Controller Chips Shrink Hot-swap Designs

Oct 12, 2005 3:36 PM
By David Morrison, Editor, PETech

A variety of applications in telecom and networking require insertion and removal of circuit cards in live backplanes. Hot-swap controller ICs provide the power management and protection circuitry needed to perform these operations safely. Building on the capabilities of previous devices, the latest generation of hot-swap controllers provides more integrated and efficient designs, as well as more sophisticated protection and power monitoring. These enhancements can be found in recent hot-swap controllers from Freescale Semiconductor, Summit Microelectronics and Linear Technology.

The MC34652 and MC34653 single-chip hot-swap controllers from Freescale Semiconductor reduce board space requirements and cut system costs. These devices minimize external circuitry by integrating the power MOSFET. The MC34652 features a maximum output current of 2 A, while the MC34653 has a max output current of 1 A.

Input voltage operation ranges from -15 V to -80 V on the MC34652 and -39 V to -74 V on the MC34653. Other features include overcurrent limiting with auto retry (default or programmable); charging current limit independent of load capacitor (default or programmable); and start-up and retry delay timer (with a programmable option on the MC34652). There’s also overvoltage and undervoltage detection (programmable option on the MC34652); active high- and active-low power-good output signals; a disable input control; and thermal shutdown.

Available now, the MC34652 comes in a 16-lead SOIC, priced at $2.15 in 1000-piece quantities, while the MC34653 is housed in an 8-lead SOIC priced at $1.82 in 1000-piece quantities.

From Summit Microelectronics, the SMH4814 is a dual-feed active ORing hot-swap controller. The SMH4814 device can monitor and control two independent -48-V feeds, allowing for redundant power supply control. It eliminates the need for bulky ORing diodes, which degrade system efficiency.

The SMH4814 continuously monitors the incoming feeds and switches to the most negative feed as necessary. In addition, it hot swaps and sequences up to four independent downstream dc-dc converters with programmable sequence order and delay times. Programming is achieved via an I²C bus and configuration data is stored in non-volatile EEPROM. The controller is housed in an SOIC or a 5-mm × 5-mm QFN.

Among the chip’s protection features are soft-start power-up, "overcurrent circuit-breaker" functions, and overvoltage and undervoltage monitors. The overcurrent trip levels, forced shutdown mode and overvoltage/undervoltage monitor thresholds are fully programmable. Additionally, a programmable glitch filter is provided on the monitor circuits to prevent false alarms during transients.

Available now, the SMH4814 is priced at $4.18 each in quantities of 1000 devices in the commercial temperature range and in the SOIC package. Unit pricing for the QFN is $4.37 in the commercial temperature range in quantities of 1000 units.

The LTC4261 negative hot-swap controller from Linear Technology is distinguished by an onboard 10-bit ADC and I²C-compatible interface as well as its high-voltage operation. These features allow sophisticated power monitoring by measuring card voltages and currents, and recording past and present fault conditions. The LTC4261 complements Linear Technology's LTC4260—a positive 48-V hot-swap controller that also features an onboard ADC and I²C interface.

Information in the ADCs registers can be queried via the I²C bus, and then used to determine if a card is actually using its allocated power or operating abnormally. An irregular card can be flagged for service even before it fails. In addition, the controller specifies a wide input voltage range of -12 V to -100 V .

Other features include independently adjustable inrush and overcurrent limits; adjustable undervoltage and overvoltage thresholds and hysteresis; and programmable latchoff or auto-retry after faults. The controller also provides alerts to the host after faults and foldback current limiting.

Specified over the commercial and industrial temperature ranges, the LTC4261 is available from stock in 28-lead SSOP and 24-lead 4-mm × 5-mm QFN packages. Pricing begins at $5.95 each in 1000-piece quantities.

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