LM5068 LM5068 Negative Voltage Hot Swap Controller Literature Number: SNVS254B LM5068 Negative Voltage Hot Swap Controller General Description Features The LM5068 hot-swap controller provides intelligent control of power supply connections during the insertion and removal of circuit cards powered by live system backplanes. n Safe module insertion and removal from live backplanes n In-rush current limiting for safe board insertion into live backplanes n Fast response to over-current fault conditions with active current limiting n -10V to -90V input range n Programmable under-voltage/over-voltage shutdown protection with adjustable hysteresis n Programmable multi-function timer for board insertion de-bounce delay n Fault timer avoids nuisance trips caused by short duration load transients n Active gate clamping during initial power application n Available in both latched fault and automatic re-try versions n Available with either active HIGH or active LOW power good flag The LM5068 provides both in-rush current control and shortcircuit protection functions, and limits power supply transients in the backplane caused by the insertion of additional circuit cards. The LM5068 controls the external N-Channel MOSFET to provide programmable load current limiting and circuit breaker functions using a single external current sense resistor. The LM5068 issues a power good (PWRGD) signal at the conclusion of a successful power-on sequence. Input over-voltage or under -voltage fault conditions will cancel the PWRGD indication. The LM5068-1 and -2 indicate power-good as an open-drain active HIGH PWRGD state. The LM5068-3 and -4 indicate power-good as an open-drain active LOW PWRGD state. The LM5068-1 and -3 latch off after a fault condition is detected while the LM5068-2 and -4 continuously re-try at intervals set by a programmable timer. The LM5068 is available in a MSOP-8 package. Applications n n n n n n - 48V Power Modules Central Office Switching Distributed Power Systems Electronic Circuit Breaker PBX Systems Negative Power Supply Control Typical Application 20078601 Negative Power Supply Control (c) 2004 National Semiconductor Corporation DS200786 www.national.com LM5068 Negative Voltage Hot Swap Controller December 2004 LM5068 Connection Diagram 20078602 Pin Description PIN NAME 1 PWRGD 2 3 DESCRIPTION APPLICATION INFORMATION Open Drain Power Good indicator Following a successful power-up sequence the PWRGD signal will be active. The LM5068-1 and -2 are configured for an active power-good state as HIGH, while the LM5068-3 and -4 are configured for an active power-good state as LOW. OV Line Over-Voltage Shutdown An external resistor divider from the power source sets the over-voltage shutdown level. Hysteresis is generated by an internal current source which sources 20 A into the external divider when the OV pin exceeds 2.5V. UV Line Under-Voltage Shutdown An external resistor divider from the power source sets the under-voltage shutdown level. Hysteresis is set by an internal current source which sinks 20 A from the external divider when the UV pin falls below 2.5V. 4 VEE 5 SENSE 6 Negative Supply Voltage Input Current Sense Input Load current is monitored via an external current sense resistor (Rs). If the voltage across Rs exceeds 50mV the fault timer is initiated. Load current is actively limited to 100mV/Rs. If the sense voltage exceeds 200mV due to a catastrophic fault, the fast gate pull down circuit will reduce the MOSFET gate voltage and initiate active current limiting. GATE N-Channel MOSFET Gate Drive Output This output is pulled high by a 60 A current source to turn on the MOSFET. 7 TIMER Timer Input An external capacitor connected to this pin sets the initial start-up delay and the delay to shutdown in the event of an over-current condition. This pin is also used for the automatic re-try timing sequence, following fault shutdown (-2 and -4 versions). 8 VDD www.national.com Positive Supply Voltage Input 2 Latch Off /Successive Re-try Power Good Polarity Package LM5068MM-1/MMX-1 Part Number Latch Off Active HIGH MSOP- 8 LM5068MM-2/MMX-2 Auto Re-try Active HIGH LM5068MM-3/MMX-3 Latch Off Active LOW LM5068MM-4/MMX-4 Auto Re-try Active LOW Ordering Information Order Number Package Marking NSC Package Drawing Supplied As LM5068MM-1 S66B Available Soon LM5068MMX-1 S66B Available Soon LM5068MM-2 S67B 1000 Units on Tape and Reel LM5068MMX-2 S67B LM5068MM-3 S68B LM5068MMX-3 S68B 3500 Units on Tape and Reel LM5068MM-4 S69B 1000 Units on Tape and Reel LM5068MMX-4 S69B 3500 Units on Tape and Reel MUA08A 3 3500 Units on Tape and Reel 1000 Units on Tape and Reel www.national.com LM5068 Configuration Table LM5068 Absolute Maximum Ratings (Note 1) Junction Temperature (TJ) +150C If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Storage Temperature (TS) -55C to +150C VDD (VDD to VEE) 100V PWRGD (PWRGD to VEE) 100V SENSE (SENSE to VEE) 8V UV/OV (Clamped) (UV/OV to VEE) 8V All Other Inputs to VEE Soldering Information ESD Rating (Note 2) 2kV Operating Ratings 16V Supply Voltage Range (VDD) 10V to 90V Junction Temp. Range -40C to +105C Electrical Characteristics Specifications in standard typeface are for TJ = +25C, and those in boldface type apply over the full operating junction temperature range. Unless otherwise noted VDD - VEE = 48V. Symbol Parameter Conditions Min Typ Max Units 0.82 1.3 mA 580 1000 A 90 V VDD Supply IIN Supply Current ISD Shutdown Current VDD - VEE Operating Supply Range UV/OV = 0V 10 UV/OV Shutdown VUVS VDD Under-voltage Shutdown 8.5 V VUVSH VDD Under-voltage Shutdown Hysteresis 0.6 V VUV Under-voltage Comparator Threshold IUVHCS 2.45 2.5 2.55 V Under-voltage Hysteresis Current Source 18 20 22 A VOV Over-voltage Comparator Threshold 2.45 2.5 2.55 V IOVHCS Over-voltage Hysteresis Current Sink 18 20 22 A tUVCD UV Comparator Delay UV Low to Gate Low 1100 ns tOVCD OV Comparator Delay OV High to Gate Low 500 ns Current Limit Voltage VCB Circuit Breaker Current Limit Voltage 40 50 60 mV VAC Analog Current Limit Voltage 80 100 120 mV VFDC Fast Discharge Current Limit Voltage (Fast Gate Pull Down Threshold) 150 200 250 mV -30 -15 A V Sense Input ISENSE Sense Input Current VSENSE = 50mV Timer VTHVT Timer High Voltage Threshold 4 VTLVT Timer Low Voltage Threshold 1 ITIMER Timer On (Initial Cycle, Sourcing) VTIMER = 2V 4 6 Timer Off (Initial Cycle, Sinking) VTIMER = 2V www.national.com V 8 27 A mA Timer On (Circuit Breaker, Sourcing) VTIMER = 2V 200 240 280 A Timer Off (Cooling Cycle, Sinking) VTIMER = 2V 4 6 8 A 4 (Continued) Specifications in standard typeface are for TJ = +25C, and those in boldface type apply over the full operating junction temperature range. Unless otherwise noted VDD - VEE = 48V. Symbol Parameter Conditions Min Typ Max Units 9 10.6 12 V Gate Drive VG Saturation Gate Drive Voltage VDD- VEE = 48V VDD- VEE = 10V 7.8 V VGLT Gate Low Threshold Before Gate ramp-up IGATE Gate Pin Current (Sourcing) VSENSE = 0V Gate Pin Current (Sinking) VSENSE = 150mV VGATE = 3V 2.7 mA Gate Pin Current (Sinking) VSENSE = 300mV VGATE = 1V 300 mA 0.2 0.5 40 60 V 80 A PWRGD VPGLV PWRGD Low Voltage ISINK = 1mA IPGLC PWRGD High Leakage Current VPWRGD = 90V VPGV GATE Voltage at onset of PWRGD 0.6 V 1 A 8 V Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics. Note 2: The ESD rating of Pin 7 is 1.5kV. It is recommended that proper ESD precautions are taken to avoid performance degradation or loss of functionality. 5 www.national.com LM5068 Electrical Characteristics LM5068 Block Diagram 20078603 www.national.com 6 LM5068 Typical Performance Characteristics IIN vs Temperature IIN vs VDD 20078633 20078632 VDD Under-Voltage Shutdown Hysteresis (VUVSH) vs Temperature VDD Under-Voltage Shutdown (VUVS) vs Temperature 20078635 20078634 Under-Voltage Comparator Threshold (VUV) and Over-Voltage Comparator Threshold (VOV) vs Temperature Under-Voltage Comparator Threshold Hysteresis Current Source (IUVHCS) vs Temperature 20078636 20078637 7 www.national.com LM5068 Typical Performance Characteristics (Continued) Over-Voltage Comparator Threshold Hysteresis Current Sink (IOVHCS) vs Temperature UV Comparator Delay (tUVCD) and OV Comparator Delay (tOVCD) vs Temperature 20078638 20078639 Circuit Breaker Current Limit Voltage (VCB) vs Temperature Analog Current Limit Voltage (VAC) vs Temperature 20078640 20078641 Fast Discharge Current Limit Voltage (VFDC) vs Temperature Timer High Voltage Threshold (VTHVT) vs Temperature 20078642 www.national.com 20078643 8 (Continued) Timer Low Voltage Threshold (VTLVT) vs Temperature Timer On (Initial Cycle, Sourcing) vs Temperature 20078644 20078645 Timer On (Circuit Breaker, Sourcing) vs Temperature Timer Off (Cooling Cycle, Sinking) vs Temperature 20078647 20078648 Saturation Gate Drive Voltage (VG) vs Temperature (48V) Saturation Gate Drive Voltage (VG) vs Temperature 20078650 20078649 9 www.national.com LM5068 Typical Performance Characteristics LM5068 Typical Performance Characteristics (Continued) Gate Pin Current (Sourcing) (IGATE) vs Temperature PWRGD Low Voltage (VPGLV) vs Temperature 20078655 20078652 Gate Voltage at onset of PWRGD (VPGV) vs Temperature 20078656 www.national.com 10 LM5068 Function Description The LM5068 is designed to facilitate the insertion and removal of circuit cards into live backplanes in a controlled manner. Because the supply bypass capacitors on the circuit card can draw large transient currents, it is critical to control the supply current during insertion to limit system power glitches and connector damage. Controlling in-rush current prevents other boards in the system from resetting during board insertion. Load short-circuit protection is accomplished by active current limiting of the load current. The topology of the LM5068 is illustrated in the simplified application circuit shown in Figure 1. 20078605 FIGURE 2. Hot Swap Controller Over and Under-Voltage Lockout 20078604 The line Under-voltage lockout (UVLO) circuitry of the LM5068 monitors VDD for under-voltage conditions, where VUVS is the negative going threshold and the hysteresis is VUVSH (see Electrical Characteristics). A VDD - VEE voltage less than 8.5V (VUVS) keeps the controller in a disabled mode. Raising the VDD voltage above 9.1V (VUVS + VUVSH) releases the VDD UVLO and enables the controller. In addition to the internal UVLO circuit, the UV and OV comparators monitor the input line voltage through an external resistor divider. Programmable UV and OV comparator hysteresis is implemented with switched 20A current sources that raise or lower the OV and UV pins when the comparators reach their threshold. Either UV or OV fault conditions will switch the GATE pin low and disconnect the power to the load. To restart the GATE pin, the supply voltage must return to a level which is greater than the UV fault and less than the OV fault threshold and all of the interlock conditions (with the exception of the TIMER) must be met. Removal of the circuit card from the backplane initiates an under-voltage condition. The series MOSFET is then disabled to disconnect the source of power to the load. The under-voltage threshold and hysteresis are programmed by the external resistor divider connected to the UV pin. FIGURE 1. LM5068 Topology Start-Up Operation The LM5068 resides on a removable circuit card. Power is applied to the load or power conversion circuitry through an external N-Channel MOSFET switch and current sense resistor. When power is initially applied to the card, the gate of the external MOSFET is held low. When certain interlock conditions are met, a turn-on sequence begins and an internal 60 A current source charges the gate of the MOSFET. To initiate the start-up sequence, all of the following interlock conditions must be satisfied: * The input voltage VDD - VEE exceeds 9V(VUVS) * The voltage at UV is above 2.5V (VUV) * The voltage at OV falls below 2.5V (VOV) * The voltage on the Timer capacitor (CT) is less than 1V (VTLVT) * The GATE pin is below 0.5V (VGLT) When all of the interlock conditions are met, a 6 A TIMER current source is enabled to charge the timer capacitor CT. During this initial timer sequence the GATE output is held low. When the CT capacitor successfully charges up to 4V, the TIMER circuit resets the timer capacitor to 1V and activates a 60 A current source (IGATE) into the MOSFET gate. Timer The value of the CT capacitor sets the duration of the LM5068's timer delay and filter functions. There are four charging and discharging modes: 1. 6A slow charge for initial timing delay and post-fault re-try timer (LM5068-2 and -4) 2. 240A fast charge for circuit breaker delay. 3. 6A slow discharge for circuit breaker "cool-off". 4. Low impedance switch to reset capacitor after initial timing delay, input under-voltage lockout, and during over-voltage and under-voltage initial timing. Current Control The LM5068 has three current sense thresholds which protect the backplane supply and circuit card from overload 11 www.national.com LM5068 Current Control current source. If the fault condition persists, the LM5068 will again turn off the MOSFET and another 8-cycle fault timer sequence will begin. (Continued) conditions. The voltage drop across the sense resistor (RS) is monitored at the SENSE pin. The over-current protection functions are determined through the following three distinct thresholds at the SENSE pin: 1. Circuit Breaker (CB) threshold (typically 50mV) Power Good Flag The power good flag (PWRGD) is activated when the MOSFET GATE is fully enhanced ( > 8V) and the voltage input UV and OV comparators are satisfied. The power good output is a 90V capable open drain N-Channel MOSFET. The LM5068-1 and LM5068-2 provide an active HIGH powergood state, while the LM5068-3 and LM5068-4 are configured for an active LOW power-good state. The UV comparator, OV comparator, VDD UVLO, or a circuit breaker time-out will reset the power good flag. 2. Analog Current Limit (ACL) loop threshold (typically 100mV) 3. Fast Discharge Current (FDC) threshold (typically 200mV) When the voltage drop across RS exceeds 50mV the Circuit Breaker comparator indicates an over-load condition. The TIMER sources 240A into CT when SENSE exceeds 50mV and sinks 6A from CT when SENSE falls below 50mV. If the CT capacitor ramps to a 4V threshold, a fault condition is declared and the gate of the MOSFET is forced low, disconnecting the power to the load. Internal Soft-Start An internal soft-start feature ramps the (positive) input of the analog current limit amplifier during initial start-up. The ramp duration is approximately 200s. This feature reduces the load current slew rate (di/dt) at start-up. Active Current Limiting (ACL) is activated when the voltage across sense resistor RS reaches 100mV. The LM5068 controls the gate of the MOSFET and maintains a constant output load current equal to 100mV/ RS. In the ACL mode the SENSE pin is greater than 50mV and the TIMER charges CT with 240A. A fault will be declared if the LM5068 remains in the ACL mode longer than the circuit breaker timer period. Design Information The LM5068 contains an internal regulator enabling the VDD pin to be connected directly to the line voltage from 10 to 90V. A local RC filter (0.1F ceramic capacitor and 499 resistor) connected between VDD and VEE is recommended to filter supply transients that exceed the 100V Absolute Maximum Rating. Fast Discharge Current (FDC) responds to fast rising overloads such as short circuit faults. During a short circuit event the fast rising current may overshoot past the ACL threshold due to the finite response time of the ACL loop. If the SENSE voltage reaches 200mV a fast discharge comparator quickly pulls GATE pin low. The rapid response of the FDC circuit assures a fast and safe transition to the ACL mode. The LM5068 circuit breaker action filters low duty cycle over-load conditions to avoid declaring a fault during short duration load transients. The timer charges capacitor CT with 240A when the SENSE voltage is greater than 50mV. When the SENSE pin voltage falls below 50mV, a 6A current discharges the TIMER capacitor. Repetitive over-current faults with duty cycle greater than 2.5% will eventually charge CT and trip the fault timer. This feature protects the pass MOSFET which has a fast heating and slow cooling characteristic. UV and OV Thresholds and Voltage Divider Selection for R1, R2, and R3 Two comparators detect under-voltage and over-voltage conditions at the UV and OV pins. The threshold voltages (VUV , VOV) of the UV and OV comparators are nominally 2.5V. Hysteresis is accomplished by 20A current sources (IUVHCS), into the external resistor divider connected to the UV and OV pins as shown in Figure 3 Latch-Off and Auto-Retry If the fault conditions persist long enough for TIMER to charge CT to 4V, the LM5068 latches off (LM5068-1, -3) or switches off and initiates the re-try timer (LM5068-2, -4). At the fault condition, after reaching the 4V, the TIMER pin will continue to ramp-up with 6A current source until it reaches the internal regulated voltage, which is equivalent to the saturation GATE drive voltage. The LM5068-1 and LM5068-3 remains off until the controller is reset by either temporarily pulling the UV pin low, pulling the TIMER pin below 1 volt, or decreasing the input voltage below the internal VDD under-voltage lockout (UVLO) threshold. The LM5068-2 and LM5068-4 respond to a fault condition by pulling the GATE and TIMER pins low and then initiating a timer sequence for automatic re-try. The re-try timer sequence begins with CT capacitor being charged slowly to 4V with a 6A current source and then discharged quickly to 1V with a 30mA discharge current. After 8 charge/discharge cycles the GATE pin is released and charged with a 60A www.national.com 20078606 FIGURE 3. UV/OV Setting 12 LM5068 UV and OV Thresholds and Voltage Divider Selection for R1, R2, and R3 (Continued) (1) If the SENSE pin detects more than 50mV across RS, the TIMER pin charges CT with 240A. The Circuit Breaker timeout period tCBT is calculated from: Hysteresis is necessary to prevent a possible "chattering" condition when the controller enables or disables the external MOSFET. The change in line current interacts with the line impedance. This interaction can cause several rapid on/off cycles on the MOSFET. A hysteresis window larger than the line impedance voltage drop prevents this condition. The impedance seen looking into the resistor divider from the UV and OV pin determines the hysteresis level. UV/OV ON and OFF thresholds are calculated as follow: (2) When the LM5068-2 or LM5068-4 is latched, it pulls down the GATE pin and initiates eight, 6A charging cycles between 1V and 4V on CT. The total re-try time period tRT is given by: (3) Sense Resistor (Rs), Timer Capacitor (CT) and N-Channel Mosfet (Q1) Selection To select the proper MOSFET, the following safe operating area (SOA) parameters are needed: maximum input voltage, maximum current and the maximum current conduction time. First, RS is calculated for the maximum operating load current (IL(MAX)) and the minimum circuit breaker trip point (VCB(MIN)): The independent UV and OV pins provide complete flexibility for the user to select the operational voltage range of the system. However, due to the UV Abs Max rating, the UV and OV thresholds can't be simultaneously set to extremes in one resistor string. For the wide ranges of input voltages (i.e. UV threshold to12V and OV threshold to 90V) it is recommended to use two separate voltage dividers to set the UV and OV thresholds independently. The typical operating ranges of under-voltage and overvoltage thresholds are calculated from the above equations with known resistors. For example, for resistor values: R1=130K, R2=5.5K, and R3=4.5K, the computed thresholds are: * UV turn-on = 37.60V * UV turn-off = 35.0V (4) During the initial charging process, the LM5068 may operate the MOSFET in current limit, forcing VAC(MIN) (80mV) to VAC(MAX) (120mV) across RS. The minimum in-rush current and maximum short-circuit limit are calculated from: (5) * OV turn-off = 77.78V * OV turn-on = 75.07V To maintain the threshold's accuracy, a resistor tolerance of 1% or better is recommended. (6) The value of TIMER capacitor (CT) is calculated in order to prevent CT from timing out before the load capacitor is fully charged using the slowest expected charging rate of the load capacitor. Assuming there is no initial resistive loading, the time necessary to charge the load capacitor CL is calculated from: Calculation of Normal, Circuit Breaker, and Retry Timing The CT capacitor at the TIMER pin controls the timing functions of the LM5068. When the interlock conditions are met the timer capacitor is charged to 4V in a slow initial delay time period tIDT calculated from: (7) 13 www.national.com LM5068 Sense Resistor (Rs), Timer Capacitor (CT) and N-Channel Mosfet (Q1) Selection (Continued) VDD=100V and I(MAX)=3A for 7.5ms in the worst case fault condition. A device that meets the established criteria is the Vishay - 5UB85N10-10. External Sense Resistor Applying Equation (5) and Equation (7) to Equation (2) gives the TIMER capacitor value of: Precise current measurement depends on the accuracy of the sense resistor (RS). For the optimal results, Kelvin connection and close location of RS to the LM5068 should be considered. Figure 4 demonstrates PCB layout for the Kelvin sensing. The RS power rating should be greater than I2L*R, where IL is the normal maximum operating load. (8) Finally, the SOA curves of a prospective MOSFET are checked using VIN (MAX), and ISHORT-CIRCUIT (MAX) calculated from equation Equation (6) and time of the current flow from Equation (2). Example: For: IL=1A, VDD = 48V, VDD (MAX) = 100V and CL=100F, To account for tolerances of RS, CL, TIMER current and TIMER threshold voltage, the computed CT value should be increased, for this example 50% was selected, therefore: CT = 300nF * 1.5 = 450nF The maximum active current limiting value and duration are: 20078623 FIGURE 4. Sense Resistor Connections (9) (10) The N-channel MOSFET selection for use with the LM5068 controller in this example must be capable of sustaining www.national.com 14 LM5068 Timing Diagrams 20078625 FIGURE 5. System Power-Up Timing Behavior Assuming all of the initial conditions are met, the power-up sequence starts with Timer capacitor (CT) getting charged. CT is charged with 6A current source up to VTHVT (4V) then quickly discharge to VTLVT (1V). At time point (2) the 60A GATE current source is enabled. The GATE voltage increases until the MOSFET starts conducting causing the SENSE voltage to increase until Active Current Limiting is activated (3). During the current limiting period (3-4), CT is charged again, but there is not enough time to reach the 4V threshold before the load capacitor is fully charged and the SENSE voltage falls below VCB. The GATE continues to fully enhance the MOSFET and activating the PWRGD when the GATE voltage exceeds 8V. 15 www.national.com LM5068 Timing Diagrams (Continued) 20078626 FIGURE 6. Under-Voltage Timing Behavior UV drops below UV HIGH (time point 1) puts the controller into a disabled mode. Later, UV increases over the UV LOW threshold (time point 3), which initiates a system power-up sequence. www.national.com 16 LM5068 Timing Diagrams (Continued) 20078627 FIGURE 7. Over-Voltage Timing Behavior During normal operation, if the OV pin exceeds OV HIGH, as shown at time point 1 in the above diagram, the TIMER status is unaffected. The GATE and PWRGD ( for LM5068-1 & -2) pins are pulled low and the load is disconnected. At time point 2, OV recovers and drops below the OV LOW threshold, the GATE start-up cycle begins. If the load capacitor is completely depleted during OV conditions, a full start-up cycle is initiated. 17 www.national.com LM5068 Timing Diagrams (Continued) 20078628 FIGURE 8. Circuit Breaker Current Limit Fault capacitor will be discharged with 6A. In the above figure when TIMER exceeds VTHVT, GATE is pulled low immediately to disconnect power to the load. The above timing waveform shows the circuit breaker current limit fault behavior. The timer capacitor is charged with 240A when the SENSE pin exceeds VCB. If the SENSE pin drops below VCB before the TIMER reaches VTHVT, the timer www.national.com 18 LM5068 Timing Diagrams (Continued) 20078629 FIGURE 9. Analog Current Limit Fault SENSE voltage falls below VAC, GATE is allowed to charge with a 60A current source. A compensation circuit consisting of a resistor and a capacitor in series, connected between GATE and VEE stabilizes the current limit loop. The above diagram shows analog current limit behavior when the SENSE pin voltage exceeds VAC for a period of time, which activates the Analog Current Limit but never reaches the fault timer threshold. At that time the GATE is regulated by the analog current limit amplifier loop. When the 19 www.national.com LM5068 Timing Diagrams (Continued) 20078630 FIGURE 10. Fast Current Limit Fault Careful selection of TIMER capacitor and MOSFET with adequate current and voltage ratings will prevent damage to MOSFET low impedance faults. In case of a severe fault (for example sudden short-circuit of the output load) the SENSE pin exceeds the VFDC threshold and GATE immediately pulls down until the Active Current Limit loop establishes control of the current in the MOSFET. www.national.com 20 LM5068 Timing Diagrams (Continued) 20078631 FIGURE 11. Shutdown Cooling Timing Behavior starts the fault re-try cycle by discharging CT with 30mA to the VTLVT threshold. The TIMER then charges CT with 6A to the VTHVT threshold. After eight charging phases and nine discharging phases, LM5068-2, -4 initiates an automatic retry start-up cycle. Figure 11 shows the timer behavior for LM5068-2, -4 during fault re-try time. During normal operation, whenever the SENSE pin exceeds the 50mV, circuit breaker fault limit, the timer capacitor begins to charge. If the TIMER pin voltage exceeds 4V, the GATE is pulled down immediately, and LM5068-2, -4 disconnects power to the load. The TIMER 21 www.national.com LM5068 Evaluation Board Schematic 20078657 PART VALUE C1 NOT USED PACKAGE C2 NOT USED C3 0.022uF/ 50V C0805 C4 0.33uF / 50V C0805 C5 100uF / 100V C6 0.1uF / 100V C1206 F1 10A FUSE SMD_FUSE J1 J2 Q1 100V / 60A N-Channel Power MOSFET,TO263 R1 0 R2 100K R3 DESCRIPTION PART NUMBER CAPACITOR, CERAMIC,KEMET C0805C223K5RAC CAPACITOR,CERAMIC,KEMET C0805C334K5RAC CAPACITOR, ALUMINIUM ELECTROLYTIC, SURFACE MOUNT,PANASONIC EEV-FK2A101M CAPACITOR, CERAMIC, TDK C3216X7R2A104KT COOPER BUSSMAN FAST ACTING FUSE TRON TR/SFT-10 (Digikey # 283-2439-2-ND) PCB terminal Blocks/ 10A MOUSER TERMINAL BLOCKS 651-1727010 PCB terminal Blocks/ 10A MOUSER TERMINAL BLOCKS 651-1727010 VISHAY SUB85N10-10 R1206 SMD RESISTOR, 1% TOL CRCW12060000F R1206 SMD RESISTOR, 1% TOL CRCW12061003F 4.02K R0805 SMD RESISTOR, 1% TOL CRCW08053401F R4 3.04K R0805 SMD RESISTOR, 1% TOL CRCW08053040F R5 100K R0805 SMD RESISTOR, 1% TOL CRCW08051003F R6 0 R0805 SMD RESISTOR, 1% TOL CRCW08050000F R7 50m R2512 SMD RESISTOR, 1% TOL WSL-2512 .050F R8 0 R1206 SMD RESISTOR, 1% TOL CRCW12060000F R9 0 R1206 SMD RESISTOR, 1% TOL CRCW12060000F R10 499 R1206 SMD RESISTOR, 1% TOL CRCW1206499RF www.national.com 22 (Continued) PART VALUE PACKAGE U1 LM5068 MSOP-8 DESCRIPTION PART NUMBER National Semiconductor LM5068 20078660 20078661 23 www.national.com LM5068 Evaluation Board Schematic LM5068 20078662 20078673 www.national.com 24 LM5068 20078674 25 www.national.com LM5068 Negative Voltage Hot Swap Controller Physical Dimensions inches (millimeters) unless otherwise noted Package Number MU08A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. 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