LINEAR dn359f Data Sheet

advertisement

Dual DC/DC Converter with Integrated Schottkys Generates ±40V Outputs and Consumes Only 40µA Quiescent Current Design Note 359 David Kim Introduction Dual Output ±20V Converter As portable devices become more sophisticated and Figure 1 shows a ±20V LCD bias voltage supply using the require higher display resolution, there is an increased LT3463. This circuit generates both positive and nega- demand for accurate, high voltage bias supply solutions tive 20V outputs from a Li-Ion battery. Low profile with wide input and output voltage ranges. The traditional inductors and capacitors keep the circuit under 9mm × methods of using arrays of capacitors to implement a 9.5mm × 1.2mm, making this circuit ideal for small charge pump or a bulky and expensive transformer no wireless devices such as cellular phones or DSCs. longer meet the accuracy and size requirements of today’s

This design can produce ±20V at 9m A from a 2.7V input

portable devices. EF FI CI EN CY

and up to 20m A from a 5V input. The efficiency shown in

The LT®3463 is both accurate and compact. It fits both a Figure 2 exceeds 70% over a wide load current range reach-

positive output converter plus a negative output converter ing 75% at 20m A. The LT3463’s constant off-time archi- into a tiny (3mm × 3mm)DFN package, including Schottky tecture allows 20µA quiescent current operation for each diodes and switches capable of 250m A (400m A on the output, making the LCD bias circuit efficient even at 100µA negative channel of the LT3463A). load current. This circuit can accommodate different load voltages as the LCD bias voltage varies for different manu-

The LT3463 works in a wide range of applications due to

facturers (typically 9V ~ 25V).

its 2.3V to 15V input voltage range and output capability

, LTC and LT are registered trademarks of Linear Technology Corporation.

to ±40V. Each converter is designed to operate with a

All other trademarks are the property of their respective owners.

quiescent current of only 20µA, which drops to less than 1µA in shutdown, making the LT3463 solution ideal for battery-powered portable applications.

L1 VIN 10µH VOUT1

2.7V 20V TO 5V C1 R2 9m A

20V OUTPUT

VIN SW1 VOUT1

–20V OUTPUT

SHDN1 FB1 LT3463 VREF

SHDN2 FB2

GND SW2 D2

10µH VOUT2 –20V

D1: DIODES, INC. B0540W LOAD CURRENT (m A)

L1, L2: MURATA LQH32CN100K53 DN359 F02

DN359 F01

Figure 1. Dual Output ±20V Converter Figure 2. Efficiency of Circuit in Figure 1 at VIN = 3.6V