TCA9803: TCA9803 quesiton

Patrick Chen

Mastermind 8875 points

Part Number: TCA9803

Hello

Below is customer question.

a) Could TCA9803 A side connect with PCA9511?

b) Master Vcc, TCA9803 buffer1 Vcca, buffer2 Vcca use different 3.3V power rail, is it ok?

Patrick

over 6 years ago

0 BOBBY over 6 years ago

TI__Guru 73271 points

Hey Patrick,

A) A side should work. One thing to note is A side of TCA980x has a deglitch filter which turns on when you pull A side low temporarily, typically you do not see this on an o-scope unless your VoL on A side is larger enough. You may see TCA980x drive the line low for some nano seconds when you use this device with something with a dynamic offset like PCA9511. This is normal behavior and i do not expect any problems.

B) This is also okay. TCA980x is meant to be high impedance when the power supply is not present.

Thanks,

-Bobby

0 Patrick Chen over 6 years ago in reply to BOBBY

Mastermind 8875 points

Hello

1. Per Fig 1, does the topology have any problem for it?

2. Per Fig 2 topology, A side of TCA9803 connect to input side or output side of PCA9511 has no problem, right?

3. Per Fig 3. , if TCA9803 B side-B side connect with PCA9511, has any risk for it? salve EXP1/EXP2 independently communicate with BMC master. Thank you.

Fig 1

Fig 2

Fig 3

0 BOBBY over 6 years ago in reply to Patrick Chen

TI__Guru 73271 points

Hey Patrick,

Figure 1 and figure 2 are okay.

Figure 3 has both B sides connected on TCA9803 which is not recommended.

Thanks,

-Bobby

0 Patrick Chen over 6 years ago in reply to BOBBY

Mastermind 8875 points

Hello

Some questions below also.

1.As B side with internal pull up ,there will be two pull up resistor respectively to different power(P3V3_EXP1,P3V3_EXP2) when B side connect with B side, is it ok?

2.Is this topology connection be effective for isolate P3V3_EXP1,P3V3_EXP2, P3V3_STBY?

3.PCA9511 has rise time accelerater (we only use PCA9511 hot swap function, don't need repeater function),B side connect with it, ok?

Patrick

0 Clemens Ladisch over 6 years ago in reply to Patrick Chen

Guru 317000 points

When TRX Bobby said "not recommended", he actually meant "strictly forbidden". Connecting two TCA980x B sides together does not work.

The TCA9803 B side does not have a pull-up resistor but a current source. For the direction sensing to work correctly, there must not be any other current source connected to it; in other words, the PCA9511's rise-time accelerator would break it.