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19-3378; Rev 0; 8/04
FireWire Current Limiter and Low-Drop ORing Switch Controller
General Description
The MAX5943 is a fully integrated power-management IC for FireWire(R) applications. This device controls two external power n-channel MOSFETs to regulate current from the input power supply to the load and performs low-voltage-drop, power-supply ORing. The MAX5943 operates over a 7.5V to 37V input range and provides inrush and output current limit in addition to a diode ORing function suitable for FireWire applications. The MAX5943 allows the safe insertion and removal of FireWire peripherals into a live FireWire port by providing inrush current control and an output current-limiting function. The ORing feature provides a very efficient way to protect the FireWire port when connected to another FireWire peripheral that sources a higher voltage. By turning off both external MOSFETS, the MAX5943 provides a true bidirectional load disconnect. A low-current shutdown mode disables the MAX5943, resulting in less than 10A supply current. A pin-selectable input allows latched or autoretry fault management after a fault. The MAX5943A features a current-limit function that actively limits the current drawn by the load with a programmable timeout. The MAX5943B-MAX5943E do not actively limit the load current but provide a circuit-breaker function. See the Selector Guide for the default and programmable circuit-breaker timeouts. The MAX5943 operates over the -40C to +85C extended temperature range and is available in a 16-pin QSOP package.
Features
Provides Safe Hot Swap for 7.5V to 37V Power Supplies Low-Drop Power ORing with Ultra-Fast Turn-Off Programmable Active Current Limit (MAX5943A) Programmable Circuit Breaker (MAX5943B-MAX5943E) 5% Current-Limit Sensing Accuracy Programmable Current-Limit/Circuit-Breaker Timeout Fast Current-Limit Response to Output ShortCircuit Conditions (MAX5943A) Drives External N-Channel Power MOSFETs Overcurrent Fault Status Output Latched or Autoretry Overcurrent Fault Management 10A Shutdown Current ON/OFF Control Allows Undervoltage Lockout Programming Fast Load Disconnect Control Through ON Input
MAX5943
Ordering Information
PART MAX5943AEEE MAX5943BEEE MAX5943CEEE MAX5943DEEE MAX5943EEEE TEMP RANGE -40C to +85C -40C to +85C -40C to +85C -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 16 QSOP 16 QSOP 16 QSOP 16 QSOP
Applications
FireWire Desktop/Notebook Port FireWire Peripheral Device Current Limit FireWire Hub Hot Swap
Pin Configuration
TOP VIEW
ON 1 FAULT 2 TIM 3 ILIM 4 LATCH 5 OR_ADJ 6 N.C. 7 16 IN 15 SENSE 14 GATE1
MAX5943
13 N.C. 12 GATE2 11 OUT 10 N.C. 9 GND
Typical Operating Circuit and Selector Guide appear at end of data sheet. FireWire is a registered trademark of Apple Computers, Inc.
ONQ1 8
QSOP
________________________________________________________________ Maxim Integrated Products
1
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FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
ABSOLUTE MAXIMUM RATINGS
(Voltages referenced to GND, unless otherwise noted.) IN ............................................................................-0.3V to +80V OUT ........................................................................-0.3V to +80V SENSE to IN..............................................................-1V to +0.3V GATE1 to SENSE......................................................-0.3V to +8V GATE2 to OUT (internally clamped).........................-0.3V to +8V FAULT.....................................................................-0.3V to +85V ON, TIM, ILIM, LATCH, OR_ADJ, ONQ1 ..........-0.3V to (IN + 0.3V) Continuous Power Dissipation (TA = +70C) 16-Pin QSOP (derate 8.3mW/C above +70C)...........667mW Operating Temperature Range ...........................-40C to +85C Maximum Junction Temperature .....................................+150C Storage Temperature Range .............................-60C to +150C ESD Rating (Human Body Model)......................................2000V 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 = 7.5V to 37V, GND = 0V, and TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = 12V, TA = +25C.) (Note 1)
PARAMETER SUPPLIES Supply Voltage Range Supply Current Shutdown Current IN Default Undervoltage Lockout IN Default Undervoltage Lockout Hysteresis ON Undervoltage Lockout Threshold ON Undervoltage Lockout Threshold Hysteresis ON Input Bias Current GATE2 Pullup Current GATE2 High Voltage Current-Limit/Circuit-Breaker Threshold Voltage ION IG2U VG2 (Note 2) VGATE2 - VOUT 7.5V VIN 8V 8V VIN 37V ILIM = GND VTH VIN - VSENSE ILIM = floating ILIM = IN ILIM = GND Fast Pulldown Current-Limit Threshold Voltage (MAX5943A) GATE2 Pulldown Current (MAX5943A) GATE2 Fast Pulldown Current (MAX5943A) GATE2 Peak Pulldown Current (MAX5943A) VTHF VIN - VSENSE (Note 3) ILIM = floating ILIM = IN IG2D IG2DF IG2DP VTH < (VIN - VSENSE) < VTHF, t < tILIM (VIN - VSENSE) > VTHF, VGATE2 = VOUT + 4.5V (VIN - VSENSE) = 1V 36 4.25 4.5 47.5 37 55 70 54 83 335 80 45 5.5 5.5 50 39 58.5 75 59 88 435 125 1.0 GATE2 (current-limit/circuit-breaker control) 54 6.5 6.5 52.5 41 61 80 64 93 535 200 A mA A mV mV A V VON_REF VON rising 1.20 VIN IIN ISD VUVLO VON = 3V, no load VON = 0.4V VIN rising, ON = IN 6.2 7.5 1.3 5 6.5 0.35 1.24 70 1 1.275 37 2.3 10 6.8 V mA A V V V mV A SYMBOL CONDITIONS MIN TYP MAX UNITS
2
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FireWire Current Limiter and Low-Drop ORing Switch Controller
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 7.5V to 37V, GND = 0V, and TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = 12V, TA = +25C.) (Note 1)
PARAMETER GATE2 Pulldown Current During Any GATE2 Turn-Off Condition GATE1 (ORing control) OR_ADJ = GND ORing Switch Turn-On Current Threshold Voltage ORing Switch Turn-On Current Threshold Voltage Hysteresis GATE1 Pullup Current GATE1 High Voltage GATE1 Turn-Off Switch OnResistance LOGIC INPUTS ILIM, OR_ADJ Input-Logic Tristate Current Tolerance (Note 6) LATCH, ONQ1 Input-Logic Low Voltage LATCH, ONQ1 Input-Logic High Voltage LATCH, ONQ1 Input Current TIM, ILIM, LATCH, OR_ADJ, OUT, ONQ1 Shutdown Mode Input Current FAULT Output Low Voltage FAULT Output High Leakage Current TIMING TIM = IN Current-Limit Timeout (MAX5943A) tILIM Current-limit mode (Note 7) RTIM = 4k RTIM = 50k TIM = floating 1.78 0.87 9.2 120 2.02 1.04 11.05 175 2.26 1.21 12.9 225 ms ms ms ms IIX IIXL IIH VIL IIL VIH IIH Current into or out of input for tri-state logic condition Current out of input for logic low Current into input for logic high VON > VON_REF LATCH, ONQ1 = GND, VON > VON_REF VON > VON_REF All voltages = VIN, VON > VON_REF 1.8 1 -3 +3 20 20 0.7 1 V A V A A IG1U VG1 RG1 VOR (VIN - VSENSE) rising OR_ADJ = floating OR_ADJ = IN (VIN - VSENSE) falling (Note 5) VGATE1 - VSENSE 7.5V VIN 8V 8V VIN 37V 36 4.25 4.5 3 5.5 8.5 5 7.5 10.5 0.5 45 5.5 5.5 2 54 6.5 6.5 3 7 9.5 12.8 mV A V mV SYMBOL IG2OFF CONDITIONS VGATE2 = VOUT + 4.5V (Note 4) MIN 80 TYP 125 MAX 200 UNITS mA
MAX5943
Measured between GATE1 and SENSE when (VIN - VSENSE) < VOR
IIH_SD VOL IOH
All voltages = VIN, VON 0.4V Low-impedance state, I FAULT = 5mA High-impedance state, V FAULT = 37V 0.12
1 0.25 1
A V A
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FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 7.5V to 37V, GND = 0V, and TA = -40C to +85C, unless otherwise noted. Typical values are at VIN = 12V, TA = +25C.) (Note 1)
PARAMETER SYMBOL CONDITIONS TIM = IN or TIM 3.4V RTIM = 4k RTIM = 50k TIM = floating TIM = IN or TIM 3.4V Circuit-breaker mode, MAX5943C Circuit-Breaker Timeout (MAX5943B-MAX5943E) (Note 7) tCB Circuit-breaker mode, MAX5943D RTIM = 4k RTIM = 50k TIM = floating TIM = IN RTIM = 4k RTIM = 50k TIM = floating TIM = IN or TIM 3.4V Circuit-breaker mode, MAX5943E RTIM = 4k RTIM = 50k TIM = floating Automatic Restart Delay After Current-Limit/Circuit-Breaker Timeout GATE1 Turn-Off Time (ORing Response Time) MIN 0.45 27 228 3.75 0.89 54 575 7.5 1.78 109 1.15 15 3.56 217 2.3 30 TYP 0.51 32.5 345 5.5 1.00 65 690 10.9 2.02 130 1.38 21.9 4.05 260 2.76 44 128 x (tILIM OR tCB) MAX 0.57 38 403 7 1.13 76 806 14 2.26 151 1.61 28 4.52 303 3.23 56 UNITS ms s s ms ms s s ms ms s ms ms ms s ms ms
Circuit-breaker mode, MAX5943B
tOFF
LATCH = GND (Note 8)
ms
tOR
From VOR trigger until (VGATE1 - VIN) < 1V, CGATE1 = 10nF Time from VON < (VON_OFF - Hysteresis) until (VGATE2 - VOUT) < 1V, GATE2 = open (Note 9) ON step from 1.3V to 0.4V
100
ns
Turn-Off Response Time
tON_OFF
0.34
0.6
s
Minimum Delay from ON Low to Low-Current Shutdown Mode
tSD
50
s
All min/max parameters are tested at +25C and +85C. Limits at -40C are guaranteed by design. Measured at both VGATE2 = VOUT = 0V and VGATE2 = VOUT = VIN. The typical value of parameter VTHF is 1.5 x VTH. Current-Limit/Circuit-Breaker Timeout; IN or ON low. See the Typical Operating Circuit. Measured at VGATE1 = VSENSE. The tristate ("floating") logic condition will be entered if the pin current is within these limits. RTIM is connected from TIM to GND. The maximum timeout period is enforced to prevent arbitrarily long operation in current-limit mode. Therefore, the relationship between resistor value and timeout changes for large values of RTIM. See Current-Limit Timeout vs. RTIM in the Typical Operating Characteristics for nominal values. Note 8: Parameter tOFF is a direct multiple of tILIM (or tCB), so the limits for tOFF track the limits for tILIM (or tCB). Note 9: If the ON voltage goes below VON_REF - Hysteresis, then GATE2 goes low immediately to disconnect power from the load quickly (within tON_OFF). Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: 4 _______________________________________________________________________________________
FireWire Current Limiter and Low-Drop ORing Switch Controller
Typical Operating Characteristics
(VIN = +12V, TA = +25C, unless otherwise noted.)
MAX5943
SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX5943 toc01
SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE
MAX5943 toc02
CURRENT-LIMIT/CIRCUIT-BREAKER THRESHOLD VOLTAGE vs. TEMPERATURE
52.0 51.5 51.0 50.5 50.0 49.5 49.0 48.5 48.0 47.5 47.0 46.5 46.0 -40 -15 10 35 60 85 VIN = 12V VIN = 7.5V ILIM = GND VIN = 32V
MAX5943 toc03
2.0 1.9 1.8 SUPPLY CURRENT (mA) 1.7 1.6 1.5 1.4 1.3 1.2 1.1 1.0 5 10 15 20 25 30 35 TA = -40C TA = +85C TA = +25C
6.0 5.5 SHUTDOWN SUPPLY CURRENT (A) 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 5 10 15 20 25 30 35
40
40
THRESHOLD VOLTAGE (mV)
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
CURRENT-LIMIT/CIRCUIT-BREAKER THRESHOLD VOLTAGE vs. TEMPERATURE
MAX5943 toc04
CURRENT-LIMIT/CIRCUIT-BREAKER THRESHOLD VOLTAGE vs. TEMPERATURE
ILIM = FLOATING
MAX5943 toc05
TIMEOUT PERIOD vs. RTIM
MAX5943 toc06
62.0 61.5 THRESHOLD VOLTAGE (mV) 61.0 60.5 60.0 59.5 59.0 58.5 58.0 57.5 57.0 56.5 56.0 -40
ILIM = IN
42.0 41.5 THRESHOLD VOLTAGE (mV) 41.0 40.5 40.0 39.5 39.0 38.5 38.0 37.5 37.0 36.5 36.0 -40
100
VIN = 32V VIN = 12V
TIMEOUT PERIOD (s)
10
MAX5943A
1 MAX5943E 0.1
VIN = 7.5V
0.01 -15 10 35 60 85 1 10 RTIM (k) 100 1000 TEMPERATURE (C)
-15
10
35
60
85
TEMPERATURE (C)
ORing THRESHOLD VOLTAGE vs. TEMPERATURE
12.0 11.5 11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 -40
MAX5943 toc07
GATE CURRENTS vs. TEMPERATURE
MAX5943 toc08
GATE1 DRIVE VOLTAGE vs. TEMPERATURE
5.257 GATE1 DRIVE VOLTAGE (V) 5.254 5.251 5.248 5.245 5.242 5.239 5.236 5.233
MAX5943 toc09
47.0 46.5 GATE CURRENTS (A) 46.0 45.5 45.0 GATE2 44.5 44.0 GATE1
5.260
ORing THRESHOLD VOLTAGE (mV)
OR_ADJ = IN OR_ADJ = OPEN
OR_ADJ = GND
5.230 -40 -15 10 35 60 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
-15
10
35
60
85
TEMPERATURE (C)
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FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25C, unless otherwise noted.)
GATE2 DRIVE VOLTAGE vs. TEMPERATURE
MAX5943 toc10
ON HIGH VOLTAGE vs. TEMPERATURE
MAX5943 toc11
ON LOW VOLTAGE vs. TEMPERATURE
1.198 1.196 ON LOW VOLTAGE (V) 1.194 1.192 1.190 1.188 1.186 1.184 1.182
MAX5943 toc12
5.230 5.227 GATE2 DRIVE VOLTAGE (V) 5.224 5.221 5.218 5.215 5.212 5.209 5.206 5.203 5.200 -40 -15 10 35 60
1.260
1.200
1.258 ON HIGH VOLTAGE (V)
1.256
1.254
1.252
1.250 85 -40 -15 10 35 60 85 TEMPERATURE (C) TEMPERATURE (C)
1.180 -40 -15 10 35 60 85 TEMPERATURE (C)
FAULT LOW VOLTAGE vs. TEMPERATURE
MAX5943 toc13
ORing THRESHOLD RESPONSE TIME
MAX5943 toc14
200 180 FAULT LOW VOLTAGE (mV) 160 140 120 100 80 60 40 20 0
IFAULT = 5mA
OR_ADJ = IN
VIN 10V/div IIN 500mA/div (VGATE - VSENSE) 5V/div VOUT 5V/div
-40
-15
10
35
60
85
100s/div
TEMPERATURE (C)
TURN-OFF RESPONSE TIME
MAX5943 toc15
MAX5943A SHORT-CIRCUIT EVENT (VIN = 37V)
VON 2V/div IIN 1A/div VGATE2 10V/div TIM = IN ILIM = GND
MAX5943 toc16
VIN 50V/div IIN 1A/div
VGATE2 50V/div VOUT 50V/div VFAULT 50V/div 400s/div
VOUT 10V/div 200ns/div
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FireWire Current Limiter and Low-Drop ORing Switch Controller
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25C, unless otherwise noted.)
MAX5943
MAX5943A SHORT-CIRCUIT EVENT (VIN = 37V)
ILIM = GND
MAX5943 toc17
MAX5943A SHORT-CIRCUIT RESPONSE (VIN = 8V)
MAX5943 toc18
VIN 50V/div IIN 10A/div
VIN 10V/div IIN 1A/div
VGATE2 10V/div VGATE2 50V/div VOUT 50V/div VFAULT 50V/div 100ns/div 400s/div VOUT 10V/div VFAULT 10V/div
TIM = IN
MAX5943A SHORT-CIRCUIT RESPONSE (VIN = 8V)
MAX5943 toc19
MAX5943E SHORT-CIRCUIT RESPONSE (VIN = 24V)
VIN 10V/div IIN 10A/div
MAX5943 toc20
VIN 50V/div IIN 166A/div
VGATE2 10V/div VOUT 10V/div VFAULT 10V/div 100ns/div 200s/div
VGATE2 50V/div
VOUT 50V/div VFAULT 50V/div
MAX5943E SHORT-CIRCUIT RESPONSE (VIN = 8V)
ORing SWITCHOVER WAVEFORM
MAX5943 toc22
MAX5943 toc21
VIN 10V/div IIN 60A/div VGATE2 10V/div
VOUT 1V/div
IIN1 500mA/div
VOUT 10V/div VFAULT 10V/div VIN1 = 12V VIN2 = 128V 200s/div VON2 RISING = 12V COUT = 0 IIN2 500mA/div
TIM = IN 100s/div
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FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25C, unless otherwise noted.)
ORing SWITCHOVER WAVEFORM (VIN2 RISING ABOVE VIN1) ORing SWITCHOVER WAVEFORM (VIN2 FALLING BELOW VIN1)
VOUT 1V/div
MAX5943 toc23
MAX5943 toc24
VOUT 1V/div
IIN1 500mA/div
IIN1 500mA/div
IIN2 500mA/div 10s/div VON2 RISING = 12V COUT = 0 20s/div VON2 FALLING = 12V COUT = 0
IIN2 500mA/div
VIN1 = 12V VIN2 = 13V
VIN1 = 12V VIN2 = 13V
MAX5943A HOT PLUG-IN LOAD CAPACITANCE INTO ACTIVE PORT (NO FAULT)
MAX5943 toc25
MAX5943A HOT PLUG-IN LOAD CAPACITANCE INTO ACTIVE PORT (CURRENT-LIMIT TIMEOUT)
MAX5943 toc26
VFAULT 10V/div
VFAULT 10V/div IIN 1A/div VGATE2 10V/div
IIN 2A/div
VGATE2 10V/div VOUT 10V/div 400s/div CLOAD = 220F TIM = IN CLOAD = 470F TIM = IN 400s/div
VOUT 10V/div
8
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FireWire Current Limiter and Low-Drop ORing Switch Controller
Pin Description
PIN NAME FUNCTION On/Off-Control Input. ON sets the undervoltage lockout threshold and resets the part after a fault latch. Drive ON high to enable the device. Drive ON low to disable the device. Connect ON to IN for the default undervoltage lockout threshold. Connect a resistor-divider from IN to ON and GND to program the desired undervoltage lockout threshold. Current-Fault, Active-Low, Open-Drain Output. FAULT asserts and latches low after a current-limit/circuitbreaker fault has exceeded the current-limit/circuit-breaker timeout period (see the FAULT section). Current-Limit/Circuit-Breaker Timeout Adjustment Input. Connect TIM to IN for the default timeout period or connect a resistor from TIM to GND to program the current-limit/circuit-breaker timeout period. Current-Limit/Circuit-Breaker Threshold Input. Leave ILIM open for a 40mV circuit-breaker threshold, connect to GND for a 50mV circuit-breaker threshold, or connect to IN for a 60mV circuit-breaker threshold (see the Current Limiting section). Latch or Autoretry Fault Management Selection Input. Connect LATCH to IN to select latch-off mode after a current-limit/circuit-breaker timeout. Connect LATCH to GND for autorestart mode after a currentlimit/circuit-breaker timeout. ORing Switch Turn-On Current Threshold Adjustment Input. Select one of three ORing switch turn-on threshold settings: connect OR_ADJ to GND, connect OR_ADJ to IN, or leave OR_ADJ floating (see the Power-Supply ORing section). No Connection. Not internally connected. ORing Switch Manual Turn-On Input. Drive ONQ1 low to enable power-supply ORing. Drive ONQ1 high to set GATE1 high to allow reverse current flow. ONQ1 is disabled when VIN is below the UVLO threshold, VON is below the VON_REF threshold, and after a current/circuit-breaker fault. Ground Output Voltage Sense. Connect to the output. Current-Limiter Switch Gate Drive Output. Connect GATE2 to the gate of the 2nd n-channel MOSFET. GATE2 is a charge pump with a 45A pullup current to 5.5V (typ) above OUT when active (see the Typical Operating Circuit). ORing Switch Gate-Drive Output. Connect GATE1 to the gate of the 1st n-channel MOSFET. GATE1 is a charge pump with a 45A pullup current to 5.5V (typ) above SENSE when active (see the Typical Operating Circuit). Current-Sense Negative Input. Connect a current-sense resistor, RSENSE, from IN to SENSE (see the Typical Operating Circuit). Input Power and Current-Sense Positive Input. Connect IN to the positive terminal of the current-sense resistor and to the power source (see the Typical Operating Circuit).
MAX5943
1
ON
2 3
FAULT TIM
4
ILIM
5
LATCH
6 7, 10, 13 8 9 11 12
OR_ADJ N.C. ONQ1 GND OUT GATE2
14
GATE1
15 16
SENSE IN
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FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
POWER SOURCE RSENSE Q1 Q2
SENSE ONQ1 OR COMPARATOR THRESHOLD
GATE1
GATE2
OUT
OR_ADJ
+ +
SENSE GATE1 GATE1 DRIVE
GATE2 OUT GATE2 DRIVE
ILIM
CIRCUIT-BREAKER (CURRENT-LIMIT) THRESHOLD
-
FAULT TIMEOUT
+
TIM
(FAST CURRENTLIMIT THRESHOLD) UVLO COMPARATOR
+
-
X128
6.5V ON 1.24V
+
+ -
AUTORETRY TIMEOUT PERIOD CP1 CP2 GATE CHARGE PUMPS
ON COMPARATOR SHUTDOWN MODE
FAULT MANAGEMENT LATCH OR AUTORETRY
LATCH FAULT
0.4V
-
MAX5943A-MAX5943E
GND ( ) MAX5943A ONLY.
Figure 1. MAX5943 Functional Diagram
Detailed Description
The MAX5943 performs hot-swapping, power-supply ORing, and current limiting for FireWire power-supply applications. The MAX5943 incorporates two MOSFET drivers (GATE1 and GATE2) to control two external n-channel power MOSFETs to perform low-voltage-drop power-supply ORing (GATE1) and hot swapping and current limiting (GATE2) from the input power supply to the load. A sense resistor provides accurate currentlimiting/circuit-breaker function. GATE1 and GATE2 provide true load disconnect to prevent current flowing from either direction between IN and OUT. The MAX5943 remains in low-current shutdown mode when VON is below the 0.4V threshold. Low-current shutdown mode disables the MAX5943, resulting in less than 10A supply current. Shutdown places all
10
logic inputs in a high-impedance state allowing the inputs to be connected to IN without drawing additional current from the supply. When the input supply voltage (VIN) is above 7.5V and VON is above the VON_REF threshold, the MAX5943 turns on, sourcing 45A current from GATE2 (current regulation) to enhance Q2 slowly. For the MAX5943A, if the voltage across the current-sense resistor, VIS, is greater than the programmed current-limit threshold, the MAX5943A regulates the GATE2 voltage to limit the load current at the current-limit level so that VIS is equal to VTH. In normal operation, VIS drops below VTH and GATE2 rises to approximately 5.5V above OUT. Since the MAX5943B-MAX5943E do not regulate the load current, a capacitor can be added from GATE2 to GND to limit inrush current during startup (see the Applications Information section).
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FireWire Current Limiter and Low-Drop ORing Switch Controller
The MAX5943 current-limit/circuit-breaker timeout is programmable by connecting an external resistor from TIM to GND. The MAX5943A has a default 2ms currentlimit timeout. The MAX5943B, MAX5943C, MAX5943D, and MAX5943E have 0.5ms, 1ms, 2ms, and 4ms default circuit-breaker timeouts, respectively. GATE1 controls the MAX5943 ORing function. Initially, GATE1 is off (ONQ1 = low) and the load current conducts through the body diode of Q1. GATE1 rises to 5.5V above SENSE when VIS exceeds VOR, thereby enhancing Q1 and reducing the voltage drop, power dissipation, and heat generation in the power-supply path. When a voltage greater than VIN is connected at OUT, the higher voltage source commences, providing current to the load. The MAX5943 rapidly turns off GATE1 upon VIS falling below VOR - hysteresis, thus blocking the higher voltage from back-driving V IN . GATE1 also turns off when the load current drops, causing VIS to fall below the VOR hysteresis.
MAX5943
VFAULT tILIM ILIMIT
IOUT
VIN
VGATE1
VGATE2
Current Limiting/Circuit Breaker
Current Limiting (MAX5943A Only) The MAX5943A limits the load current by monitoring the voltage across RSENSE at all times and by regulating the current to the load as necessary to keep VIS to its programmable current-limit threshold voltage (VTH). Set the maximum current limit (ILIMIT) by placing the appropriate sense resistor between IN and SENSE, where ILIMIT = VTH/RSENSE. When the load current is less than ILIMIT, GATE2 rises to VG2 (5.5V) to fully enhance MOSFET Q2 (see the Typical Operating Circuit). When the load current attempts to draw more than ILIMIT, the MAX5943A's GATE2 pulldown current (IG2D) regulates the current through Q2 causing OUT to act as a constant-current source. The output current is limited to the programmed ILIMIT. If the current-limit condition persists after the current-limit timeout (tILIM) period has expired, GATE2's strong pulldown current (IG2 OFF) quickly turns off GATE2 to disconnect the load from the power supply. FAULT then asserts low (Figure 2a). If the current-limit duration is less than tILIM, GATE2 pulls to VG2 (Figure 2b). During an output short circuit or a gross overload, the load current overshoots and causes VIS to exceed the fast pulldown current-limit threshold voltage (VTHF). The MAX5943A responds with much stronger GATE2 pulldown currents (IG2DP and/or IG2DF) to quickly bring the load current back down to the programmed current limit.
VOUT
ILIMIT x RLOAD
(a)
VFAULT < tILIM ILIMIT
IOUT
VGATE1
VGATE2 ILIMIT x RLOAD VOUT
(b)
Figure 2. MAX5943A Current-Limit Timing Diagram
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11
FireWire Current Limiter and Low-Drop ORing Switch Controller
MAX5943B-MAX5943E Circuit Breaker The MAX5943B-MAX5943E provide a circuit-breaker function that protects against excessive load currents and short-circuit conditions. The load current is monitored by sensing the voltage across an external sense resistor (R SENSE ) and disconnects the load from the power source when the voltage across RSENSE, VIS, exceeds the programmed circuit-breaker thresholds (VTH) for longer than the circuit-breaker timeout period, tCB. Unlike the MAX5943A, when an output short circuit or overcurrent occurs, the MAX5943B-MAX5943E keep GATE2 fully enhanced. The short-circuit current is limited only by the input source impedance, RSENSE, Q1's RDS(ON), Q2's RDS(ON), and any parasitic impedance in the power path. If the excessive current condition persists (as indicated by VIS > VTH) for longer than tCB, GATE2 turns off with a strong pulldown (IG2 OFF) to quickly disconnect the power source from the load and FAULT asserts low (Figure 3). Exercise caution when using the MAX5943B-MAX5943E. Unlike the MAX5943A, the MAX5943B-MAX5943E do not limit the load current during tCB. High current during tCB may cause damage to external devices connected in the power path.
MAX5943
Current-Limit/Circuit-Breaker Thresholds
The MAX5943 allows three selectable current-limit/circuit-breaker thresholds (V TH ). Choose the voltage threshold by connecting ILIM to the appropriate level; see Table 1.
Table 1. Current-Limit/Circuit-Breaker Trip Threshold Level
ILIM CONNECTION Open GND IN VTH (mV) 40 50 60
Current-Limit/Circuit-Breaker Timeout Period (tILIM/tCB)
The MAX5943's current-limit/circuit-breaker timeout function disconnects power from the load if the currentlimit or circuit-breaker threshold voltage exceeds its maximum limit for a programmable amount of time. Connect TIM to IN for the MAX5943 default timeout periods (see Table 2). Adjust the fault timeout period (tILIM/ tCB) by connecting a resistor (RTIM) from TIM to GND (see the Typical Operating Characteristics). Calculate the fault-limit timeout period using the following equation: tILIM (ms) = t CB (ms) = 0.25 x R TIM (k) K
VFAULT
where RTIM is in k, tILIM/tCB is in ms, and K = 1 for MAX5943A, K = 32 for MAX5943B, K = 16 for MAX5943C, K = 8 for MAX5943D, and K = 4 for the MAX5943E.
ILIMIT tCB
Table 2. MAX5943_ Timeout Periods
DEFAULT TIMEOUT, TIM = IN (ms) 2 0.5 1 2 4 PROGRAMMABLE TIMEOUT RANGE (4k < RTIM < 50k) 1.04ms to 11.05ms 32.5s to 345s 65s to 690s 130s to 1.38ms 260s to 2.76ms MAXIMUM TIMEOUT, TIM = FLOATING (ms) 12.5 4.8 9.6 19.2 38.4
IOUT VIN VGATE1 VGATE2 VG2 VOUT VG2
PART
MAX5943A MAX5943B MAX5943C MAX5943D MAX5943E
Figure 3. MAX5943B-MAX5943E Circuit-Breaker Timing Diagram 12 ______________________________________________________________________________________
FireWire Current Limiter and Low-Drop ORing Switch Controller
Timing accuracy is guaranteed for RTIM ranging from 4k to 50k. Large RTIM values can be used, which reduces timing accuracy. A maximum timeout period is enforced to prevent arbitrarily long operation in currentlimit/circuit-breaker conditions. Long durations in current-limit/circuit-breaker mode may produce excessive heating and electrical stresses in RSENSE, Q1, Q2, and any other components in the power path. Use component values rated to handle electrical stresses during the timeout period.
MAX5943
IINA = 0 VINA FROM BATTERY SOURCE ON IN
RSENSE
TO FireWire PORT VINB > VINA ILOAD SENSE GATE1 GATE2 OUT
MAX5943 GND OR_ADJ ONQ1
Power-Supply ORing (ONQ1 = Low)
GATE1 controls the MAX5943 ORing function. The MAX5943 accomplishes a very-low-voltage-drop diode ORing function using an n-channel power MOSFET, Q1. Initially, GATE1 is off (ONQ1 = low) and the load current conducts through the body diode of Q1 (Figure 4). GATE1 rises to 5.5V above SENSE when VIS exceeds VOR, enhancing Q1. Q1's low RDS(ON) provides a verylow-voltage drop across its source to drain, reducing voltage drop, power dissipation, and heat generation in the power-supply path created by a traditional diode. The MAX5943 continuously monitors the load current by the voltage drop, VIS, across the current-sensing resistor. Q1 turns off rapidly when VIS decreases below VOR minus its hysteresis. Set the MAX5943 ORing threshold (VOR) by connecting OR_ADJ to GND for a 5mV threshold, or to IN for a 10mV threshold, or leave it open for a 7.5mV threshold. Connect ONQ1 to GND for normal ORing function. Drive ONQ1 high to force Q1 on, regardless of the load current condition, as long as the voltages at IN and ON exceed V UVLO and V ON_REF , respectively, and the device is not in a current fault shutdown.
IINB VINB FROM POWER SOURCE ON IN SENSE GATE1 GATE2 OUT RSENSE
MAX5943 GND OR_ADJ ONQ1
Figure 5. MAX5943 ORing Controller Rerouting Load Current
When a higher voltage supply is connected at OUT (Figure 5), the sense voltage drops below the programmable ORing threshold. The MAX5943 immediately turns off Q1, blocking reverse current flow from OUT to IN. The power is then routed from the higher supply input to the load (Figure 6). Reverse Current Override (ONQ1 = High) Drive ONQ1 high to disable the power-supply ORing function. Disabling the MAX5943 ORing function allows reverse current flow through the power-supply system. When ONQ1 is high, GATE1 remains fully enhanced as long as VIN is greater than VUVLO, VON is above the VON_REF threshold, and the MAX5943 is not in a current-limit or circuit-breaker fault condition. The MAX5943 reverse-current flow feature permits a higher voltage source connected to one port to route power to another port, as long as the voltage at IN remains above the minimum 7.5V operating range (see Figure 7).
+ VIN
VIS RSENSE
-
TO FireWire PORT Q1 Q2
ON IN
SENSE
GATE1
GATE2
OUT
MAX5943 GND OR_ADJ ONQ1
Figure 4. Q1 Current Path During Inital Startup ______________________________________________________________________________________ 13
FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
VINA
PORT1
IINA
TIM IN ON ONQ1 ILIM LATCH
SENSE GATE1
GATE2 OUT
MAX5943 GND OR_ADJ
FAULT
IINB
PORT2
TIM IN ON
SENSE GATE1
GATE2 OUT
VOUT
ONQ1 ILIM
MAX5943 LATCH GND
FAULT OR_ADJ
VINB VINB > VINA
Figure 6. MAX5943 Power Switch Over ORing Timing Diagram
Figure 7. MAX5943 Operating in Reverse-Current Mode (Routing Power from Port 1 to Port 2)
VIN IN R1
Undervoltage Lockout
The MAX5943 operates from 7.5V to 37V and has a default 6.5V undervoltage lockout threshold. The external MOSFETs remain off as long as VIN > 6.5V and VON < VON_REF. The turn-on threshold is programmable by connecting a resistor-divider at ON. When VON > 1.24V and VIN > 7.5V, GATE2 is enhanced to 5.5V, with respect to OUT and the MAX5943 goes into normal operation. Program the MAX5943's turn-on voltage using the following formula: VTURN _ ON R1 = - 1 x R2 1.24 where VTURN_ON is the desired turn-on voltage of the MAX5943. Choose an R2 value in the 1k range to minimize error due to the ON bias current. When operating the MAX5943, ON must remain above its 1.24V threshold. If VON falls below its 1.24V threshold, the power-supply MOSFETs (Q1 and Q2) turn off immediately (less than 1s). This allows the power supply to disconnect in the event of a fault condition
14
MAX5943
ON R2 GND
Figure 8. Setting the MAX5943 Turn-On Voltage
detected by the system, such as shorting of the output to a different power-supply voltage or a FireWire signal pin. If possible transient conditions exist at the main power-supply line (IN), place an RC filter at ON to reject transient voltage dips and to prevent unnecessary power-supply interruptions.
______________________________________________________________________________________
FireWire Current Limiter and Low-Drop ORing Switch Controller
The MAX5943 remains in low-current shutdown mode when VON is below the 0.4V threshold. Low-current shutdown mode disables the MAX5943 resulting in less than 10A supply current. Shutdown places all logic inputs in a high-impedance state allowing the inputs to be connected to IN without drawing additional current from the supply. An internal delay, tSD, allows Q1 and Q2 to be turned off before the MAX5943 enters lowcurrent shutdown mode.
MAX5943
VIN IN LATCH R1
MAX5943
ON R2 GND
Fault Status Output (FAULT)
FAULT is a high-voltage open-drain output that pulls low when a current-limit/circuit-breaker fault shutdown has occurred. FAULT remains low until the next startup cycle.
Fault Management
The MAX5943 offers either latch or autoretry fault management configurable by the LATCH input. Connect LATCH to IN for latch fault management or connect LATCH to GND for autoretry fault management. In latch fault management, FAULT latches low, GATE1 and GATE2 latch off indefinitely. Cycle ON low and then high to unlatch and restart the MAX5943. However, the MAX5943 will not enter a startup cycle until tOFF has expired. Figure 9 illustrates a way to reset the MAX5943 after a fault using a pushbutton switch. In autoretry fault management, the MAX5943_ attempt to restart after a tOFF of 128 x tILIM (or 128 x tCB) limiting the duty cycle of the MOSFETs to 1/129 under continuous fault conditions. FAULT deasserts every time a restart attempt is made.
Figure 9. Resetting MAX5943 After a Latched Fault Condition
RSENSE +
Q1
Q2 1k CGATE IC ILOAD
45A IN VIN SENSE GATE1 GATE2 OUT COUT LOAD
MAX5943B-MAX5943E GND
-
Applications Information
Startup Consideration
MAX5943A During startup, a large capacitor at OUT may result in a charging current equivalent to the current limit. Choose a current-limit timeout that will allow a successful startup. The timeout can be approximated using the following equation: tILIM > COUT x VIN ILIMIT - ILOAD
Figure 10. Controlling the MAX5943B-MAX5943E Inrush Current
MAX5943B-MAX5943E The MAX5943B-MAX5943E do not control the inrush current during startup. Inrush current control can be implemented by placing a resistor and capacitor at GATE2 (Figure 10) to slowly ramp up the gate voltage, thus limiting the inrush current. The inrush current can be approximated using the following formula: IINRUSH = COUT x IG2U + ILOAD CGATE2
where ILIMIT is the programmed current limit, COUT is the capacitor at OUT, VIN is the supply voltage, and ILOAD is the load current during startup. With IN = 12V, C OUT = 330F, I LIMIT = 1.5A, and I LOAD = 0, the MAX5943 commences by charging the output capacitor with 1.5A for approximately 2.7ms. Therefore, the MAX5943A current-limit timeout period (tILIM) should be greater than 2.7ms for a successful startup. Otherwise, the MAX5943A powers up in fault management mode by exceeding the current-limit timeout period.
Where I G2U is GATE2's 45A sourcing current and ILOAD is the load current at startup. To prevent the MAX5943B-MAX5943E from starting up in a fault condition set: IINRUSH < VTH RSENSE
15
______________________________________________________________________________________
FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
Optimizing for Short-Circuit Conditions
Choosing RSENSE Select a sense resistor that causes the circuit-breaker voltage drop at a current-limit/circuit-breaker level above the maximum normal operating current. Typically, set the overload current at 1.2 to 1.5 times the full load current. Choose the sense-resistor power rating to accommodate an overcurrent condition: PRSENSE = I2LIMIT x RSENSE where PRSENSE is the power dissipated across RSENSE during a current-limit/circuit-breaker fault. Under short-circuit conditions, it is imperative that the appropriate sense resistor is utilized. Operating the MAX5943B-MAX5943E at high input voltages can cause very large currents during the circuit-breaker timeout period. The peak current will be limited by the saturation current of Q2 or the series resistance in the power path (RTOTAL). Using a 30m on-resistance MOSFET at GATE1 and GATE2 and a 30m sense resistor results in a short-circuit current approximately equal to: ISC = VIN/RTOTAL where: RTOTAL = RSENSE + 2 x (RON) = 30m + 2 x (30m) = 90m For example, an input voltage of 20V produces a current at approximately 222A (or ISAT of Q2, whichever is less) in the power path for the circuit-breaker timeout period. Choose an RSENSE capable of handling the high power dissipation during a short-circuit event. MOSFET Selection Select external MOSFETs according to the application current level. The MOSFETs' on-resistance (RDS(ON)) should be chosen low enough to have minimum voltage drop at full load to limit the MOSFET power dissipation. High RDS(ON) also causes large output ripple if there is a pulsating load. Determine the device power rating to accommodate startup, a short-circuit condition, and when the device is in autoretry mode. During normal operation, the external MOSFETs dissipate little power. The power dissipated in normal operation is: P = ILOAD2 x RDS(ON) The most power dissipation occurs during a short-circuit event, resulting in high power dissipated in Q2 (Figure 11) during the timeout period for the MAX5943A, where the power dissipated across Q2 is: PQ2 = (VIN - VIS - VQ1 ) x ILIMIT For the MAX5943B-MAX5943E, a short-circuit event results in high power dissipated in both Q1 and Q2 during the timeout period (Figure 12) where the total power dissipated in either MOSFET is: P = ISC2 x RDS(ON) where: ISC = VIN/REQ and REQ = RSENSE +RDS(ON1) + RDS(ON2) The programmable timeout of the MAX5943 allows the use of MOSFETs with low power ratings. A MOSFET typically withstands single-shot pulses with higher dissipation than the specified package rating.
FireWire Power Management
The MAX5943 serves to regulate and protect FireWire power over a system interface. The MAX5943 programmable features make it suitable for both power provider and power receiver applications. Figure 13 shows a high-end two-port FireWire power management system using two MAX5943As and a dual-channel MAX5944 FireWire current-limiting IC.
VIN
+
VIS
-
+ VQ1 -
+ VQ2 -
IN
SENSE GATE1
GATE2
OUT
MAX5943A
Figure 11. Power Dissipated Across MOSFETs During a ShortCircuit Fault for MAX5943A
16
______________________________________________________________________________________
FireWire Current Limiter and Low-Drop ORing Switch Controller
Transient Protection
If IN or OUT experiences a fast voltage transient, the drain-to-gate parasitic capacitance of Q1 and/or Q2 may be sufficient to briefly enhance one of the transistors, allowing current glitch. If the circuit is subjected to large transients, connect capacitors from the gate to source across the appropriate MOSFET, preventing the parasitic capacitance from turning on the device. Caution: The additional gate-to-source capacitance causes the turn-off time of the MOSFETs to increase due to the additional charge of the capacitor. Use the minimum capacitor value to prevent currents from flowing in hot-plug situations.
VIN RSENSE RDS(ON)1 RDS(ON)1
MAX5943
ISC
IN
SENSE GATE1
GATE2
OUT
MAX5943B-MAX5943E
Figure 12. Power Dissipated Across MOSFETs During a ShortCircuit Fault for MAX5943B-MAX5943E
______________________________________________________________________________________
17
FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
FB BST
VIN ON
CPA SENSE
MAX5033
PHY POWER OUT LX IN4148 VD GND SGND IN4148
IN4148 CABLE POWER SOURCE TIM IN ON 15m SI7958DP SI7958DP 30m SI7958DP SI7958DP
PORT 0
SENSE GATE1
GATE2 OUT ONA
INA ONQ1 GND
SENSEA GATE1A
GATE2A OUTA
MAX5943A ILIM LATCH GND ONQ1
FAULT OR_ADJ
FAULTA MAX5944 FAULTB
ONB INB SENSEB GATE1B GATE2B OUTB
BATTERY-POWER SOURCE
15m
SI7958DP
SI7958DP 30m IRF7478 IRF7478 IN4148
PORT 1
TIM IN ON
SENSE GATE1
GATE2 OUT
MAX5943A ILIM LATCH GND ONQ1
FAULT OR_ADJ
CABLE NOT ON SLEEP
CURRENT-LIMIT SENSE
PORT 1 PORT 0 SENSE SENSE
Figure 13. Two-Port FireWire Power Provider Using MAX5943A and MAX5944 18 ______________________________________________________________________________________
FireWire Current Limiter and Low-Drop ORing Switch Controller
Typical Operating Circuit
FireWire PORT SUPPLY + VIS RSENSE Q1 R1 R3
VIN = 12V TIM IN FAULT ON 7.15k SENSE GATE1 GATE2 OUT
Typical Application Circuit
FireWire PORT SUPPLY + 1k 10k 4k 30m SI7958DP Q1 SI7958DP Q2 TO FireWire PORT
MAX5943
TO FireWire PORT Q2
TIM IN FAULT ON R2
SENSE GATE1
GATE2
OUT
MAX5943A ILIM LATCH GND OR_ADJ ONQ1
MAX5943A ILIM LATCH GND OR_ADJ ONQ1
Selector Guide
MAX5943 EQUIVALENT CIRCUIT VERY-LOW-DROP ORing DIODE LOAD DISCONNECT SWITCH
PART
CURRENT LIMITER/ CIRCUIT BREAKER Current limit
DEFAULT PROGRAMMABLE TIMEOUT TIMEOUT RANGE (ms) 2 0.5 1 2 4 1.04ms to 11.05ms 32.5s to 345s 65s to 690s 130s to 1.38ms 260s to 2.76ms
CURRENT-LIMIT/CIRCUIT-BREAKER AND INRUSH CONTROL
MAX5943A
MAX5943B Circuit breaker MAX5943C Circuit breaker MAX5943D Circuit breaker MAX5943E Circuit breaker
Chip Information
TRANSISTOR COUNT: 2324 PROCESS: BiCMOS
______________________________________________________________________________________
19
FireWire Current Limiter and Low-Drop ORing Switch Controller MAX5943
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.)
QSOP.EPS
PACKAGEOUTLINE,QSOP.150",.025"LEADPITCH
21-0055
E
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.
20 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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