HD3SS3212: AC Coupling Capacitors location while common is higher than 2V in one side

Wesley He

Part Number: HD3SS3212

Tool/software:

Hi team.

Customer is designing HD3SS3212 in their system. In CPU side, common voltage is 0V. But in endpoint side, it's 2.4 or 2.8V.

Question, which typology should be used for the AC Coupling Capacitors?

Figure 4 or figure 6 in datasheet?

Is below figure 4 works?

Thanks.

Regards,

Wesley

4 months ago

+1 Kameron Hill 4 months ago

TI__Mastermind 24440 points

Hi wesley,

Here is a helpful e2e faq for this application but looking into this I can say that figure 4 is the right setup for this application to protect the mux from the common mode voltage on the endpoints

Please let me know if you have any additional questions

Regards,

Kameron

0 Wesley He 4 months ago in reply to Kameron Hill

TI__Expert 6205 points

Hi Kameron,

Follow up question, with the AC coupling, the Vpp in HD3SS3212 side is -400 to +400mV, is this can be accept by HD3SS3212?

Since the datasheet had mention the Vdiff is from 0-1.8Vpp

Thanks.

Regards,

Wesley

0 Kameron Hill 4 months ago in reply to Wesley He

TI__Mastermind 24440 points

Hi Wesley,

This device should support a -400 to 400mv signal.

This is because for this device and other devices with VCM and Vdiff specifications the recommended io voltage can be found using the equation Vcm+ Vdiff/4

So for this device the recommended io voltage can range from (2+ 1.8/4)=2.45V to (0-1.8/4)=-0.45v.

2.45V to -0.45V

Here is another e2e post where I explained this topic to another engineer about a similar device.( Just adding this to see if this can conceptual help you understand if needed.)

However let me know if you need any other help and I can try to explain more.

Regards,

Kameron

0 Wesley He 4 months ago in reply to Kameron Hill

TI__Expert 6205 points

Hi Kameron,

Thanks for your answer. Following question listed below:

1. If the Vdiff is 1900mV which is higher than datasheet max 1800mV, any risk here? And any workaround for this case?

2. If the figure 4 already support the >2V common voltage case, question: which case need the figure 6 AC coupling structure? Is it >2V common voltage in bost side?

Thanks.

Regards,
Wesley

0 Kameron Hill 4 months ago in reply to Wesley He

TI__Mastermind 24440 points

Hi Wesley,

1.If Vdiff is outside recommended operating conditions we cant guarantee performance of the device long term .however this is only 100mv higher than recommended operating conditions so this could work. Ti cannot guarantee however

Im not sure of a work around here but I would try to have the system meet the Vdiff=1.8V recommended specification.

2. You are correct that Figure 6 is what you would need to do if both sides of the mux are exposed to VCM>2V. The FAQ has a good description of this.

Please let me know if you need any further assistance.

Regards,

Kameron

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HD3SS3212: AC Coupling Capacitors location while common is higher than 2V in one side