LTC7004 recommended maximum VCC

I am successfully using the LTC7004 high side NMOS driver in a design but have had issues with damaged parts. Due to the nature of the design there can be brief positive transients on the rail powering VCC on the order of +1 V over the nominal value of 16 Volts. I believe the root of the issue is that I am powering the IC at the recommended maximum of 15 Volts which is also the absolute maximum VCC voltage and any transient on the VCC rail exceeds the absolute maximum value on the VCC pin. It seems unsafe to operate the LTC7004 at the recommended maximum VCC value of 15 V when that is also the absolute maximum.

What is a recommended voltage for the VCC rail that is below the absolute maximum value? Considering the transients on my VCC rail would it be better to set the rail powering VCC to 14 V to provide some headroom between the nominal value and the abs max of the VCC pin? Is there a drawback to powering the LTC7004 at a voltage lower than 15 V?

Thanks,

Robert

  • 0
    •  Analog Employees 
    on May 21, 2020 5:16 PM

    Hi Robert,

    Recommended voltage for VCC pin is from 10V to 12V with VCCUV pin floating.  Using VCC source higher than 12V is not necessary since most power MOSFETs are fully ON at gate to source voltage around 8V (typical).

  • Hi Gene,

    I don't see the correlation between the VCC voltage and the gate to source voltage of the MOSFET attached to the LTC7004. It's true that power MOSFETs are typically fully on at about 8 V VGS, this is the voltage between the MOSFET gate and source, not the voltage between the MOSFET gate and the LTC7004 ground.

    The LTC7004 uses an internal charge pump to generate a gate voltage greater than VCC by sourcing power from the VCC pin until the TS pin voltage becomes greater than VCC. Since a higher voltage at the VCC pin would allow more energy to be transferred to the bootstrap capacitor per cycle, this would mean the LTC7004 would recharge the capacitor more quickly. However, as I mentioned in my original post, powering the LTC7004 at the recommended maximum value of 15V resulted in part failures.

    It's not clear to me why Linear recommends operating this device at 15V which is also their published absolute maximum VCC voltage. Regardless, I have changed my design to power the LTC7004 with 12V and modified the other circuitry on this power rail accordingly. I hope changing the VCC voltage to 12V will reduce part failures without negatively affecting the performance of the LTC7004.