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LX1691 Datasheet(PDF) 10 Page - Microsemi Corporation |
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LX1691 Datasheet(HTML) 10 Page - Microsemi Corporation |
10 / 15 page Microsemi Integrated Products 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 Copyright © 2003 Rev. 1.0, 7/16/2004 LX1691 Enhanced Multi-Mode CCFL Controller PRODUCTION DATA SHEET TM ® DE TAILED DESCRIP T ION FEATURE REVIEW On-Chip LDO Regulator An LDO regulator keeps critical analog control circuits operating optimally over the entire input voltage range. Brightness control voltage and operating frequency are extremely stable. Under Voltage Lockout If the battery input voltage is too low for the controller to function properly, it will turn itself off, preventing spurious operation. If the battery voltage falls to less than 1V where UVLO is no longer guaranteed, 10K pull down resistors on the AOUT and BOUT pins insure the external power FETs cannot be biased on. Power On Delay A power up reset that delays AOUT and BOUT turn on for approximately 100 milliseconds after power is applied. This give 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. Enhanced BRITE Conditioning Circuitry The BRITE_IN pin offers a high impedance input with a linear 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 LX1691 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 be the clocks frequency divided by 512. When using the internal clock source the burst frequency will be the internal oscillator divided by 1024 which is equivalent to lamp current frequency divided by 512. Brightness Polarity and Dual Mode Dimming Control In Analog dimming mode the IC can be programmed to either increase or decrease lamp current amplitude as a function of 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 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. Lamp current amplitude can be set and varied by applying a separate DC voltage at the BRITE_OUT pin. This voltage can range from zero to 2.0 VDC. Zero volts will produce zero current (and therefore a lamp fault). 2.0V will produce the maximum current as defined by the value of the current sensing resistor from ISNS to GND. Strike Voltage Generation Improved strike voltage generation circuits ramp strike voltage slowly to programmed maximum potential and hold it there for approximately 350mSec @65Hz operating frequency. This 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. Strike Detection The LX1691 includes a new lamp strike detection scheme that saves a package pin and three external components. Internal circuits monitor lamp current pulses at the I_SNS input to determine if the lamp strikes and if it stays ignited once operational. Fault Time Out If the lamp fails to ignite within approximately 350mSec, 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 three lamp inputs significantly reduces lamp feedback component count. Current Sense (I_SNS), Over Current Sense (OC_SNS) and Over Voltage Sense (OV_SNS) signals are detected using only one external scaling resistor or capacitor each. Rectification accuracy is improved with high performance on chip rectifiers to provide better lamp current and voltage regulation. Complete Fault Protection In addition to the lamp fault time out, maximum output voltage and current under all fault conditions is regulated. Open circuit voltage can never go higher than the preset maximum strike potential and total current from the circuit is safely limited with a scaling resistor. UL safety specifications can now be easily met in any application. Familiar Magnetics The LX1691 can use the same magnetics as all other Direct Drive controllers. Refer to Application Note 13 for transformer design and power FET selection criteria. |
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