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SN65HVD75: Drive strength and long term reliability

Part Number: SN65HVD75

Team,

My customer has the following question.

A question came up on the SN65HVD75 part listed above.

This device is connected to an EMI filter that has a 4.7 nF capacitor to ground. There is no series device between the driver and the capacitor.

At 9600 baud rate, a 160 mA peak current is being driven by the above part for a time period of less than 0.4 microsecond, see the attached diagram. Is there any long term reliability on the part by doing this? 

Regards,

Aaron

  • Aaron,
    Could you elaborate more about the test condition? 1) Does the peak current come from the device (HVD75) or from external source? 2) When it happens, how's the corresponding bus voltage look like? 3) Does the peak occur to one bus pin (A or B) or both? If it's one pin, how is the state of the other one? These information would help me evaluate the impact on the device.
    Regards,
    Hao
  • Per customer:

    Here's a quick mockup I did, the data in pins aren't shown. The current would come from the HVD75. The peak current would occur on both pins of the device at the same time. We don't have voltage waveforms of the actual situation in the lab as we aren't that far along yet. The device would be operating at 9600 baud.

  • Aaron,

    Other than the LCs, are there any other loading on the bus, or any termination resistor between A and B pins? Usually we recommend 120Ohm resistor to match the characteristic impedance of the cable for better signal integrity. You can refer to this guideline (www.ti.com/.../slla272c.pdf). Anyway, I think what you see is the shoot-through current. During the transition, for example, P side driver is turning off and N side is turning on. There might be a short period of time that both side are ON, which generates a current flowing from supply to ground. In HVD75, the driver has a current limit at 160mA, which matches your test data. This is normal behavior of the device, which should not have any reliability concerns. Please let me know if you have other questions.

    Regards,

    Hao