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User's Guide

SNVA642A–May 2012–Revised May 2013

AN-2255 LM3463 Evaluation Board

1 Introduction

The LM3463 is a 6-channel linear LED driver with Dynamic Headroom Control (DHC) designed to drive six

strings of high brightness LEDs at maximum supply voltage up to 95V. Each output channel of the

LM3463 evaluation board is designed to deliver 200 mA of LED driving current. The LED turn on voltage

is set to 48V by default, thus the board is able to deliver up to 57.6W total output power. The six output

channels are divided into 4 individual groups to facilitate average LED current control by means of PWM

dimming. The PWM dimming control interface of the LM3463 can accept standard TTL level PWM signals,

analog voltage or serial data to control the dimming duty of the four LED groups individually. The analog

dimming control interface accepts an analog control voltage in the range from 0V to 2.5V to adjust the

reference voltage of the linear current regulators, which enables true LED current adjustment. This

evaluation board is designed to be connected to an external primary power supply. Using three connection

wires, the VIN, GND and VFB, the dynamic Headroom Control (DHC) circuit of the LM3463 adjusts the

output voltage of the primary power supply to maximize system efficiency.

2 Standard Settings of the LM3463 Evaluation Board

• Input voltage range: 12V to 95V

• LED turn on voltage: 48V

• Nominal forward voltage of a LED string: 42V

• Output current per ch.: 200 mA

• System clock freq.: 246 kHz

• DHC cut-off freq.: 0.1Hz

• Mode of dimming control: Direct PWM Mode

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SNVA642A–May 2012–Revised May 2013 AN-2255 LM3463 Evaluation Board

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Summary of content (17 pages)

PAGE 1
User's Guide SNVA642A – May 2012 – Revised May 2013 AN-2255 LM3463 Evaluation Board 1 Introduction The LM3463 is a 6-channel linear LED driver with Dynamic Headroom Control (DHC) designed to drive six strings of high brightness LEDs at maximum supply voltage up to 95V. Each output channel of the LM3463 evaluation board is designed to deliver 200 mA of LED driving current. The LED turn on voltage is set to 48V by default, thus the board is able to deliver up to 57.6W total output power.
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LM3463 Evaluation Board Schematic 3 www.ti.com LM3463 Evaluation Board Schematic J0 TP1 VRAIL TP2 J1 R2 150 k C1 1µF 100V TP3 R4 8.
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Bill Of Materials www.ti.com 4 Bill Of Materials Designator Description Package Part Number Manufacturer U1 LED driver WQFN-48 LM3463 Texas Instruments C1, C2 Capacitor, 1uF, 100V, X7R 1206 GRM31CR72A105KA01L MuRata C3, C4 Capacitor, 1uF, 16V, X7R 0603 C1608X7R1C105K TDK C5 Capacitor, 2200 pF, 25V, X7R 0603 GRM188R71E222KA01D MuRata C6 Capacitor, 0.
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Board Layout 5 www.ti.com Board Layout Figure 2. Top Layer Figure 3.
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Connection Diagram www.ti.com 6 Connection Diagram LED strings x 6 Default operation conditions of the board: IOUT per channel: 200 mA No. of LED per string: 14 (~3.2V forward voltage per LED) LED turn on voltage: VRAIL = 48V Dimming mode: Direct PWM dimming mode @ 100% dimming duty Assumed characteristics of the primary power supply: VFB = 2.5V RVFB1 = 39.8 k RVFB2 = 3.9 k CH3 CH4 J15 CH5 J16 CH2 J14 J0 CH1 J13 CH0 J11 VRAIL J12 Primary power supply (e.g.
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Primary Power Supply www.ti.com Generally the required range of the VRAIL is determined by the highest and lowest possible forward voltages of the LED strings (respectively, VLED-MAX-COLD and VLED-MIN-HOT). Since the forward voltage of the LED strings varies according to the changing of the ambient temperature, the voltage for turning the LEDs on at system startup must be set higher than the VLED-MAX-COLD.Figure 5 shows the different voltage level of VRAIL at system startup.
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Primary Power Supply www.ti.com PROCEDURES REMARKS Begin of design Identify VLED-MAX-COLD Identify VLED-MIN-HOT Adjust the nominal output voltage of the primary power supply, VRAIL(nom) = VLED-MIN-HOT - 5V Set the peak output voltage of the primary power supply (at VOutP = 0.
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Response of the DHC Loop www.ti.com PROCEDURES REMARKS Begin of power supply selection Determine: ILEDx, VRAIL(peak) and VRAIL(nom) Calculate the required maximum output Power, PRAIL(peak) of the power supply Prepare a power converter which has a maximum output power > POUT(nom) and a maximum output voltage > VRAIL(peak) Adjust R1 and R2 to reduce the nominal output voltage of the power converter to VRAIL(nom) VRAIL(peak) is the highest output voltage that the power converter needs to deliver.
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Reducing the System Startup Time www.ti.com 9 Reducing the System Startup Time The total system startup time is generally dependent on the frequency response of both the primary power supply and DHC loop of the LM3463. The slower response of the two circuits, the longer time the system takes to startup.
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PWM Dimming Control www.ti.com (4) The IOUTADJ pin can be biased by a positive voltage in the range of 0V to 2.5V across the terminals TP31and TP39. If the IOUTADJ pin is going to be biased by an external voltage source, the R10 and R11 should be removed.
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PWM Dimming Control www.ti.com In the serial interface mode the LM3463 evaluation board accepts a data frame which consists of four data bytes to control the on duty of the four groups of output channels via the terminal TP12 (DIM01). Every data byte contains 8 bits in LSB (Least Significant Bit) first ordering and is clocked into the data buffer of the LM3463 at every rising edge of clock signal at the terminal TP14 (DIM23).
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PWM Dimming Control www.ti.com PWM dimming duty 256/256 255/256 254/256 253/256 252/256 6/256 5/256 4/256 3/256 2/256 (Skipped)1/256 Input Data Code (Decimal) 1 2 3 4 5 25 25 25 25 25 5 4 3 2 1 0 0 Figure 10. PWM dimming duty vs code value of a data byte In the serial interface mode, the six output channels are grouped into four individual groups.
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Disabling Output Channel(s) www.ti.com Output channel Terminal CH0, CH1 TP12 CH2, CH3 TP14 CH4 TP16 CH5 TP18 The voltage being applied to the terminals should be in the range of 0.8V to 5.7V. The dimming duty in the DC interface mode is governed by the following equation: (6) In this mode, the conversion of analog voltage to dimming duty is accomplished by an internal 8-bit ADC of the LM3463, thus the step size of the LED current is equal to 1/256 of the full scale current.
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Cascading the LM3463 evaluation board 14 www.ti.com Cascading the LM3463 evaluation board A number of the LM3463 evaluation boards can be cascaded to expand the number of output channels. The connection among boards differs depending on the selected mode for dimming control. The connection diagrams for the serial interface mode, DC interface mode and direct PWM mode are as illustrated in the Figure 12, Figure 13, and Figure 14, respectively.
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PCB Design www.ti.
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Typical Waveforms 16 www.ti.com Typical Waveforms All curves taken at VIN = 48V with configuration in typical application for driving twelve power LEDs with six output channels active and 200 mA output current per channel. TA = 25°C, unless otherwise specified. 16 Figure 15. Direct PWM Dimming Mode 250Hz 50% dimming duty at DIMn pin Figure 16. DC Interface Mode 10Hz 3V to 2V ramp at DIMn pin Figure 17. PWM dimming IOUTn delay at VDIMn rising Figure 18.
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