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19-2946; Rev 0; 9/03
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current
General Description
The MAX5921/MAX5939 hot-swap controllers allow a circuit card to be safely hot plugged into a live backplane. The MAX5921/MAX5939 operate from -20V to -80V and are well suited for -48V power systems. These devices are pin compatible with both the LT1640 and LT4250 and provide improved features over these devices. The MAX5921/MAX5939 provide a controlled turn-on to circuit cards preventing damage to board connectors, board components, and preventing glitches on the power-supply rail. The MAX5921/MAX5939 provide undervoltage, overvoltage, and overcurrent protection. These devices ensure that the input voltage is stable and within tolerance before applying power to the load. Both the MAX5921 and MAX5939 protect a system against overcurrent and short-circuit conditions by turning off the external MOSFET in the event of a fault condition. The MAX5921/MAX5939 protect against input voltage steps by limiting the load current to a safe level without turning off power to the load. The device features an open-drain power-good status output, PWRGD or PWRGD for enabling downstream converters (see Selector Guide). A built-in thermal shutdown feature is also included to protect the external MOSFET in case of overheating. The MAX5939 features a latched fault output. The MAX5921 contains built-in autoretry circuitry after a fault condition. The MAX5921/MAX5939 are available in an 8-pin SO package and operate in the extended -40C to +85C temperature range.
Features
o Allows Safe Board Insertion and Removal from a Live -48V Backplane o Pin-Compatible with LT1640 and LT4250 o Circuit Breaker Immunity to Input Voltage Steps and Current Spikes o 450mA GATE Pulldown Current During ShortCircuit Condition o Exponential GATE Pulldown Current o Withstands -100V Input Transients with No External Components o Programmable Inrush and Short-Circuit Current Limits o Operates from -20V to -80V o Programmable Overvoltage Protection o Programmable Undervoltage Lockout with Built-In Glitch Filter o Overcurrent Fault Integrator o Powers Up into a Shorted Load o Power-Good Control Output o Thermal Shutdown Protects External MOSFET
MAX5921/MAX5939
Ordering Information
PART MAX5921AESA MAX5921BESA TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 8 SO 8 SO
Applications
Telecom Line Cards Network Switches/Routers Central-Office Line Cards Server Line Cards Base-Station Line Cards
Ordering Information continued at end of data sheet.
Pin Configuration
TOP VIEW
PWRGD (PWRGD)
1 2 3
8 7
VDD DRAIN GATE SENSE
Typical Operating Circuit and Selector Guide appear at end of data sheet.
OV UV
MAX5921 MAX5939
6 5
VEE 4
SO
() FOR MAX5921B/F AND MAX5939B/F.
________________________________________________________________ Maxim Integrated Products
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
ABSOLUTE MAXIMUM RATINGS
All Voltages Are Referenced to VEE, Unless Otherwise Noted Supply Voltage (VDD - VEE )................................-0.3V to +100V DRAIN, PWRGD, PWRGD ....................................-0.3V 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 Current into SENSE...........................................................+40mA Current into GATE...........................................................+300mA Current into Any Other Pin................................................+20mA Continuous Power Dissipation (TA = +70C) 8-Pin SO (derate 5.9mW/C above +70C)..................471mW Operating Temperature Range ...........................-40C to +85C Junction Temperature .....................................................+150C Storage Temperature Range .............................-65C to +150C 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
(VEE = 0V, VDD = 48V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C, unless otherwise noted.) (Notes 1, 4)
PARAMETER POWER SUPPLIES Operating Input Voltage Range Supply Current VDD IDD Current into VDD with UV = 3V, OV, DRAIN, SENSE = VEE, GATE = floating GATE drive on, VGATE = VEE VSENSE - VEE = 100mV, VGATE = 2V (Note 2) VGATE - VEE, steady state, 20V VDD 80V VGATE - VEE, IGS = 30mA VCL = VSENSE - VEE VSENSE = 50mV -30 24 10 15 40 -1 20 0.7 80 2 V mA SYMBOL CONDITIONS MIN TYP MAX UNITS
GATE DRIVER AND CLAMPING CIRCUITS Gate Pullup Current Gate Pulldown Current External Gate Drive GATE to VEE Clamp Voltage CIRCUIT BREAKER Current-Limit Trip Voltage SENSE Input Current UNDERVOLTAGE LOCKOUT Supply Internal Undervoltage Lockout Voltage High Supply Internal Undervoltage Lockout Voltage Low UV INPUT UV High Threshold UV Low Threshold UV Hysteresis UV Input Current OV INPUT OV High Threshold OV Low Threshold OV Voltage Reference Hysteresis OV Input Current VOVH VOVL VOVHY IINOV OV = VEE -0.5 OV voltage rising OV voltage decreasing 1.235 1.189 1.255 1.205 50 0 1.275 1.221 V V mV A VUVH VUVL VUVHY IINUV UV = VEE -0.5 UV voltage increasing UV voltage decreasing 1.240 1.105 1.255 1.125 130 0 1.270 1.145 V V mV A VUVLOH VUVLOL VDD increasing VDD decreasing 13.8 11.8 15.4 13.4 17.0 15.0 V V VCL ISENSE 50 -0.2 60 0 mV A IPU IPD VGATE VGSCLMP -45 50 13.5 16.4 -60 70 18 18 A mA V V
2
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current
ELECTRICAL CHARACTERISTICS (continued)
(VEE = 0V, VDD = 48V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C, unless otherwise noted.) (Notes 1, 4)
PARAMETER DRAIN Input Current DRAIN Threshold for PWRGD GATE High Threshold PWRGD, PWRGD Output Leakage PWRGD Low Voltage (V PWRGD - VEE) PWRGD Low Voltage (VPWRGD - VDRAIN) OVERTEMPERATURE PROTECTION Overtemperature Threshold Overtemperature Hysteresis AC PARAMETERS OV High to GATE Low UV Low to GATE Low OV Low to GATE High UV High to GATE High SENSE High to GATE Low tPHLOV tPHLUV tPLHOV tPLHUV tPHLSENSE Figures 1a, 2 Figures 1a, 3 Figures 1a, 2 Figures 1a, 3 Figures 1a, 4a Time from continuous A, B versions current limit to GATE shutdown (see Overcurrent Fault Integrator section), E, F versions Figures 1b, 4b Figures 1a, 5a; A and E versions tPHLDL Figures 1a, 5a; B and F versions Figures 1a, 5b; A and E versions tPHLGH Figures 1a, 5b; B and F versions 8.2 8.2 8.2 ms 0.35 1.4 0.5 0.4 3.3 8.4 1 0.5 2.0 8.2 ms 0.65 ms 2.6 s s s ms s TOT(TH) THYS Junction temperature, temperature rising See Thermal Shutdown section 135 20 C C SYMBOL IDRAIN VDL VGH IOH VOL VOL VDRAIN = 48V VDRAIN - VEE threshold for power-good condition, DRAIN decreasing VGATE - VGATE, decreasing V PWRGD = 80V, VDRAIN = 48V VPWRGD = 80V, VDRAIN = 0V VDRAIN - VEE < VDL, ISINK = 5mA (A, E versions) VDRAIN = 5V, ISINK = 5mA (B, F versions) 0.11 0.11 CONDITIONS MIN 10 1.1 1.0 TYP 80 1.7 1.6 MAX 250 2.0 2.0 10 10 0.4 0.4 UNITS A V V A V V PWRGD OUTPUT SIGNAL (REFERENCED TO DRAIN)
MAX5921/MAX5939
Current Limit to GATE Low
tPHLCL
DRAIN Low to PWRGD Low DRAIN Low to (PWRGD - DRAIN) High GATE High to PWRGD Low GATE High to (PWRGD - DRAIN) High TURN-OFF Latch-Off Period
tOFF
(Note 3)
A, B, E, F versions
128 x tPHLCL
ms
Note 1: Note 2: Note 3:
Note 4:
All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to VEE, unless otherwise specified. Gate pulldown current after the current limit to GATE low (tPHLCL) time has elapsed. Minimum duration of GATE pulldown following a circuit breaker fault. The MAX5921_ automatically restarts after a circuit breaker fault. The MAX5939_ is latched off and can be reset by toggling UV low. The GATE pulldown does not release until tOFF has elapsed. The min/max limits are 100% production tested at +25C and +85C and guaranteed by design at -40C.
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
Typical Operating Characteristics
(VDD = +48V, VEE = 0V, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX5921TOC01
GATE VOLTAGE vs. SUPPLY VOLTAGE
MAX5921TOC02
CURRENT-LIMIT TRIP VOLTAGE vs. TEMPERATURE
58 56 TRIP VOLTAGE (mV) 54 52 50 48 46 44 42 40
MAX5921TOC03
900 800 SUPPLY CURRENT (A) 700 600 500 400 300 200 100 0 0 20 40 60 80 TA = -40C TA = +25C TA = +85C
15 14 13 GATE VOLTAGE (V) 12 11 10 9 8 7 TA = +25C
60
100
0
20
40
60
80
100
-40
-15
10
35
60
85
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
GATE PULLUP CURRENT vs. TEMPERATURE
MAX5921TOC04
GATE PULLDOWN CURRENT vs. TEMPERATURE AFTER A FAULT
MAX5921TOC05
GATE PULLDOWN CURRENT vs. OVERDRIVE DURING A CURRENT FAULT
VGATE = 2V
MAX5921TOC06
45.0 44.8 GATE PULLUP CURRENT (A) 44.6 44.4 44.2 44.0 43.8 43.6 43.4 43.2 43.0 -40
VGATE = 0V
70 65 GATE PULLDOWN CURRENT (mA) 60 55 50 45 40 35 30 25
VGATE = 2V
90 GATE PULLDOWN CURRENT (mA) 75 60 45 30 15 0
-15
10
35
60
85
-40
-15
10
35
60
85
0
20
40
60
80
100
TEMPERATURE (C)
TEMPERATURE (C)
OVERDRIVE (mV)
GATE PULLDOWN CURRENT vs. OVERDRIVE DURING A SHORT CIRCUIT
MAX5921TOC07
PWRGD OUTPUT LOW VOLTAGE vs. TEMPERATURE (MAX5921A)
MAX5921TOC08
PWRGD OUTPUT LEAKAGE CURRENT vs. TEMPERATURE (MAX5921B)
PWRGD OUTPUT LEAKAGE CURRENT (nA) VDRAIN - VEE > 2.4V
MAX5921TOC09
500 GATE PULLDOWN CURRENT (mV)
VGATE = 2V
180 PWRGD OUTPUT LOW VOLTAGE (mV) 160 140 120 100 80 60 40 20
IOUT = 5mA
100
400
10
300
1
200
0.1
100
0.01
0 600 750 900 OVERDRIVE (mV) 1050 1200
0 -40 -15 10 35 60 85 TEMPERATURE (C)
0.001 -40 -15 10 35 60 85 TEMPERATURE (C)
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
R 5k PWRGD/PWRGD OV VOV VDD + DRAIN VS VDRAIN +48V -
V+ 5V
MAX5921 MAX5939
UV VEE VUV
GATE SENSE VSENSE
Figure 1a. Test Circuit 1
+ PWRGD/PWRGD OV VDD + DRAIN VS +48V 10k VS +20V -
MAX5921 MAX5939
GATE UV VEE SENSE 0.1F
10 IRF530
VUV
Figure 1b. Test Circuit 2
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
Timing Diagrams
2V 1.255V OV 1.205V UV 0V 0V tPHLOV GATE 1V 1V tPHLUV tPLHOV GATE 1V 1V tPLHUV 2V 1.125V 1.255V
Figure 2. OV to GATE Timing
Figure 3. UV to GATE Timing
100mV 60mV SENSE VEE tPHLSENSE
UV tPHLCL
GATE 1V 1V
GATE
1V
Figure 4a. SENSE to GATE Timing
Figure 4b. Active Current-Limit Threshold
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current
Timing Diagrams (continued)
DRAIN 1.4V VGATE - VGATE = 0V GATE tPHLGH PWRGD 1V PWRGD
MAX5921/MAX5939
1.4V VEE
tPHLDL
VEE
1V
VEE
1.4V DRAIN 1.4V VEE VGATE - VGATE = 0V GATE tPHLDL PWRGD 1V tPHLGH VEE 1V
PWRGD VDCEN - VDRAIN = 0V
VDCEN - VDRAIN = 0V
Figure 5a. DRAIN to PWRGD/PWRGD Timing
Figure 5b. GATE to PWRGD/PWRGD Timing
Block Diagram
VDD
UV
UVLO
VDD AND REFERENCE GENERATOR
VDD
MAX5921/MAX5939
REF OUTPUT DRIVER PWRGD PWRGD
REF
LOGIC
OV 50mV
GATE DRIVER
VDL
VGH
VGATE VEE VEE SENSE GATE DRAIN
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
Pin Description
PIN MAX5921A/ MAX5921E MAX5939A/ MAX5939E 1 MAX5921B/ MAX5921F MAX5939B/ MAX5939F -- NAME FUNCTION
PWRGD
Power-Good Signal Output. PWRGD is an active-low open-drain status output referenced to VEE. PWRGD latches low when VDRAIN - VEE VDL and VGATE > VGATE indicating a power-good condition. PWRGD is open drain otherwise. 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. Overvoltage Detection Input. OV is referenced to VEE. When OV is pulled above VOVH voltage, GATE pulls low. GATE remains low until the OV voltage reduces to VOVH VOVHY. Undervoltage Detection Input. UV is referenced to VEE. When UV is pulled above VUVH voltage, the GATE is enabled. When UV is pulled below VUVL, GATE pulls 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 will not restart until a tOFF delay time has elapsed after the fault condition is removed. Negative Power-Supply Input. Connect to the negative power-supply rail. Current-Sense Input. Connect to the external sense resistor and the source of the external MOSFET. 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. Gate Drive Output. Connect to the gate of the external N-channel MOSFET. Output Voltage Sense Input. Connect to the output voltage node (drain of external Nchannel MOSFET). Place the MAX5921/MAX5939 such that DRAIN is close to the drain of the external MOSFET for the best thermal protection. Positive Power-Supply Input. This is the power ground in the negative supply voltage system. Connect to the higher potential of the power-supply inputs.
--
1
PWRGD
2
2
OV
3
3
UV
4
4
VEE
5
5
SENSE
6 7
6 7
GATE DRAIN
8
8
VDD
Detailed Description
The MAX5921/MAX5939 integrated hot-swap controllers for -48V power systems 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, the bypass capacitors at the input of the board's power module or switching power supply can draw large inrush currents as they charge. Uncontrolled inrush currents can cause glitches on the system power supply and damage components on the board.
The MAX5921/MAX5939 provide a controlled turn-on to circuit cards preventing damage to connectors, board components, and prevent glitches on the power-supply rail. Both the MAX5921/MAX5939 provide undervoltage, overvoltage, and overcurrent protection. The MAX5921/MAX5939 ensure that the input voltage is stable and within tolerance before applying power to the load. The device also provides protection against input voltage steps by limiting the load current to a safe level without turning off power to the load.
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current
Board Insertion
Figure 6a 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 IV EE x (Cgd/Cgd + Cgs)I. The MAX5921/MAX5939 feature an internal dynamic clamp between GATE and V EE 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 clamp between GATE and V EE of the MAX5921/ MAX5939 eliminates the need for an external gate-tosource capacitor. The resistor R3 limits the current into the clamp circuitry during card insertion. The inrush current can be calculated: IINRUSH = IPU x CL / C2 where CL is the total load capacitance, C3 + C4, and IPU is the gate pullup current. Figure 6b 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 VGATE to 18V.
MAX5921/MAX5939
Board Removal
If the circuit card is removed from the backplane, the voltage at the UV falls below the UVLO detect threshold, and the MAX5921/MAX5939 turn off the external MOSFET.
Power-Supply Ramping
The MAX5921/MAX5939 can reside either on the backplane or the removable circuit board (Figure 6a). Power is delivered to the load by placing an external N-channel MOSFET pass transistor in the power-supply path. 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 MAX5921/MAX5939 gradually turn on the external MOSFET by charging the gate of Q1 with a 45A current source. Capacitor C2 provides a feedback signal to accurately limit the inrush current.
Current Limit and Electronic Circuit Breaker
The MAX5921/MAX5939 provide current-limiting and circuit-breaker 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.
-48V RTN SHORT PIN -48V RTN R4 549k 1% UV R5 6.49k 1% OV R6 10k 1% VEE SENSE VDD
MAX5921 MAX5939
GATE
PWRGD
DRAIN VIN+ GATE IN
4.7nF
R1 0.02 5%
R2 10 5%
R3 1k 5%
C2 15nF 100V
C4 100F 100V
C3 0.1F 100V VIN-
VICOR VI-J3D-CY
-48V
Q1 IRF530
Figure 6a. Inrush Control Circuitry/Typical Application Circuit _______________________________________________________________________________________ 9
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
Load Current Regulation (Short-Circuit Condition)
INRUSH CURRENT 1A/div GATE - VEE 10V/div
DRAIN 50V/div VEE 50V/div 4ms/div
The MAX5921/MAX5939 devices also include a very fast high-current pulldown source connected to GATE (see Typical Operating Characteristics). The high-current pulldown activates if V SENSE exceeds V EE by 650mV (typ) during a catastrophic overcurrent or shortcircuit fault condition. The high-current pulldown circuit sinks as much as 450mA from GATE to turn off the external MOSFET.
Immunity to Input Voltage Steps
The MAX5921/MAX5939 guard 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, proportional to the input voltage slew rate (VIN / t). If the load current exceeds VCL / RSENSE during an input voltage step, the MAX5921/ MAX5939 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 (see the Power-Supply Ramping section). 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 below the current limit, the circuit breaker does not trip.
Figure 6b. Inrush Control Waveforms
If the voltage between VEE and SENSE reaches the current-limit trip voltage (VCL), the MAX5921/MAX5939 pull down the GATE and regulate the current through the external MOSFET such that VSENSE - VEE < VCL. If the current drawn by the load drops below VCL / RSENSE limit, the GATE voltage rises again. However, if the load current is at the regulation limit of VCL / RSENSE for a period of tPHLCL, the electronic circuit breaker trips, causing the MAX5921/MAX5939 to turn off the external MOSFET. After an overcurrent fault condition, the MAX5921 automatically restarts after tOFF has elapsed. The MAX5939 circuit breaker is reset by toggling UV or by cycling power. Unless power is cycled to the MAX5939, the device waits until tOFF has elapsed before turning on the gate of the external FET.
Load-Current Regulation
The MAX5921/MAX5939 accomplish load-current regulation by pulling current from GATE whenever VSENSE VEE > VCL. This decreases the gate-to-source voltage of the external MOSFET, thereby reducing the load current. When VSENSE - VEE < VCL, the MAX5921/MAX5939 pulls GATE high by a 45A (IPU) current. Exponential Current Regulation The MAX5921/MAX5939 provide an exponential pulldown current to turn off the external FET in response to overcurrent conditions. The GATE pulldown current increases (see Typical Operating Characteristics) in response to VSENSE - VEE potentials greater than 50mV (VCL).
Undervoltage and Overvoltage Protection
Use UV and OV to detect undervoltage and overvoltage conditions. UV and OV internally connect to analog comparators with 130mV (UV) and 50mV (OV) of hysteresis. When the UV voltage falls below its threshold or the OV voltage rises above its threshold, GATE pulls low. GATE is held low until UV goes high and OV is low, indicating that the input supply voltage is within specification. The MAX5921/MAX5939 includes an internal lockout (UVLO) that keeps the external MOSFET off until the input supply voltage exceeds 15.4V, regardless of the UV input. UV is also used to reset the circuit breaker after a fault condition has occurred. Pull UV below VUVL to reset the circuit breaker.
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
DRAIN 50V/div
VEE 20V/div
GATE - VEE 10V/div
DRAIN 20V/div
INRUSH CURRENT 5A/div 1ms/div 400s/div
ID (Q1) 2A/div
Figure 7. Short-Circuit Protection Waveform
Figure 8. Voltage Step-On Input Supply
Figure 10 shows how to program the undervoltage and overvoltage trip thresholds using three resistors. With R4 = 549k, R5 = 6.49k, and R6 = 10k, the undervoltage threshold is set to 38.5V (with a 43V release from undervoltage), and the overvoltage is set to 71V. The resistor-divider also increases the hysteresis and overvoltage lockout to 4.5V and 2.8V at the input supply, respectively.
PWRGD/PWRGD Output
Use the PWRGD (PWRGD) output to enable a power module after hot insertion. Use the MAX59__A (PWRGD) to enable modules with an active-low enable input (Figure 12), or use the MAX59__B (PWRGD) to enable modules with an active-high enable input (Figure 11). 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. When the DRAIN voltage of the MAX5921A (see Selector Guide for complete selection) or MAX5939A is high with respect to VEE or the GATE voltage is low from an undervoltage condition, then the internal pulldown MOSFET Q2 is off. The PWRGD output goes into a high-impedance state (Figure 13). PWRGD is pulled high by the module's internal pullup current source, turning the module off. When the DRAIN voltage drops below V DL and the GATE voltage is greater than V GATE - V GH, Q2 turns on and PWRGD 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 13) (see the Component Selection Procedure section). 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 high, enabling the module. When the DRAIN voltage of the MAX5921B/MAX5939B (see Selector Guide for complete selection) is high with respect to VEE (Figure 12) or the GATE voltage is low due to an undervoltage condition, the internal MOSFET Q3 is turned off so that I1 and the internal MOSFET Q2 clamp PWRGD to the DRAIN turning off the module. Once the PWRGD and PWRGD outputs are active, the MAX5921/MAX5939 output does not toggle due to an overvoltage (OV) fault.
GATE Voltage Regulation
GATE goes high when the following startup conditions are met: UV is high, OV is low, the supply voltage is above VUVLOH, and (VSENSE - VEE) is less than 50mV. The gate is pulled up with a 45A current source and is regulated at 13.5V above VEE. The MAX5921/MAX5939 include an internal clamp that ensures the GATE voltage of the external MOSFET never exceeds 18V. During a fast-rising VDD, an additional dynamic clamp keeps the GATE and SENSE potentials as close as possible to prevent the FET from accidentally turning on. When a fault condition is detected, GATE is pulled low (see the Load Current Regulation section).
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-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
-48V RTN (SHORT PIN) -48V RTN VGATE - VEE 2V/div VUV = 1.255 R4 + R5 + R6 R5 + R6 R5 ID (Q1) 2A/div VOV = 1.255 R4 + R5 + R6 R6 R6 2 OV VEE 4 R4 3 UV 8 VDD
MAX5921 MAX5939
10ms/div
-48V
Figure 9. Automatic Restart After a Short Circuit
Figure 10. Undervoltage and Overvoltage Sensing
Overcurrent Fault Integrator
The MAX5921/MAX5939 feature an overcurrent fault integrator. When an overcurrent condition is detected, an internal digital counter is incremented. The clock period for the digital counter is 32s for the 500s maximum current-limit duration version and 128s for 2ms maximum current-limit duration devices. An overcurrent of less than 32s is interpreted as an overcurrent of 32s. When the counter reaches 500s (the maximum currentlimit duration) for the MAX5921/MAX5939A, an overcurrent fault is generated. If the overcurrent fault does not last 500s, then the counter begins decrementing at a rate 128 (maximum current-limit duty cycle) times slower than the counter was incrementing. Repeated overcurrent conditions generate a fault if the duty cycle of the overcurrent condition duty ratio is greater than the maximum current-limit duty cycle (see Figure 14).
MAX5921/MAX5939 near the drain of the external MOSFET offers the best thermal protection because most of the power is dissipated in its drain. After a thermal shutdown fault has occurred, the MAX5921_ turns the external FET off for a minimum time of tOFF, allowing the MOSFET to cool down. The MAX5921_ device restarts after the temperature drops 20C below the thermal-shutdown threshold. The MAX5939_ latches off after a thermal shutdown fault. The MAX5939_ can be restarted by toggling UV low or cycling power. However, the device keeps the external FET off for a minimum time of tOFF when toggling UV.
Applications Information
Sense Resistor
The circuit-breaker current-limit threshold is set to 50mV (typ). 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 dynamic load-capacitance charging current during startup. Choose the sense resistor power rating to be greater than (VCL)2 / RSENSE.
Thermal Shutdown
The MAX5921/MAX5939 include internal die-temperature monitoring. When the die temperature reaches the thermal-shutdown threshold, T OT , the MAX5921/ MAX5939 pull GATE low and turn off the external MOSFET. If a good thermal path is provided between the MOSFET and the MAX5921/MAX5939, the device offers thermal protection for the external MOSFET. Placing the
12
______________________________________________________________________________________
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
-48V RTN (SHORT PIN) -48V RTN VDD R4 ACTIVE-HIGH ENABLE MODULE VIN+ VOUT+
UV
MAX5921B/F MAX5939B/F
I1 Q2
PWRGD ON/OFF C3
R5
VGH VGATE OV
Q3 VINVEE VDL VOUT-
*
R6 VEE SENSE GATE R3
DRAIN
C2
R2 R1 -48V *DIODES INC. SMAT70A Q1
Figure 11. Active-High Enable Module
-48V RTN (SHORT PIN) -48V RTN VDD R4
ACTIVE-LOW ENABLE MODULE VIN+ VOUT+
UV
MAX5921A/E MAX5939A/E
PWRGD ON/OFF C3
R5
VGH VGATE
Q2 VINVEE VDL VOUT-
*
OV
R6 VEE SENSE GATE R3
DRAIN
C2
R2 R1 -48V *DIODES INC. SMAT70A Q1
Figure 12. Active-Low Enable Module ______________________________________________________________________________________ 13
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
-48V RTN (SHORT PIN) GND R7 51k 5% PWRGD
R4 549k 1% UV R5 6.49k 1% * R6 10k 1% OV VEE SENSE
VDD
MAX5921A MAX5921E MAX5939A MAX5939E
GATE
PWRGD
DRAIN
R1 0.02 5% -48V *DIODES INC. SMAT70A
R2 10 5%
R3 1k 5%
C2 15nF 100V
C3 100F 100V
Q1 IRF530
Figure 13. Using PWRGD to Drive an Optoisolator
Component Selection Procedure:
* 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: IINRUSH 0.8 x 40mV - ILOAD or RSENSE IINRUSH + ILOAD 0.8 x ICB(MIN)
R3 =
150s C2
* Set R2 = 10. * If an optocoupler is utilized as in Figure 14, determine the LED series resistor: R7 = VIN(NOMINAL) - 2V 3 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 51k, 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-voltagesuppression diode (TVS) to limit maximum voltage on the MAX5921/MAX5939 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
* Determine value of C2: C2 = * Calculate value of C1: VIN(MAX) - VGS( TH) C1 = (C2 + Cgd ) x VGS( TH) * Determine value of R3: 45A x CL IINRUSH
14
______________________________________________________________________________________
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
4000F x 1.25V = 1ms 5A Entering the data sheet transient-thermal-resistance curves at 1ms provides a JC = 0.9C/W. PD = 6.25W, so tJC = 5.6C. Clearly, this is not a problem. Example 2: ILOAD = 10A, efficiency = 98%, allowing VDS = 0.96V but RDS(ON) 96m. An IRF530 in a D2PAK exhibits RDS(ON) 90m at +25C and 135m at +80C. Power dissipation is 9.6W at +25C or 14.4W at +80C. Junction-to-case thermal resistance is 1.9W/C, so the junction temperature rise would be approximately 5C above the +25C case temperature. For higher efficiency, consider IRL540NS with R DS(ON) 44m. This allows = 99%, P D 4.4W, and T JC = +4C (JC = 1.1C/W) at +25C. Thermal calculations for the transient condition yield I CB = 20A, V DS = 1.8V, t = 0.5ms, transient JC = 0.12C/W, PD = 36W and tJC = 4.3C. t=
t1 VOL VSENSE
t3H t5H t2L t4L
VGATE
500s x 128
Figure 14. MAX5921A Overcurrent Fault Example
The lowest practical RDS(ON), within budget constraints and with values from 14m to 540m, 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) 384m at operating temperature is acceptable. An IRL520NS 100V NMOS with R DS(ON) 180m and I D(ON) = 10A is available in D2PAK. (A Vishay Siliconix SUD40N10-25 100V NMOS with RDS(ON) 25m 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 +80C so efficiency 98.6% at 80C. PD 1.56W and junction temperature rise above case temperature would be 5C due to the package JC = 3.1C/W thermal resistance. Of course, using the SUD40N10-25 will yield an efficiency greater than 99.8% to compensate for the increased cost. If ICB is set to twice ILOAD, or 5A, VDS momentarily doubles to 1.25V. If COUT = 4000F, transient-line input voltage is 36V, the 5A charging-current pulse is:
Layout Guidelines
Good thermal contact between the MAX5921/MAX5939 and the external MOSFET is essential for the thermalshutdown feature to operate effectively. Place the MAX5921/MAX5939 as close as possible to the drain of the external MOSFET and use wide circuit-board traces for good heat transfer. See Figure 15 for an example of recommended layout for Kelvin-sensing current through a sense resistor on a PC board.
HIGH-CURRENT PATH
SENSE RESISTOR
SENSE VEE MAX5921 MAX5939
Figure 15. Recommended Layout for Kelvin-Sensing Current Through Sense Resistor
______________________________________________________________________________________
15
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
Selector Guide
PART MAX5921AESA MAX5921BESA MAX5921EESA MAX5921FESA MAX5939AESA MAX5939BESA MAX5939EESA MAX5939FESA DCEN POLARITY Active-Low PWRGD Active-High PWRGD Active-Low PWRGD Active-High PWRGD Active-Low PWRGD Active-High PWRGD Active-Low PWRGD Active-High PWRGD FAULT MANAGEMENT Autoretry Autoretry Autoretry Autoretry Latched Latched Latched Latched MAXIMUM CURRENT-LIMIT MAXIMUM CURRENT-LIMIT DURATION (ms) DUTY CYCLE 0.5 0.5 2 2 0.5 0.5 2 2 1/128 1/128 1/128 1/128 1/128 1/128 1/128 1/128
Ordering Information (continued)
PART MAX5921EESA* MAX5921FESA* MAX5939AESA MAX5939BESA MAX5939EESA* MAX5939FESA* TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 8 SO 8 SO 8 SO 8 SO 8 SO 8 SO
Chip Information
TRANSISTOR COUNT: 2645 PROCESS: BiCMOS
*Future product--contact factory for availability.
16
______________________________________________________________________________________
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current
Typical Operating Circuit
BACKPLANE CIRCUIT CARD
MAX5921/MAX5939
GND GND (SHORT PIN)
UV
VDD
MAX5921 MAX5939
OV VEE SENSE GATE
PWRGD
DRAIN VIN+
INPUT1 -48V (INPUT1) N -48V (INPUT2) INPUT2 VIN-
LUCENT JW050A1-E
______________________________________________________________________________________
17
-48V Hot-Swap Controllers with External RSENSE and High Gate Pulldown Current MAX5921/MAX5939
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.)
INCHES DIM A A1 B C e E H L MAX MIN 0.069 0.053 0.010 0.004 0.014 0.019 0.007 0.010 0.050 BSC 0.150 0.157 0.228 0.244 0.016 0.050
MILLIMETERS MAX MIN 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 1.27 BSC 3.80 4.00 5.80 6.20 0.40 1.27
N
E
H
VARIATIONS:
1
INCHES
MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.00 N MS012 8 AA 14 AB 16 AC
TOP VIEW
DIM D D D
MIN 0.189 0.337 0.386
MAX 0.197 0.344 0.394
D C
A e B A1
0 -8 L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL DOCUMENT CONTROL NO. REV.
21-0041
B
1 1
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 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
SOICN .EPS

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