LX1689
I N T E G R A T E D
P R O D U C T S
Third Generation CCFL Controller
P
RODUCTION
D
ATA
S
HEET
FUNCTIONAL PIN DESCRIPTION
(CONTINUED)
P
IN
N
AME
D
ESCRIPTION
BRITE Filter Capacitor and FAULT Output. Used to convert higher frequency digital PWM inputs to proportional
DC currents at the BRITE_OUT pin. The capacitor forms a low pass filter with an internal 200K resistor. This
pin will be driven to VDD_A if a lamp fault is detected by the LX1689. If no fault is present the voltage at this pin
will vary from 50mV to 1.05V as BRITE_IN varies from 0 to 2V. A CMOS gate may be connected to this pin to
sense the fault condition. TTL gates or other low impedance (less than 20 megohm) must not be connected to
this node as their DC resistance will load the internal 200K resistor and create error in the BRITE_OUT current
level.
Error Amp Inverting Input. Frequency Compensation input for the Error Amplifier. See EA_OUT below. A
100K, negative TC on chip resistor connected between the inverting input of the error amplifier and the output of
the I_SNS full wave rectifier is the resistor in an R/C loop compensation network.
Dedicated Bias resistor for BRITE_OUT current source.
Error Amp Output. Error amplifier is a GM type and does not require a external capacitor for stability. An
external capacitor is connected from this pin to EA_IN to adjust the loop response of the inverter module. This
capacitor value can vary from 100pF to 5000pF in various applications. This capacitor may also be connected
from the EA_OUT to ground.
Brightness Control Input. The input signal can be a DC voltage, a low frequency pulse width modulated digital
signal, or a high frequency pulse width modulated digital signal. Active DC voltage range is 0.5 to 2.0V. Signals
above 2V are clipped and signals below 0.5V make output current from the BRITE_OUT pin near zero. Low
frequency digital PWM signals up to 500Hz can be applied to affect Digital Dimming. Higher frequency PWM
signals, up to 100KHz are filtered to an equivalent DC current at the BRITE_OUT pin by adding a capacitor at
the BRITE_C pin. On chip signal conditioning amplifiers clip inputs above 2V so that lamp current amplitude is
not sensitive to the voltage level variations of a digital PWM input signal.
Brightness Reference Current Output. This variable current source is the mirror of BRITE_R current multiplied
by the voltage at BRITE_C (0 to 1.0V) when analog dimming is selected, or by 1.0V when digital dimming is
selected. It becomes the reference voltage to the lamp current error amplifier when applied to an external
precision resistor connected from the BRITE_OUT pin to ground. BRITE_OUT current:
WWW .
Microsemi
.C
OM
BRITE_C
EA_IN
BRITE_R
EA_OUT
BRITE_IN
I
BRITE_OUT
=
I
BRITE_R
×
1.0 (Digital Dimming Mode)
BRITE_OUT
I
BRITE_OUT
=
I
BRITE_R
×
V
BRITE_C
(Analog Dimming Mode)
V
BRITE_OUT
=
I
BRITE_R
×
R
BRITE_OUT
I
BRITE_R
=
1.00V
R
BRITE_R
ENABLE
Chip Enable Input. If logic high, all functions are enabled. If logic low, internal power is disconnected from the
V
_BATT
pin, disabling all functions. Logic threshold is about 1.2V. Maximum current into V_BATT when
ENABLE < 0.3V, V_BATT <28V, is 28 µA. ENABLE may be connected to V_BATT through a series resistor if
the disable function is not used. Resistor tolerance is ± 10%; and R value is:
[V_BATT
MIN
−
1.5V]
R
=
−
6
30x10 Amp
The Enable pin can be connected directly to 3.3/5V logic.
Current Reference Resistor Input. Connects to an external resistor that determines the magnitude of internal
bias currents. The nominal lamp frequency can be adjusted by varying this resistor value in the range of 10K to
150K Ohms.
1.00V
I
I_R
=
R
I_R
P
ACKAGE
D
ATA
P
ACKAGE
D
ATA
I_R
Copyright
2000
Rev. 1.0b, 2003-03-31
Microsemi
Integrated Products
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
Page 4
MICROSEMI [ MICROSEMI CORPORATION ]
