20-V, 2.5-A synchronous monolithic buck with current and temperature monitoring

April 29, 2013 //By Keith Bassett
20-V, 2.5-A synchronous monolithic buck with current and temperature monitoring
Keith Bassett, Design Engineering Section Leader, Linear Technology Corp. explains how a synchronous, monolithic step-down regulator has been developed to provide a flexible, highly efficient DC/DC conversion while occupying a small footprint.

Increases in digital IC integration, coupled with advances in printed circuit board layout and assembly techniques, continue to push system performance and power density higher.

Many of these systems, powered from a 12 V rail or battery stack, utilize point-of-load regulators to maximize power chain efficiency while maintaining a small form factor. The LTC3626 synchronous, monolithic step-down regulator is ideally suited for these operating environments, given its ability to provide a flexible, highly efficient DC/DC conversion while occupying a small footprint.

The device is capable of supplying 2.5 A of output current over an input voltage range of 3.6 V to 20 V from a 3 mm × 4 mm, 20-pin QFN package. Its patented controlled on-time architecture yields outstanding transient response and enables high step-down ratios at high switching frequencies, minimizing board footprint.

The LTC3626 integrates a number of easy-to-use, but powerful, features that would normally require additional ICs and design time to implement. Specifically, with the addition of just a couple of passive components, the device can be configured to provide accurate measures of its output current, input current, and on-die temperature. It can be just as easily programmed to limit each measured parameter.
 
These built-in features expand the designer’s insight into the performance of the system and increase the level of control with remarkably little extra design investment. Additionally, optional internal loop compensation is available to minimize the design effort. 

The device also includes user-selectable Burst Mode operation or forced-continuous mode, resistor-programmable switching frequencies from 500 kHz to 3 MHz, power good status output, output tracking capability, and external clock synchronization.

Current monitor and limit

One way to measure the overall performance of a system is to monitor the current at the output of the power supply. Supply current monitoring also informs designers if downstream ICs are operating as expected - useful in design and debug, and during normal operation.

The device makes it easy to

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