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SN74LS73A: Cascade connection

Marvin Gasis Arcangel
Genius 9675 points
Part Number: SN74LS73A
Other Parts Discussed in Thread: CD74HC73, CD74AC112

Hi Team,

Can you help with the customer question in the document below?

Question.docx

Thank you in advance.

Regards,

Marvin

  • 0
    Guru 265760 points

    The schematic is incomplete; the LEDs are not shown.

    If you are driving the LEDs' anodes, then you are likely to violate the VOH limit; TTL devices are not rated for more than 400 µA. To work around this, drive the LEDs' cathodes from the /Q outputs.

    If you are driving the LEDs' cathodes, then I see nothing obviously wrong; please provide an oscilloscope trace of the 1Q output.

    Nowadays, there is no reason to use a bipolar device. Use the CD74HC73, or the CD74AC112 for more drive strength.

  • 0 in reply to Clemens Ladisch
    TI__Genius 9675 points

    Hi Clemens,

    Disregarding the LEDs, the customer can get the 4FF in 2 ICs to work to work perfectly driving the anodes of the LEDs, but only when they connect them as shown in diagram "MOD2". Can you explain further how connecting them in this order will allow them to work when in cascade, ie FF1 driving FF2 in IC1 the FF2 of IC1 driving FF1 of IC2 then FF2 in IC2? They want to know why the circuit only work when cross connected as shown in diagram "MOD2", there must be something significant in the way the IC is operating.

  • 0 in reply to Marvin Gasis Arcangel
    Guru 265760 points

    There should be no difference.

    Please show an oscilloscope trace.