LINEAR LT8415 User Manual

DESIGN IDEAS L

Low Power Boost Regulator with Dual Half-Bridge in 3mm × 2mm DFN Drives MEMS and Piezo Actuators

by Jesus Rosales

Introduction

Advances in manufacturing technol- making it an ideal match for driving 2.6V–5V Input to 34V Output ogy have made it possible for actuators, low current MEMS. MEMS Driver

sensors, RF relays, and other moveable The LT8415 generates output volt- Figure 2 shows a MEMS driver that parts to be manufactured at a very ages up to 40V from sources ranging takes a 2.6V–5V input and produces small scale. These devices, referred from 2.5V to 16V. The output is then a 34V output. This circuit draws very to as MEMS (micro-electro-mechani- available for the integrated comple- little source current when the dual cal systems) or micro-machines, are mentary half-bridge drivers and is half-bridge is disabled. The input finding their way into daily life in available via OUT1 and OUT2 (see Fig- current is only 320µA at 2.6VIN and applications unheard of just a few ure 1). Each half-bridge is made up of 128µA at 5VIN. A logic level signal at years ago. MEMS are used in automo- an N-channel MOSFET and a P-chan- IN1 and IN2 activates the dual half- tive, military, medical and consumer nel MOSFET, which are synchronously bridge switches. Figure 3 shows the product applications. controlled by a single pin and never turn-on delay and rise time for OUT1 Many types of MEMS devices con- turn on at the same time. OUT1 and and OUT2 with both half-bridges ac- sume very little power to operate and OUT2 are of the same polarity as IN1 tivated. Figure 4 shows the turn-off generally require the use of two sup- and IN2, respectively. When the part is delay and fall time with the 200p F port circuits, a step-up converter and a turned off, all MOSFETs are turned off, and 1n F capacitive loads shown in dual half-bridge driver. These support and the OUT1 and OUT2 nodes revert Figure 2. See the data sheet details circuits must be very small and highly to a high impedance state with 20MΩ for measuring delay time. efficient to keep pace with ever-shrink- pull-down resistors to ground. ing MEMS applications. To this end, the LT8415 integrates the step-up

converter power switch and diode and

the dual half-bridge driver in a 12-pin, VIN 2.6V to 5V C1

3mm × 2mm DFN package. Its novel 22n F

SW CAP

switching architecture consumes very

VCC VOUT

little power throughout the load range,

LT8415 0.1µF SHDN OUT 1 34V/0V

IN 1 OUT 2 34V/0V

LOGIC 1n F

LEVEL VREF IN 2

BOOST VOUT

GND FBP

ENABLE

CONVERTER 40V MAX

L1: COILCRAFT DO2010-104ML

Figure 2. 2.6V–5V input to 34V dual half-bridge boost converter

IN1 OUT1

OUT1 10V/DIV OUT2 10V/DIV

OUT1 10V/DIV OUT2

IN2 OUT2

10V/DIV

IN1/IN2

IN1/IN2

1V/DIV

1V/DIV

LT8415

5µs/DIV 5µs/DIV

Figure 1. Simplified block diagram of the Figure 3. Turn-on delay and rise time for OUT1 Figure 4. Turn-off delay and fall time for OUT1 LT8415 and OUT2 and OUT2

Linear Technology Magazine • September 2009