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SN74AVCH4T245 as MOS driver, consumption issue

Martin Besnard
Prodigy 70 points
Other Parts Discussed in Thread: SN74AVCH4T245

Hi,

 

I have a 1.25V @ 7MHz (fixed values) signal which comes from a DSP. This signals goes into a MOSFET which have a 30-40pF input capacitance.

I'm using a SN74AVCH4T245 as MOS driver, It shifts the voltage from 1.25V to 2V (fixed value).

The problem is :

-The current consumption of the level shifter is 1.55mA (measured)

-The transient current consumption is theoretically 180µA

-The capacitive-load current consumption is theoretically 500µA (http://www.ti.com/lit/an/scaa035b/scaa035b.pdf)

This means that the static current consumption of the level shifter is 1.55 - (0.18+0.5) = 870µA.

The question : Does that seem normal?

I also tried some inverters but I can't go below  a total consumption of 1.2 mA. I need to go below 600µA. Do you have any ideas?

 

Best regards,

Martin

 

  • 0
    TI__Expert 6430 points

    Hi Martin,

    For SN74AVCH4T245, if Vinput=0 or VccI and Iout=0, its max current is about magnitude of tens of microamperes.

    If there is a continuous output current, Iout>0, the value or total current will depend on Iout.

    Dose the output of SN74AVCH4T245 connect to MOSFET gate terminal? Could you provide MOFET part number? It will help to analyze the issue.

    Thanks

    Lawrence

  • 0 in reply to Wei Lang
    Prodigy 70 points

    Hi Lawrence,

     

    The SN74AVCH4T245 is connected to a BSS138PW (NMOS) gate. The main consumption seems to be caused by the high frequency of the input signal.

    There is another parameter. The input signal for SN74AVCH4T245 has a maximum value of 1.25V and Vcc=2V.

    Thanks for your time.

    Martin

  • 0 in reply to Martin Besnard
    TI__Expert 6430 points

    Hi Martin,

    If lower current is our goal, could you choose lower input capacitor NMOS? For BSS138PW, its input capacitor is more 38pF.

    When data transmission,  SN74AVCH4T245 will provide output current to drive load. The load is greater the output current is greater up to its max value.

    If the data rate is fixed, current could be less when capacitor load is decreased.

    Lawrence