IRPLLED1 International Rectifier, IRPLLED1 Datasheet - Page 17

• 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

RS2
RS1 may be rounded up to 1K
The bootstrap diode (DBOOT) and supply capacitor (CBOOT) comprise the supply voltage for the high side driver
circuitry. To guarantee that the high-side supply is charged up before operation commences, the first pulse from the
output drivers comes from the LO pin. During under voltage lock-out mode, the high and low-side outputs are both
held low.
During an open circuit condition, without the watchdog timer, the HO output would remain high at all times and the
charge stored in the bootstrap capacitor (CBOOT) would slowly leak until reaching zero, thus eliminating the
floating power supply for the high side driver. To maintain sufficient charge on CBOOT, a watchdog timer has been
implemented. In the condition where VIFB remains below VIFBTH, the HO output will be forced low roughly after
20µs and the LO output forced high. This toggling of the outputs will last for 1µs to maintain and replenish
sufficient charge on CBOOT.
The bootstrap capacitor value needs to be chosen so that it maintains sufficient charge for at least the 20µs interval
until the watchdog timer allows the capacitor to recharge. If the capacitor value is too small, the charge will fully
dissipate in less than 20µs. The bootstrap capacitor should be at least 100nF. A larger value within reason can be
used if preferred.
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RS
RS
1
2
1
W
2
7. VBS Supply
=
=
=
512
(
V
(
V
Out
Out
Ω
max
1
max
≤
2
RS
−
1
W
−
k
14
2
Ω
14
V
V
)
2
)
2
=
(
30
V
1
−
2
Fig. 21 Illustration of Watchdog Timer
14
W
V
)
2
RD-0608
17