ISSI IS31LT3948 Manuel utilisateur

IS31LT3948 MR16 DEMO Board Guide

Integrated Silicon Solution, Inc. – www.issi.com 1

R1.0, 18/12/2012

Description

IS31LT3948 is a PFM step-up DC-DC converter

designed for driving the white LED arrays for large size

LCD panel backlighting applications. With internal OVP

circuit, the chip and the system can be safe even if the

load is not connected. The device features external

PWM dimming or DC dimming, which allows the

flexible control of the backlighting luminance.

IS31LT3948 incorporates a unique FB scheme which

automatically adjusts the integrated DC/DC converter

to the optimum output voltage for the system,

maximizing the efficiency.

IS31LT3948 general DEMO board is used in general

lamp.

Features

Wide input voltage range: 5V-100V

Constant Current Output limited only by external

component selection (Note)

No loop compensation required

Internal over-voltage protection

Internal over-temperature protection

Note: The maximum output current is determined by Vout/Vin

ratio as well as the external components. If output current and

Vout/Vin ratio is high, high current components of inductor

and NMOS are needed.

Order information

Part Number Package Type

IS31LT3948-GRLS2-EBMR16 SOP-8

Quick Start

Recommended Equipment

30VDC Power supply

LED panel (1W LED, 7 LEDs in series)

Multi-meter

Recommended Input and Output Ratings

Input: 10-17VDC

Output: 7LEDs in series/333mA

Note: The input voltage must be lower than the output

voltage(total Vf).

Absolute Maximum Ratings

Input voltage ≤ 35VDC

Output voltage≤ 28VDC

Caution: Do not exceed the conditions listed above, otherwise

the board will be damaged or the output current will be

limited.

Procedure

The IS31LT3948 DEMO 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 negative terminal of the power supply

to the VIN1 pin and the positive terminal to the

VIN2 pin.

2) Connect the negative of the LED panel (LED

arrays) to the LED- terminal.

3) Connect the positive of the LED panel (LED arrays)

to the LED+ terminal.

4) Turn on the power supply and the LED panel (LED

arrays) will be light.

Bill of Materials

No.

Name

Description

Ref Des.

Qty.

Mfr

AL Capacitor

470uF±10%,35V

AL Capacitor

220uF±10%,50V,Low ESR

SMD Capacitor

10uF±10%,50V

SMD Resistor

2.4KΩ±1%,1206

SMD Resistor

24KΩ±1%,0805

SMD Resistor

270KΩ±1%,0805

SMD Resistor

10KΩ±1%,0805

SMD Resistor

0.21Ω±1%,0805

SMD Resistor

0.9Ω±1%,0805

Schottky Diode

SS36,3A,60V,SMA

D1-D5

Diode

1N4007,1A,1000V,SMA

SMD Inductor

100uH,Isat≥3A

IS31LT3948 MR16 DEMO Board Guide

Integrated Silicon Solution, Inc. – www.issi.com 2

R1.0, 18/12/2012

MOS

3A,60V,AP2310,SOT-23,NMOS

IS31LT3948,SOP8

Figure 1 IS31LT3948 MR16 DEMO Board Schematic

Detailed Description

Component Selection

The component selection is very important. They have

a significant effect on the operating state of the demo

board. The output capacitor must be a low ESR

capacitor so as to minimize it’s affect on the line

regulation and load regulation.

Please read the datasheet carefully to get more

information about the component selection.

PCB layout consideration

As for all switching power supplies, especially those

providing high current and using high switching

frequencies, layout is an important design step. If layout

is not carefully done, the regulator could show

instability as well as EMI problems.

•Wide traces should be used for connection of the

high current loop to minimize the EMI and

unnecessary loss.

•The external components ground should be

connected to IS31LT3948 ground as short as

possible. Especially theRcs and Rfb ground to

IS31LT3948 ground connection should be as short

and wide as possible to have an accurate LED

current.

•The capacitor C1, C2, C3 should be placed as close

as possible to IS31LT3948 for good filtering.

Especially the output capacitor C3 connection should

be as short and wide as possible.

•NMOS drain is a fast switching node. The inductor

and Schottky diode should be placed as close as

possible to the drain and the connection should be

kept as short and wide as possible. Avoid other

traces crossing and routing too long in parallel with

this node to minimize the noise coupling into these

traces. The feedback pin (e.g. CS, FB, OVP) should

be as short as possible and routed away from the

inductor, the schottky diode and NMOS. The

feedback pin and feedback network should be

shielded with a ground plane or trace to minimize

noise coupling into this circuit.

The thermal pad on the back of NMOS package must

be soldered to the large ground plane for ideal power

dissipation.

IS31LT3948 MR16 DEMO Board Guide

Integrated Silicon Solution, Inc. – www.issi.com 3

R1.0, 18/12/2012

PCB Layout

Figure 2 Board PCB Layout- Top Layer Figure 3 Board PCB Layout-Bottom Layer

Figure 4 Component Placement Guide -Top Layer Figure 5 Component Placement Guide -Bottom Layer

Revision history

Date Revision Changes

2012.03.06 R1.0 Initial release

2012.04.19 R1.1

1. Recommend output 1-7LEDs change to 7LEDs

2. BOM: Add tolerance to cap.

3. BOM: R1 3KΩchange to 2.4KΩ.

4. BOM: L1 Isat>2.5A change to Isat>3A.

5. BOM: MOS 13N06L change to AP2310.

6. Correct the schematic with ISSI part number.

7. Add order information.

8. Change EVB photo.

products at any time without notice. ISSI assumes no liability arising out of the application or use of any information, products or services

described herein. Customers are advised to obtain the latest version of this device specification before relying on any published information and

before placing orders for products.

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