TXB0108: TXB0108DQSR

wu huaitao

Part Number: TXB0108
Other Parts Discussed in Thread: TXU0104, TXU0204,

One of our circuits uses the level conversion chip of your company TXB0108DQSR. The load device is the scanner dock (3.3V), and the control signal is output by the CPU (1.8v). The current phenomena are as follows:

1, when connected to the scanner dock, the CPU will not pull up, and the waveform is a high level with concussion. Remove the scanner dock, the high level can be pulled up normally;

2, if the oscilloscope point at the load end can be normal output high level, if you do not use the oscilloscope probe point here, it is not working normally.

3, replace Onsemi's level conversion chip(NLSX3018MUTAG) can normally output high levels.

over 2 years ago

0 Clemens Ladisch over 2 years ago

Guru 317370 points

Section 6 of Do’s and Don’ts for TXB and TXS Voltage Level-Shifters with Edge Rate Accelerators says:

Minimize reflections / ringing.
Consider the impact of temperature on the output impedance, as mismatched impedance with PCB traces yield reflections.
Reflections or ringing can be amplified by the one-shot as false edge triggers.
Excessive ringing can cause false triggers observed as oscillating outputs.
Ringing is also caused by capacitance and inductance of long cables or traces and can be amplified by unstable GND or VCC voltages.

The capacitance and inductance of your traces/cables are too high.

Please note that the NLSX3018 has similar one-shot circuits and can have similar oscillation problems. Apparently, its analog characteristics are just different enough that you got lucky with your circuit.

For unidirectional signals, you should use unidirectional translators like the TXU0104/TXU0204.

0 wu huaitao over 2 years ago in reply to Clemens Ladisch

Prodigy 10 points

The capacitance and inductance of your traces/cables are too high.--------you mean the The TXB0108 is designed to drive capacitive loads of up to 70 pF???our PCB's capacititance is too large?

Is there any way to solve this problem?You can see eight signals in our circuit diagram,including UART_TX,UART_RX,so we can't choose TXU0104/0204.

How do we measure this capacitance? Can we solve this problem by connecting a resistor in series?

0 Clemens Ladisch over 2 years ago in reply to wu huaitao

Guru 317370 points

The TXB should be used only between devices that are near each other on the same board.

One TXU0104 and one TXU0204 should have the number and direction of channels you need.

A series resistor is unlikely to help.

0 wu huaitao over 2 years ago in reply to Clemens Ladisch

Prodigy 10 points

What are the driving capacitive load design values for the TXU0104 and TXU0204? And how to measure the capcitance?

+1 Jack Guan over 2 years ago in reply to wu huaitao

TI__Mastermind 41216 points

Hey Wu,

Please see the below FAQs in regards to your questions:

[FAQ] What is the maximum capacitive load that a logic device can drive?

[FAQ] What is the maximum trace length that a logic device can drive?

Regards,

Jack

Logic

Logic forum

TXB0108: TXB0108DQSR