SN54SLC8T245-SEP: Vih and Vil

Jack Zhang

Hello TI e2e, I plan on using SN54SLC8T245-SEP for level shifting of single-ended discretes from 1.5 V to 1.8 V, 1.5V to 3.3 V, 1.8 V to 1.5V and 3.3V to 1.5V. What is the VOH and VIL for this application? I see the datasheet specified VOH ad VOL for ranges of VCCA/VCCB, and would like some clarification. Thank you for your time.

over 3 years ago

0 Michael Ikwuyum over 3 years ago

TI__Guru 51346 points

Hi Jack,

Please see the referenced FAQ1 and FAQ2 to help estimate the VOH and VOL values for the specifications given in the datasheet, thanks!

Best Regards,

Michael.

0 Clemens Ladisch over 3 years ago

Guru 317080 points

The datasheet specifies both V_CCA and V_CCB, but those columns are identical. The drive strength depends only on the supply voltage on the output side.

0 Jack Zhang over 3 years ago in reply to Clemens Ladisch

Intellectual 540 points

Thanks for the replies. How do I interpret the drive strength currents, I_IL, I_IH, I_OL, I_OH for my application?

0 Michael Ikwuyum over 3 years ago in reply to Jack Zhang

TI__Guru 51346 points

Hi Jack,

You can use ohms law to interpret the values for the min/max input current and min/max output current in your application.

Drive strength is often given as a resistance, which is the ratio of the voltage drop across the output transistor to the current through the output transistor.

For example, given the highlighted values from the datasheet, the resistance = (3-2.3)/0.012 = 58.33 ohms.

Please note that this is for the maximum resistance as the datasheet specs are rated for the worst case scenarios. I.e when the resistance is at a maximum and typical values should be about half, thanks.

Best Regards,

Michael.

0 Jack Zhang over 3 years ago in reply to Michael Ikwuyum

Intellectual 540 points

Thanks for the reply. One last question: I do not see an output impedance spec for the data ports. I was planning on adding source series terminations to all digital outputs from the translator. Any insights or recommendations here?

+1 Michael Ikwuyum over 3 years ago in reply to Jack Zhang

TI__Guru 51346 points

Hi Jack,

We recommend about a 33 ohm source resistor to help match closer to 50 ohms, thanks.

Best Regards,

Michael.

0 Jack Zhang over 3 years ago in reply to Michael Ikwuyum

Intellectual 540 points

Great, thank you for the recommendation. If you don't mind another question: do any of the A/B pins include pull-up/down resistors internal to the part? I recall some translators do and some do not.

+1 Clemens Ladisch over 3 years ago in reply to Jack Zhang

Guru 317080 points

No; such resistors would have been mentioned somewhere, and would at least be visible in the input leakage current. Also see footnote (3) in section 6.3.

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SN54SLC8T245-SEP: Vih and Vil