THVD1552: Some questions about THVD1552

ttd said:

Q1) Capacitance of THVD1552DGSR Signal Terminals
The datasheet does not include this information. Are there any measurement data or reference values available?

We don't measure the capacitance of our pins or place any kind of spec limit on them. Generally what you will see is the input pins will have more capacitance due to them being CMOS inputs and the output pins will have less capacitance since they are CMOS outputs. For 1552 which is a full duplex device, you will likely end up with higher capacitance on the differential input pins vs the differential output pins. 

ttd said:

Does this device incorporate protection elements like TVS diodes on the signal pins?

Yes, there are some protection cells on the differential pins to ensure they can handle transient events. These are spec'd on the ESD table of the datasheet.

ttd said:

I'd like to confirm the presence/type of internal protection, as this affects whether external TVS selection is necessary and impacts capacitance estimation.

Yes there are internal protection devices present on the differential pins. They should not bias when the pins are within the abs max ratings.

ttd said:

Q3) Other Recommended Products
If any products meet the following conditions, please advise.

・If protection elements are integrated on signal pins: Input capacitance ≤ 25 pF
・Package type: SOIC-14 (if possible)

Most of our devices don't have an input cap spec. 

From a longevity standpoint, we generally recommend our THVD family as these are our newer devices made in the 300mm wafer technology. 

-Bobby

Hi Bobby,

Thank you for your reply.

The background to this question , when connecting multiple THVD1552 devices on the bus, it is necessary to understand the impact on waveform rise time and communication speed, so I hope to know the capacitance.

If there are reference values (xx pF) for 1 and 2, it is helpful for me.

1. Differential input capacitance between signal terminals (A–B)
2. Input capacitance between signal terminals and GND (Single-ended capacitance, A–GND, B–GND)

Generally, I believe IBIS models also include capacitance for A and B. The THVD152 homepage does not include an IBIS model. Could you provide it?

Best Regards,

ttd

ttd said:

Generally, I believe IBIS models also include capacitance for A and B. The THVD152 homepage does not include an IBIS model. Could you provide it?

We generally don't make IBIS models for our devices anymore.

I also went through our entire validation and ATE database and could not locate any capacitance measurements for this device.

-Bobby

Hi Bobby,

Thank you for your reply.

I understand that there are no measured capacitance values ​​or IBIS models available.
So what should I use as a reference when considering the communication speed (6Mbps or more) and waveform quality when connecting 15 devices? Is the only way to measure the capacitance with an LCR meter, such as by ordering actual samples?

Best Regards,

ttd

Asking our designers won't work since I've heard the actual lab measurements compared to design simulated results can differ by 4x some times. 

Best way to check is to get lab measurements. You would probably need to order the samples and test with the LCR. Statistically, it's best to test 30x units. Best results would include devices from 3 different lots. 

My initial guess is the capacitance to GND for A/B will be in the 15pF range and maybe differential is 10pF and Y/Z probably less. Since we don't guarantee or test these values, the best I can do is guess....