DS26LS31C: input structure question

Kannan Sockalingam

Part Number: DS26LS31C
Other Parts Discussed in Thread: DS26LS31MQML, AM26LS31, SN74LS04

Tool/software:

Yes, this part is obselsete. I need to find the single ended input structure details for my customer to do analysis for a failure to rule it out.

In the data sheet there is no simplified input diagram like usually TI has in its data sheets.

Can someone please help with the output structure of this device?

4 months ago

0 Muhammad Ahmad 4 months ago

Prodigy 40 points

Sorry meant input structure. Thanks

0 Muhammad Ahmad 4 months ago in reply to Muhammad Ahmad

Prodigy 40 points

0 Muhammad Ahmad 4 months ago in reply to Muhammad Ahmad

Prodigy 40 points

Something like the above picture.

0 Clemens Ladisch 4 months ago in reply to Muhammad Ahmad

Guru 288210 points

The DS26LS31MQML is not obsolete, but its datasheet does not provide this information either. These DSxxx devices were acquired from National Semiconductor, so I guess this information does not exist.

However, the logic I/Os of "LS" devices all use the same structure, so the input should be identical to that shown in the AM26LS31 datasheet, or the one shown in the SN74LS04 datasheet.

0 Muhammad Ahmad 4 months ago in reply to Clemens Ladisch

Prodigy 40 points

Thank you so much Clemens. Greatly appreciate your reply. If that is the case, then it seems like the input may present as a 20-22K pull up to VCC, when input is low, Schottky is forward biased, so a strong pull down on outside is needed to keep the input low, when NOT actively driven. Or am I missing something here?

Thanks

0 BOBBY 4 months ago in reply to Muhammad Ahmad

TI__Guru 60850 points

Hi Muhammad,

Clemens is correct.

The input stage for these devices likely have the schotty diode feeding into the input pin from a ~20k pull up. I think your understanding of it is correct, a low low will bias the schotty diode (BJT base will see Vfd of the schotty) and a logic high on the input pin will unbias the schotty diode so the BJT base will be pulled up to Vcc with the 20k pull up.

-Bobby

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DS26LS31C: input structure question