HM9284AS6 [HMSEMI]

1.2MHz, High Efficiency Boost White LED Driver;


型号：	HM9284AS6
厂家：	H&M Semiconductor
描述：	1.2MHz, High Efficiency Boost White LED Driver
文件：	总9页 (文件大小：1095K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

HM9284

1.2MHz, High Efficiency

Boost White LED Driver

FEATURES

GENERAL DESCRIPTION

The HM9284 is

a step-up converter designed for

 High Efficiency: Up to 90%

 1.2MHz Constant Frequency Operation

 Integrated internal Power MOSFET

 Drives up to 7 Series WLEDs

 Soft-start/Dimming with wide Frequency

Range

driving up to 7 series white LEDs from a single cell

Lithiu

lon battery The HM9284 uses current

mode

，

fixed frequency architecture to regulate an

LED current. which is measured through an

external current sense resistor.

The HM9284 includes unde voltage lockout

，

 UVLO, Thermal Shutdown

 Internal Current limit

current limiting and thermal overload protection

 Over Voltage Protection

 Small LC Filter

preventing damage in the event of an output

overload.

 Minimize the External Component

 <1µA Shutdown Current

 SOT23-6 Package

Optimized operation frequency can meet the

requirement of small LC filters value and low

operation current with high efficiency. Internal soft

start function can reduce the inrush current. Tiny

package type provide the best solution for PCB

space saving and total BOM cost.

APPLICATIONS

 Camera Flash White LED

 Mobile Phone, Smart Phone LED Backlight

 PDA LED Backlight

 Digital Still Cameras

 Camcorder

TYPICAL APPLICATION

LED Current vs. PWM Dimming

L 4.7μH to 22μH

V_IN

V_OUT

C_IN

1μF

C_OUT

1μF

VIN

7 WLEDs

GND

F=100kHz

R_CS

7S1P WLEDs

100

Figure 1. Basic Application Circuit

PWM Duty Cycle(%)

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

ABSOLUTE MAXIMUM RATINGS (Note 1)

Input Supply Voltage……………….-0.3V to 6V

EN,FB Voltages……………………..-0.3V to 6V

SW Voltage………………………..-0.3V to 30V

Power Dissipation………………………...0.6W

Thermal Resistance θ_JC……………….130°C/W

Thermal Resistance θ_JA……………….250°C/W

Junction Temperature(Note2)……….........160°C

Operating Temperature Range…….-40°C to 85°C

Lead Temperature(Soldering,10s)………...300°C

Storage Temperature Range……..-65°C to 150°C

ESD HBM(Human Body Mode)……………...2kV

ESD MM(Machine Mode)………………….200V

PACKAGE/ORDER INFORMATION

Order Part Number

Package

Remark

Top Marking

TOP VIEW

GND

VIN

HM9284AS6

SOT23-6

V_FB=104mV

V_FB=250mV

V_FB=300mV

B11G8W

B1B8DC

B1C8DC

HM9284BS6

HM9284CS6

6-LEAD PLASTIC SOT-23

T_JMAX= 160°C, θ_JA= 250°C/ W, θ_JC= 130°C/W

PIN DESCRIPTION

Pin Name

Pin Number

Description

Inductor Connection. Connect to the switched side of the external

inductor as well as the anode of the external diode. SW is high

impedance during shutdown.

GND

Ground Pin.

Current-Sense Feedback Input. Connect a resistor from FB to GND to set

the LED current.

Enable and LED Brightness Control Input. Pull high to turn on IC.Drive EN

with a 20kHz to 1MHz unfiltered PWM dimming signal for DC LED

current that is proportional to the signal’s duty cycle.

Over Voltage Input.The HM9284 turn off the N-channel MOSFET

when

V_OUTexceeds 28V .Connect OV to the output at the top of the LED string.

Power Supply Input. Must be closely decoupled to GND with a 1µF or

greater ceramic capacitor.

VIN

HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

(Note 3)

ELECTRICAL CHARACTERISTICS

(V_IN=V_EN=3.7V,T_A= 25°C, unless otherwise noted.)

PARAMETER

CONDITIONS

MIN

2.5

TYP

MAX

5.5

2.45

UNIT

Operating Input Voltage

Under Voltage Lockout

Hysteresis

2.2

100

Current (Shutdown)

Quiescent Current

Supply Current

Regulated Feedback

Voltage

V_EN<0.4V

0.1

200

0.6

104

250

300

1.2

300

114

262

315

µA

MHz

µA

V_FB=0.15V，No switching

V_FB=0V，switching

HM9284AS6

238

285

HM9284BS6

HM9284CS6

Switching Frequency

ON Resistance of NMOS

Peak Current Limit

EN Shutdown Voltage

EN Enable Voltage

EN Leakage Current

OVP Threshold

0.5

1.5

V_IN= 4.2V,Duty cycle=50%

0.4

1.5

±0.01

±1.0

Open LED,V_OUTRising

Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.

Note 2: T_Jis calculated from the ambient temperature T_Aand power dissipation P_Daccording to the

following formula: T_J= T_A+ (P_D) x (250°C/W).

Note 3: 100% production test at 25°C. Specifications over the temperature range are guaranteed by design

and characterization.

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

TYPICAL PERFORMANCE CHARACTERISTICS

LED Current vs. PWM Dimming @ 7S WLEDs

F=100kHz

7S1P WLEDs

100

PWM Duty Cycle(%)

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

Normal Operation @ V_IN=3V

Normal Operation @ V_IN=3.7V

Normal Operation @ V_IN=4.3V

Normal Operation @ V_IN=5.5V

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

FUNCTIONAL BLOCK DIAGRAM

VIN

UVLO

OVP

Internal

Soft Start

Error

Amplifier

PWM

Compartor

Control Logic

LPF

V_REF

OCP

Current Sense

Compartor

Enable Logic

OSC

GND

Figure 2. HM9284 Block

Diagram

FUNCTIONAL DESCRIPTION

an amplified version of the difference between

the reference voltage and the feedback voltage.

In this way the peak current level keeps the

output in regulation. If the feedback voltage starts

The HM9284 uses

constant frequency

，

peak

current mode boost regulator architecture to

regulate the series string of white LEDs. At the

start of each oscill or cycle the FET is turned on

through the control circuitry

To prevent

to drop

，

the output of the error amplifier

sub-harmonic oscillations at duty cycles greater

increases. This results in more current flowing

through the power FET

，

thus increasing the

than 50 percen

t，

stabilizing ramp is added to

the output of the current sense amplifier and the

result is fed into the positive input of the PWM

comparator.

power delivered to the output

When this voltage equals the output voltage of

the error amplifier the power FET is turned off.

The voltage at the output of the error amplifier is

Shenzhen H&M Semiconductor Co.Ltd

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HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

APPLICATIONS INFORMATION

Adjusting LED Current

voltage drop on R1 decreases, i.e. the LED

current decreases. For example, if the V_DCrange

is from 0V to 2.8V, the selection of resistors sets

dimming control of LED current from 20mA to

0mA.The LED current can be calculated by the

following equation:

Set the maximum LED current using a resistor

from FB to GND. Calculate the resistance as

follows:.

V_FB

R_CS

I_LED

R1×(V_DC− V_FB)

V_FB−

where I_LEDis the desired maximum current

through the LEDs.

R_CS

I_LED

LED Dimming Control

V_OUT

 Using a PWM Signal to EN Pin

For controlling the LED brightnes

s，

the HM9284

can pe orm the dimming control by applying a

PWM signal to EN pin. The internal soπstart and

the wide range dimming frequency can eliminate

inrush current and audio noise when dimming

The average LED current is proportional to the

PWM signal duty cycle. The magnitude of the

PWM signal should be higher than the maximum

7 WLEDs

R_CS

V_DC

Figure4

enable voltage of EN pin

，

in order to let the

dimming control pe orm correctly for preventing

 Using a Filtered PWM signal

the flicker issue

，

the suggested PWM frequency

Another common application is using a filtered

PWM signal as an adjustable DC voltage for

LED dimming control. A filtered PWM signal acts

as the DC voltage to regulate the output current.

The recommended application circuit is shown in

the Figure 5. In this circuit, the output ripple

depends on the frequency of PWM signal. For

smaller output voltage ripple (<100mV), the

recommended frequency of 2.8V PWM signal

should be above 20kHz. To fix the frequency of

PWM signal and change the duty cycle of PWM

signal can get different output current. Figure 5.

shows the relationship between LED current and

PWM duty cycle.The LED current can be

calculated by the following equation:

is ≥20kHz and ≤1MHz.

Figure 3

 Using a DC Voltage

Using a variable DC voltage to adjust the

brightness is a popular method in some

applications. According to the Superposition

Theorem, as the DC voltage increases, the

voltage contributed to V_FBincreases and the

Shenzhen H&M Semiconductor Co.Ltd

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HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

diode must meet the root mean square of

peak current and output average cur

ent

R1×(V_PWM×Duty − V_FB)

V_FB−

multiplication as following

R3 + R2

I_LED

R_CS

I_D(RMS) = I_OUT×I_PEAK

V_OUT

The diode’s reverse breakdown voltage should

be larger than the output voltage.

Layout Consideration

7 WLEDs

For best performance of the HM9284,

the

following guidelines must be strictly ll ed.

R_CS

 Input and Output capacitors should be

placed close to the IC and connected to

ground plane to reduce noise coupling.

 The GND should be connected to a strong

ground plane for heat sinking and noise

protection.

PWM Signal

1μF

Figure5

 Keep the main current traces as possible as

short and wide.

Inductor Selection

The recommended value of inductor are 4.7 to

22μH. Small size and better efficiency are the

major concerns for portable device

 SW node of DC-DC converter is with high

frequency voltage swing. It should be kept at

a small area.

 Place the feedback components as close as

possible to the IC and keep away from the

noisy device

， such as

HM9284 used for mobile phone. The inductor

should have low core loss at 1.2MHz and low

DCR for better efficiency. To avoid inductor

saturation current rating should be considered.

Capacitor Selection

Input and output ceramic capacitors of 4. μF are

recommended for HM9284 applications. For

better voltage filterin

g，

ceramic capacitors with

low ESR are recommended. X5R and X7R types

are suitable because of their wider voltage and

temperature ranges.

Diode Selection

Schottky diode is

because of its low forward voltage drop and

good choice for HM9284

reverse recovery. Using Schottky diode can get

better efficiency. The high speed rectification is

also a good characteristic of Schottky diode for

high switching frequency. Current rating of the

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

HM9284 1.2MHz High Efficiency Boosf Whtte Led Oriver

PACKAGE DESCRIPTION

SOT23-6

0.95

BSC

2.80

3.00

0.60

TYP

1.20

TYP

EXAMPLE

TOP MARK

2.60

TYP

1.50

1.70

2.60

3.00

AAAA

PIN 1

TOP VIEW

RECOMMENDED SOLDER PAD LAYOUT

GAUGE PLANE

0.25 BSC

0.90

1.30

1.45 MAX

SEATING PLANE

0.30

0.00

0.15

0.09

0.20

0.30

0.55

0.95 BSC

0.50

0°~8°

FRONT VIEW

SIDE VIEW

NOTE:

1.DIMENSIONS ARE IN MILLIMETERS.

2.DRAWING NOT TO SCALE.

3.DIMENSIONS ARE INCLUSIVE OF PLATING.

4.DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR.

Shenzhen H&M Semiconductor Co.Ltd

http：//www.hmsemi.com

HM9284AS6 [HMSEMI]

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