Bidirectional buffer with Better VOH and VOL

Vignesh M26

Other Parts Discussed in Thread: SN74AUC245

Hi,

I would like to interface two chips, Where VDDIO = 1.8V. Due to the negative noise margin issue I need to use a bidirectional buffer or level translator with better Voh, Vol. (Like Voh is more or equal to than 1.6V and Vol lesser or equal to 0.2V) . Pls suggest the suitable bidirectional auto detection translator or buffer with above requirement, Or is there any way to suppress this negative noise margin pls give advice on this.

Awaiting for the reply,

Thanks,

Vignesh

over 6 years ago

0 Emrys Maier over 6 years ago

TI__Guru* 97046 points

Hi Vignesh,

What is the output drive current? If you are driving a purely capacitive load, then the output voltage of any CMOS device will be ~Vdd and GND. if you are driving a heavy resistive load, the VOH/VOL will suffer significantly. I would recommend reading this FAQ for details:

My first recommendation would be the SN74AUC245, which is optimized for 1.8-V operation.

If this answers your question, please click the green "this resolved my issue" button, or respond and I will continue to help.

0 Vignesh M26 over 6 years ago in reply to Emrys Maier

Intellectual 590 points

Hi Emrys,
Thanks for the reply. I need bidirectional transceiver with auto direction control. Load is also the CMOS logic chip's GPIO pins. The drive current not mentioned on the datasheet. No other load are connected. Pls advice ...

Thanks,
Vignesh.

0 Emrys Maier over 6 years ago in reply to Vignesh M26

TI__Guru* 97046 points

For an auto-bidirectional transceiver, there's only one option -- the TXB family of autobidirectional translators.

http://www.ti.com/logic-circuit/voltage-level-translation/auto-bidirectional-voltage-translation/products.html#p1512=TXB

0 Vignesh M26 over 6 years ago in reply to Emrys Maier

Intellectual 590 points

Thanks Emrys..

In my case, margin levels are Input IC's Vih min = 1.44V.
output IC's Vohh min= 1.40V and input IC's Vil max= 0.36V output IC's Vol max = 0.4V.

Datasheet didn't mention the drive current level. But we can manage the drive strength through register settings. Pls advice...

0 Emrys Maier over 6 years ago in reply to Vignesh M26

TI__Guru* 97046 points

VOH and VOL are _always_ rated with a load current, because otherwise they would be meaningless. If you're looking at a connection between two typical CMOS devices, then VOH will be ~VDD and VOL will be ~GND... the only current is leakage. If you also have pull-up or pull-down resistors, then you must take that current into account.

If you can share a schematic showing everything connecting to the TXB device, then I can help with determining the loading and VOH/VOL.

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Bidirectional buffer with Better VOH and VOL