1. IRS2980
Buck LED Driver
Peter Green
Under embargo until 10/25/11

2. 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

3. 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

4. Passive LED Driver 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

5. 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 tradeoff 5

6. IR Solution IRS2980: Trademark and logo for IR new LED driver family:
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:

7. IRS2980 LED Driver 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

8. 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)

9. 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. 9

10. 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

11. Typical Results (IRPLLED7 Demo Board)
Input = 60VDC Input = 180VDC
Output = 20V / 350mA Output = 20V / 350mA
Efficiency = 80.2% Efficiency = 75.3%
Green Trace = Gate Drive
Blue Trace = Output Current

12. PWM Dimming Option 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)

13. PWM Dimming
Analog or Digital dimming signal is applied to the DIM input
ADIM voltage relationship to light output 10 20 30 40 50 60 70 80 90
100
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Duty Cycle (%)  Percentage of Light Output
ADIM pin voltage 13

14. 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