Milpitas, Calif. - Hot-swap controller chips are coming to market in greater numbers and packed with more smarts. They've quickly evolved from discrete circuits into highly integrated chips, equipped with thermal sensing, that are proactive in maintaining power and board stability during transient events, as when a card is inserted into a live backplane.
The new arrivals can better respond to a wider classification of power events that often lead to system malfunction and even failure. In addition, they are stepping beyond their initial functionality into related areas, such as supply sequencing, and are being used in such applications as power-over-Ethernet.
"The first hot-swap controllers used a basic n-channel MOSFET and discrete circuitry in the path of the first dc/dc converter, ramping current slowly to handle problems at the input caused by a large bulk capacitance . . . and to limit the effects of transients during live insertion of a circuit board," said Todd Nelson, product-marketing manager for Linear Technology Corp. (Milpitas). Next, sense resistors were added. "Now we've moved from a comparator watching a sense resistor to active current limiting: an amplifier in the loop to regulate current for several types of faults, ranging from slight overcurrent to catastrophic events."
Hot-swap chips are of three types: those that apply to traditional 48-volt telecom backplanes, those suited to a wide (12- to 48-V) range and those aimed at general applications. Among the latest chips for telecom is the Smart Hot Plug NIS5101, from ON Semiconductor (Phoenix), which integrates analog controller, MOSFET and sensor. It's touted as the only MOSFET-based device with a linear current amp and a 40-milliohm, 100-V-rated smart MOSFET.
"Any device on a telecom -48-V bus must survive a 100-V transient for 100 milliseconds," said Sue Nee, strategic marketing manager. "Also, the product of Rds(on) and area is much higher in an analog process vs. a power-MOSFET process at this voltage rating."
Using the NIS5101 reduces external component count about 75 percent over typical layouts, the company said. The device requires just three external resistors to set current limit and undervoltage and overvoltage trip points. The NIS5101 is priced at $2.80 each in lots of 10,000.
Also developed for telecom is the TPS2350 hot-swap power manager from Texas Instruments Inc. (Dallas). It protects supply-redundant -48-V systems and meets PICMG's Advanced Telecom Computing Architecture spec. Operating from a -12- to -80-V input, it's intended to do away with the need for traditional OR-ing diodes, which otherwise can lead to uncontrolled inrush currents. The TPS2350, in a 14-pin TSSOP, sells for $1.90 each in lots of 1,000.
Maxim Integrated Products (Sunnyvale, Calif.) is aiming its MAX5920, -5921 and -5939 at telecom, networking and computer server line cards. The parts are designed to pull down the MOSFET's gate current exponentially in response to severe overcurrent fault conditions or to otherwise provide a fast pulldown in the event of short-circuits. The devices are designed as drop-in second sources for Linear Technology's LT1640 and LT4250. The MAX5920 is priced at $1.47 per unit and the MAX5921/ 5939 at $1.80, all in quantities of 1,000.
Hot-swap chips are also arriving to serve different power functions. Two from Linear Technology, the LTC2921 and LTC2922, provide supply tracking to coordinate power-up of up to five high-current supplies. Available for supplies working at 2.2, 3.3 and 5 V, the chips ensure that multiple supplies ramp up at the same time and same rate to protect ASICs, processors and other circuitry from lock-up or damage.
The LTC2921, equipped with three remote-sense switches, is available in an SSOP-16 and sells for $2.50 each in quantities of 1,000. The LTC2922, with five remote-sense switches, comes in an SSOP-20 and is priced at $2.75.
In addition, the company's LTC2923 controller implements both power supply tracking and sequencing. Packaged in an MSOP-10, it is priced at $2.95.
Meanwhile, the MAX8533 from Maxim is a 12-V, Infiniband-compliant hot-swap controller and power sequencer that can be applied in blade servers and RAID cards, as well as network switch and router line cards. The chip has two-level current protection, for overcurrent and severe-overcurrent conditions, responding to the latter in less than 100 ns. It is rated at 16 V and is priced at $1.90 each in lots of 1,000. An evaluation kit is available.
Maxim is among the vendors eyeing power-over-Ethernet applications. The MAX5922 and MAX5935 comply with the latest version of the IEEE 802.3af (48-V) power-over-Ethernet spec, which calls for detecting the presence of a power device as well as determining its power classification.
Maxim Integrated Products