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RT8498 Step-Down Converter Evaluation Board

EVB_RT8498GE

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The RT8498 is a current-mode LED driver supporting wide input voltage range from 3V to 18V and output voltage up to 18V. With internal 350kHz operating frequency, the size of the external PWM inductor and input/output capacitors can be minimized. High efficiency is achieved by a 100mV current sensing control. LED dimming control can be done from either analog or PWM signal. The RT8498 provides an internal soft-start function to avoid inrush current and thermal shutdown to prevent the device from overheat. The RT8498 is available in the SOT-23-6 package.

Purpose

The RT8498 is specifically designed to be operated in Buck, Boost and Buck-Boost converter applications. This document explains the function and use of the RT8498 evaluation board (EVB), and provides information to enable operation, modification of the evaluation board and circuit to suit individual requirements.


Introduction

General Product Information

The RT8498 is a current-mode LED driver supporting wide input voltage range from 3V to 18V and output voltage up to 18V. With internal 350kHz operating frequency, the size of the external PWM inductor and input/output capacitors can be minimized. High efficiency is achieved by a 100mV current sensing control. LED dimming control can be done from either analog or PWM signal. The RT8498 provides an internal soft-start function to avoid inrush current and thermal shutdown to prevent the device from overheat. The RT8498 is available in the SOT-23-6 package.


Product Feature

  • High Voltage : VIN Up to 18V, VOUT Up to 18V
  • Built-In 2A Power Switch
  • Current-Mode PWM Control
  • 350kHz Fixed Switching Frequency
  • Analog, PWM Digital or PWM Converting to Analog with One External Capacitor
  • Internal Soft-Start to Avoid Inrush Current
  • Under-Voltage Lockout
  • Internal Over Voltage Protection to Limit Output Voltage
  • Cycle-by Cycle Current Limit
  • Thermal Shutdown


Key Performance Summary Table

Key Features

Evaluation Board Number: PCB082_V1

Default Input Voltage

4.5V to 18V

Max Output Current

1A

Default Output Voltage

3.0V

Default Marking & Package Type

RT8498GE, SOT-23-6

Operation Frequency

Steady 350kHz at all loads


Bench Test Setup Conditions

Headers Description and Placement

Technical Document Image Preview

Carefully inspect all the components used in the EVB according to the following Bill of Materials table, and then make sure all the components are undamaged and correctly installed. If there is any missing or damaged component, which may occur during transportation, please contact our distributors or e-mail us at evb_service@richtek.com.


Test Points

The EVB is provided with the test points and pin names listed in the table below.

Test point/

Pin name

Signal

Comment (expected waveforms or voltage levels on test points)

SW

Switch node test point

Switch node of the PWM converter.

GND

Ground

Ground.

DCTL

DCTL Input Voltage

Digital dimming control input.

ACTL

ACTL Input Voltage

Analog dimming control input. Effective programming range is 0.65V to 1.2V.

VCC

Supply Voltage Input

Supply voltage input. For good bypass, connect a low ESR capacitor between this pin and GND.

ISN

Current sense input

Current sense input. Voltage threshold between VCC and ISN is 100mV.


Power-up & Measurement Procedure

1. Connect input power (4.5V < VIN < 18V) and input ground to VIN and GND test pins respectively.

2. Connect positive end and negative terminals of load to VOUT2 and VOUT1 test pins respectively..

3. Verify the output voltage/output current (approximately 3.0V/1A) between VOUT2 and VOUT1.

4. VIN = 12V, VOUT = 3V, IOUT = 1A (Buck) ,

LED+ = VOUT2, LED- = VOUT1, LOAD = 1LEDs or Electronic Load CV mode

measure check SW pin freq = 350kHZ , ISP-ISN Threshold = 100mV


LED Current Setting

The LED current can be calculated by the following equation :

Technical Document Image Preview

where (VVCC - VISN) is the voltage between the VCC and ISN pins (100mV typ. if ACTL dimming is not applied) and

the RSENSE is the resister between the VCC and ISN pins.


Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

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Bill of Materials

Reference

Qty

Part number

Description

Package

Manufacturer

U1

1

RT8498GE

SOT-23-6

Richtek

C1, C5

2

GRM31CR71H475KA12L

4.7µF/50V/X7R/1206

C-1210

muRata

C2, C3

2

C3216X5R1H106K160AB

10µF/50V/X7R/1206

C-1210

TDK

C4

1

NC

C-0805

C6, C7

2

NC

C-1210

C8

1

C2012X7R1H105KT

1µF/50V/X7R/0805

C-0805

TDK

C9, C11

2

NC

C-1210

TDK

C10

1

C1608X7R1C474K000N

0.47µF/16V/X7R/0603

C-0603

TDK

D1

1

PMEG 4020

D-CR-73

NXP

L1

1

NRS8040T6R8NJGJ

6.8µH

L-SU1028

TAIYO YUDEN

R1, R4

2

Short

CP-0603

R2, R3

2

NC

CP-0603

R5, R6

2

SHORT

CP-0805C

R9

1

2512T-1-R100

100mohm

RC-1A

RALEC

R10, R11, R12, R13

4

NC

R-0805

R14

1

RTT05000JTP

0R/0805

R-0805

RALEC

R17

1

NC

R-0603

R18

1

WR06X000 PTL

0R/0603

R-0603

WALSIN


Efficiency:

VIN (V)

IIN (A)

VOUT (V)

IOUT (A)

Eff. (%)

ISP-ISN (mV)

4.5

0.834

3.405

0.974

88.369

97.9

7

0.538

3.395

0.978

88.165

98.3

10

0.379

3.382

0.974

86.915

97.9

12

0.317

3.372

0.972

86.162

97.7

15

0.257

3.369

0.97

84.771

97.6

18

0.216

3.368

0.966

83.68

97.3

Technical Document Image Preview


Line regulation:

Technical Document Image Preview

VIN (V) IOUT (A)
4.5 995.2
7 986.1
10 981.8
12 981.5
15 979.1
18 976.8


Load regulation:

Technical Document Image Preview

LEDs VOUT (V) IOUT (mA)
5LED 16.21 974.8
4LED 12.88 977.5
3LED 9.38 978.1
2LED 6.46 980.5
1LED 3.38 983.8


Waveform:

Test condition:VIN = 10V, VOUT = 3V, IOUT = 1A
CH1 = SW, CH2 = VOUT, CH3 = VIN, CH4 = IL CH1 = SW, CH2 = VOUT, CH3 = VIN, CH4 = IOUT
Technical Document Image Preview Technical Document Image Preview


Analog / PWM Dimming :

PCB Layout

Technical Document Image Preview

Top View (1st layer)

Technical Document Image Preview

Bottom View (4th Layer)

Title Last Update Share Download
Evaluation Board User Guide 2016/12/02
Bill of Materials 2016/12/02
Gerber File 2016/12/02
Schematic 2018/04/26
RT8498

18V Multi-Topology LED Driver with Dimming Control

RT8498

The RT8498 is a current-mode LED driver supporting wide input voltage range from 3V to 18V and output voltage up to 18V. With internal 350kHz operating frequency, the size of the external PWM inductor and input/output capacitors can be minimized. High efficiency is achieved by a 100mV current sensing control. LED dimming control can be done from either analog or PWM signal. The RT8498 provides an internal soft-start function to avoid inrush current and thermal shutdown to prevent the device from overheat.

The RT8498 is available in the SOT-23-6 package.

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