19-2850; Rev 0; 4/03 +60V Simple Swapper Hot-Swap Switch During startup, an integrated 0.45Ω power MOSFET regulates the current and voltage between the backplane power source and the load. After startup, the MOSFET is fully enhanced to reduce its on-resistance. To ensure robust operation, the MAX5923 contains built-in safety features that monitor fault conditions and prevent damage to the internal MOSFET. The MAX5923 monitors three parameters for fault conditions: zero current, overcurrent, and thermal overload. The output overcurrent limit counts the time the MAX5923 spends in an overcurrent condition and shuts down the pass transistor if the current limit is exceeded for the overcurrent time limit. The zero-current detection counts the time the output current is below the zero-current threshold and shuts down the pass transistor if the counter reaches the zero-current time limit. The thermal monitoring feature shuts down the pass transistor if the die temperature reaches the overtemperature limit. A fault logic output indicates when an overtemperature or an overcurrent condition has occurred and a zero-current logic output indicates if there is a zero-current condition. An undervoltage detection circuitry keeps the pass transistor off until the input voltage is above the undervoltage lockout (UVLO) threshold, which is internally set or can be set externally with a resistive divider. A power-OK (POK) output is provided to signal when the output voltage has reached to within 0.75V of the input voltage. An Enable input allows the host system to disconnect the system from the load and/or reset a fault condition by toggling Enable. The MAX5923 is available in a 20-pin TSSOP package and operates in the extended -40°C to +85°C temperature range. Applications Network Routers/Switches Current Limiter Features ♦ Wide Operating Input Range: +16V to +60V ♦ 0.45Ω Integrated Power Switch ♦ Programmable Output Current Up to 800mA ♦ Over/Undercurrent-Limit Detection ♦ Input Logic Signals Compatible with 1.8V to 5V CMOS Logic ♦ Separate Analog and Digital Grounds with Up to ±4V Offset ♦ Power-OK Status Output ♦ Overcurrent Protection with Status Outputs ♦ Built-In Thermal Shutdown ♦ Internal Switch Protection Circuitry ♦ Current-Limit Foldback with Timeout and DutyCycle Control ♦ Latch or Autorestart Fault Management Ordering Information PART MAX5923EUP TEMP RANGE PIN-PACKAGE -40°C to +85°C 20 TSSOP Typical Operating Circuit +16V TO +60V IN OUT D1 RSENSE +1.65V TO +5.5V VDIG DRAIN RPU MAX5923 UVLO ON OFF LATCH RPU ZC_EN RPU EN ZC FAULT POK AGND_S DGND Servers Industrial Equipment ALL SIGNAL AND DIGITAL INPUTS/OUTPUTS ARE REFERENCED TO DGND. DGND CAN BE ±4V FROM AGND_S. Simple Swapper is a trademark of Maxim Integrated Products, Inc. Pin Configuration appears at end of data sheet. ________________________________________________________________ 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 MAX5923 General Description The MAX5923 is a fully integrated Simple Swapper™ hot-swap switch for positive supply rails. The device allows the safe insertion and removal of circuit cards into live backplanes or ports without causing glitches on the power-supply rail. The device also monitors various circuit parameters and disconnects the load if a fault condition occurs, alerting the host with a logiclevel FAULT output. The MAX5923 operates over the +16V to +60V input voltage range. MAX5923 +60V Simple Swapper Hot-Swap Switch ABSOLUTE MAXIMUM RATINGS All Voltages with Respect to AGND_S, Unless Otherwise Noted IN ............................................................................-0.3V to +76V UVLO ........................................................................-0.3V to +6V VDIG to DGND .........................................................-0.3V to +6V OUT .......................................................-0.3V to (VDRAIN + 0.3V) DRAIN ..........................................................-0.3V to (VIN + 0.3V) EN, ZC_EN, ZC, FAULT, POK and LATCH to DGND ...............................................-0.3V to +6V DGND ..........................................................................-5V to +5V Maximum Current into DRAIN...............................................0.8A Maximum Current into POK, ZC, FAULT (sinking)..............20mA Continuous Power Dissipation (TA = +70°C) 20-Pin TSSOP (derate 11.1mW/°C above +70°C) .......879mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10s) .................................+300°C 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 = 48V, VDIG = 3.3V, AGND_S = AGND = DGND = 0V, RSENSE = 0.5Ω ±1%, UVLO = open, EN = VDIG, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL Analog Input Voltage Range VIN Analog Input Supply Current IIN Digital Input Voltage Range VDIG Digital Input Supply Current IDIG CONDITIONS VIN = 72V, measured at AGND after OUT has stopped slewing OUT Current-Limit Foldback Voltage VFBSTOP Current-Limit Sense Voltage (VIN - VDRS) (Note 3) VILIM DMOS On-Resistance 1 1.65 VDIG = 5V 0.05 -4 Current-Limit Response Time Overcurrent Timeout TYP 16 DGND-to-AGND Operating Voltage Range Current-Limit Sense Foldback Voltage (VIN - VDRS) MIN VILIM_fb tOC RDSON MAX UNITS 60 V 1.6 mA 5.5 V 0.1 mA +4 V OUT shorted to AGND (Note 1) 1 µs (Note 2) 18 V Maximum voltage across RSENSE at VOUT > VFBSTOP 198 212 225 0°C to +85°C 203 212 221 VOUT = 0V 64 70 76 0°C to +85°C 50 60 75 60 70 OUT shorted to AGND (Note 4) IOUT = 100mA 50 TA = +25°C 0.45 TA = +85°C 0.75 mV ms Ω Power-Off OUT Sink Current EN = DGND, VOUT = 48V Maximum Output Voltage Slew Rate dVOUT/dt, VOUT rising, no load 100 V/ms Maximum Output Current Slew Rate dIOUT/dt, VOUT rising, CLOAD = 100µF 35 A/ms Power-OK Threshold (VIN - VOUT) POK Output Low Voltage POK Output Leakage Current 2 VTHPOK VOUT rising, POK from low to high Hysteresis VPOK_LOW IPOK = 3mA VPOK = 3.3V 15 mV 650 750 850 10 0.05 _______________________________________________________________________________________ µA mV % 0.4 V 1 µA +60V Simple Swapper Hot-Swap Switch (VIN = 48V, VDIG = 3.3V, AGND_S = AGND = DGND = 0V, RSENSE = 0.5Ω ±1%, UVLO = open, EN = VDIG, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER POK Output Delay (Note 5) Zero-Current Detection Threshold Voltage (VIN - VDRS) ZC Output Low Voltage SYMBOL MIN TYP MAX POK from high to low, VOUT falling 1 1.4 1.8 tPOK_HIGH POK from low to high, VOUT rising 74 88 102 2.7 3.75 4.8 tPOK_LOW VZCTH VZC_LOW ZC Output Leakage Current Zero-Current Detection Delay Zero-Current Deglitch Time IZC = 3mA VZC = 3.3V tZCDEL tZC_DEG Thermal Shutdown Shutdown Autorestart Time CONDITIONS tRESTART ZC from high to low, IOUT falling (Note 6) 300 UNITS ms mV 0.4 V 0.05 1 µA 350 400 ms IOUT rising 10 Temperature rising 150 Hysteresis 30 ms °C LATCH = low (Note 7) 1.6 1.92 2.24 UVLO floating, VIN rising 26 28 30 s UNDERVOLTAGE LOCKOUT Default VIN UVLO UVLOTH UVLO Comparator Threshold VREF Hysteresis Referenced to AGND 2.5 1.31 Hysteresis UVLO Input Resistance 1.33 1.36 110 V V mV 50 kΩ 0.7 × VDIG V LOGIC SIGNALS EN, LATCH, and ZC_EN Input High Voltage VIH EN, LATCH, and ZC_EN Input Low Voltage VIL 1.65V < VDIG < 5.5V 1.65V < VDIG < 2.0V 0.3V × VDIG 2.0V < VDIG < 5.5V 0.8 EN, LATCH, and ZC_EN Input Current -1 EN Low Pulse Width 3 FAULT Output Low Voltage FAULT Output Leakage Current VOL +1 µA µs ISINK = 3mA V FAULT = 3.3V V 0.05 0.4 V 1 µA This is the time from an output overcurrent or short-circuit condition until the output goes into regulated current limit. OUT voltage above which the output current limit is at its full value. See the Overcurrent Protection section. This is the time the part stays in current-limit mode during overload condition. After tOC elapses (or when the junction temperature hits +150°C) the part shuts down. Note 5: See Typical Operating Characteristics. Note 6: This is the delay from IOUT falling below the zero-current threshold until ZC goes low. A ZC condition shuts down and latches off the IC. Note 7: See the Fault Management section. Note 1: Note 2: Note 3: Note 4: _______________________________________________________________________________________ 3 MAX5923 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 48V, VDIG, EN, LATCH, CLASS, ZC_EN = 3.3V, DCA, AGND_S = AGND = DGND = 0V, RSENSE = 0.5Ω, UVLO floating, TA = +25°C, unless otherwise noted.) VIN SUPPLY CURRENT vs. TEMPERATURE TA = +85°C 0.85 TA = +25°C 0.80 MAX5923 toc02 12.0 VIN = 60V 11.9 11.8 11.7 0.90 0.85 IDIG (µA) SUPPLY CURRENT (mA) 0.90 MEASURED AT AGND 0.95 SUPPLY CURRENT (mA) MEASURED AT AGND 0.95 1.00 MAX5923 toc01 1.00 DIGITAL SUPPLY CURRENT vs. TEMPERATURE MAX5923 toc03 VIN SUPPLY CURRENT vs. INPUT VOLTAGE VIN = 48V 11.6 11.5 11.4 0.80 11.3 VIN = 32V TA = -40°C 0.75 0.75 0.70 0.70 11.2 11.1 40 44 48 52 56 -25 -10 20 35 50 TEMPERATURE (°C) VIN UNDERVOLTAGE LOCKOUT vs. TEMPERATURE MOSFET RDS-ON vs. TEMPERATURE MAX5923 toc04 39 VIN RISING 0.60 65 80 35 VIN FALLING 34 -10 5 20 35 50 65 80 215 IOUT = 100mA 214 SENSE TRIP VOLTAGE (V) ON-RESISTANCE (Ω) 36 -25 SENSE TRIP VOLTAGE vs. TEMPERATURE 38 37 -40 TEMPERATURE (°C) 0.55 0.50 0.45 0.40 213 VIN = 60V VIN = 48V 212 211 210 209 VIN = 32V 208 207 0.35 33 206 0.30 20 35 50 65 80 205 -40 -25 -10 TEMPERATURE (°C) 50 65 80 -40 -25 -10 3.68 0.40 0.35 0.30 0.25 0.20 0.15 0.10 VIN = 60V 3.66 3.64 3.62 VIN = 48V 3.60 VIN = 32V 3.58 5 20 35 50 65 80 TEMPERATURE (°C) 3.70 ON-RESISTANCE (Ω) 0.50 0.45 35 ZERO-CURRENT DETECTION THRESHOLD VOLTAGE vs. TEMPERATURE MAX5923 toc07 0.55 20 TEMPERATURE (°C) FOLDBACK CURRENT LIMIT (ILIM vs. VOUT) 0.60 5 ON-RESISTANCE vs. VDRAIN 0.8 IOUT = 100mA 0.7 ON-RESISTANCE (Ω) 5 MAX5923 toc08 -40 -25 -10 3.56 TA = +85°C MAX5923 toc09 32 0.6 TA = +25°C 0.5 TA = -40°C 0.4 0.3 3.54 0.2 3.52 0.05 0 3.50 0 5 10 15 20 25 30 35 40 45 50 OUTPUT VOLTAGE (V) 4 5 INPUT VOLTAGE (V) 40 DEFAULT VIN UVLO (V) 11.0 -40 60 MAX5923 toc06 36 MAX5923 toc05 32 ILIM (A) MAX5923 +60V Simple Swapper Hot-Swap Switch 0.1 -40 -25 -10 5 20 35 50 TEMPERATURE (°C) 65 80 28 33 38 43 48 53 58 INPUT VOLTAGE (V) _______________________________________________________________________________________ 63 68 73 +60V Simple Swapper Hot-Swap Switch OVERCURRENT TIMEOUT (RLOAD FROM 240Ω TO 75Ω) IDIG (µA) DIGITAL SUPPLY CURRENT vs. VDIG MAX5923 toc11 MAX5923 toc10 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 20V/div VOUT 0V 5V/div POK 0V 200mA/div IOUT 0A 5V/div FAULT 0V 0 1.0 2.0 3.0 4.0 5.0 6.0 20ms/div VDIG (V) SHORT-CIRCUIT RESPONSE TIME POK LOW-TO-HIGH DELAY TIME MAX5923 toc12 20V/div MAX5923 toc13 VOUT POK 5V/div 0V 5V/div 0V POK 200mA/div 0A IOUT 5V/div 0V VOUT 20V/div FAULT 20ms/div 40ms/div POK HIGH-TO-LOW DELAY TIME ZC TO OUT DELAY MAX5923 toc14 MAX5923 toc15 20V/div 20V/div VOUT 0V 5V/div 0V POK 1ms/div VOUT 0V 5V/div 0V 5V/div 0V POK ZC IOUT 1.25mA/div 0A 400µs/div _______________________________________________________________________________________ 5 MAX5923 Typical Operating Characteristics (continued) (VIN = 48V, VDIG, EN, LATCH, CLASS, ZC_EN = 3.3V, DCA, AGND_S = AGND = DGND = 0V, RSENSE = 0.5Ω, UVLO floating, TA = +25°C, unless otherwise noted.) MAX5923 +60V Simple Swapper Hot-Swap Switch Typical Operating Characteristics (continued) (VIN = 48V, VDIG, EN, LATCH, CLASS, ZC_EN = 3.3V, DCA, AGND_S = AGND = DGND = 0V, RSENSE = 0.5Ω, UVLO floating, TA = +25°C, unless otherwise noted.) ZERO CURRENT HIGH-TO-LOW DETECTION TIME WAVEFORM ZERO CURRENT LOW-TO-HIGH DEGLITCH TIME WAVEFORM (11ms GLITCH) MAX5923 toc16 MAX5923 toc17 OUT 20V/div VOUT 20V/div POK 5V/div ZC 5V/div POK 5V/div ZC 5V/div tZCDEL GLITCH > tZC_DEG tZCDEL IOUT 100mA/div 100ms/div 100ms/div ZERO CURRENT LOW-TO-HIGH DEGLITCH TIME WAVEFORM (10ms) OVERCURRENT RESTART DELAY MAX5923 toc18 MAX5923 toc19 VOUT 20V/div VOUT 20V/div tRESTART tZCDEL POK 5V/div POK 5V/div ZC 5V/div FAULT 5V/div GLITCH > tZC_DEG IOUT 100mA/div IOUT 500mA/div 100ms/div 400ms/div STARTUP WITH OUT SHORTED TO AGND OVERCURRENT TIMEOUT (RLOAD FROM 240Ω to 75Ω) MAX5923 toc20 MAX5923 toc21 VOUT 20V/div 5V/div 0V 5V/div 0V VOUT POK IOUT 500µA/div IOUT 200mA/div 0A 2V/div EN POK 5V/div 0V 100ms/div 6 2ms/div _______________________________________________________________________________________ +60V Simple Swapper Hot-Swap Switch OUTPUT SHORT-CIRCUIT RESPONSE OUTPUT SHORT-CIRCUIT RESPONSE MAX5923 toc22 MAX5923 toc23 IOUT 10A/div IOUT 200mA/div VOUT VOUT 20V/div 20V/div 4µs/div 200µs/div Pin Description PIN NAME FUNCTION — AGND Analog Ground. This is the return of analog power input. AGND can vary ±4V from DGND. AGND and DGND must be connected together at a single point in the system. 1, 2 DRAIN Drain connection for the integrated MOSFET. Connect a sense resistor, RSENSE, from DRAIN to IN. These pins are also the current-sense resistor negative terminal. RSENSE sets the overcurrent-limit and open-circuit detection threshold. These two pins must be connected together. 3 IN 4, 12, 18, 19 N.C. 5 AGND_S 6 UVLO Undervoltage Lockout Adjustment Input. Referenced to AGND. Connect to the center point of a resistive divider from IN to AGND to adjust the UVLO threshold. Leave open for default value. 7 FAULT Fault Signal Open-Drain Logic Output. Reference to DGND. FAULT is latched low when: • An overtemperature condition occurs and/or, • An overcurrent condition that has lasted for more than tOC. 8 POK Power-OK Open-Drain Logic Output. Reference to DGND. POK goes open drain a time tPOK_HIGH after VOUT raises to within VTHPOK from VIN. POK goes low a time tPOK_LOW after VOUT falls out of the VTHPOK from VIN. 9 ZC Zero-Current Fault Signal. Open-drain logic output. Reference to DGND. ZC is latched low when there is a zero-current condition lasting longer than tZCDEL. ZC is open drain otherwise. The zero-current detection circuit is enabled immediately after the POK signal goes high. 10 TP1 Must be left open or connected to AGND 11 TP3 Must be left open or connected to AGND Input Voltage. Connect to a positive voltage source between 16V to 60V from IN to AGND. This is the current-sense resistor positive terminal. Bypass to AGND with a 100µF, 100V electrolytic capacitor and 0.1µF, 100V ceramic capacitor. Place the ceramic capacitor close to this pin. No Connection. Not internally connected. Leave pins open. Pins are left unconnected to provide additional spacing between the high-voltage pins and other pins. Analog Ground Sense. Connect a 1Ω resistor from AGND_S to AGND. This resistor protects the IC during an output short-circuit condition. _______________________________________________________________________________________ 7 MAX5923 Typical Operating Characteristics (continued) (VIN = 48V, VDIG, EN, LATCH, CLASS, ZC_EN = 3.3V, DCA, AGND_S = AGND = DGND = 0V, RSENSE = 0.5Ω, UVLO floating, TA = +25°C, unless otherwise noted.) MAX5923 +60V Simple Swapper Hot-Swap Switch Pin Description (continued) PIN NAME FUNCTION 13 DGND Digital Ground. DGND can vary ±4V from AGND. DGND and AGND must be connected together at a single point in the system. 14 LATCH Fault Management Selection Digital Input. Referenced to DGND. Connect to logic high to latch off after a fault condition. Connect to logic low for automatic restart after a fault condition (see the Fault Management section). 15 ZC_EN Zero-Current Detection Enable Logic Input. Referenced to DGND. Connect ZC_EN to a logic high to enable the zero-current detection circuitry. Connect ZC_EN to a logic low to disable this function. 16 EN 17 VDIG Digital Supply Voltage. VDIG is the supply voltage for the internal digital logic circuity. EN, LATCH, and ZC_EN input logic thresholds are automatically scaled to the voltage on VDIG. See the Typical Application Circuit for proper filtering. 20 OUT Output Voltage ON/OFF Control-Logic Input. Referenced to DGND. Connect to logic high to enable the device. Connect to logic low to disable the device and reset a latched-off condition. Detailed Description The MAX5923 is a fully integrated hot-swap switch that contains a 0.45Ω integrated power MOSFET and operates from a +16V to +60V supply rail. The device allows the safe insertion and removal of circuit cards into live backplanes without causing problematic glitches on the supply rail. The device also monitors various circuit parameters and disconnects the load if a fault condition occurs, alerting the host with a logic-level FAULT output. The MAX5923 provides an Enable input to enable/disable the device with a logic signal and logic output POK that indicates when the output voltage has reached within 750mV of the input voltage. Three fault conditions are monitored: a zero-current condition, an overcurrent condition, and a thermal overload condition. A FAULT output indicates to the host if an overcurrent or thermal fault occurs and a ZC output indicates if the output has a zerocurrent condition. An undervoltage lockout circuitry shuts down the device if the input voltage falls below the UVLO threshold. Power-Up Mode During power-up, the MAX5923 gradually turns on the integrated N-channel MOSFET. To minimize EMI, the MAX5923 limits the output voltage slew rate at the OUT pin to dVOUT/dt = 100V/ms (max) and the output current slew rate out of the OUT pin to dIOUT/dt = 35A/ms (max). The MAX5923 has an integrated 0.45Ω N-channel power MOSFET. The MOSFET’s drain is connected to the DRAIN pin and its source is connected to the OUT pin. The MAX5923 monitors and provides current-limit protection to the load at all times. The current limit is programmable using an external current-sensing resistor 8 connected from IN to DRAIN. The MAX5923 features current-limit foldback and duty-cycle limit to ensure robust operation during load-fault and short-circuit conditions (see the Overcurrent Protection section). When V OUT is within 750mV of V IN for more than tPOK_HIGH, POK goes open-drain. After POK is asserted, the MAX5923 activates the zero-current detection function. This function monitors the output for an undercurrent condition and eventually turns off the power to the output if the load is disconnected (see the ZeroCurrent Detection section). Undervoltage Lockout (UVLO) The MAX5923 operates from a +16V to +60V supply voltage range and has a default UVLO set at +28V. The UVLO threshold is adjustable using a resistive divider connected to the UVLO pin (see Figure 1). When the input voltage is below the UVLO threshold, all operation stops and the MOSFET is held off. When the input voltage is above the UVLO threshold and EN is high, the MAX5923 goes into operation. To adjust the UVLO threshold, connect an external resistive divider from IN to UVLO and then from UVLO to AGND. Use the following equation to calculate the new UVLO threshold: R1 VUVLO _ TH = VREF 1 + R2 VREF is typically 1.33V. The UVLO pin input resistance is 50kΩ (min), so keep the R1 and R2 parallel combination value at least 20 times smaller than 50kΩ to minimize the new UVLO threshold error. _______________________________________________________________________________________ +60V Simple Swapper Hot-Swap Switch MAX5923 VIN = 16V TO 60V VILM IN R1 MAX5923 UVLO VILM/3 R2 AGND VFBSTART (2V) Figure 1. Setting Undervoltage Lockout with an External Resistive Divider Digital Logic VDIG is the input supply for the internal logic circuitry. The logic input thresholds of EN, LATCH, and ZC_EN are CMOS compatible and are determined by the voltage at VDIG, which can range from 1.65V to 5.5V. The POK and FAULT outputs are open-drain. VDIG and all logic inputs and outputs are referenced to DGND. DGND is not connected to AGND_S internally and must be connected externally at a single point in the system to AGND_S. The maximum allowable difference in the voltage between DGND and AGND is ±4V. Enable (EN) EN is a logic input to enable MAX5923. Bringing EN low halts all operations and turns off the internal power MOSFET. When EN is high and the input voltage is above the UVLO threshold, the MAX5923 begins operating. Enable is also used to unlatch the part after a latched fault condition. This is done by toggling EN low and high again after a fault condition. Overcurrent Protection The MAX5923 provides a sophisticated overcurrent protection circuitry to ensure the robust operation under output current transient and current-fault conditions. The current protection circuitry employs a Constant Current Limit, a Current Foldback, and an Overcurrent Timeout. The device monitors the voltage drop, VSENSE (VSENSE = VIN - VDRAIN) in order to determine the load current. Constant Current Limit The MAX5923 monitors VSENSE at all times and regulates the current through the power MOSFET as necessary to keep VSENSE (max) to the current-limit sense voltage (VILIM = 212mV). The load-current limit, ILIM, is programmed by the current-sense resistor, RSENSE, connected from IN to DRAIN (ILIM = VILIM/RSENSE). VFBSTOP (18V) VOUT (V) Figure 2. Current Foldback Characteristic When the load current is less than ILIM, the MOSFET is fully on. When the load is trying to draw more than ILIM, the OUT pin works like a constant current source, limiting the output current to ILIM. If IOUT is greater than ILIM for greater than the current-limit timeout, a currentlimit fault is generated and the power MOSFET is turned off (see the Overcurrent Timeout and Fault Management section). Current Foldback While in current-limit condition, the voltage at the OUT pin drops. As the load resistance reduces (more loading), the output voltage reduces accordingly to maintain a constant load current. The power dissipation in the power MOSFET is (VDRAIN - VOUT) × ILIM. As the output voltage drops lower, more power is dissipated across the power MOSFET. To reduce this power dissipation, the MAX5923 offers a current foldback feature where it linearly reduces the VILIM value when VOUT drops below the OUT currentlimit foldback voltage (VFBSTOP = 18V). Figure 2 illustrates this current foldback limit behavior. Overcurrent Timeout The MAX5923 keeps track of the time it is in current limit. An internal digital counter begins incrementing its count at 1count/ms when VSENSE exceeds its limit (either VILIM or VILIM foldback in foldback mode). The counter is reset to zero if the current falls back below the current limit. When the cumulative count reaches 60, an overcurrent fault is generated. After an overcurrent fault condition, the switch is turned off and the FAULT signal goes low. This overcurrent timeout enables the MAX5923 to operate in a periodic overcurrent condition without causing a fault. See Figure 3 for an example of periodic overcurrent condition without causing a fault. _______________________________________________________________________________________ 9 +60V Simple Swapper Hot-Swap Switch MAX5923 Zero-Current Detection Zero-current detection is enabled if ZC_EN is high and only after the startup period has finished (indicated by POK going high). When VSENSE falls below the zerocurrent threshold (VZCTH) for a continuous tZCDEL = 350ms, a zero-current fault is generated. The MOSFET is turned off and ZC is latched low. ZC is open drain during initial power-up. After a zero-current fault has occurred, the MAX5923 is latched off and is restarted by applying a low-to-high transition on the EN pin. ILIMIT IOUT 0V VFAULT 0V t tOC tRESTART t < tOC Figure 3. Periodic Overcurrent Without Generating a Fault Output Clamping During Short Circuit During an output short-circuit condition, the energy stored in the output capacitor is dumped onto the short and builds up a large current in the power path and its parasitic inductance. The larger the output capacitor, the larger the current buildup. The parasitic inductive current circulates through the short circuit and brings OUT below ground level. A Schottky diode is needed at the output to provide the path for this circulating current and to prevent OUT from going too far below ground and exceeding the MAX5923’s absolute maximum ratings. For an output capacitor with low ESR (ceramic and film type), and with values of 0.47µF or less, a B1100LB (100V, 1A Schottky) is required as shown in the Typical Application Circuit. For higher values of capacitance, more robust clamping is required. For applications using aluminum electrolytic capacitors, which have relatively high ESR, the requirement of the clamp diode is reduced. Good layout with less parasitic trace inductance also helps in reducing the clamping diode requirement and should be examined on a case-by-case basis. Power-OK (POK) POK goes open-drain tPOK_HIGH (88ms) after VOUT rises to within 0.75V (VTHPOK) from VIN. POK goes low tPOK_LOW (1.4ms) after VOUT drops 0.75V below VIN. 10 At any time during a zero-current condition, if VSENSE goes above VZCTH for the zero-current deglitch time (tZC_DEG = 10ms), the zero-current counter resets to zero and a zero-current fault is not generated. Bring ZC_EN low to disable the zero-current detection function. ZC stays high impedance in this mode. Thermal Shutdown If the MAX5923 die temperature reaches +150°C, an overtemperature fault is generated. The MOSFET turns off and FAULT goes low. The MAX5923 die temperature must cool down below +120°C before the overtemperature fault condition is removed (see the Fault Management section). Fault Report (FAULT) FAULT goes low when there is an overcurrent fault and/or an overtemperature fault. FAULT is open drain otherwise. After a fault, the FAULT signal is latched low. FAULT is unlatched at the beginning of the next power mode. Fault Management The MAX5923 offers either latched-off or autoretry fault management configurable by the LATCH input. Bringing LATCH high puts the device into latch mode while pulling LATCH low selects the autoretry option. In latch mode, the MAX5923 turns the MOSFET off and keeps it off after an overcurrent fault or an overtemperature fault. After the fault condition goes away, recycle the power supplies or toggle the EN pin low and high again to unlatch the part. However, the part waits a tRESTART period (1.92s) before recovering from a fault condition and resuming normal operation. In autoretry mode, MAX5923 turns the MOSFET off after an overcurrent or overtemperature fault. After the fault condition is removed, the device waits a tRESTART period (1.92s) and then automatically restarts. If the fault was due to an overtemperature condition, the MAX5923 waits for its die temperature to cool down below the hysteresis level before starting the tRESTART time. ______________________________________________________________________________________ +60V Simple Swapper Hot-Swap Switch +16V TO +60V IN 100µF (100V) 0.5Ω (1W) OUT 1µF (100V) D1 B1100LB (100V, 1A) +1.65V TO +5.5V 100Ω VDIG DRAIN 0.1µF 2kΩ 10µF MAX5923 UVLO ON OFF LATCH ZC_EN EN 2kΩ 2kΩ ZC FAULT 1Ω (1/16W) POK AGND_S DGND ALL SIGNAL AND DIGITAL INPUTS/OUTPUTS ARE REFERENCED TO DGND. DGND CAN BE ±4V FROM AGND_S. Pin Configuration Chip Information TRANSISTOR COUNT: 8,687 PROCESS: BiCMOS TOP VIEW DRAIN 1 20 OUT DRAIN 2 19 N.C. IN 3 18 N.C. N.C. 4 17 VDIG AGND_S 5 UVLO 6 16 EN MAX5923 15 ZC_EN FAULT 7 14 LATCH POK 8 13 DGND ZC 9 12 N.C. TP1 10 11 TP3 TSSOP ______________________________________________________________________________________ 11 MAX5923 Typical Application Circuit 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.) TSSOP4.40mm.EPS MAX5923 +60V Simple Swapper Hot-Swap Switch 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. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.