User's Guide
SNOA566A–October 2011–Revised April 2013
AN-2182 LM3466 Demonstration Board Reference Design
1 Introduction
The LM3466 integrates a linear LED driver for lighting systems that consist of multiple LED strings
powered by a constant current power supply. The LM3466 equalizes the current provided by the supply in
a pre-set ratio for each active LED string, where an active string is a fully turned on LED string, regardless
of the number of strings connected to the supply or the forward voltage of each LED string. If any LED
string opens during operation, the LM3466 automatically equalizes the supply current through all of the
remaining active LED strings. As a result, the overall brightness of the lighting system is maintained even
if some LED strings open during operation. The LM3466 consists of only linear circuitry so that the EMI of
the application circuit is not deteriorated.
This application report details the design of an LM3466 evaluation board that drives five LED strings, each
of which consists of 14 LEDs. The input current IS(of the constant current power supply) is 1.75A such
that the LED current is 0.35A per string. The evaluation board schematic, PCB layout, Bill of Materials,
and circuit design procedures are shown. Typical performance and operating waveforms are also provided
for reference.
2 Demonstration Board Schematic and PCB
Figure 1. LM3466 Evaluation Board PCB Top Overlay
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Demonstration Board Schematic and PCB
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Figure 2. LM3466 Evaluation Board Top View
Figure 3. LM3466 Evaluation Board Bottom View
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Demonstration Board Schematic and PCB
Figure 4. LM3466 Evaluation Board Schematic
Table 1. Evaluation Board Quick Setup Procedures
Step Description Notes
1 Connect a constant current power supply to VLED and PGND. The The supply current ISis set to 1.75A, with a maximum
VIN terminal can be connected to VLED, or another voltage source output voltage of 48 V.
ranged from 6 V to 70 V.
2 Connect five LED strings from VLED to LED1 to LED5 terminals. Each LED string consists of 14 LEDs with a forward
string voltage of lower than 48 V at 0.35A.
3 Turn on the power supply. The five LED strings are turned on and The voltage on R11-R51 is 0.35 V.
the current is 0.35A each.
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Design Procedure
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Figure 5. LM3466 Evaluation Board Connection Diagram
3 Design Procedure
The LM3466 evaluation board has 5 channels driving five LED strings powered by a constant current
power supply (IS= 1.75A). It is expected that the current of every LED string is 0.35A. From the schematic
(see Figure 4), each channel consists of an LM3466 (Ui), a sense resistor (Ri1), and two capacitors (Ci1
and Ci2), where i = 1 to 5. An RC circuit connecting the VEQ pin to ground is required for the whole circuit.
The above components are determined as follows.
Step 1: Determine the sense resistor
The current provided by the constant current power supply is equalized through each channel in a pre-set
ratio determined by the sense resistor Ri1. This LM3466 evaluation board is designed so that the current of
each channel is the same, the sense resistor of each channel is designed to be the same. It is
recommended that the nominal voltage of the SEN pin VSEN should be around 0.3 V. Therefore, Ri1 is
selected to be 1 Ω. As a result, VSEN should be 0.35 V if the LED current is 0.35A.
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PC Board Layout
Step 2: Determine the capacitors
Ci1:A high quality ceramic capacitor for decoupling should be connected from the VIN pin to ground. In
this LM3466 evaluation board, a 100 V, 0.01 µF ceramic capacitor is used.
Ci2:If the cable connecting the LED string and the evaluation board is long, the parasitic inductance of the
cable may generate noise. If this happens, a high quality ceramic capacitor should be connected between
the ILED pin and ground. In this LM3466 evaluation board, a 100V, 1 µF ceramic capacitor is used.
Step 3: Determine other components
REQ and CEQ:The VEQ pins of all LM3466 are shorted together and then connected to ground through
REQ and CEQ for normal operation. Only one REQ and one CEQ are required for one lighting system. It is
recommended that REQ be 51.1Ωand CEQ be 1 µF.
Step 4: Optional circuit for fault reporting
For simplicity, the COMM pins of all LM3466 can be shorted directly to a common bus COMM_ALL for
normal operation (Ri0 =0Ω). If fault reporting upon LED string open of a corresponding channel is
required, an optional circuit can be used to connect the COMM pin of each LM3466 to COMM_ALL. Since
the COMM pin pulls low during LED string open, the small signal LED in the optional circuit shown in
Figure 6 will light during a fault.
Figure 6. Optional COMM Circuit
4 PC Board Layout
To minimize the effect of noise, the ground connections of the LM3466 and the sense resistor Ri1 should
be closed. Good heat dissipation helps optimize the performance of the LM3466. The ground plane should
be used to connect the exposed pad of the LM3466, which is internally connected to the LM3466 die
substrate. The area of the ground plane should be extended as much as possible on the same copper
layer above and below the LM3466. Using numerous vias beneath the exposed pad to dissipate heat of
the LM3466 to another copper layer is also a good practice.
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Bill of Materials
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5 Bill of Materials
Item Part Number Mfg name Part Description Qty Ref Designator(s) Size
1 GRM21BR72A103KA01L MuRata CAP, CERM, 0.01 µF, 100V, ±10%, 5 C11, C21, C31, 0805
X7R, 0805 C41, C51
2 GRM32ER72A105KA01L MuRata CAP, CERM, 1 µF, 100V, ±10%, 5 C12, C22, C32, 1210
X7R, 1210 C42, C52
3 GRM188R71A105KA61D MuRata CAP, CERM, 1 µF, 10V, ±10%, 1 CEQ 0603
X7R, 0603
4 1502-2 Keystone Terminal, Turret, TH, Double 8 GND, LED1, LED2,
Electronics LED3, LED4, LED5,
PGND, VIN
5 CRCW06030000Z0EA Vishay-Dale RES, 0 Ω, 5%, 0.1W, 0603 10 R10, R12, R20, 0603
R22, R30, R32,
R40, R42, R50, R52
6 CRCW25121R00FKEG Vishay RES, 1.00 Ω1W 1% 2512 5 R11, R21, R31, 2512
R41, R51
7 CRCW060351R1FKEA Vishay-Dale RES, 51.1 Ω, 1%, 0.1W, 0603 1 REQ 0603
8 LM3466/NOPB Texas Instruments Simple Linear LED driver for Multi- 5 U1, U2, U3, U4, U5 SO
Channel LED Systems PowerPAD
-8
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Typical Performance and Waveforms
6 Typical Performance and Waveforms
All curves and waveforms are taken at IS= 1.75A with the evaluation board and TA= 25°C, unless
otherwise specified.
Figure 7. Current Regulation vs VLED Figure 8. Current Regulation vs Input Voltage
Figure 9. Current Regulation (Channel to Channel) vs Figure 10. Efficiency vs Input Voltage
Temperature
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