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Original question:

LM3410: Checking if I understand power dissipation in my LM3410 design

LM3410: Could you give me a quick review of this schematic?

Eric Steimle
Expert 2240 points
Part Number: LM3410
Other Parts Discussed in Thread: TPS92692

This is an 8-LED 5V input 350mA max output design. 

Partlist exported from C:/Users/ERICST~1.BAN/AppData/Local/Temp/Neutron/ElectronFileOutput/83224/sch-5a5b68b7-665e-4f45-8b1f-9199d7c59e68/LM3410X v1.sch at 8/28/2023 12:21 PM

Qty

Value

Device

Package

Parts

Description

CVALUE

LVALUE

MANUFACTUERER_PART_NUMBER

MANUFACTURER_PART_NUMBER

MFR_NAME

MPN

OC_FARNELL

OC_NEWARK

PACKAGE

RVALUE

SUPPLIER

1

0402_100K0_1W16

0402_100K0_1W16

RESC1005X40

R1

RES SMD 10K OHM 1% 1/16W 0402

RMCF0402FT100K

Stackpole

100K

1

0402_10UF_10V_X5R

0402_10UF_10V_X5R

CAPC1005X85N

C1

SMD Capacitor X5R(EIA) with Capacitance: 10uF Tol. 20%. Rated Voltage: 10Vdc

10uF

ZRB15XR61A106ME01D

MURATA

1

0805_4_7UF_25V_X5R

0805_4_7UF_25V_X5R

CAPC2012X145N

C2

4.7µF ±10% 25V Ceramic Capacitor X5R 0805 (2012 Metric)

4.7uF

C2012X5R1E475K125AB

TDK

1

1020_0R549_1P_2W

1020_0R549_1P_2W

RESC2550X70N

R2

RESISTOR, CURRENT SENSE, 0R549, 1%, 1020

RCWE1020R549FKEA

VISHAY_DALE

0.549

1

1206_2_2UF_25V_X5R

1206_2_2UF_25V_X5R

CAPC3216X180N

C3

CAP CER 2.2UF 25V X5R 1206

2.2uF

C3216X5R1E225M

TDK

2

4.7UH_3A_43MOHM

4.7UH_3A_43MOHM

MSS6132-472

L1, L2

4.7uH

MSS6132-472

COILCRAFT

1

DFLS120LQ-7

DFLS120LQ-7

DFLS120LQ-7

D1

DFLS120LQ-7

DIODES INC

1

LM3410XSD

LM3410XSD

DFN300X300X80-7N

U1

Constant Current Boost and SEPIC LED Driver

LM3410XSD

-

11N9218

DFN-6

National Semiconductor

2

WIRE_CONN

WIRE_CONN

WIRE_CONN

J1, J2

DNP

NONE

Thank you!

  • 0
    TI__Genius 16200 points

    just curious the reason of using SEPIC circuit. Can Boost be used in this application as 8LED output is definitely higher than 5Vin? 

  • 0 in reply to Xiaoguang
    Expert 2240 points

    Probably but the eval board was SEPIC so I was trying to stick close to it. That's the only reason. 

  • 0 in reply to Eric Steimle
    TI__Genius 16200 points

    If output is higher than VIN, it's no necessary to use SEPIC considering higher cost, lower efficiency and higher voltage/ current stress. Boost is ok. 

    However, what is actual LED spec and VF voltage? LM3410 can only support Vo <= 24V, it means VF of each LED can never be higher than 3V.  

    However, it seems that neither boost nor SEPIC can deliver so high power with TPS3410 due to current limitation. A simple calculation is shown below, considering 5V input voltage with 24V 350mA output.  SEPIC didn't consider efficiency yet. For Boost, efficiency is assumed as 80% (It can be more lower in real application).  

    You may also calculate with equations shown in datasheet. To reduce ripple current, 10uH inductor was selected in the calculation, 4.7uH will lead to higher peak current. 

    You may consider TPS92692 or LP8868 (preview) for higher current instead. 

  • 0 in reply to Xiaoguang
    Expert 2240 points

    Okay, that's interesting I had not realized the SEPIC current would be so high. Can you share your spreadsheet? I'd like to stick with the lm3410, I was just trying to design to its limit so I can reduce the current. The minimum current on the largest LED I want to use has a Ifw of 100ma and Vfw max of 3V.  So maybe I should switch to a boost topology and limit my current to say 200mA. In that case I guess I'll follow the typical boost schematic on the first page of the datasheet and re-use the components I'm using for SEPIC.  Maybe increase that inductor to 10uH.

  • 0 in reply to Xiaoguang
    Expert 2240 points

    To change to boost only it looks like I just have to remove the blocking cap C3 and the second inductor L2 right?

  • 0 in reply to Eric Steimle
    TI__Genius 16200 points

    LM3410 effienciency calculation.xlsx

    FYI. A quick calculation about the current; You may refer to equations in datasheet to calculate in details. 

    You need to also replace other devices like diode and output capacitors with acceptable voltage & current tolerance. Please make sure that  SW voltage is always within recommended operation condition. 

    Regards, 

    Xiaoguang