19-3494; Rev 1; 8/11 -48V Hot-Swap Controllers with External RSENSE The MAX5949A/MAX5949B are hot-swap controllers that allow a circuit card to be safely hot plugged into a live backplane. The MAX5949A/MAX5949B operate from -20V to -80V and are well-suited for -48V power systems. These devices are pin and function compatible with the LT4250 and pin compatible with the LT1640. The MAX5949A/MAX5949B provide a controlled turn-on to circuit cards preventing glitches on the power-supply rail and damage to board connectors and components. The MAX5949A/MAX5949B provide undervoltage, overvoltage, and overcurrent protection. These devices ensure the input voltage is stable and within tolerance before applying power to the load. Both the MAX5949A and MAX5949B protect a system against overcurrent and short-circuit conditions by turning off the external MOSFET in the event of a fault condition. The MAX5949A/MAX5949B also provide protection against input voltage steps. During an input voltage step, the MAX5949A/MAX5949B limit the current drawn by the load to a safe level without turning off power to the load. Both devices feature an open-drain power-good status output (PWRGD for the MAX5949A or PWRGD for the MAX5949B) that can be used to enable downstream converters. The MAX5949A/MAX5949B are available in an 8-pin SO package. Both devices are specified for the extended -40°C to +85°C temperature range. Applications Features o Allow Safe Board Insertion and Removal from a Live -48V Backplane o Pin and Function Compatible with LT4250L (MAX5949A) o Pin Compatible with LT1640L (MAX5949A) o Pin and Function Compatible with LT4250H (MAX5949B) o Pin Compatible with LT1640H (MAX5949B) o Circuit-Breaker Immunity to Input Voltage Steps and Current Spikes o Withstand -100V Input Transients with No External Components o Programmable Inrush and Short-Circuit Current Limits o Operate from -20V to -80V o Programmable Overvoltage Protection o Programmable Undervoltage Lockout o Power Up into a Shorted Load o Power-Good Control Output Ordering Information TEMP RANGE PIN-PACKAGE Telecom Line Cards MAX5949AESA+ -40°C to +85°C 8 SO Network Switches/Routers MAX5949BESA+ -40°C to +85°C 8 SO Central-Office Line Cards PART +Denotes a lead(Pb)-free/RoHS-compliant package. Server Line Cards Pin Configuration Base-Station Line Cards Central-Office Switching TOP VIEW -48V Distributed Power Systems Negative Power-Supply Controls 1 OV 2 UV Typical Operating Circuit and Selector Guide appear at end of data sheet. + PWRGD (PWRGD) 3 MAX5949A MAX5949B VEE 4 8 VDD 7 DRAIN 6 GATE 5 SENSE SO ( ) FOR MAX5949B. ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX5949A/MAX5949B General Description MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE ABSOLUTE MAXIMUM RATINGS (All voltages are referenced to VEE, unless otherwise noted.) Supply Voltage (VDD - VEE ) .................................-0.3V to +100V PWRGD, PWRGD .................................................-0.3V to +100V DRAIN (Note 1)........................................................-2V to +100V PWRGD to DRAIN .............................................… -0.3V to +95V PWRGD to VDD ........................................................-95V to +85V SENSE (Internally Clamped) .................................-0.3V to +1.0V GATE (Internally Clamped) ....................................-0.3V to +18V UV and OV..............................................................-0.3V to +60V Note 1: Current Through SENSE ...................................................±40mA Current into GATE...........................................................±300mA Current into DRAIN .........................................-100mA to +20mA Current into Any Other Pin................................................±20mA Continuous Power Dissipation (TA = +70°C) 8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature .....................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) .......................................+260°C Test condition per Figure 1. DRAIN current must be limited to the specified 100mA maximum. 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 (VEE = 0V, VDD = 48V, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Notes 2, 5) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS POWER SUPPLIES Operating Input Voltage Range VDD Supply Current IDD 20 (Note 3) 80 V 0.7 2 mA GATE DRIVE AND CLAMPING CIRCUITS GATE Pin Pullup Current IPU Gate drive on, VGATE = VEE -30 -45 -60 µA GATE Pin Pulldown Current IPD Gate drive off, VGATE = 2V, TA = +25°C 24 50 70 mA VGATE - VEE, 20V ≤ VDD ≤ 80V 10 13.5 18 V VGATE - VEE, IGS = 30mA 15 16.4 18 V External Gate Drive GATE to VEE Clamp Voltage ∆VGATE VGSCLMP CIRCUIT BREAKER Current-Limit Trip Voltage VCL VCL = VSENSE - VEE 40 50 60 mV SENSE Input Bias Current ISENSE VSENSE = 50mV 0 -0.2 -2 µA Internal Undervoltage-Lockout Voltage High VUVLOH VDD increasing 13.8 15.4 17.0 V Internal Undervoltage-Lockout Voltage Low VUVLOL VDD decreasing 11.8 13.4 15.0 V VUVH UV voltage increasing 1.240 1.255 1.270 V VUVL UV voltage decreasing 1.105 1.125 1.145 UNDERVOLTAGE LOCKOUT UV PIN UV High Threshold UV Low Threshold UV Hysteresis UV Input Bias Current VUVHY 130 IINUV VUV = VEE OV High Threshold VOVH OV voltage increasing OV Low Threshold VOVL OV voltage decreasing V mV 0 -0.5 µA 1.235 1.255 1.275 V 1.210 1.235 1.255 V OV PIN OV Hysteresis OV Input Bias Current 2 VOVHY IINOV 20 VOV = VEE 0 _______________________________________________________________________________________ mV -0.5 µA -48V Hot-Swap Controllers with External RSENSE (VEE = 0V, VDD = 48V, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Notes 2, 5) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS VDRAIN = 48V 10 80 250 µA 1.1 1.4 2.0 V 1.0 1.4 2.0 V 10 µA PWRGD OUTPUT SIGNAL REFERENCED TO DRAIN DRAIN Input Bias Current IDRAIN DRAIN Threshold for Power-Good VDL VDRAIN - VEE threshold for power-good condition, DRAIN decreasing GATE High Threshold VGH ∆VGATE - VGATE threshold for power-good condition, ∆VGATE - VGATE decreasing PWRGD, PWRGD Output Leakage IOH PWRGD (MAX5949A) = 80V, VDRAIN = 48V, PWRGD (MAX5949B) = 80V, VDRAIN = 0V PWRGD Output Low Voltage VOL V PWRGD - VEE; VDRAIN - VEE < VDL, ISINK = 5mA (MAX5949A) 0.11 0.4 V PWRGD Output Low Voltage VOL VPWRGD - VDRAIN; VDRAIN = 5V, ISINK = 1mA (MAX5949B) 0.11 0.4 V AC PARAMETERS OV High to GATE Low tPHLOV Figures 2a, 3 0.5 µs UV Low to GATE Low tPHLUV Figures 2a, 4 0.4 µs OV Low to GATE High tPLHOV Figures 2a, 3 4 µs UV High to GATE High tPLHVL Figures 2a, 4 5.5 SENSE High to GATE Low tPHLSENSE Figures 2a, 5a 1 3 µs Current Limit to GATE Low tPHLCB Figures 2b, 5b 500 650 µs DRAIN Low to PWRGD Low DRAIN Low to (PWRGD - DRAIN) High tPHLDL GATE High to PWRGD Low GATE High to (PWRGD - DRAIN) High tPHLGH 350 MAX5949A, Figures 2a, 6a 1.8 MAX5949B, Figures 2a, 6a 3.4 MAX5949A, Figures 2a, 6b 1.6 MAX5949B, Figures 2a, 6b 2.5 µs µs µs TURN-OFF Latch-Off Period Note 2: Note 3: Note 4: Note 5: tOFF (Note 4) 51 64 78 ms All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to VEE, unless otherwise specified. Current into VDD with UV = 3V, OV = DRAIN = PWRGD = SENSE = VEE, GATE = open. Minimum duration of GATE pulldown following a circuit-breaker fault. The circuit breaker can be reset during this time by toggling UV low, but the GATE pulldown does not release until tOFF has elapsed. Limits are 100% tested at TA = +25°C and +85°C. Limits at -40°C are guaranteed by design. _______________________________________________________________________________________ 3 MAX5949A/MAX5949B ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VDD = 48V, VEE = 0V, TA = +25°C, unless otherwise noted.) SUPPLY CURRENT vs. SUPPLY VOLTAGE 14 600 500 TA = -40°C 400 300 53 13 TA = -45°C 52 TA = +25°C TRIP VOLTAGE (mV) GATE VOLTAGE (V) 700 TA = +85°C MAX5949 toc03 15 MAX5949 toc02 TA = +25°C TA = +85°C 800 CURRENT-LIMIT TRIP VOLTAGE vs. TEMPERATURE GATE VOLTAGE vs. SUPPLY VOLTAGE MAX5949 toc01 900 SUPPLY CURRENT (µA) 12 11 51 50 49 10 48 9 47 200 100 0 46 8 20 40 60 80 100 20 0 SUPPLY VOLTAGE (V) 40 60 80 44.6 44.4 44.2 44.0 43.8 43.6 43.4 70 43.0 55 50 45 40 35 25 -15 10 35 60 85 -40 -15 10 35 60 TEMPERATURE (°C) TEMPERATURE (°C) PWRGD OUTPUT LOW VOLTAGE vs. TEMPERATURE (MAX5949A) PWRGD OUTPUT IMPEDANCE vs. TEMPERATURE (MAX5949B) IOUT = 1mA OUTPUT IMPEDANCE (GΩ) 40 10,000 35 30 25 20 15 10 85 MAX5949 toc07 MAX5920 toc06 -40 45 60 30 43.2 50 VGATE = 2V 65 GATE PULLDOWN CURRENT (mA) VGATE = 0V 35 GATE PULLDOWN CURRENT vs. TEMPERATURE MAX5949 toc04 GATE PULLUP CURRENT (µA) 44.8 10 TEMPERATURE (°C) SUPPLY VOLTAGE (V) GATE PULLUP CURRENT vs. TEMPERATURE 45.0 -15 -40 100 MAX5949 toc05 0 PWRGD OUTPUT LOW VOLTAGE (mV) MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE 1000 100 10 5 0 1 -40 -15 10 35 TEMPERATURE (°C) 4 60 85 -50 -25 0 25 50 75 100 TEMPERATURE (°C) _______________________________________________________________________________________ 60 85 -48V Hot-Swap Controllers with External RSENSE R 5kΩ V+ 5V PWRGD/PWRGD VDD VDD UV VEE SENSE GATE 48V VOV MAX5949_ OV VS DRAIN OV PWRGD/PWRGD MAX5949A MAX5949B DRAIN VUV 100mA MAX VDRAIN UV GATE VEE SENSE TEST VOLTAGE 2V VSENSE Figure 2a. Test Circuit 1 Figure 1. -2V DRAIN Voltage Test Circuit PWRGD/PWRGD VDD DRAIN OV VS 48V VS 20V 10kΩ UV MAX5949A MAX5949B 10Ω GATE 0.1µF N IRF530 VUV VEE SENSE 10Ω Figure 2b. Test Circuit 2 _______________________________________________________________________________________ 5 MAX5949A/MAX5949B Test Circuits MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE Timing Diagrams 2V 2V 1.255V 1.235V OV 1.255V 1.125V UV 0V tPLHUV tPHLUV 0V tPHLOV tPLHOV GATE GATE Figure 3. OV to GATE Timing 100mV 1V 1V 1V 1V Figure 4. UV to GATE Timing 60mV UV SENSE tPHLCB VEE tPHLSENSE GATE GATE 1V 50mV 1V SENSE Figure 5a. SENSE to GATE Timing 6 Figure 5b. Active Current-Limit Threshold _______________________________________________________________________________________ 1V -48V Hot-Swap Controllers with External RSENSE 1.4V DRAIN 1.4V ∆VGATE - VGATE = 0V GATE VEE tPHLDL tPHLGH PWRGD 1V PWRGD VEE 1V VEE 1.4V DRAIN ∆VGATE - VGATE = 0V 1.4V GATE VEE tPHLDL VEE tPHLGH PWRGD PWRGD 1V VPWRGD - VDRAIN = 0V 1V VPWRGD - VDRAIN = 0V Figure 6a. DRAIN to PWRGD/PWRGD Timing Figure 6b. GATE to PWRGD/PWRGD Timing Block Diagram VDD UVLO VCC AND REFERENCE GENERATOR UV MAX5949A MAX5949B VCC REF PWRGD PWRGD OUTPUT DRIVE REF LOGIC 500µs DELAY OV GATE DRIVER 50mV VGH VDL ∆VGATE VEE VEE SENSE GATE DRAIN _______________________________________________________________________________________ 7 MAX5949A/MAX5949B Timing Diagrams (continued) MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE Pin Description PIN MAX5949A MAX5949B 1 — NAME FUNCTION PWRGD Power-Good Signal Output. PWRGD is an active-low open-drain status output referenced to VEE. PWRGD is latched low when VDRAIN - VEE ≤ VDL and VGATE > (∆VGATE - VGH), indicating a power-good condition. PWRGD is open drain otherwise. — 1 PWRGD Power-Good Signal Output. PWRGD is an active-high open-drain status output referenced to DRAIN. PWRGD latches in a high-impedance state when VDRAIN - VEE ≤ VDL and VGATE > (∆VGATE - VGH), indicating a power-good condition. PWRGD is pulled low to DRAIN otherwise. 2 2 OV Input Pin for Overvoltage Detection. OV is referenced to VEE. When OV is pulled above the VOVH voltage, the GATE pin is immediately pulled low. The GATE pin remains low until the OV pin voltage reduces to VOVL. 3 3 UV 4 4 VEE Input Pin for Undervoltage Detection. UV is referenced to VEE. When UV is pulled above the VUVH voltage, the GATE is enabled. When UV is pulled below VUVL, GATE is pulled low. UV is also used to reset the circuit breaker after a fault condition. To reset the circuit breaker, pull UV below VUVL. The reset command can be issued immediately after a fault condition; however, the device does not restart until a tOFF delay time has elapsed after the fault. Device Negative Power-Supply Input. Connect to the negative power-supply rail. 5 5 SENSE Current-Sense Voltage Input. Connect to an external sense resistor and the external MOSFET source. The voltage drop across the external sense resistor is monitored to detect overcurrent or short-circuit fault conditions. Connect SENSE to VEE to disable the currentlimiting feature. 6 6 GATE Gate-Drive Output. Connect to the gate of the external n-channel MOSFET. 7 7 DRAIN Output-Voltage Sense Input. Connect to the output-voltage node (drain of the external n-channel MOSFET). 8 8 VDD Positive Power-Supply Rail Input. This is the power ground in the negative-supply voltage system. Connect to the higher potential of the power-supply inputs. Detailed Description The MAX5949A/MAX5949B are integrated hot-swap controllers for -48V power systems. They allow circuit boards to be safely hot plugged into a live backplane without causing a glitch on the power-supply rail. When circuit boards are inserted into a live backplane without hot-swap control, the bypass capacitors at the input of the board’s power module or switching power supply can draw large inrush currents as they charge. The inrush currents can cause glitches on the system power-supply rail and damage components on the board. 8 The MAX5949A/MAX5949B provide a controlled turn-on to circuit cards, preventing glitches on the power-supply rail and damage to board connectors and components. Both the MAX5949A and MAX5949B provide undervoltage, overvoltage, and overcurrent protection. The MAX5949A/MAX5949B ensure the input voltage is stable and within tolerance before applying power to the load. The devices also provide protection against input voltage steps. During an input voltage step, the MAX5949A/MAX5949B limit the current drawn by the load to a safe level without turning off power to the load. _______________________________________________________________________________________ -48V Hot-Swap Controllers with External RSENSE Capacitor C2 provides a feedback signal to accurately limit the inrush current. The value of C 2 can be calculated: I x CL C2 = PU IINRUSH where CL is the total load capacitance, C3 + C4, and IPU is the MAX5949_ gate pullup current. Figure 7b shows the inrush current waveform. The current through C2 controls the GATE voltage. At the end of the DRAIN ramp, the GATE voltage is charged to its final value. The GATE-to-SENSE clamp limits the maximum VGS to about 18V under any condition. Power-Supply Ramping Board Removal The MAX5949_ can reside either on the backplane or the removable circuit board (Figure 7a). Power is delivered to the load by placing an external n-channel MOSFET pass transistor in the power-supply path. If the card is removed from a live backplane, the output capacitor on the card may not be immediately discharged. While the output capacitor is discharging, the MAX5949_ continues to operate as if the input supply were still connected because the output capacitor temporarily supplies operating current to the IC. If the circuit is connected as in Figure 7a, the voltage at the UV pin falls below the VUVL, and the MAX5949_ turns off the external MOSFET. If R4 in the circuit is connected directly to the -48V return, the external MOSFET remains on until the capacitor is discharged sufficiently to drop the UV pin voltage to VUVL. After the circuit board is inserted into the backplane and the supply voltage at VEE is stable and within the undervoltage and overvoltage tolerance, the MAX5949_ turn on Q1. The MAX5949_ gradually turn on the external MOSFET by charging the gate of Q1 with a 45µA current source. -48V RTN (SHORT PIN) -48V RTN R4 549kΩ 1% VDD UV R5 6.49kΩ 1% * 10nF R6 10kΩ 1% PWRGD MAX5949B OV VEE SENSE GATE DRAIN R3 1kΩ 5% R1 0.02Ω 5% C1** 470nF 25V R2 10Ω 5% C2 15nF 100V GATE IN VIN+ C3 0.1µF 100V C4 100µF 100V VICOR VI-J3D-CY C5 100µF 10V -48V *DIODES INC. SMAT70A. **OPTIONAL. Q1 IRF530 VIN- Figure 7a. Inrush Control Circuitry _______________________________________________________________________________________ 9 MAX5949A/MAX5949B Board Insertion Figure 7a shows a typical hot-swap circuit for -48V systems. When the circuit board first makes contact with the backplane, the DRAIN to GATE capacitance (Cgd) of Q1 pulls up the GATE voltage to roughly IVEE x Cgd / (C gd + C gs )I. The MAX5949_ features an internal dynamic clamp between GATE and VEE to keep the gate-to-source voltage of Q1 low during hot insertion, preventing Q1 from passing an uncontrolled current to the load. For most applications, the internal dynamic clamp between GATE and V EE of the MAX5949A/ MAX5949B eliminates the need for an external gate-tosource capacitor C1. Resistor R3 limits the current into the clamp circuitry during card insertion. MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE the device waits until tOFF has elapsed before turning on the gate of the external FET. INRUSH CURRENT 1A/div GATE - VEE 10V/div DRAIN 50V/div VEE 50V/div CONTACT BOUNCE 4ms/div Figure 7b. Input Inrush Current In either case, when the MOSFET is turned off, the output capacitor continues to discharge by the IC supply current, IDD. The IDD flows into the IC at the VDD terminal, out at the VEE terminal, and back to the capacitor through the external MOSFET’s substrate diode. There is also a parallel current path between the VEE and DRAIN terminals through multiple internal ESD-protection diodes. Protection circuits built into the IC allow the DRAIN terminal voltage to drop below that of the VEE terminal so long as the allowed absolute-maximum DRAIN terminal current (-100mA) is not exceeded. As IDD is only 2mA maximum, this limiting current will not even be approached. Current Limit and Electronic Circuit Breaker The MAX5949_ provides current-limiting and circuitbreaker features that protect against excessive load current and short-circuit conditions. The load current is monitored by sensing the voltage across an external sense resistor connected between VEE and SENSE. If the voltage between VEE and SENSE reaches the current-limit trip voltage (VCL), the MAX5949_ pulls down the GATE pin and regulates the current through the external MOSFET so VSENSE - VEE < VCL. If the current drawn by the load drops below VCL / RSENSE limit, the GATE pin voltage rises again. However, if the load current is at the regulation limit of VCL / RSENSE for a period of tPHLCB, the electronic circuit breaker trips, causing the MAX5949A/MAX5949B to turn off the external MOSFET. After an overcurrent fault condition, the circuit breaker is reset by pulling the UV pin low and then pulling UV high or by cycling power to the MAX5949A/MAX5949B. Unless power is cycled to the MAX5949A/MAX5949B, 10 Overcurrent Fault Integrator The MAX5949_ features an overcurrent fault integrator. When an overcurrent condition exists, an internal digital counter increments its count. When the counter reaches 500µs (the maximum current-limit duration) for the MAX5949_, an overcurrent fault is generated. If the overcurrent fault does not last 500µs, then the counter begins decrementing at a rate 128 (maximum currentlimit duty cycle) times slower than the counter was incrementing. Repeated overcurrent conditions will generate a fault if duty cycle of the overcurrent condition is greater than 1/128. Load-Current Regulation The MAX5949_ accomplishes load-current regulation by pulling current from the GATE pin whenever VSENSE - VEE > VCL (see the Typical Operating Characteristics). This decreases the gate-to-source voltage of the external MOSFET, thereby reducing the load current. When VSENSE - VEE < VCL, the MAX5949A/MAX5949B pull the GATE pin high by a 45µA (IPU) current. Driving into a Shorted Load In the event of a permanent short-circuit condition, the MAX5949_ limits the current drawn by the load to VCL / RSENSE for a period of tPHLCB, after which the circuit breaker trips. Once the circuit breaker trips, the GATE of the external FET is pulled low by 50mA (IPD) turning off power to the load. Immunity to Input Voltage Steps The MAX5949_ guards against input voltage steps on the input supply. A rapid increase in the input supply voltage (VDD - VEE increasing) causes a current step equal to I = CL x ∆VIN / ∆T. If the load current exceeds VCL / RSENSE during an input voltage step, the MAX5949A/MAX5949B current limit activates, pulling down the gate voltage and limiting the load current to VCL / RSENSE. The DRAIN voltage (VDRAIN) then slews at a slower rate than the input voltage. As the drain voltage starts to slew down, the drain-to-gate feedback capacitor C2 pushes back on the gate, reducing the gate-to-source voltage (VGS) and the current through the external MOSFET. Once the input supply reaches its final value, the DRAIN slew rate (and therefore the inrush current) is limited by the capacitor C2 just as it is limited in the startup condition. To ensure correct operation, RSENSE must be chosen to provide a current limit larger than the sum of the load current and the dynamic current into the load capacitance in the slewing mode. If the load current plus the capacitive charging current is ______________________________________________________________________________________ -48V Hot-Swap Controllers with External RSENSE MAX5949A/MAX5949B DRAIN 50V/div VEE 20V/div GATE - VEE 10V/div DRAIN 20V/div ID (Q1) 5A/div ID (Q1) 5A/div 1ms/div 400µs/div Figure 8. Short-Circuit Protection Waveform Figure 9. Voltage Step on Input Supply -48V RTN (SHORT PIN) -48V RTN R4 549kΩ 1% VDD UV R5 6.49kΩ 1% * R6 10kΩ 1% PWRGD MAX5949A OV VEE SENSE GATE R3 1kΩ 5% R7 220Ω 5% R1 0.02Ω 5% -48V DRAIN D1 BAT85 C2 3.3nF 100V C3 0.1µF 100V C4 22µF 100V R2 10Ω 5% C1 150nF 25V *DIODES INC. SMAT70A. Q1 IRF530 Figure 10. Circuit for Input Steps with Small C1 below the current limit, the circuit breaker does not trip. For C2 values less than 10nF, a positive voltage step on the input supply can result in Q1 turning off momentarily, which can shut down the output. By adding an additional resistor and diode, Q1 remains on during the voltage step. This is shown as D1 and R7 in Figure 10. The purpose of D1 is to shunt current around R7 when the power pins first make contact and allow C1 to hold the GATE low. The value of R7 should be sized to generate an R7 x C1 time constant of 33µs. Undervoltage and Overvoltage Protection The UV and OV pins can be used to detect undervoltage and overvoltage conditions. The UV and OV pins are internally connected to analog comparators with 130mV (UV) and 20mV (OV) of hysteresis. When the UV voltage falls below its threshold or the OV voltage rises above its threshold, the GATE pin is immediately pulled low. The GATE pin is held low until UV goes high and OV is low, indicating that the input supply voltage is within specification. The MAX5949_ includes an internal lockout (UVLO) that keeps the external MOSFET off until the input supply voltage exceeds 15.4V, regardless of the UV input. ______________________________________________________________________________________ 11 MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE -48V RTN (SHORT PIN) -48V RTN R7 1MΩ 5% C4 1µF 100V NODE2 R6 549kΩ 1% R4 549kΩ 1% VDD UV NODE2 50V/div PWRGD MAX5949A * R9 6.49kΩ 1% OV VEE R5 10kΩ 1% SENSE GATE DRAIN R3 1kΩ 5% Q2 2N2222 D1 1N4148 Q3 ZVN3310 R8 510kΩ 5% R1 0.02Ω 5% -48V C1 470nF 25V R2 10Ω 5% C3 100µF 100V C2 15nF 100V GATE 2V/div 1s/div N Q1 IRF530 *DIODES INC. SMAT70A. Figure 11. Automatic Restart After Current Fault -48V RTN (SHORT PIN) -48V RTN R4 VUV = 1.255 8 3 R4 + R5 + R6 R5 + R6 VDD UV R5 R4 + R5 + R6 VOV = 1.255 R6 2 MAX5949A MAX5949B OV VEE R6 4 -48V Figure 12. Undervoltage and Overvoltage Sensing 12 The UV pin is also used to reset the circuit breaker after a fault condition has occurred. The UV pin can be pulled below VUVL to reset the circuit breaker. Figure 12 shows how to program the undervoltage and overvoltage trip thresholds using three resistors. With R4 = 549kΩ, R5 = 6.49kΩ, and R6 = 10kΩ, the undervoltage threshold is set to 38.5V (with a 43V release from undervoltage), and the overvoltage is set to 71V. The resistordivider also increases the hysteresis of the overvoltage and overvoltage lockout, to 4.5V and 1.1V at the input supply, respectively. PWRGD/PWRGD Output The PWRGD (PWRGD) output can be used directly to enable a power module after hot insertion. The MAX5949A (PWRGD) can be used to enable modules with an active-low enable input (Figure 14), while the MAX5949B (PWRGD) is used to enable modules with an active-high enable input (Figure 13). The PWRGD signal is referenced to the DRAIN terminal, which is the negative supply of the power module. The PWRGD signal is referenced to VEE. ______________________________________________________________________________________ -48V Hot-Swap Controllers with External RSENSE MAX5949A/MAX5949B ACTIVE-HIGH ENABLE MODULE -48V RTN (SHORT PIN) -48V RTN VIN+ VOUT+ VDD R4 MAX5949B GATE PWRGD I1 ON/OFF UV N Q2 C3 N VGH R5 Q3 * VIN- VOUT- VEE ∆VGATE VDL OV DRAIN R6 VEE SENSE GATE R3 C2 R2 C1 R1 -48V Q1 *DIODES INC. SMAT70A. Figure 13. Active-High Enable Module ACTIVE-LOW ENABLE MODULE -48V RTN (SHORT PIN) -48V RTN VIN+ VOUT+ VDD R4 MAX5949A GATE PWRGD ON/OFF UV C3 N VGH R5 Q2 VIN- * OV VOUT- VEE ∆VGATE VDL DRAIN R6 VEE SENSE GATE R3 C2 R2 C1 R1 -48V *DIODES INC. SMAT70A. Q1 Figure 14. Active-Low Enable Module ______________________________________________________________________________________ 13 MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE -48V RTN (SHORT PIN) PWRGD -48V RTN R7** 51kΩ 5% R4 549kΩ 1% VDD UV R5 6.49kΩ 1% * R6 10kΩ 1% PWRGD MAX5949A OV VEE SENSE GATE DRAIN R3 1kΩ 5% R1 0.02Ω 5% C1** 470nF 25V R2 10Ω 5% MOC207 C2 15nF 100V C3 100µF 100V -48V *DIODES INC. SMAT70A. **OPTIONAL. Q1 IRF530 Figure 15. Using PWRGD to Drive an Optoisolator When the DRAIN voltage of the MAX5949A is high with respect to VEE or the GATE voltage is low, the internal pulldown MOSFET Q2 is off and the PWRGD pin is in a high-impedance state (Figure 14). The PWRGD pin is pulled high by the module’s internal pullup current source, turning the module off. When the DRAIN voltage drops below VDL and the GATE voltage is greater than ∆VGATE - VGH, Q2 turns on and the PWRGD pin pulls low, enabling the module. The PWRGD signal can also be used to turn on an LED or optoisolator to indicate that the power is good (Figure 15) (see the Component Selection Procedure section). When the DRAIN voltage of the MAX5949B is high with respect to VEE (Figure 13) or the GATE voltage is low, the internal MOSFET Q3 is turned off so that I1 and the internal MOSFET Q2 clamp the PWRGD pin to the DRAIN pin. MOSFET Q2 sinks the module’s pullup current, and the module turns off. When the DRAIN voltage drops below V DL and the GATE voltage is greater than ∆VGATE - VGH, MOSFET Q3 turns on, shorting I1 to VEE and turning Q2 off. The pullup current in the module pulls the PWRGD pin high, enabling the module. 14 GATE Pin Voltage Regulation The GATE pin goes high when the following startup conditions are met: the UV pin is high, the OV pin is low, the supply voltage is above VUVLOH, and (VSENSE - VEE) is less than 50mV. The gate is pulled up with a 45µA current source and is regulated at 13.5V above V EE . The MAX5949A/MAX5949B include an internal clamp that ensures the GATE voltage of the external MOSFET never exceeds 18V. During a fast-rising VDD, the clamp also keeps the GATE and SENSE potentials as close as possible to prevent the FET from accidentally turning on. When a fault condition is detected, the GATE pin is pulled low with a 50mA current. Applications Information Sense Resistor The circuit-breaker current-limit threshold is set to 50mV (typically). Select a sense resistor that causes a drop equal to or above the current-limit threshold at a current level above the maximum normal operating current. Typically, set the overload current to 1.5 to 2.0 times the nominal load current plus the load-capacitance charging current during startup. Choose the sense-resistor power rating to be greater than (VCL)2 / RSENSE. ______________________________________________________________________________________ -48V Hot-Swap Controllers with External RSENSE • • • • Determine load capacitance: CL = C2 + C3 + module input capacitance Determine load current, ILOAD. Select circuit-breaker current; for example: ICB = 2 x ILOAD Calculate RSENSE: 50mV RSENSE = ICB Realize that ICB varies ±20% due to trip-voltage tolerance. Set allowable inrush current: 40mV − ILOAD or RSENSE IINRUSH + ILOAD ≤ 0.8 x ICB(MIN) IINRUSH ≤ 0.8 x • Determine value of C2: 45µA x CL C2 = IINRUSH • Calculate value of C1: ⎛ VIN(MAX) − VGS( TH) ⎞ C1 = (C2 + Cgd ) x ⎜ ⎟ VGS( TH) ⎝ ⎠ • Determine value of R3: 150µs R3 ≤ (typically 1kΩ) C2 • Set R2 = 10Ω. • If an optocoupler is utilized as in Figure 15, determine the LED series resistor: VIN(NOMINAL) − 2V R7 = 3mA ≤ ILED ≤ 5mA Although the suggested optocoupler is not specified for operation below 5mA, its performance is adequate for 36V temporary low-line voltage where LED current would then be ≈2.2mA to 3.7mA. If R7 is set as high as 51kΩ, optocoupler operation should be verified over the expected temperature and input voltage range to ensure suitable operation when LED current ≈0.9mA for 48V input and ≈0.7mA for 36V input. If input transients are expected to momentarily raise the input voltage to >100V, select an input transient-voltage-suppression diode (TVS) to limit maximum voltage on the MAX5949 to less than 100V. A suitable device is the Diodes Inc. SMAT70A telecom-specific TVS. Select Q1 to meet supply voltage, load current, efficiency, and Q1 package power-dissipation requirements: BVDSS ≥ 100V ID(ON) ≥ 3 x ILOAD DPAK, D2PAK, or TO-220AB The lowest practical RDS(ON), within budget constraints and with values from 14mΩ to 540mΩ, are available at 100V breakdown. Ensure that the temperature rise of Q1 junction is not excessive at normal load current for the package selected. Ensure that ICB current during voltage transients does not exceed allowable transient-safe operating-area limitations. This is determined from the SOA and transient-thermal-resistance curves in the Q1 manufacturer’s data sheet. Example 1: ILOAD = 2.5A, efficiency = 98%, then VDS = 0.96V is acceptable, or RDS(ON) ≤ 384mΩ at operating temperature is acceptable. An IRL520NS 100V NMOS with R DS(ON) ≤ 180mΩ and I D(ON) = 10A is available in D2PAK. (A Vishay Siliconix SUD40N10-25 100V NMOS with RDS(ON) ≤ 25mΩ and ID(ON) = 40A is available in DPAK, but may be more costly because of a larger die size.) Using the IRL520NS, VDS ≤ 0.625V even at +80°C so efficiency ≥ 98.6% at 80°C. PD ≤ 1.56W and junction temperature rise above case temperature would be 5°C due to the package θJC = 3.1°C/W thermal resistance. Of course, using the SUD40N10-25 would yield an efficiency greater than 99.8% to compensate for the increased cost. ______________________________________________________________________________________ 15 MAX5949A/MAX5949B Component Selection Procedure • MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE If ICB is set to twice ILOAD, or 5A, VDS momentarily doubles to ≤1.25V. If COUT = 4000µF, transient-line input voltage is ∆36V, and the 5A charging-current pulse is: 4000µF x 1.25V = 1ms 5A Entering the data sheet transient-thermal-resistance curves at 1ms provides a θJC = 0.9°C/W. PD = 6.25W, so ∆tJC = 5.6°C. Clearly, this is not a problem. Example 2: ILOAD = 10A, efficiency = 98%, allowing VDS = 0.96V but RDS(ON) ≤ 96mΩ. An IRF530 in a D2PAK exhibits RDS(ON) ≤ 90mΩ at +25°C and ≤ 135mΩ at +80°C. Power dissipation is 9.6W at +25°C or 14.4W at +80°C. Junction-to-case thermal resistance is 1.9W/°C, so the junction-temperature rise would be approximately 5°C above the +25°C case temperature. For higher efficiency, consider IRL540NS with R DS(ON) ≤ 44mΩ. This allows η = 99%, PD ≤ 4.4W, and TJC = +4°C (θJC = 1.1°C/W) at +25°C. Thermal calculations for the transient condition yield I CB = 20A, V DS = 1.8V, t = 0.5ms, transient θ JC = 0.12°C/W, PD = 36W and ∆tJC = 4.3°C. HIGH-CURRENT PATH t = SENSE RESISTOR SENSE VEE MAX5949A MAX5949B Figure 16. Recommended Layout for Kelvin-Sensing Current Through Sense Resistor Selector Guide PART 16 PWRGD POLARITY FAULT MANAGEMENT MAX5949AESA Active low (PWRGD) Latched MAX5949BESA Active high (PWRGD) Latched ______________________________________________________________________________________ -48V Hot-Swap Controllers with External RSENSE BACKPLANE CIRCUIT CARD -48V RTN -48V RTN (SHORT PIN) R4 549kΩ 1% VDD UV R5 649kΩ 1% 0.1µF 10V -48V (INPUT1) R6 10kΩ 1% INPUT1 PWRGD MAX5949A OV VEE SENSE R1 0.02Ω 5% C1 490nF 25V GATE DRAIN R3 1kΩ 5% R2 10Ω 5% C2 15nF 100V VIN+ C3 0.1µF 100V C4 100µF 100V LUCENT JW050A1-E N VIN- -48V (INPUT2) INPUT2 Package Information Chip Information PROCESS: BiCMOS For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 8 SO S8+5 21-0041 90-0096 ______________________________________________________________________________________ 17 MAX5949A/MAX5949B Typical Operating Circuit MAX5949A/MAX5949B -48V Hot-Swap Controllers with External RSENSE Revision History REVISION NUMBER REVISION DATE 0 11/04 Initial release 1 8/11 Updated the Electrical Characteristics and Figure 11. DESCRIPTION PAGES CHANGED — 3, 12 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. 18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.