Buck Converter Steps Size Down to Chip Scale

Aug 1, 2008 12:00 PM
By David Morrison, Editor in Chief

When Texas Instruments developed the TPS62601 500-mA synchronous buck converter, it had one paramount goal in mind: small size. To achieve this objective, the company upped its switching frequency to 6 MHz, fixed the output voltage at 1.8 V and squeezed its monolithic converter into a 0.9-mm × 1.3-mm chip-scale package.

When paired with two small ceramic capacitors and a 0.47-µH inductor, the TPS62601 forms a complete buck converter in just 13 mm² of pc-board area (Fig. 1). With that solution size, the company claims it offers the industry's smallest 500-mA stepdown dc-dc converter. And with a 0.6-mm profile — for both the converter and the recommended inductor — the buck converter design is among the industry's thinnest.

These claims can be evaluated by comparing the TPS62601 against devices such as Micrel's MIC2285 (500 mA) and MIC2285A (600 mA), National Semiconductor's LM3691 (1000 mA) and Enpirion's EP5368 (600 mA). (Note: see table of comparative specifications for these devices.)

The TPS62601 is intended to generate secondary voltage rails in portable applications such as smart and media phones, cell phones, media players and mobile Internet devices. Within these types of products, the chip can be used to power various types of modules such as those for WLAN, WiFi, Bluetooth and memory. The TPS62601 accepts an input voltage ranging from 2.3 V to 5.5 V to produce a 1.8-V output with ±1.5% total dc voltage accuracy.

According to the vendor, the device was developed with a fixed output voltage to eliminate the need for the two external resistors that would otherwise be needed to program the output voltage.

The TPS62601 operates with up to 89% efficiency when stepping down a 2.7-V input to 1.8 V. With a 3.6-V input, the efficiency peaks in the mid-80s (Fig. 2). Efficiency also will depend on whether the device operates in pulse-width modulation (PWM) or pulse-frequency modulation (PFM) mode.

The part switches automatically between these two modes or can be forced to remain in the PWM mode for noise-sensitive applications. In the PFM mode, quiescent current drops to 30 µA typ. (45 µA max). In the shutdown mode, current draw falls to 1 µA max.

Other features include a 35-ns minimum on-time, internal soft-start with less than 200 µs required for startup and protection against overcurrent and overtemperature conditions. The company also claims best-in-class performance for load and line transient response. (See pages 7-9 of the product data sheet for data on transient performance.)

The operating temperature range is specified at -40°C to 85°C. The TPS62601 is available now with pricing at $1.45 each in 1000-unit quantities. The company also offers an evaluation module (TPS62601EVM-327) and application notes. For more information, see www.ti.com/tps62601-pr.

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