SN74LVC8T245: overshoot and undershoot limit for SN74LVC8T245DBR

prasanna kumara G

Part Number: SN74LVC8T245

Dear Team,

Please share me the Overshoot and undershot withstand of SN74LVC8T245DBR.

We are transiting 4Mhz clock through SN74LVC8T245DBR and same signal is looped back to another SN74LVC8T245DBR using VME connector and 20awg PTFE cable, while probing the signal out from SN74LVC8T245DBR we observed more than 7.5V overshoot and a lot of ringing .

Since it is very low speed why this overshoot and ringing happening.

over 8 years ago

0 Emrys Maier over 8 years ago

TI__Guru* 97046 points

Hello prasanna,

This device is only rated to handle 6.5V maximum at an input, so 7.5V is going to cause problems.

Typically the ringing is caused by very fast edges into LC loads - note that the edge rate, not the bit rate is what matters here. The long wires likely add significant inductance and capacitance without adding enough damping resistance to kill off the oscillations. Would it be possible for you to add a series resistor to the outputs of the transceiver to dampen out the ringing? 30 ohms is typically used for this.

0 Clemens Ladisch over 8 years ago

Guru 317260 points

Please note that the oscilloscope probe will also add significant inductance and capacitance, unless you take special steps to reduce it.

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SN74LVC8T245: overshoot and undershoot limit for SN74LVC8T245DBR