TCA9617B: TCA9617B Wave

Derek Xie

Genius 12255 points

Part Number: TCA9617B
Other Parts Discussed in Thread: TCA9617A

Hi Team:

Need your help to check whether the waves are right.

Below is the connection block:

The master output wave is good. But the port A clock will have a step:

Could you tell me why will have a step? Due to I2C will check voltage level to see the "0" or "1". Whether will cause potential risk?

When the I2C send out, the slave will reponse. But the slave signal will be like below:

Why the response signal can't get zero level, will always have 500mV bias? Thanks.

over 7 years ago

0 Jonathan Valdez over 7 years ago

TI__Genius 16430 points

Hello,

Everything you are seeing is normal, and expected behavior.

Please read the datasheet, section 9.3.3 High to Low Transition Characteristics

0 Derek Xie over 7 years ago in reply to Jonathan Valdez

TI__Genius 12255 points

Hi Jonathan:

Would you please tell me why it will have a step? Thanks.

0 Derek Xie over 7 years ago in reply to Derek Xie

TI__Genius 12255 points

The datasheet mention the step is around 0.5V, but why customer test is higher than 0.5V? Thanks.

0 fhoude over 7 years ago in reply to Derek Xie

TI__Genius 17205 points

Hello Derek,

What you are seeing is the static voltage off-set of the device. This is how we can tell which direction the zero is coming from.

Here is a post that describes how buffered parts work.

https://e2e.ti.com/support/interface/i2c/f/390/p/548966/2006051?tisearch=TI-e2e&keyMatch=static%20voltage%20off-set%20fhoude

-Francis Houde

0 Derek Xie over 7 years ago in reply to fhoude

TI__Genius 12255 points

Hi Francis:
Thanks. It make me clear. I have 3 question below:
1. Why we will have a buffer to output 0.5V and why we have 0.4V comparator?
2. If the voltage is 1.8V at B port. If we use A to B, A is master then B output will close to 0.3*1.8V = 0.54V. How to solve it?
3. For serial application, whether our part can support A port input, B port output then connect the other TCA9716 B port for input, then A port output?
Thanks.

0 fhoude over 7 years ago in reply to Derek Xie

TI__Genius 17205 points

Hello Derek,

1. When the zero comes from the A side then the B side is set to 0.5V, when the slave device pulls the voltage below 0.4V than the zero is propagated back to the A side. This allows the device to know when to force a zero onto the A side from the B side.

2. The TCA9617A doesn't support 1.8V on the B side. I didn't know that was a requirement. What are the two voltage levels you are working with?

3. I am not sure what you are asking. Are you asking if you can put two buffers in series? Yes, but must NOT connect two B sides together.

-Francis Houde

Interface

Interface forum

TCA9617B: TCA9617B Wave