IRS2980
Buck LED Driver
Peter Green
Under embargo until 10/25/11
1
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
• 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
1MOhm
LEDs
22uF
1uF x 3
15Ohm
Peak Current Buck Regulator
• Fixed frequency oscillator
DC B US
2
• Buck regulator with low-side
• Can be unstable above 50%
VDD
duty cycle
VIN
1
switch
LED
RT
PWM_D
• Vin > 2 x Vout
G ND
LD
GA TE
CS
• Ripple must be small so that Iav
is close to Ipk
• Inductor needs to be large
enough to maintain small ripple
current
Iout
Iout_peak
Ioutavg
 Accuracy vs inductor size tradeoff
FixedFrequency
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
RCS
VBUS
DBUCK
HV
CVF
CBUS
ADIM
COM
IRS2980
1
VS
2
VCC
3
CVCC
COM
4
8
IRS2980
• 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
7
LBUCK
CS
OUT
RG
MBUCK
RAMP
6
5
ADIM
CRAMP
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
Iout_peak
Iout avg
Low Cost IRS2980 LED Driver
RCS
DBUCK
CBUS1
DB1
DB2
D1
LIN
HV
1
VS
CIN
D2
2
VCC
3
CVCC
COM
DB4
D3
4
8
IRS2980
CVF
DB3
RF
CF
7
LBUCK
CS
OUT
RG
MBUCK
RAMP
6
5
ADIM
CRAMP
CBUS2
• 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.
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
Output = 20V / 350mA
Efficiency = 80.2%
Green Trace = Gate Drive
Blue Trace = Output Current
Input = 180VDC
Output = 20V / 350mA
Efficiency = 75.3%
PWM Dimming Option
RCS
DBUCK
RF
CF
DB1
DB2
HV
LIN
1
VS
CIN
2
VCC
3
CVCC
COM
DB3
DB4
4
IRS2980
CVF
CBUS
8
7
LBUCK
CS
OUT
RG
MBUCK
RAMP
6
5
ADIM
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)
CRAMP
PWM Dimming
Duty Cycle (%)  Percentage of Light Output
Analog or Digital dimming signal is applied to the DIM input
ADIM voltage relationship to light output
100
90
80
70
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1.0
1.2
ADIM pin voltage
1.4
1.6
1.8
2.0
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