FireWire Current Limiter and Low-Drop ORing Switch Controller

Industry's First IEEE 1394/FireWire-Compliant Hot-Swap Controllers

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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 of the full data sheet) is UL® recognized.

The MAX5943 allows the safe insertion and removal of FireWire peripherals into a live FireWire port by providing inrush current control and an output current-limiting function. The ORing feature provides a very efficient way to protect the FireWire port when connected to another FireWire peripheral that sources a higher voltage. By turning off both external MOSFETS, the MAX5943 provides a true bidirectional load disconnect. A low-current shutdown mode disables the MAX5943, resulting in less than 10µA supply current. A pin-selectable input allows latched or autoretry fault management after a fault.

The MAX5943A features a current-limit function that actively limits the current drawn by the load with a programmable timeout. The MAX5943B–MAX5943E do not actively limit the load current but provide a circuit-breaker function. See the Selector Guide in the full data sheet 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.
MAX5943: Typical Operating Circuit MAX5943: Typical Operating Circuit Enlarge+

Key Features

  • Provides Safe Hot Swap for 7.5V to 37V Power Supplies
  • UL-Recognized FireWire/IEEE 1394 Protective Circuit
  • 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


  • FireWire® Desktop/Notebook Port
  • FireWire® Hub
  • FireWire® Peripheral Device Current Limit
  • Hot Swap
Part NumberVIN
Circuit Breaker/ Current LimitCircuit Breaker/Current Limit Threshold
Fault Condition ControlChannelsPositive/Negative RailFeaturesPackage/PinsBudgetary
minmaxSee Notes
MAX5943 7.537
Circuit Breaker
Current Limit
Latched Off
Periodic Retry
1PositiveSingle Firewire Controller
$1.97 @1k
See All Hot Swap Controllers (49)

Part NumberReverse Current Protect.Under Voltage ProtectCharge Pump Cap.Soft StartEnableFault IndicatorPackage/PinsOper. Temp.
See Notes
MAX5943 YesYesNoYesYesYes
-40 to +85$1.97 @1k
See All ORing MOSFET Controllers (5)
Pricing Notes:
This pricing is BUDGETARY, for comparing similar parts. Prices are in U.S. dollars and subject to change. Quantity pricing may vary substantially and international prices may differ due to local duties, taxes, fees, and exchange rates. For volume-specific and version-specific prices and delivery, please see the price and availability page or contact an authorized distributor.

MAX5943AEVKIT: Evaluation Kit for the MAX5943A/B/C/D/E

CAD Symbols and Footprints

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  • Device   Fab Process   Technology   Sample size   Rejects   FIT at 25°C   FIT at 55°C  

    Note : The failure rates are summarized by technology and mapped to the associated material part numbers. The failure rates are highly dependent on the number of units tested.

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