TXB0106: output(A->B) low level does not reach to 0V

Kang Seunggoo

Part Number: TXB0106
Other Parts Discussed in Thread: SN74LXC8T245, SN74AHC367, SN74AHCT367, SN74AHC541, SN74AHCT541

I used TXB0106 as UART level shifter

V_CCA as 3.3V, V_CCB as 5V

The problem is the higher peak of translated level(3.3 to 5) shows well and low side also until I connect something(just test by oscillator), after connect other sensors or sth, low side can't reach to 0V that makes the logic hesitates to recognize low level while high level goes well.

I tried to apply a pulldown resistors(0, 51K, 1M) but no effect

I used STM32F4VE (3.3V based logic) board to make signal

since STM board should already had capacitors, I first had no other bypasses

I directly connected V_CCA to OE

thanks

over 4 years ago

+1 Clemens Ladisch over 4 years ago

Guru 317000 points

The TXB has very low drive strength (20 µA). What load do you have on the output?

Better use a direction-controlled or unidirectional translator.

0 Kang Seunggoo over 4 years ago in reply to Clemens Ladisch

Prodigy 10 points

I am trying several sensors... so the problem since that output signal is weak...
I will check them then,
thanks!

0 Kang Seunggoo over 4 years ago in reply to Clemens Ladisch

Prodigy 10 points

may it will be better when I use TXS series?

0 Clemens Ladisch over 4 years ago in reply to Kang Seunggoo

Guru 317000 points

All auto-bidirectional translators have weak outputs (TXB) or are passive (LSF, TXS) to allow other devices to override the voltage level.

How many signals are there in each direction?

0 Kang Seunggoo over 4 years ago in reply to Clemens Ladisch

Prodigy 10 points

six UARTs, 6 + 6
I already made PCB(TSSOP 16)s, so now I'm discussing replace TXB0106PWR to TXS0108EPWR. cut 7, 8 leg and connect GND and OE leg to pad
If it does not work, I will make new PCB for SN74LXC8T245.

0 Clemens Ladisch over 4 years ago in reply to Kang Seunggoo

Guru 317000 points

To convert 5 V to 3.3 V, you can use any buffer with overvoltage-tolerant inputs, such as the SN74AHC367.
To convert 3.3 V to 5 V, you can use any buffer with TTL-compatible inputs, such as the SN74AHCT367.

(8-bit devices like the SN74AHC541/SN74AHCT541 have an easier pinout and are cheaper.)

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TXB0106: output(A->B) low level does not reach to 0V