IRPLLED1 International Rectifier, IRPLLED1 Datasheet - Page 19

• 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

Since the IRS2540/1 does not include an onboard oscillator, a soft start feature is not easily implemented. This is
only a concern when operating in the dimming mode. Since PWM dimming is required of LEDs, the output is
essentially turning on and off at a rate of the dimming frequency. In the absence of soft start a large spike of current
would be observed in the load each time the output is turned on. This current spike stresses the load possibly
decreasing LED operating lifetime. The IRPLLED1includes a jumper setting to define whether or not the board is
being used in the dimming mode. This two position jumper allows the designer to either include or exclude the
resistor Rout, which is in series with the output capacitor. The inclusion of this resistor will sufficiently damp the
output stage, such that output current spikes are reduced or eliminated. The presence of such current spikes may
cause the inductor to hum or buzz where the emitted sound will be that of the dimming frequency. The inrush of
current causes mechanical movement in the inductor which can be heard since the PWM signal is within the audible
range of the human ear. The effects of adding in Rout can be seen in Fig. 25 – 28.
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Fig. 23 Light Output vs Enable Pin Duty Cycle
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Enable Duty Cycle Relationship to Light Output
Fig. 24 IRS2540 Dimming Signals
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RD-0608
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Percentage of Light Output
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