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High Voltage High Current LED Driver Controller for Buck, Boost or Buck-Boost Topology

EVB_RT8494GS

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The RT8494 is a current mode PWM controller designed to drive an external MOSFET for high current LED applications. With a current sense amplifier threshold of 190mV, the LED current is programmable with one external current sense resistor. With the maximum operating input voltage of 36V and output voltage up to 90V, the RT8494 is ideal for Buck, Boost or Buck-Boost operation.
With the switching frequency programmable over 100kHz to 1MHz, the external inductor and capacitors can be small while maintaining high efficiency.
Dimming can be done by either analog or digital. The builtin clamping comparator and filter allow easy low noise analog dimming conversion from digital signal with only one external capacitor. The RT8494 is available in SOP-14 package.

Purpose

The startup voltage of the RT8494 is around 4.5V. When VCC voltage is greater than 4.5V, the RT8494 starts operation and a regulated GBIAS supply voltage is generated by an internal LDO circuit. With VCC greater than 10V, the GBIAS supply will be regulated around 8.5V to supply the power for the internal GATE pin driver circuit.


Introduction

General Product Information

The RT8494 is a current mode PWM controller designed to drive an external MOSFET for high current LED applications. With a current sense amplifier threshold of 190mV, the LED current is programmable with one external current sense resistor. With the maximum operating input voltage of 36V and output voltage up to 90V, the RT8494 is ideal for Buck, Boost or Buck-Boost operation.

With the switching frequency programmable over 100kHz to 1MHz, the external inductor and capacitors can be small while maintaining high efficiency.

Dimming can be done by either analog or digital. The builtin clamping comparator and filter allow easy low noise analog dimming conversion from digital signal with only one external capacitor. The RT8494 is available in SOP-14 package.


Product Feature

  • High Voltage Capability : VIN up to 36V, LED Sensing Threshold Common Mode Voltage up to 90V
  • Buck, Boost or Buck-Boost Operation
  • Programmable Switching Frequency
  • Easy Dimming Control : Analog or Digital Converting to Analog with One External Capacitor
  • Programmable Soft-Start to Avoid Inrush Current
  • Programmable Over-Voltage Protection
  • VIN Under-Voltage Lockout and Thermal Shutdown
  • AEC-Q100 Compliance

 

Key Performance Summary Table

Key Features

Evaluation Board Number : PCB042_V1

Input Voltage Range

4.5V to 36V

Input Threshold (VISP - VISN)

190mV

Threshold Common Mode Voltage

90V

Default Marking & Package Type

RT8494GS, SOP-14

Switching Frequency

Programmable Switching Frequency



Bench Test Setup Conditions

Headers Description and Placement

Technical Document Image Preview

Please carefully inspect the EVB IC and external components, comparing them to the following Bill of Materials, to ensure that all components are installed and undamaged. If any components are missing or damaged during transportation, please contact the distributor or send e-mail to 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)

RSET

Switch Frequency Setting

Switch Frequency Setting. Connect a resistor from RSET to GND. RRSET = 30kΩ will set fSW = 350kHz.

ISW

Switch Current Sense

External MOSFET Switch Current Sense. Connect the current sense resistor between external N-MOSFET switch and the ground.

ISP

LED Current Sense

LED Current Sense Amplifier Positive Input with Common Mode up to 90V.

ISN

LED Current Sense

LED Current Sense Amplifier Negative Input. Voltage threshold between ISP and ISN is 190mV with common mode voltage up to 90V.

VC

Compensation

PWM Control Loop Compensation.

ACTL

Analog Dimming Control

Analog Dimming Control. The effective programming voltage range of the pin is between 0.2V and 1.2V.

DCTL

PWM dimming

By adding a 0.47µF filtering capacitor on ACTL pin, the PWM dimming signal on DCTL pin can be averaged and converted into analog dimming signal on the ACTL pin.

SS

Soft-Start

Soft-Start Time Setting. A capacitor of at least 10nF is required for proper soft-start.

EN

Enable Control

Enable Control Input (Active High). When this pin voltage is low, the chip is in shutdown mode.

OVP

Over-Voltage

Over-Voltage Protection. The PWM converter turns off when the voltage of the pin goes to higher than 1.18V.

VCC

Internal Driver voltage

Power Supply of the Chip. For good bypass, a low ESR capacitor is required.

GND

Ground

Ground. The Exposed Pad must be Soldered to a Large PCB and Connected to GND for Maximum Power Dissipation.

GBIAS

Gate Driver Bias

Internal Gate Driver Bias. A good bypass capacitor is required.

GATE

Switch Gate Driver

External MOSFET Switch Gate Driver Output.



Power-up & Measurement Procedure

1. Connect input power (4.5V < VIN < 36V) to VIN test pin.

2. ACTL to 2V, see SW switch is working.

3. Observe the output voltage and output current is correct.



Output Over-Voltage Setting

The RT8494 is equipped with an Over-Voltage Protection (OVP) function. When the voltage at OVP pin exceeds a threshold of approximately 1.18V, the power switch is turned off. The power switch can be turned on again once the voltage at OVP pin drops below 1.18V. For the Boost and Buck-Boost application, the output voltage could be clamped at a certain voltage level. The OVP voltage can be set by the following equation :

Technical Document Image Preview



LED Current Setting

The LED current is programmed by placing an appropriate value current sense resistor between the ISP and ISN pins. Typically, sensing of the current should be done at the top of the LED string. The ACTL pin should be tied to a voltage higher than 1.2V to get the full-scale 190mV (typical) threshold across the sense resistor. The ACTL pin can also be used to dim the LED current to zero, although relative accuracy decreases with the decreasing voltage sense threshold. When the ACTL pin voltage is less than 1.2V, the LED current is :

Technical Document Image Preview



Schematic, Bill of Materials & Board Layout

EVB Schematic Diagram

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Bill of Materials

Reference

Qty

Part Number

Description

Package

Manufacture

U1

1

RT8494GS

LED Driver Controller

SOP-14

RICHTEK

C1, C4

2

0603B472K500

4.7µF/50V

C-1210/2.159

WALSIN

C2, C3

2

C1608X7R1C474K

0.47µF

C0603

TDK

C5

1

C1608COG1H332J

3.3nF

C0603

TDK

C6

1

0603B103K500

10nF

C0603

WALSIN

C8, C10

2

C3225Y5V1H106Z

10µF/50V

C-1210/3.048

TDK

C9

1

0603B472K500

4.7µF/50V

C-1210/2.159

WALSIN

D1

1

SR26, 2A, 60V

SMC

PANJIT

VOUT1, GND, VIN, VOUT2,

6

GP

SIP-1P-GP

L1

1

22µH

L-SH8018

美磊/乾坤

Q2

1

FTU36N06N

TO-252-123

營格

R19

1

470mΩ

RC-1A

Viking

R10

1

30mΩ

RC-1A

Viking

R13

1

WR06X3002F

30k

R0603

WALSIN

R2, R14

2

WR06X1002F

10k

R0603

WALSIN

R12

1

WR06X4303F

430k

R0603

WALSIN

R5,R6

2

WR06X1003F

100k

R0603

WALSIN

R3, R7, R9, R16, R27

5

0 (short)



PCB Layout

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Top View

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Bottom View

Title Last Update Share Download
Evaluation Board User Guide 2015/12/10
Bill of Materials 2015/12/10
Gerber File 2015/12/10
Schematic 2015/12/10
RT8494

多拓扑高压大电流LED驱动控制器

RT8494

RT8494 是经外推 MOSFET 提供大电流 LED 驱动应用的电流模式 PWM 控制器,其电流检测放大器的阈值为 190mV,使用一只外接电阻即可设定其输出电流。其最高工作输入电压为 36V,最高输出电压则可高达 90V,是 Buck、Boost 和 Buck-Boost 应用的理想选择。其开关切换工作频率为 100kHz~1MHz 可调,在维持高效工作的同时,可以使用小型电感和电容。调光操作可用模拟或数字方式进行,它内置的限幅比较器和滤波器可将数字式调光转换为无噪声的模拟调光,仅需使用一只外接电容。其封装为SOP-14。

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