This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLC555-Q1: SCH review

Part Number: TLC555-Q1
Other Parts Discussed in Thread: SN74CB3Q3245

Hi Team,

The customer found that the IO model of SN74CB3Q3245 cannot be set as output, why? Could you pls help? The output high-level duration tH:  0.939 x 49.9k x 4.7uF = 162ms.Is this right? 

TLC555QDRQ1 schematic review.pdf


  • Hello Hailiang, 

    The timing will be approximately t_High = 1.1*(49.9k)*(4.7uF) = 257.9 ms. I verified this in Tina Ti as shown below. 

    In order to achieve a high time of about 162 ms, the resistor value could be changed to 31.3k as shown below. 

    It couldn't hurt to place an optional resistor possibly 100k from the gate of the FET (Q172) to ground such that it allows for a current path to ground if needed. Additionally, depending on the type of load that is being driven in the circuit we sometimes recommend an optional TVS diode on the output of the 555 to the supply if inductive kickback is a concern in the system. For example if there are long cables or inductive elements being driven. I do see that there is a capacitor on the control pin which is good. This will help filter the control pin line. Let me know if I can be of further assistance.

    Best Regards, 

    Chris Featherstone