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TLC555: RESET input

Vidhya J
Intellectual 415 points
Part Number: TLC555

Tool/software:

Hi Team,

Reset input of timer 

0.3V to 1.8V is considered as reset active low?

greater that 1.8V input is out of reset?

Kindly confirm.

Regards,

Vidhya

  • 0
    TI__Guru**** 152406 points

    Hello Vidhya,

    Below 0.3V will put timer in RESET mode.

    Above 1.8V will put timer in normal operation mode.

    Between 0.3V and 1.8V, the timer may be RESET, running in normal operation, or may even have unusual operation (if held at this voltage).  

  • 0 in reply to Ron Michallick
    Intellectual 415 points

    Hi Ron,

    If between 0.3V to 1.8V it is undefined state, why the table in datasheet specifies VReset as 0.3V to 1.8V??

    <1.8V is considered as reset? >1.8V it is out of reset?

    Kindly clarify.

    Thanks,

    Vidhya

  • 0 in reply to Vidhya J
    TI__Guru**** 152406 points

    Vidhya,

    To be technical, the parameter is owned by each sample of 555. It is the actual point where each 555 switches between reset and normal modes. Per data sheet this point is typically 1.1V. This is interesting if your task is to build 555 chips.

    If your task is to use 555 chips in an application, then you need to know that 555 chips that happen to switch modes at 0.35V or 1.75V are considered good by datasheet. Therefore your application better apply only voltages less than 0.3V or greater than 1.8V; otherwise good samples may cause an application malfunction.

    Vidhya J said:
    <1.8V is considered as reset?

    Maybe

    Vidhya J said:
    >1.8V it is out of reset?

    Yes

  • 0 in reply to Ron Michallick
    Intellectual 415 points

    Hi Ron,

    555 timer is powered by 5V.

    In my application, two 555 Timer is used to drive LED blinking and timer has to be out of reset.

    Reset pin of 555 timer is controlled by level translator (SN74LXCH8T245RHLR) and NOR gate (SN74LVC1G02DBVR)

    For Logic high level, there is no issue as VOH min= 2.4V for level translator and NOR gate and 555 timer reset pin is >1.8V

    I see issue with Logic low levels.

    SN74LXCH8T245RHLR level translator VOLmax =0.55V but VILmin of 555 timer is 0.3V

    SN74LVC1G02DBVR NOR gate VOL =0.55V but VILmin of 555 timer is 0.3V

    Kindly suggest.

    Thanks and Regards,

    Vidhya

  • 0 in reply to Vidhya J
    Intellectual 415 points

    HI Ron,

    using TLC555 in Astable mode.

    1blink /second Green LED.

    Do I need pull up on OUT pin of TLC555?

    IC32 output shows leakage for 2.5V (red curve)

    should add a pull down?

    Thanks,

    Vidhya

  • 0 in reply to Vidhya J
    TI__Guru**** 152406 points
    Vidhya J said:
    VOLmax =0.55V but VILmin of 555 timer is 0.3V

    Sure at 32mA of current, why would such a high current flow? It would be less than 100uA = 0.1V max

    Vidhya J said:
    Do I need pull up on OUT pin of TLC555?

    No you do not. TLC555 output is push pull.

    Vidhya J said:
    IC32 output shows leakage for 2.5V (red curve)

    Red curve looks wrong for U32 out, is it shorted to another output? 

    The schematic pieces do not match up well. Things are missing. 

  • 0 in reply to Ron Michallick
    Intellectual 415 points

    1. VOL output from level translator or NOR gate will be less than 100uA as there is no much load capacitance and voltage will be 0.1V? so there can be no extreme case and IO logic low will still be a PASS?

    2. ok. will remove the pull up at OUT pin

    3. Red curve: U32 output is input to IC28 (AND gate). I will check and get back on this.

    Thanks,

    Vidhya