TI E2E Community
Voltage Level Translation Forum
issue voltage with TXB0108PWR
I try to use the TXB0108PWR by putting 3,3V (with a wire) on the A pins and obtain 5V on the B.
But with these schematics I'm using (see attached files) I don't obtain exactly 5V : sometimes the B pins are around 2,4V and sometimes it's 5V.The values are stable but they can change between 2 mesures.
However I used the same schematic as in the datasheet, OE is linked to VccA... I don't understand.
Help me please.
Could you please let me know which pin on which part did you measured?
Actually, in your design, for U1, you have the I2C signal and also the B side SCL and SDA have the 4.7Kohms pull up resistor, this design is not correct.
The TXB0108 can not be used to transfer the I2C signal(open drain) , also for any pins, if you want to add the pull up resistor, the resistor should be larger or equal to 50Kohms. you can see the detail in the datasheet.
So you can replace U1 with TXS0108, I think you can find the Pin-Pin compatible part, this TXS part can be used for both Open drain and push pull signal translation. the key concern is about the input frequency, the TXS0108 can handle 60Mbps at 3.3V to 5V translation while the TXB0108 can handle 100Mbps.
If you still have issue, please let me know.
OK concerning the I2C, I didn't check it yet ...And for the pins, I checked everyones (from A1 to A8 for U1 and U2). That's my main issue...Maybe I shouldn't use a wire to verify a pin by linking the Inputs with the 3,3V from the card (that's how I simulate a high level transition) ?Is the TXS0108 have more stability?thank you.
For either TXB and TXS part, please use the switch signal to check these parts. that will be better. Because the transfer direction and transfer trigger is caused by the signal rising or falling at the input pins. actually if you connect the input to the 3.3V directly, the output side should be work an have high output. if you still have the issue, please make sure you have the stable connection for the input and also easure the waveform of input and output to see whether any findings.
Hello Junjie,I checked the waveform signals with an oscilloscope, it's OK...I tried to put a serial RS232 protocol (9600bps) side 3,3V but it doesn't work, is it too quick ?I read in the datasheet tha it is recommanded to put all the i/o unused at the GND, and on my schematics as you can see it's not done...So, do you think it doesn't work because of this ?...cordially.
sorry the exact designation is UART, not RS232.
Could you please let me know which part and which pins did you measured? and what your input and output waveform looks like?
For TXB0108, it is OK to transfer the signal with 9.6MPBS from 3.3V to 5V translation, it should be no issue. so please let me know the details.
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