LT3965

Question

Hi - 
 I have a quick question about the LT3965. I've designed the device into an system and it works fine. Right now a 1Mhz clock from an oscillator is driving all the RTCLK pins of all the LT3965s in the system. I'm going to stop using the 1Mhz external clock and instead rely on pull down resistors connected to each RTCLK pin right at the chip to set the PWM clock frequency to around 500Hz. Does any of the PWM or fault detection functionality change if I stop using the external 1Mhz clock? 
 Thanks, 
 Larry Welch 
 EPAM Continuum 
 Boston, MA

ADIApproved · Accepted Answer

Hi Larry, 
 
 Glad to hear you have LT3965 working well in your system! 
 If you were to remove the SYNC signal driving the RTCLK pin of your LT3965's and instead replaced this with a set resistor for each LT3965 used, then you shouldn't really run into any issues in terms of the fault reporting or PWM functionality. Assuming you are setting the resistor to match what the 1MHz clock source is accomplishing in terms of setting the PWM dimming frequency, you can expect similar performance to the synced version of the system over the majority of the dimming range. 
 The reason for running a sync signal into the LT3965 is to be able to synchronize the switching of the LED driver with the PWM dimming to prevent any unwanted shimmer or flicker that could potentially happen with an unsynchronized system while performing PWM dimming. This is most notable when trying to accomplish 1/128 PWM dimming, as the LED will be at its most dim state and any flicker will be easier to notice. 
 I think that your system should run just fine with the oscillator removed and RTCLK set resistors installed.)

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