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LX1692B

Full Bridge Resonant CCFL Controller

Microsemi Corporation 

LX1692B

TM

®

Full Bridge Resonant CCFL Controller

PRODUCTION DATA SHEET

Name

C_BST

C_TO

VDDA

ENABLE

BRITE_D

ICOMP

VCOMP

BRITE_A

VIN_SNS

FUNCTIONAL PIN DESCRIPTION (CONTINUED)

Description

Burst dimming mode frequency set capacitor. Internal bias currents set via the I_R pin are scaled down and

used to charge and discharge the capacitor connected at the C_BST pin. The voltage at the C_BST pin is a

sawtooth waveform displaying a voltage that ranges from 0.5V to 2.5V. The frequency of the PWM for digital

dimming is set by the I_R and C_BST pins.

FDIM

= 98039

CC _ BST .RI _ R

where RI_R is in KΩ

and CC_BST is in nF, FDIM is Hz

The internal burst oscillator frequency can also be forced to follow an external clock signal at this pin. In this

case, the programmed frequency must be lower than the external frequency.

Time Out set capacitor. An external capacitor is charged with an on chip current source to create a voltage

ramp. Over voltage fault shutdown is disabled until C_TO voltage rises above 3.5V, providing a user

programmed strike interval. Strike Interval time is t = 0.035RI _ R ⋅ CC _ TO where RI_R is in KΩ and CC_TO is in µF

Analog Voltage Regulator Output. This output pin is used to connect an external capacitor to stabilize and filter

the on-chip LDO regulator. The input of the LDO is the switched VDDP supply. The LDO output is nominally

4.0V and is used to drive all circuitry except the output buffers at AOUT, BOUT, COUT and DOUT. The drop

out voltage is typically 0.05V at 2mA; the average internal load. This output can supply up to a 5mA external

load. The output capacitor should be a 100nF ceramic dielectric type.

Chip Enable Input. If logic high, all functions are enabled. If logic low, internal power is disconnected from the

VDDP pin, disabling all functions. Logic threshold is 1.85V/1.35V maximum over supply and temperature range.

Maximum current into VDDP when ENABLE < 0.8V, is 50µA. ENABLE may be connected directly to VDDP if

the disable function is not used.

Brightness Control Input for digital dimming. The input signal can be a DC voltage or low frequency PWM

signal. Active DC voltage range is 0.5V to 2.5V. Signals above 2.5V makes continuous operation, voltages

between 0.5V and 2.5V makes PWM digital dimming. Digital dimming pulse width varies from 100% duty at

2.5V to 0% duty at 0.5V. A minimum BRITE_D input voltage (externally supplied) of approximately TBDV is

required to prevent fault stop. PWM inputs from either 3.3V or 5V logic are permissible. Frequency may range

up to 1KHz. Max jitter of more than 1µs/V on this input may cause noticeable lamp flicker. Refer to Dimming

configuration Table for setting.

Error Amp Output for the lamp current regulator. This error amplifier is a gm type and does not require an

external capacitor for stability. An External capacitor is connected from this pin to Ground to adjust loop

response of the inverter module. This capacitor value can vary from 0.1nF to 33nF as required by specific

applications. Error amplifier output voltage is not allowed to exceed the peak voltage of its associated

comparator ramp by more than 10%.

Voltage loop compensation pin for transformer output voltage regulation. An external capacitor is connected

from this pin to Ground to adjust loop response. An external resistor divider can be connected to limit the

maximum output duty cycle while the IC is operating in strike mode.

Brightness control input for analog dimming. The input signal can be a DC voltage or a PWM signal that has

been externally filtered to DC. Active DC voltage range is 0 to 2V. Signals above 2V and below 0.45V are

clamped and do not change amplitude of output current.

Input voltage sense pin. An external resistor and capacitor are connected to this pin to control slope of the

oscillator timing ramp. Ramp slope becomes steeper as the external bridge power supply increases providing

rapid line voltage transient response.

Copyright © 2005

Rev. 1.1, 12/20/2006

Microsemi

Integrated Products Division

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

Page 3

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