LX1691A Ver la hoja de datos (PDF) - Microsemi Corporation

Número de pieza

componentes Descripción

Fabricante

LX1691A

Enhanced Multi-Mode CCFL Controller

Microsemi Corporation 

LX1691A

TM

®

Enhanced Multi-Mode CCFL Controller

PRODUCTION DATA SHEET

DETAILED DESCRIPTION

FEATURE REVIEW

On-Chip LDO Regulator

Lamp current amplitude can be set and varied by applying a

An LDO regulator keeps critical analog control circuits operating separate DC voltage at the BRITE_OUT pin. This voltage can range

optimally over the entire input voltage range. Brightness control from zero to 2.0 VDC. Zero volts will produce zero current (and

voltage and operating frequency are extremely stable.

therefore a lamp fault). 2.0V will produce the maximum current as

Under Voltage Lockout

defined by the value of the current sensing resistor from ISNS to

If the battery input voltage is too low for the controller to GND.

function properly, it will turn itself off, preventing spurious

Strike Voltage Generation

operation. If the battery voltage falls to less than 1V where UVLO Improved strike voltage generation circuits ramp strike voltage

is no longer guaranteed, 10K pull down resistors on the AOUT and slowly to programmed maximum potential and hold it there for

BOUT pins insure the external power FETs cannot be biased on.

approximately 1400mSec @65KHz operating frequency. This

Power On Delay

A power up reset that delays AOUT and BOUT turn on for

approximately 120 milliseconds after power is applied. This give

insures a worst case lamp will strike at any temperature. Strike

potential is removed immediately when the lamp strikes or if the

time limit is reached.

extra time for the BRITE_IN source voltage to stabilize so the lamp

is not inadvertently powered up at high brightness and then

suddenly lowered, creating an undesirable light flash.

Strike Detection

The LX1691A includes a new lamp strike detection scheme that

saves a package pin and three external components. Internal circuits

Enhanced BRITE Conditioning Circuitry

monitor lamp current pulses at the I_SNS input to determine if the

The BRITE_IN pin offers a high impedance input with a linear lamp strikes and if it stays ignited once operational.

control range of 0 to 2.0V The function of the pin depends on

which of six dimming modes the controller is programmed. (see

dimming table page 4) A new feature of the LX1691A allows the

DD_CLK input to control the burst frequency and duty cycle while

the BRITE_IN input controls the output current amplitude (see

additional information below).

Digital or Analog Dimming Modes

A DIM_MODE input pin selects either Analog or Digital mode.

In Analog mode DC voltage at BRITE_IN controls lamp current

amplitude. In Digital mode it controls digital dimming duty cycle.

When in Digital mode, the dimming burst frequency can be

synchronous to lamp current by selecting internal clocking, or to an

external clock. With an external clock source, burst frequency will

Fault Time Out

If the lamp fails to ignite within approximately 1400mSec, or if it

extinguishes after ignition, or if the clock signal at the DD_CLK pin

terminates when in external digital dim mode, the output drive is

shut down.

Fault mode will also be invoked if the lamp is short circuited or

left open for more than 350mSec.

On Chip Rectifiers

Integrating full wave rectifiers for each of two lamp inputs

significantly reduces lamp feedback component count. Rectification

accuracy is improved with high performance on chip rectifiers to

provide better lamp current and voltage regulation.

be the clocks frequency divided by 512. When using the internal

clock source the burst frequency will be the internal oscillator

Complete Fault Protection

In addition to the lamp fault time out, maximum output voltage

divided by 1024 which is equivalent to lamp current frequency and current under all fault conditions is regulated. Open circuit

divided by 512.

voltage can never go higher than the preset maximum strike potential

Brightness Polarity and Dual Mode Dimming Control

and total current from the circuit is safely limited with a scaling

In Analog dimming mode the IC can be programmed to either resistor. UL safety specifications can now be easily met in any

increase or decrease lamp current amplitude as a function of application.

increasing signal at the BRITE_IN pin by simply connecting the

DD_CLK input to VDDA or ground (see Dimming Table). If

simultaneous amplitude control and digital dimming is desired,

apply a PWM signal to DD_CLK. The lamp current waveform will

exactly follow DD_CLK (DD_CLK is not divided in this mode);

e.g., lamp current flows when DD_CLK is high and stops when it is

low.

In Digital dimming mode, lamp current duty cycle is either

directly or inversely proportional to DC input voltage at the

BRITE_IN pin, depending on the state of DD_CLK. If external

Familiar Magnetics

The LX1691A can use the same magnetics as all other Direct

Drive controllers. Refer to Application Note 13 for transformer

design and power FET selection criteria.

With external high side FET drivers, the LX1691A can be used in

full bridge resonant mode applications. It can employ industry

standard high voltage transformers commonly used in notebook

computers and desktop monitors. Please see separate application

note for more details.

clock is selected, duty cycle will be directly proportional to voltage

at BRITE_IN and the burst period will be DD_CLK period X 512.

Copyright © 2003

Rev. 1.0, 8/31/2004

Microsemi

Integrated Products

11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570

Page 10

Share Link: