MAX3243: Undershoot

user6213590

Part Number: MAX3243

Hello.

According to the MAX 3243 data sheet, the undershoot voltage is -0.3 V (T1IN_pin).
Is there any risk if the undershoot voltage is lower than -0.3 V?
We observed -0.8V/2.7ns, that should be ok or not?

Best regards.
Jungo

over 6 years ago

0 Hao L over 6 years ago

TI__Mastermind 25705 points

Jungo,

If the voltage goes below -0.3V, internal diode of IC could be turned on to conduct big current from the ground. In your case, since the duration is short, you may not see immediate failure (how often does the undershoot happen?). If it's possible, you can check the pin's current with -0.8V input voltage. However there is no way to guarantee the device won't have reliability risk in life time in this application.

Regards,

Hao

0 user6213590 over 6 years ago in reply to Hao L

Prodigy 120 points

Hao,

Thank you for your response.
The baud rate is 115200 bps.
The input current is 12mA, that should be ok or not?

Best regards.
Jungo

0 Hao L over 6 years ago in reply to user6213590

TI__Mastermind 25705 points

Jungo,

Do you mean the dip happens at very transition? Theoretically it could show up in every 8.68us. I think based on the frequency and current level, it should not be OK. Please let me know if you have more questions.

Regards,

Hao

0 user6213590 over 6 years ago in reply to Hao L

Prodigy 120 points

Hao,

Thank you for your response.
Your understanding is correct.
Dip is show up in every 8.68 us.
I recognized that there was a problem.

Please tell me for reference.
12 mA seems to be smaller than input clamp current -20 mA, but why is it not OK?

Best regards.
Jungo

0 user6213590 over 6 years ago in reply to user6213590

Prodigy 120 points

There is a correction.
Dip could show up in 17.36 us at minimum.

0 Hao L over 5 years ago in reply to user6213590

TI__Mastermind 25705 points

Jungo,

Where does the 20mA clamping current come from? I don't see it on the datasheet. TIN is logic input, which generally takes current in uA.

Regards,

Hao

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MAX3243: Undershoot