Hot Swap Controllers For Live System Backplanes


Linear Technology has launched Hot Swap controllers with integrated MOSFET and current sensing providing a small footprint hot ­plug solution for high density circuit boards. These controllers allow electronic circuit boards and cards to be inserted into live system backplanes, eliminating the need to power them down. Mission critical systems, such as servers and communication equipment, operate continuously as boards are hot plugged in or pulled out, either for system maintenance or to adjust load handling capacity.

The basic functions of a Hot Swap controller are inrush current control and fault isolation. When boards are plugged in, the Hot Swap controller detects power first, and then ramps up the board’s capacitors gently, avoiding connector sparks, backplane supply glitches and system resets. On a downstream short-circuit fault, the controller’s electronic circuit breaker shuts off power to the card, preventing the fault from propagating upstream to the rest of the system. Being the gateway to board power, Hot Swap Controllers have evolved from these two basic functions to also providing sophisticated board power monitoring via digital measurements of the current and voltage levels by integrated ADCs, accessible through I2C/SMBus interfaces.

According to the media release, “The LTC4234 integrates the two most critical and largest Hot Swap components ­ power MOSFET and sense resistor in order to reduce the design time and saves valuable board area. Upon insertion, the LTC4234 waits for connector contact bounce to finish before soft ­starting the output. A ground referenced signal proportional to the load current is provided for monitoring with an external analog ­to­ digital converter (ADC). The current limit can be reduced from its 22.5A default with a single resistor, affording quick adjustment for dynamic load changes and various applications.” Further it states, “During over current conditions, the controller limits MOSFET power dissipation by folding back its current limit for an adjustable timeout period. Undervoltage and overvoltage thresholds protect downstream loads against voltages outside a valid window, preventing circuit malfunction and damage.” In reference to the media release, the hot swap controller is specified over 0°C to 70°C for commercial applications while ­40°C to 85°C for industrial applications and ­40°C to 125°C for automotive temperature range.

Next generation 12-bit ADC Offers 5.4GSps And Very Low Noise

The LTC4234 controller offered in a 38­pin 5mm x 9mm QFN package is priced at US$ 4.95 each for 1000 ­piece, mentioned as per the company release.

Features of LTC4234 as listed below:

  • Enables Safe Board Insertion Into Live Backplane
  • 20A Hot Swap Controller with Integrated MOSFET & Sense Resistor
  • Integrated 4mΩ MOSFET Including Sense Resistor
  • Guaranteed Safe Operating Area
  • Wide Operating Voltage Range: 2.9V to 15V
  • Current Limit for Overcurrent Fault Protection
    • 11% Accurate at 22.5A Full Scale
    • Adjustable with Single Resistor
    • Output Voltage Dependent Foldback
    • Adjustable Fault Timer
  • Undervoltage, Overvoltage & Overtemperature Protection
  • Current & Temperature Monitor, Power Good & Fault Outputs
  • Output Voltage Soft­Start
  • Operating Temperature Range: ­40°C to 125°C
  • 38­Pin 5mm x 9mm QFN Package


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