highpowerZONE Products for the week of October 24, 2005

Linear Technology Says . . .
LTM4600: 10-A Dc-Dc Module Provides High Power Density In Compact Package

A new uModuleTM (micro-module) from Linear Technology Corporation provides designers a complete 10A switching power supply in a tiny (15mm x 15mm) footprint, low profile (2.8mm) land grid array (LGA) package. The LTM4600 is a synchronous switchmode DC/DC step-down regulator with built-in inductor, supporting power components and compensation circuitry. The LTM4600 is the first in a new family of uModules from Linear Technology that leverages the company's core strengths in power management and conversion. By simplifying power system development, this new high-density power supply reduces development time for a broad range of systems, including network routers, blade servers, cellular basestations, medical diagnostic equipment, test instrumentation and RAID systems.

The LTM4600 accommodates a wide input voltage range of 4.5V to 28V. The high level of integration and synchronous current mode operation allows the LTM4600 to deliver superior transient response and up to 10A continuous current (14A peak) at up to 92% efficiency. It simplifies power supply design and construction, requiring only input and output bulk capacitors and a single resistor to set the output voltage within a range of 0.6V to 5V. Containing all Linear Technology silicon and supported by Linear Technology's rigorous in-house testing and high reliability processes, the LTM4600 brings component-level reliability and industry-leading performance to demanding applications.

EN-Genius Says...

No one could describe Linear's team of field application engineers as anything but the best in our business, but they cannot be everywhere at once. More and more, over the years, the design of the power supply for products has been getting closer and closer to the release of designs to manufacturing, and I have actually seen occasions when the design and component sourcing period was less than thirty days after the final decisions had been made as to margined voltage levels and current requirements!

When you throw into the equation the fact that many OEMs don't have the design talent in house for power supplies, have less and less real estate for the supplies, and want less volume of varied inventory, they are hungry for a solution that simply just works.

The uModule solution is an interesting business direction for Linear to take but an obvious engineering one. If you look at the contents of the uModule it is all LTC silicon plus an embedded inductor, three resistors and three capacitors -- the largest being a 15 µF on the output line, reducing the size of the external capacitor, which is a nice extra benefit. But if an FAE went in to a customer to design a supply that the uModule could replace what silicon would LTC sell for that design? Probably just the controller because the customer would go elsewhere for the 10-A n-channel switching power MOSFETs. The value-added proposition is something I'm sure LTC very carefully worked on before going in this direction.

Customers will be immediately relieved at not having to do things such as sizing the switching inductor, but what will concern customers will be part handling, reliability and efficiency at the loads they are actually using them -- not just maximum load. LTC seems to have addressed all three. For the first the use of the recently-developed surface-mount land-grid array (LGA) -- and this is only the second product I have seen to use this package, the first being a MEMS part -- allows a lot more circuitry to be put into one place, but it can still be handled by today's conventional mounting equipment. The second concern is being vigorously pushed by LTC, "supported by Linear Technology's rigorous in-house testing and high reliability processes…" and I would not doubt that the company will publish, as they always have, reliability data once production is in full swing. The third point is clearly addressed by the data sheet which shows that, whatever the conditions, efficiency is within 10% of its peak number by the time the part is delivering just 1 A.

Efficiencies are highest when, of course, the input and output voltage levels are closest ranging, for example, from about 90% down to 70% with a 12-V input being converted to 3.3 V down to 0.6 V outputs. You cannot take a 48-V telecom rail directly to the part anyway (with a maximum input of 28 V for the HV version and 20 V for the standard part) and if you were using such a rail you would probably want to dc-dc convert down to a couple of volts above the highest supply that you need in your application.

The 2.8-mm profile of the LTM4600 is, as LTC points out, an obvious -- among the few -- component that can be attached the backside of a PCB offering additional real estate on the top. Two of the parts can also be paralleled to offer 20-A continuous load (28 A peak). The undervoltage lock-out threshold is a typical 1.5 V with inrush current limited to about 700 mA. To allow for the input current, which could reach 4 A in some conditions, 15 of the balls in the LGA-104 are used for Vin, while 33 each are used for power ground and Vout.

The LTM6400 is a complete non-isolated synchronous switching dc-dc switching supply with current control. The switching frequency is not defined in the data sheet and its only concern to the user is what is the output ripple frequency, which is quoted as a nominal 800 kHz. The output voltage (in a range from 0.6 V to 5 V) is chosen by a single resistor to ground from a set pin, which is actually the feedback pin to the controller with an internal 100 kΩ 0.5% resistor forming the top end of the potential divider from the output line although the load regulation accuracy (quoted as a maximum ±1%) must also be dependent on that external resistor's tolerance. Peak output current is limited to 17 A and there is both output overvoltage and short-circuit protection.

Either ceramic or bulk capacitance is suggested for the input and output lines and LTC provides a complete table in the data sheet with value suggestions across the potential voltage combinations. The values required with ceramics are considerably lower than bulk. Compensation is in-module.

Thermal impedance of the uModule is only 20ºC/W with 125ºC maximum junction temperatures.

This product and subsequent ones to follow, probably at lower output currents and noise (and maybe boost conversion?) at first, to fill more holes in the market -- at the right price -- could have very significant revenue implications for Linear Technology. Of all the vendors of silicon the company is uniquely positioned to put itself into this completely new market: not new in application because it is already completely proven by discrete designs. The range of markets is huge.

The LTM4600 is sampling in its Pb-free LGA-104 and will be priced at $16.50 in 1000-piece lots. The HV version will be priced at $19.50, also in 1000-piece lots. Linear is accepting volume orders this quarter (Q4, 2005).

Data Sheet