LXMG1930-28-0x
PRODUCTION DATASHEET
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 800-877-6458, 714-898-8121, Fax: 714-893-2570
Page 7
Copyright © 2009
Rev. 1.1, 2009-11-25
3-String 5W LED Backlight Boost Driver Module
TM
®
WWW.Microsemi .COM
L
L
X
X
M
M
G
G
1
1
9
9
3
3
0
0
-
-
2
2
8
8
-
-
0
0
x
x
APPLICATION INFORMATION
LXMG1930-28-0x
4.75V to 28V
GND
BRITE_A
V
IN
ENABLE
500k
Voltage Source,
DAC, or
Potentiometer
0V to 2.2V
CSA
ANODE
CSB
CSC
ANODE
ANODE
Figure 1
20.5k
+5V
R
T
NTC
OT (pin 6)
V
RT
V
RT
=
5
20.5k + R
T
x R
T
Figure 2
The LED string current and therefore the brightness may be
controlled by the BRITE_A input. The typical dimming
range using the BRITE_A input alone is 10:1.
The BRITE_A input may come from a voltage output DAC
or other voltage source, a 500k digital or manual pot, or a
PWM signal in the range of 100 Hz to 25 kHz. The module
contains an internal 422k pull-up to typically 5V to provide
bias if using a pot. Logic levels may be used up to 5V,
however the inverter will reach maximum current at less than
100% duty cycle. This can be calculated as approximately
2.2V divided by the logic high voltage level; with 3.3V logic
level this corresponds to about 66% duty cycle for maximum
string current.
If you need to turn the module ON/OFF remotely, connect to
TTL logic signal to the ENABLE input.
It is to be noted that although the module provides for a wide
input voltage range 4.75V to 28V it is designed as a boost
only converter. Therefore the input voltage should not
exceed the LED string voltage.
Use of an external thermistor connected from OT pin to
ground will provide over temperature protection (see figure
2). The module can provide for the gradual scaling back of
LED string current until it is completely shut off based on the
voltage level impressed on the OT input. When the voltage
on the OT pin decreases below 2.48V the string current will
begin to decrease until it is completely shut off when OT
reaches 1.47V. This corresponds to a thermistor value of
about 8542 ohms at string current shutdown.
As an example using a 100k (at 25°C) NTC thermistor with a
B Constant of 4250 will provide a thermal profile where the
module will begin to scale back the LED string currents at a
temperature (as measured by the thermistor) greater than
60°C and shut down the string current if the temperature
exceeds 85°C.
Although the module provides open circuit string protection,
if the common LED high side drive voltage (Anode) is
directly shorted to ground this will result in damage to the
fuse and possible damage to the Schottky diode. Likewise if
any of the low side current sink drivers (CSx) are directly
shorted to ground it will result in damage to the fuse,
Schottky diode and possibly the LED string.
