• TI Thinks Resolved

TXB0304: Slow charge and discharge waveform

Intellectual 2090 points

Replies: 1

Views: 9

Part Number: TXB0304

Team,

One TV customer is using TXB0304 on their TV project, because the board is big, the output trace run for 20cm on the PCB.

Its schematics is under here, because they found big ringing on the edge, so they changed those 0ohms resisters to 200ohm.

Using 0ohms resistors:The waveform are got from test point.

Change to 200ohms:

But there is slow charge and discharge when it become low and high. As the start point is close to the sink IC's determine threshold, so the time constant is not stable. The customer want to get ride of the slow charge.

So the questions:

1. Do you know what make the slow charge?

2. If the 200 ohms is not a good idea, and suggestion to remove the ringing.

3. If it is necessary to let them to add some buffer. Ideally they will not add a buffer, since TV is cheap, the cost is very important.

  • The slow charge is caused by the extremely high output impedance of the TXB (1 kΩ). This is needed to allow other devices to override the voltage level, which is required for automatic direction sensing.

    For unidirectional signals, a voltage translator with automatic direction sensing is not necessary. I recommend a translator with proper output buffers, such as the SN74AXC4T245.