGE PROTECTION
UVP Fault Voltage
UVP Bias Current
VUVP
UVP rising threshold
1.219
1.25
1.281
UVP falling threshold
1.119
1.15
1.181
0.4
V
µA
_______________________________________________________________________________________
3
MAX8535/MAX8536
ELECTRICAL CHARACTERISTICS (continued)
MAX8535/MAX8536
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
ELECTRICAL CHARACTERISTICS
(VCC = 12V (MAX8535), 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)
4.5
VCC = 6V (MAX8536)
3
VCC = 14V (MAX8535)
4.5
VCC = 6V (MAX8536)
3
VCC Supply Current
TIMER = 2.5V
VCC Shutdown Current
TIMER = 0V
VCC Input Voltage
TIMER = 2.5V MAX8536, charge pump on
MAX8535, charge pump on
8
14
3.0
5.5
MAX8535, charge pump off
VCC Undervoltage Lockout
VCCOK
VCC Overvoltage Internal
Threshold
mA
V
17
CS = max operating voltage, VCC = 0V,
I(VCC)
CS Isolation
mA
-1
(MAX8535) rising threshold
6.0
7.0
(MAX8536) rising threshold
2.5
2.9
µA
V
Rising threshold
14
15
Falling threshold
13.3
14.5
Measured from VGATE to VCC, VCC = 3.3V
(MAX8536)
5
6
VCC = 5V (MAX8536)
5
6
VCC = 12V (MAX8535)
9
12
1.200
1.281
80
120
µA
20
µA
(MAX8535
only)
V
CHARGE-PUMP VOLTAGE
Gate Voltage
VGATE
V
TIMER
TIMER Voltage
TIMER Maximum Source Current
VTIMER = 1.0V
TIMER High-Input Current
VTIMER = 1.5V
TIMER Maximum Frequency
Select Voltage Input Range
MAX8535
1.5
MAX8536
1.5
1.1
TIMER Logic High
VIH
Charge pump enabled
TIMER Logic Low
VIL
Charge pump disabled
3.4
VCC - 0.6
V
V
V
0.5
V
FAULT
Fault Output Low Voltage
IFAULT = 0.5mA
Fault Sink Current
FAULT = 0.8V
Fault Leakage Current
0.8
0.5
V
mA
FAULT = 18V (MAX8535)
5
FAULT = 6V (MAX8536)
5
µA
GATE
Gate On Threshold
Gate-Drive Current
4
Measured from VCC to CS
0.3
0.5
VGATE =
VCC = 12V
ITIMER = 0µA (MAX8535)
35
65
ITIMER = 50µA (MAX8535)
15
36
VGATE =
VCC = 5V
ITIMER = 0µA (MAX8536)
17
33
ITIMER = 50µA (MAX8536)
8
16
_______________________________________________________________________________________
V
µA
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
(VCC = 12V (MAX8535), 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
300
ns
Gate Shutdown Delay
From fault sense to the start of gate voltage
falling, or from TIMER to the start of gate
voltage falling
Gate Discharge Current
GATE = VCC + 5V
100
400
mA
Reverse-Current Threshold
Measured from CS to VCC
20
40
mV
Forward-Current Threshold
Measured from VCC to CS
5
15
mV
1.20
1.281
V
0.2
µA
CURRENT SENSE
OVERVOLTAGE PROTECTION
OVP Fault Threshold
VOVP
OVP rising
OVP Bias Current
UNDERVOLTAGE PROTECTION
UVP Fault Voltage
VUVP
UVP rising threshold
1.200
1.281
UVP falling threshold
1.10
1.19
UVP Bias Current
0.4
V
µA
Note 1: Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________
5
MAX8535/MAX8536
ELECTRICAL CHARACTERISTICS (continued)
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
MAX8535/MAX8536
State Diagram
CS
VCC > VCCOK
CS + 0.01V
ALL TRANSITIONS ARE ASYNCHRONOUS
CS - 0.03V
CS - 0.4V
STANDBY:
CPMP: OFF
GATE: LOW
VCC
VSHARE LATCH
IREVERSE BLANKING
IFORWARD
500ms
TIMER >1V
IREVERSE
VSHARE = (CS - VCC) < 0.4V
IFORWARD = (VCC - CS) > 0.01V
IREVERSE = (CS - VCC) > 0.03V
WAIT
FOR
VSHARE
CS - VCC > 0.4V
CS - VCC < 0.4V
VCC OR
TIMER
CYCLED
UVP FAULT
ON:
SET
VSHARE LATCH,
CHARGE PUMP
ON
UVP FAULT
SHUTDOWN GATE:
FAULT NOT LATCHED
OVP OK AND
IREVERSE DURING
FIRST 500ms
IFORWARD
AND OVP FAULT
UVP = OK
FAULT
SHUTDOWN GATE:
FAULT LATCHED
UVP = OK
IREVERSE CONDITION DETECTED AFTER
500ms BLANK TIME
FAULT
SHUTDOWN GATE:
FAULT LATCHED
6
VCC OR
TIMER
CYCLED
_______________________________________________________________________________________
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
SUPPLY CURRENT
vs. TEMPERATURE
GATE-CHARGE CURRENT
vs. TIMER RESISTANCE (RTIMER)
TA = +25°C
40
TA = -40°C
30
20
3.2
10
3.0
TIMER = GND
2.8
2.6
TIMER IS UNCONNECTED
2.4
2.2
0
2.0
100
10
1000
-40
-20
0
20
40
60
80
RESISTANCE (kΩ)
TEMPERATURE (°C)
MAX8535
REVERSE-CURRENT THRESHOLD
vs. TEMPERATURE
UVP AND OVP LEAKAGE CURRENT
vs. TEMPERATURE
34
33
32
31
30
29
28
140
120
LEAKAGE CURRENT (nA)
MAX8535/MAX8536 toc03
35
REVERSE-CURRENT THRESHOLD (mV)
MAX8535/MAX8536 toc02
50
3.4
MAX8535/MAX8536 toc04
GATE-CHARGE CURRENT (µA)
TA = +85°C
SUPPLY CURRENT (mA)
MAX8535/MAX8536 toc01
60
UVP
100
80
60
40
27
OVP
20
26
0
25
-40
-15
10
35
60
-40
85
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
POWER-UP WAVEFORM (VBUS = 0V)
POWER-UP WAVEFORM (VBUS = 12V)
MAX8535/MAX8536 toc05
4ms/div
MAX8535/MAX8536 toc06
VCC
10V/div
VCC
10V/div
IMOSFET
10A/div
IMOSFET
2A/div
VGATE
20V/div
VGATE
20V/div
VCS
10V/div
VCS
10V/div
4ms/div
_______________________________________________________________________________________
7
MAX8535/MAX8536
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
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
MAX8535 Typical Operating Characteristics (continued)
(VCC = 12V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE = 0.01µF, BUS = 100µF, TA = +25°C, unless otherwise specified.)
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 12V, VBUS = 12V)
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 12V, VBUS = 0V)
MAX8535/MAX8536 toc07
MAX8535/MAX8536 toc08
VTIMER
2V/div
VTIMER
1V/div
IMOSFET
50mA/div
IMOSFET
10A/div
VGATE
20V/div
VGATE
20V/div
VCS
10V/div
VCS
10V/div
4ms/div
4ms/div
UVP FAULT WAVEFORM
(R1 = 100Ω)
REVERSE-CURRENT FAULT WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc10
MAX8535/MAX8536 toc09
VCS
1V/div
12V
IMOSFET
5A/div
1.25V
VUVP
1V/div
VFAULT
10V/div
VGATE
20V/div
VGATE
20V/div
VCS
10V/div
VFAULT
10V/div
1µs/div
400ns/div
SELECTIVE OVP SHUTDOWN WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc11
VCS
1V/div
12V
VGATE1
(OVP UNIT)
20V/div
VGATE2
(GOOD UNIT)
20V/div
VFAULT
10V/div
1µs/div
8
_______________________________________________________________________________________
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
GATE-CHARGE CURRENT
vs. TIMER RESISTANCE (RTIMER)
SUPPLY CURRENT
vs. TEMPERATURE
15
10
2.0
5
1.8
TIMER IS UNCONNECTED
1.6
TIMER = GND
1.4
1.2
0
1.0
100
10
1000
-40
-20
0
20
40
60
80
RESISTANCE (kΩ)
TEMPERATURE (°C)
MAX8536
REVERSE-CURRENT THRESHOLD
vs. TEMPERATURE
UVP AND OVP LEAKAGE CURRENT
vs. TEMPERATURE
33
32
31
30
29
28
140
120
MAX8535/MAX8536 toc15
34
LEAKAGE CURRENT (nA)
MAX8535/MAX8536 toc14
35
REVERSE-CURRENT THRESHOLD (mV)
MAX8535/MAX8536 toc13
TA = -40°C
TA = +85°C
20
2.2
SUPPLY CURRENT (mA)
TA = +25°C
25
GATE-CHARGE CURRENT (µA)
MAX8535/MAX8536 toc12
30
UVP
100
80
60
40
27
OVP
20
26
25
0
-40
-15
10
35
60
85
-40
-20
0
20
40
60
80
TEMPERATURE (°C)
TEMPERATURE (°C)
POWER-UP WAVEFORM (VBUS = 0V)
POWER-UP WAVEFORM (VBUS = 5V)
MAX8535/MAX8536 toc16
MAX8535/MAX8536 toc17
VCC
5V/div
VCC
5V/div
IMOSFET
2A/div
4ms/div
IMOSFET
1A/div
VGATE
10V/div
VGATE
10V/div
VCS
5V/div
VCS
5V/div
4ms/div
_______________________________________________________________________________________
9
MAX8535/MAX8536
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
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
MAX8536 Typical Operating Characteristics (continued)
(VCC = 12V, RTIMER = 25kΩ, UVP = 2V, OVP = 1V, CGATE = 0.01µF, BUS = 100µF, TA = +25°C, unless otherwise specified.)
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 5V, VBUS = 5V)
TIMER-ENABLED STARTUP AND SHUTDOWN
WAVEFORMS (VCC = 5V, VBUS = 0V)
MAX8535/MAX8536 toc18
MAX8535/MAX8536 toc19
VTIMER
2V/div
VTIMER
2V/div
IMOSFET
50mA/div
IMOSFET
1A/div
VGATE
10V/div
VGATE
10V/div
VCS
5V/div
VCS
5V/div
4ms/div
10ms/div
UVP FAULT WAVEFORM
(R1 = 100Ω)
REVERSE-CURRENT FAULT WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc21
MAX8535/MAX8536 toc20
VCS
1V/div
5V
IMOSFET
5A/div
1.25V
VUVP
2V/div
VFAULT
5V/div
VGATE
10V/div
VGATE
VFAULT
5V/div
VCS
1V/div
400ns/div
1µs/div
SELECTIVE OVP SHUTDOWN WAVEFORM
(R1 = 10Ω)
MAX8535/MAX8536 toc22
VCS
1V/div
5V
VGATE2
(GOOD UNIT)
10V/div
VGATE1
(OVP UNIT)
10V/div
VFAULT
5V/div
1µs/div
10
______________________________________________________________________________________
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
PIN
NAME
1
GATE
FUNCTION
2
GND
Ground
3
VCC
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.
7
FAULT
8
CS
Gate Drive Output. Bypass GATE with a 0.01µF capacitor to ground.
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.
Current-Sensing Input. Connect CS to the positive side of the system bus. Bypass with 1nF capacitor
to GND.
Detailed Description
Critical loads often employ parallel-connected power
supplies with redundancy to enhance system reliability.
The MAX8535/MAX8536 are highly integrated but inexpensive MOSFET controllers that provide isolation and
redundant power capability in high-reliability systems.
The MAX8535 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 monitor the
voltage drop across external MOSFETs. Once V CC
approaches or exceeds the bus voltage, the MOSFETs
are turned on. The MAX8535/MAX8536 feature a dualpurpose 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 monitor the load, protecting
against overvoltage, undervoltage, 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’ R DS(ON) ,
reducing component count. An open-drain logic-low
fault output indicates if an overvoltage, undervoltage, or
reverse-current fault occurs.
VCC
V CC is the power-supply input for the MAX8535/
MAX8536 and the input to the internal charge pump
that drives the gate of the external MOSFETs. The
MAX8535/MAX8536 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 V CC rises above the undervoltage threshold
VCCOK. After VCC exceeds VCCOK and VCC is greater
than (CS - 0.4V), the charge pump turns on, driving
GATE high and turning on the external MOSFETs.
TIMER
The MAX8535/MAX8536 provide a programmablefrequency charge pump and shutdown function through
TIMER. Slowing down the charge-pump frequency allows
a user to program soft-start. Connecting a resistor from
TIMER to GND sets the charge-pump frequency 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 frequency. At 250kHz, the GATE drive current for the
MAX8535 is 25µA and the GATE drive current for the
______________________________________________________________________________________
11
MAX8535/MAX8536
Pin Description
MAX8535/MAX8536
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
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 measured 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.
Reverse-Current Fault
The MAX8535/MAX8536 contain a reverse-current protection 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
V BUS - 0.4V. Reducing charge-pump frequency
increases the startup blanking time.
FAULT Conditions
Applications Information
The MAX8535/MAX8536 contain a versatile FAULT output
that signals overvoltage, undervoltage, or reverse-current
conditions. During a FAULT condition, the charge pump
shuts down and the GATE discharges to ground.
To set the frequency of the internal charge-pump operation, connect a resistor from TIMER to GND.
Determine the frequency by using the equation:
Undervoltage Fault
The MAX8535/MAX8536 turn off the external MOSFET if
the input voltage falls below the UVP threshold. 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 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 turn off the external MOSFET and a fault is
latched. If there is no I FORWARD condition, an OVP
detection has no effect. In this way, only the input supply, which is causing the overvoltage condition, is turned
off in a redundant power system application. An overvoltage fault is a latching fault condition, and requires VCC
or TIMER to be cycled to reset the part.
Selecting the Timer Resistor

1.25V 
Frequency = 5 × 100µA kHz / µA
RTIMER 

Pull TIMER above 1.5V for maximum charge-pump frequency. 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.
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, place a local bypass capacitor
(0.01µF, typ) across GATE and GND. For slower turnon times, add a small capacitor between GATE and
GND and a series resistor between GATE and the gate
of the MOSFETs.
Table 1. MAX8535/MAX8536 Fault Modes
PIN CONDITIONS
GATE PIN
FAULT PIN
VCC UVLO
VCC < VCCOK
Low
High impedance
No
UVP pin undervoltage protection
UVP < 1.25V
Low
Low
No
OVP > 1.25V
VCC > CS + 0.01V
Low
Low
Yes
VCC < CS - 0.03V
Gate ON for t > 0.5s
Low
Low
Yes
VCC > 14.5V
Low
Low
No
FAULT MODE
OVP pin overvoltage protection
Reverse-current protection
VCC internal (MAX8535 only)
overvoltage protection
12
______________________________________________________________________________________
LATCHING
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
V

R3 = R4  UVLO - 1
 VUVP

where VUVLO is the desired undervoltage lockout voltage 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 connected between CS and GND, with the center node of
the divider connected to OVP. For example, use a
10kΩ resistor (R6 in Figure 4) from OVP to GND and
calculate the other resistor, R5, using:
V

R5 = R6  OVLO - 1
 VOVP

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 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 monitor VDS of the MOSFETs at all times. The
MAX8535/MAX8536 determine the state of the monitored power supply by measuring the voltage drop
across the external MOSFETs. With two external
MOSFETs, the equation 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 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 undesirable 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 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 V CC and CS to the external
MOSFET.
______________________________________________________________________________________
13
MAX8535/MAX8536
Set the UVP Fault Threshold
To set the undervoltage lockout threshold, use a resistordivider connected between VCC and GND, with the
center node of the divider connected to UVP. For
example, use a 10kΩ resistor (R4 in Figure 4) from UVP
to GND and calculate the other resistor (R3) using:
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
MAX8535/MAX8536
Functional Diagrams
GATE
VCC
VCC
CHARGE
PUMP
400mV
30mV
CS
10mV
CLK
SHUTDOWN
VCC
FAULT
CONTROL
LOGIC
VOLTAGE
SHARE
REVERSE CURRENT
FORWARD CURRENT
14.5V
OVERVOLTAGE INTERNAL
OVP
OVERVOLTAGE EXTERNAL
UNDERVOLTAGE
1.25V
IOSC
TIMER
ENABLE
UVP
1.25V REF
MAX8535
1.25V
GND
Figure 1. MAX8535 Functional Diagram
GATE
VCC
VCC
CHARGE
PUMP
400mV
30mV
CS
10mV
CLK
SHUTDOWN
VCC
FAULT
CONTROL
LOGIC
VOLTAGE
SHARE
REVERSE CURRENT
FORWARD CURRENT
OVP
OVERVOLTAGE EXTERNAL
UNDERVOLTAGE
1.25V
IOSC
TIMER
ENABLE
1.25V REF
UVP
MAX8536
1.25V
GND
Figure 2. MAX8536 Functional Diagram
14
______________________________________________________________________________________
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
Q1 AND Q2
2XSUB75N03-04
30V/4mΩ
+VO -VO
OUTPUT:
12V/20A
OUT+
C3
1nF
R3
SILVER BOX 53.6kΩ
OR
RECTIFIERS
C1
0.01µF,
50V
R5
100kΩ
GATE
R2
51kΩ
OUTPUT BUS
R1
10Ω
CS
FAULT
VCC
C2
0.1µF,
16V
MAX8535
UVP
R4
10kΩ
OVP
TIMER
GND
R6
10kΩ
R7
24.9kΩ
OUTENABLE
Figure 3. Typical Application Circuit for 12V/20A Output with OVP and UVP
Q1 AND Q2
2XSUB75N03-04
30V/4mΩ
+VO -VO
OUTPUT:
3.3V OR 5V/20A
OUT+
R3
SILVER BOX 13.3kΩ
OR
RECTIFIERS
C1
0.01µF,
50V
R5
35.7kΩ
GATE
CS
VCC
FAULT
C2
0.1µF,
16V
MAX8536
UVP
OVP
TIMER
R4
10kΩ
R2
51kΩ
OUTPUT BUS
C3
1nF
R1
10Ω
GND
R7
24.9kΩ
R6
10kΩ
OUT-
Figure 4. Typical Application Circuit for 3.3V or 5V/20A Output with OVP and UVP
______________________________________________________________________________________
15
MAX8535/MAX8536
Typical Application Circuits
MAX8535/MAX8536
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
Q1
SUB75N03-04
30V/4mΩ
+VO -VO
OUTPUT:
12V/20A
OUT+
SILVER BOX
OR
RECTIFIERS
R2
51kΩ
C1
0.01µF,
50V
GATE
ON
C2
0.1µF,
16V
OFF
MAX8535
R4
7.5kΩ
TIMER
ENABLE
CS
FAULT
VCC
GND
UVP
N.C.
OVP
R3
7.5kΩ
OUT-
Figure 5. Typical Application Circuit for 12V/20A Output without OVP and UVP
16
______________________________________________________________________________________
OUTPUT BUS
C3
1nF
R1
10Ω
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
Q1A AND Q2A
2XSUB75N03-04
30V/4mΩ
MAX8535/MAX8536
V+
+VO -VO
VCCA = 12V/20A
OUT+
R3A
SILVER BOX 53.6kΩ
A
C1A
0.01µF,
50V
R5A
100kΩ
GATE
R2A
51kΩ
CS
FAULT
VCC
C2A
0.1µF,
16V
OUTPUT BUS
C3A
1nF
R1A
10Ω
MAX8535
A
UVP
R4A
10kΩ
GND
TIMER
OVP
R6A
10kΩ
R7A
24.9kΩ
OUTQ1B AND Q2B
2XSUB75N03-04
30V/4mΩ
VCCB = 12V/20A
OUT+
R3B
SILVER BOX 53.6kΩ
B
C1B
0.01µF,
50V
R2B
51kΩ
CS
GATE
VCC
FAULT
C2B
0.1µF,
16V
MAX8535
B
UVP
R4B
10kΩ
OUTPUT BUS
C3B
1nF
R1B
10Ω
TIMER
GND
OVP
R7B
24.9kΩ
OUT-
N+1
Figure 6. N + 1 Redundant Power System Connections
______________________________________________________________________________________
17
MAX8535/MAX8536
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
Pin Configuration
Chip Information
TRANSISTOR COUNT: 3011
PROCESS: BiCMOS
TOP VIEW
CS
GATE
1
8
GND
2
7
FAULT
VCC
3
6
OVP
UVP
4
5
TIMER
MAX8535
MAX8536
µMAX
18
______________________________________________________________________________________
ORing MOSFET Controllers with Fastest
Fault Isolation for Redundant Power Supplies
8
INCHES
DIM
A
A1
A2
b
E
ÿ 0.50±0.1
H
c
D
e
E
H
0.6±0.1
L
1
1
α
0.6±0.1
S
BOTTOM VIEW
D
MIN
0.002
0.030
MAX
0.043
0.006
0.037
0.014
0.010
0.007
0.005
0.120
0.116
0.0256 BSC
0.120
0.116
0.198
0.188
0.026
0.016
6∞
0∞
0.0207 BSC
8LUMAXD.EPS
4X S
8
MILLIMETERS
MAX
MIN
0.05
0.75
1.10
0.15
0.95
0.25
0.36
0.13
0.18
2.95
3.05
0.65 BSC
2.95
3.05
4.78
5.03
0.41
0.66
0∞
6∞
0.5250 BSC
TOP VIEW
A1
A2
A
α
c
e
b
L
SIDE VIEW
FRONT VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
21-0036
REV.
J
1
1
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 19
© 2003 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX8535/MAX8536
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.)