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RD-0608

Fig. 27 Load Current Spike Including Rout (5ohm)

Iout = 350mA, Vin = 100V, Vout = 17V

Fig. 28 Load Current Ripple Including Rout (5ohm)

Iout = 350mA, Vin = 100V, Vout = 17V

Although the inclusion of the resistor Rout minimizes or eliminates the load current spikes, the overall current

regulation and operating frequency will be slightly compromised. The resistor reduces the overall effectiveness of

the output capacitor, which means the switching frequency will marginally increase. The output ripple current will

also increase, which ultimately leads to a larger current regulation tolerance. Although the overall current regulation

capabilities may decrease with the inclusion of this resistor, the actual stability of the PWM dimming signal will still

be the dominant factor of the overall output current regulation capabilities.

It should be noted that the IRPLLED1 reference design board reflects the schematic of Figure 16 where a high speed

diode is used in place of the lower MOSFET switch indicated in Figure 1.

The addition of resistor RSYNC and diode DSYNC synchronizes the ENN input signal such that, when ENN

transitions from low to high to disable the oscillator during a period when HO is high, the IRS2540 will not react