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LSF0102: Logic levels VOH,VIH, VOL, VIL

Vidhya J
Intellectual 400 points
Part Number: LSF0102
Other Parts Discussed in Thread: TXS0104E, TXS0102

Tool/software:

Hi Team,

For LSF0102, there are no Logic levels defined in datasheet as it is a passive switch.

1. Should I consider 0V to 3.3V in that case if VrefA=VrefB=3.3V? 

2. If VrefA is 1.8V, should levels be 0V to 1.8V? and If VrefB is 3.3V, Should levels be 0V to 3.3V?

Thanks and REgards,

Vidhya

  • 0
    Guru 316780 points

    No.

    For how to compute VOL, see Factors Affecting VOL for TXS/ LSF.

    The outputs are open drain, so there is no VOH.

  • 0
    TI__Mastermind 40316 points

    Hi Vidhya,

    You can think of the logic levels to be referenced to the lower voltage supply. For input voltages lower than VREFA, the switch is closed and the VOL is determined similar to the app note Clemens' shared. For input voltages equal to VREFA or higher, the FET is open and VOH can be close to VCC assuming external pullups are populated and pulled up to VREFx. 

    Regards,

    Jack

  • 0 in reply to Jack Guan
    Intellectual 400 points

    HI Jack, Clemens

    VOH=3.3V for VREFB =3.3V

    VOH=1.8V for VREFA=1.8V

    For VOL, refer to the snap from datasheet.

    1. Here VOL is considered to be 0.35V? or 0.175V??

    2, Also, Bias resistor should not be 200KOhms? should it be 963Ohms for 3mA?? Please clarify. 

    3. As per the link shared by clemens, 

    Ron=18ohms in my case.

    which one to consider for VOL??

    4. what about VIH and VIL? should it be VIH= Vrefx and VIL=0V?

    Thanks and Regards,

    Vidhya

  • 0 in reply to Vidhya J
    Guru 316780 points

    1. VOL depends on the input voltage and on the current through the switch. See the document I linked to. (Table 8-3 shows example values; you are not required to use them.)

    2. The bias resistor should always be 200 kΩ. The values in the table are for the pull-up resistors.

    3. VIL is the VOL of the other device that pulls the line low. IOL is the current through the switch, i.e., the current through the pull-up resistor on the output side.

    4. There is no VIH. There is no maximum VIL; the actual VIL is the same as the VOL of the other device that pulls the line low.

  • 0 in reply to Clemens Ladisch
    Intellectual 400 points

    My comments inline.

    1,3 If VIL of other device is taken, VOL of LSF part will be greater which violates VILmax>VOLmax condition to interface other device with LSF part

    In my case, following are the specs of other device

    VILmax= 0.54V

    IOL=1mA

    If I use the formula from 

    VOL=VIL+ (IOL*ron)

    Ron is 18Ohm in LSF datasheet for 10mA current. There is no detail for 1mA current.

    If I consider 50Ohms for 1mA current, VOL of LSF= 0.54+(0.001* 50)=0.59V which violates as 0.59V > 0.54V

    Please clarify.

    2. ok

    4. VIL of LSF is same as VOL of other device. can VIH of LSF be considered similarly as VOH of other device?

    Thanks,

    Vidhya

  • 0 in reply to Vidhya J
    Guru 316780 points

    1. Ron does not change with a smaller current. And your VOL value does not look realistic; what is the test current for that 0.54 V value?

    4. LSF does not have a VIH. But when the input voltage is at VREFA or higher, then the switch is open, and the pull-up resistor at the output puts the output high.

  • 0 in reply to Clemens Ladisch
    Intellectual 400 points

    Find my responses in line.

    1. If RON doesn't change , VOL= 0.54+(0.001* 18)=0.558V which still violates as 0.558V > 0.54V

    0.54V of other device is at 1mA current with VDD=1.8V

    4. what about pins referenced to VREFB?

    Please clarify.

  • 0 in reply to Vidhya J
    Guru 316780 points

    1. If your other device has an actual VOL of 0.54 V, then you cannot use the LSF to connect it to a device with VIL ≤ 0.558 V.

    4. There are no pins referenced to VREFB; all I/O pins on both sides are clamped at VREFA.

  • 0 in reply to Clemens Ladisch
    Intellectual 400 points

    1. Any part suggestion ?

    I need a bidirectional level translator for MDC and MDIO interface from CPU which has 1.8V logic level. 

    Also, for Reset and interrupt signals I need to level translate between 1.8V and 3.3V 

    4. If B1 and B2 are clamped to VRefA, there is no level translation? 

    In my case, VREFA=1.8V and VREFB=3.3V

    for down translation B to A, when B1/B2 is high (3.3V), A1/A2 will be clamper to VrefA which is the expected behavior.

    On up translation A to B, when A1/A2 is high (1.8V), B1/B2 will not be at 3.3V and clamp to 1.8V? There is no level translation at B1 and B2 pins. Expected behavior is to have Voltage level at 3.3V. Please calarify.

  • 0 in reply to Vidhya J
    Guru 316780 points

    1. What is the signal frequency? In general, TXS0102 or TXS0104E work for this. Please note that the TXS has internal pull-up resistors and should not be used with external pull-ups or pull-downs.

    4. The LSF itself clamps to VREFA. The pull-up resistor then generates a higher voltage.

  • 0 in reply to Clemens Ladisch
    Intellectual 400 points

    1. Can LSF0102 be used ?

    2. So, external pull up can be to 3.3V at B1 and B2 pins?

  • 0 in reply to Vidhya J
    Guru 316780 points

    1. Yes, but only if the pull-up resistors are strong enough (depending on the speed and the total capacitance), and if the other device have enough drive strength to sink the current through these resistors.

    2. Yes; on both sides, you can pull up to any voltage that is not below VREFA.