19-3813; Rev 0; 9/05 KIT ATION EVALU E L B A IL AVA Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control The MAX5955 and MAX5956 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 MAX5955 and MAX5956 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 MAX5955 and MAX5956 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 MAX5955B and MAX5956B must be unlatched after a fault, and the MAX5955A and MAX5956A automatically restart after a fault. The MAX5955 and MAX5956 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 MAX5955 provides output undervoltage/overvoltage protection for each channel, while the MAX5956 provides undervoltage/overvoltage monitoring for each channel. The MAX5955 and MAX5956 are available in a spacesaving 16-pin QSOP package. 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 Ordering Information TEMP RANGE PIN-PACKAGE MAX5955AEEE PART -40C to +85C 16 QSOP MAX5955AEEE+ -40C to +85C 16 QSOP MAX5955AUEE 0C to +85C 16 QSOP MAX5955AUEE+ 0C to +85C 16 QSOP MAX5955BEEE -40C to +85C 16 QSOP MAX5955BEEE+ -40C to +85C 16 QSOP MAX5955BUEE 0C to +85C 16 QSOP MAX5955BUEE+ 0C to +85C 16 QSOP +Denotes lead-free package. Ordering Information continued at end of data sheet. Selector Guide and Typical Operating Circuit appear at end of data sheet. Pin Configuration TOP VIEW Applications PGOOD1 1 Base Station Line Cards Power-Supply Sequencing TIM 2 15 ON2 Network Switches, Routers, Hubs Hot Plug-In Daughter Cards IN1 3 14 IN2 Solid-State Circuit Breakers Portable Computer Device Bays (Docking Stations) RAID SENSE1 4 GATE1 5 16 PGOOD2 MAX5955 MAX5956 12 GATE2 GND 6 11 ON1 LIM1 7 10 LIM2 MON1 8 Variable Speed/BiLevel is a trademark of Maxim Integrated Products, Inc. 13 SENSE2 9 MON2 QSOP ________________________________________________________________ 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 MAX5955/MAX5956 General Description MAX5955/MAX5956 Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control ABSOLUTE MAXIMUM RATINGS Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.3mW/C above +70C)...........667mW Operating Temperature Range MAX59_ _ _U_ _ ...................................................0C to +85C MAX59_ _ _E_ _ ................................................-40C to +85C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C 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 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 = TMIN to TMAX, unless otherwise noted. Typical values are at VIN1 = +5V, VIN2 = +3.3V, and TA = +25C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS POWER SUPPLIES IN_ Input Voltage Range VIN Other VIN +2.7V Supply Current IIN IIN1 + IIN2, VIN1 = +5V, VIN2 = +3.3V 1.0 13.2 V 1.2 2.3 mA 25 27.5 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 VSC,TH LIM = GND TA = +25C 22.5 TA = -40C to +85C 20.5 RLIM = 300k tSCD 80 27.5 100 3 ms 10mV overdrive 110 s During startup 2 x VSC,TH VFC,TH VIN_ - VSENSE_; normal operation 4 x VSC,TH IB SENSE 130 1mV overdrive VSU,TH tFCD mV 10mV overdrive, from overload condition 260 VSENSE_ = VIN_ 0.03 mV ns 1 A MOSFET DRIVER RTIM = 100k Startup Period (Note 4) Average Gate Current Gate-Drive Voltage tSTART IGATE VDRIVE 6 10.8 16 0.31 0.45 0.58 TIM floating 4 9 17 Charging, VGATE_ = +5V, VIN_ = +10V (Note 5) 65 100 130 RTIM = 4k (minimum value) Discharging, triggered by a fault or when VON_ < 0.875V VGATE_ - VIN_, IGATE_ < 1A 3 ms A mA VIN_ = 3V to 13.2V 4.8 5.4 6.0 VIN_ = 2.7V to 3.0V 4.1 5.0 6.0 0.85 0.875 0.90 V ON_ COMPARATOR ON_ Threshold ON_ Propagation Delay 2 VON_,TH Low to high V Hysteresis 25 mV 10mV overdrive 50 s _______________________________________________________________________________________ Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control (VIN_ = +1V to +13.2V provided at least one supply is higher than +2.7V, VON1 = VON2 = +2.7V, TA = TMIN to TMAX, unless otherwise noted. Typical values are at VIN1 = +5V, VIN2 = +3.3V, and TA = +25C.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN VON_ < 4.5V ON_ Input Bias Current ON_ Pulse-Width Low IBON tUNLATCH VIN1 = VIN2 = +13.2V TYP UNITS 0.03 VON_ > 4.5V 100 VON_ = 4.5V 0.03 To unlatch after a latched fault MAX A 1 100 s DIGITAL OUTPUT (PGOOD_) Output Leakage Current VPGOOD_ = 13.2V Output Voltage Low VOL PGOOD_ Delay tPGDLY 1 ISINK = 1mA 0.4 After tSTART, MON_ = VIN_ 0.75 A V ms OUTPUT VOLTAGE MONITORS (MON1, MON2) MON_ Trip Threshold VMON Overvoltage 657 687 707 Undervoltage 513 543 563 MON_ Glitch Filter MON_ Input Bias Current VMON_ = 600mV mV 20 s 0.03 A UNDERVOLTAGE LOCKOUT (UVLO) UVLO Threshold VUVLO Startup is initiated when this threshold is reached by VIN1 or VIN2, VON_ > 0.875V 2.10 Hysteresis UVLO to Startup Delay 2.67 100 VIN_ toggled below UVLO to unlatch after a fault 100 tD,UVLO VIN_ step from 0 to 2.8V 20 tRETRY Delay time to restart after fault shutdown UVLO Glitch Filter Reset Time 2.4 V mV s 37.5 66 ms SHUTDOWN LATCH/RESTART Autoretry Delay 64 x tSTART ms Note 1: All devices are 100% tested at TA = +25C and TA = +85C. Limits at TA = 0C and -40C are guaranteed by design. Note 2: The MAX5955/MAX5956 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). _______________________________________________________________________________________ 3 MAX5955/MAX5956 ELECTRICAL CHARACTERISTICS (continued) 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.) 1.8 1.6 IINX + IINY IIN (mA) 1.0 IINX 0.8 B 1.0 0.2 0 0 2 4 6 8 10 12 14 0.2 2 4 6 8 10 12 -40 14 10 35 60 TEMPERATURE (C) GATE-DRIVE VOLTAGE vs. INPUT VOLTAGE GATE CHARGE CURRENT vs. GATE VOLTAGE GATE CHARGE CURRENT vs. TEMPERATURE 2 1 160 140 VINX = 13.2V 120 VINX = 5V 100 VINX = 1V 80 60 40 200 180 20 VINY = 2.7V 2 4 6 8 10 12 5 10 15 VGATEX (V) GATE STRONG DISCHARGE CURRENT vs. GATE VOLTAGE GATE STRONG DISCHARGE CURRENT vs. TEMPERATURE 3 VON1 = VON2 = 0 2 VINX = 1V VINY = 2.7V VGATEX = VINX + 6.2V 5 10 VGATEX (V) 15 20 80 VINX = 1V 60 40 VINY = 2.7V VGATEX = 0 VINX = 13.2V VINX = 5V 4 -15 10 35 60 85 TURN-OFF TIME vs. SENSE VOLTAGE VON1 = VON2 = 0 VINY = 2.7V VGATEX = VINX + 6.2V 2 10 SLOW-COMP. THRESHOLD 1 FAST-COMP. THRESHOLD 0.1 0.01 0.001 1 VINX = 1V 0 0 100 -40 MAX5955/56 toc08 5 3 VINX = 5V 120 20 TURN-OFF TIME (ms) 4 140 TEMPERATURE (C) 6 GATE DISCHARGE CURRENT (mA) VINX = 13.2V VINX = 5V 5 MAX5955/56 toc07 VINX (V) 6 VINX = 13.2V 0 0 14 160 20 0 0 85 MAX5955/56 toc06 VINY = 2.7V 180 GATE CHARGE CURRENT (A) 3 200 MAX5955/56 toc05 MAX5955/56 toc04 4 0 -15 VINX (V) 5 1 IIN2 0.4 VINX (V) 6 0 IIN1 0 0 GATE CHARGE CURRENT (A) 0 1.0 0.6 VINY = 5.0V A) VON1 = VON2 = 3.3V B) VON1 = VON2 = 1.5V C) VON1 = VON2 = 0 0.4 0.2 1.2 0.8 0.6 IINY 0.4 GATE-DRIVE VOLTAGE (V) C 1.2 0.8 0.6 4 1.4 1.4 1.2 IIN1 + IIN2 1.6 IIN (mA) 1.4 A VON1 = VIN1 VON2 = VIN2 1.8 MAX5955/56 toc09 1.6 2.0 MAX5955/56 toc02 VINY = VON1 = VON2 = 2.7V 1.8 IIN (mA) 2.0 MAX5955/56 toc01 2.0 SUPPLY CURRENT vs. TEMPERATURE TOTAL SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX5955/56 toc03 SUPPLY CURRENT vs. SUPPLY VOLTAGE GATE DISCHARGE CURRENT (mA) MAX5955/MAX5956 Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control 0.0001 -40 -15 10 35 TEMPERATURE (C) 60 85 0 25 50 75 100 125 150 175 200 VIN - VSENSE (mV) _______________________________________________________________________________________ Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control SLOW-COMPARATOR THRESHOLD vs. RLIM STARTUP PERIOD vs. RTIM 100 1 50 40 80 tSTART (ms) SLOW-COMP. THRESHOLD 60 MAX5955/56 toc11 MAX5955/56 toc10 120 VSC,TH (mV) TURN-OFF TIME (ms) 10 60 30 40 20 20 10 0 0 0.1 0 20 25 30 35 40 45 50 55 60 65 70 75 80 MAX5955/56 toc12 TURN-OFF TIME vs. SENSE VOLTAGE (EXPANDED SCALE) 100 200 300 0 400 100 200 300 400 500 VIN - VSENSE (mV) RLIM (k) RTIM (k) TURN-OFF TIME SLOW-COMPARATOR FAULT TURN-OFF TIME FAST-COMPARATOR FAULT STARTUP WAVEFORMS FAST TURN-ON MAX5955/56 toc15 MAX5955/56 toc14 MAX5955/56 toc13 600 VON 2V/div 0 VPGOOD 5V/div tSCD VPGOOD 5V/div 0 tFCD VPGOOD 2V/div 0 0 IOUT 5A/div 125mV STEP 26mV STEP VSENSE - VIN 100mV/div VSENSE - VIN 100mV/div VGATE 5V/div VGATE 5V/div 0 VOUT 5V/div VGATE 5V/div 0 400ns/div VIN = 5.0V 1ms/div VIN = 5.0V STARTUP WAVEFORMS SLOW TURN-ON 1ms/div VIN = 5.0V, RSENSE = 10m, RTIM = 27k, CBOARD = 1000F AUTORETRY DELAY MAX5955/56 toc17 MAX5955/56 toc16 VON 2V/div VGATE 5V/div VPGOOD 2V/div IOUT 5A/div VOUT 5V/div VOUT 5V/div IOUT 5A/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 _______________________________________________________________________________________ 5 MAX5955/MAX5956 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.) Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control MAX5955/MAX5956 Pin Description PIN 1 NAME FUNCTION Channel 1 Status Output (Open Drain, see the 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. 2 TIM 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. 3 IN1 Channel 1 Supply Input. Connect to a supply voltage of 1V to 13.2V. 4 SENSE1 5 GATE1 6 GND Ground 7 LIM1 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). 8 MON1 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. 9 MON2 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. 10 LIM2 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). 11 ON1 Channel 1 On/Off Control Input. Channel 1 is turned on when VON1 > 0.875V. 12 GATE2 Channel 2 Gate-Drive Output. Connect to the gate of an external n-channel MOSFET. 13 SENSE2 Channel 2 Current-Sense Input. Connect RSENSE2 from IN2 to SENSE2. Connect to IN2 to disable circuitbreaker function of channel 2. 14 IN2 Channel 2 Supply Input. Connect to a supply voltage of 1V to 13.2V. 15 ON2 Channel 2 On/Off Control Input. Channel 2 is turned on when VON2 > 0.875V. 16 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 the gate of an external n-channel MOSFET. Channel 2 Status Output (Open Drain, see the 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 MAX5955 and MAX5956 are circuit breaker ICs for hot-swap applications where a line card is inserted into a live backplane. The MAX5955 and MAX5956 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 MAX5955 and MAX5956 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 6 on-chip comparators. The startup period and currentlimit threshold of the MAX5955/MAX5956 can be adjusted with external resistors. Figure 1 shows the MAX5955/MAX5956 functional diagram. The MAX5955/MAX5956 pull both PGOODs low and both external FETs off for an overcurrent condition. The MAX5955 also pulls both PGOODs low and both external FETs off (protection) for an undervoltage/overvoltage fault, whereas, the MAX5956 ONLY pulls the corresponding fault channel's PGOOD_ low (monitoring). When the overvoltage/undervoltage fault disappears on the MAX5956, the corresponding PGOOD_ automatically goes high impedance. _______________________________________________________________________________________ OUT1 Q1 RSENSE1 MON1 GATE1 SENSE1 IN1 3mA VSC, TH CHARGE PUMP VFS, TH 543mV 687mV RTIM TIM STARTUP OSCILLATOR TO STARTUP LOGIC BLOCKS ON2 0.875V UVLO CURRENT CONTROL AND STARTUP LOGIC SLOW COMP. FAST COMP. FAST DISCHARGE LIM1 ON1 2.4V PGOOD1 DEVICE CONTROL LOGIC TIMING OSCILLATOR BIAS AND REFERENCES 2.4V N PGOOD2 CHARGE-PUMP OSCILLATOR TO STARTUP LOGIC BLOCKS CHARGE PUMP 543mV 687mV 100A FAST DISCHARGE SLOW COMP. FAST COMP. CURRENT CONTROL AND STARTUP LOGIC UVLO VFS, TH MAX5955 MAX5956 LIM2 RLIM2 3mA VSC, TH MON2 GATE2 SENSE2 IN2 Q2 OUT2 RSENSE2 MAX5955/MAX5956 RLIM1 Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control Figure 1. Functional Diagram _______________________________________________________________________________________ 7 Startup Period RTIM sets the duration of the startup period from 0.45s 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 MAX5955/MAX5956 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 MAX5955/MAX5956 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 MAX5955B and MAX5956B stay latched off and the MAX5955A and MAX5956A 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. ON PGOOD SLOW COMPARATOR tSTART + tPGDLY VGATE 4.3V TO 5.8V VOUT VTH VGATE VOUT 3ms TURN-OFF TIME MAX5955/MAX5956 Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control FAST COMPARATOR 110s CBOARD = LARGE VSU,TH 260ns RSENSE CBOARD = 0 VSC,TH ILOAD tON Figure 2. Startup Waveform 8 VFC,TH (4 x VSC,TH) SENSE VOLTAGE (VIN - VSENSE) Figure 3. VariableSpeed/BiLevel Response _______________________________________________________________________________________ Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control 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). Undervoltage Lockout (UVLO) The UVLO prevents the MAX5955/MAX5956 from turning on the external MOSFETs until one input voltage exceeds the UVLO threshold (2.4V) for tD,UVLO. The MAX5955/ MAX5956 use power from the higher input voltage rail for the charge pumps. This allows for more efficient chargepump 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 tD,UVLO and the startup period. Latched and Autoretry Overcurrent Fault Management The MAX5955B/MAX5956B 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 MAX5955A/MAX5956A 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 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. Output Overvoltage/Undervoltage Fault Management The MAX5955/MAX5956 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 MAX5955 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 MAX5955A, 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 MAX5955B, 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 MAX5956 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 MAX5956 does not allow an output overvoltage/undervoltage fault to disrupt operation by shutting down the channels. The MAX5956'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 MAX5955/MAX5956 can be disabled by connecting VIN1 to MON1 and VIN2 to MON2. 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). _______________________________________________________________________________________ 9 MAX5955/MAX5956 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 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 MAX5955/MAX5956 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. MAX5955/MAX5956 Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control Table 1. Status Output Truth Table PART OVERCURRENT FAULT (VOUT1) OVERCURRENT FAULT (VOUT2) OVER/UNDERVOLTAGE FAULT (VOUT1) OVER/UNDERVOLTAGE FAULT (VOUT2) PGOOD1/ PGOOD2 GATE1/ GATE2 Yes X X X Yes X X X X Yes X X X Yes X X X X Yes X X X Yes No X X X Yes X X No Yes Low/Low Low/Low Low/Low Low/Low Low/Low Low/Low Low/High High/Low Off/Off Off/Off Off/Off Off/Off Off/Off Off/Off On/On On/On MAX5955 UV/OV Protection MAX5956 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 MAX5955B/MAX5956B 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. Table 2. Recommended n-Channel MOSFETs PART NUMBER MANUFACTURER IRF7413 IRF7401 11m, 8 SO, 30V International Rectifier IRL3502S 22m, 8 SO, 20V 20m, 8 SO, 30V Motorola 30m, 8 SO, 20V MTB60N05H 14m, D2PAK, 50V FDS6670A 10m, 8 SO, 30V NDS8426A FDB8030L 10 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: 6m, D2PAK, 20V MMSF3300 MMSF5N02H DESCRIPTION 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. Fairchild V - 25mV RLIM = TH 0.25A where VTH is the desired slow-comparator threshold voltage. 13.5m, 8 SO, 20V 4.5m, D2PAK, 30V ______________________________________________________________________________________ Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control COMPONENT MANUFACTURER Dale-Vishay Sense Resistors MOSFETs IRC 704-264-8861 www.irctt.com 888-522-5372 www.fairchildsemi.com International Rectifier 310-233-3331 www.irf.com Motorola 602-244-3576 www.mot-sps.com/ppd t START 128 x 800pF where tSTART is the desired startup period. 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. 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= WEBSITE www.vishay.com Fairchild Setting the Startup Period, RTIM The startup period (tSTART) is adjustable from 0.45ms to 50ms. The adjustable startup period feature allows systems 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: RTIM = PHONE 402-564-3131 CGATE x VGATE + QGATE IGATE 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 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 MAX5955/MAX5956 have a 100A gate-charging current and a 3mA strong discharging current. RSENSE VOUT VIN CBOARD 0.1F RPULLUP IN_ PGOOD_ SENSE GATE CGATE MAX5955 MAX5956 ON_ * GND * REQUIRED COMPONENTS. SEE THE ON_ COMPARATORS SECTION. Figure 4. Operating with an External Gate Capacitor ______________________________________________________________________________________ 11 MAX5955/MAX5956 Table 3. Component Manufacturers MAX5955/MAX5956 Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control 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 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 IINRUSH = With a 22nF gate capacitor the inrush current, charge, and discharge times are: 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 IINRUSH = 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 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 MAX5955/MAX5956. 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. An RC time delay must be added to the ON_ inputs with delay set to at least 20s. This 12 allows the internal circuits to stabilize after application of a steeply rising VIN_. Using the MAX5955/MAX5956 on the Backplane Using the MAX5955/MAX5956 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 MAX5955/MAX5956 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. 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 (MAX5955B/MAX5956B) 2) The continuous automatic retry after a fault (MAX5955A/MAX5956A) 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: Z JA(MAX) TJMAX - TA VIN x ISTART where ISTART = VSU,TH / RSENSE ______________________________________________________________________________________ Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control BACKPLANE VIN REMOVABLE CARD WITH NO HOT-INSERTION PROTECTION VOUT HIGH-CURRENT PATH CBOARD 0.1F IN_ 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 MAX5956 EV Kit data sheet). SENSE RESISTOR SENSE_ GATE_ MAX5955 MAX5956 ON_ * * * MAX5955 MAX5956 * REQUIRED COMPONENTS. SEE THE ON_ COMPARATORS SECTION. Figure 6. Kelvin Connection for the Current-Sense Resistors Figure 5. Using the MAX5955/MAX5956 on a Backplane Selector Guide OUTPUT UNDERVOLTAGE/OVERVOLTAGE PROTECTION/MONITOR FAULT MANAGEMENT Protection Autoretry MAX5955AUEE Protection Autoretry MAX5955BEEE Protection Latched MAX5955BUEE Protection Latched MAX5956AEEE Monitor Autoretry MAX5956AUEE Monitor Autoretry MAX5956BEEE Monitor Latched MAX5956BUEE Monitor Latched PART MAX5955AEEE ______________________________________________________________________________________ 13 MAX5955/MAX5956 Layout Considerations To take full 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 resistance and inductance. Place the MAX5955/ MAX5956 close to the card's connector, and a 0.01F capacitor to GND should be placed as close as possible to each VIN pin. 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). Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control MAX5955/MAX5956 Typical Operating Circuit Q1 VOUT1 VIN1 0.1F * IN1 ON1 * ON1 SENSE1 GATE1 CBOARD1 * * * ON2 ON2 MON1 * PGOOD1 PGOOD1 PGOOD2 PGOOD2 GND MAX5955 MAX5956 IN2 * MON2 GND SENSE2 GATE2 LIM2 LIM1 * * CBOARD2 TIM * * VIN2 VOUT2 Q2 0.1F *OPTIONAL * REQUIRED COMPONENTS. SEE THE ON_ COMPARATORS SECTION. Ordering Information (continued) PART TEMP RANGE PIN-PACKAGE MAX5956AEEE -40C to +85C 16 QSOP MAX5956AEEE+ -40C to +85C 16 QSOP 0C to +85C 16 QSOP MAX5956AUEE MAX5956AUEE+ 0C to +85C 16 QSOP MAX5956BEEE -40C to +85C 16 QSOP MAX5956BEEE+ -40C to +85C 16 QSOP MAX5956BUEE 0C to +85C 16 QSOP MAX5956BUEE+ 0C to +85C 16 QSOP Chip Information TRANSISTOR COUNT: 3542 PROCESS: BiCMOS +Denotes lead-free package. 14 ______________________________________________________________________________________ Low-Voltage, Dual Hot-Swap Controllers with Independent On/Off Control 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) 2005 Maxim Integrated Products Quijano Printed USA is a registered trademark of Maxim Integrated Products, Inc. MAX5955/MAX5956 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.)