LSF0204: Level Shifter Schematic Review

David Tandri

Part Number: LSF0204
Other Parts Discussed in Thread: SN74AXC4T245, SN74AXC4T774

Hi,

The schematics contain TI parts and Non-TI parts to review is as attached in this email. Please review the TI parts only.

TI components:

2x Level shifters

Please verify and comment on the connections to the components above.

What is the format should I send for layout review?

Thanks

TI Level Shifter Schematic Review.pdf

LSF0204

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 316510 points

The note says "All the pullups removed". The LSF usually needs pullups on its outputs, and you need to size the pullups correctly to balance between speed and power usage.

For unidirectional signals, a direction-controlled level shifter like the SN74AXC4T774 or SN74AXC4T245 would be simpler and more robust.

For a layout review, an image should be sufficient.

0 David Tandri over 5 years ago in reply to Clemens Ladisch

Expert 1355 points

Hi,

Thanks for the recommended parts. SN74AXC4T774 or SN74AXC4T245 has active-low Enable pin. Active-low Enable pin is not suitable for our application.

What if the modules which are interfacing with the level shifters already have internal pullups?

Will these internal pullups help without additional pullups?

Thanks

0 Clemens Ladisch over 5 years ago in reply to David Tandri

Guru 316510 points

The schematic shows the LSF0204 EN pins connected directly to Vref_A. Connecting OE to GND has exactly the same effect.

Internal pullups can work, if they are small enough to reach the desired speed.

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LSF0204: Level Shifter Schematic Review