Tiny DC-DC Converter Supports Wide Input Voltage Range

Nov 1, 2005 12:00 PM
By Mark Valentine, Technical Editor, Power Electronics Technology

For the PDF version of this article, click here.

The LTM4600 from Linear Technology is a complete stepdown dc-dc converter packaged in a 15-mm × 15-mm × 2.8-mm land grid array (LGA). This module, Linear's first in the µModule product line, is an analog solution developed in response to customer requirements for ease of use and high power density (see the figure). Requiring only three external passive support components, and featuring a rapid transient response and wide input range, it is particularly suited for a variety of point-of-load power supply applications.

The LTM4600EV device supports a wide range of input voltages from 4.5 V to 20 V, and the high-voltage version of this module, the LTM4600HVEV, expands that range to 28 V. The output voltage, which is programmed with a single external resistor, can range from 0.6 V to 5 V (not to exceed 80% of V_IN). The output can drive loads up to 10 A. A single module can deliver peak currents of 14 A, and the outputs of two modules can be connected in parallel to drive 20-A loads. (Future versions of this module will support the parallel interconnection of multiple device outputs.) A feature is available to synchronize the module's switching with a master clock, allowing phase interleaving to reduce voltage ripple when the outputs of several modules are connected in parallel. The module also features a built-in soft-start delay of 0.7 ms for a 200-µF output capacitance that can be extended through the use of an external capacitor tied to the appropriate control signal.

The LTC4600 employs current mode control. The inductor and bypass capacitors are contained within the module. All silicon components, which are exclusively Linear Technology devices, also are included within the part, including a new proprietary power FET technology for the switching devices. The switching frequency for the module is fixed and is typically 800 kHz. However, any switching frequency within the range of 50 kHz to 1.2 MHz is supported. Internal temperature compensation provides an output regulation of 1.5% across the operating temperature range of -40°C to 85°C. The modules operate with up to 92% efficiency.

One unique aspect of the LTC4600 is its ability to maintain operational performance without utilizing a heatsink through the use of a thermally enhanced package. The package has a stand-alone junction-to-ambient thermal resistance of 13.5°C/W. This can be reduced to as little as 4.5°C/W with the addition of a BGA heatsink exposed to a 400-LFM airflow. Without a heatsink, the low profile package can enable the part to be mounted on the backside of a circuit board.

While this first product is implemented with analog techniques, future products in the µModule series are poised to partake in the digital revolution now underway in the realm of power management. This might include the use of standard control bus interfaces, such as those for the I²C or PMBus protocols, enabling standard system features such as power sequencing and low-power modes. Future modules will see improvements in analog characteristics as well. For example, the broad input voltage range will be further extended to include voltages below 3.3 V. Furthermore, boost and buck-boost (inverting) topologies will be developed to expand the available range of output capabilities for these modules. Modules with ultralow switching noise also will be introduced.

The LTC4600 is lead-free and RoHS compliant. The units are priced in 1000-unit quantities each at $16.50 for the LTC4600EV and $19.50 for the LTC4600HVEV. The LTM4600IV and LTM4600HVIV, which are tested and guaranteed to operate over the -40°C to 85°C temperature range, are also available. For more information, see www.linear.com.