Point-of-load regulator

Ultralow VIN DC/DC µModule® Regulator with Onboard 5V MOSFET Gate Drive Delivers 15A from 3.3VIN down to 1.5VIN

The LTM4611, which has been released on Monday 28th June 2010 by Linear Technology, is a complete switch mode DC/DC µModule point-of-load regulator capable of generating its own 5V N-channel MOSFET gate drive for very efficient voltage conversion from 3.3VIN or less to loads as low as 0.8V at up to 15A.

Alternative traditional low input voltage high power switch mode DC/DC converters with N-channel MOSFETs require a second regulator circuit to provide the 5V gate drive needed for logic level MOSFETs. Conversion efficiency for the LTM4611 at full load (15A) is 92% for 3.3VIN to 2.5VOUT.

Applications include systems with only 3.3V, 2.8V or 2.5V as the main power rail such as compact data storage and RAID systems, ATCA and optical networking cards, as well as medical and industrial equipment.

So what is the Story behind the LTM4611?

Background
Many densely populated and sophisticated board designs such as multi-ASIC embedded systems or dual-core single-board computers use an isolated brick to convert a 48V bus to 3.3V as the main power rail. There are several reasons:

1) With only a 3.3V bus, power consumption of the board (total circuit) can be improved if proper DC/DC point-of-load converters are chosen to convert 3.3V to lower voltages (2.5V, 1.2V, 1.0V, 0.9V) to power DDR memory, FPGA core, transceivers, for example.
2) Running only one bus line (3.3V) simplifies circuit design by eliminating the requirement for 5V or 12V rails often required to bias higher power DC/DC point-of-load regulator.
3) Isolated bricks have improved their efficiency in converting 48V to 3.3V even at higher output power and their prices are more attractive than in the past.

The challenge is when the load that is powered from the 3.3V rail requires more than 5A to as much as 12A. Although this requirement seems rare, because of the advancements in FPGAs, processors and ASIC technologies, more designers are relying on these devices to boost performance in smaller circuit boards especially when multiple of them are used in parallel. It is not rare to see applications with 10A load requirement. One recent customer asked for 30A for 1V rail powered from 3.3V input. However, traditional low input voltage high power switchmode DC/DC converters with N-channel MOSFETs rely on a second regulator circuit to provide higher than VIN voltage for MOSFET gate drive which increases layout complexity, size and cost. When 5V is not available, delivering high current to loads from 3.3V input bus is very inefficient and power dissipated will increase the junction temperature of the regulator and surrounding components.
New Solution
The LTM4611 is a complete switchmode DC/DC system-in-a-package point-of-load regulator capable of generating its own 5V N-channel MOSFET gate drive for very efficient voltage conversion from 3.3V or less to loads as low as 0.8V at up to 15A. Conversion efficiencies for the LTM4611 at full load (15A) are 92% for 3.3VIN to 2.5VOUT, 88% for 2.5VIN to 1.5VOUT, and 81% for 1.5VIN to 0.9VOUT. Examples of applications include systems with only 3.3V, 2.8V or 2.5V as the main power bus such as in very compact data storage and RAID systems, ATCA and networking cards as well as medical and industrial equipment. The LTM4611 includes the main DC/DC power circuit and the gate drive circuit which contain inductors, MOSFETs, input and output bypass capacitors and compensation circuitry in a small 15mm x 15mm x 4.32mm LGA (land grid array) package weighing only 2.6g. The device boasts +/-2% total DC output error over temperature, line and load regulation as a result of its architecture, precision reference voltage and differential remote sense amplifier; a very key specification for loads such as FPGAs and ASICS that require better than +/-3% voltage accuracy for their optimum performance. To increase output load to 30A, 45A or 60A, two, three or four LTM4611 DC/DC µModule devices can be paralleled to share current.

Features:

• Complete DC/DC system-in-a-package regulator with onboard gate driver in 15mm x 15mm x 4.32 mm LGA package
  
• Ultra low VIN: 1.5V to 5.5V (6V abs max)
  
• 0.8V to 5V output, 15A
  
• Differential remote sensing for precision regulation
  
• Clock synchronizable from 360kHz to 710kHz