Monolithic Regulators Migrate to Higher Voltages

Aug 1, 2007 12:00 PM
By David Morrison, Editor, Power Electronics Technology

Click here for the enhanced PDF version of this article including diagrams and/or equations.

In last month's column, we looked at the development of monolithic switching regulators that were primarily aimed at portable applications, as reflected in their small sizes and low input-voltage ranges. However, several new regulator chips are springing up to address higher-voltage and higher-power requirements for buck converters.

Like their low-voltage counterparts, these monolithic regulators promise high efficiency and compact designs, though at lower switching frequencies than the low-voltage parts and with the conventional external inductor. Two recently introduced ICs illustrate some of the performance capabilities of the higher-voltage parts.

For example, in July, Intersil unveiled a family of high-efficiency 2-A stepdown regulators that support input voltages as high as 60 V, while handling transient spikes as high as 100 V for 400 msec. One family member, the ISL8560, accepts input voltages ranging from 9 V to 60 V and produces a programmable output ranging from 1.21 V to 55 V.

Another device in this family, the ISL8540, accepts an input-voltage range of 9 V to 40 V and produces programmable output in the range of 1.21 V to 35 V. The ISL8560 and ISL8540 target applications such as industrial and automotive power supplies, portable computers, battery chargers and distributed power systems. The ISL8540 and ISL8560 include an integrated boot diode and high-side, integrated power DMOS low-resistance (R_DSON = 1.9 mΩ typical) transistor capable of supporting up to 2-A continuous load current. Switching frequency is adjustable from 100 kHz to 600 kHz, and the regulator allows for external frequency synchronization.

The ISL8540 and ISL8560 provide enable and power-good pins that allow output sequencing. Both devices contain protection features such as overtemperature, undervoltage, pulse-by-pulse overcurrent and hiccup-mode short-circuit protections.

The ISL8540 is currently available in a 20-lead HTSSOP package starting at $2.79 per device in quantities of 1000. The ISL8560 is available now in a 20-lead 6-mm × 6-mm QFN starting at $2.97 per device in quantities of 1000. For more details, see www.intersil.com.

This month, Linear Technology is introducing a high-efficiency high-power synchronous buck regulator. Housed in a 64-pin, 9-mm × 9-mm QFN, the LTC3610 delivers up to 12 A at voltages as low as 0.6 V, while operating from inputs ranging from 4 V to 24 V (see the figure).

This input-voltage range makes the LTC3610 well suited for applications powered by multi-cell Li-ion or lead-acid batteries. The regulator can also be used as a point-of-load converter in applications with a 5-V, 12-V or even 24-V intermediate voltage bus. The company is also planning to introduce a version with an input-voltage range that extends up to 36 V. This device, the LTC3610HV, is due out in the fourth quarter.

The LTC3610 uses valley current control to permit very low duty-cycle operation (minimum on time is ≤ 100 nsec) at high frequencies with fast transient response. The operating frequency is selected by an external resistor and is compensated for variations of V_IN and V_OUT. Switching frequencies of up to 1 MHz allow the utilization of small ceramic capacitors and low-profile inductors. Depending on duty cycle and output-current conditions, the regulator may even be operated at switching frequencies as high as 2 MHz.

On-chip switches feature R_DSON values of 12 mΩ and 6.5 mΩ, enabling efficiencies as high as 95%. The LTC3610 can be configured for discontinuous or forced continuous operation. Quiescent current is just 900 µA typical under normal operation and reduces to 15 µA typical in shutdown.

Additional features include a power-good voltage monitor, an adjustable current limit, output-overvoltage protection and programmable soft-start. Pricing for the LTC3610 starts at $8.50 each in 1000-piece quantities. For more information, visit www.linear.com.