TPS650250 with AM3354

Jin-Suk Choi

Other Parts Discussed in Thread: AM3354, TPS650250

Hello~ Team.

I have two question on TPS650250 design with AM3354.

1. To meet power on/off sequence, reference suggested to use schottky diode(slvu731a.pdf), but power schottky what used reference MBR0540 is too expensive, so can it be change to other diode? like signal diode or others?

2. Customer uses DDR voltage as 1.5V not 1.8V so 1.5V pull up bias enable signal can't fully turn on EN3(DCDC3) due to lack of Vih spec(Vih=1.45V but EN_DCDC3 level is 1.5V level from 1.5V bias). Any good recommendation to resolve this problem?

Thanks.

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi,

1. Schottky diodes are chosen here, because of their very low forward voltage drop. You don't need to use exactly MBR0540 if you can find a cheaper type.

2. See section 5 of the document you refer (slvu731a.pdf).

0 Jin-Suk Choi over 10 years ago in reply to Biser Gatchev-XID

TI__Intellectual 2270 points

Hi~ Biser, I understood to make 1.5V for DCDC2, but what I asking is if DCDC2 makes 1.5V, VO_1.8 changed to 1.5V level and it's level is lack of Vih 1.45v level so can't turn on properly EN3.3 net for DCDC3 in slvu731a.pdf.
Need other way to turn on EN3.3 properly with 1.5V signal level.

0 Biser Gatchev-XID over 10 years ago in reply to Jin-Suk Choi

TI__Guru**** 393215 points

I don't understand your concern. 1.5V is higher than 1.45V, so why shouldn't it work?

0 Biser Gatchev-XID over 10 years ago in reply to Biser Gatchev-XID

TI__Guru**** 393215 points

If you feel the margin is too low you can design a transistor switch to feed 1.8V to the DCDC3 enable. This switch should be easily driven by 1.5V

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TPS650250 with AM3354