Power supply config

[keisukewatanabe]

Limitation is not listed in a datasheet, is the constitution of power supply such as follows possible?

Case1 VDD=1.2V OFF VDD33=3.3V OFF SDRAMC_VDD1P5=1.5V ON

Case 2 VDD=1.2V ON VDD33=3.3V ON SDRAMC_VDD1P5=1.5V OFF

[naoumgitnik]

Dear Keisuke,

• VDD33=3.3V is applied to Vybrid first in the power-up sequence.
• VDD=1.2V is generated by Vybrid itself, without any user's intervention.
• SDRAMC_VDD1P5=1.5V - is applied to Vybrid with arbitrary timing with respect to the above rails.
• Regarding the mutual timing of the 3.3V rail and the transistor collector voltage (if different than VDD33) – to not overload the BCTRL output pin, the transistor collector voltage should appear no later than 3.3V.

Sincerely yours, Naoum Gitnik.

[keisukewatanabe]

Dear Naoum,

Thank you for your reply.

I think that case1 does not have any problem from your answer.

Does case2 not have any problem?

Best regards,

Keisuke Watanabe

[naoumgitnik]

Dear Keisuke,

Case 2 cannot happen - 1.2V is generated from 3.3V (see attachment).

Sincerely yours, Naoum Gitnik.

[keisukewatanabe]

Dear Naoum,

In figure 4.Power supply, "SDRAMC_VDD1P5" seems to be provided from external power supply.

Therefore I think the case2 can happen.

Please correct me if I am missing some point.

Best regards,

Keisuke Watanabe

[naoumgitnik · Accepted solution]

Dear Keisuke,

Regarding "Case 2: VDD=1.2V ON, VDD33=3.3V ON, SDRAMC_VDD1P5=1.5V OFF".

Yes, the case when SDRAMC_VDD1P5 is not applied (but VDD and VDD33 are) is possible.

I replied "impossible" and sent the scope screenshots because I thought you also meant the sequence:

• first VDD=1.2V is applied,
• second VDD33=3.3V is applied,
• third SDRAMC_VDD1P5=1.5V is applied.

That is why I replied "1.2V is generated from 3.3V".

If you only meant their presence, without sequence, then this case is indeed possible.

Best regards, Naoum.

[keisukewatanabe]

Dear Naoum,

Thank you for your reply.

Even a state of regular case1 (or case2) does not have any problem.

Is it right by the interpretation mentioned above ?

Best regards,

Keisuke Watanabe

[naoumgitnik]

Dear Keisuke,

Yes, it is right.

Best regards, Naoum.

[keisukewatanabe]

Dear Naoum,

I mistake, case1 and case2 was the reverse.

Does case1 not have any problem?

Best regards,

Keisuke Watanabe

[naoumgitnik]

Dear Keisuke,

Regarding "Case1: VDD=1.2V OFF, VDD33=3.3V OFF, SDRAMC_VDD1P5=1.5V ON".

No problem with Case1 because the SDRAMC_VDD1P5 power rail order is NA (Not Applicable = Do not care = Arbitrary) in the sequence table.

Best regards, Naoum.