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19-2850; Rev 0; 4/03
+60V Simple Swapper Hot-Swap Switch
General Description
The MAX5923 is a fully integrated Simple SwapperTM 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. During startup, an integrated 0.45 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 -40C to +85C temperature range. o 0.45 Integrated Power Switch o Programmable Output Current Up to 800mA o Over/Undercurrent-Limit Detection o Input Logic Signals Compatible with 1.8V to 5V CMOS Logic o Separate Analog and Digital Grounds with Up to 4V Offset o Power-OK Status Output o Overcurrent Protection with Status Outputs o Built-In Thermal Shutdown o Internal Switch Protection Circuitry o Current-Limit Foldback with Timeout and DutyCycle Control o Latch or Autorestart Fault Management
Features
o Wide Operating Input Range: +16V to +60V
MAX5923
Ordering Information
PART MAX5923EUP TEMP RANGE -40C to +85C PIN-PACKAGE 20 TSSOP
Typical Operating Circuit
+16V TO +60V IN RSENSE DRAIN VDIG RPU OUT D1 +1.65V TO +5.5V
MAX5923
UVLO LATCH RPU
ON OFF EN
ZC_EN RPU ZC FAULT POK AGND_S DGND
Applications
Network Routers/Switches Current Limiter 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. 1
________________________________________________________________ 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.
+60V Simple Swapper Hot-Swap Switch MAX5923
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 = +70C) 20-Pin TSSOP (derate 11.1mW/C above +70C) .......879mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10s) .................................+300C
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 = 0.5 1%, UVLO = open, EN = VDIG, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER Analog Input Voltage Range Analog Input Supply Current Digital Input Voltage Range Digital Input Supply Current DGND-to-AGND Operating Voltage Range Current-Limit Response Time OUT Current-Limit Foldback Voltage Current-Limit Sense Voltage (VIN - VDRS) (Note 3) Current-Limit Sense Foldback Voltage (VIN - VDRS) Overcurrent Timeout DMOS On-Resistance Power-Off OUT Sink Current Maximum Output Voltage Slew Rate Maximum Output Current Slew Rate Power-OK Threshold (VIN - VOUT) POK Output Low Voltage POK Output Leakage Current VTHPOK VFBSTOP OUT shorted to AGND (Note 1) (Note 2) Maximum voltage across RSENSE at VOUT > VFBSTOP 0C to +85C VILIM_fb tOC RDSON VOUT = 0V 0C to +85C OUT shorted to AGND (Note 4) IOUT = 100mA TA = +25C TA = +85C 198 203 64 50 50 SYMBOL VIN IIN VDIG IDIG VDIG = 5V -4 1 18 212 212 70 60 60 0.45 0.75 15 100 35 650 750 10 0.4 0.05 1 850 225 221 76 75 70 mV ms A V/ms A/ms mV % V A VIN = 72V, measured at AGND after OUT has stopped slewing 1.65 0.05 CONDITIONS MIN 16 1 TYP MAX 60 1.6 5.5 0.1 +4 UNITS V mA V mA V s V
VILIM
mV
EN = DGND, VOUT = 48V dVOUT/dt, VOUT rising, no load dIOUT/dt, VOUT rising, CLOAD = 100F VOUT rising, POK from low to high Hysteresis
VPOK_LOW IPOK = 3mA VPOK = 3.3V
2
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+60V Simple Swapper Hot-Swap Switch
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 48V, VDIG = 3.3V, AGND_S = AGND = DGND = 0V, RSENSE = 0.5 1%, UVLO = open, EN = VDIG, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER POK Output Delay (Note 5) Zero-Current Detection Threshold Voltage (VIN - VDRS) ZC Output Low Voltage ZC Output Leakage Current Zero-Current Detection Delay Zero-Current Deglitch Time Thermal Shutdown Shutdown Autorestart Time UNDERVOLTAGE LOCKOUT Default VIN UVLO UVLO Comparator Threshold UVLO Input Resistance LOGIC SIGNALS EN, LATCH, and ZC_EN Input High Voltage EN, LATCH, and ZC_EN Input Low Voltage EN, LATCH, and ZC_EN Input Current EN Low Pulse Width FAULT Output Low Voltage FAULT Output Leakage Current VOL ISINK = 3mA V FAULT = 3.3V 0.05 VIH 1.65V < VDIG < 5.5V 1.65V < VDIG < 2.0V 2.0V < VDIG < 5.5V -1 3 0.4 1 0.7 x VDIG 0.3V x VDIG 0.8 +1 A s V A V UVLOTH VREF UVLO floating, VIN rising Hysteresis Referenced to AGND Hysteresis 50 1.31 26 28 2.5 1.33 110 1.36 30 V V mV k tRESTART tZCDEL tZC_DEG SYMBOL tPOK_LOW CONDITIONS POK from high to low, VOUT falling MIN 1 74 2.7 IZC = 3mA VZC = 3.3V ZC from high to low, IOUT falling (Note 6) IOUT rising Temperature rising Hysteresis LATCH = low (Note 7) 1.6 300 0.05 350 10 150 30 1.92 2.24 TYP 1.4 88 3.75 MAX 1.8 102 4.8 0.4 1 400 UNITS ms mV V A ms ms C s
MAX5923
tPOK_HIGH POK from low to high, VOUT rising VZCTH VZC_LOW
VIL
V
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 +150C) 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:
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+60V Simple Swapper Hot-Swap Switch MAX5923
Typical Operating Characteristics
(VIN = 48V, VDIG, EN, LATCH, CLASS, ZC_EN = 3.3V, DCA, AGND_S = AGND = DGND = 0V, RSENSE = 0.5, UVLO floating, TA = +25C, unless otherwise noted.)
VIN SUPPLY CURRENT vs. INPUT VOLTAGE
MAX5923 toc01
VIN SUPPLY CURRENT vs. TEMPERATURE
MAX5923 toc02
DIGITAL SUPPLY CURRENT vs. TEMPERATURE
11.9 11.8 11.7 IDIG (A) 11.6 11.5 11.4
MAX5923 toc03
1.00 0.95 SUPPLY CURRENT (mA) 0.90 0.85 TA = +25C 0.80 TA = -40C 0.75 0.70 32 36 40 44 48 52 56 MEASURED AT AGND
1.00 0.95 SUPPLY CURRENT (mA) 0.90 0.85 0.80 VIN = 32V 0.75 0.70 VIN = 48V MEASURED AT AGND VIN = 60V
12.0
TA = +85C
11.3 11.2 11.1 11.0
60
-40
-25
-10
5
20
35
50
65
80
-40
-25
-10
5
20
35
50
65
80
INPUT VOLTAGE (V)
TEMPERATURE (C)
TEMPERATURE (C)
VIN UNDERVOLTAGE LOCKOUT vs. TEMPERATURE
MAX5923 toc04
MOSFET RDS-ON vs. TEMPERATURE
MAX5923 toc05
SENSE TRIP VOLTAGE vs. TEMPERATURE
214 SENSE TRIP VOLTAGE (V) 213 212 211 210 209 208 207 206 VIN = 32V VIN = 48V VIN = 60V
MAX5923 toc06
40 39 DEFAULT VIN UVLO (V) 38 VIN RISING
0.60 0.55 ON-RESISTANCE () 0.50 0.45 0.40 0.35 0.30
IOUT = 100mA
215
37 36 35 34 33 32 -40 -25 -10 5 20 35 50 65 80 TEMPERATURE (C) VIN FALLING
205 -40 -25 -10 5 20 35 50 65 80 -40 -25 -10 5 20 35 50 65 80 TEMPERATURE (C) TEMPERATURE (C)
FOLDBACK CURRENT LIMIT (ILIM vs. VOUT)
MAX5923 toc07
ZERO-CURRENT DETECTION THRESHOLD VOLTAGE vs. TEMPERATURE
MAX5923 toc08
ON-RESISTANCE vs. VDRAIN
IOUT = 100mA 0.7 ON-RESISTANCE () 0.6 TA = +25C 0.5 0.4 0.3 0.2 0.1 TA = -40C TA = +85C
MAX5923 toc09
0.60 0.55 0.50 0.45 ILIM (A) 0.40 0.35 0.30 0.25 0.20 0.15 0.10 0.05 0 0 5 10 15
3.70 3.68 3.66 ON-RESISTANCE () 3.64 3.62 3.60 3.58 3.56 3.54 3.52 3.50 VIN = 32V VIN = 48V VIN = 60V
0.8
20 25 30 35 40 45 50
-40 -25 -10
5
20
35
50
65
80
28
33
38
43
48
53
58
63
68
73
OUTPUT VOLTAGE (V)
TEMPERATURE (C)
INPUT VOLTAGE (V)
4
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+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 = 0.5, UVLO floating, TA = +25C, unless otherwise noted.)
OVERCURRENT TIMEOUT (RLOAD FROM 240 TO 75)
MAX5923 toc10
MAX5923
DIGITAL SUPPLY CURRENT vs. VDIG
30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 0 1.0 2.0 3.0 VDIG (V) 4.0 5.0
MAX5923 toc11
20V/div 0V 5V/div 0V 200mA/div 0A 5V/div 0V
VOUT
IDIG (A)
POK
IOUT
FAULT 20ms/div
6.0
SHORT-CIRCUIT RESPONSE TIME
MAX5923 toc12
POK LOW-TO-HIGH DELAY TIME
MAX5923 toc13
20V/div 0V 5V/div 0V 200mA/div 0A 5V/div 0V 20ms/div
VOUT
POK 5V/div
POK IOUT VOUT 20V/div
FAULT 40ms/div
POK HIGH-TO-LOW DELAY TIME
MAX5923 toc14
ZC TO OUT DELAY
MAX5923 toc15
20V/div 20V/div 0V VOUT 0V 5V/div 0V 5V/div 0V 1.25mA/div 0A
VOUT
POK ZC
5V/div 0V
POK
IOUT
1ms/div
400s/div
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5
+60V Simple Swapper Hot-Swap Switch MAX5923
Typical Operating Characteristics (continued)
(VIN = 48V, VDIG, EN, LATCH, CLASS, ZC_EN = 3.3V, DCA, AGND_S = AGND = DGND = 0V, RSENSE = 0.5, UVLO floating, TA = +25C, unless otherwise noted.)
ZERO CURRENT HIGH-TO-LOW DETECTION TIME WAVEFORM
MAX5923 toc16
ZERO CURRENT LOW-TO-HIGH DEGLITCH TIME WAVEFORM (11ms GLITCH)
MAX5923 toc17
VOUT 20V/div POK 5V/div ZC 5V/div tZCDEL
OUT 20V/div
POK 5V/div ZC 5V/div IOUT 100mA/div
GLITCH > tZC_DEG tZCDEL
100ms/div
100ms/div
ZERO CURRENT LOW-TO-HIGH DEGLITCH TIME WAVEFORM (10ms)
MAX5923 toc18
OVERCURRENT RESTART DELAY
MAX5923 toc19
VOUT 20V/div tZCDEL POK 5V/div ZC 5V/div IOUT 100mA/div 100ms/div GLITCH > tZC_DEG
VOUT 20V/div
tRESTART
POK 5V/div FAULT 5V/div IOUT 500mA/div 400ms/div
STARTUP WITH OUT SHORTED TO AGND
MAX5923 toc20
OVERCURRENT TIMEOUT (RLOAD FROM 240 to 75)
MAX5923 toc21
5V/div 0V 5V/div 0V
20V/div VOUT POK
VOUT
500A/div 0A 2V/div 0V 100ms/div
IOUT
200mA/div
IOUT
EN
5V/div
POK
2ms/div
6
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+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 = 0.5, UVLO floating, TA = +25C, unless otherwise noted.)
OUTPUT SHORT-CIRCUIT RESPONSE
MAX5923 toc22
MAX5923
OUTPUT SHORT-CIRCUIT RESPONSE
MAX5923 toc23
10A/div
IOUT 200mA/div
IOUT
VOUT 20V/div 20V/div
VOUT
4s/div
200s/div
Pin Description
PIN -- NAME AGND FUNCTION 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. 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. 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 100F, 100V electrolytic capacitor and 0.1F, 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 1 resistor from AGND_S to AGND. This resistor protects the IC during an output short-circuit condition. 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. 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. 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. 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. Must be left open or connected to AGND Must be left open or connected to AGND
1, 2
DRAIN
3
IN
4, 12, 18, 19 5 6
N.C. AGND_S UVLO
7
FAULT
8
POK
9 10 11
ZC TP1 TP3
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+60V Simple Swapper Hot-Swap Switch MAX5923
Pin Description (continued)
PIN 13 NAME DGND FUNCTION Digital Ground. DGND can vary 4V from AGND. DGND and AGND must be connected together at a single point in the system. 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). 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. 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. 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. Output Voltage
14
LATCH
15 16
ZC_EN EN
17 20
VDIG OUT
Detailed Description
The MAX5923 is a fully integrated hot-swap switch that contains a 0.45 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.
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 50k (min), so keep the R1 and R2 parallel combination value at least 20 times smaller than 50k to minimize the new UVLO threshold error.
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 0.45 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
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+60V Simple Swapper Hot-Swap Switch MAX5923
VIN = 16V TO 60V
VILM
IN R1
MAX5923
UVLO
VILM/3
R2 AGND
VFBSTART (2V) VFBSTOP (18V) VOUT (V)
Figure 1. Setting Undervoltage Lockout with an External Resistive Divider
Figure 2. Current Foldback Characteristic
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.
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) x 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.
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).
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9
+60V Simple Swapper Hot-Swap Switch MAX5923
Zero-Current Detection
ILIMIT
IOUT 0V
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. 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.
VFAULT 0V t tOC tRESTART t < tOC
Thermal Shutdown
If the MAX5923 die temperature reaches +150C, an overtemperature fault is generated. The MOSFET turns off and FAULT goes low. The MAX5923 die temperature must cool down below +120C before the overtemperature fault condition is removed (see the Fault Management section).
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 0.47F 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.
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.
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.
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+60V Simple Swapper Hot-Swap Switch
Typical Application Circuit
+16V TO +60V IN 100F (100V) 0.5 (1W) 1F (100V) OUT D1 B1100LB (100V, 1A) DRAIN VDIG 2k 0.1F 10F
MAX5923
100
+1.65V TO +5.5V
MAX5923
UVLO LATCH 2k
ON OFF EN
ZC_EN
2k
ZC FAULT 1 (1/16W) AGND_S POK DGND
ALL SIGNAL AND DIGITAL INPUTS/OUTPUTS ARE REFERENCED TO DGND. DGND CAN BE 4V FROM AGND_S.
Pin Configuration
TOP VIEW
DRAIN 1 DRAIN 2 IN 3 N.C. 4 AGND_S 5 UVLO 6 FAULT 7 POK 8 ZC 9 TP1 10 20 OUT 19 N.C. 18 N.C. 17 VDIG 16 EN
Chip Information
TRANSISTOR COUNT: 8,687 PROCESS: BiCMOS
MAX5923
15 ZC_EN 14 LATCH 13 DGND 12 N.C. 11 TP3
TSSOP
______________________________________________________________________________________
11
+60V Simple Swapper Hot-Swap Switch MAX5923
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
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 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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