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LSF0108-Q1: LSF0108

Rana LM-S
Prodigy 210 points

Part Number: LSF0108-Q1
Other Parts Discussed in Thread: LSF0108

Hello, 

I would like to know how to calculate the power dissipation of LSF0108-Q1 ?? 

Best Regards

Rana 

  • 0
    TI__Mastermind 25235 points
    Hello,

    The power dissipation depends on a couple of things.
    1. The bias current going from VrefB to VrefA multiplied by the device voltage drop from the VrefB pin to the VrefA pin.
    The current depends on the VrefB to VpullupB voltage across the 200kOhm resistor.

    2. The second part of the power consumption is dependent upon the current being drawn from the output back to the input when the device is driving the output low and the Rdson of the pass transistor. You can use I2R to calculate the power dissipation.

    For further information regarding how this device operates, please refer to the video training series in the link below:
    training.ti.com/logicminute

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Prodigy 210 points
    Hi Michael,

    Thank you for your Replay.

    In my Schematic, I use 4 channels data (inputs), and I'm using 3.3V to 5V.


    Could you please confirm if this is the right equation to calculate the power dissipation of the level shifter ?


    P = (Vref-VrefA)²/200000 + (V_5V / Rpullup)*ron*4


    Kind Regards,

    Rana
  • 0 in reply to Rana LM-S
    TI__Guru* 97676 points

    Hi Rana,

    The power consumed by the LSF0108 device can be approximated with:

    P = Vbias*Ibias + N*I^2*Ron/D

    With:

    Vbias := voltage from VrefB pin to VrefA pin (typical 0.85V)

    Ibias := current from 200kohm resistor (calculated by (VB+

    N := number of channels

    I := channel current (usually generated by the pull-up resistor)

    Ron := internal LSF channel resistance - estimate high as 50ohms

    D := duty cycle of signal (channel current is only applicable during LOW state)

    The external resistors' power can be calculated as P = I^2*R =V^2/R = I*V

  • 0 in reply to Emrys Maier
    Prodigy 210 points
    I really appreciate your support.

    Thank you and have a nice day.

    Best regards,

    Rana