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19-2735; Rev 0; 1/03
KIT ATION EVALU E AILABL AV
ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
General Description Features
o Simple, Integrated, and Inexpensive ORing MOSFET Controller o ORing MOSFET Drive for 12V (MAX8535) and 3.3V or 5V (MAX8536) Bus o Eliminates ORing Diode Power Dissipation and Reverse Leakage Current o Provides N + 1 Redundant Supply Capability for Highly Reliable Systems o Isolates Failed Supply from Output Bus in <1s o Reverse-Current Flow Detection o Programmable Soft-Start o Logic-Enable Input o Adjustable Overvoltage and Undervoltage Trip Points o Fault-Indicator Output o Space-Saving 8-Pin MAX Package
MAX8535/MAX8536
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 MAX package and are specified over the extended -40C to +85C temperature range.
Ordering Information
PART MAX8535EUA MAX8536EUA TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 8 MAX 8 MAX
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
SILVER BOX OR RECTIFIERS OUT+
Typical Operating Circuit
OUTPUT: 3.3V/5V (MAX8536), 12V (MAX8535) +VO -VO
GATE VCC
CS FAULT
MAX8535 MAX8536
TIMER GND
UVP OVP
N.C.
Pin Configuration, Functional Diagrams, and Typical Application Circuits appear at end of data sheet.
OUT-
________________________________________________________________ Maxim Integrated Products
REDUNDANT OUTPUT BUS
1
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
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 = +70C) 8-Pin MAX (derate 4.5mW/C above +70C) .............362mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +150C Junction Temperature ....................................................+150C Lead Temperature (soldering, 10s) .................................+300C
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 = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, TA = 0C to +85C, unless otherwise noted.)
PARAMETER VCC SUPPLY VCC Supply Current VCC Shutdown Current TIMER = 2.5V TIMER = 0V VCC = 14V (MAX8535) VCC = 6V (MAX8536) VCC = 14V (MAX8535) VCC = 6V (MAX8536) MAX8535, charge pump on VCC Input Voltage TIMER = 2.5V MAX8536, charge pump on MAX8535, charge pump off CS Input Current CS Isolation VCC Undervoltage Lockout VCC Overvoltage Internal Threshold CHARGE-PUMP VOLTAGE Measured from VGATE to VCC, VCC = 3.3V (MAX8536) Gate Voltage VGATE VCC = 5V (MAX8536) VCC = 12V (MAX8535) RTIMER = 20k Charge-Pump Switching Frequency RTIMER = 125k RTIMER = open VTIMER = 1.5V 5 5 9 5.5 5.5 11 187 450 500 550 kHz 6 6 12 V VCCOK TIMER = 2.5V CS = 14V (MAX8535) CS = 5.5V (MAX8536) 100 50 -0.05 6 2.5 14 13.3 6.5 2.7 14.5 13.9 -1 7 2.9 15 14.5 8 3.0 2 2 4.5 3 4.5 3 14 5.5 17 A A V V V mA mA SYMBOL CONDITIONS MIN TYP MAX UNITS
CS = max operating voltage, VCC = 0V, I(VCC) MAX8535, rising threshold MAX8536, rising threshold MAX8535 only Rising threshold Falling threshold
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 12V (MAX8535), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, TA = 0C to +85C, unless otherwise noted.)
PARAMETER TIMER TIMER Voltage TIMER Maximum Source Current TIMER High-Input Current TIMER Maximum Frequency Select Voltage Input Range TIMER Logic High TIMER Logic Low FAULT Fault Output Low Voltage Fault Sink Current Fault Leakage Current GATE Gate On Threshold Measured from VCC to CS VGATE = VCC = 12V VGATE = VCC = 5V Gate Shutdown Delay Gate Discharge Current Gate Fall Time CURRENT SENSE Reverse-Current Threshold Startup Reverse-Current Blank Time Forward-Current Threshold OVERVOLTAGE PROTECTION OVP Fault Threshold OVP Bias Current UNDERVOLTAGE PROTECTION UVP Fault Voltage UVP Bias Current VUVP UVP rising threshold UVP falling threshold 1.219 1.119 1.25 1.15 1.281 1.181 0.4 V A VOVP Measured from CS to VCC TIMER = open Measured from VCC to CS OVP rising OVP falling 5 1.219 20 30 524 10 1.25 1.2 0.2 15 1.281 40 mV ms mV ITIMER = 0A (MAX8535) ITIMER = 50A (MAX8535) ITIMER = 0A (MAX8536) ITIMER = 50A (MAX8536) 0.3 35 15 17 8 0.4 50 25 25 12 200 100 200 0.7 0.5 65 36 33 16 300 400 ns mA s A V IFAULT = 0.5mA FAULT = 0.8V FAULT = 18V (MAX8535) FAULT = 6V (MAX8536) 0.5 5 5 0.8 V mA A VIH VIL VTIMER = 1V VTIMER = 1.5V MAX8535 MAX8536 Charge pump enabled Charge pump disabled 1.5 1.5 1.0 0.5 1.219 80 1.25 100 10 1.281 120 20 3.4 VCC - 0.6 V A A V V V SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX8535/MAX8536
Gate Drive Current
From fault sense to the start of gate voltage falling, or from TIMER to the start of gate voltage falling GATE = VCC + 5V Gate voltage fall from fault to VGATE = VCC, CGATE = 0.01F (200ns + CV/I = 700ns, typ)
V A
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
ELECTRICAL CHARACTERISTICS
(VCC = 12V (MAX8535), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER VCC SUPPLY VCC Supply Current VCC Shutdown Current TIMER = 2.5V TIMER = 0V VCC = 14V (MAX8535) VCC = 6V (MAX8536) VCC = 14V (MAX8535) VCC = 6V (MAX8536) MAX8535, charge pump on VCC Input Voltage TIMER = 2.5V MAX8536, charge pump on MAX8535, charge pump off CS Isolation VCC Undervoltage Lockout VCC Overvoltage Internal Threshold CHARGE-PUMP VOLTAGE Measured from VGATE to VCC, VCC = 3.3V (MAX8536) Gate Voltage VGATE VCC = 5V (MAX8536) VCC = 12V (MAX8535) TIMER TIMER Voltage TIMER Maximum Source Current TIMER High-Input Current TIMER Maximum Frequency Select Voltage Input Range TIMER Logic High TIMER Logic Low FAULT Fault Output Low Voltage Fault Sink Current Fault Leakage Current GATE Gate On Threshold Measured from VCC to CS VGATE = VCC = 12V VGATE = VCC = 5V ITIMER = 0A (MAX8535) ITIMER = 50A (MAX8535) ITIMER = 0A (MAX8536) ITIMER = 50A (MAX8536) 0.3 35 15 17 8 0.5 65 36 33 16 A V IFAULT = 0.5mA FAULT = 0.8V FAULT = 18V (MAX8535) FAULT = 6V (MAX8536) 0.5 5 5 0.8 V mA A VIH VIL VTIMER = 1.0V VTIMER = 1.5V MAX8535 MAX8536 Charge pump enabled Charge pump disabled 1.5 1.5 1.1 0.5 1.200 80 1.281 120 20 3.4 VCC - 0.6 V A A V V V 5 5 9 6 6 12 V VCCOK CS = max operating voltage, VCC = 0V, I(VCC) (MAX8535) rising threshold (MAX8536) rising threshold (MAX8535 only) Rising threshold Falling threshold 6.0 2.5 14 13.3 8 3.0 4.5 3 4.5 3 14 5.5 17 -1 7.0 2.9 15 14.5 A V V V mA mA SYMBOL CONDITIONS MIN TYP MAX UNITS
Gate-Drive Current
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VCC = 12V (MAX8535), VCC = 5V (MAX8536), VCS = VCC - 0.1V, RTIMER = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, TA = -40C to +85C, unless otherwise noted.) (Note 1)
PARAMETER Gate Shutdown Delay Gate Discharge Current CURRENT SENSE Reverse-Current Threshold Forward-Current Threshold OVERVOLTAGE PROTECTION OVP Fault Threshold OVP Bias Current UNDERVOLTAGE PROTECTION UVP Fault Voltage UVP Bias Current VUVP UVP rising threshold UVP falling threshold 1.200 1.10 1.281 1.19 0.4 V A VOVP OVP rising 1.20 1.281 0.2 V A Measured from CS to VCC Measured from VCC to CS 20 5 40 15 mV mV SYMBOL CONDITIONS From fault sense to the start of gate voltage falling, or from TIMER to the start of gate voltage falling GATE = VCC + 5V 100 MIN TYP MAX 300 400 UNITS ns mA
MAX8535/MAX8536
Note 1: Specifications to -40C are guaranteed by design and not production tested.
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
State Diagram
CS
CS + 0.01V CS - 0.03V CS - 0.4V
VCC > VCCOK ALL TRANSITIONS ARE ASYNCHRONOUS
VCC VSHARE LATCH IREVERSE BLANKING IFORWARD IREVERSE VSHARE = (CS - VCC) < 0.4V IFORWARD = (VCC - CS) > 0.01V IREVERSE = (CS - VCC) > 0.03V 500ms
STANDBY: CPMP: OFF GATE: LOW
TIMER >1V
WAIT FOR VSHARE
CS - VCC > 0.4V
CS - VCC < 0.4V UVP FAULT UVP FAULT SHUTDOWN GATE: FAULT NOT LATCHED UVP = OK UVP = OK IREVERSE CONDITION DETECTED AFTER 500ms BLANK TIME ON: SET VSHARE LATCH, CHARGE PUMP ON OVP OK AND IREVERSE DURING FIRST 500ms FAULT SHUTDOWN GATE: FAULT LATCHED VCC OR TIMER CYCLED
IFORWARD AND OVP FAULT
FAULT SHUTDOWN GATE: FAULT LATCHED
VCC OR TIMER CYCLED
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
MAX8535 Typical Operating Characteristics
(VCC = 12V, RTIMER = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, BUS = 100F, TA = +25C, unless otherwise specified.)
MAX8535/MAX8536
GATE-CHARGE CURRENT vs. TIMER RESISTANCE (RTIMER)
MAX8535/MAX8536 toc01
SUPPLY CURRENT vs. TEMPERATURE
MAX8535/MAX8536 toc02
60 TA = +85C GATE-CHARGE CURRENT (A) 50 TA = +25C 40 TA = -40C 30 20 10 0 10 100 RESISTANCE (k)
3.4 3.2 SUPPLY CURRENT (mA) 3.0 2.8 2.6 2.4 2.2 2.0 TIMER IS UNCONNECTED TIMER = GND
1000
-40
-20
0
20
40
60
80
TEMPERATURE (C)
MAX8535 REVERSE-CURRENT THRESHOLD vs. TEMPERATURE
REVERSE-CURRENT THRESHOLD (mV) 34 33 32 31 30 29 28 27 26 25 -40 -15 10 35 60 85 TEMPERATURE (C) 20 0 -40
MAX8535/MAX8536 toc03
UVP AND OVP LEAKAGE CURRENT vs. TEMPERATURE
MAX8535/MAX8536 toc04
35
140 120 LEAKAGE CURRENT (nA) 100 80 60 40 OVP
UVP
-20
0
20
40
60
80
TEMPERATURE (C)
POWER-UP WAVEFORM (VBUS = 0V)
MAX8535/MAX8536 toc05
POWER-UP WAVEFORM (VBUS = 12V)
MAX8535/MAX8536 toc06
VCC 10V/div
VCC 10V/div
IMOSFET 10A/div
IMOSFET 2A/div
VGATE 20V/div VCS 10V/div 4ms/div 4ms/div
VGATE 20V/div VCS 10V/div
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
MAX8535 Typical Operating Characteristics (continued)
(VCC = 12V, RTIMER = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, BUS = 100F, TA = +25C, unless otherwise specified.)
TIMER-ENABLED STARTUP AND SHUTDOWN WAVEFORMS (VCC = 12V, VBUS = 12V)
MAX8535/MAX8536 toc07
TIMER-ENABLED STARTUP AND SHUTDOWN WAVEFORMS (VCC = 12V, VBUS = 0V)
MAX8535/MAX8536 toc08
VTIMER 2V/div
VTIMER 1V/div
IMOSFET 50mA/div VGATE 20V/div VCS 10V/div 4ms/div 4ms/div
IMOSFET 10A/div VGATE 20V/div VCS 10V/div
REVERSE-CURRENT FAULT WAVEFORM (R1 = 10)
MAX8535/MAX8536 toc09
UVP FAULT WAVEFORM (R1 = 100)
MAX8535/MAX8536 toc10
VCS 1V/div 12V IMOSFET 5A/div
1.25V VUVP 1V/div
VFAULT 10V/div VGATE 20V/div
VFAULT 10V/div 400ns/div 1s/div
VGATE 20V/div VCS 10V/div
SELECTIVE OVP SHUTDOWN WAVEFORM (R1 = 10)
MAX8535/MAX8536 toc11
VCS 1V/div 12V
VGATE1 (OVP UNIT) 20V/div VGATE2 (GOOD UNIT) 20V/div VFAULT 10V/div 1s/div
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
MAX8536 Typical Operating Characteristics
(VCC = 12V, RTIMER = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, BUS = 100F, TA = +25C, unless otherwise specified.)
GATE-CHARGE CURRENT vs. TIMER RESISTANCE (RTIMER)
MAX8535/MAX8536 toc12
MAX8535/MAX8536
SUPPLY CURRENT vs. TEMPERATURE
MAX8535/MAX8536 toc13
30 25 GATE-CHARGE CURRENT (A) 20 15 10 5 0 10 100 RESISTANCE (k) TA = +25C TA = -40C TA = +85C
2.2 2.0 SUPPLY CURRENT (mA) 1.8 1.6 TIMER = GND 1.4 1.2 1.0
TIMER IS UNCONNECTED
1000
-40
-20
0
20
40
60
80
TEMPERATURE (C)
MAX8536 REVERSE-CURRENT THRESHOLD vs. TEMPERATURE
MAX8535/MAX8536 toc14
UVP AND OVP LEAKAGE CURRENT vs. TEMPERATURE
MAX8535/MAX8536 toc15
35 REVERSE-CURRENT THRESHOLD (mV) 34 33 32 31 30 29 28 27 26 25 -40 -15 10 35 60
140 120 LEAKAGE CURRENT (nA) 100 80 60 40 OVP 20 0
UVP
85
-40
-20
0
20
40
60
80
TEMPERATURE (C)
TEMPERATURE (C)
POWER-UP WAVEFORM (VBUS = 0V)
MAX8535/MAX8536 toc16
POWER-UP WAVEFORM (VBUS = 5V)
MAX8535/MAX8536 toc17
VCC 5V/div
VCC 5V/div
IMOSFET 2A/div
IMOSFET 1A/div VGATE 10V/div VCS 5V/div 4ms/div
VGATE 10V/div VCS 5V/div 4ms/div
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
MAX8536 Typical Operating Characteristics (continued)
(VCC = 12V, RTIMER = 25k, UVP = 2V, OVP = 1V, CGATE = 0.01F, BUS = 100F, TA = +25C, unless otherwise specified.)
TIMER-ENABLED STARTUP AND SHUTDOWN WAVEFORMS (VCC = 5V, VBUS = 5V)
MAX8535/MAX8536 toc18
TIMER-ENABLED STARTUP AND SHUTDOWN WAVEFORMS (VCC = 5V, VBUS = 0V)
MAX8535/MAX8536 toc19
VTIMER 2V/div
VTIMER 2V/div
IMOSFET 50mA/div VGATE 10V/div VCS 5V/div 4ms/div 10ms/div
IMOSFET 1A/div VGATE 10V/div VCS 5V/div
REVERSE-CURRENT FAULT WAVEFORM (R1 = 10)
MAX8535/MAX8536 toc20
UVP FAULT WAVEFORM (R1 = 100)
MAX8535/MAX8536 toc21
VCS 1V/div 5V IMOSFET 5A/div
1.25V VUVP 2V/div
VFAULT 5V/div VGATE 10V/div VGATE VFAULT 5V/div 400ns/div 1s/div VCS 1V/div
SELECTIVE OVP SHUTDOWN WAVEFORM (R1 = 10)
MAX8535/MAX8536 toc22
VCS 1V/div 5V VGATE2 (GOOD UNIT) 10V/div VGATE1 (OVP UNIT) 10V/div VFAULT 5V/div 1s/div
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
Pin Description
PIN 1 2 3 4 NAME GATE GND VCC UVP Ground Power-Supply Input. Bypass VCC with a 0.1F capacitor to ground. 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. 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 100A. If pulled low (<0.5V), the gate drive is disabled. If pulled high (above 1.25V), the charge pump operates at 550kHz. Overvoltage Input. Connect a resistor-divider from the CS to GND with the center point connected to OVP. Connect to GND if not used. Open-Drain Fault Output. FAULT is low during a fault, high impedance during normal operation. Connect a pullup resistor of 50k 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. FUNCTION Gate Drive Output. Bypass GATE with a 0.01F capacitor to ground.
MAX8535/MAX8536
5
TIMER
6 7 8
OVP FAULT CS
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 25A and the GATE drive current for the
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
MAX8536 is 12A. 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. 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.
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.
FAULT Conditions
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. 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.
Applications Information
Selecting the Timer Resistor
To set the frequency of the internal charge-pump operation, connect a resistor from TIMER to GND. Determine the frequency by using the equation: 1.25V Frequency = 5 x 100A kHz / A 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 (0.01F, 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
FAULT MODE VCC UVLO UVP pin undervoltage protection OVP pin overvoltage protection Reverse-current protection VCC internal (MAX8535 only) overvoltage protection PIN CONDITIONS VCC < VCCOK UVP < 1.25V OVP > 1.25V VCC > CS + 0.01V VCC < CS - 0.03V Gate ON for t > 0.5s VCC > 14.5V GATE PIN Low Low Low Low Low FAULT PIN High impedance Low Low Low Low LATCHING No No Yes Yes No
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ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
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 10k resistor (R4 in Figure 4) from UVP to GND and calculate the other resistor (R3) using: 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. 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.
MAX8535/MAX8536
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 0.1F 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.
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 10k 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
______________________________________________________________________________________
13
ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
Functional Diagrams
GATE VCC CS
VCC
CHARGE PUMP
400mV
30mV
10mV
CLK SHUTDOWN VOLTAGE SHARE REVERSE CURRENT FORWARD CURRENT 14.5V OVP
VCC FAULT CONTROL LOGIC
OVERVOLTAGE INTERNAL OVERVOLTAGE EXTERNAL UNDERVOLTAGE
1.25V IOSC TIMER ENABLE UVP
1.25V REF
MAX8535
1.25V
GND
Figure 1. MAX8535 Functional Diagram
GATE
VCC
CS
VCC
CHARGE PUMP
400mV
30mV
10mV
CLK SHUTDOWN VOLTAGE SHARE REVERSE CURRENT FORWARD CURRENT
VCC FAULT CONTROL LOGIC
OVP OVERVOLTAGE EXTERNAL UNDERVOLTAGE 1.25V IOSC TIMER ENABLE UVP
1.25V REF
MAX8536
1.25V
GND
Figure 2. MAX8536 Functional Diagram 14 ______________________________________________________________________________________
ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
Typical Application Circuits
Q1 AND Q2 2XSUB75N03-04 30V/4m OUT+ +VO -VO OUTPUT: 12V/20A
MAX8535/MAX8536
R1 10 R3 SILVER BOX 53.6k OR RECTIFIERS C1 0.01F, 50V GATE VCC C2 0.1F, 16V UVP TIMER CS FAULT
C3 1nF
MAX8535
OVP GND R6 10k
R4 10k OUT-
R7 24.9k
ENABLE
Figure 3. Typical Application Circuit for 12V/20A Output with OVP and UVP
Q1 AND Q2 2XSUB75N03-04 30V/4m OUT+
+VO -VO OUTPUT: 3.3V OR 5V/20A
R1 10 R3 SILVER BOX 13.3k OR RECTIFIERS C1 0.01F, 50V GATE VCC C2 0.1F, 16V UVP TIMER R4 10k OUTGND CS FAULT
C3 1nF
MAX8536
OVP
R7 24.9k
R6 10k
Figure 4. Typical Application Circuit for 3.3V or 5V/20A Output with OVP and UVP ______________________________________________________________________________________ 15
OUTPUT BUS
R5 35.7k
R2 51k
OUTPUT BUS
R5 100k
R2 51k
ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
Q1 SUB75N03-04 30V/4m OUTPUT: 12V/20A OUT+ +VO -VO
R1 10 SILVER BOX OR RECTIFIERS
C3 1nF OUTPUT BUS R2 51k
C1 0.01F, 50V ON C2 0.1F, 16V OFF ENABLE R4 7.5k
GATE VCC
CS FAULT
MAX8535
TIMER R3 7.5k GND
UVP OVP
N.C.
OUT-
Figure 5. Typical Application Circuit for 12V/20A Output without OVP and UVP
16
______________________________________________________________________________________
ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
V+ Q1A AND Q2A 2XSUB75N03-04 30V/4m VCCA = 12V/20A OUT+ +VO -VO
R1A 10 R3A SILVER BOX 53.6k A C1A 0.01F, 50V GATE VCC C2A 0.1F, 16V UVP TIMER CS FAULT
C3A 1nF
MAX8535
A GND OVP
R4A 10k OUT-
R7A 24.9k
R6A 10k
Q1B AND Q2B 2XSUB75N03-04 30V/4m VCCB = 12V/20A OUT+
R1B 10 R3B SILVER BOX 53.6k B C1B 0.01F, 50V GATE VCC C2B 0.1F, 16V UVP TIMER CS FAULT
C3B 1nF
MAX8535
B GND OVP
R4B 10k OUT-
R7B 24.9k
N+1
Figure 6. N + 1 Redundant Power System Connections ______________________________________________________________________________________ 17
OUTPUT BUS
R2B 51k
OUTPUT BUS
R5A 100k
R2A 51k
ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies MAX8535/MAX8536
Pin Configuration
TOP VIEW
GATE GND VCC UVP 1 2 3 4 8 CS FAULT OVP TIMER
Chip Information
TRANSISTOR COUNT: 3011 PROCESS: BiCMOS
MAX8535 MAX8536 MAX
7 6 5
18
______________________________________________________________________________________
ORing MOSFET Controllers with Fastest Fault Isolation for Redundant Power Supplies
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
MAX8535/MAX8536
4X S
8
8
INCHES DIM A A1 A2 b MIN 0.002 0.030 MAX 0.043 0.006 0.037
MILLIMETERS MAX MIN 0.05 0.75 1.10 0.15 0.95
y 0.500.1
E
H
0.60.1
c D e E H L
1
1
0.60.1
S
D
BOTTOM VIEW
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
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
A2
A1
A
c e b L
SIDE VIEW
FRONT VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, 8L uMAX/uSOP
APPROVAL DOCUMENT CONTROL NO. REV.
21-0036
1 1
J
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 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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