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IRS2980Buck LED DriverPeter GreenUnder embargo until 10/25/11

Target Applications and Markets

• Non-isolated LED drivers where input voltage > output voltage• LED light bulb replacements (non-dimmable)

• LED tube replacements

• LED street lighting

• LED office light fixtures

• LED refrigerator lighting

• LED runway lighting

• Solar LED street light

• Gaming machines

Existing Solutions

• Passive LED driver circuits

• Use diodes, resistors and capacitors only

• LED current is limited (many small LEDs)

• Cheap but poor performance and reliability

• Low-voltage Buck LED drivers

• Peak current regulated Buck LED drivers

Passive LED Driver

1uF x 3

15Ohm

LEDs1MOhm

22uF

• Minimum cost solution• No current regulation• LED current varies with line voltage• LED current varies with temperature• Low power factor / high harmonics• Standard white LEDs not HBLEDs• If one LED fails open circuit the product no longer operates• Cannot comply with Energy Star

Peak Current Buck Regulator

• Fixed frequency oscillator

• Buck regulator with low-side switch

• Can be unstable above 50% duty cycle

• Vin > 2 x Vout

• Ripple must be small so that Iav is close to Ipk

• Inductor needs to be large enough to maintain small ripple current

Accuracy vs inductor size tradeoffIout avg

Fixed Frequency

Iout_peakIout

LED

VDD

LD

PWM_D

VIN RT

GATECS

GND

12

DC BUS

IR Solution

IRS2980:• Available in SO8 package

• High-voltage Buck continuous mode LED driver (up to 375V continuous)

• Floating differential current sense

• Accurate constant current control (average current control)

• Internal HV regulator (no separate VCC supply needed)

• On board PWM dimming oscillator (not triac dimmable without additional circuitry)

• Frequency limiter (150kHz prevents internal regulator overheating and limits switching losses in the MOSFET and diode)

• May be used with passive valley fill PFC to obtain PF > 0.7

Trademark and logo for IR new LED driver family:

IRS2980 LED Driver

VBUS

COM

1

2

3

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8

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5

IRS

2980

HV

VS

COM ADIM

RAMP

OUT

CS

VCC

ADIM

RCS

RG

LBUCK

MBUCK

CRAMP

CVCC

CBUS

DBUCK

CVF

• Free running frequency• Buck regulator with low-side switch• High-side current sensing• Average current hysteretic control• Stable over full operating range• Higher ripple can be tolerated without• excessive loss in accuracy• PWM Dimming with analog control• Inductor needs to be large enough to• limit ripple current• Accuracy vs inductor size tradeoff

IRS2980

How Does the Product Work?

• Contains HV regulator for IC supply

• Uses Gen 5 HVIC technology

• Floating differential current sense for LED current sensing

• Hysteretic current regulation

• Free running operation (no Buck oscillator, no fixed frequency)

• Maximum frequency limiter (150kHz)

• Efficiency is best at high duty cycle where Vout is close to Vin

• Low-side MOSFET gate drive

• PWM dimming from external DC control voltage (0 to 2V)

Iout avgIout_peak

Iout

Low Cost IRS2980 LED Driver

• Low cost passive “Valley fill” PFC can be used in off line Buck regulators.• Provides power factor ~0.9.• It is constrained by ripple on DC bus being regulated out to provide a constant output current.

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2

3

4

8

7

6

5IR

S2980

HV

VS

COM ADIM

RAMP

OUT

CS

VCC

RCS

RG

LBUCK

MBUCK

CRAMP

CVCC

CBUS1

DBUCK

CVF

LIN

CIN

DB1 DB2

DB3 DB4

CFRF

CBUS2

D1

D2

D3

Product Literature/Support Literature

• Datasheet IRS2980

• Application Note AN-1171 relates to reference design IRPLLED7

IRS2980

•SPECIFICATIONS

• Input Voltage 70V to 240V (AC)• Output Voltage 0V to 50V (DC)• Regulated Output Current: 350mA• Power Factor ~ 0.9• Dimmable by on board potentiometer - 0 to 100%• Non-isolated Buck regulator

Typical Results (IRPLLED7 Demo Board)

Input = 60VDC Input = 180VDCOutput = 20V / 350mA Output = 20V / 350mAEfficiency = 80.2% Efficiency = 75.3%Green Trace = Gate DriveBlue Trace = Output Current

PWM Dimming Option

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3

4

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5

IRS

2980

HV

VS

COM ADIM

RAMP

OUT

CS

VCC

RCS

RG

LBUCK

MBUCK

CRAMP

CVCC

CBUS

DBUCK

CVF

LIN

CIN

DB1 DB2

DB3 DB4

CFRF

RDIM

RVDIM

• 0 to 2VDC analog control on ADIM input

• Adjusts PWM duty cycle for dimming (0 to 100%)

• CRAMP determines the PWM frequency

• PWM direct input is possible through ADIM

(replace CRAMP with resistor to set threshold)

PWM Dimming

Analog or Digital dimming signal is applied to the DIM input

ADIM voltage relationship to light output

0

10

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60

70

80

90

100

0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0Du

ty C

ycle

(%

)

Per

cen

tag

e o

f L

igh

t O

utp

ut

ADIM pin voltage

IRS2980 IC Summary

• For LED driver applications (typically < 50W)• For off line AC input voltage range 90 to 265VAC• Internal High Voltage Regulator• Power Factor > 0.9 with passive valley fill input stage• Continuous Conduction Mode (CCM) Buck Regulator• Typical Efficiency >80% (depending on line and load)• Suitable for non-isolated LED drivers• Protected against output short circuit• Regulated output current for LED driving• Hysteretic Average Current Control (for accurate regulation)• PWM dimming input, controlled by analog or PWM input