TXB0108: High level input is not confirmed

user4986490

Part Number: TXB0108
Other Parts Discussed in Thread: TXS0108E

For unavoidable reasons, FETs are used for level conversion of external 24V equipment, connected to TXB0108 and input to FPGA.

I have the following connections

FPGA(3.3V) <- A:TXB0108:B <- (5V 10kΩPU)Drain:FET:Gate <- 24Vsystem Device with voltage device resistor

The 24V device was connected, and it was confirmed that the drain voltage of the FET alone was HI: 5V and LOW: 0V.

When TXB0108 is connected to the drain of the FET, the HI level potential becomes about 2V, and HI level detection does not work well.

How can I determine the HI level?

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 316780 points

You cannot use an open-drain signal to drive the TXB; see section 8.3.2 of the datasheet.

For this application, you can use the TXS0108E, which also uses FET translation. It might also be possible to use only FETs that work with a 3.3 V gate voltage, without a second translator.

0 user4986490 over 4 years ago in reply to Clemens Ladisch

Prodigy 60 points

Is it possible to solve the problem simply by using a 74 series CMOS inverter between the FET drain and TXB0108 port B?

+1 Emrys Maier over 4 years ago in reply to user4986490

TI__Guru* 97046 points

I dontt see any reason why not - as long as you only need a unidirectional signal, a buffer or inverter could be used to redrive the signal / convert it from open-drain to push-pull.

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TXB0108: High level input is not confirmed