IS31LT3350-V1SDLS2-EB3CH Datasheet IS31LT3350-V1SDLS2-EB3CH | P1-P3

IS31LT3350 3CH Evaluation Board Guide

Integrated Silicon Solution, Inc. – www.issi.com

R1.0, 08/26/2011

Description

The IS31LT3350 is a continuous mode inductive

step-down converter, designed for driving a single LED

or multiple series connected LEDs efficiently from a

voltage source higher than the LED voltage. The chip

operates from an input supply between 6V and 40V and

provides an externally adjustable output current of up to

750mA. Depending upon supply voltage and external

components, this can provide up to 30 watts of output

power.

The IS31LT3350 includes an integrated output switch

and a high-side output current sensing circuit, which

uses an external resistor to set the nominal average

output current.

Output current can be adjusted linearly by applying an

external control signal to the ADJ pin. The ADJ pin will

accept either a DC voltage or a PWM waveform. This will

provide either a continuous or a gated output current.

Applying a voltage of 0.2V or lower to the ADJ pin turns

the output off and switches the chip into a low current

standby state.

The chip is assembled in SOT23-5, SOT89-5 and SOP8

package. SOT23-5 is available for 350mA output current

application; SOT89-5 and SOP8 is available for 700mA

output current application.

IS31LT3350 3CH Evaluation board is used in RGB lamp

or the general LED lamp.

Features

 Simple low parts count

 Internal 40V power switch

 Wide input voltage range: 6V to 40V

 Up to 750mA output current

 High efficiency (up to 95% )

 Typical 1200:1 dimming rate

 Typical 5% output current accuracy

 Single pin on/off and brightness control using DC

voltage or PWM

 Up to 1MHz switching frequency

 Inherent open-circuit LED protection

 Thermal shutdown protection circuitry

Applications

 Low voltage halogen replacement LEDs

 Automotive lighting

 Low voltage industrial lighting

 LED back-up lighting

 Illuminated sign

Quick Start

Recommended Equipment

 60VDC Power supply

 3 pcs of LED panel (1W LED, 10 LEDs in series on

each panel)

 Multi-meter

Recommended Input and Output Ratings

 Input: 6-40VDC

 Output: 1-10 LEDs in series/333mA

Note: The input voltage must be 2V higher than the output

voltage (total Vf).

Absolute Maximum Ratings

 Input voltage ≤ 40VDC

Caution: Do not exceed the conditions listed above,

otherwise the board will be damaged.

Procedure

The IS31LT3350 Evaluation Board is fully assembled

and tested. Follow the steps listed below to verify board

operation.

Caution: Do not turn on the power supply until all

connections are completed.

1) Connect the terminals of the power supply to the AC1 and

AC2 pin(If the board don’t have the rectifier(D1-D4),

Connect the positive terminal of the power supply to the

VCC of the board and the negative terminal of power

supply to the GND of the board) .

2) Connect the negative of the one of LED panel (LED

arrays) to the LED1- terminal. And connect the positive of

the same LED panel (LED arrays) to the LED1+ terminal.

3) Connect the other two LED panels to LED2 and LED3 as

above.

Turn on the power supply and the LED panels (LED

arrays) will be light.

Ordering Information

PART #

TEMP

RANGE

PACKAGE

IS31LT3350-V1SDLS2-EB3CH

-40 °C to

105°C

SOT23-5

(5.0x6.0mm)

For pricing, delivery, and ordering information, please contact ISSI at analog_mkt@issi.com or call +1-408-969-6600

IS31LT3350 3CH Evaluation Board Guide

Integrated Silicon Solution, Inc. – www.issi.com

R1.0, 08/26/2011

Detailed Description

LED Current Control

The nominal average output current in the LED(s) is

determined by the value of the external current sense

resistor (R

) connected between V

and I

SENSE

and in is

given by:

OUT nom

= 0.1/Rs [for Rs>0.13Ω]

The table below gives values of nominal average

output current for several preferred values of current

setting resistor (Rs) in the typical application circuit

shown on page 1:

(Ω)

Nominal average

output current (mA)

0.13 769

0.15 667

0.27 370

0.3 333

Vsense is divided into two range to improve current

accuracy, please refer to bin information on page 3.

The above values assume that the ADJ pin is floating

and at a nominal voltage of V

REF

=1.2V.

Note that R

=0.13Ω is the minimum allowed value of

sense resistor under these conditions to maintain

switch current below the specified maximum value.

It is possible to use different values of R

if the ADJ pin

is driven from an external voltage.

Inductor selection

Recommended inductor values are in the range 47μH

to 220μH.

Higher values of inductance are recommended at

higher supply voltages and low output current in order

to minimize errors due to switching delays, which result

in increased ripple and lower efficiency. Higher values

of inductance also result in a smaller change in output

current over the supply voltage range. The inductor

should be mounted as close to LX pin as possible with

low resistance connections to LX and V

pins.

PCB layout consideration

Decoupling capacitors and coil

It is particularly important to mount the coil and the

input decoupling capacitor close to the chip to minimize

parasitic resistance and inductance, which will degrade

efficiency. The input decoupling capacitor (0.1uF fixed)

must be placed as close to the Vin and GND pins as

possible. It is also important to take account of any

trace resistance in series with current sense resistor

LX pin

The LX pin of the chip is a fast switching node, so PCB

traces should be kept as short as possible. To minimize

ground 'bounce', the ground pin of the chip should be

soldered directly to the ground plane.

ADJ pin

The ADJ pin is a high impedance input, so when left

floating, PCB traces to this pin should be as short as

possible to reduce noise pickup. ADJ pin can also be

connected to a voltage between 1.2V~5V. In this case,

the internal circuit will clamp the output current at the

value which is set by ADJ=1.2V.

High voltage traces

Avoid running any high voltage traces close to the ADJ

pin, to reduce the risk of leakage due to board

contamination. Any such leakage may raise the ADJ

pin voltage and cause excessive output current. A

ground ring placed around the ADJ pin will minimize

changes in output current under these conditions.

IS31LT3350 3CH Evaluation Board Guide

Integrated Silicon Solution, Inc. – www.issi.com

R1.0, 08/26/2011

Figure 1 IS31LT3350 3CH Evaluation Board Schematic

Bill of Materials

No. Name Description Ref Des. Qty. Mfr

1 AL Capacitor 220uF,50V

2 AL Capacitor 100uF,50V

C2,C3,C4

2 SMD Capacitor 100nF,50V

C5,C6,C7

3 SMD Capacitor 10nF,50V

C8,C9,C10

4 SMD Capacitor 1uF,50V

C11,C12,C13

5 SMD Resistor 1KΩ±5%,0805 R4,R6,R8 3

6 SMD Resistor 0.3Ω±1%,0805 R4,R6,R8 3

7 Schottky Diode SS26,2A,60V

D1-D7

8 SMD Inductor 47uH,Isat≥600A L1,L2,L3 3

9 IC IS31LT3350,SOT89-5 U1,U2,U3 3

Note: C8,C9, C10 is the optional components. They can filter the noise coupling to the ADJ pin.

RES

CAP1

CAP2

DI ODE

INDOCT OR

GND

VCC

GND

ADJ

Is ens e

Vi n

SN3350

GND

ADJ

Isense

Vi n

SN3350

GND

ADJ

Isense

Vi n

SN3350

DI ODE

INDOCT OR

VCC

C11

CAP1

C12

CAP1

C13

CAP1

CAP2

RES

DIODE

DI ODE

DIODE

DI ODE

LED1+

LED1-

LED2+

LED2-

LED3+

LED3-

AC1

AC2

PWM1

CAP1

PWM2

PWM3

CAP1

C10

CAP1

RES

P1-P3 P4-P4

IS31LT3350-V1SDLS2-EB3CH

Mfr. #:

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Manufacturer:

ISSI

Description:

LED Lighting Drivers Eval Board for IS31LT3350-V1SDLS2

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IS31LT3350-V1SDLS2-EB3CH