User's Guide
SNVA336A–August 2008–Revised April 2013
AN-1823 LM3528 Evaluation Board
1 Introduction
The LM3528 is an asynchronous boost converter with two separate outputs. The first output (MAIN) is a
constant current source for driving up to six series white LED's. The second output (SUB) is configurable
as a constant current source for driving up to six series white LEDs, or as a feedback input to set a
constant supply voltage for organic light-emitting diodes (OLED) panel power. The maximum LED current
per output is set via a single external low power resistor. An I2C compatible interface allows for
independent adjustment of the LED current in either output from 0 to max current in 128 exponential
steps. When configured as a white LED + OLED bias supply the LM3528 can independently and
simultaneously drive a string of up to six white LED’s and deliver a constant output voltage of up to 21 V
for OLED panels.
The evaluation board is set up to drive two strings of six white LEDs (Nichia , NSSW008C, VF= 3.2 V at
20 mA). These are set up with six LEDs in the MAIN string and six LEDs in the SUB string. Alternatively,
resistors can be installed in the R1 and R2 pads to make the device a voltage output boost converter for
OLED display powering (see the output voltage setting OLED mode).
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USBL
1 2
15 16
RSCL
RSDA
D1
CIN
COUT
VIN
SW PGND
RSET
R1
HWEN/PGEN/GPIO
VIN/VUSB
SCL
SDA
USBR
15
12
16
SW
IN
OVP
MAIN
SUB/FB
SCL
SDA
GND VIO
SET
HWEN/PGEN/GPIO0
LM3528
A1
A2
A3
B1 B2 B3
C1
C2
C3
D1D2D3
GPIO1
R4
R5
D5S D4S D3S D2S D1S
D1MD2M
D3M
D4M
D5M
L1
RGPIO1
R2
OLED/LED
J1
1 3
2
PGND
MOPEN
SOPEN
D2
R3
VOUT
GPIO1
RGPIO
D6M
D6S
Introduction
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Figure 1. LM3528 Evaluation Board Schematic
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LM3528 Evaluation Board Bill of Materials (BOM)
2 LM3528 Evaluation Board Bill of Materials (BOM)
Texas Instruments Silicon Revision Package Mark Package
LM3528 A1 SE YFQ0012AAA
Table 1. Board Bill of Materials
Component Symbol Value Mfr. Part No
L1 10 µH, ISAT = 790 mA TDK VLF4012AT-100MR79
CIN 1 µF, 10 V TDK C1608JB1A105M
COUT 1 µF, 25 V TDK C1608JB1E105M
D1M-D6M White LED Nichia NSSW008C
D1S-D6S White LED Nichia NSSW008C
RSDA 10 kΩVishay CRCW06031002F
RSCL 10 kΩVishay CRCW06031002F
RPU 1 MΩVishay CRCW06031004F
Diodes
D1 Schottky, 500 mA Incorporated SDM20U30 (SOD-523)
D2 Red LED Stanley Electric HKR1105W
R1 Not Installed
R2 Not Installed
R3 205 ΩVishay CRCW06032050F
R4 0 ΩVishay CRCW0603
R5 0 ΩVishay CRCW0603
RSET 12.1kΩVishay CRCW06031212F
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Board Operation
Figure 4. Mid Layer 2(Board Layout)
Figure 5. Bottom View (Board Layout)
4 Board Operation
To operate the LM3528 evaluation board, connect a 2.5 V to 5.5 V supply between the IN header and
GND and attach an I2C interface using one of the methods described in Section 5.
5 External Control Interface
There are two methods for controlling the LM3528 evaluation board. The first option is via a Texas
Instruments USB interface board. The second option is by using the SDA and SCL headers available on
the upper left corner of the board. When option 1 is used, the USBL and USBR connectors plug directly
into a Texas Instruments USB interface board. The connectors are keyed so they will only fit one way. On
the LM3528 evaluation board the VIN/VUSB jumper allows for power to come from IN or from the USB .
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Basic Connections (see )
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The USB board can supply 3.3 V from an on board regulator or 5 V directly from the PC (see
documentation for the Texas Instruments USB interface board). When power from the USB is desired
connect a jumper across VIN/VUSB, if power is supplied from the IN header leave VIN/VUSB open. DO
NOT jumper VIN/VUSB while an external source is connected to IN as this will make a conflict between the
USB board and the external power supply.
The USB interface board interfaces directly with the LM3528.exe graphical interface via the PC, see
Section 7. If the LM3528.exe program is not used, control of the LM3528 evaluation board can be done by
connecting an external I2C compatible interface directly to the SCL and SDA headers. Both the SDA and
SCL lines have 10 kΩpull-ups installed on the board.
6 Basic Connections (see Figure 1)
The LM3528 evaluation board is configured for two strings of six LEDs. There are two resistor pads on the
bottom side of the board, R1 and R2, that serve as feedback resistors for the operation of the LM3528 in
voltage output mode (OLED mode). When operating in OLED mode (with D1S – D6S installed), the
OLED/LED jumper must be installed in order to connect the center tap of the resistive divider (R1 and R2)
to the SUB/FB pin. Additionally (in OLED mode), the SOPEN header should be removed, otherwise, the
secondary LED string interferes with the feedback divider and causes erratic operation.
6.1 Jumper Connections/Component Descriptions
• J1 is a 3-pin, 3-position jumper. The leftmost pin (pin 1 in Figure 1) connects to the 3.3 V supply from
the USB board (pin 14 on the USBL connector). The rightmost pin (pin 3 in Figure 1) connects to IN.
The top middle pin (pin 2 in Figure 1) connects to VIO of the LM3528, the top side of the pull-up
resistors (RSDA, RSCL, RGPIO, RGPIO1), and the anode of the indicator diode D2.
• The SOPEN and MOPEN jumpers allow for the disconnection of the LEDs from the LM3528’s output.
SOPEN opens the SECONDARY (SUB/FB) LED string while MOPEN opens the MAIN LED string.
This is useful in testing OVP or disabling a string if OLED mode is required.
• The 5-pin, 5-position jumpers (2/3/4/5/6 LEDM and 2/3/4/5/6 LEDS) located above the MAIN and
SECONDARY LED strings, respectively, allow for shorting out of different LEDs in both the MAIN and
the SECONDARY strings. Both jumpers have their center pin (pin 5 in Figure 1) connected to the
cathode of the sixth LED in each string. Referring to jumper 2/3/4/5/6 LEDs, connecting pin 4 to pin 5
will short D6S, thus, making the SECONDARY string a five-LED configuration. Connect pin 3 to pin 5
to short D5S and D6S resulting in a four-LED configuration. Connect pin 2 to pin 5 for a three-LED
configuration (D4S – D6S shorted). Connect pin 1 to pin 5 for a two-LED configuration (D3S – D6S
shorted), and leave jumper 2/3/4/5/6 LEDS open for a six-LED configuration. The operation for jumper
2/3/4/5/6 LEDM is the same, only it applies to the MAIN LED string.
• Resistors R4 and R5 have 0 Ω’s across them. The 0 Ωresistors can be replaced with current sense
resistors for measuring LED current. Two vias have been placed at the terminals of each resistor,
which fit standard 0.1” headers.
• The OLED/LED jumper connects or disconnects the resistive divider from the SUB/FB node. In white
LED mode, the jumper should be open. In OLED mode, the jumper should be shorted so the SUB/FB
node can regulate VOUT at a constant voltage.
• D2 is a RED indicator diode that flashes the programmed pattern, programmed into the PGEN
registers (see the LM3528 High Efficiency, Multi Display LED Driver With 128 Exponential Dimming
Steps and Integrated OLED Power Supply in a 1.2mm × 1.6mm DSBGA Package Data Sheet
(SNVS513)). R3 is a 205 Ωcurrent limiting resistor for D2. RGPIO is a 1 MΩpull-up resistor for the
HWEN/PGEN/GPIO output. On power up, the HWEN/PGEN/GPIO output defaults as an active high
hardware enable (HWEN). RGPIO is installed to ensure that HWEN/PGEN/GPIO pulls high on start-
up.
7 LM3528–USB Interface Board and I2C Compatible Interface Program
In order to fully evaluate the LM3528, the use of an “I2C Compatible” interface must be used for any
functionality to occur. The detailed description regarding the interface control, the LM3528 registers, and
OLED mode is described in the LM3528 High Efficiency, Multi Display LED Driver With 128 Exponential
Dimming Steps and Integrated OLED Power Supply in a 1.2mm × 1.6mm DSBGA Package Data Sheet
(SNVS513).
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LM3528–USB Interface Board and I2C Compatible Interface Program
TI has created an I2C-compatible program (see Figure 6) and a USB interface board that can help
exercise the part in a simple way. The USB interface board provides all of the control signals for the
simple interface and can provide power to the part as well. A jumper on the LM3528 evaluation board
labeled V/VUSB allows you to connect either an external power supply to the VIN header on the LM3528
evaluation board, or draw power from the USB board. Removal of the jumper disables the connection of
the USB power supply. Once removed, an external supply is required. If the jumper is installed, the USB
board supplies power to the LM3528 evaluation board. No adjustments to the USB board are needed. A
standard USB cable must be connected to the board from a PC in order to communicate with the LM3528
Evaluation Kit.
For proper operation, the USB interface board must be plugged into the PC before the LM3528.exe
interface program is opened. Once connected, and the program is executed, a basic interface window will
open. At the top of the interface, you can read or write to any of the data registers on the LM3528 using
the two pull down menus for the slave I.D. and the desired data address. The data field to the right of the
address pull-down menu accepts hex data while the read and write buttons directly below the Address
pull-down menu execute the Read or Write command.
Just below the Read and Write buttons are five enable buttons. Two dedicated enable bits (ENM and
ENS) enable the two LED strings (MAIN and SUB). A dedicated bit (UNI) enables the Unison Mode of the
two LED banks, and another bit (OLED) puts the part in OLED mode. The Enable All button
simultaneously enables both ENS and ENM.
Below the Enable buttons are two sliding bars and data fields that allow all 128 levels of brightness for the
MAIN and SUB banks. Just below the two brightness level slider bars are six convenient action buttons:
three set buttons and three reset buttons.
SetM sets the MAIN brightness level to full-scale and enables the MAIN bank.
ResetM resets the MAIN brightness level to zero and disables the MAIN bank.
SetS sets the SUB brightness level to full-scale and enables the SUB bank.
ResetS resets the SUB brightness level to zero and disables the SUB bank.
Set sets the MAIN and the SUB brightness levels to full scale and enables the MAIN and SUB banks.
Reset resets the MAIN and SUB brightness levels to zero and disables the MAIN and SUB banks.
To the right of the two brightness level slider bars is a pull-down menu that controls the ramp rate of the
brightness level. To the left of the two brightness level slider bars are convenient controls for the GPIO1
pin and the HWEN/PGEN/GPIO pin.
The HWEN/PGEN/GPIO pin has three functions: an active high hardware enable (HWEN), a pattern
generator output (PGEN), and a general purpose I/O (GPIO). At the bottom of the user interface are
button controls for creating the output pattern when HWEN/PGEN/GPIO is in PGEN mode. For a detailed
explanation of the pattern generator, see the LM3528 High Efficiency, Multi Display LED Driver With 128
Exponential Dimming Steps and Integrated OLED Power Supply in a 1.2mm × 1.6mm DSBGA Package
Data Sheet (SNVS513). The output pattern is determined by the concatenation of four 8-bit data registers:
x90, x91, x92 and x93. Each bit for each of these data registers can be set in the user interface (Byte 0 –
Byte 3). The hex value of the data register is displayed to the right of the data bits in a data field. To the
right of the register data fields are convenient buttons to set all the bits to 1’s or reset all the bits to 0’s.
Once you have selected the desired pattern, load the pattern into the LM3528 by clicking the “Load”
button. Once the output pattern has been loaded, select the bit period and duty cycle of the pattern using
the pull-down menus. Finally, the output pattern is executed by clicking the “Run” button.
NOTE: If the part is enabled to any brightness level and the program is closed, the LM3528 part will
remain in the last programmed state.
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