LINEAR LTC3587 User Guide Manual

L DESIGN FEATURES

±32V Triple-Output Supply for LCDs, CCDs and LEDs Includes Fault Protection in a 3mm × 3mm QFN

by Eko T. Lisuwandi

Introduction The task of designing a battery pow- component count produces a small, the switches are disabled. The LT3587 ered system with multiple high voltage efficient solution. Typical applications also includes a bidirectional fault pin supplies is a daunting one. In such include digital still and video cameras, (FLT), which can be used for fault systems board space is at a premium high performance portable scanners indication (output) or for emergency and high efficiency is required to and display systems, PDAs, cellular shutdown (input). extend battery life. Supplies must be phones and handheld computers that The LT3587 offers a wide output sequenced in start-up and shut-down, have high voltage peripherals such as range, up to 32V for the positive chan- and multiple supplies must be able to CCD sensors, LED backlights, LCD nels (channels 1 and 3) and –32V for maintain regulation without interac- displays or OLED displays. the inverter (channel 2). Channel 3 tion across supplies. is configurable as either a voltage or

The LT3587 is a 1-chip solution Features current regulator. When configured as

that combines three switching regu- To keep the component count low, the a current regulator, channel 3 uses a lators and three internal high voltage LT3587 integrates three high voltage 1-wire output that requires no current switches to produce two high voltage power switches capable of switching sense or high current ground return boost converters and a single high volt- 0.5A, 1A and 1.1A at up to 32V in lines, easing board layout. A single age inverter. The LT3587 is designed to a 3mm × 3mm QFN package. Each resistor programs each of the three run from inputs ranging from 2.5V to of the positive channels includes an channels output voltage levels and/or 6V, making it ideal for battery powered output disconnect to prevent a direct the channel 3 output current level. systems. Small package size and low DC path from input to output when Intelligent soft-start allows for

sequential soft-start of channel 1 fol- lowed by the inverter negative output

LED DRIVER

20m A UP TO 24V using a single capacitor. Internal sequencing circuitry disables the RVFB3 inverter until channel 1 output has

C4 VVIN

2.2µF 2.5V TO 6V reached 87% of its final value.

(OPTIONAL) L4 L1

DS3 C6

Triple-Output Supply for CCD

VFB3 VOUT3 CAP3 SW3 VIN SW1 Imager and LED Backlight

DS1RIFB3 C1 10µF

8.06k Figure 1 shows a typical application

IFB3 CAP1

providing a positive and negative volt-

age bias for a CCD imager and a 20m A

LT3587

current bias for an LED backlight. All

FLT three channels of the LT3587 use a

EN/SS1 1M

constant frequency, current mode con-

FB1 CCD POSITIVE

EN/SS3

VOUT1 15V trol scheme to provide voltage and/or

C3 SW2 GND FB2

100n F current regulation at the output.

100n F C2 RFB2 CFB2 The positive CCD bias is config-

2.2µFL2 L3

CCD NEGATIVE ured as a simple non-synchronous

VVIN 15µH 15µH

2.5V TO 6V

100m A boost converter. Its output voltage is

DS2 C7

22µF set to 15V via the feedback resistor RFB1. The 15µH inductor (L1) is sized

C1: MURATA GRM21BR61C106KE15L CFB1: MURATA GRM1555C1H2R7BZ01D for a maximum load of 50m A. The C2: MURATA GRM188R61C225KE15D CFB2: MURATA GRM1555C1H6R8BZ01D

C3, C5: MURATA GRM033R60J104KE19D L1, L2, L3: SUMIDA CDRH2D18/HP-150N negative CCD bias is configured as a

C4: MURATA GRM21BR71E225KA73L L4: TOKO 1071AS-100M

non-synchronous Ćuk converter. Its

C6: MURATA GRM155R61A105KE15D DS1, DS2, DS3: IR IR05H40CSPTR C7: TAIYO YUDEN LMK212BJ226MG-T output voltage is set at –8V using the

feedback resistor RFB2. The two 15µH Figure 1. Solution for a Li-Ion powered camera provides positive and negative

supplies for biasing a CCD imager and an LED driver for a 5-LED backlight

Linear Technology Magazine • January 2009