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TL7700: Changin the detect viltage of TL7700

Part Number: TL7700
Hi
My customer  evaluate TL7700 for adjustable power up time.
The detect voltage is different in the start up and the instantaneous interruption.
Is there the reason for such a result?
The detect voltage is 1.25V at the start up and 1.29V at the instantaneous interruption.
Best regards,
Yokota
  • Hi,

     Can you please provide the R1 & R2 values used for the sense pin. When there is instantaneous interruption you have to consider the hysteresis voltage as well. See the datasheet section 8.3.2  pasted below

    Vhys = Is × R1 where • Is = 2.5 μA typ at TA = 25°C

    At room temperature, Is has variations of 2.5 µA ± 0.5 µA. Therefore, in the circuit shown in Figure 18, Vhys has variations of (±0.5 × R1) µV

    Thanks

    Chintan

  • Hi

    Thank you for the reply.
    The R1 & R2 values is 10kΩ.
    Best regards,
    Yokota
  • Yokota,

    Please let us know if you have any more questions or need any additional support. Thanks!

    -Michael

  • HI Michael-san

     
    Im sorry I couldn't understand my customer's questions.
    1.25V and 1.29V are the CT terminal voltage.
    Under my customer conditions, the reset terminal is high when the CT terminal voltage is 1.25V in start up and 1.29V in instantaneous interruption.
     
     
    ・Does the hysteresis cause this variation?
    ・Are there the tolerance of the CT terminal voltage?
     
     
    Best regards,
    Yokota

     

  • Yokota,

    The capacitor voltage is dependent on the internal current source that charges the capacitor. Chintan mentioned above that the hysteresis is dependent on on R1. At room temperature, Is (current source that charges the delay capacitor) has variations of 2.5 µA ± 0.5 µA. Therefore, in the circuit shown in Figure 18, Vhys has variations of (±0.5 × R1) µV.

    The tolerance of the CT terminal voltage and tolerance of current source is captured in the accuracy spec of the device. This device have 1% sense voltage tolerance at 25C.

    There should be no difference between "start up and instantaneous interruption". But there is a difference between the threshold when SENSE voltage is falling (0.5V typical) and when SENSE voltage is rising (0.5V typical + voltage defined by hysteresis set by R1).

    Please let me know if you have any more questions. Thanks!

    -Michael
  • Hi Michael-san


    Thank you for your explanations.
    The Vsense accuracy is defined 1% at Ta=25℃ in datasheet.
    Could you tell me it from -40 to 85℃?


    Best regards,
    Yokota
  • Yokota,

    Across all temperature and all input voltage conditions, the Vsense accuracy is 2%.

    -Michael