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LT3743EUFD - SW Pin is burning out

Category: Hardware
Product Number: LT3743EUFD


I'm using the LT3743 on a laser diode driver PCB. The input supply voltage is +36V DC and the driver output voltage is around +27V at up to 10A. I've discovered that on some PCBs the output current can run at 1A but when increasing the output to 2A or higher the driver shuts down. Testing the resistance of the SW pin (pin 24) I measure 4.7 Ohms permanently, suggesting that it's burned out somehow. 

During measurement I can see that the the CBOOST voltage may be approaching > 40V and wondered if this was travelling through the boost capacitor on to the SW pin?

Current regulator sheet from Altium.PDF



  • Hi  ,

    Thank you very much for reaching out and for your participation in this community.
    I have contacted the ADI experts on this device to help respond to this query.
    We hope to give you an update as soon as possible.
    You may also try reaching out to local FAE to provide support on the product.



  • Hi Jason,

    It is not common that bootstrap circuit causes damage of SW. Abs. maximum of SW pin is 40V, while Vin is 36V. During switching there might be SW pin voltage overshoot and exceeds the abs. maximum. Other possibility is input supply has transients >40V. You may probe and check these voltages. 

  • Hi Gengyao,

    Thanks for your reply and help. Yes, I can confirm that there is an overshoot on the SW pin which approaches the absolute maximum of 40V. For now, I'll have to use the driver PCB at lower voltage stages of the laser (seed and preamplifier) and redesign the high power stage. 40V is too close to our supply voltage, so I'll use the LT3763 instead which does have a higher 60V rating.

    Best regards,