LTM4676 output voltage error

Hi,

    I plan to design a 12V to 3.3V power supply module with LTM4676. The hardware design refers to a development kit of Altera, which can output 3.3V correctly.

After powering up, the following digital IO pins of LTM4676 function correctly:VDD25, VDD33, INTVCC. But both the two channels‘ output volatge measured are 90mV, instead of 3.3V.

  The value of resistors connected to ASEL, VOUT0CFG and VOUT1CFG is 22.6KΩ. FSWPHCFG, VTRIM0CFG and VTRIM1CFG left open.

  Monitor the SW0 pin, the waveform displayed by oscilloscope is a interrupted and irregular pulse, while the waveform of the same point of LTM4676 on Altera development kit is a standard 500KHz pulse signal.

   Is there any suggestions?

   Thanks. 

   Regards.

  • 0
    •  Analog Employees 
    on Dec 14, 2018 3:10 AM

    Hello Yiwen,

    I can help review your schematic and project file to ensure the design is all right.

    Meantime, can you monitor the Vo, SW and COMPa pin for one channel and any fault signal monitored from LTpowerPlay?

    Usually every 250ms they will start to retry and if the output will not be regulated within 5ms, all the switching will stop again.

    Thank you.