LINEAR dn428f Data Sheet

Tiny Synchronous Step-Up Converter Starts Up at 700m V Design Note 428 Dave Salerno Introduction a typical startup voltage of just 700m V, with operation

Alkaline batteries are convenient because they’re easy to down to 400m V once started. Despite the LTC3526L’s fi nd and relatively inexpensive, making them the power tiny solution size, it includes many advanced features, source of choice for portable instruments and devices including output disconnect, short circuit protection, low used for outdoor recreation. Their long shelf life also noise fi xed frequency operation, internal compensation, makes them an excellent choice for emergency equipment soft-start, thermal shutdown and Burst Mode® operation that may see infrequent use but must be ready to go on a for high effi ciency at light load. For low noise applica-

moment’s notice. It is important that the DC/DC convert- tions, the LTC®3526LB offers fi xed frequency operation ers in portable devices operate over the widest possible at all load currents. With an output voltage range that battery voltage range to extend battery run time, and thus extends down to 1.5V, the LTC3526L and LTC3526LB can save the user from frequent battery replacement. even be used in applications previously requiring a boost

converter followed by a buck converter.

Single-cell alkaline batteries, with a 1.6V to 0.9V range, present a special challenge to DC/DC converters because A typical single-cell boost application is shown in Figure of their low voltage and the fact that their internal resis- 1. In this example the LTC3526LB is used to generate tance increases as the battery discharges. Thus, a DC/DC 1.8V for a Bluetooth radio application. The LTC3526LB converter that can both start up and operate effi ciently at was selected for its small size, minimal external com- low input voltages is ideally suited for single-cell alkaline ponent count and low-noise, fi xed frequency operation products. at all load currents. A graph of output current capability

versus input voltage is shown in Figure 2. Note that the

The LTC®3526L is a 1MHz, 550m A synchronous step-

converter starts up at 700m V at no load and once run-

up (boost) converter with a wide input voltage range of 0.7V to 5V and an output voltage range of 1.5V to 5.25V.

, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Housed in a 2mm × 2mm DFN package, the LTC3526L has Corporation. All other trademarks are the property of their respective owners.

STARTUP (RESISTIVE LOAD)

STARTUP (CONSTANT CURRENT LOAD) AFTER STARTUP

0.7V TO 1.8V

VIN VOUT

LTC3526LB

CIN COUT

2.2μF OFF ON SHDN FB

GND R1 1.62MEG DN428 F01

CIN: MURATA GRM188R61A225K L1: FDK MIPF2520D4R7 COUT: MURATA GRM188R60J475K

0.4 1.20.8 1.4 1.6 1.81.00.6 VIN (V)

DN428 F02

Figure 1. Single-Cell 1.8V Boost Converter for a Bluetooth Radio Application Features a Low Startup Voltage Figure 2. Maximum Load and Uses a Monolithic Chip Inductor for a Maximum Capability During and After Component Height of Just 1mm. Startup for the Circuit in Figure 1.