MAX5943_07 [MAXIM]
FireWire Current Limiter and Low-Drop ORing Switch Controller; FireWire限流器和低压差或门开关控制器
| 型号： | MAX5943_07 |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | FireWire Current Limiter and Low-Drop ORing Switch Controller |
| 文件： | 总20页 (文件大小：407K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-3378; Rev 2; 10/07
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
General Description
Features
o Provides Safe Hot Swap for 7.5V to 37V Power
The MAX5943 is a fully integrated power-management
®
Supplies
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.
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
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 func-
tion. 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 turn-
ing off both external MOSFETS, the MAX5943 provides a
true bidirectional load disconnect. A low-current shut-
down mode disables the MAX5943, resulting in less than
10µA supply current. A pin-selectable input allows
latched or autoretry fault management after a fault.
o Programmable Current-Limit/Circuit-Breaker
Timeout
o Fast Current-Limit Response to Output Short-
Circuit 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
The MAX5943A features a current-limit function that
actively limits the current drawn by the load with a pro-
grammable 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 pro-
grammable circuit-breaker timeouts.
Programming
o Fast Load Disconnect Control Through ON Input
Ordering Information
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
The MAX5943 operates over the -40°C to +85°C extended
temperature range and is available in a 16-pin QSOP
package.
MAX5943AEEE
MAX5943BEEE
MAX5943CEEE
MAX5943DEEE
MAX5943EEEE
16 QSOP
16 QSOP
Applications
16 QSOP
FireWire Desktop/Notebook Port
FireWire Peripheral Device Current Limit
FireWire Hub
16 QSOP
Pin Configuration
Hot Swap
TOP VIEW
ON
1
2
3
4
5
6
7
8
16 IN
FAULT
TIM
15 SENSE
14 GATE1
ILIM
MAX5943
13 N.C.
12 GATE2
11 OUT
10 N.C.
LATCH
Typical Operating Circuit and Selector Guide appear at end
of data sheet.
OR_ADJ
N.C.
FireWire is a registered trademark of Apple Computers, Inc.
ONQ1
9
GND
IEEE 1394 is a trademark of the Institute of Electrical and
Electronics Engineers trademark.
QSOP
UL is a registered trademark of Underwriters Laboratories, Inc.
________________________________________________________________ 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.
FireWire Current Limiter and Low-Drop
ORing Switch Controller
ABSOLUTE MAXIMUM RATINGS
(Voltages referenced to GND, unless otherwise noted.)
Continuous Power Dissipation (T = +70°C)
A
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)
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
MAX5943
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
(V = 7.5V to 37V, GND = 0V, and T = -40°C to +85°C, unless otherwise noted. Typical values are at V = 12V, T = +25°C.)
IN
A
IN
A
(Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SUPPLIES
Supply Voltage Range
Supply Current
V
7.5
37
2.3
10
V
mA
µA
V
IN
I
V
V
V
= 3V, no load
1.3
5
IN
ON
ON
Shutdown Current
I
= 0.4V
SD
IN Default Undervoltage Lockout
V
rising, ON = IN
6.2
6.5
6.8
UVLO
IN
IN Default Undervoltage Lockout
Hysteresis
0.35
1.24
70
V
V
ON Undervoltage Lockout
Threshold
V
V
rising
1.20
1.275
1
ON_REF
ON
ON Undervoltage Lockout
Threshold Hysteresis
mV
µA
ON Input Bias Current
I
ON
GATE2 (current-limit/circuit-breaker control)
GATE2 Pullup Current
I
(Note 2)
36
4.25
4.5
45
5.5
5.5
54
6.5
6.5
µA
V
G2U
7.5V ≤ V ≤ 8V
IN
GATE2 High Voltage
V
V
- V
OUT
G2
TH
GATE2
8V ≤ V ≤ 37V
IN
ILIM = GND
ILIM = floating
ILIM = IN
47.5
37
50
39
52.5
41
Current-Limit/Circuit-Breaker
Threshold Voltage
V
V
- V
mV
mV
IN
SENSE
SENSE
55
58.5
75
61
ILIM = GND
70
80
Fast Pulldown Current-Limit
Threshold Voltage (MAX5943A)
V
V
V
- V
(Note 3) ILIM = floating
ILIM = IN
54
59
64
THF
IN
83
88
93
GATE2 Pulldown Current
(MAX5943A)
< (V - V
IN
< V
,
THF
TH
SENSE)
I
335
80
435
125
1.0
535
200
µA
mA
A
G2D
t < t
ILIM
GATE2 Fast Pulldown Current
(MAX5943A)
(V - V
IN
> V
, V
= V
+
SENSE)
THF GATE2
OUT
I
G2DF
4.5V
GATE2 Peak Pulldown Current
(MAX5943A)
I
(V - V
= 1V
G2DP
IN
SENSE)
2
_______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
ELECTRICAL CHARACTERISTICS (continued)
(V = 7.5V to 37V, GND = 0V, and T = -40°C to +85°C, unless otherwise noted. Typical values are at V = 12V, T = +25°C.)
IN
A
IN
TYP
125
A
(Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
MAX
UNITS
GATE2 Pulldown Current During
Any GATE2 Turn-Off Condition
I
V
= V + 4.5V (Note 4)
OUT
80
200
mA
G2OFF
GATE2
GATE1 (ORing control)
OR_ADJ = GND
3
5
7
ORing Switch Turn-On Current
Threshold Voltage
V
(V - V
) rising
) falling
mV
OR_ADJ = floating
OR_ADJ = IN
5.5
8.5
7.5
10.5
9.5
12.8
OR
IN
SENSE
ORing Switch Turn-On Current
Threshold Voltage Hysteresis
(V - V
0.5
mV
µA
V
IN
SENSE
GATE1 Pullup Current
I
(Note 5)
36
4.25
4.5
45
5.5
5.5
54
6.5
6.5
G1U
7.5V ≤ V ≤ 8V
IN
GATE1 High Voltage
V
V
- V
GATE1 SENSE
G1
G1
8V ≤ V ≤ 37V
IN
GATE1 Turn-Off Switch On-
Resistance
Measured between GATE1 and SENSE
when (V - V ) < V
R
2
3
Ω
IN
SENSE
OR
LOGIC INPUTS
Current into or out of input for tri-state logic
condition
I
-3
+3
IX
ILIM, OR_ADJ Input-Logic
Tristate Current Tolerance
(Note 6)
µA
I
Current out of input for logic low
20
20
IXL
I
IH
Current into input for logic high
V
V
> V
ON_REF
0.7
1
V
IL
ON
LATCH, ONQ1 Input-Logic Low
Voltage
I
IL
LATCH, ONQ1 = GND, V
> V
µA
ON
ON_REF
LATCH, ONQ1 Input-Logic High
Voltage
V
V
> V
ON_REF
1.8
V
IH
ON
LATCH, ONQ1 Input Current
I
All voltages = V , V
> V
1
1
µA
IH
IN ON
ON_REF
TIM, ILIM, LATCH, OR_ADJ,
OUT, ONQ1 Shutdown Mode
Input Current
I
All voltages = V , V
≤ 0.4V
µA
IH_SD
IN ON
FAULT Output Low Voltage
V
Low-impedance state, I
= 5mA
0.12
0.25
1
V
OL
FAULT
FAULT Output High Leakage
Current
I
High-impedance state, V
= 37V
FAULT
µA
OH
TIMING
TIM = IN
1.78
0.87
9.2
2.02
1.04
11.05
175
2.26
1.21
12.9
225
ms
ms
ms
ms
R
TIM
R
TIM
= 4kΩ
Current-Limit Timeout
(MAX5943A)
Current-limit mode
(Note 7)
t
ILIM
= 50kΩ
TIM = floating
120
_______________________________________________________________________________________
3
FireWire Current Limiter and Low-Drop
ORing Switch Controller
ELECTRICAL CHARACTERISTICS (continued)
(V = 7.5V to 37V, GND = 0V, and T = -40°C to +85°C, unless otherwise noted. Typical values are at V = 12V, T = +25°C.)
IN
A
IN
A
(Note 1)
PARAMETER
SYMBOL
CONDITIONS
TIM = IN or
TIM ≥ 3.4V
MIN
TYP
MAX
UNITS
0.45
0.51
0.57
ms
Circuit-breaker mode,
MAX5943B
R
= 4kΩ
27
32.5
345
5.5
38
403
7
µs
µs
TIM
TIM
R
= 50kΩ
228
3.75
MAX5943
TIM = floating
ms
TIM = IN or
TIM ≥ 3.4V
0.89
1.00
1.13
ms
Circuit-breaker mode,
MAX5943C
R
R
= 4kΩ
54
575
7.5
65
76
806
14
µs
µs
TIM
TIM
= 50kΩ
690
10.9
2.02
130
1.38
21.9
Circuit-Breaker Timeout
(MAX5943B–MAX5943E) (Note 7)
TIM = floating
TIM = IN
ms
ms
µs
t
CB
1.78
109
1.15
15
2.26
151
1.61
28
R
TIM
R
TIM
= 4kΩ
Circuit-breaker mode,
MAX5943D
= 50kΩ
ms
ms
TIM = floating
TIM = IN or
TIM ≥ 3.4V
3.56
4.05
4.52
ms
Circuit-breaker mode,
MAX5943E
R
R
= 4kΩ
217
2.3
30
260
2.76
44
303
3.23
56
µs
ms
ms
TIM
TIM
= 50kΩ
TIM = floating
Automatic Restart Delay After
Current-Limit/Circuit-Breaker
Timeout
128 x
t
LATCH = GND (Note 8)
(t
ms
ns
OFF
ILIM
t
OR CB)
GATE1 Turn-Off Time
(ORing Response Time)
From V
trigger until (V
- V ) < 1V,
GATE1 IN
OR
t
100
OR
C
= 10nF
GATE1
Time from V
< (V
- Hysteresis)
ON_OFF
ON
Turn-Off Response Time
t
until (V
(Note 9)
- V ) < 1V, GATE2 = open
OUT
0.34
50
0.6
µs
µs
ON_OFF
GATE2
Minimum Delay from ON Low to
Low-Current Shutdown Mode
t
ON step from 1.3V to 0.4V
SD
Note 1: All min/max parameters are tested at +25°C and +85°C. Limits at -40°C are guaranteed by design.
Note 2: Measured at both V
= V
= 0V and V
= V
= V .
OUT IN
GATE2
OUT
GATE2
Note 3: The typical value of parameter V
is 1.5 x V .
TH
THF
Note 4: Current-Limit/Circuit-Breaker Timeout; IN or ON low.
Note 5: See the Typical Operating Circuit. Measured at V
= V
.
SENSE
GATE1
Note 6: The tristate (“floating”) logic condition will be entered if the pin current is within these limits.
Note 7: R is connected from TIM to GND. The maximum timeout period is enforced to prevent arbitrarily long operation in cur-
TIM
rent-limit mode. Therefore, the relationship between resistor value and timeout changes for large values of R . See
TIM
Current-Limit Timeout vs. R
in the Typical Operating Characteristics for nominal values.
TIM
Note 8: Parameter t
is a direct multiple of t
(or t ), so the limits for t
track the limits for t (or t ).
ILIM CB
OFF
ILIM
CB
OFF
Note 9: If the ON voltage goes below V
- Hysteresis, then GATE2 goes low immediately to disconnect power from the load
ON_REF
quickly (within t
).
ON_OFF
4
_______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
Typical Operating Characteristics
(V = +12V, T = +25°C, unless otherwise noted.)
IN
A
CURRENT-LIMIT/CIRCUIT-BREAKER
THRESHOLD VOLTAGE vs. TEMPERATURE
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
SHUTDOWN SUPPLY CURRENT
vs. SUPPLY VOLTAGE
2.0
1.9
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
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
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0
ILIM = GND
V
= 32V
IN
T
= +85°C
A
V
= 7.5V
IN
T
= +25°C
A
V
= 12V
IN
T
= -40°C
A
5
10
15
20
25
30
35
40
-40
-15
10
35
60
85
1000
85
5
10
15
20
25
30
35
40
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
CURRENT-LIMIT/CIRCUIT-BREAKER
THRESHOLD VOLTAGE vs. TEMPERATURE
CURRENT-LIMIT/CIRCUIT-BREAKER
THRESHOLD VOLTAGE vs. TEMPERATURE
TIMEOUT PERIOD vs. R
TIM
100
10
62.0
61.5
61.0
60.5
60.0
59.5
59.0
58.5
58.0
57.5
57.0
56.5
56.0
42.0
41.5
41.0
40.5
40.0
39.5
39.0
38.5
38.0
37.5
37.0
36.5
36.0
ILIM = IN
ILIM = FLOATING
MAX5943A
V
= 32V
IN
V
= 12V
IN
1
MAX5943E
V
= 7.5V
IN
0.1
0.01
1
10
100
-40
-15
10
35
60
85
-40
-15
10
35
60
85
R
(kΩ)
TEMPERATURE (°C)
TEMPERATURE (°C)
TIM
ORing THRESHOLD VOLTAGE
vs. TEMPERATURE
GATE1 DRIVE VOLTAGE
vs. TEMPERATURE
GATE CURRENTS vs. TEMPERATURE
47.0
46.5
46.0
45.5
45.0
44.5
44.0
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
5.260
5.257
5.254
5.251
5.248
5.245
5.242
5.239
5.236
5.233
5.230
OR_ADJ = IN
GATE1
OR_ADJ = OPEN
GATE2
OR_ADJ = GND
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
_______________________________________________________________________________________
5
FireWire Current Limiter and Low-Drop
ORing Switch Controller
Typical Operating Characteristics (continued)
(V = +12V, T = +25°C, unless otherwise noted.)
IN
A
GATE2 DRIVE VOLTAGE
vs. TEMPERATURE
ON HIGH VOLTAGE vs. TEMPERATURE
ON LOW VOLTAGE vs. TEMPERATURE
1.260
1.258
1.256
1.254
1.252
1.250
1.200
1.198
1.196
1.194
1.192
1.190
1.188
1.186
1.184
1.182
1.180
5.230
5.227
5.224
5.221
5.218
5.215
5.212
5.209
5.206
5.203
5.200
MAX5943
-40
-15
10
35
60
85
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
FAULT LOW VOLTAGE
vs. TEMPERATURE
ORing THRESHOLD RESPONSE TIME
MAX5943 toc14
200
OR_ADJ = IN
V
I
= 5mA
IN
FAULT
180
160
140
120
100
80
10V/div
I
IN
500mA/div
(V
5V/div
- V
)
SENSE
GATE
V
OUT
60
5V/div
40
20
0
100μs/div
-40
-15
10
35
60
85
TEMPERATURE (°C)
MAX5943A SHORT-CIRCUIT EVENT
TURN-OFF RESPONSE TIME
(V = 37V)
IN
MAX5943 toc15
MAX5943 toc16
TIM = IN
ILIM = GND
V
IN
V
ON
50V/div
2V/div
I
IN
I
IN
1A/div
1A/div
V
GATE2
V
10V/div
GATE2
50V/div
V
OUT
V
OUT
50V/div
V
10V/div
FAULT
50V/div
200ns/div
400μs/div
6
_______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
Typical Operating Characteristics (continued)
(V = +12V, T = +25°C, unless otherwise noted.)
IN
A
MAX5943A SHORT-CIRCUIT EVENT
MAX5943A SHORT-CIRCUIT RESPONSE
(V = 37V)
IN
(V = 8V)
IN
MAX5943 toc17
MAX5943 toc18
V
IN
ILIM = GND
10V/div
V
IN
50V/div
I
IN
1A/div
I
IN
10A/div
V
GATE2
10V/div
V
GATE2
V
OUT
50V/div
10V/div
V
OUT
50V/div
FAULT
50V/div
V
V
FAULT
10V/div
TIM = IN
100ns/div
400μs/div
MAX5943A SHORT-CIRCUIT RESPONSE
MAX5943E SHORT-CIRCUIT RESPONSE
(V = 8V)
(V = 24V)
IN
IN
MAX5943 toc19
MAX5943 toc20
V
V
IN
IN
10V/div
50V/div
I
IN
I
IN
10A/div
166A/div
V
GATE2
V
GATE2
10V/div
50V/div
V
OUT
10V/div
V
OUT
50V/div
V
FAULT
V
FAULT
10V/div
50V/div
100ns/div
200μs/div
MAX5943E SHORT-CIRCUIT RESPONSE
ORing SWITCHOVER WAVEFORM
(V = 8V)
IN
MAX5943 toc22
MAX5943 toc21
V
IN
V
OUT
10V/div
1V/div
I
IN
60A/div
V
GATE2
I
10V/div
IN1
500mA/div
V
OUT
10V/div
I
IN2
500mA/div
V
FAULT
TIM = IN
10V/div
200μs/div
100μs/div
V
V
= 12V
= 128V
V
C
RISING = 12V
= 0
IN1
IN2
ON2
OUT
_______________________________________________________________________________________
7
FireWire Current Limiter and Low-Drop
ORing Switch Controller
Typical Operating Characteristics (continued)
(V = +12V, T = +25°C, unless otherwise noted.)
IN
A
ORing SWITCHOVER WAVEFORM
(V FALLING BELOW V )
IN2 IN1
MAX5943 toc24
ORing SWITCHOVER WAVEFORM
(V RISING ABOVE V
)
IN2
IN1
MAX5943 toc23
V
V
OUT
OUT
1V/div
1V/div
MAX5943
I
I
IN1
IN1
500mA/div
500mA/div
I
I
IN2
IN2
500mA/div
500mA/div
20μs/div
10μs/div
V
V
= 12V
= 13V
V
FALLING = 12V
C = 0
OUT
V
V
= 12V
= 13V
V
C
RISING = 12V
ON2
IN1
IN2
ON2
IN1
IN2
= 0
OUT
MAX5943A HOT PLUG-IN LOAD CAPACITANCE
MAX5943A HOT PLUG-IN LOAD CAPACITANCE
INTO ACTIVE PORT (NO FAULT)
INTO ACTIVE PORT (CURRENT-LIMIT TIMEOUT)
MAX5943 toc25
MAX5943 toc26
V
FAULT
V
FAULT
10V/div
10V/div
I
IN
I
IN
2A/div
1A/div
V
GATE2
V
GATE2
10V/div
10V/div
V
OUT
V
OUT
10V/div
10V/div
400μs/div
400μs/div
C
= 220μF
C
= 470μF
LOAD
LOAD
TIM = IN
TIM = IN
8
_______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
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.
1
ON
Current-Fault, Active-Low, Open-Drain Output. FAULT asserts and latches low after a current-limit/circuit-
breaker fault has exceeded the current-limit/circuit-breaker timeout period (see the FAULT section).
2
3
FAULT
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.
TIM
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).
4
5
ILIM
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 current-
limit/circuit-breaker timeout.
LATCH
ORing Switch Turn-On Current Threshold Adjustment Input. Select one of three ORing switch turn-on
6
7, 10, 13
8
OR_ADJ threshold settings: connect OR_ADJ to GND, connect OR_ADJ to IN, or leave OR_ADJ floating (see the
Power-Supply ORing section).
N.C.
No Connection. Not internally connected.
ORing Switch Manual Turn-On Input. Drive ONQ1 low to enable power-supply ORing. Drive ONQ1 high
ONQ1
to set GATE1 high to allow reverse current flow. ONQ1 is disabled when V is below the UVLO threshold,
IN
V
is below the V
threshold, and after a current/circuit-breaker fault.
ON_REF
ON
9
GND
OUT
Ground
11
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 45µA pullup current to 5.5V (typ) above OUT when active (see the Typical
Operating Circuit).
12
14
GATE2
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).
Current-Sense Negative Input. Connect a current-sense resistor, R
Typical Operating Circuit).
from IN to SENSE (see the
SENSE,
15
16
SENSE
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
FireWire Current Limiter and Low-Drop
ORing Switch Controller
POWER
SOURCE
R
SENSE
Q1
Q2
SENSE
GATE1
GATE2
OUT
ONQ1
OR
SENSE GATE1
GATE2 OUT
OR_ADJ
COMPARATOR
THRESHOLD
+
-
GATE1
DRIVE
GATE2
DRIVE
MAX5943
+
-
CIRCUIT-BREAKER
(CURRENT-LIMIT)
THRESHOLD
ILIM
FAULT
TIMEOUT
TIM
+
-
(FAST CURRENT-
LIMIT
THRESHOLD)
X128
UVLO COMPARATOR
+
AUTORETRY
TIMEOUT
PERIOD
-
6.5V
+
ON
CP1
CP2
-
1.24V
GATE
CHARGE
PUMPS
FAULT
ON COMPARATOR
MANAGEMENT
LATCH OR
AUTORETRY
LATCH
FAULT
+
-
SHUTDOWN
MODE
0.4V
MAX5943A–MAX5943E
GND
( ) MAX5943A ONLY.
Figure 1. MAX5943 Functional Diagram
logic inputs in a high-impedance state allowing the
inputs to be connected to IN without drawing additional
current from the supply.
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 current-
limiting/circuit-breaker function. GATE1 and GATE2
provide true load disconnect to prevent current flowing
from either direction between IN and OUT.
When the input supply voltage (V ) is above 7.5V and
IN
V
is above the V
threshold, the MAX5943
ON
ON_REF
turns on, sourcing 45µA current from GATE2 (current
regulation) to enhance Q2 slowly. For the MAX5943A, if
the voltage across the current-sense resistor, V , is
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 V is equal
IS
to V . In normal operation, V drops below V and
TH
IS
TH
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).
The MAX5943 remains in low-current shutdown mode
when V
is below the 0.4V threshold. Low-current
ON
shutdown mode disables the MAX5943, resulting in
less than 10µA supply current. Shutdown places all
10 ______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
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 current-
limit timeout. The MAX5943B, MAX5943C, MAX5943D,
and MAX5943E have 0.5ms, 1ms, 2ms, and 4ms
default circuit-breaker timeouts, respectively.
V
FAULT
t
I
LIMIT
ILIM
GATE1 controls the MAX5943 ORing function. Initially,
GATE1 is off (ONQ1 = low) and the load current con-
ducts through the body diode of Q1. GATE1 rises to
I
OUT
5.5V above SENSE when V exceeds V , thereby
IS
OR
enhancing Q1 and reducing the voltage drop, power
dissipation, and heat generation in the power-supply
V
IN
path. When a voltage greater than V is connected at
IN
V
OUT, the higher voltage source commences, providing
current to the load. The MAX5943 rapidly turns off
GATE1
GATE1 upon V falling below V
- hysteresis, thus
OR
IS
blocking the higher voltage from back-driving V
.
IN
GATE1 also turns off when the load current drops,
causing V to fall below the V hysteresis.
V
GATE2
IS
OR
Current Limiting/Circuit Breaker
V
OUT
I
x R
LOAD
LIMIT
Current Limiting (MAX5943A Only)
The MAX5943A limits the load current by monitoring the
(a)
voltage across R
at all times and by regulating the
SENSE
current to the load as necessary to keep V to its pro-
IS
grammable current-limit threshold voltage (V ). Set the
TH
maximum current limit (I
) by placing the appropriate
LIMIT
sense resistor between IN and SENSE, where I
=
LIMIT
V
FAULT
LIMIT
V
/R
. When the load current is less than I
,
TH SENSE
< t
ILIM
I
LIMIT
GATE2 rises to V (5.5V) to fully enhance MOSFET Q2
G2
(see the Typical Operating Circuit).
When the load current attempts to draw more than
I
, the MAX5943A’s GATE2 pulldown current (I
)
LIMIT
G2D
I
OUT
regulates the current through Q2 causing OUT to act as
a constant-current source. The output current is limited
to the programmed I
persists after the current-limit timeout (t
expired, GATE2’s strong pulldown current (I
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 t
V
. If the current-limit condition
LIMIT
) period has
ILIM
V
V
GATE1
)
G2 OFF
, GATE2 pulls to
ILIM
(Figure 2b). During an output short circuit or a
GATE2
G2
gross overload, the load current overshoots and causes
to exceed the fast pulldown current-limit threshold
I
x R
LOAD
LIMIT
V
IS
V
OUT
voltage (V
). The MAX5943A responds with much
THF
stronger GATE2 pulldown currents (I
and/or I
)
G2DP
G2DF
to quickly bring the load current back down to the pro-
grammed current limit.
(b)
Figure 2. MAX5943A Current-Limit Timing Diagram
______________________________________________________________________________________ 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
Current-Limit/Circuit-Breaker Thresholds
The MAX5943 allows three selectable current-limit/cir-
cuit-breaker thresholds (V ). Choose the voltage
TH
threshold by connecting ILIM to the appropriate level;
see Table 1.
(R
) and disconnects the load from the power
SENSE
source when the voltage across R
, V , exceeds
SENSE IS
Table 1. Current-Limit/Circuit-Breaker
Trip Threshold Level
the programmed circuit-breaker thresholds (V ) for
TH
longer than the circuit-breaker timeout period, t
.
CB
MAX5943
ILIM CONNECTION
V
TH
(mV)
Unlike the MAX5943A, when an output short circuit or
overcurrent occurs, the MAX5943B–MAX5943E keep
GATE2 fully enhanced. The short-circuit current is limit-
Open
GND
IN
40
50
60
ed only by the input source impedance, R
, Q1’s
SENSE
R
Q2’s R
, and any parasitic impedance in
DS(ON),
DS(ON)
the power path. If the excessive current condition per-
sists (as indicated by V > V ) for longer than t
,
CB
) to
IS
TH
Current-Limit/Circuit-Breaker
Timeout Period (t /t
GATE2 turns off with a strong pulldown (I
G2 OFF
)
ILIM CB
quickly disconnect the power source from the load and
FAULT asserts low (Figure 3).
The MAX5943’s current-limit/circuit-breaker timeout
function disconnects power from the load if the current-
limit 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).
Exercise caution when using the MAX5943B–MAX5943E.
Unlike the MAX5943A, the MAX5943B–MAX5943E do not
limit the load current during t . High current during t
CB
CB
may cause damage to external devices connected in the
power path.
Adjust the fault timeout period (t
t
) by connect-
ILIM/ CB
ing a resistor (R ) from TIM to GND (see the Typical
TIM
Operating Characteristics). Calculate the fault-limit
timeout period using the following equation:
R
(kΩ)
TIM
t
(ms) = t
(ms) = 0.25 ×
CB
ILIM
K
where R
is in kΩ, t
/t
is in ms, and K = 1 for
TIM
ILIM CB
MAX5943A, K = 32 for MAX5943B, K = 16 for
MAX5943C, K = 8 for MAX5943D, and K = 4 for the
MAX5943E.
V
FAULT
I
LIMIT
t
CB
Table 2. MAX5943_ Timeout Periods
MAXIMUM
TIMEOUT,
TIM =
FLOATING
(ms)
I
DEFAULT
OUT
PROGRAMMABLE
TIMEOUT RANGE
TIMEOUT,
TIM = IN
(ms)
PART
V
IN
(4kΩ < R
< 50kΩ)
TIM
V
V
GATE1
MAX5943A
MAX5943B
MAX5943C
MAX5943D
MAX5943E
2
0.5
1
1.04ms to 11.05ms
32.5µs to 345µs
65µs to 690µs
175
4.8
GATE2
V
G2
9.6
V
OUT
V
G2
2
130µs to 1.38ms
260µs to 2.76ms
19.2
38.4
4
Figure 3. MAX5943B–MAX5943E Circuit-Breaker Timing Diagram
12 ______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
Timing accuracy is guaranteed for R
ranging from
TIM
TO FireWire
PORT
4kΩ to 50kΩ. Large R
values can be used, which
TIM
I
= 0
INA
R
SENSE
reduces timing accuracy. A maximum timeout period is
enforced to prevent arbitrarily long operation in current-
limit/circuit-breaker conditions.
V
INA
FROM
BATTERY
SOURCE
V
> V
INA
INB
I
LOAD
Long durations in current-limit/circuit-breaker mode
may produce excessive heating and electrical stresses
ON IN
SENSE GATE1
GATE2 OUT
MAX5943
in R
, Q1, Q2, and any other components in the
SENSE
GND OR_ADJ ONQ1
power path. Use component values rated to handle
electrical stresses during the timeout period.
I
INB
R
SENSE
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).
V
INB
FROM
POWER
SOURCE
ON IN
SENSE GATE1
GATE2 OUT
MAX5943
GATE1 rises to 5.5V above SENSE when V exceeds
IS
GND OR_ADJ ONQ1
V
, enhancing Q1. Q1’s low R
provides a very-
OR
DS(ON)
low-voltage drop across its source to drain, reducing volt-
age drop, power dissipation, and heat generation in the
power-supply path created by a traditional diode.
Figure 5. MAX5943 ORing Controller Rerouting Load Current
The MAX5943 continuously monitors the load current
by the voltage drop, V , across the current-sensing
IS
resistor. Q1 turns off rapidly when V decreases below
IS
V
OR
minus its hysteresis.
V
INA
Set the MAX5943 ORing threshold (V ) by connecting
OR
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
I
I
INA
INB
exceed V
and V
, respectively, and the
ON_REF
UVLO
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 program-
mable 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).
+
V
-
IS
TO FireWire
PORT
R
SENSE
V
IN
V
OUT
Q1
Q2
OUT
ON IN
SENSE
GATE1
GATE2
V
INB
MAX5943
OR_ADJ ONQ1
GND
V
INB
> V
INA
Figure 4. Q1 Current Path During Inital Startup
Figure 6. MAX5943 Power Switch Over ORing Timing Diagram
______________________________________________________________________________________ 13
FireWire Current Limiter and Low-Drop
ORing Switch Controller
Reverse Current Override (ONQ1 = High)
V
IN
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
IN
R1
R2
MAX5943
long as V is greater than V
, V
is above the
ON
IN
UVLO
ON
GND
V
threshold, and the MAX5943 is not in a cur-
ON_REF
rent-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).
MAX5943
Figure 8. Setting the MAX5943 Turn-On Voltage
When operating the MAX5943, ON must remain above
its 1.24V threshold. If V
falls below its 1.24V thresh-
PORT1
ON
old, the power-supply MOSFETs (Q1 and Q2) turn off
immediately (less than 1µs). This allows the power sup-
ply 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 unneces-
sary power-supply interruptions.
TIM IN
ON
SENSE GATE1
GATE2 OUT
FAULT
ONQ1
ILIM
MAX5943
LATCH
GND
OR_ADJ
PORT2
The MAX5943 remains in low-current shutdown mode
when V
is below the 0.4V threshold. Low-current
ON
TIM IN
ON
SENSE GATE1
GATE2 OUT
FAULT
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
MAX5943
ONQ1
ILIM
LATCH
GND
OR_ADJ
from the supply. An internal delay, t , allows Q1 and
SD
Q2 to be turned off before the MAX5943 enters low-
current shutdown mode.
Figure 7. MAX5943 Operating in Reverse-Current Mode
(Routing Power from Port 1 to Port 2)
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.
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 V > 6.5V and V
<
IN
ON
V
IN
V
. The turn-on threshold is programmable by
ON_REF
connecting a resistor-divider at ON. When V
> 1.24V
ON
IN
and V > 7.5V, GATE2 is enhanced to 5.5V, with respect
IN
LATCH
to OUT and the MAX5943 goes into normal operation.
R1
R2
Program the MAX5943’s turn-on voltage using the fol-
lowing formula:
MAX5943
ON
V
⎛
⎜
⎞
⎟
TURN_ON
R1=
− 1 × R2
1.24
⎝
⎠
GND
where V
is the desired turn-on voltage of the
TURN_ON
MAX5943. Choose an R2 value in the 1kΩ range to
minimize error due to the ON bias current.
Figure 9. Resetting MAX5943 After a Latched Fault Condition
14 ______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
To prevent the MAX5943B–MAX5943E from starting up
in a fault condition set:
Fault Management
The MAX5943 offers either latch or autoretry fault man-
agement 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
V
TH
I
<
INRUSH
R
SENSE
R
SENSE
Q1
Q2
+
C
GATE
I
C
I
LOAD
1kΩ
MAX5943 will not enter a startup cycle until t
has
OFF
expired. Figure 9 illustrates a way to reset the MAX5943
after a fault using a pushbutton switch.
45μA
GATE2
IN
SENSE GATE1
OUT
In autoretry fault management, the MAX5943_ attempt
LOAD
C
OUT
V
-
IN
to restart after a t
of 128 x t (or 128 x t ) limit-
ILIM CB
OFF
MAX5943B–MAX5943E
ing the duty cycle of the MOSFETs to 1/129 under con-
tinuous fault conditions. FAULT deasserts every time a
restart attempt is made.
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:
Choosing R
SENSE
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.
C
× V
OUT
IN
LOAD
Choose the sense-resistor power rating to accommodate
an overcurrent condition:
t
>
ILIM
I
− I
LIMIT
P
= I2
x R
LIMIT SENSE
RSENSE
\where I
is the programmed current limit, C
is
LIMIT
OUT
the capacitor at OUT, V is the supply voltage, and
where P
is the power dissipated across R
SENSE
IN
RSENSE
I
is the load current during startup. With IN = 12V,
= 330µF, I
during a current-limit/circuit-breaker fault.
LOAD
C
= 1.5A, and I
= 0, the
LOAD
OUT
LIMIT
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
MAX5943 commences by charging the output capacitor
with 1.5A for approximately 2.7ms. Therefore, the
MAX5943A current-limit timeout period (t
greater than 2.7ms for a successful startup. Otherwise,
the MAX5943A powers up in fault management mode
by exceeding the current-limit timeout period.
) should be
ILIM
power path (R
).
TOTAL
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:
Using a 30mΩ on-resistance MOSFET at GATE1 and
GATE2 and a 30mΩ sense resistor results in a short-cir-
cuit current approximately equal to:
I
= V /R
IN TOTAL
SC
where:
R
= R
+ 2 x (R
)
TOTAL
SENSE
ON
= 30mΩ + 2 x (30mΩ) = 90mΩ
For example, an input voltage of 20V produces a current
at approximately 222A (or I of Q2, whichever is less)
C
OUT
I
=
× I
+ I
INRUSH
G2U LOAD
C
GATE2
SAT
in the power path for the circuit-breaker timeout period.
Choose an R capable of handling the high power
Where I
LOAD
is GATE2’s 45µA sourcing current and
G2U
SENSE
I
is the load current at startup.
dissipation during a short-circuit event.
______________________________________________________________________________________ 15
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MOSFET Selection
For the MAX5943B–MAX5943E, a short-circuit event
Select external MOSFETs according to the application
results in high power dissipated in both Q1 and Q2 dur-
ing the timeout period (Figure 13) where the total power
dissipated in either MOSFET is:
current level. The MOSFETs’ on-resistance (R
)
DS(ON)
should be chosen low enough to have minimum voltage
drop at full load to limit the MOSFET power dissipation.
P = I 2 x R
SC
DS(ON)
High R
also causes large output ripple if there is
DS(ON)
where:
and
a pulsating load. Determine the device power rating to
accommodate startup, a short-circuit condition, and
when the device is in autoretry mode.
I
= V /R
IN EQ
SC
MAX5943
During normal operation, the external MOSFETs dissipate
little power. The power dissipated in normal operation is:
R
EQ
= R
+R
+ R
DS(ON1) DS(ON2)
SENSE
P = I
2 x R
LOAD
DS(ON)
V
IS
+
-
+ V
-
+ V
-
V
Q1
Q2
IN
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:
IN
SENSE GATE1
GATE2 OUT
P
Q2
= (V - V – V ) x I
IN IS Q1 LIMIT
MAX5943A
Figure 11. Power Dissipated Across MOSFETs During a Short-
Circuit Fault for MAX5943A
TP3
PORT 0
L1
FERRITE
250Ω
N1
N2A
Si2318DS Si7222DN
N2B
1
2
3
5
6
J3
C4
0.1μF
R7
100kΩ
C3
1μF
R3
1kΩ
R4
1kΩ
PORT 0
DMMT3906
Q1B
Q1A
R5
100kΩ
R6
100kΩ
4
R2
0.020Ω
1%
0.25W
TP1
V
IN
J1
U1
MAX5943AEEE
V
IN
TP5
ON
R1
200kΩ
C1
1μF
C2
0.01μF
J2
GND
R8
100kΩ
TP6
TP4
FAULT
TP2
GND
V
PULLUP
Figure 12. UL-Recognized Single-Port FireWire Protective Circuit
16 ______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
The programmable timeout of the MAX5943 allows the
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.
use of MOSFETs with low power ratings. A MOSFET
typically withstands single-shot pulses with higher dis-
sipation 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
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
ISC
R
SENSE
V
R
R
DS(ON)1
IN
DS(ON)1
Automatic-restart attempts after a fault shutdown
condition
<0.8% current-limited duty cycle in continuous fault
condition
IN
SENSE GATE1
GATE2 OUT
MAX5943B–MAX5943E
•
•
6.5V undervoltage shutdown protection
Low-drop ORing in multiple power-source applica-
tions, and
Figure 13. Power Dissipated Across MOSFETs During a Short-
Circuit Fault for MAX5943B–MAX5943E
•
Fault reporting
CPA SENSE
FB
V
IN
BST
ON
IN4148
IN4148
PHY
POWER OUT
MAX5033
LX
VD
GND SGND
IN4148
15mΩ
30mΩ
CABLE
POWER
SOURCE
SI7958DP SI7958DP
SI7958DP SI7958DP
PORT 0
TIM IN
ON
SENSE GATE1
GATE2 OUT
FAULT
ONQ1 OR_ADJ
INA
ONA
SENSEA GATE1A
GATE2A OUTA
MAX5943A
ONQ1
GND
FAULTA
FAULTB
ILIM
LATCH
GND
MAX5944
ONB
INB
SENSEB GATE1B
GATE2B OUTB
15mΩ
SI7958DP SI7958DP
BATTERY-
POWER
PORT 1
IRF7478
IRF7478
30mΩ
SOURCE
IN4148
TIM IN
ON
SENSE GATE1
MAX5943A
GATE2 OUT
FAULT
ILIM
LATCH
GND
ONQ1 OR_ADJ
CABLE NOT
ON SLEEP
CURRENT-LIMIT
SENSE
PORT 1 PORT 0
SENSE SENSE
Figure 14. Two-Port FireWire Power Provider Using MAX5943A and MAX5944
______________________________________________________________________________________ 17
FireWire Current Limiter and Low-Drop
ORing Switch Controller
Caution: The additional gate-to-source capacitance
FireWire Power Management
The MAX5943 serves to regulate and protect FireWire
power over a system interface. The MAX5943 program-
mable 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.
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 flow-
ing in hot-plug situations.
Typical Application Circuit
FireWire
PORT
SUPPLY
+
TO
FireWire
PORT
MAX5943
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 transis-
tors, 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.
30mΩ
SI7958DP
SI7958DP
GATE2
Q1
Q2
1kΩ
10kΩ
4kΩ
TIM IN
FAULT
ON
SENSE GATE1
OUT
V
IN
= 12V
MAX5943A
7.15kΩ
ILIM
LATCH
GND
OR_ADJ ONQ1
Typical Operating Circuit
-
FireWire
PORT
SUPPLY
TO
FireWire
PORT
+
V
-
IS
R
SENSE
Q1
Q2
Selector Guide
R1
R2
R3
CURRENT
LIMITER/
CIRCUIT
DEFAULT
TIMEOUT
PROGRAMMABLE
TIMEOUT RANGE
TIM IN
FAULT
ON
SENSE GATE1
GATE2
OUT
PART
(ms)
BREAKER
MAX5943A
MAX5943A
Current limit
2
0.5
1
1.04ms to 11.05ms
32.5µs to 345µs
65µs to 690µs
ILIM
LATCH
GND
OR_ADJ ONQ1
MAX5943B Circuit breaker
MAX5943C Circuit breaker
MAX5943D Circuit breaker
MAX5943E Circuit breaker
2
130µs to 1.38ms
260µs to 2.76ms
MAX5943 EQUIVALENT CIRCUIT
4
VERY-LOW-DROP
ORing DIODE
LOAD DISCONNECT
SWITCH
Chip Information
TRANSISTOR COUNT: 2324
CURRENT-LIMIT/CIRCUIT-BREAKER
AND INRUSH CONTROL
PROCESS: BiCMOS
18 ______________________________________________________________________________________
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.)
______________________________________________________________________________________ 19
FireWire Current Limiter and Low-Drop
ORing Switch Controller
Revision History
REVISION REVISION
PAGES
CHANGED
DESCRIPTION
NUMBER
DATE
0
1
8/04
Initial release
—
1/05
Corrected Table 2 and Figures 10, 11, and 12
12, 15, 16, 17
Added FireWire/IEEE and UL information, inserted new Figure 12, and updated
Package Outline
2
10/07
1, 16, 17, 18, 20
MAX5943
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.
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