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19-3378; Rev 2; 10/07
FireWire Current Limiter and Low-Drop
ORing Switch Controller
General Description
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 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.
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.
The MAX5943 operates over the -40°C to +85°C extended
temperature range and is available in a 16-pin QSOP
package.
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 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
Programming
o
Fast Load Disconnect Control Through ON Input
MAX5943
Ordering Information
PART
MAX5943AEEE
MAX5943BEEE
MAX5943CEEE
MAX5943DEEE
MAX5943EEEE
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
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
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.
IEEE 1394 is a trademark of the Institute of Electrical and
Electronics Engineers trademark.
UL is a registered trademark of Underwriters Laboratories, Inc.
LATCH 5
OR_ADJ 6
N.C. 7
ONQ1 8
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.
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 = +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
(V
IN
= 7.5V to 37V, GND = 0V, and T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= 12V, T
A
= +25°C.)
(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
I
ON
I
G2U
V
G2
(Note 2)
V
GATE2
- V
OUT
7.5V
≤
V
IN
≤
8V
8V
≤
V
IN
≤
37V
ILIM = GND
V
TH
V
IN
- V
SENSE
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)
V
THF
V
IN
- V
SENSE
(Note 3)
ILIM = floating
ILIM = IN
I
G2D
I
G2DF
I
G2DP
V
TH
< (V
IN
- V
SENSE)
< V
THF
,
t < t
ILIM
(V
IN
- V
SENSE)
> V
THF
, V
GATE2
= V
OUT
+
4.5V
(V
IN
- V
SENSE
) = 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
µA
mA
A
mV
mV
µA
V
V
ON_REF
V
ON
rising
1.20
V
IN
I
IN
I
SD
V
UVLO
V
ON
= 3V, no load
V
ON
= 0.4V
V
IN
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
µA
V
V
V
mV
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
2
_______________________________________________________________________________________
FireWire Current Limiter and Low-Drop
ORing Switch Controller
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 7.5V to 37V, GND = 0V, and T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= 12V, T
A
= +25°C.)
(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 On-
Resistance
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)
t
ILIM
Current-limit mode
(Note 7)
R
TIM
= 4kΩ
R
TIM
= 50kΩ
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
I
IX
I
IXL
I
IH
V
IL
I
IL
V
IH
I
IH
Current into or out of input for tri-state logic
condition
Current out of input for logic low
Current into input for logic high
V
ON
> V
ON_REF
LATCH, ONQ1 = GND, V
ON
> V
ON_REF
V
ON
> V
ON_REF
All voltages = V
IN
, V
ON
> V
ON_REF
1.8
1
-3
+3
20
20
0.7
1
V
µA
V
µA
µA
I
G1U
V
G1
R
G1
V
OR
(V
IN
- V
SENSE
) rising
OR_ADJ = floating
OR_ADJ = IN
(V
IN
- V
SENSE
) falling
(Note 5)
V
GATE1
- V
SENSE
7.5V
≤
V
IN
≤
8V
8V
≤
V
IN
≤
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
µA
V
Ω
mV
SYMBOL
I
G2OFF
CONDITIONS
V
GATE2
= V
OUT
+ 4.5V (Note 4)
MIN
80
TYP
125
MAX
200
UNITS
mA
MAX5943
Measured between GATE1 and SENSE
when (V
IN
- V
SENSE
) < V
OR
I
IH_SD
V
OL
I
OH
All voltages = V
IN
, V
ON
≤
0.4V
Low-impedance state, I
FAULT
= 5mA
High-impedance state, V
FAULT
= 37V
0.12
1
0.25
1
µA
V
µA
_______________________________________________________________________________________
3
FireWire Current Limiter and Low-Drop
ORing Switch Controller
MAX5943
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 7.5V to 37V, GND = 0V, and T
A
= -40°C to +85°C, unless otherwise noted. Typical values are at V
IN
= 12V, T
A
= +25°C.)
(Note 1)
PARAMETER
SYMBOL
CONDITIONS
TIM = IN or
TIM
≥
3.4V
R
TIM
= 4kΩ
R
TIM
= 50kΩ
TIM = floating
TIM = IN or
TIM
≥
3.4V
Circuit-breaker mode,
MAX5943C
Circuit-Breaker Timeout
(MAX5943B–MAX5943E) (Note 7)
t
CB
Circuit-breaker mode,
MAX5943D
R
TIM
= 4kΩ
R
TIM
= 50kΩ
TIM = floating
TIM = IN
R
TIM
= 4kΩ
R
TIM
= 50kΩ
TIM = floating
TIM = IN or
TIM
≥
3.4V
Circuit-breaker mode,
MAX5943E
R
TIM
= 4kΩ
R
TIM
= 50kΩ
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
(t
ILIM
OR
t
CB)
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
µs
µs
ms
ms
µs
µs
ms
ms
µs
ms
ms
ms
µs
ms
ms
Circuit-breaker mode,
MAX5943B
t
OFF
LATCH = GND (Note 8)
ms
t
OR
From V
OR
trigger until (V
GATE1
- V
IN
) < 1V,
C
GATE1
= 10nF
Time from V
ON
< (V
ON_OFF
- Hysteresis)
until (V
GATE2
- V
OUT
) < 1V, GATE2 = open
(Note 9)
ON step from 1.3V to 0.4V
100
ns
Turn-Off Response Time
t
ON_OFF
0.34
0.6
µs
Minimum Delay from ON Low to
Low-Current Shutdown Mode
t
SD
50
µs
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
All min/max parameters are tested at +25°C and +85°C. Limits at -40°C are guaranteed by design.
Measured at both V
GATE2
= V
OUT
= 0V and V
GATE2
= V
OUT
= V
IN
.
The typical value of parameter V
THF
is 1.5 x V
TH
.
Current-Limit/Circuit-Breaker Timeout; IN or ON low.
See the
Typical Operating Circuit.
Measured at V
GATE1
= V
SENSE
.
The tristate (“floating”) logic condition will be entered if the pin current is within these limits.
R
TIM
is connected from TIM to GND. The maximum timeout period is enforced to prevent arbitrarily long operation in cur-
rent-limit mode. Therefore, the relationship between resistor value and timeout changes for large values of R
TIM
. See
Current-Limit Timeout vs. R
TIM
in the
Typical Operating Characteristics
for nominal values.
Note 8:
Parameter t
OFF
is a direct multiple of t
ILIM
(or t
CB
), so the limits for t
OFF
track the limits for t
ILIM
(or t
CB
).
Note 9:
If the ON voltage goes below V
ON_REF
- Hysteresis, then GATE2 goes low immediately to disconnect power from the load
quickly (within t
ON_OFF
).
4
_______________________________________________________________________________________
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