LT3465 applications advice needed. Hi, my name is Larry Welch. I'm working on a board design that uses the LT3465 to drive two strings of LEDs. I'm working at Continuum in Boston with Jay Petrie. We have 2 LED strings one Amber and on Blue. Each st

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  • Hi -

    My name is Larry Welch. I'm working on a Medical Device product development at Continuum in Boston. I've attached schematics and a BOM for the LT3465 application contained in the product. We're driving two strings of LEDs with LT3465 chips. The schematics show 4 LEDs per string. Ideally we would like to have 6 LEDs in each string. The product has strict radiated EMI requirements. The board has not yet been laid out. When we do so we will strictly adhere to the layout guidelines on page 12 of the LT3465 data sheet.

    In our design:

    Vin = 5V

    Vctrl = 1.8V (No PWM, No Dimming, full LED current)

    Rfb is set to 27 ohms (Iled = 7.4ma) 

     This table shows Vout for the Amber and Blue strings.

    #LEDs Vout Amber Vout Blue
    4 9.52 12.6
    5 11.85 15.7
    6 14.18 18.8

    Will these 6 cases work? Are there any issues?  A previous board Continuum built using the LT3465 in the same configuration exhibited severely degraded  EMI performance when 6 LEDS were connected in the string. The measured EMI was good for a 4 LED string.

    A response by Monday June 4 would be very helpful for us.

    Thanks,

    Larry

Reply
  • Hi -

    My name is Larry Welch. I'm working on a Medical Device product development at Continuum in Boston. I've attached schematics and a BOM for the LT3465 application contained in the product. We're driving two strings of LEDs with LT3465 chips. The schematics show 4 LEDs per string. Ideally we would like to have 6 LEDs in each string. The product has strict radiated EMI requirements. The board has not yet been laid out. When we do so we will strictly adhere to the layout guidelines on page 12 of the LT3465 data sheet.

    In our design:

    Vin = 5V

    Vctrl = 1.8V (No PWM, No Dimming, full LED current)

    Rfb is set to 27 ohms (Iled = 7.4ma) 

     This table shows Vout for the Amber and Blue strings.

    #LEDs Vout Amber Vout Blue
    4 9.52 12.6
    5 11.85 15.7
    6 14.18 18.8

    Will these 6 cases work? Are there any issues?  A previous board Continuum built using the LT3465 in the same configuration exhibited severely degraded  EMI performance when 6 LEDS were connected in the string. The measured EMI was good for a 4 LED string.

    A response by Monday June 4 would be very helpful for us.

    Thanks,

    Larry

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