LTC4444-5 PWM 3,3V problem

Hello dear community,    

in a university project we are developing a 48V/12V buck converter using the LTC4444-5 as driver (picture 1: schematic).We currently have the problem that it is not possible to control the high and low side MOSFET with a PWM logic of 3.3V (Figure 2: Gate-source voltage at 3.3V logic voltage).  If the amplitude of the PWM is increased to 5V, the driver works (Figure 3: gate-source voltage at 5V logic voltage).The problem is independent of the duty cycle and the frequency of the PWM (Figure 4). When permanently applying 3.3V to the BINP pin the low side MOSFET is driven correctly.  Do you have experience with this problem or a possible solution?    

Thanks for your help!

Parents
  • 0
    •  Analog Employees 
    on Feb 26, 2021 8:05 PM

    Hi,

    From the pictures provided, it looks like your PWM signal for BINP/TINP from the signal generator has an amplitude of 3.3V with no offset, does this give you a signal from 0V to 3.3V or is it -1.65V to 1.65V? If it is going from -1.65V to 1.65V, this is not enough to turn on the top or bottom gate. From the datasheet the typical TG and BG Turn-On Input Threshold is 2.75V.

    Regards,

    Luis

Reply
  • 0
    •  Analog Employees 
    on Feb 26, 2021 8:05 PM

    Hi,

    From the pictures provided, it looks like your PWM signal for BINP/TINP from the signal generator has an amplitude of 3.3V with no offset, does this give you a signal from 0V to 3.3V or is it -1.65V to 1.65V? If it is going from -1.65V to 1.65V, this is not enough to turn on the top or bottom gate. From the datasheet the typical TG and BG Turn-On Input Threshold is 2.75V.

    Regards,

    Luis

Children
No Data