AM5716: Clamping circuit for 3.3V rail

Patrick Ruf

Part Number: AM5716
Other Parts Discussed in Thread: TPS650250,

Hi,

Ti implements clamp circuits for the 3.3V rail to ramp down this rail simultaneous with the 1.8V rail preventing the 3.3V rail from beeing 2V higher than the 1.8V rail.
I have seen an implementation of this in the AM571x IDK EVM as well as in an AM335x/TPS650250 documentation (slvu731a). The implementation in the AM571x IDK EVM has recently been modified to address tolerance issues of the two power rails. Despite of this there is a small structural difference in the implementation (please see pictures).
R1 is directly on the 3.3V rail in one solution. In the other one this resistor is indirectly connected to the 3.3V rail with the 499Ohm resistance.

Is there any advantage of doing the circuit in one or the other way?

Thanks and best regards,
Patrick

over 8 years ago

0 Biser Gatchev-XID over 8 years ago

TI__Guru**** 393215 points

If you are doing an AM571x design, please follow the AM571x reference design. Also see Appendix A.10 in the AM571x IDK User Guide: www.ti.com/.../sprui97a.pdf

0 Patrick Ruf over 8 years ago in reply to Biser Gatchev-XID

Genius 5015 points

I just try to understand why the structure has been changed. Both circuits have the same purpose independent of the target (AM335x or AM5716) as for my understanding. It looks as if the designer of the AM571x IDK EVM wasn't quite shure as well because of the R896 that is not populated. With this it is possible to build the other structure as well.

0 Biser Gatchev-XID over 8 years ago in reply to Patrick Ruf

TI__Guru**** 393215 points

I don't have information about the designer's considerations, but you should know that EVM designs are done very early during device development stages, and a lot of precautions are taken in them, some of which are verified to be unnecessary at a later stage. This is the reason I pointed you to the IDK User Guide appendix, which contains updated information.

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AM5716: Clamping circuit for 3.3V rail