QUICK START GUIDE FOR DEMONSTRATION CIRCUIT
949A-A/949A-B
4.5A BOOST LED DRIVER WITH PWM DIMMING
4
50%
55%
60%
65%
70%
75%
80%
85%
90%
95%
100%
0 5 10 15 20 25
VS INP UT (V)
31.5V L ED
19V L ED12.5V LED
5V IN
Figure 2.
DC949A-A efficiency
TWO ICS, THREE TOPOLOGIES
DC949A has two build versions. DC949A-A uses the
LT3478-1 1A fixed LED current IC with internal
sense resistor. It can be set at full 1A current or less
than 1A LED current with CTRL1,2 resistor divider
network. DC949A-B uses the LT3478 adjustable
LED current IC with a required external sense resis-
tor to set the LED current. It can be set at LED cur-
rents above and below 1A. Please see the datasheet
for details regarding the use of the sense resistor
and setting the LED current. Both DC949A-A and
DC949A-B are built to provide 350mA LED current
in the boost LED driver topology.
Although DC949A is a boost LED driver, it can be
reconfigured for buck-boost mode LED driving and
buck mode LED driving. The datasheet details some
of these changes and the figures below show sam-
ple schematics with the demonstration circuit refer-
ence designators that can be used in the different
modes. There may be a cut or two required on the
PCB to make these changes. Please ask for further
documentation detailing the changes in DC949A for
conversion to buck mode or buck-boost mode LED
driving.
OPTIONAL LT3003 BALLASTER
The LT3003 is available for three-channel LED bal-
lasting. With 1A or less output using the DC949A,
three parallel channels of LED strings can be driven
and PWM dimmed in all three topologies using the
LT3003 with the LT3478-1 or LT3478. For details
regarding the connection of the LT3003 and the
LT3478 please see the LT3003 and LT3478 data-
sheets. When not being used, the LT3003 circuit
should be left unstuffed. Please note that there is a
small pad near the LT3478 Vc pin that connects in-
ternally to the LT3003 /OT2 output for overtemp
protection. It is shown in the schematic of the
LT3478 and it is easy to connect these functions
using the DC949A.
