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RD-0608

until the end of the current HO cycle as shown in the waveform diagram below. The reason for this is to avoid the

possibility off ENN transitioning from low to high at the exact time that HO transitions from low to high, which may

trigger the HO output to latch up under a low VBS supply condition. This is caused by propagation delays that exist

inside the IC. RSYNC and DSYNC are not necessary in non-dimming applications. Synchronization as described will

not affect the operation or dimming functionality of the circuit. It will serve only to protect the circuit against a

possible fault condition, without any detrimental effect to operation. The revised IRS25401 and IRS25411 contain

internal circuitry to protect against possible latch up conditions and do not require RSYNC and DSYNC.

Fig. 28a: Dimming Synchronization Waveforms.

9. Open circuit protection

Fig. 29 IRPLLED1 Improved Open Circuit Protection Scheme