Resistor-programmed switching regulator IC goes rail-to-rail down 0V, easily paralleled with siblings for more current

Milpitas, Calif.—It's often a designer's dilemma: should you use an LDO or a switcher? Also, do you go with a single, larger regulator or with several smaller ones?

The LTC3600 synchronous buck regulator from Linear Technology Corp. gives you another option: a DC/DC buck regulator which can be easily paralleled with other LTC3600s for greater current output capability, and which you can program down to 0V. This gives you the choice of locating ganged regulators close to each other or spreading them—and their inevitable, associated dissipation—around your PC board; as well as simplifying your BOM by using the same regulator in many places, both as a solo device and as part of higher-current groups.

The LTC3600 synchronous buck regulator from Linear Technology Corp.

delivers a resistor-programmable 0-15V/1.5A

and can be paralleled for higher output currents,

 [If you are having a déjà vu moment right now, perhaps you are thinking of their LTC3080 regulator, which also has the paralleling capability, but is a linear regulator (LDO). Both implement unique topologies developed by Bob Dobkin, LTC's Chief Technical Officer. In addition to the obvious LDO/switcher difference, the LTC3080 LDO can float, while the LTC3600 switcher requires a ground.]

The IC is programmed using a single resistor, and can deliver 0 to 15V at up to 1.5A. It includes an internal 50 μA reference used to establish the output voltage, which can adjusted dynamically. It accepts inputs spanning +4 to +15V, making it a good fit for dual-cell Li-ion designs, or fixed-rail 5V and 12V IBCs (intermediate bus converters). The output voltage can be set between 0V and 0.5V below V_IN, effectively making it a rail-to-rail regulator; The 0V setting is useful for powering-down individual rails in a system.

Accuracy is ±1% over temperature and is load independent, a result of the laser-trimmed reference. For applications which require output-voltage tracking or soft-start operation for multirail sequencing, the LTC3600 offers those capabilities via a programmable package pin. Internal N-channel power MOSFETs eliminate the need for separate discrete devices. Quiescent supply current is below 1 μA, and the regulator is designed to provide output regulation and fast transient response independent of the output voltage.

Users can set the operational switching frequency between 200 kHz and 4 MHz, which lets them select small, low-cost passive components. Efficiency is in the 96% zone although Dobkin pointed out that he prefers to also look at power loss; the graph shows the relationship between the two factors versus output current values.

Graph shows the relationship between efficiency and power loss

at various load currents.

Packaging, pricing, and availability: The LTC3600 is available in a 12-lead 3×3 mm DFN, as well as a thermally enhanced MSOP; it is priced at $2.80 each in either package (1000 pieces). Wider-range industrial-grade versions are also available for -40⁰C to +125⁰C operation, priced at $3.22.

For more information: go to http://www.linear.com/product/LTC3600.