User's Guide
SNVA506A–October 2011–Revised May 2013
AN-2196 LM3435 Evaluation Board
1 Introduction
The Texas Instruments LM3435 Evaluation Board has been designed for evaluating the performance of
the device in a typical pico projector application. The end user can interface his own system to the
evaluation board to test out the performance of the system. With LM3435, the system requires only single
DC-DC converter to drive three color LEDs instead of using three DC-DC converters with conventional
design. The suggested approach not only saves components cost, but also releases invaluable PCB
space to the system and enhances system reliability. Assuming the handy projector is powered by a single
lithium battery cell or a 5Vdc wall mount adaptor, the key specifications of the evaluation board are:
Supply voltage range, V
IN
= 2.7V to 5.5V
Preset LED current per channel, I
LED
= 1.5A
Minimum LED current per channel, I
LED(MIN)
= 600mA
Maximum LED forward voltage drop, V
LED
= 3.5V @ 1.5A
Flyback converter switching frequency, F
SW
= ~500kHz
2 Evaluation Board Schematic Diagram
The complete schematic diagram of the evaluation board is shown in Figure 1. For the details of the
design, please see LM3435 Compact Sequential Mode RGB LED Driver with I2C Control Interface
(SNVS724).
3 Connecting the Evaluation Board to the System
The LM3435 Evaluation Board is optimized to run with input voltages ranging from 2.7V to 5.5V and
requires a supply current not less than 4.1A for full range operation. A connection diagram to show the
configuration between the system and the evaluation board is shown in Figure 2. Proper connections to
the I/Os must be confirmed before powering up the board. In order to avoid false triggering of the
OPEN/SHORT fault detect of the device, the control pins GCTRL, BCTRL, and RCTRL must be kept in
logic “LOW” during power-up.
4 Interfacing with the I
2
C Bus
The current setting resistors only determine the nominal maximum LED current and the actual LED
current can be further adjusted on-the-fly by the internal ten bits register for individual channel. The
content of these registers are user programmable via standard I
2
C bus. The connection between the
system MCU and the I
2
C bus is illustrated in Figure 2. The resolution is 1 out of 1024 part of the LED
current setting. The user can program the registers in the range from full output, that is, 1023 (3FFH) to
minimum LED current that is restricted by the inductor ripple current amplitude. For Projected On-Time
(POT) scheme used in LM3435, a minimum inductor ripple current of 300mA
PK-PK
is required to maintain
proper operation. For the details of the registers addresses and definitions, please see LM3435 Compact
Sequential Mode RGB LED Driver with I2C Control Interface (SNVS724).
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SNVA506A–October 2011–Revised May 2013 AN-2196 LM3435 Evaluation Board
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