Rainbow Electronics MAX5943 User Manual

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 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
FireWire Peripheral Device Current Limit
FireWire Hub
Hot Swap

Features

♦ Provides Safe Hot Swap for 7.5V to 37V Power

Supplies

♦ Low-Drop Power ORing with Ultra-Fast Turn-Off
♦ Programmable Active Current Limit (MAX5943A)
♦ Programmable Circuit Breaker

(MAX5943B–MAX5943E)

♦ ±5% Current-Limit Sensing Accuracy
♦ Programmable Current-Limit/Circuit-Breaker

Timeout

♦ Fast Current-Limit Response to Output Short-

Circuit Conditions (MAX5943A)

♦ Drives External N-Channel Power MOSFETs
♦ Overcurrent Fault Status Output
♦ Latched or Autoretry Overcurrent Fault

Management

♦ 10µA Shutdown Current
♦ ON/OFF Control Allows Undervoltage Lockout

Programming

♦ Fast Load Disconnect Control Through ON Input

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

Ordering Information

19-3378; Rev 0; 8/04

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Typical Operating Circuit and Selector Guide appear at end
of data sheet.

FireWire is a registered trademark of Apple Computers, Inc.

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

TOP VIEW

FAULT

TIM

ILIM

LATCH

OR_ADJ

N.C.

ONQ1

ON

1

2

3

MAX5943

4

5

6

7

8

QSOP

16

IN

15

SENSE

14

GATE1

13

N.C.

12

GATE2

OUT

11

10

N.C.

9

GND

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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)

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.

(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

SUPPLIES

Supply Voltage Range V
Supply Current I
Shutdown Current I
IN Default Undervoltage Lockout V

IN Default Undervoltage Lockout
Hysteresis

ON Undervoltage Lockout
Threshold

ON Undervoltage Lockout
Threshold Hysteresis

ON Input Bias Current I
GATE2 (current-limit/circuit-breaker control)
GATE2 Pullup Current I

GATE2 High Voltage V

Current-Limit/Circuit-Breaker
Threshold Voltage

Fast Pulldown Current-Limit
Threshold Voltage (MAX5943A)

GATE2 Pulldown Current
(MAX5943A)

GATE2 Fast Pulldown Current
(MAX5943A)

GATE2 Peak Pulldown Current
(MAX5943A)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

IN

IN

SD

UVLO

V

ON_REFVON

ON

G2U

G2

V

TH

V

THF

I

G2D

I

G2DF

I

G2DP

VON = 3V, no load 1.3 2.3 mA
VON = 0.4V 5 10 µA
VIN rising, ON = IN 6.2 6.5 6.8 V

rising 1.20 1.24 1.275 V

(Note 2) 36 45 54 µA

V

GATE2

VIN - V

VIN - V

VTH < (V
t < t

ILIM

(VIN - V

4.5V

(VIN - V

- V

OUT

SENSE

(Note 3)

SENSE

- V

IN

SENSE)

> V

SENSE)

= 1V 1.0 A

SENSE)

7.5V ≤ VIN ≤ 8V 4.25 5.5 6.5
8V ≤ VIN ≤ 37V 4.5 5.5 6.5

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

< V

,

THF

THF

, V

GATE2

= V

OUT

+

7.5 37 V

0.35 V

70 mV

1µA

335 435 535 µA

80 125 200 mA

V

mV

mV

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

_______________________________________________________________________________________ 3

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)

GATE2 Pulldown Current During
Any GATE2 Turn-Off Condition

GATE1 (ORing control)

ORing Switch Turn-On Current
Threshold Voltage

ORing Switch Turn-On Current
Threshold Voltage Hysteresis

GATE1 Pullup Current I

GATE1 High Voltage V

GATE1 Turn-Off Switch On­Resistance

LOGIC INPUTS

ILIM, OR_ADJ Input-Logic
Tristate Current Tolerance
(Note 6)

LATCH, ONQ1 Input-Logic Low
Voltage

LATCH, ONQ1 Input-Logic High
Voltage

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

I

G2OFF

V

GATE2

= V

+ 4.5V (Note 4) 80 125 200 mA

OUT

OR_ADJ = GND 3 5 7

V

OR

(VIN - V

SENSE

) rising

OR_ADJ = floating 5.5 7.5 9.5

mV

OR_ADJ = IN 8.5 10.5 12.8

) falling 0.5 mV

- V

IN

SENSE

- V

SENSE

) < V

7.5V ≤ V
8V ≤ V

OR

≤ 8V 4.25 5.5 6.5

IN

≤ 37V 4.5 5.5 6.5

IN

23Ω

-3 +3

ON_REF

ON_REF

ON_REF

1.8 V

V

µA

0.7 V

1µA

G1U

G1

R

G1

I

IX

I

IXL

I

IH

V

I

IL

V

(V

IN - VSENSE

(Note 5) 36 45 54 µA

V

GATE1

Measured between GATE1 and SENSE
when (V

Current into or out of input for tri-state logic
condition

Current out of input for logic low 20
Current into input for logic high 20

VON > V

IL

LATCH, ONQ1 = GND, VON > V

VON > V

IH

LATCH, ONQ1 Input Current I

TIM, ILIM, LATCH, OR_ADJ,
OUT, ONQ1 Shutdown Mode

I

Input Current

FAULT Output Low Voltage V
FAULT Output High Leakage

Current

TIMING

Current-Limit Timeout
(MAX5943A)

IH

IH_SD

OL

I

OH

t

ILIM

All voltages = VIN, VON > V

ON_REF

1µA

All voltages = VIN, VON ≤ 0.4V 1 µA

Low-impedance state, I

High-impedance state, V

= 5mA 0.12 0.25 V

FAULT

= 37V 1 µA

FAULT

TIM = IN 1.78 2.02 2.26 ms
R

= 4kΩ 0.87 1.04 1.21 ms

Current-limit mode
(Note 7)

TIM

R

= 50kΩ 9.2 11.05 12.9 ms

TIM

TIM = floating 120 175 225 ms

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

4 _______________________________________________________________________________________

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)

)

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

GATE2

= V

OUT

= 0V and V

GATE2

= V

OUT

= VIN.

Note 3: The typical value of parameter V

THF

is 1.5 x VTH.

Note 4: Current-Limit/Circuit-Breaker Timeout; IN or ON low.
Note 5: See the Typical Operating Circuit. Measured at V

GATE1

= V

SENSE

.

Note 6: The tristate (“floating”) logic condition will be entered if the pin current is within these limits.
Note 7: 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 tCB), so the limits for t

OFF

track the limits for t

ILIM

(or tCB).

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

).

Circuit-Breaker Timeout
(MAX5943B–MAX5943E) (Note 7)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Circuit-breaker mode,
MAX5943B

TIM = IN or
TIM ≥ 3.4V
R

= 4kΩ 27 32.5 38 µs

TIM

R

= 50kΩ 228 345 403 µs

TIM

0.45 0.51 0.57 ms

TIM = floating 3.75 5.5 7 ms
TIM = IN or

TIM ≥ 3.4V

Circuit-breaker mode,
MAX5943C

t

CB

R

= 4kΩ 54 65 76 µs

TIM

R

= 50kΩ 575 690 806 µs

TIM

TIM = floating 7.5 10.9 14 ms

0.89 1.00 1.13 ms

TIM = IN 1.78 2.02 2.26 ms
R

= 4kΩ 109 130 151 µs

Circuit-breaker mode,
MAX5943D

TIM

R

= 50kΩ 1.15 1.38 1.61 ms

TIM

TIM = floating 15 21.9 28 ms

Circuit-breaker mode,
MAX5943E

TIM = IN or
TIM ≥ 3.4V

R

= 4kΩ 217 260 303 µs

TIM

R

= 50kΩ 2.3 2.76 3.23 ms

TIM

3.56 4.05 4.52 ms

TIM = floating 30 44 56 ms

Automatic Restart Delay After
Current-Limit/Circuit-Breaker
Timeout

GATE1 Turn-Off Time
(ORing Response Time)

Turn-Off Response Time t

t

OFF

t

OR

ON_OFF

LATCH = GND (Note 8)

From VOR trigger until (V

= 10nF

C

GATE1

Time from VON < (V
until (V

GATE2

ON_OFF

- V

) < 1V, GATE2 = open

OUT

- VIN) < 1V,

GATE1

- Hysteresis)

128 x
(t

ILIM

t

CB

OR

100 ns

0.34 0.6 µs

(Note 9)

Minimum Delay from ON Low to
Low-Current Shutdown Mode

t

SD

ON step from 1.3V to 0.4V 50 µs

ms

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

_______________________________________________________________________________________ 5

Typical Operating Characteristics

(VIN= +12V, TA= +25°C, unless otherwise noted.)

SUPPLY CURRENT

vs. SUPPLY VOLTAGE

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1.3

SUPPLY CURRENT (mA)

1.2

1.1

1.0
540

TA = +85°C

TA = +25°C

TA = -40°C

353020 251510

SUPPLY VOLTAGE (V)

CURRENT-LIMIT/CIRCUIT-BREAKER

THRESHOLD VOLTAGE vs. TEMPERATURE

62.0
ILIM = IN

61.5

61.0

60.5

60.0

59.5

59.0

58.5

58.0

THRESHOLD VOLTAGE (mV)

57.5

57.0

56.5

56.0

-40 85

VIN = 12V

VIN = 32V

VIN = 7.5V

603510-15

TEMPERATURE (°C)

6.0

5.5

5.0

MAX5943 toc01

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

SHUTDOWN SUPPLY CURRENT (µA)

0.5
0

540

THRESHOLD VOLTAGE vs. TEMPERATURE

42.0

41.5

41.0

MAX5943 toc04

40.5

40.0

39.5

39.0

38.5

38.0

THRESHOLD VOLTAGE (mV)

37.5

37.0

36.5

36.0

-40 85

CURRENT-LIMIT/CIRCUIT-BREAKER

ILIM = FLOATING

SHUTDOWN SUPPLY CURRENT

vs. SUPPLY VOLTAGE

SUPPLY VOLTAGE (V)

603510-15

TEMPERATURE (°C)

CURRENT-LIMIT/CIRCUIT-BREAKER

THRESHOLD VOLTAGE vs. TEMPERATURE

52.0
ILIM = GND

51.5

51.0

MAX5943 toc02

50.5

50.0

49.5

49.0

48.5

48.0

THRESHOLD VOLTAGE (mV)

47.5

47.0

46.5

46.0

353020 251510

MAX5943 toc05

-40 85

100

MAX5943A

10

1

TIMEOUT PERIOD (µs)

0.1

0.01

1 1000

VIN = 32V

VIN = 12V

TEMPERATURE (°C)

VIN = 7.5V

TIMEOUT PERIOD vs. R

MAX5943E

10010

R

(kΩ)

TIM

MAX5943 toc03

603510-15

TIM

MAX5943 toc06

ORing THRESHOLD VOLTAGE

vs. TEMPERATURE

12.0

11.5

11.0

10.5

10.0

9.5

9.0

8.5

8.0

7.5

7.0

6.5

6.0

5.5

ORing THRESHOLD VOLTAGE (mV)

5.0

4.5

4.0

-40 85

OR_ADJ = OPEN

OR_ADJ = GND

TEMPERATURE (°C)

OR_ADJ = IN

GATE CURRENTS vs. TEMPERATURE

47.0

46.5

MAX5943 toc07

46.0

45.5

45.0

GATE CURRENTS (µA)

44.5

6035-15 10

44.0

TEMPERATURE (°C)

GATE1

GATE2

603510-15-40 85

5.260

5.257

MAX5943 toc08

5.254

5.251

5.248

5.245

5.242

5.239

GATE1 DRIVE VOLTAGE (V)

5.236

5.233

5.230

-40 85

vs. TEMPERATURE

MAX5943 toc09

603510-15

TEMPERATURE (°C)

GATE1 DRIVE VOLTAGE

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VIN= +12V, TA= +25°C, unless otherwise noted.)

GATE2 DRIVE VOLTAGE

vs. TEMPERATURE

MAX5943 toc10

TEMPERATURE (°C)

GATE2 DRIVE VOLTAGE (V)

603510-15

5.203

5.206

5.209

5.212

5.215

5.218

5.221

5.224

5.227

5.230

5.200

-40 85

ON HIGH VOLTAGE vs. TEMPERATURE

MAX5943 toc11

TEMPERATURE (°C)

ON HIGH VOLTAGE (V)

603510-15

1.252

1.254

1.256

1.258

1.260

1.250

-40 85

ON LOW VOLTAGE vs. TEMPERATURE

MAX5943 toc12

TEMPERATURE (°C)

ON LOW VOLTAGE (V)

603510-15-40 85

1.182

1.184

1.186

1.188

1.190

1.192

1.194

1.196

1.198

1.200

1.180

FAULT LOW VOLTAGE

vs. TEMPERATURE

MAX5943 toc13

TEMPERATURE (°C)

FAULT LOW VOLTAGE (mV)

603510-15-40 85

20

40

60

80

100

120

140

160

180

200

0

I

FAULT

= 5mA

ORing THRESHOLD RESPONSE TIME

MAX5943 toc14

I

IN

500mA/div

V

OUT

5V/div

(V

GATE

- V

SENSE

)

5V/div

V

IN

10V/div

100µs/div

OR_ADJ = IN

TURN-OFF RESPONSE TIME

MAX5943 toc15

I

IN

1A/div

V

OUT

10V/div

V

GATE2

10V/div

V

ON

2V/div

200ns/div

MAX5943A SHORT-CIRCUIT EVENT

(V

IN

= 37V)

MAX5943 toc16

I

IN

1A/div

V

OUT

50V/div

V

GATE2

50V/div

V

IN

50V/div

400µs/div

TIM = IN
ILIM = GND

V

FAULT

50V/div

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

_______________________________________________________________________________________ 7

Typical Operating Characteristics (continued)

(VIN= +12V, TA= +25°C, unless otherwise noted.)

MAX5943A SHORT-CIRCUIT EVENT

= 37V)

(V

IN

ILIM = GND

100ns/div

MAX5943A SHORT-CIRCUIT RESPONSE

= 8V)

(V

IN

MAX5943 toc17

MAX5943 toc19

V

IN

50V/div

I

IN

10A/div

V

GATE2

50V/div
V

OUT

50V/div
V

FAULT

50V/div

V

IN

10V/div

I

IN

10A/div

MAX5943A SHORT-CIRCUIT RESPONSE

MAX5943E SHORT-CIRCUIT RESPONSE

(V

IN

400µs/div

(V

IN

= 8V)

= 24V)

MAX5943 toc18

TIM = IN

MAX5943 toc20

V

IN

10V/div

I

IN

1A/div

V

GATE2

10V/div
V

OUT

10V/div

V

FAULT

10V/div

V

IN

50V/div

I

IN

166A/div

100ns/div

MAX5943E SHORT-CIRCUIT RESPONSE

= 8V)

(V

IN

100µs/div

MAX5943 toc21

TIM = IN

V

GATE2

10V/div
V

OUT

10V/div

V

FAULT

10V/div

V

IN

10V/div
I

IN

60A/div

V

GATE2

10V/div

V

OUT

10V/div

V

FAULT

10V/div

200µs/div

ORing SWITCHOVER WAVEFORM

V

= 12V V

IN1

= 128V C

V

IN2

200µs/div

RISING = 12V

ON2

= 0

OUT

MAX5943 toc22

V

GATE2

50V/div

V

OUT

50V/div
V

FAULT

50V/div

V

OUT

1V/div

I

IN1

500mA/div

I

IN2

500mA/div

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(VIN= +12V, TA= +25°C, unless otherwise noted.)

ORing SWITCHOVER WAVEFORM

RISING ABOVE V

(V

IN2

IN1

)

MAX5943 toc23

V

OUT

1V/div

ORing SWITCHOVER WAVEFORM

FALLING BELOW V

(V

IN2

)

IN1

MAX5943 toc24

I

IN1

500mA/div

I

IN2

500mA/div

V

OUT

1V/div

I

IN1

500mA/div

I

IN2

500mA/div

V

= 12V V

IN1

= 13V C

V

IN2

10µs/div

RISING = 12V

ON2

= 0

OUT

MAX5943A HOT PLUG-IN LOAD CAPACITANCE

INTO ACTIVE PORT (NO FAULT)

C

LOAD

TIM = IN

= 220µF

400µs/div

MAX5943 toc25

V

= 12V V

IN1

= 13V C

V

IN2

20µs/div

MAX5943A HOT PLUG-IN LOAD CAPACITANCE

INTO ACTIVE PORT (CURRENT-LIMIT TIMEOUT)

V

FAULT

10V/div

I

IN

2A/div

V

GATE2

10V/div

V

OUT

10V/div

C

LOAD

TIM = IN

= 470µF

400µs/div

FALLING = 12V

ON2

= 0

OUT

MAX5943 toc26

V

FAULT

10V/div

I

IN

1A/div

V

GATE2

10V/div

V

OUT

10V/div

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

_______________________________________________________________________________________ 9

Pin Description

PIN NAME FUNCTION

On/Off-Control Input. ON sets the undervoltage lockout threshold and resets the part after a fault latch.

1ON

2 FAULT

3 TIM

4 ILIM

5 LATCH

6 OR_ADJ

7, 10, 13 N.C. No Connection. Not internally connected.

8 ONQ1

9 GND Ground

11 OUT Output Voltage Sense. Connect to the output.

12 GATE2

Drive ON high to enable the device. Drive ON low to disable the device. Connect ON to IN for the default
undervoltage lockout threshold. Connect a resistor-divider from IN to ON and GND to program the desired
undervoltage lockout threshold.

Current-Fault, Active-Low, Open-Drain Output. FAULT asserts and latches low after a current-limit/circuit­breaker fault has exceeded the current-limit/circuit-breaker timeout period (see the

Current-Limit/Circuit-Breaker Timeout Adjustment Input. Connect TIM to IN for the default timeout period or
connect a resistor from TIM to GND to program the current-limit/circuit-breaker timeout period.

Current-Limit/Circuit-Breaker Threshold Input. Leave ILIM open for a 40mV circuit-breaker threshold,
connect to GND for a 50mV circuit-breaker threshold, or connect to IN for a 60mV circuit-breaker threshold
(see the Current Limiting section).

Latch or Autoretry Fault Management Selection Input. Connect LATCH to IN to select latch-off mode
after a current-limit/circuit-breaker timeout. Connect LATCH to GND for autorestart mode after a current­limit/circuit-breaker timeout.

ORing Switch Turn-On Current Threshold Adjustment Input. Select one of three ORing switch turn-on
threshold settings: connect OR_ADJ to GND, connect OR_ADJ to IN, or leave OR_ADJ floating (see the
Power-Supply ORing section).

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,

is below the V

V

ON

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).

threshold, and after a current/circuit-breaker fault.

ON_REF

FAULT

section).

14 GATE1

15 SENSE

16 IN

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).

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).

from IN to SENSE (see the

SENSE,

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

10 ______________________________________________________________________________________

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 VONis 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.

When the input supply voltage (V

IN

) is above 7.5V and

VONis above the V

ON_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 V

IS

is equal
to VTH. In normal operation, VISdrops below VTHand
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).

Figure 1. MAX5943 Functional Diagram

ONQ1

OR_ADJ

ILIM

ON

POWER
SOURCE

1.24V

0.4V

R

SENSE

OR

COMPARATOR

THRESHOLD

CIRCUIT-BREAKER

(CURRENT-LIMIT)

THRESHOLD

(FAST CURRENT-

LIMIT

THRESHOLD)

UVLO COMPARATOR

+

-

6.5V

+

-

ON COMPARATOR

+

-

SHUTDOWN

MODE

Q1 Q2

SENSE

+

-

+

-

+

-

SENSE GATE1

GATE1 GATE2 OUT

GATE1
DRIVE

CP1 CP2

GATE

CHARGE

PUMPS

OUTGATE2

GATE2
DRIVE

FAULT

TIMEOUT

AUTORETRY

TIMEOUT

PERIOD

FAULT

MANAGEMENT

LATCH OR

AUTORETRY

TIM

X128

LATCH

FAULT

MAX5943A–MAX5943E

GND

( ) MAX5943A ONLY.

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

______________________________________________________________________________________ 11

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 VISexceeds VOR, thereby
enhancing Q1 and reducing the voltage drop, power
dissipation, and heat generation in the power-supply
path. When a voltage greater than VINis connected at
OUT, the higher voltage source commences, providing
current to the load. The MAX5943 rapidly turns off
GATE1 upon VISfalling below VOR- hysteresis, thus
blocking the higher voltage from back-driving VIN.
GATE1 also turns off when the load current drops,
causing VISto fall below the VORhysteresis.

Current Limiting/Circuit Breaker

Current Limiting (MAX5943A Only)

The MAX5943A limits the load current by monitoring the
voltage across R

SENSE

at all times and by regulating the

current to the load as necessary to keep V

IS

to its pro­grammable current-limit threshold voltage (VTH). Set the
maximum current limit (I

LIMIT

) by placing the appropriate

sense resistor between IN and SENSE, where I

LIMIT

=

V

TH/RSENSE

. When the load current is less than I

LIMIT

,

GATE2 rises to V

G2

(5.5V) to fully enhance MOSFET Q2

(see the Typical Operating Circuit).
When the load current attempts to draw more than

I

LIMIT

, the MAX5943A’s GATE2 pulldown current (I

G2D

)
regulates the current through Q2 causing OUT to act as
a constant-current source. The output current is limited
to the programmed I

LIMIT

. If the current-limit condition

persists after the current-limit timeout (t

ILIM

) period has

expired, GATE2’s strong pulldown current (I

G2 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 t

ILIM

, GATE2 pulls to
VG2(Figure 2b). During an output short circuit or a
gross overload, the load current overshoots and causes
V

IS

to exceed the fast pulldown current-limit threshold

voltage (V

THF

). The MAX5943A responds with much

stronger GATE2 pulldown currents (I

G2DP

and/or I

G2DF

)
to quickly bring the load current back down to the pro­grammed current limit.

Figure 2. MAX5943A Current-Limit Timing Diagram

V

FAULT

I

OUT

V

GATE1

V

GATE2

I

LIMIT

(a)

V

V

FAULT

OUT

< t

I

V

OUT

GATE1

ILIM

V

GATE2

I

x R

LIMIT

V

OUT

LOAD

(b)

x R

LOAD

I

LIMIT

I

LIMIT

V

IN

t

ILIM

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

12 ______________________________________________________________________________________

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 R

SENSE,VIS

, exceeds

the programmed circuit-breaker thresholds (V

TH

) for

longer than the circuit-breaker timeout period, t

CB

.

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, R

SENSE

, Q1’s

R

DS(ON),

Q2’s R

DS(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 (I

G2 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 t

CB

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 (VTH). Choose the voltage
threshold by connecting ILIM to the appropriate level;
see Table 1.

Current-Limit/Circuit-Breaker

Timeout Period (t

ILIM/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 (t

ILIM/ tCB

) by connect-

ing a resistor (R

TIM

) from TIM to GND (see the Typical
Operating Characteristics). Calculate the fault-limit
timeout period using the following equation:

where R

TIM

is in kΩ, t

ILIM/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.

Figure 3. MAX5943B–MAX5943E Circuit-Breaker Timing Diagram

Table 1. Current-Limit/Circuit-Breaker
Trip Threshold Level

Table 2. MAX5943_ Timeout Periods

ILIM CONNECTION V

Open 40
GND 50

IN 60

tmstms

() () .

ILIM CB

==×025

(mV)

TH

Rk

()

Ω

TIM

K

V

FAULT

I

LIMIT

t

CB

I

OUT

V

IN

V

GATE1

V

GATE2

V

G2

V

OUT

V

G2

PART

MAX5943A 2 1.04ms to 11.05ms 12.5
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

DEFAULT
TIMEOUT,

TIM = IN

(ms)

PROGRAMMABLE

TIMEOUT RANGE

(4kΩ < R

TIM

< 50kΩ)

MAXIMUM

TIMEOUT,

TIM =

FLOATING

(ms)

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

______________________________________________________________________________________ 13

Timing accuracy is guaranteed for R

TIM

ranging from

4kΩ to 50kΩ. Large R

TIM

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 R

SENSE

, Q1, Q2, and any other components in the
power path. Use component values rated to handle
electrical stresses during the timeout period.

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 VISexceeds
VOR, enhancing Q1. Q1’s low R

DS(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 VISdecreases below
VORminus 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).

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 V

IN

is greater than V

UVLO

, VONis above the

V

ON_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).

Figure 4. Q1 Current Path During Inital Startup

Figure 5. MAX5943 ORing Controller Rerouting Load Current

+ VIS -

R

V

IN

ON

SENSE

Q1 Q2

IN

SENSE GATE1

MAX5943

OR_ADJ ONQ1GND

GATE2 OUT

TO
FireWire
PORT

= 0

I

INA

V

INA

FROM
BATTERY
SOURCE

I

INB

V

INB

FROM
POWER
SOURCE

R

SENSE

R

SENSE

SENSE GATE1

MAX5943

OR_ADJ ONQ1GND

SENSE GATE1

MAX5943

OR_ADJ ONQ1GND

ON

ON

GATE2 OUTIN

GATE2 OUTIN

TO FireWire
PORT

V

> V

INB

I

LOAD

INA

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

14 ______________________________________________________________________________________

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<
V

ON_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:

where V

TURN_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.

When operating the MAX5943, ON must remain above
its 1.24V threshold. If V

ON

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.

Figure 6. MAX5943 Power Switch Over ORing Timing Diagram

Figure 7. MAX5943 Operating in Reverse-Current Mode
(Routing Power from Port 1 to Port 2)

Figure 8. Setting the MAX5943 Turn-On Voltage

V

INA

PORT1

I

INA

I

INB

V

OUT

V

INB

V

> V

INB

INA

V



TURN ON

R

1




124

.

_



12= −

×




R

TIM
ON

ONQ1

TIM

ON

ONQ1

R1

R2

SENSE GATE1

MAX5943

SENSE GATE1

MAX5943

V

IN

IN

MAX5943

ON

GND

GATE2

OUTIN

FAULT

OR_ADJGNDLATCHILIM

GATE2

OUTIN

FAULT

OR_ADJGNDLATCHILIM

PORT2

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

______________________________________________________________________________________ 15

The MAX5943 remains in low-current shutdown mode
when VONis 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.

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 t

OFF

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 t

OFF

of 128 x t

ILIM

(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.

Applications Information

Startup Consideration

MAX5943A

During startup, a large capacitor at OUT may result in a
charging current equivalent to the current limit. Choose a
current-limit timeout that will allow a successful startup.
The timeout can be approximated using the following
equation:

where I

LIMIT

is the programmed current limit, C

OUT

is
the capacitor at OUT, VINis the supply voltage, and
I

LOAD

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 (t

ILIM

) 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.

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:

Where I

G2U

is GATE2’s 45µA sourcing current and

I

LOAD

is the load current at startup.

To prevent the MAX5943B–MAX5943E from starting up
in a fault condition set:

Figure 9. Resetting MAX5943 After a Latched Fault Condition

Figure 10. Controlling the MAX5943B–MAX5943E Inrush Current

V

IN

IN
LATCH

R1

R2

R

+

V

IN

-

SENSE

IN

Q1 Q2

SENSE GATE1 GATE2

MAX5943B–MAX5943E

GND

ON

GND

45µA

MAX5943

C

1kΩ

GATE

OUT

I

I

C

LOAD

LOAD

C

OUT

t

>

ILIM

II

LIMIT LOAD

CV

×

OUT IN

−

I

INRUSH

C

OUT

=×+

C

GATE

II

2

GU LOAD

2

V

I

INRUSH

<

R

SENSE

TH

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

16 ______________________________________________________________________________________

Optimizing for Short-Circuit Conditions

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.

Choose the sense-resistor power rating to accommodate
an overcurrent condition:

P

RSENSE

= I

2

LIMIT

x R

SENSE

where P

RSENSE

is the power dissipated across R

SENSE

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 (R

TOTAL

).

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/R

TOTAL

where:

R

TOTAL

= R

SENSE

+ 2 x (RON)

= 30mΩ + 2 x (30mΩ) = 90mΩ

For example, an input voltage of 20V produces a current
at approximately 222A (or I

SAT

of Q2, whichever is less)
in the power path for the circuit-breaker timeout period.
Choose an R

SENSE

capable of handling the high power

dissipation during a short-circuit event.

MOSFET Selection

Select external MOSFETs according to the application
current level. The MOSFETs’ on-resistance (R

DS(ON)

)
should be chosen low enough to have minimum voltage
drop at full load to limit the MOSFET power dissipation.
High R

DS(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 = I

LOAD

2

x R

DS(ON)

The most power dissipation occurs during a short-circuit
event, resulting in high power dissipated in Q2 (Figure

11) during the timeout period for the MAX5943A, where
the power dissipated across Q2 is:

PQ2= (V

IN

- VIS– VQ1) x I

LIMIT

For the MAX5943B–MAX5943E, a short-circuit event
results in high power dissipated in both Q1 and Q2 dur­ing the timeout period (Figure 12) where the total power
dissipated in either MOSFET is:

P = I

SC

2

x R

DS(ON)

where:

ISC= VIN/R

EQ

and

REQ= R

SENSE+RDS(ON1)

+ R

DS(ON2)

The programmable timeout of the MAX5943 allows the
use of MOSFETs with low power ratings. A MOSFET
typically withstands single-shot pulses with higher dis­sipation than the specified package rating.

FireWire Power Management

The MAX5943 serves to regulate and protect FireWire
power over a system interface. The MAX5943 program­mable features make it suitable for both power provider
and power receiver applications. Figure 13 shows a
high-end two-port FireWire power management system
using two MAX5943As and a dual-channel MAX5944
FireWire current-limiting IC.

Figure 11. Power Dissipated Across MOSFETs During a Short­Circuit Fault for MAX5943A

V

IS

+-

V

IN

V

+- +-

Q1

V

Q2

SENSE GATE1 GATE2 OUTIN

MAX5943A

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

______________________________________________________________________________________ 17

Transient Protection

If IN or OUT experiences a fast voltage transient, the
drain-to-gate parasitic capacitance of Q1 and/or Q2
may be sufficient to briefly enhance one of the transis­tors, allowing current glitch. If the circuit is subjected to
large transients, connect capacitors from the gate to
source across the appropriate MOSFET, preventing the
parasitic capacitance from turning on the device.

Caution: The additional gate-to-source capacitance
causes the turn-off time of the MOSFETs to increase due
to the additional charge of the capacitor. Use the mini­mum capacitor value to prevent currents from flowing in
hot-plug situations.

Figure 12. Power Dissipated Across MOSFETs During a Short­Circuit Fault for MAX5943B–MAX5943E

R

V

IN

SENSE

IN

R

DS(ON)1

SENSE GATE1 GATE2 OUT

MAX5943B–MAX5943E

R

DS(ON)1

ISC

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

18 ______________________________________________________________________________________

Figure 13. Two-Port FireWire Power Provider Using MAX5943A and MAX5944

PHY

POWER OUT

CABLE

POWER

SOURCE

BATTERY-POWER

SOURCE

FB

BST

V

IN

ON

CPA SENSE

MAX5033

LX

VD

SGND

GND

IN4148

15mΩ

TIM

ON

ILIM

15mΩ

TIM

ON

ILIM

SI7958DP SI7958DP

SENSE GATE1

MAX5943A

SI7958DP SI7958DP

SENSE GATE1

MAX5943A

GATE2 OUTIN

FAULT

OR_ADJONQ1GNDLATCH

GATE2 OUTIN

FAULT

OR_ADJONQ1GNDLATCH

IN4148 IN4148

30mΩ

ONA

ONQ1

GND

ONB

30mΩ

SI7958DP SI7958DP

SENSEA GATE1A GATE2A OUTAINA

MAX5944

SENSEB GATE1B GATE2B OUTBINB

IRF7478 IRF7478

PORT 0

FAULTA

FAULTB

PORT 1

IN4148

CABLEONNOT

SLEEP

CURRENT-LIMIT

SENSE

PORT 1

SENSE

PORT 0
SENSE

MAX5943

FireWire Current Limiter and Low-Drop

ORing Switch Controller

______________________________________________________________________________________ 19

Chip Information

TRANSISTOR COUNT: 2324
PROCESS: BiCMOS

SENSE GATE1

OR_ADJ ONQ1GND

MAX5943 EQUIVALENT CIRCUIT

LATCHILIM

FAULT
ON

GATE2 OUT

Q1 Q2

LOAD DISCONNECT
SWITCH

VERY-LOW-DROP
ORing DIODE

CURRENT-LIMIT/CIRCUIT-BREAKER
AND INRUSH CONTROL

IN

TO
FireWire
PORT

FireWire
PORT
SUPPLY

MAX5943A

TIM

R3

+ V

IS

-

R

SENSE

R1

R2

Typical Operating Circuit

PART

CURRENT

LIMITER/

CIRCUIT

BREAKER

DEFAULT

TIMEOUT

(ms)

PROGRAMMABLE

TIMEOUT RANGE

MAX5943A

2

1.04ms to 11.05ms

MAX5943B

0.5 32.5µs to 345µs

MAX5943C

1 65µs to 690µs

MAX5943D

2

130µs to 1.38ms

MAX5943E

4

260µs to 2.76ms

Selector Guide

30mΩ

SI7958DP SI7958DP

SENSE GATE1

OR_ADJ ONQ1GNDLATCHILIM

FAULT
ON

GATE2 OUT

Q1 Q2

IN

+

-

V

IN

= 12V

TO
FireWire
PORT

FireWire
PORT
SUPPLY

MAX5943A

TIM

4kΩ

10kΩ1kΩ

7.15kΩ

Typical Application Circuit

Current limit
Circuit breaker
Circuit breaker
Circuit breaker
Circuit breaker

MAX5943

FireWire Current Limiter and Low-Drop
ORing Switch Controller

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.

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© 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages

.)

QSOP.EPS

PACKAGEOUTLINE,QSOP.150",.025"LEADPITCH

1

21-0055

E

1