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SN74ABT541B: Overshoot of Output (Yn) is observed.

Kazuya Nakai59
Guru 21515 points
Part Number: SN74ABT541B

 Hello guys,

 One of our customers is evaluating SN74ABT541B. When they checked output (Y1) of the device on their PCB, a overshoot of output (Y1) as the attached data. Input signal (A1, ch2_skyblue), Output signal (Y1, ch1_blue), VCC voltage (Vcc, ch3_pink) are shown on the data. As you can see, Y1 signal goes to 4.5V just after A1 changed from 0V to 3V and Y1 converged to 4V after 300us.

 My question is,

 Is this overshoot (about 0.5V) a normal characteristics of SN74ABT541B?

 Your reply would be appreciated.

 Best regards,

 Kazuya Nakai.

 sn74abt541b_CH1(pin18_Y1)_CH2(pin2_A1)_CH3(pin20_Vcc)_Sweep200us.TIF

   

  • 0
    TI__Guru* 97046 points
    Hello Nakai-san,
    The SN74ABT541B is expected to have about 0.5V overshoot (over the settling voltage, not over Vcc) due to the BiCMOS output stage, however it is typically much shorter than what you show. Can you tell me your loading conditions?
  • 0 in reply to Emrys Maier
    Guru 21515 points
    Hello Emrys,

    Thank you very much for your reply.
    Any load (C/R/L) is not connected between the output of SN74ABT541B and GND. The output is connected to a connector pin with 15mm (0.015meter) PCB signal pattern. Any load (R?) should be connected between the output and GND? Is the overshoot a normal characteristics in case of no load output?

    Thank you again and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Guru* 97046 points
    Nakai-san,
    Since this device has a BJT output stage, having no load will definitely cause some issues. Our timing tests were all done with a 500 ohm load to provide a proper path to ground for the BJT bias currents. Adding a terminating resistor should reduce the overshoot time to the nanosecond range.