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LP2985-N: Enable threshold

Yee Yong Teo
Expert 4335 points
Part Number: LP2985-N

Hi,

In datasheet, 1.6V is the minimum to enable and 0.15V is the maximum to disable. Questions:

  1. What is the accuracy for this threshold value?
  2. What happen to Vout if Ven falls in between 0.15V and 1.6V?
  3. Can I have the Ven vs Vout graph from 0V to 5V with Vin = 7.5V, Vout = 2.5V, I = 50mA?

Thanks.

- YY

  • 0
    Guru 140200 points
    Hi Yee,

    the answer is similar to that:

    e2e.ti.com/.../677106

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 23361 points

    Hi YY,

    This is an old device, unfortunately, no enable thresholds curves are available in the datasheet. Based on the information provided in the datasheet, enable needs to be set higher than 1.6V to guarantee the ON state of the device; less than 0.15V to set the OFF state of the device.

    Regards, 
    Jason Song

  • 0 in reply to Jason Song
    TI__Expert 4335 points
    Hi Jason,

    When the enable voltage fall in between 0.15V to 1.6V, is the output stay regulated if the device is turned on?

    Thanks.

    - YY
  • 0 in reply to Yee Yong Teo
    TI__Mastermind 23361 points
    Hi YY,

    For this device, there is no Enable thresholds' curves available. If application needs to turn off the device, enable pin voltage needs to be lower than 0.15V; when you need the device to be on, the enable threshold needs to be higher than 1.6V. Between 0.15V to 1.6V, the on or off state of the device is not defined for this device.

    Regards,
    Jason
  • 0 in reply to Jason Song
    TI__Expert 4335 points
    Hi Jason,

    If that's case, we cannot guarantee that the device will regulate the output when enable is between 0.15V to 1.6V?

    Thanks.

    - YY
  • 0 in reply to Yee Yong Teo
    TI__Mastermind 23361 points
    YY,

    The enable function provided by this device does not have the accurate control on the threshold voltage for the device to turn on or off. The LDO will be turned once it exceeds a certain voltage between 0.15V and 1.6V.

    If accurate control on the turn on/off voltage is needed, you may need to consider adding a supervisor chip. You can find more information here: www.ti.com/.../products.html

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    TI__Expert 4335 points

    Hi Jason,

    Well noted on the threshold. But I need a confirmation on the output which it will not go higher than the expected when on/off pin voltage fall within 0.15V to 1.6V. Example LP2985-2.5, the output voltage will not go more that 2.5V if on/off pin voltage fall within 0.15V to 1.6V.

    Thanks.

    - YY

     

  • 0 in reply to Yee Yong Teo
    Guru 140200 points
    Hi Yee,

    have you read section 8.2.2.3 of datasheet of LP2985-2.5? There you will find the statement:

    "To assure proper operation, the signal source used to drive the ON/OFF input must be able to swing above and
    below the specified turn-on/turn-off voltage thresholds listed in the Electrical Characteristics section under
    VON/OFF. To prevent mis-operation, the turn-on (and turn-off) voltage signals applied to the ON/OFF input must
    have a slew rate which is ≥ 40 mV/µs.

    CAUTION
    The regulator output voltage cannot be ensured if a slow-moving AC (or DC) signal is
    applied that is in the range between the specified turn-on and turn-off voltages listed
    under the electrical specification VON/OFF (see Electrical Characteristics)."

    This means, that the voltage at ON/OFF pin must not stay too long in the range between 0.15V and 1.6V and that changes from the proper low level to the proper high level, and vice versa, must be carried out with a minimum speed of 40mV/µs. Only then proper performance of regulator can be guaranteed.

    Kai
  • 0 in reply to Yee Yong Teo
    TI__Mastermind 23361 points
    Hi YY,

    Like I was suggesting in a similar post, if you need accurate control on the turn on voltage, you may need to consider to add supervisor circuit to your application. More product information about supervisor products can be find here:
    www.ti.com/.../products.html

    Regards,
    Jason Song