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19-2496; Rev 0; 7/02
Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control
General Description
The MAX5918 and MAX5919 are +1V to +13.2V dual hot-swap controllers with independent on/off control for complete protection of dual-supply systems. They allow the safe insertion and removal of circuit cards into live backplanes. The MAX5918 and MAX5919 operate down to 1V provided one of the inputs is above 2.7V The discharged filter capacitors of the circuit card provide low impedance to the live backplane. High inrush currents from the backplane to the circuit card can burn up connectors and components, or momentarily collapse the backplane power supply leading to a system reset. The MAX5918 and MAX5919 hot-swap controllers prevent such problems by gradually ramping up the output voltage and regulating the current to a preset limit when the board is plugged in, allowing the system to stabilize safely. After the startup cycle is completed, two on-chip comparators provide VariableSpeed/BiLevelTM protection against short-circuit and overcurrent faults, as well as immunity against system noise and load transients. In the event of a fault condition, the load is disconnected. The MAX5918L and MAX5919L must be unlatched after a fault and the MAX5918A and MAX5919A automatically restart after a fault. The MAX5918 and MAX5919 integrate an on-board charge pump to drive the gates of low-cost, external Nchannel MOSFETs. The devices offer integrated features like startup current regulation and current glitch protection to eliminate external timing resistors and capacitors. These devices provide open-drain status outputs, an adjustable startup timer and adjustable current limits. The MAX5918 provides output undervoltage/overvoltage protection for each channel, while the MAX5919 provides undervoltage/overvoltage monitoring for each channel. The MAX5918 and MAX5919 are available in a spacesaving 16-pin QSOP package and are specified over the extended -40C to +85C temperature range.
KIT ATION EVALU ABLE AVAIL
Features
o Safe Hot Swap for +1V to +13.2V Power Supplies with VIN1 or VIN2 2.7V o Independent On/Off Control for Each Channel o Internal Charge Pumps Generate N-Channel MOSFET Gate Drives o Inrush Current Regulated at Startup o Circuit Breaker Function o Adjustable Circuit Breaker/Current-Limit Threshold from 25mV to 100mV o VariableSpeed/BiLevel Circuit Breaker Response o Autoretry or Latched Fault Management o Status Outputs Indicate Fault/Safe Condition o Output Undervoltage and Overvoltage Monitoring or Protection
MAX5918/MAX5919
Ordering Information
PART MAX5918AEEE MAX5918LEEE MAX5919AEEE MAX5919LEEE TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 16 QSOP 16 QSOP 16 QSOP
Selector Guide and Typical Application Circuit appear at end of data sheet.
Pin Configuration
TOP VIEW
PGOOD1 1 TIM 2 IN1 3 SENSE1 4 GATE1 5 GND 6 LIM1 7 MON1 8 16 PGOOD2 15 ON2 14 IN2
Applications
Base Station Line Cards Network Switches, Routers, Hubs Solid-State Circuit Breakers RAID Power-Supply Sequencing Hot Plug-In Daughter Cards Portable Computer Device Bays (Docking Stations)
MAX5918 MAX5919
13 SENSE2 12 GATE2 11 ON1 10 LIM2 9 MON2
Variable Speed/BiLevel is a trademark of Maxim Integrated Products, Inc.
QSOP 1
________________________________________________________________ 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.
Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
ABSOLUTE MAXIMUM RATINGS
IN_ to GND...........................................................................+14V GATE_ to GND ...........................................-0.3V to (VIN_ + 6.2V) ON_, PGOOD_, TIM to GND.......................-0.3V to the higher of (VIN1 + 0.3V) and (VIN2 + 0.3V) SENSE_, MON_, LIM_ to GND ...................-0.3V to (VIN_ + 0.3V) Current into Any Pin .........................................................50mA Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.3mW/C above +70C)...........667mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +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
(VIN_ = +1V to +13.2V provided at least one supply is higher than +2.7V, VON1 = VON2 = +2.7V, TA = -40C to +85C, unless otherwise noted. Typical values are at VIN1 = +5V, VIN2 = +3.3V, and TA = +25C.) (Note 1)
PARAMETER POWER SUPPLIES IN_ Input Voltage Range Supply Current CURRENT CONTROL Slow-Comparator Threshold (VIN_ - VSENSE_) (Note 2) Slow-Comparator Response Time (Note 3) Fast-Comparator Threshold (VIN_ - VSENSE_) Fast-Comparator Response Time (VIN_ - VSENSE_) SENSE Input Bias Current MOSFET DRIVER RTIM = 100k (maximum value) Startup Period (Note 4) tSTART TA = 0C to +85C TA = -40C to +85C 8.0 6 0.35 5 80 10.8 10.8 0.45 9 100 3 4.8 4.3 0.85 5.4 5 0.875 25 50 5.8 5.8 0.90 13.6 16 0.55 14 130 A mA V ms VSC,TH LIM = GND RLIM = 300k tSCD VSU,TH VFC,TH tFCD IB SENSE 1mV overdrive 10mV overdrive During startup VIN_ - VSENSE_; normal operation 10mV overdrive, from overload condition VSENSE_ = VIN_ TA = +25C TA = -40C to +85C 22.5 20.5 80 100 3 110 2 x VSC,TH 4 x VSC,TH 260 0.03 1 25 27.5 27.5 130 ms s mV ns A mV VIN IIN Other VIN +2.7V IIN1 + IIN2, VIN1 = +5V, VIN2 = +3.3V 1.0 1.2 13.2 2.3 V mA SYMBOL CONDITIONS MIN TYP MAX UNITS
RTIM = 4k (minimum value) TIM floating Charging, VGATE_ = +5V, VIN_ = +10V (Note 5)
Average Gate Current
IGATE
Discharging, triggered by a fault or when VON < 0.875V VGATE_ - VIN_, IGATE_ < 1A Low to high Hysteresis 10mV overdrive VIN_ = 3V to 13.2V VIN_ = 2.7V to 3.0V
Gate-Drive Voltage ON COMPARATOR ON Threshold ON Propagation Delay
VDRIVE
VON_,TH
V mV s
2
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control
ELECTRICAL CHARACTERISTICS (continued)
(VIN_ = +1V to +13.2V provided at least one supply is higher than +2.7V, VON1 = VON2 = +2.7V, TA = -40C to +85C, unless otherwise noted. Typical values are at VIN1 = +5V, VIN2 = +3.3V, and TA = +25C.) (Note 1)
PARAMETER ON Input Bias Current ON Pulse Width Low DIGITAL OUTPUT (PGOOD_) Output Leakage Current Output Voltage Low PGOOD_ Delay VOL tPGDLY VPGOOD_ = 13.2V ISINK = 1mA After tSTART, MON_ = VIN_ Overvoltage Undervoltage VMON_ = 600mV Startup is initiated when this threshold is reached by VIN1 or VIN2, VON_ > 0.875V Hysteresis UVLO Glitch Filter Reset Time UVLO to Startup Delay SHUTDOWN LATCH/RESTART Autoretry Delay tRETRY Delay time to restart after fault shutdown 64 x tSTART ms tD,UVLO VIN_ toggled below UVLO to unlatch after a fault VIN_ step from 0 to 2.8V 100 20 37.5 60 657 513 0.75 687 543 20 0.03 707 563 1 0.4 A V ms SYMBOL IBON tUNLATCH CONDITIONS VON_ < 4.5V VIN1 = VIN2 = +13.2V VON_ > 4.5V VON_ = 4.5V To unlatch after a latched fault 100 MIN TYP 0.03 100 0.03 1 s A MAX UNITS
MAX5918/MAX5919
OUTPUT VOLTAGE MONITORS (MON1, MON2) MON_ Trip Threshold MON_ Glitch Filter MON_ Input Bias Current UNDERVOLTAGE LOCKOUT (UVLO) UVLO Threshold VUVLO 2.10 2.4 100 2.67 V mV s ms VMON mV s A
Note 1: All devices are 100% tested at TA = +25C and TA = +85C. Limits at TA = -40C are guaranteed by design. Note 2: The MAX5918/MAX5919 slow-comparator threshold is adjustable. VSC,TH = RLIM 0.25A + 25mV (see the Typical Operating Characteristics). Note 3: The current-limit slow-comparator response time is weighted against the amount of overcurrent, the higher the overcurrent condition, the faster the response time (see the Typical Operating Characteristics). Note 4: The startup period (tSTART) is the time during which the slow comparator is ignored and the device acts as a current-limiter by regulating the sense current with the fast comparator (see the Startup Period section). Note 5: The current available at GATE is a function of VGATE (see the Typical Operating Characteristics).
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
Typical Operating Characteristics
(Typical Operating Circuits, Q1 = Q2 = Fairchild FDB7090L, VIN1 = +5V, VIN2 = +3.3V, VON1 = VON2 = +2.7V, TA = +25C, unless otherwise noted. Channels 1 and 2 are identical in performance. Where characteristics are interchangeable, channels 1 and 2 are referred to as X and Y.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX5918/19 toc01
TOTAL SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX5918/19 toc02
SUPPLY CURRENT vs. TEMPERATURE
1.8 1.6 1.4 C VON1 = VIN1 VON2 = VIN2
MAX5918/19 toc03
2.0 1.8 1.6 1.4 IIN (mA) 1.2 1.0 0.8 0.6 0.4 0.2 0 0
VINY = VON1 = VON2 = 2.7V
2.0 1.8 1.6 1.4 IIN (mA) B A
2.0 IIN1 + IIN2
IINX + IINY
IIN (mA)
1.2 1.0 0.8 0.6
1.2 1.0 0.8 IIN1
IINX
IINY
0.4 0.2 0
VINY = 5.0V A) VON1 = VON2 = 3.3V B) VON1 = VON2 = 1.5V C) VON1 = VON2 = 0 0 2 4 6 8 10 12 14
0.6 0.4 0.2 0 -40 -15 10 35 60 85 IIN2
2
4
6
8
10
12
14
VINX (V)
VINX (V)
TEMPERATURE (C)
GATE-DRIVE VOLTAGE vs. INPUT VOLTAGE
MAX5918/19 toc04
GATE CHARGE CURRENT vs. GATE VOLTAGE
MAX5918/19 toc05
GATE CHARGE CURRENT vs. TEMPERATURE
180 GATE CHARGE CURRENT (A) 160 140 120 100 80 60 40 20 0 VINY = 2.7V VGATEX = 0 -40 -15 10 35 60 85 VINX = 1V VINX = 13.2V VINX = 5V
MAX5918/19 toc06
MAX5918/19 toc09
6 5 GATE-DRIVE VOLTAGE (V) 4 3 2 1 VINY = 2.7V 0 0 2 4 6 8 10 12
200 180 GATE CHARGE CURRENT (A) 160 140 120 100 80 60 40 20 0 VINX = 13.2V VINX = 5V VINX = 1V VINY = 2.7V
200
14
0
5
VINX (V)
10 VGATEX (V)
15
20
TEMPERATURE (C)
GATE STRONG DISCHARGE CURRENT vs. GATE VOLTAGE
MAX5918/19 toc07
GATE STRONG DISCHARGE CURRENT vs. TEMPERATURE
MAX5918/19 toc08
TURN-OFF TIME vs. SENSE VOLTAGE
10 SLOW-COMP. THRESHOLD 1 TURN-OFF TIME (ms) FAST-COMP. THRESHOLD 0.1
6 GATE DISCHARGE CURRENT (mA) 5 4 3 2 1 0 0 5 10 VGATEX (V) 15 VINX = 1V VINY = 2.7V VGATEX = VINX + 6.2V VINX = 5V VINX = 13.2V
6 GATE DISCHARGE CURRENT (mA) 5 4 3 2 1 0 VINX = 5V VINX = 13.2V
VON1 = VON2 = 0
VON1 = VON2 = 0 VINY = 2.7V VGATEX = VINX + 6.2V
0.01
0.001 VINX = 1V 0.0001 -40 -15 10 35 60 85 0 25 50 75 100 125 150 175 200 TEMPERATURE (C) VIN - VSENSE (mV)
20
4
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control
Typical Operating Characteristics (continued)
(Typical Operating Circuits, Q1 = Q2 = Fairchild FDB7090L, VIN1 = +5V, VIN2 = +3.3V, VON1 = VON2 = +2.7V, TA = +25C, unless otherwise noted. Channels 1 and 2 are identical in performance. Where characteristics are interchangeable, channels 1 and 2 are referred to as X and Y.)
TURN-OFF TIME vs. SENSE VOLTAGE (EXPANDED SCALE)
MAX5918/19 toc10
MAX5918/MAX5919
SLOW-COMPARATOR THRESHOLD vs. RLIM
MAX5918/19 toc11
STARTUP PERIOD vs. RTIM
MAX5918/19 toc12
10
120 100 80 60 40 20
60 50 40 tSTART (ms) 30 20 10 0
TURN-OFF TIME (ms)
SLOW-COMP. THRESHOLD 1
VSC,TH (mV)
0.1 20 25 30 35 40 45 50 55 60 65 70 75 80 VIN - VSENSE (mV)
0 0 100 200 RLIM (k) 300 400
0
100
200
300 RTIM (k)
400
500
600
TURN-OFF TIME SLOW-COMPARATOR FAULT
MAX5918/19 toc13
TURN-OFF TIME FAST-COMPARATOR FAULT
MAX5918/19 toc14
STARTUP WAVEFORMS FAST TURN-ON
MAX5918/19 toc15
VON 2V/div 0 0 26mV STEP VSENSE - VIN 100mV/div VGATE 5V/div 0 0 1ms/div VIN = 5.0V 400ns/div VIN = 5.0V 1ms/div VIN = 5.0V, RSENSE = 10m, RTIM = 27k, CBOARD = 1000F tSCD VPGOOD 5V/div 0 tFCD 0 125mV STEP VSENSE - VIN 100mV/div VGATE 5V/div IOUT 5A/div VOUT 5V/div VGATE 5V/div VPGOOD 5V/div VPGOOD 2V/div
STARTUP WAVEFORMS SLOW TURN-ON
MAX5918/19 toc16
AUTORETRY DELAY
MAX5918/19 toc17
VON 2V/div VPGOOD 2V/div IOUT 5A/div VOUT 5V/div VGATE 5V/div 1ms/div VIN = 5.0V, RSENSE = 10m, RTIM = 47k, CBOARD = 1000F, CGATE = 22nF 40ms/div VIN = 5.0V, RSENSE = 10m, RTIM = 47k, CBOARD = 1000F, RBOARD = 1.4 VOUT 5V/div IOUT 5A/div VGATE 5V/div
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5
Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
Pin Description
PIN 1 NAME FUNCTION Channel 1 Status Output (Open Drain, see Absolute Maximum Ratings). PGOOD1 asserts high when hot PGOOD1 swap is successful and channel 1 is within regulation. PGOOD1 asserts low during startup, when ON1 is low, when channel 1 is off, or when channel 1 has any fault condition. TIM IN1 SENSE1 GATE1 GND LIM1 MON1 MON2 LIM2 ON1 GATE2 SENSE2 IN2 ON2 Startup Timer Setting. Connect a resistor from TIM to GND to set the startup period. Leave TIM unconnected for the default startup period of 9ms. Channel 1 Supply Input. Connect to a supply voltage of 1V to 13.2V. Channel 1 Current-Sense Input. Connect RSENSE1 from IN1 to SENSE1. Connect to IN1 to disable circuit breaker function of channel 1. Channel 1 Gate-Drive Output. Connect to gate of external N-channel MOSFET. Ground Channel 1 Current-Limit Setting. Connect a resistor from LIM1 to GND to set the current trip level. Connect to GND for the default 25mV threshold (see the Slow-Comparator Threshold, RLIM section). Channel 1 Output-Voltage Monitor. Window comparator input. Connect through a resistive-divider from OUT1 to GND to set the channel 1 overvoltage and undervoltage threshold. Connect to IN1 to disable. Channel 2 Output-Voltage Monitor. Window comparator input. Connect through a resistive-divider from OUT2 to GND to set the channel 2 overvoltage and undervoltage threshold. Connect to IN2 to disable. Channel 2 Current-Limit Setting. Connect a resistor from LIM2 to GND to set the current trip level. Connect to GND for the default 25mV threshold (see the Slow-Comparator Threshold, RLIM section). Channel 1 On/Off Control Input. Channel 1 is turned on when VON1 > 0.875V. Channel 2 Gate-Drive Output. Connect to gate of external N-channel MOSFET. Channel 2 Current-Sense Input. Connect RSENSE2 from IN2 to SENSE2. Connect to IN2 to disable circuit breaker function of channel 2. Channel 2 Supply Input. Connect to a supply voltage of 1V to 13.2V. Channel 2 On/Off Control Input. Channel 2 is turned on when VON2 > 0.875V.
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Channel 2 Status Output (Open Drain, see Absolute Maximum Ratings). PGOOD2 asserts high when hot PGOOD2 swap is successful and channel 2 is within regulation. PGOOD2 asserts low during startup, when VON2 is low, when channel 2 is off, or when channel 2 has any fault condition.
Detailed Description
The MAX5918 and MAX5919 are circuit breaker ICs for hot-swap applications where a line card is inserted into a live backplane. The MAX5918 and MAX5919 operate down to 1V provided one of the inputs is above 2.7V. Normally, when a line card is plugged into a live backplane, the card's discharged filter capacitors provide low impedance that can momentarily cause the main power supply to collapse. The MAX5918 and MAX5919 reside either on the backplane or on the removable card to provide inrush current limiting and short-circuit protection. This is achieved by using external N-channel MOSFETs, external current-sense resistors, and two on-chip comparators. The startup period and currentlimit threshold of the MAX5918/MAX5919 can be
adjusted with external resistors. Figure 1 shows the MAX5918/MAX5919 functional diagram. The MAX5918/MAX5919 pull both PGOODs low and both external FETs off for an overcurrent condition. The MAX5918 also pulls both PGOODs low and both external FETs off (protection) for an undervoltage/overvoltage fault, whereas, the MAX5919 ONLY pulls the corresponding fault channel's PGOOD low (monitoring). When the overvoltage/undervoltage fault disappears on the MAX5919, the corresponding PGOOD automatically goes high impedance.
6
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Figure 1. Functional Diagram
RLIM1 LIM1 IN2 VFS, TH VFS, TH VSC, TH RSENSE2 FAST COMP. UVLO 2.4V TIMING OSCILLATOR SLOW COMP. GATE2 CHARGE PUMP DEVICE CONTROL LOGIC CURRENT CONTROL AND STARTUP LOGIC CURRENT CONTROL AND STARTUP LOGIC CHARGE PUMP Q2 OUT2 FAST DISCHARGE FAST DISCHARGE 100A 687mV 0.875V 687mV MON2 3mA 2.4V SLOW COMP. UVLO BIAS AND REFERENCES FAST COMP. SENSE2 LIM2 RLIM2 543mV TO STARTUP LOGIC BLOCKS TO STARTUP LOGIC BLOCKS 543mV MAX5918/ MAX5919 STARTUP OSCILLATOR N CHARGE-PUMP OSCILLATOR TIM RTIM ON2 ON1 PGOOD1 PGOOD2
IN1
VSC, TH
RSENSE1
SENSE1
GATE1
Q1
OUT1
3mA
Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control
MAX5918/MAX5919
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MON1
7
Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
Startup Period
RTIM sets the duration of the startup period from 0.4ms to 50ms (see the Setting the Startup Period, RTIM section). The default startup period is fixed at 9ms when TIM is floating. The startup period begins after the following three conditions are met: 1) VIN1 or VIN2 exceeds the UVLO threshold (2.4V) for the UVLO to startup delay (37.5ms). 2) VON1 and VON2 exceed the ON threshold (0.875V). 3) The device is not latched or in its autoretry delay (see the Latched and Autoretry Overcurrent Fault Management section). The MAX5918/MAX5919 limit the load current if an overcurrent fault occurs during startup instead of completely turning off the external MOSFETs. The slow comparator is disabled during the startup period and the load current can be limited in two ways: 1) Slowly enhancing the MOSFETs by limiting the MOSFET gate-charging current. 2) Limiting the voltage across the external currentsense resistor. During the startup period the gate-drive current is limited to 100A and decreases with the increase of the gate voltage (see the Typical Operating Characteristics). This allows the controller to slowly enhance the MOSFETs. If the fast comparator detects an overcurrent, the MAX5918/MAX5919 regulate the gate voltage to ensure that the voltage across the sense resistor does not exceed VSU,TH. This effectively regulates the inrush current during startup. Figure 2 shows the startup waveforms. PGOOD_ goes high impedance 0.75ms after the startup period if no fault condition is present.
VariableSpeed/BiLevel Fault Protection
VariableSpeed/BiLevel fault protection incorporates two comparators with different thresholds and response times to monitor the load current (Figure 3). During the startup period, protection is provided by limiting the load current. Protection is provided in normal operation (after the startup period has expired) by discharging both MOSFET gates with a strong 3mA pulldown current in response to a fault condition. After a fault, PGOOD_ is pulled low, the MAX5918L and MAX5919L stay latched off and the MAX5918A and MAX5919A automatically restart Slow-Comparator Startup Period The slow comparator is disabled during the startup period while the external MOSFETs are turning on. Disabling the slow comparator allows the device to ignore the higher-than-normal inrush current charging the board capacitors when a card is first plugged into a live backplane. Slow-Comparator Normal Operation After the startup period is complete, the slow comparator is enabled and the device enters normal operation. The comparator threshold voltage (VSC,TH) is adjustable from 25mV to 100mV. The slow-comparator response
ON PGOOD tSTART + tPGDLY VGATE 3ms SLOW COMPARATOR
4.3V TO 5.8V TURN-OFF TIME FAST COMPARATOR
VOUT VTH VGATE VOUT VSU,TH RSENSE CBOARD = 0 ILOAD tON CBOARD = LARGE
110s 260ns
VSC,TH
VFC,TH (4 x VSC,TH)
SENSE VOLTAGE (VIN - VSENSE)
Figure 2. Startup Waveform 8
Figure 3. VariableSpeed/BiLevel Response
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control
time decreases to a minimum of 100s with a large overdrive voltage. Response time is 3ms for a 1mV overdrive. The variable speed response time allows the MAX5918/MAX5919 to ignore low-amplitude momentary glitches, thus increasing system noise immunity. After an extended overcurrent condition, a fault is generated, both PGOODS are pulled low and the MOSFET gates are discharged with a strong 3mA pulldown current. Fast-Comparator Startup Period During the startup period, the fast comparator regulates the gate voltage to ensure that the voltage across the sense resistor does not exceed the startup fast-comparator threshold voltage (VSU,TH), VSU,TH is scaled to two times the slow-comparator threshold (VSC,TH). Fast-Comparator Normal Operation In normal operation, if the load current reaches the fastcomparator threshold, a fault is generated, both PGOODS are pulled low, and the MOSFET gates are discharged with a strong 3mA pulldown current. This happens in the event of a serious current overload or a dead short. The fast-comparator threshold voltage (VFC,TH) is scaled to four times the slow-comparator threshold (VSC,TH). This comparator has a fast response time of 260ns (Figure 3). the startup period to begin immediately by toggling one of the supply voltages below/above the UVLO threshold. When toggling a supply voltage to clear a fault, remember that the supply voltage must go below and then above the UVLO threshold for at least 100s regardless of the final value of the supply voltage.
MAX5918/MAX5919
Output Overvoltage/Undervoltage Fault Management
The MAX5918/MAX5919 monitor the output voltages with the MON1 and MON2 window comparator inputs. These voltage monitors are enabled after the startup period. Once enabled, the voltage monitor detects a fault if VMON_ is less than 543mV or greater than 687mV. When the MAX5918 protection device detects an output overvoltage/undervoltage fault on either MON1 or MON2, both external MOSFET gates are discharged at 3mA and both PGOODs pull low. For the MAX5918A, the part continuously attempts to restart after each autoretry period. The part successfully restarts after the fault is removed and after waiting the autoretry period. For the MAX5918L, the GATEs are latched off until the output voltage fault is removed and the fault latch is cleared by toggling ON_ or by cycling one of the supply voltages above/below the UVLO threshold. When the MAX5919 monitoring device detects an output overvoltage/undervoltage fault on either MON1 or MON2, neither external MOSFET gates are affected, but the PGOOD of the channel experiencing the fault pulls low. Thus the fault is reported on the channel with the problem, but the MAX5919 does not allow an output overvoltage/undervoltage fault to disrupt operation by shutting down the channels. The MAX5919's PGOOD output immediately goes high impedance after the output overvoltage/undervoltage fault is removed. The voltage monitors do not react to output glitches of less than 20s. A capacitor from MON_ to GND increases the effective glitch filter time. The voltage monitoring function of the MAX5918/MAX5919 can be disabled by connecting VIN1 to MON1 and VIN2 to MON2.
Undervoltage Lockout (UVLO)
The UVLO prevents the MAX5918/MAX5919 from turning on the external MOSFETs until one input voltage exceeds the UVLO threshold (2.4V) for tD,UVLO. The MAX5918/MAX5919 use power from the higher input voltage rail for the charge pumps. This allows for more efficient charge-pump operation. The UVLO protects the external MOSFETs from an insufficient gate-drive voltage. tD,UVLO ensures that the board is fully inserted into the backplane and that the input voltages are stable. Any input voltage transient on both supplies below the UVLO threshold reinitiates the t D,UVLO and the startup period.
Latched and Autoretry Overcurrent Fault Management
The MAX5918L/MAX5919L latch the external MOSFETs off when an overcurrent fault is detected. Toggling ON below 0.875V or one of the supply voltages below/above the UVLO threshold for at least 100s clears the fault latch and reinitiates the startup period. Similarly, the MAX5918A/MAX5919A turn the external MOSFETs off when an overcurrent fault is detected, then automatically restart after the autoretry delay that is internally set to 64 times tSTART. During the autoretry delay, toggling ON below 0.875V does not clear the fault latch. The autoretry can be overridden, causing
Status Outputs (PGOOD_)
The status output is an open-drain output that pulls low in response to one of the following conditions: * Overcurrent fault * Output undervoltage/overvoltage fault PGOOD_ goes low when the corresponding channel is forced off (ON_ < 0.875V) (Table 1).
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
Table 1. Status Output Truth Table
PART OVERCURRENT FAULT (VOUT1) Yes X X X Yes X X X OVERCURRENT FAULT (VOUT2) X Yes X X X Yes X X OVER/UNDERVOLTAGE FAULT (VOUT1) X X Yes X X X Yes No OVER/UNDERVOLTAGE FAULT (VOUT2) X X X Yes X X No Yes PGOOD1/ PGOOD2 LOW/LOW LOW/LOW LOW/LOW LOW/LOW LOW/LOW LOW/LOW LOW/HIGH HIGH/LOW GATE1/ GATE2 OFF/OFF OFF/OFF OFF/OFF OFF/OFF OFF/OFF OFF/OFF ON/ON ON/ON
MAX5918 UV/OV Protection MAX5919 UV/OV Monitor
Applications Information
Component Selection
N-Channel MOSFET Select the external MOSFETs according to the application's current levels. Table 2 lists some recommended components. The MOSFET's on-resistance (RDS(ON)) should be chosen low enough to have a minimum voltage drop at full load to limit the MOSFET power dissipation. High RDS(ON) causes output ripple if there is a pulsating load. Determine the device power rating to accommodate a short-circuit condition on the board at startup and when the device is in automatic-retry mode (see the MOSFET Thermal Considerations section). Using the MAX5918L/MAX5919L in latched mode allows the use of MOSFETs with lower power ratings. A MOSFET typically withstands single-shot pulses with higher dissipation than the specified package rating. Table 3 lists some recommended manufacturers and components.
Sense Resistor The slow-comparator threshold voltage is adjustable from 25mV to 100mV. Select a sense resistor that causes a drop equal to the slow-comparator threshold voltage at a current level above the maximum normal operating current. Typically, set the overload current at 1.2 to 1.5 times the full load current. The fast-comparator threshold is four times the slow-comparator threshold in normal operating mode. Choose the sense resistor power rating to be greater than (IOVERLOAD)2 x VSC,TH. Slow-Comparator Threshold, RLIM The slow-comparator threshold voltage is adjustable from 25mV to 100mV, allowing designers to fine-tune the current-limit threshold for use with standard-value sense resistors. Low slow-comparator thresholds allow for increased efficiency by reducing the power dissipated by the sense resistor. Furthermore, the low 25mV slow-comparator threshold is beneficial when operating with supply rails down to 1V because it allows a small percentage of the overall output voltage to be used for current sensing. The VariableSpeed/BiLevel fault protection feature offers inherent system immunity against load transients and noise. This allows the slow-comparator threshold to be set close to the maximum normal operating level without experiencing nuisance faults. To adjust the slow-comparator threshold calculate RLIM as follows: V - 25mV RLIM = TH 0.25A where VTH is the desired slow-comparator threshold voltage. Setting the Startup Period, RTIM The startup period (tSTART) is adjustable from 0.4ms to 50ms. The adjustable startup period feature allows sys-
Table 2. Recommended N-Channel MOSFETs
PART NUMBER IRF7413 IRF7401 IRL3502S MMSF3300 MMSF5N02H MTB60N05H FDS6670A NDS8426A FDB8030L Fairchild Motorola International Rectifier MANUFACTURER DESCRIPTION 11m, 8 SO, 30V 22m, 8 SO, 20V 6m, D2PAK, 20V 20m, 8 SO, 30V 30m, 8 SO, 20V 14m, D PAK, 50V 10m, 8 SO, 30V 13.5m, 8 SO, 20V 4.5m, D2PAK, 30V
2
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
Table 3. Component Manufacturers
COMPONENT Sense Resistors IRC Fairchild MOSFETs International Rectifier Motorola MANUFACTURER Dale-Vishay PHONE 402-564-3131 704-264-8861 888-522-5372 310-233-3331 602-244-3576 WEBSITE www.vishay.com www.irctt.com www.fairchildsemi.com www.irf.com www.mot-sps.com/ppd
tems to be customized for MOSFET gate capacitance and board capacitance (CBOARD). The startup period is adjusted with the resistance connected from TIM to GND (RTIM). RTIM must be between 4k and 500k. The startup period has a default value of 9ms when TIM is left floating. Calculate RTIM with the following equation: t START RTIM = 128 x 800pF where tSTART is the desired startup period.
Case A: Slow Turn-On (without current limit) There are two ways to turn on the MOSFETs without reaching the fast-comparator current limit: * If the board capacitance (C BOARD) is small, the inrush current is low. * If the gate capacitance is high, the MOSFETs turn on slowly. In both cases, the turn-on time is determined only by the charge required to enhance the MOSFET. The small gate-charging current of 100A effectively limits the output voltage dV/dt. Connecting an external capacitor between GATE and GND extends turn-on time. The time required to charge/discharge a MOSFET is as follows: t= CGATE x VGATE + QGATE IGATE
Startup Sequence
There are two ways of completing the startup sequence. Case A describes a startup sequence that slowly turns on the MOSFETs by limiting the gate charge. Case B uses the current-limiting feature and turns on the MOSFETs as fast as possible while still preventing a high inrush current. The output voltage ramp-up time (tON) is determined by the longer of the two timings, case A and case B. Set the startup timer tSTART to be longer than tON to guarantee enough time for the output voltage to settle.
where: C GATE is the external gate to ground capacitance (Figure 4). VGATE is the change in gate voltage. QGATE is the MOSFET total gate charge. IGATE is the gate-charging/discharging current. In this case, the inrush current depends on the MOSFET gate-to-drain capacitance (Crss) plus any additional capacitance from GATE to GND (CGATE), and on any load current (ILOAD) present during the startup period. IINRUSH = CBOARD x IGATE + ILOAD Crss + CGATE
RSENSE VIN
VOUT CBOARD
RPULLUP IN_ SENSE GATE CGATE
PGOOD_
MAX5918 MAX5919
ON_ GND
Example: Charging and Discharging times using the Fairchild FDB7030L MOSFET If VIN1 = 5V then GATE1 charges up to 10.4V (VIN1 + VDRIVE), therefore VGATE = 10.4V. The manufacturer's data sheet specifies that the FDB7030L has approximately 60nC of gate charge and Crss = 600pF. The MAX5918/MAX5919 have a 100A gate-charging current and a 3mA strong discharging current.
Figure 4. Operating with an External Gate Capacitor ______________________________________________________________________________________ 11
Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
CBOARD = 6F and the load does not draw any current during the startup period. With no gate capacitor the inrush current, charge, and discharge times are: 6F IINRUSH = x 100A + 0 = 1A 600pF + 0 0 x 10.4V + 60nC t CHARGE = = 0.6ms 100A 0 x 10.4V + 60nC tDISCHARGE = = 0.02ms 3mA With a 22nF gate capacitor the inrush current, charge, and discharge times are: IINRUSH = 6F x 100A + 0 = 26.5mA 600pF + 22nF 22nF x 10.4V + 60nC t CHARGE = = 2.89ms 100A 22nF x 10.4V + 60nC tDISCHARGE = = 0.096ms 3mA
Using the MAX5918/MAX5919 on the Backplane
Using the MAX5918/MAX5919 on the backplane allows multiple cards with different input capacitance to be inserted into the same slot even if the card does not have on-board hot-swap protection. The startup period can be triggered if IN is connected to ON through a trace on the card (Figure 5).
Input Transients
The voltage at IN1 or IN2 must be above the UVLO during inrush and fault conditions. When a short-circuit condition occurs on the board, the fast comparator trips causing the external MOSFET gates to be discharged at 3mA. The main system power supply must be able to sustain a temporary fault current, without dropping below the UVLO threshold of 2.4V, until the external MOSFET is completely off. If the main system power supply collapses below UVLO, the MAX5918/ MAX5919 force the device to restart once the supply has recovered. The MOSFET is turned off in a very short time resulting in a high di/dt. The backplane delivering the power to the external card must have low inductance to minimize voltage transients caused by this high di/dt.
Case B: Fast Turn-On (with current limit) In applications where the board capacitance (CBOARD) is high, the inrush current causes a voltage drop across R SENSE that exceeds the startup fast-comparator threshold. The fast comparator regulates the voltage across the sense resistor to VSU,TH. This effectively regulates the inrush current during startup. In this case, the current charging CBOARD can be considered constant and the turn-on time is: t ON = CBOARD x VIN x RSENSE VSU,TH
MOSFET Thermal Considerations
During normal operation, the external MOSFETs dissipate little power. The MOSFET RDS(ON) is low when the MOSFET is fully enhanced. The power dissipated in normal operation is PD = ILOAD2 x RDS(ON). The most power dissipation occurs during the turn-on and turnoff transients when the MOSFETs are in their linear regions. Take into consideration the worst-case scenario of a continuous short-circuit fault, consider these two cases: 1) The single turn-on with the device latched after a fault (MAX5918L/MAX5919L) 2) The continuous automatic retry after a fault (MAX5918A/MAX5919A) MOSFET manufacturers typically include the package thermal resistance from junction to ambient (RJA) and thermal resistance from junction to case (RJC), which determine the startup time and the retry duty cycle (d = tSTART/tSTART + tRETRY). Calculate the required transient thermal resistance with the following equation:
-T T Z JA(MAX) JMAX A VIN x ISTART
The maximum inrush current in this case is: IINRUSH = VSU,TH RSENSE
Figure 2 shows the waveforms and timing diagrams for a startup transient with current regulation (see Typical Operating Characteristics). When operating under this condition, an external gate capacitor is not required.
ON Comparators
The ON comparators control the on/off function of the MAX5918/MAX5919. ON_ allows independent control over channel 1 and channel 2. Drive ON1 and ON2 high (> 0.875V) to enable channel 1 and channel 2, respectively. Pull ON_ low (< 0.875V) to disable the respective channel.
12
where ISTART = VSU,TH / RSENSE
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control
Layout Considerations
To take full tracking advantage of the switch response time to an output fault condition, it is important to keep all traces as short as possible and to maximize the high-current trace dimensions to reduce the effect of undesirable parasitic inductance. Place the MAX5918/ MAX5919 close to the card's connector. Use a ground plane to minimize impedance and inductance. Minimize the current-sense resistor trace length (< 10mm), and ensure accurate current sensing with Kelvin connections (Figure 6). When the output is short circuited, the voltage drop across the external MOSFET becomes large. Hence, the power dissipation across the switch increases, as does the die temperature. An 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 top side of the board (refer to the MAX5919 EV Kit).
MAX5918/MAX5919
Chip Information
TRANSISTOR COUNT: 3542 PROCESS: BiCMOS
Selector Guide
PART MAX5918AEEE MAX5918LEEE MAX5919AEEE MAX5919LEEE OUTPUT UNDERVOLTAGE/OVERVOLTAGE PROTECTION/MONITOR Protection Protection Monitor Monitor FAULT MANAGEMENT Autoretry Latched Autoretry Latched
BACKPLANE VIN
REMOVABLE CARD WITH NO HOT-INSERTION PROTECTION VOUT CBOARD
HIGH-CURRENT PATH
SENSE RESISTOR
IN_ SENSE_ GATE_ MAX5918 MAX5919 ON_
MAX5918 MAX5919
Figure 6. Kelvin Connection for the Current-Sense Resistors
Figure 5. Using the MAX5918/MAX5919 on a Backplane
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control MAX5918/MAX5919
Typical Operating Circuit
Q1 VIN1 * IN1 ON1 ON2 PGOOD1 PGOOD2 GND ON1 ON2 PGOOD1 PGOOD2 GND IN2 SENSE2 GATE2 LIM2 * VIN2 Q2 LIM1 * SENSE1 GATE1 MON1 * CBOARD1 VOUT1
MAX5918/ MAX5919
MON2 TIM *
* CBOARD2 * VOUT2 *OPTIONAL
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Low-Voltage, Dual Hot-Swap Controllers with Independent ON/OFF Control
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.)
QSOP.EPS
MAX5918/MAX5919
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 ____________________15 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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