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ACT6330

Dual PWM Step-Up DC/DCs in TQFN33

Active-Semi, Inc 

ACT6330

Rev0, 02-Apr-08

WLED BIAS DC/DC CONVERTER (REG1)

FUNCTIONAL DESCRIPTION

General Description

REG1 is highly efficient step-up DC/DC converter

that employs a fixed frequency, current-mode,

PWM architecture. This regulator is optimized for

white-LED bias applications consisting of up to six

white-LEDs.

Over-Voltage Protection

REG1 features internal over-voltage protection

(OVP) circuitry which protects the system from LED

open-circuit fault conditions. The ACT6330’s OVP

threshold is set at 22V, and if necessary, regulates

the voltage at the top of the LED string to ensure

that it never exceeds this voltage. REG1 requires a

10kΩ resistor connected from output capacitor to

OVP1 pin.

Thermal Shutdown Protection

The ACT6330 integrates thermal shutdown protec-

tion circuitry to prevent damage resulting from ex-

cessive thermal stress, as may be encountered un-

der fault conditions. This circuitry disables all regu-

lators if the ACT6330 die temperature exceeds

160°C, and prevents the regulators from being en-

abled until the IC temperature drops by 20°C (typ).

Enabling and Disabling REG1

REG1 is enabled or disabled using ON1. Drive ON1

to a logic-high to enable REG1. Drive ON1 to a

logic-low to disable REG1, reducing supply current

to less than 1µA. As with all non-synchronous step-

up DC/DC converter, REG1’s application circuit pro-

cedures a DC current path between the input and

the output in shutdown mode. Although the forward

drop of the WLEDs makes this leakage current very

small in most applications, it is important to con-

sider the effect that this may have in your applica-

tion particularly when using fewer than three

WLEDs.

Compensation and Stability

REG1 utilizes current-mode control and an internal

compensation network to optimize transient per-

formance, ease compensation, and improve stabil-

ity over a wide range of operating conditions. REG1

is a flexible regulator, and with just a simple compo-

nent, choice can be optimized to achieve minimum

total solution size in applications that require the

smallest possible footprint, or can be optimized to

achieve the highest possible efficiency.

Inductor Selection

REG1 has been designed to provide excellent per-

formance across a wide range of applications, al-

lowing a design to be optimized for both a small

footprint as well as for achieving the highest possi-

ble efficiency. REG1 was designed for operation

with inductor in the 10µH to 22µH range, in order to

achieve a small footprint , although larger inductor

values of up to 68µH can be used in order to opti-

mize a design to achieve the highest possible effi-

ciency.

Optimizing for Smallest Footprint

REG1 is capable of operating with very low inductor

values in order to achieve the smallest possible

footprint . When solution size is of primary concern,

best results are achieved when an inductance value

that ensures discontinuous conduction mode (DCM)

operation over the full load current range is used.

Optimizing for Highest Efficiency

REG1 achieves excellent efficiency in applications

that demand the longest possible battery life. When

efficiency is the primary design consideration, best

results are achieved when an inductance value that

both results in continuous conduction mode (CCM)

operation and achieves a very small inductor ripple

current is chosen.

Output Capacitor Selection

REG1 is designed to operate with output capacitors

ranging from 1µF to 10µF, providing design flexibil-

ity. A 1µF output capacitor is suitable for most appli-

cations, although larger output capacitors may be

used to minimize output voltage ripple, if needed.

Ceramic capacitors are recommended for most ap-

plications.

Rectifier Selection

REG1 requires a Shottky diode to rectify the induc-

tor current. Select a low forward voltage drop Shot-

tky diode with a forward current (IF) rating that is

sufficient to support the maximum switch current

and a sufficient peak repetitive reverse voltage

(VRRM) to support the output voltage.

Innovative PowerTM

-7-

ActivePMUTM is a trademark of Active-Semi.

www.active-semi.com

Copyright © 2008 Active-Semi, Inc.

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