SN74VMEH22501A: Imin and Imax value in IBIS model

Hung Ching Hsu

Part Number: SN74VMEH22501A
Other Parts Discussed in Thread: SN74LV14A

Hi Team,

Since following thread is locked, let me open a new thread.

https://e2e.ti.com/support/logic-group/logic/f/logic-forum/1093626/sn74vmeh22501a-undershoot-for-around-10ns/4053794#4053794

Since datasheet said "device can exceed -0.5V as long as IIK is lower than 50mA(SN74VMEH22501A) and 20mA(SN74LV14A) respectively", and Clemens said IIK can be estimated from IBIS model. Customer have 2 questions as following.

1. Customer confirmed VMEH22501A_IO_3B pin, but it comes out I(min) is larger than I(max) when V=-0.665V, is it normal?

2. Vpeak of undershoot = -0.54V in customer application, I is -30mA for worst case when VIN=-0.6V, so does it mean it is NG since exceeding abs. max rating which is 20mA?

Thanks.

Regards,

over 2 years ago

+1 Emrys Maier over 2 years ago

TI__Guru* 96661 points

Hi Jo,

A voltage at the input does not guarantee a specific current, as implied by your question. I would recommend to measure the current to determine if it is in excess of the absolute maximum rating, rather than relying on a diode model for an estimation.

If it is a large area of concern for the customer, a series resistor can be added to the input to limit current in the event of undershoot. Typically, 33 ohms will be sufficient to prevent excessive current. With bus-hold inputs, I would not recommend exceeding 100 ohms in series with the input.

0 Hung Ching Hsu over 2 years ago in reply to Emrys Maier

TI__Expert 3086 points

Hi Emrys,

Thank you for the advice. But customer can't neither measure IIK nor add resistor this time due to board configuration.

So customer wants to estimate IIK from IBIS model as Clemens suggested. Will the value in IBIS model be a guarantee or just a reference(not guaranteed)?

BTW, from SN74LV14A IBIS Model (Rev. A), I is 0.353mA when VIN is -0.5V, which is lower than 20mA(abs. max rating), so I think it should be okay, do you agree?

Thanks.

Regards,

0 Emrys Maier over 2 years ago in reply to Hung Ching Hsu

TI__Guru* 96661 points

Hi Jo,

Hung Ching Hsu said:
Will the value in IBIS model be a guarantee or just a reference(not guaranteed)?

The IBIS model can be used as a reference, but it's not a guarantee of the current flowing in the circuit. The IBIS model's clamp diode current is based on DC measurements -- not transients.

Hung Ching Hsu said:
BTW, from SN74LV14A IBIS Model (Rev. A), I is 0.353mA when VIN is -0.5V, which is lower than 20mA(abs. max rating), so I think it should be okay, do you agree?

The datasheet also indicates that -0.5V is within the absolute maximum voltage range of the device. It is only beyond this value that damaging current could occur.