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LMZM23601: the definition of VEN, VEN_HYST, VEN_WAKE

Noriyuki Takahashi
Genius 10980 points
Part Number: LMZM23601

Hi team,

I am confused withe the definition of  VEN, VEN_HYST, VEN_WAKE.

It would be very helpful that you could explain of the definition of these with picture like attached.

I am also not sure what is the output when the input is between VEN and VEN_WAKE like the attached.example.pdf

And, when we would like to enable this device at more than 14.3V, RENT＝75K、　RENB=10K is ok?

I mean, RENT and RENB are defined in datasheet P25.

Regards,

Noriyuki Takahashi

  • 0
    TI__Guru 50120 points

    Hi Takahashi-san,

    There are two internal thresholds tied to enable that you need to be aware. First is the "wake" threshold that requires  at least 0.4V( Wake threshold - Max EN hysteresis) to turn on the internal VCC circuitry.  The other is the actual EN rising threshold set at 1.8V with 0.5 typica hysteresis for the regulator to begin switching if VIN and EN are directly tied together. 

    Let's say you want to use the voltage divider such that the device will start switching after VIN is 14.3V, the regulator will wake up and bias the internal circuitry after the input voltage is at least 0.4V but the regulator will not start switching until the input voltage is at least 14.3V. The voltage divider resistors are picked such that EN sees 1.8V when VIN is at least 14.3. After the EN sees 1.8V, if the input voltage drops such that EN now sees 1.3V, the device will stop regulation and switching.

    Using the pdf you've attached as an example, the LMZM23601 will start switching and produce a well regulated output after VIN is above UVLO(14.3V). We can now calculate VEN_HYST since we now know the ratio is 14.3V/1.8V = 7.94. The VEN_HYST where the device will stop switching is 7.94*1.3V = 10.32V. When VIN is 10.32 or less, there will be no switching and output voltage will slowly collapse to 0V through capacitor discharge and resistor loading.  

    Hope this helps clarify things for you. 

    Regards,

    Jimmy 

  • 0 in reply to Jimmy Hua
    TI__Genius 10980 points

    Jimmy,

    I understand that when Vin exceeds VEN, the output would start to be regulated. After the output is regulated and when Vin becomes below (VEN - VEN_HYST), the output goes down to 0V.

    Then, I have still a question.

    When VEN_WAKE  is usually considered in customer system?

    It looks that VEN_WAKE is not needed to be considered.

    Regards,

    Noriyuki Takahashi 

  • 0 in reply to Noriyuki Takahashi
    TI__Genius 10980 points
    Jimmy

    One more request.
    Are there any excel sheet to calculate there VEN threshold?

    Regards,
    Noriyuki Takahashi
  • 0 in reply to Noriyuki Takahashi
    TI__Guru 50120 points

    Hi Takahashi-san,

    The VEN_wake on the LMZM23601 is just a voltage threshold to help understand when the device is in shutdown mode(ie. device is off and puling 1.8uA at 12V input). If the EN pin is higher than 0.4V, the device is biasing internal circuitry and will consume more power. If the customer does not want to consume unnecessary current when not using the LMZM23601, they can pull the EN pin less than 0.4V to keep the device in shutdown. 

    Instead of an excel sheet, the datasheet provides an equation to help customers set the Vstart and Vstop threshold for the enable divider in section 9.2.2.6. 

    Regards,

    Jimmy