TXB0108: optocoupler interface

Part Number: TXB0108
Other Parts Discussed in Thread: SN74LVC1G34, SN74AXC4T774,

Hello,

We have built a circuit where the level shifter drives optocoupler inputs. The problem is that for a logic high the voltage at the level shifter output drops to about 1.5V (which means that it is getting loaded). Now appropriate series resistors have been added between the levelshifter o/p and the optocoupler i/p but the problem persists. Please advise.

over 3 years ago

0 Clemens Ladisch over 3 years ago

Guru 316960 points

The TXB has a drive strength of 20 µA. Either add a buffer (e.g., SN74LVC1G34) in front of the optocoupler, or use a level shifter with buffered outputs (e.g., SN74AXC4T774).

0 SM over 3 years ago in reply to Clemens Ladisch

Expert 1760 points

Thanks a lot Clemens for the quick answer. May I ask you to please suggest a part that is foot print compatible with the TXB0108 as our pcb is already made. Also, what is the input current drawn (logic input)?

Thanks again,

0 Dylan Hubbard over 3 years ago in reply to SM

TI__Mastermind 45835 points

Hi SM,

There is no footprint compatible device that can solve this unfortunately, there will need to be a footprint change.

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TXB0108: optocoupler interface