IRPLLED1 International Rectifier, IRPLLED1 Datasheet - Page 16

• Manufacturer Part Number: IRPLLED1
• Description: BOARD EVALUATION FOR IRS2540PBF
• Manufacturer: International Rectifier

Specifications of IRPLLED1

• Current - Output / Channel: 1.5A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 24V
• Features: Dimmable
• Voltage - Input: 50 ~ 170V
• Utilized Ic / Part: IRS2540PBF
• Core Chip: IRS2540, IRS2541, IRS25401
• Topology: Buck (Step Down)
• No. Of Outputs: 1
• Output Current: 1.5A
• Output Voltage: 500mV
• Dimming Control Type: PWM
• Development Tool Type: Hardware - Eval/Demo Board
• Lead Free Status / RoHS Status: Contains lead / RoHS compliant by exemption

The resistance between VBUS and V CC (RS1) should be large enough to minimize the current sourced directly
from the input voltage line. Through this supply resistor a current will flow to charge the V CC capacitor. Once the
capacitor is charged up to the V CCUV+ threshold, the IRS2540/1/01/11 begins to operate activating the LO and HO
outputs. After the first few cycles of switching the resistor RS2 connected between the output and V CC will take
over and source current for VCC from the output. The RS2 resistor provided in the evaluation board has been
designed for an output of 16 to 24V. If a higher output voltage is desired, RS2 will need to be increased accordingly.
Conversely, if the output voltage is below 20V the value of RS2 may need to be reduced in order to supply sufficient
voltage to VCC.
A 10uF capacitor has been used at VCC of the IRS2540/1/01/11, which removes most low frequency ripple that
could originate from VBUS due to a rectified voltage waveform.
If the input and output voltages are defined for the evaluation board, enough information is provided to calculate
values for RS1, RS2, and RS3 (see Fig. 23 for component definition). All three supply resistors were chosen to be
1W devices since they source all current to the chip. Efficiency can be improved by optimizing these values for
specific applications.
By making each component 1W, the work in supplying VCC can be split up equally making it a more robust
solution instead of relying entirely on one component. This also allows the chip to turn on at a lower bus voltage.
Assuming that a 14V external zener diode will be used on Vcc, exact values of RS1, RS2, and RS3 are calculated as
follows (values calculated to operate the components just below half their rated power):
RS1
RS3
www.irf.com
P
RS
RS
min
RS
RS
1
1
2
2
=
1
1
1
3
W
W
V
duty
=
=
=
=
2
=
=
48
43
(
(
V
1
R
(
(
V
Bus
6 .
1
−
8 .
ratio
−
Bus
0
k
k
max
Ω
1 .
Ω
1
0
max
2
1 .
)
RS
≈
≈
≈
−
⋅
W
)
(
V
⋅
14
10
−
56
47
1
(
1
V
Bus
14
2
V
RS
%
k
Bus
k
W
Ω
Ω
V
max
)
2
3
max
)
2
=
−
−
14
(
170
14
V
V
)
V
2
1
)
2
2
−
=
W
14
(
1
V
−
)
0
2
1 .
) (
⋅
170
1
2
W
RD-0608
V
−
14
V
)
2
16