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TLC555-Q1: TLC555-Q1 - Monostable timer

zabbza
Prodigy 160 points

Part Number: TLC555-Q1
Other Parts Discussed in Thread: TLC555

Tool/software:

Dear Team,

555 is used for monostable timer.

After triggered 555, a timer work on MC  and measure time.

1- TL55Q 26M AJQHG4

2- TL55Q 87K A2QTQ4

There is two different 555 chip which are ordered different time.

if 87K chip is used, measured time is 200ms

if 26M chip is used, measured time is 100ms

All other component is same, Also the chips are interchanged on PCB.

is there any difference between 26M and 87K chips

Best Regards.

  • 0
    TI__Guru**** 170196 points

    Hello Zabbza,

    There is no difference between these old samples. 

    What is the expected time? Does trigger go high before that expected time?

  • 0 in reply to Ron Michallick
    Prodigy 160 points

    Hello Ron,

    "What is the expected time?"

    Expected time must not change according to chips.

    "Does trigger go high before that expected time?"

    Trigger go high at 200ms if 87K chip is used

    Trigger go high at 100ms if 26M chip is used

    All other component is same, Also the chips are interchanged on PCBs.

    Best Regards.

  • 0 in reply to zabbza
    TI__Guru**** 170196 points

    Zabbza,

    Trigger is an input; the TLC555 doesn't generate that signal. 

    Could you share schematic and waveforms? 

  • 0 in reply to Ron Michallick
    Prodigy 160 points

    Hello Ron,

    Sorry about definition. You are right.

    MC output is goes low for next measurement. I write definition according to MC

    In datasheet max frequency change between 1.2MHz to 2.1MHz on test.

    Because of this specification, reading values change, do it?

    Best Regards.

  • 0 in reply to zabbza
    TI__Guru**** 170196 points

    Zabba,

    In this circuit, TRG_IN should be low for a short time. It must go high before the cap probe charges to 2/3 VDD; other wise the output pulse won't end until trigger goes high, an incorrect output high time.  

    zabbza said:

    n datasheet max frequency change between 1.2MHz to 2.1MHz on test.

    Because of this specification, reading values change, do it?

    No, not related. This is more about propagation delay 

    100ms with 10M ohms should be 9.1nF

    200ms with 10M ohms should be 18.2nF

    During the comparison , what is the cap probe capacitance?