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highpowerZONE Products for the week of November 24, 2008
Semtech Says…
SC417: Miniaturized Feature Rich 10 A Synchronous Buck Regulator Platform
Excellent power efficiency, wide input voltage range, integrated power MOSFETS, bootstrap switch and adjustable LDO in an ultra-compact 5mm x 5mm package
Semtech Corp., a leading supplier of analog and mixed-signal semiconductors, announced the SC417, the first device in a new family of high current point-of-load voltage regulators which are inherently easy to use without sacrificing electrical performance. Benchmark power density is achieved through advanced packaging, optimized power circuit layout and matching of driver to internal power switches. As the number of power rails in a system grows, driven by increasing bandwidth, content and functionality, a versatile 10A regulator in what approaches chip-scale packaging enables the next generation of complex system loads.
The SC417 has a wide input voltage range of 3V to 28V and achieves high efficiencies over an extended load range. The programmable LDO can be used to provide the 5V necessary for the gate drive bias, allowing the part to operate from a single rail. Internal crossover circuitry bypasses the LDO after startup if the LDO and buck outputs are the same, for optimum efficiency. Pseudo fixed frequency adaptive on-time control gives the part excellent transient response, reduces the output filter capacitance required and greatly simplifies the design process by removing external compensation components.
Featuring Semtech’s proven SmartDrive technology, which reduces EMI and eliminates snubbing components and gate drive resistors, the SC417 regulator also features attractive power save functions. Selectable ultrasonic power save allows the device to operate in discontinuous conduction mode at light load conditions, saving quiescent current, while limiting the “floor” frequency to avoid audible noise. The second device in the SC4x7 family, the SC427, with regular power save (no frequency floor) will release next quarter. Semtech’s Smart Power Save technique enables these devices to re-enter continuous conduction mode when active loads attempt to pull the output high while in power save mode, pulling the output back down and avoiding over voltage latch-off.
Another new feature in the SC417 is its temperature compensated RDS(ON) sensed current limit, which effectively doubles the current limit precision.
“The SC417 10A buck regulator in a 5mm x 5mm QFN package breaks new ground with regards to the footprint and profile required for point-of-load power solutions. Able to be used as a module replacement, its flexibility, ease of use and full feature set make it broadly applicable and very attractive to power supply designers,” said Alan Burchfield, Product Marketing Manager for Semtech’s Power Management Group. “The wide input operating range permits its use in a broad range of applications including ultra-mobile, industrial and notebook PCs to multi-function printers and digital TV.”
EN-Genius Says…
This is an important product introduction for Semtech. Their synchronous buck regulators, up until now, have had a maximum of 4 A (from the SC4624) and the majority of the maximum input voltages have been limited to 5.5 V (with one 7 V part). The move up to an integrated 10 A output together with a maximum input voltage of 28 V (minimum 3 V) opens up a lot of industrial and communications markets to the company.
The SC417, and the briefly mentioned SC427, are 10 A integrated FET regulators with an inbuilt, programmable LDO. In its most simplistic form the LDO could be set for a 5 V output (using the usual potential divider to the LDO feedback pin: 1% 0.75 V reference) to power the active circuitry of the regulator. If used for another purpose the remainder of the part will require a separate 5 V supply. The LDO can be set to provide an output voltage between 0.75 V and 5.25 V with a drop-out voltage of a typical 1.2 V at 10 mA. The maximum current rating with a 12 V input is 200 mA.
The switching frequency of the parts can be set by a single external resistor in a range from 200 kHz to 1 MHz, allowing the designer to balance between best efficiency and external component size and real estate. Standard electrolytics (not something you hear everyday) can be used, as well as ceramics and special polymers. Enough ESR is a critical characteristic for stability and to produce sufficient ripple on the output for the feedback pin – to avoid double pulsing. The maximum supply current at 250 kHz switching is 10 mA while typical standby mode consumes 130 µA, and maximum shutdown current is 20 µA. The low-side/high-side Rds(on) numbers are typically 7 mΩ and 17 mΩ giving efficiencies better than 90% with loads over 1 A. The output voltage is, again, set by a potential divider connected to a second feedback pin.
Power consumption at low power loads is how the SC417 and SC427 are differentiated from one another. The SC417 has an internal timer that monitors the time between high-side gate pulses. If that goes higher than 40 µs the high-side MOSFET is turned off and the low-side is turned on, until the switch inductor current ramps to zero. The frequency never falls below about 25 kHz, which Semtech labels as Ultra-sonic (sic) Power-save Operation. The SC427 uses a more conventional pulse operation for power saving.
The parts have cycle-by-cycle current limiting; independent enables for the buck converter and LDO (so the LDO could be used in an “always on” mode if wanted); soft-start; under- and over-voltage protection; power good output for the regulator; and soft shutdown.
In the 5mm x 5 mm package there are 8 power ground pins, 4 input voltage pins plus a thermal pad under the package, 5 inductor pins plus another thermal pad, while analog ground uses 2 pins plus a third thermal pad.
The SC417 will turn heads. The pricing may be on the low side for what amounts to a complete 10 A solution but Semtech needs to also attract attention to the fact that they are now in this space – and price will always do that. If they get traction, and they have the marketing talent to do so, this and parts that inevitably follow will get designed into point-of-load solutions, networking communications, industrial plant solutions, and office equipment like printers. If they develop a solution that adds multiple switching phase capabilities they will open up even more markets for themselves. It will do extremely well.
The SC418 has not been released, as yet, but the SC417 is in full production in the thermally-enhanced WEEE- and RoHS-compliant MLPQ-32 priced at $2.58 in 1000-piece lots.
Data Sheet
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