19-5553; Rev 2; 7/11 TION KIT EVALUA BLE A IL A V A 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output Features The MAX5977A/MAX5977B hot-swap controllers provide complete protection for systems with a 1V to 16V singlesupply voltage. S 1% Accurate Current-Sense Amplifier Output S Hot-Swap Monitors Operation from 1V to 16V S Integrated Charge Pump Fully Enhances the External n-Channel FET (VGATE = VIN + 5V) During the initial insertion, the hot-swap controllers limit the inrush current from damaging the board or from shorting out the backplane. When the input voltage is above the undervoltage threshold and below the overvoltage threshold, a 5FA current source powered from the internal 5V charge pump drives the gate of an external n-channel MOSFET, providing a slow turn-on response. An internal current-sense amplifier in the IC monitors the current across an external shunt resistor, providing current sensing for wide input-sense voltage range. The devices provide two levels of overcurrent circuit-breaker protections: a fast-trip threshold for a fast turn-off and a lower slow-trip threshold for a delayed turn-off. S VariableSpeed/BiLevelK Fault Protection Provides Electronic Circuit-Breaker Function S Output Latched Off After Fault Condition (MAX5977A) S Autoretry After Fault Condition (MAX5977B) S Power-Good Indicator S Calibration Mode S Small, 20-Pin, 4mm x 4mm TQFN-EP Package Applications Servers Exceeding either of the overcurrent circuit-breaker thresholds forces the device into fault mode where the external n-channel MOSFET is disabled. The MAX5977 is available in two versions that provide a latched-off (MAX5977A) or autoretry (MAX5977B) output when the device is in fault mode. Storage Systems Network Switches and Routers General Hot-Swap Ordering Information A calibration mode allows further calibration of the integrated transconductance amplifier for production testing of the final design. The devices are offered in a 20-pin, 4mm x 4mm, TQFN-EP package and are fully specified from -40NC to +85NC. PART PIN-PACKAGE MAX5977AETP+ 20 TQFN-EP* FAULT RESPONSE Latched MAX5977BETP+ 20 TQFN-EP* Autoretry Note: All devices are specified over the -40NC to +85NC operating temperature range. +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. VariableSpeed/BiLevel is a trademark of Maxim Integrated Products, Inc. Typical Operating Circuit RSENSE VIN 1V TO 16V TO LOAD RSCOMP RCAL SCOMP FCOMP CL RGATE RFCOMP IN SENSE CALSENSE CGATE GATE SOURCE CURRENT-SENSE AMPLIFIER OUTPUT CSOUT RCSOUT CALIBRATION MODE INPUT CAL MAX5977A MAX5977B +3.3V 2.7V TO 16V PWR FAULT AGND GND PG FAULT OUTPUT POWER-GOOD OUTPUT ________________________________________________________________ Maxim Integrated Products 1 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. MAX5977A/MAX5977B General Description MAX5977A/MAX5977B 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output ABSOLUTE MAXIMUM RATINGS PWR, SENSE, IN, FCOMP, SCOMP, GATE, SOURCE, CALSENSE to GND................-0.3V to +28V PG, CAL, BIAS, UV, OV, FAULT, CSOUT to GND...-0.3V to +6V REG to GND.............................................................-0.3V to +4V GATE to SOURCE....................................................-0.3V to +6V IN to FCOMP, IN to SCOMP, IN to SENSE, IN to CALSENSE...................................................-0.3V to +1V GND to AGND.......................................................-0.3V to +0.3V FAULT, PG Current............................................ -1mA to +50mA GATE, SOURCE, GND Current.........................................750mA Input/Output Current (all other pins)...................................20mA Continuous Power Dissipation (TA = +70NC) 20-Pin TQFN, Single-Layer Board (derate 16.9mW/NC above +70NC)..........................1355.9mW 20-Pin TQFN, Multilayer Board (derate 25.6mW/NC above +70NC)..........................2051.3mW Junction-to-Ambient Thermal Resistance (Note 1) BJA, Single-Layer Board............................................ +59NC/W BJA, Multilayer Board................................................. +39NC/W Junction-to-Case Thermal Resistance (Note 1) BJC, Single-Layer and Multilayer Board...................... +6NC/W Operating Temperature Range........................... -40NC to +85NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. 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 (VPWR = VIN = 12V, RSENSE = 4mI, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted. Typical Values at VPWR = VIN = 3.3V, TA = +25NC, unless otherwise noted.) (Note 2) PARAMETER SYMBOL Operating Voltage Range VPWR Undervoltage Lockout VUVLO Undervoltage-Lockout Hysteresis CONDITIONS MIN TYP MAX UNITS 2.7 3.3 16 V Minimum rising voltage on PWR 2.69 VUVLOHYS Supply Current IPWR Internal LDO Output Voltage VREG 100 0.734 2.7V < VPWR < 16V, 0 to 1mA V mV 4 mA 2.49 2.6 V CURRENT-MONITORING FUNCTION IN Input Range 1 16 V SCOMP Input Range Common-mode range 1 16 V FCOMP Input Range 1 IN Input Current SENSE Input Current VIN = VSENSE = 1V to 16V 16 V 135 FA 6 FA Circuit-Breaker Current (Slow Comparator) ISCOMP VSCOMP = 1V to 16V 24.0 25 26.0 FA Circuit-Breaker Current (Fast Comparator) IFCOMP VFCOMP = 1V to 16V 48.1 50 51.4 FA Slow Current-Limit Threshold Error VSENSE - VSCOMP = 50mV -2.0 +2.1 mV Fast Current-Limit Threshold Error VSENSE - VFCOMP = 100mV -2.2 +1.4 mV Slow-Comparator Response Time tSCD Fast-Comparator Response Time tFSD 2 1mV overdrive 1 ms 50mV overdrive 130 Fs 10mV overdrive, from overload condition, VPWR = 12V 200 ns 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output (VPWR = VIN = 12V, RSENSE = 4mI, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted. Typical Values at VPWR = VIN = 3.3V, TA = +25NC, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS CURRENT-SENSE AMPLIFIER Input Common-Mode Range VIN - VSENSE 1.5 Input Offset Error Transconductance Gain V 0.1 gM Combined Gain and Offset Accuracy Total Full-Scale Error Output Common-Mode Range mV 10mV P (VIN - VSENSE) P 50mV, -40NC P TA P +85NC 2457 2500 2537 10mV P (VIN - VSENSE) P 50mV, 0NC P TA P +25NC 2467 2500 2532 Set VIN - VSENSE = 50mV, measure ICSOUT, VCSOUT = 25mV (-40NC P TA P +85NC) 122.1 125 128 Set VIN - VSENSE = 50mV, measure ICSOUT, VCSOUT = 25mV (0N P TA P +25NC) 123.5 125 126.5 Set VIN - VSENSE = 10mV, measure ICSOUT, VCSOUT = 25mV (-40NC P TA P +85NC) 22.5 25 27.6 Set VIN - VSENSE = 10mV, measure ICSOUT, VCSOUT = 25mV (0N P TA P +25NC) 24.0 25 26.0 2mV < (VIN - VSENSE) < 10mV (-40NC P TA P +85NC), % error = (ICSOUT - (VIN - VSENSE) x 0.0025)/(10mV x 0.0025) -10 +10 2mV < (VIN - VSENSE) < 10mV (0NC P TA P +25NC), % error = (ICSOUT - (VIN - VSENSE) x 0.0025)/(10mV x 0.0025) -4.21 +4.21 2mV < (VIN - VSENSE) < 25mV (-40NC P TA P +85NC), % error = (ICSOUT - (VIN - VSENSE) x 0.0025)/(25mV x 0.0025) -4.1 +4.1 2mV < (VIN - VSENSE) < 25mV (0NC P TA P +25NC), % error = (ICSOUT - (VIN - VSENSE) x 0.0025)/(25mV x 0.0025) -1.68 +1.68 2mV < (VIN - VSENSE) < 50mV (-40NC P TA P +85NC), % error = (ICSOUT - (VIN - VSENSE) x 0.0025)/(50mV x 0.0025) -2.34 +2.3 2mV < (VIN - VSENSE) < 50mV (0NC P TA P +25NC), % error = (ICSOUT - (VIN - VSENSE) x 0.0025)/(50mV x 0.0025) -1.18 +0.9 0 2.5 CSOUT voltage range FS FA % of 10mV Full-Scale Output % of 25mV Full-Scale Output % of 50mV Full-Scale Output V POWER-GOOD PG Delay PG Threshold Rising PG Threshold Hysteresis tdPG VTHRPG VIN - VSOURCE falling 50 ms 100 mV 100 mV 3 MAX5977A/MAX5977B ELECTRICAL CHARACTERISTICS (continued) ELECTRICAL CHARACTERISTICS (continued) (VPWR = VIN = 12V, RSENSE = 4mI, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted. Typical Values at VPWR = VIN = 3.3V, TA = +25NC, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 4.5 5 5.5 V 4 8 5 10 6 12 FA CHARGE PUMP (GATE) Charge-Pump Output Voltage VOHGATE Relative to VSOURCE Charge-Pump Output Source Current IGATEPU VGATE = VSOURCE = 0V VIN - VSOURCE < 100mV Charge-Pump Pulldown Current IGATEPD VGATE = 2V, VSOURCE = 0 to 16V 500 mA OUTPUTS (FAULT, PG) Output Voltage Low VOLFAULT/ ISINK = 3.2mA VOLPG Output Leakage (Open Drain) ILKFAULT/ ILKPG Tested at 0V and 5.2V VUV/OVR UV, OV rising input voltage threshold 0.4 V 1 FA 600 mV UV/OV COMPARATOR INPUTS UV/OV Threshold UV/OV Threshold Hysteresis 580 590 VUV/OVHYS UV, OV falling input hysteresis ILKUV/ ILKOV UV/OV Input Current 4 VUV = VOV = 0V and 5.5V % -100 +100 nA 0.4 V CALIBRATION MODE CAL Low-Voltage Input VILCAL CAL High-Voltage Input VIHCAL CAL Input Current IIHCAL 1.4 V VCAL = 2.5V, the CAL input pulls low if left unconnected CALSENSE Input Current 20 FA ±300 FA 175 ms FAULT RESPONSE Retry Timeout Period tRETRY MAX5977B Note 2: All devices 100% tested at TA = +25°C. Limits over temperature guaranteed by design. Typical Operating Characteristics (VPWR = VIN = 3.3V, TA = +25NC, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.) TRANSCONDUCTANCE vs. TEMPERATURE VIN - VSENSE vs. ICSOUT 0.72 0.71 2550 MAX5977 toc02 125 MAX5977 toc01 0.73 100 2530 2520 0.68 0.67 75 Gm (µS) ICSOUT (µA) 0.69 50 2510 2500 2490 0.66 2480 0.65 25 2470 VIN = VPWR = 12V RCSOUT = 10kI 0.64 2460 0 0.63 0 5 10 VPWR (V) 4 VIN = VPWR = 12V VIN - VSENSE = 10mV AND 50mV 2540 0.70 MAX5977 toc03 IPWR vs. VPWR IPWR (mA) MAX5977A/MAX5977B 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output 15 20 0 10 20 30 VIN - VSENSE (mV) 40 50 2450 -50 -25 0 25 50 TEMPERATURE (°C) 75 100 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output VGATE vs. VIN I_COMP vs. TEMPERATURE IFCOMP 5.20 5.15 5.10 35 VGATE (V) I_COMP (µA) 40 MAX5977 toc05 50 45 5.25 MAX5977 toc04 55 30 25 20 ISCOMP 15 5.05 5.00 4.95 4.90 10 4.85 5 4.80 4.75 0 -50 -25 0 25 50 75 5 0 100 CURRENT OUTPUT ERROR vs. VIN - VSENSE MAX5977 toc07 0.4 0.2 tSCD (µs) CURRENT OUTPUT ERROR (%) 0.6 20 tSCD vs. OVERDRIVE VOLTAGE VIN = VPWR = 12V RCSOUT = 10kI 0.8 15 1000 MAX5977 toc06 1.0 10 VIN (V) TEMPERATURE (°C) 0 -0.2 -0.4 -0.6 -0.8 -1.0 0 10 20 30 40 100 50 0 5 10 15 20 25 30 35 40 45 50 VIN - VSENSE (mV) OVERDRIVE VOLTAGE (mV) SLOW-COMPARATOR RESPONSE TIME (50mV OVERDRIVE) SLOW-COMPARATOR RESPONSE TIME (50mV OVERDRIVE) MAX5997 toc08 RSENSE = 4mI 100µs/div MAX5977 toc09 VIN - VSENSE 50mV/div VIN - VSENSE 100mV/div 0V 0V VGATE 5V/div VGATE 5V/div 0V 0V VSOURCE 2V/div 0V VSOURCE 2V/div 0V RSENSE = 4mI 20µs/div 5 MAX5977A/MAX5977B Typical Operating Characteristics (continued) (VPWR = VIN = 3.3V, TA = +25NC, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.) MAX5977A/MAX5977B 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output Typical Operating Characteristics (continued) (VPWR = VIN = 3.3V, TA = +25NC, RFCOMP = RSCOMP = 2kI, RGATE = 1kI, CGATE = 330nF, CREG = 1FF, unless otherwise noted.) FAST-COMPARATOR RESPONSE TIME (10mV OVERDRIVE) FAULT RETRY TIME (MAX5977B ONLY) MAX5977 toc10 tFSD VFCOMP RSENSE = 4mI MAX5977 toc11 VIN - VSENSE 100mV/div VIN - VSENSE 50mV/div 0V 0V VGATE 5V/div VGATE 5V/div 0V 0V VSOURCE 2V/div 0V VSOURCE 2V/div 0V 2µs/div 40ms/div ICSOUT SMALL-SIGNAL PULSE RESPONSE ICSOUT LARGE-SIGNAL PULSE RESPONSE MAX5977 toc12 MAX5977 toc13 VIN - VSENSE 5mV/div VIN - VSENSE 20mV/div 0V 0V VCSOUT 100mV/div VCSOUT 500mV/div 0V RCSOUT = 10kI 20µs/div 6 RSENSE = 4mI 0V RCSOUT = 10kI 20µs/div 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output SOURCE GATE GND CSOUT PG TOP VIEW 15 14 13 12 11 FAULT 16 CAL 17 MAX5977A MAX5977B I.C. 18 I.C. 19 EP* 1 2 3 4 5 REG PWR AGND UV OV BIAS 20 10 CALSENSE 9 SENSE 8 IN 7 SCOMP 6 FCOMP THIN QFN *CONNECT TO AGND. Pin Description PIN NAME 1 REG Regulator Output. Bypass REG with a 1FF capacitor. FUNCTION 2 PWR Power-Supply Input. Bypass PWR with a 0.1FF or higher value capacitor. 3 AGND 4 UV 5 OV 6 FCOMP 7 SCOMP 8 IN 9 SENSE 10 CALSENSE 11 PG 12 CSOUT Analog Ground Active-High Precision Turn-On Input. UV is used to turn on/off the output and set the input undervoltage lockout threshold. Active-Low Precision Turn-On Input. OV is used to turn on/off the output and set the input overvoltage lockout threshold. Fast Circuit-Breaker Comparator Input. Connect FCOMP to IN with a resistor to set the fast-trip circuitbreaker threshold. Slow Circuit-Breaker Comparator Input. Connect SCOMP to IN with a resistor to set the slow-trip circuit-breaker threshold. Hot-Swap Voltage-Monitoring Input Current-Sense Voltage Input. The voltage across an external sense resistor between IN and SENSE is used to measure the channel current. Calibration Voltage Input Power-Good, Active-High Open-Drain Output Transconductance Current-Sense Amplifier Output. The output current of CSOUT is the product of the voltage measured between SENSE and IN and the transconductance gain (2500FS typ). 13 GND Ground 14 GATE Gate-Driver Output. Connect GATE to the gate of the external n-channel MOSFET switch. 15 SOURCE 16 17 FAULT CAL 18, 19 I.C. 20 BIAS Bias Input. Connect BIAS to REG. — EP Exposed Pad. Connect to AGND. MOSFET Source Voltage Input. Connect SOURCE to the source of the external n-channel MOSFET. Active-Low, Open-Drain Fault Output. When an overcurrent occurs, FAULT goes low. Calibration Mode Select Input Internally Connected. Connect to ground. 7 MAX5977A/MAX5977B Pin Configuration MAX5977A/MAX5977B 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output Functional Diagram IN CS AMPLIFIER SENSE 0 CALSENSE CSOUT MUX S 1 CHARGE PUMP CAL MAX5977A MAX5977B OVERDRIVE DELAY 5µA 2MHz OSCILLATOR GATE SCOMP SLOW CB 25µA FCOMP SOURCE GATE PULLDOWN OD DELAY/ CB TIMER IN PG FAST CB 50µA 50ms PG TIMER IN - 100mV UV UVP 0.59V 10µA 10µA FAULT OV OVP 0.59V S POR UVLO Q GND R PWR REG BIAS 8 LDO REF/ BIAS AUTORETRY ENABLE 0.6V MAX5977B ONLY RETRY TIMER AGND 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output The hot-swap controllers provide electronic circuitbreaker protection and precision current sensing for a single-supply voltage from 1V to 16V. Programmable undervoltage and overvoltage protection qualifies the supply voltage prior to enhancing the external n-channel MOSFET with the internal gate driver. The VariableSpeed/BiLevel fault levels are programmable with external resistors providing both slow and fast circuit-breaker protection. The transconductance current-sense amplifier provides continuous current monitoring with high accuracy and features a calibration mode for production testing. Programmable Undervoltage and Overvoltage Protection The programmable undervoltage and overvoltage protection enables the hot-swap channel when the voltage at UV is above 590mV, and the voltage at OV is below 590mV. After the hot-swap channel is enabled, the hotswap channel is disabled if the voltage at OV exceeds the 590mV threshold. Gate Driver An integrated 5V charge pump supplies the gate-driver output of the devices, allowing it to fully enhance the external n-channel MOSFET during normal operation. The 5FA (typ) current source at GATE slowly charges the gate-to-source capacitance of the external n-channel MOSFET to 5V (typ) relative to the SOURCE input. Programmable Fast-Trip and Slow-Trip Overcurrent Circuit Breaker During normal operation with the channel turned on, two analog comparators are used to detect an overcurrent condition by comparing the voltage across the external sense resistor (RSENSE) connected between IN and SENSE to the voltages across the respective external overcurrent circuit-breaker threshold set resistors connected from IN to FCOMP and SCOMP. Precision current sources at the FCOMP and SCOMP inputs establish these thresholds. If the voltage across the sense resistor is less than the fast-trip and slow-trip overcurrent circuit-breaker thresholds, the GATE output remains high. If either of the thresholds is exceeded due to an overcurrent condition, the GATE output is pulled down to SOURCE by a 500mA current sink, and the FAULT and PG outputs are asserted low. If the sense voltage rises above the fast circuit-breaker threshold, the devices turn off the external MOSFET in 200ns (typ). If the sense voltage rises above the slow circuit-breaker threshold, the internal timer begins counting. If the sense voltage remains above the slow circuit-breaker threshold until the timer expires, the devices turn off the external MOSFET. The slow circuit-breaker timer occurs in 1ms (typ) when the slow-current comparator threshold is overdriven by 1mV and 130Fs (typ) when overdriven by 50mV. Current-Sense Amplifier The integrated transconductance current-sense amplifier features high accuracy with less than 1% error over its 10mV to 50mV input range, and provides continuous current monitoring into the load. The sense voltage of the external sense resistor connected between IN and SENSE is multiplied by the transconductance gain (2500FS typ) of the amplifier with the resulting current output at CSOUT. Calibration Mode The devices' calibration mode bypasses the transconductance amplifier inputs to measure the voltage between IN and CALSENSE when the calibration mode select input CAL is high. This enables the user to apply a known calibration voltage across the current-sense amplifier input. This voltage corresponds to a full scale for the actual sense voltage. During the calibration mode, the current-sense amplifier only measures the calibration voltage between IN and CALSENSE. The calibration mode is completely asynchronous and does not disrupt the circuit-breaker threshold comparison. Once in calibration mode there is no expiration until the CAL input is brought low. This allows the calibration to occur at multiple voltages by applying various calibration voltages during the calibration mode. Fault Output The FAULT output goes low when a slow or fast comparator current-limit fault has occurred. On the MAX5977A, the device is latched in fault mode until it is reset either by initiating a full power-on reset or pulling UV below 590mV. On the MAX5977B, the device reenables the hot-swap output after the autoretry timer has expired in 175ms and FAULT is pulled high if the fault condition has been removed and startup conditions are met. 9 MAX5977A/MAX5977B Detailed Description MAX5977A/MAX5977B 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output Power-Good Output The open-drain, active-high output PG indicates the power-good status of the output. Once the input voltage satisfies the undervoltage and overvoltage requirements for startup and VIN - VSOURCE is less than 100mV and the VGATE - VSOURCE > 4V, the PG timer is started. At the expiration of the 50ms PG timer, PG is asserted high. Applications Information Undervoltage and Overvoltage Protection The undervoltage and overvoltage protection is programmed with a voltage-divider formed by three resistors (R1, R2, and R3) placed in series. The resistor values should be selected such that the series current, IS, is greater than 5FA. The resistor values are then calculated using the following equations with the overvoltage threshold (VOVR), undervoltage threshold (VUVR), and the overvoltage hysteresis (VOVHYS) obtained from the Electrical Characteristics table: V R3 = OVR IS VIN,OV × VUVR − 1 × R3 R2 = VIN,UV × (VOVR − VOVHYS ) VIN,UV R1 = − 1 × (R2 + R3) V UVR where VIN,UV and VIN,OV are the desired undervoltage and overvoltage thresholds for the hot-swap input voltage IN. Programmable Slow and Fast Current Limit The slow and fast current-limit thresholds are programmed by connecting resistors between the high side of RSENSE to SCOMP and FCOMP. The current-limit thresholds are set using the following equations: R SCOMP = and: R FCOMP = I SENSE, SCOMP × R SENSE 25µA I SENSE, FCOMP × R SENSE 50µA where ISENSE,_COMP is the desired circuit-breaker current limit for the slow or fast current limit. 10 Startup Sequence When all conditions for channel turn-on are met, the external n-channel MOSFET switch is fully enhanced with a typical gate-to-source voltage of 5V to ensure a low drain-to-source resistance. The charge pump at GATE sources 5FA to control the output voltage turn-on voltage slew rate. An external capacitor must be added from GATE to ground to further reduce the voltage slew rate. Placing a 1kI resistor in series with this capacitance prevents the added capacitance from increasing the gate turn-off time. Total inrush current is the load current summed with the product of the gate voltage slew rate dV/dt and the load capacitance. To determine the output dV/dt during startup, divide the GATE pullup current IGATEPU by the GATE to ground capacitance. The voltage at the source of the external MOSFET follows the gate voltage, so the load dV/dt is the same as the gate dV/dt. Inrush current is the product of the dV/dt and the load capacitance. The time to start up tSU is the hot-swap voltage VIN divided by the output dV/dt. Be sure to choose an external MOSFET that can handle the power dissipated during startup. The inrush current is roughly constant during startup and the voltage drop across the MOSFET (drain to source) decreases linearly as the load capacitance charges. The resulting power dissipation is therefore roughly equivalent to a single pulse of magnitude (VIN x Inrush current)/2 and duration tSU. Refer to the thermal resistance charts in the MOSFET data sheet to determine the junction temperature rise during startup, and ensure that this does not exceed the maximum junction temperature for worstcase ambient conditions. Transconductance Current-Sense Amplifier The current-sense resistor, RSENSE, must be connected between IN and SENSE to sense the average current into the load. The voltage drop across RSENSE should be less than or equal to the slow current-limit threshold; therefore, RSENSE should be selected based on the following equation: R SENSE × ISENSE,FS ≤ VSCOMP where ISENSE,FS is the full-scale current into the load and VSCOMP is the slow current-limit threshold. A Kelvin sense connection should be used to connect RSENSE to IN and SENSE. 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output (d = tSU/(tSU + tRETRY)). Calculate the required transient thermal resistance with the following equation: Z θJA(MAX) ≤ R CSOUT × G M × VSENSE, FS ≤ 2.5V n-Channel MOSFET Selection Select the external n-channel MOSFET according to the application’s current level. 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). The MAX5977A’s fault latch allows the use of MOSFETs with lower power ratings. A MOSFET typically withstands single-shot pulses with higher dissipation than the specified package rating. 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 turn-off 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 (MAX5977A). 2)The continuous (MAX5977B). automatic retry after a 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 devices close to the card’s connector, and a 0.01FF capacitor to GND should be placed as close as possible to VIN. Use a ground plane to minimize impedance and inductance. Minimize the current-sense resistor trace length and ensure accurate current sensing with Kelvin connections. 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. Related Parts PART DESCRIPTION MAX5970 0 to 16V, Dual Hot-Swap Controller with a 10-Bit Current and Voltage Monitor and Four LED Drivers MAX5978 0 to 16V, Single Hot-Swap Controller with a 10-Bit Current and Voltage Monitor Plus Four LED Drivers fault MOSFET manufacturers typically include the package thermal resistance from junction to ambient (RBJA) and thermal resistance from junction to case (RBJC), which determine the startup time and the retry duty cycle TJMAX × TA VIN × IINRUSH 11 MAX5977A/MAX5977B An output resistor, RCSOUT, must be connected between the transconductance current-sense amplifier output CSOUT and AGND. The transconductance GM, of the amplifier is typically 2500FS: MAX5977A/MAX5977B 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output Typical Application Circuit RSENSE VIN 1V TO 16V TO LOAD RSCOMP R1 SCOMP FCOMP IN SENSE UV 49.9I CGATE GATE SOURCE R2 MAX1393 ADC CSOUT OV 0.1µF RCSOUT R3 CALSENSE IN 125µA PRECISION CURRENT SOURCE CL RGATE RFCOMP MAX5977A MAX5977B OUTF OUTS GND 5.1kI 1µF +3.3V 4.99kI MAX6033AAUT25 10kI 2.7V TO 16V 10kI PWR 0.1µF FAULT BIAS REG *OPTIONAL 1µF AGND GND 12 CAL Package Information Chip Information PROCESS: BiCMOS I/O I/O µP I/O PG For the latest package outline information and land patterns, 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. 20 TQFN-EP T2044+3 21-0139 90-0037 1V to 16V, Single-Channel, Hot-Swap Controllers with Precision Current-Sensing Output REVISION NUMBER REVISION DATE 0 9/10 Initial release — 1 1/11 Changed current-sense amplifier specifications in Electrical Characteristics table 3 2 7/11 Updated Electrical Characteristics specifications to reflect improved yield of part 2, 3 DESCRIPTION PAGES CHANGED 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 © 2011 Maxim Integrated Products 13 Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX5977A/MAX5977B Revision History