Maxim MAX5943EEEE Firewire current limiter and low-drop oring switch controller Datasheet

19-3378; Rev 2; 10/07
FireWire Current Limiter and Low-Drop
ORing Switch Controller
The MAX5943 is a fully integrated power-management
IC for FireWire® 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 FireWire/IEEE 1394™ protective circuit
(Figure 12) is UL® recognized.
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
10µA 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 -40°C to +85°C extended
temperature range and is available in a 16-pin QSOP
package.
Applications
FireWire Desktop/Notebook Port
Features
o Provides Safe Hot Swap for 7.5V to 37V Power
Supplies
o UL-Recognized FireWire/IEEE 1394 Protective
Circuit
o Low-Drop Power ORing with Ultra-Fast Turn-Off
o Programmable Active Current Limit (MAX5943A)
o Programmable Circuit Breaker
(MAX5943B–MAX5943E)
o ±5% Current-Limit Sensing Accuracy
o Programmable Current-Limit/Circuit-Breaker
Timeout
o Fast Current-Limit Response to Output ShortCircuit Conditions (MAX5943A)
o Drives External N-Channel Power MOSFETs
o Overcurrent Fault Status Output
o Latched or Autoretry Overcurrent Fault
Management
o 10µA Shutdown Current
o ON/OFF Control Allows Undervoltage Lockout
Programming
o Fast Load Disconnect Control Through ON Input
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX5943AEEE
-40°C to +85°C
16 QSOP
MAX5943BEEE
-40°C to +85°C
16 QSOP
MAX5943CEEE
-40°C to +85°C
16 QSOP
MAX5943DEEE
-40°C to +85°C
16 QSOP
MAX5943EEEE
-40°C to +85°C
16 QSOP
FireWire Peripheral Device Current Limit
Pin Configuration
FireWire Hub
Hot Swap
TOP VIEW
ON 1
16 IN
FAULT 2
15 SENSE
TIM 3
ILIM 4
Typical Operating Circuit and Selector Guide appear at end
of data sheet.
FireWire is a registered trademark of Apple Computers, Inc.
IEEE 1394 is a trademark of the Institute of Electrical and
Electronics Engineers trademark.
UL is a registered trademark of Underwriters Laboratories, Inc.
14 GATE1
MAX5943
LATCH 5
13 N.C.
12 GATE2
OR_ADJ 6
11 OUT
N.C. 7
10 N.C.
ONQ1 8
9
GND
QSOP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
MAX5943
General Description
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
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 = +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
Operating Temperature Range ...........................-40°C to +85°C
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-60°C to +150°C
ESD Rating (Human Body Model)......................................2000V
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN = 7.5V to 37V, GND = 0V, and TA = -40°C to +85°C, unless otherwise noted. Typical values are at VIN = 12V, TA = +25°C.)
(Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
37
V
1.3
2.3
mA
5
10
µA
6.5
6.8
V
SUPPLIES
Supply Voltage Range
VIN
Supply Current
IIN
VON = 3V, no load
Shutdown Current
ISD
VON = 0.4V
IN Default Undervoltage Lockout
VUVLO
7.5
VIN rising, ON = IN
6.2
IN Default Undervoltage Lockout
Hysteresis
ON Undervoltage Lockout
Threshold
0.35
VON_REF
VON rising
1.20
ON Undervoltage Lockout
Threshold Hysteresis
ON Input Bias Current
1.24
V
1.275
70
ION
V
mV
1
µA
GATE2 (current-limit/circuit-breaker control)
GATE2 Pullup Current
IG2U
(Note 2)
GATE2 High Voltage
VG2
VGATE2 - VOUT
Current-Limit/Circuit-Breaker
Threshold Voltage
VTH
VIN - VSENSE
Fast Pulldown Current-Limit
Threshold Voltage (MAX5943A)
VTHF
VIN - VSENSE (Note 3)
36
45
54
µA
7.5V ≤ VIN ≤ 8V
8V ≤ VIN ≤ 37V
4.25
4.5
5.5
5.5
6.5
6.5
V
ILIM = GND
47.5
50
52.5
ILIM = floating
37
39
41
ILIM = IN
55
58.5
61
ILIM = GND
70
75
80
ILIM = floating
54
59
64
ILIM = IN
83
88
93
mV
mV
GATE2 Pulldown Current
(MAX5943A)
IG2D
VTH < (VIN - VSENSE) < VTHF,
t < tILIM
335
435
535
µA
GATE2 Fast Pulldown Current
(MAX5943A)
IG2DF
(VIN - VSENSE) > VTHF, VGATE2 = VOUT +
4.5V
80
125
200
mA
GATE2 Peak Pulldown Current
(MAX5943A)
IG2DP
(VIN - VSENSE) = 1V
2
1.0
_______________________________________________________________________________________
A
FireWire Current Limiter and Low-Drop
ORing Switch Controller
(VIN = 7.5V to 37V, GND = 0V, and TA = -40°C to +85°C, unless otherwise noted. Typical values are at VIN = 12V, TA = +25°C.)
(Note 1)
PARAMETER
GATE2 Pulldown Current During
Any GATE2 Turn-Off Condition
SYMBOL
IG2OFF
CONDITIONS
VGATE2 = VOUT + 4.5V (Note 4)
MIN
TYP
MAX
UNITS
80
125
200
mA
3
5
7
GATE1 (ORing control)
OR_ADJ = GND
ORing Switch Turn-On Current
Threshold Voltage
VOR
ORing Switch Turn-On Current
Threshold Voltage Hysteresis
GATE1 Pullup Current
(VIN - VSENSE) rising
OR_ADJ = floating
5.5
7.5
9.5
OR_ADJ = IN
8.5
10.5
12.8
(VIN - VSENSE) falling
IG1U
0.5
(Note 5)
mV
36
45
54
7.5V ≤ VIN ≤ 8V
4.25
5.5
6.5
8V ≤ VIN ≤ 37V
4.5
5.5
6.5
2
3
GATE1 High Voltage
VG1
VGATE1 - VSENSE
GATE1 Turn-Off Switch OnResistance
RG1
Measured between GATE1 and SENSE
when (VIN - VSENSE) < VOR
mV
µA
V
Ω
LOGIC INPUTS
IIXL
Current into or out of input for tri-state logic
condition
Current out of input for logic low
IIH
Current into input for logic high
20
VIL
VON > VON_REF
0.7
V
IIL
LATCH, ONQ1 = GND, VON > VON_REF
1
µA
LATCH, ONQ1 Input-Logic High
Voltage
VIH
VON > VON_REF
LATCH, ONQ1 Input Current
IIH
All voltages = VIN, VON > VON_REF
1
µA
TIM, ILIM, LATCH, OR_ADJ,
OUT, ONQ1 Shutdown Mode
Input Current
IIH_SD
All voltages = VIN, VON ≤ 0.4V
1
µA
0.25
V
1
µA
ILIM, OR_ADJ Input-Logic
Tristate Current Tolerance
(Note 6)
LATCH, ONQ1 Input-Logic Low
Voltage
IIX
-3
+3
20
1.8
FAULT Output Low Voltage
VOL
Low-impedance state, I FAULT = 5mA
FAULT Output High Leakage
Current
IOH
High-impedance state, V FAULT = 37V
µA
V
0.12
TIMING
Current-Limit Timeout
(MAX5943A)
tILIM
Current-limit mode
(Note 7)
TIM = IN
1.78
2.02
2.26
ms
RTIM = 4kΩ
0.87
1.04
1.21
ms
RTIM = 50kΩ
9.2
11.05
12.9
ms
TIM = floating
120
175
225
ms
_______________________________________________________________________________________
3
MAX5943
ELECTRICAL CHARACTERISTICS (continued)
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 7.5V to 37V, GND = 0V, and TA = -40°C to +85°C, unless otherwise noted. Typical values are at VIN = 12V, TA = +25°C.)
(Note 1)
PARAMETER
SYMBOL
CONDITIONS
Circuit-breaker mode,
MAX5943B
Circuit-breaker mode,
MAX5943C
Circuit-Breaker Timeout
(MAX5943B–MAX5943E) (Note 7)
tCB
Circuit-breaker mode,
MAX5943D
Circuit-breaker mode,
MAX5943E
Automatic Restart Delay After
Current-Limit/Circuit-Breaker
Timeout
tOFF
LATCH = GND (Note 8)
GATE1 Turn-Off Time
(ORing Response Time)
tOR
Turn-Off Response Time
tON_OFF
Minimum Delay from ON Low to
Low-Current Shutdown Mode
tSD
MIN
TYP
MAX
UNITS
0.45
0.51
0.57
ms
27
32.5
38
µs
RTIM = 50kΩ
228
345
403
µs
TIM = floating
3.75
5.5
7
ms
TIM = IN or
TIM ≥ 3.4V
0.89
1.00
1.13
ms
RTIM = 4kΩ
54
65
76
µs
RTIM = 50kΩ
575
690
806
µs
TIM = floating
7.5
10.9
14
ms
TIM = IN
1.78
2.02
2.26
ms
RTIM = 4kΩ
109
130
151
µs
RTIM = 50kΩ
1.15
1.38
1.61
ms
TIM = floating
TIM = IN or
TIM ≥ 3.4V
RTIM = 4kΩ
15
21.9
28
ms
TIM = IN or
TIM ≥ 3.4V
3.56
4.05
4.52
ms
RTIM = 4kΩ
217
260
303
µs
RTIM = 50kΩ
2.3
2.76
3.23
ms
TIM = floating
30
44
56
ms
128 x
(tILIM
OR tCB)
ms
From VOR trigger until (VGATE1 - VIN) < 1V,
CGATE1 = 10nF
100
ns
Time from VON < (VON_OFF - Hysteresis)
until (VGATE2 - VOUT) < 1V, GATE2 = open
(Note 9)
0.34
ON step from 1.3V to 0.4V
50
0.6
µs
µs
All min/max parameters are tested at +25°C and +85°C. Limits at -40°C 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
1.5
TA = +25°C
1.4
1.3
1.2
1.1
TA = -40°C
1.0
10
15
20
25
30
35
2.0
1.5
1.0
0.5
0
10
15
20
25
30
35
VIN = 12V
58.5
58.0
57.5
VIN = 7.5V
42.0
41.5
41.0
40.5
10
35
60
ILIM = FLOATING
40.0
39.5
39.0
38.5
38.0
37.5
35
MAX5943A
10
1
MAX5943E
0.01
-15
10
35
60
1
85
10
100
1000
TEMPERATURE (°C)
TEMPERATURE (°C)
RTIM (kΩ)
ORing THRESHOLD VOLTAGE
vs. TEMPERATURE
GATE CURRENTS vs. TEMPERATURE
GATE1 DRIVE VOLTAGE
vs. TEMPERATURE
46.5
GATE1
46.0
45.5
45.0
GATE2
OR_ADJ = GND
5.257
GATE1 DRIVE VOLTAGE (V)
OR_ADJ = OPEN
5.260
MAX5943 toc09
47.0
GATE CURRENTS (μA)
OR_ADJ = IN
85
60
0.1
-40
85
MAX5943 toc07
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
-15
10
TIMEOUT PERIOD vs. RTIM
37.0
36.5
36.0
-40
-15
100
TIMEOUT PERIOD (μs)
VIN = 32V
VIN = 7.5V
VIN = 12V
-40
MAX5943 toc05
CURRENT-LIMIT/CIRCUIT-BREAKER
THRESHOLD VOLTAGE vs. TEMPERATURE
THRESHOLD VOLTAGE (mV)
CURRENT-LIMIT/CIRCUIT-BREAKER
THRESHOLD VOLTAGE vs. TEMPERATURE
60.0
59.5
59.0
49.0
48.5
48.0
47.5
47.0
46.5
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
ILIM = IN
50.0
49.5
40
SUPPLY VOLTAGE (V)
62.0
61.5
61.0
60.5
VIN = 32V
50.5
46.0
5
57.0
56.5
56.0
ORing THRESHOLD VOLTAGE (mV)
3.0
2.5
40
MAX5943 toc04
THRESHOLD VOLTAGE (mV)
5
4.0
3.5
ILIM = GND
51.5
51.0
MAX5943 toc06
TA = +85°C
52.0
THRESHOLD VOLTAGE (mV)
1.7
5.5
5.0
4.5
MAX5943 toc08
SUPPLY CURRENT (mA)
1.8
6.0
MAX5943 toc02
1.9
SHUTDOWN SUPPLY CURRENT (μA)
MAX5943 toc01
2.0
1.6
CURRENT-LIMIT/CIRCUIT-BREAKER
THRESHOLD VOLTAGE vs. TEMPERATURE
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX5943 toc03
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
5.254
5.251
5.248
5.245
5.242
5.239
5.236
44.5
5.233
44.0
-40
-15
10
35
TEMPERATURE (°C)
60
85
5.230
-40
-15
10
35
TEMPERATURE (°C)
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
_______________________________________________________________________________________
5
MAX5943
Typical Operating Characteristics
(VIN = +12V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25°C, unless otherwise noted.)
ON LOW VOLTAGE vs. TEMPERATURE
ON HIGH VOLTAGE vs. TEMPERATURE
1.258
ON HIGH VOLTAGE (V)
5.224
5.221
5.218
5.215
5.212
5.209
1.256
1.254
1.196
1.194
1.192
1.190
1.188
1.186
1.184
1.252
5.206
1.198
ON LOW VOLTAGE (V)
5.227
1.200
MAX5943 toc11
1.260
MAX5943 toc10
5.230
MAX5943 toc12
GATE2 DRIVE VOLTAGE
vs. TEMPERATURE
GATE2 DRIVE VOLTAGE (V)
1.182
5.203
1.180
1.250
5.200
-40
-15
10
35
-40
85
60
-15
10
FAULT LOW VOLTAGE
vs. TEMPERATURE
180
60
-40
85
-15
10
MAX5943 toc14
IFAULT = 5mA
160
OR_ADJ = IN
VIN
10V/div
IIN
500mA/div
140
120
(VGATE - VSENSE)
5V/div
100
80
VOUT
5V/div
60
40
20
0
-40
-15
10
35
60
100μs/div
85
TEMPERATURE (°C)
MAX5943A SHORT-CIRCUIT EVENT
(VIN = 37V)
TURN-OFF RESPONSE TIME
MAX5943 toc15
MAX5943 toc16
VON
2V/div
TIM = IN
ILIM = GND
VIN
50V/div
IIN
1A/div
IIN
1A/div
VGATE2
10V/div
VGATE2
50V/div
VOUT
50V/div
VFAULT
50V/div
VOUT
10V/div
200ns/div
6
35
TEMPERATURE (°C)
ORing THRESHOLD RESPONSE TIME
MAX5943 toc13
200
35
TEMPERATURE (°C)
TEMPERATURE (°C)
FAULT LOW VOLTAGE (mV)
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
400μs/div
_______________________________________________________________________________________
60
85
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943A SHORT-CIRCUIT RESPONSE
(VIN = 8V)
MAX5943A SHORT-CIRCUIT EVENT
(VIN = 37V)
MAX5943 toc18
MAX5943 toc17
VIN
10V/div
ILIM = GND
VIN
50V/div
IIN
1A/div
IIN
10A/div
VGATE2
10V/div
VGATE2
50V/div
VOUT
10V/div
VOUT
50V/div
VFAULT
50V/div
TIM = IN
VFAULT
10V/div
400μs/div
100ns/div
MAX5943E SHORT-CIRCUIT RESPONSE
(VIN = 24V)
MAX5943A SHORT-CIRCUIT RESPONSE
(VIN = 8V)
MAX5943 toc20
MAX5943 toc19
VIN
50V/div
VIN
10V/div
IIN
10A/div
IIN
166A/div
VGATE2
10V/div
VGATE2
50V/div
VOUT
10V/div
VOUT
50V/div
VFAULT
50V/div
VFAULT
10V/div
200μs/div
100ns/div
MAX5943E SHORT-CIRCUIT RESPONSE
(VIN = 8V)
ORing SWITCHOVER WAVEFORM
MAX5943 toc22
MAX5943 toc21
VIN
10V/div
VOUT
1V/div
IIN
60A/div
VGATE2
10V/div
IIN1
500mA/div
VOUT
10V/div
TIM = IN
IIN2
500mA/div
VFAULT
10V/div
100μs/div
VIN1 = 12V
VIN2 = 128V
200μs/div
VON2 RISING = 12V
COUT = 0
_______________________________________________________________________________________
7
MAX5943
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25°C, unless otherwise noted.)
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
Typical Operating Characteristics (continued)
(VIN = +12V, TA = +25°C, unless otherwise noted.)
ORing SWITCHOVER WAVEFORM
(VIN2 FALLING BELOW VIN1)
ORing SWITCHOVER WAVEFORM
(VIN2 RISING ABOVE VIN1)
MAX5943 toc24
MAX5943 toc23
VIN1 = 12V
VIN2 = 13V
VOUT
1V/div
VOUT
1V/div
IIN1
500mA/div
IIN1
500mA/div
IIN2
500mA/div
IIN2
500mA/div
10μs/div
VON2 RISING = 12V
COUT = 0
VIN1 = 12V
VIN2 = 13V
MAX5943A HOT PLUG-IN LOAD CAPACITANCE
INTO ACTIVE PORT (NO FAULT)
20μs/div
VON2 FALLING = 12V
COUT = 0
MAX5943A HOT PLUG-IN LOAD CAPACITANCE
INTO ACTIVE PORT (CURRENT-LIMIT TIMEOUT)
MAX5943 toc25
MAX5943 toc26
VFAULT
10V/div
VFAULT
10V/div
IIN
2A/div
IIN
1A/div
VGATE2
10V/div
VGATE2
10V/div
VOUT
10V/div
VOUT
10V/div
400μs/div
CLOAD = 220μF
TIM = IN
8
400μs/div
CLOAD = 470μF
TIM = IN
_______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
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.
1
ON
2
FAULT
3
TIM
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.
4
ILIM
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).
5
LATCH
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.
6
OR_ADJ
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).
7, 10, 13
N.C.
8
ONQ1
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).
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.
9
GND
Ground
11
OUT
Output Voltage Sense. Connect to the output.
12
GATE2
Current-Limiter Switch Gate Drive Output. Connect GATE2 to the gate of the 2nd n-channel MOSFET.
GATE2 is a charge pump with a 45µA pullup current to 5.5V (typ) above OUT when active (see the Typical
Operating Circuit).
14
GATE1
ORing Switch Gate-Drive Output. Connect GATE1 to the gate of the 1st n-channel MOSFET. GATE1 is a
charge pump with a 45µA pullup current to 5.5V (typ) above SENSE when active (see the Typical
Operating Circuit).
15
SENSE
Current-Sense Negative Input. Connect a current-sense resistor, RSENSE, from IN to SENSE (see the
Typical Operating Circuit).
16
IN
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).
_______________________________________________________________________________________
9
MAX5943
Pin Description
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
POWER
SOURCE
RSENSE
Q1
SENSE
GATE1
Q2
GATE2
OUT
ONQ1
OR
COMPARATOR
THRESHOLD
OR_ADJ
+
-
SENSE GATE1
GATE1
DRIVE
GATE2 OUT
GATE2
DRIVE
+
CIRCUIT-BREAKER
(CURRENT-LIMIT)
THRESHOLD
ILIM
-
FAULT
TIMEOUT
TIM
+
(FAST CURRENTLIMIT
THRESHOLD)
-
X128
UVLO COMPARATOR
+
6.5V
ON
AUTORETRY
TIMEOUT
PERIOD
+
1.24V
-
ON COMPARATOR
+
0.4V
SHUTDOWN
MODE
-
CP1
CP2
GATE
CHARGE
PUMPS
FAULT
MANAGEMENT
LATCH OR
AUTORETRY
LATCH
FAULT
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 10µA 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 45µA 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).
______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
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.
MAX5943
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.
VFAULT
ILIMIT
tILIM
IOUT
VIN
VGATE1
VGATE2
ILIMIT x RLOAD
VOUT
(a)
VFAULT
< tILIM
ILIMIT
IOUT
VGATE1
VGATE2
ILIMIT x RLOAD
VOUT
(b)
Figure 2. MAX5943A Current-Limit Timing Diagram
______________________________________________________________________________________
11
MAX5943
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.
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
VTH (mV)
Open
40
GND
50
IN
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 ×
R TIM (kΩ)
K
where RTIM is in kΩ, 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.
VFAULT
ILIMIT
Table 2. MAX5943_ Timeout Periods
tCB
DEFAULT
TIMEOUT,
TIM = IN
(ms)
PROGRAMMABLE
TIMEOUT RANGE
(4kΩ < RTIM < 50kΩ)
MAXIMUM
TIMEOUT,
TIM =
FLOATING
(ms)
MAX5943A
2
1.04ms to 11.05ms
175
MAX5943B
0.5
32.5µs to 345µs
4.8
MAX5943C
1
65µs to 690µs
9.6
MAX5943D
2
130µs to 1.38ms
19.2
MAX5943E
4
260µs to 2.76ms
38.4
IOUT
VIN
PART
VGATE1
VGATE2
VG2
VOUT
VG2
Figure 3. MAX5943B–MAX5943E Circuit-Breaker Timing Diagram
12
______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
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.
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).
+
VIN
VIS RSENSE
IINA = 0
VINA
TO FireWire
PORT
RSENSE
FROM
BATTERY
SOURCE
VINB > VINA
ILOAD
ON IN
SENSE GATE1
GND
IINB
VINB
MAX5943
OR_ADJ
GATE2
OUT
GATE2
OUT
ONQ1
RSENSE
FROM
POWER
SOURCE
ON IN
SENSE GATE1
GND
MAX5943
OR_ADJ
ONQ1
Figure 5. MAX5943 ORing Controller Rerouting Load Current
VINA
IINA
IINB
TO FireWire
PORT
VOUT
Q1
ON IN
SENSE
GND
GATE1
MAX5943
OR_ADJ
Q2
GATE2
OUT
VINB
ONQ1
Figure 4. Q1 Current Path During Inital Startup
VINB > VINA
Figure 6. MAX5943 Power Switch Over ORing Timing Diagram
______________________________________________________________________________________
13
MAX5943
Timing accuracy is guaranteed for RTIM ranging from
4kΩ to 50kΩ. 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
FireWire Current Limiter and Low-Drop
ORing Switch Controller
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).
PORT1
TIM IN
ON
ONQ1
ILIM
SENSE GATE1
LATCH
MAX5943
GND
OR_ADJ
GATE2 OUT
FAULT
PORT2
TIM IN
ON
ONQ1
SENSE GATE1
ILIM
MAX5943
LATCH
GND
GATE2 OUT
FAULT
OR_ADJ
Figure 7. MAX5943 Operating in Reverse-Current Mode
(Routing Power from Port 1 to Port 2)
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⎟ × R2
1.24
⎝
⎠
VIN
IN
R1
MAX5943
ON
R2
GND
Figure 8. Setting the MAX5943 Turn-On Voltage
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 1µs). This allows the power supply to disconnect in the event of a fault condition
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.
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 10µA 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.
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.
VIN
IN
LATCH
R1
MAX5943
ON
R2
GND
where VTURN_ON is the desired turn-on voltage of the
MAX5943. Choose an R2 value in the 1kΩ range to
minimize error due to the ON bias current.
14
Figure 9. Resetting MAX5943 After a Latched Fault Condition
______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
To prevent the MAX5943B–MAX5943E from starting up
in a fault condition set:
VTH
IINRUSH <
RSENSE
RSENSE
+
Q1
Q2
1kΩ
CGATE
IC
ILOAD
45μA
IN
SENSE GATE1
GATE2
OUT
COUT LOAD
VIN
MAX5943B–MAX5943E
GND
-
Applications Information
Figure 10. Controlling the MAX5943B–MAX5943E Inrush Current
Startup Consideration
Optimizing for Short-Circuit Conditions
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:
C
× VIN
tILIM > OUT
ILIMIT − ILOAD
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.
\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 = 330µF, 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.
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 30mΩ on-resistance MOSFET at GATE1 and
GATE2 and a 30mΩ sense resistor results in a short-circuit current approximately equal to:
ISC = VIN/RTOTAL
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
× IG2U + ILOAD
CGATE2
Where I G2U is GATE2’s 45µA sourcing current and
ILOAD is the load current at startup.
Choose the sense-resistor power rating to accommodate
an overcurrent condition:
where:
RTOTAL = RSENSE + 2 x (RON)
= 30mΩ + 2 x (30mΩ) = 90mΩ
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.
______________________________________________________________________________________
15
MAX5943
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.
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)
For the MAX5943B–MAX5943E, a short-circuit event
results in high power dissipated in both Q1 and Q2 during the timeout period (Figure 13) 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)
VIN
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
VIS
+
IN
-
+ VQ1 -
+ VQ2 -
SENSE GATE1
GATE2
OUT
MAX5943A
Figure 11. Power Dissipated Across MOSFETs During a ShortCircuit Fault for MAX5943A
N1
Si2318DS
N2A
Si7222DN
L1
FERRITE
250Ω
N2B
TP3
PORT 0
1
3
5
J3
R3
1kΩ
DMMT3906
Q1B
Q1A
R4
1kΩ
C3
1μF
C4
0.1μF
R7
100kΩ
J1
VIN
GND
NC
9
10
11
OUT
12
GATE2
13
N.C.
GATE1
14
R6
100kΩ
IN
SENSE
16
R2
0.020Ω
1%
TP1
VIN 0.25W
15
R5
100kΩ
U1
TP5
ON
TP2
GND
TP6
VPULLUP
R8
100kΩ
8
N.C.
OR_ADJ
6
LATCH
5
ILIM
4
TIM
3
J2
GND
2
ON
C2
0.01μF
FAULT
C1
1μF
ONQ1
MAX5943AEEE
7
R1
200kΩ
1
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
TP4
FAULT
Figure 12. UL-Recognized Single-Port FireWire Protective Circuit
16
______________________________________________________________________________________
PORT 0
2
4
6
FireWire Current Limiter and Low-Drop
ORing Switch Controller
ISC
RSENSE
VIN
IN
RDS(ON)1
thereof, that are UL recognized. The circuit is further
described in Application Note 3984—UL Recognized,
IEEE 1394 Single- and Dual-Port FireWire Protective
Circuits available at www.maxim-ic.com/appnotes.cfm/
appnote_number/3984.
The circuit provides:
• 2.5A (adjustable) current limiting to the load at initial
connection or in overload fault condition
•
2ms (adjustable) current-limit timeout before load
disconnect for excessive load current
•
Automatic-restart attempts after a fault shutdown
condition
•
<0.8% current-limited duty cycle in continuous fault
condition
•
6.5V undervoltage shutdown protection
•
Low-drop ORing in multiple power-source applications, and
•
Fault reporting
RDS(ON)1
SENSE GATE1
GATE2
OUT
MAX5943B–MAX5943E
Figure 13. Power Dissipated Across MOSFETs During a ShortCircuit Fault for MAX5943B–MAX5943E
CPA SENSE
PHY
POWER OUT
FB
VIN
BST
ON
LX
MAX5033
GND
IN4148
IN4148
VD
SGND
IN4148
15mΩ
CABLE
POWER
SOURCE
TIM IN
ON
ILIM
SI7958DP
SENSE GATE1
MAX5943A
LATCH
GND
ONQ1
30mΩ
SI7958DP
GATE2 OUT
FAULT
INA
ONA
SI7958DP
SENSEA GATE1A
ONQ1
OR_ADJ
SI7958DP
PORT 0
GATE2A OUTA
FAULTA
GND
MAX5944
FAULTB
ONB
INB
15mΩ
BATTERYPOWER
SOURCE
SI7958DP
SENSEB GATE1B
SI7958DP
30mΩ
TIM IN
ON
ILIM
CABLE NOT
ON SLEEP
SENSE GATE1
MAX5943A
LATCH
GND
ONQ1
GATE2B OUTB
IRF7478
PORT 1
IRF7478
IN4148
GATE2 OUT
FAULT
OR_ADJ
CURRENT-LIMIT
SENSE
PORT 1 PORT 0
SENSE SENSE
Figure 14. Two-Port FireWire Power Provider Using MAX5943A and MAX5944
______________________________________________________________________________________
17
MAX5943
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.
A single-port FireWire protective circuit employing the
MAX5943A has been UL recognized as a result of
extensive safety testing by Underwriters Laboratories. It
is the circuits themselves, not any individual component
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
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 14 shows a
high-end two-port FireWire power management system
using two MAX5943As and a dual-channel MAX5944
FireWire current-limiting IC.
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.
Typical Operating Circuit
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.
Typical Application Circuit
FireWire
PORT
SUPPLY
+
30mΩ
SI7958DP
SI7958DP
Q1
1kΩ
10kΩ
VIN = 12V
Q2
4kΩ
TIM IN
SENSE GATE1
FAULT
ON
7.15kΩ
TO
FireWire
PORT
GATE2
OUT
MAX5943A
ILIM
LATCH
GND
OR_ADJ
ONQ1
-
FireWire
PORT
SUPPLY
+
TO
FireWire
PORT
VIS RSENSE
Q1
R1
Selector Guide
Q2
R3
TIM IN
SENSE GATE1
FAULT
ON
R2
GATE2
OUT
PART
CURRENT
LIMITER/
CIRCUIT
BREAKER
MAX5943A
Current limit
DEFAULT
PROGRAMMABLE
TIMEOUT
TIMEOUT RANGE
(ms)
MAX5943A
ILIM
LATCH
GND
OR_ADJ
ONQ1
MAX5943 EQUIVALENT CIRCUIT
VERY-LOW-DROP
ORing DIODE
2
1.04ms to 11.05ms
32.5µs to 345µs
MAX5943B Circuit breaker
0.5
MAX5943C Circuit breaker
1
65µs to 690µs
MAX5943D Circuit breaker
2
130µs to 1.38ms
MAX5943E Circuit breaker
4
260µs to 2.76ms
LOAD DISCONNECT
SWITCH
Chip Information
CURRENT-LIMIT/CIRCUIT-BREAKER
AND INRUSH CONTROL
18
TRANSISTOR COUNT: 2324
PROCESS: BiCMOS
______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
QSOP.EPS
______________________________________________________________________________________
19
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.)
MAX5943
FireWire Current Limiter and Low-Drop
ORing Switch Controller
Revision History
REVISION
NUMBER
REVISION
DATE
0
8/04
Initial release
1
1/05
Corrected Table 2 and Figures 10, 11, and 12
2
10/07
DESCRIPTION
PAGES
CHANGED
—
Added FireWire/IEEE and UL information, inserted new Figure 12, and updated
Package Outline
12, 15, 16, 17
1, 16, 17, 18, 20
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
© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.