SN75DP159: Violate VCC/VDD Power-Up Timing

Jim CHEN

Expert 4795 points

Part Number: SN75DP159

Dear Team,

My customer measured the power up timing of VDD and VCC. They found that sometimes Td1 is less than 200us.

The reason is that LDO TLV75511PDQNR has 550 us (typ) startup time.

We want to know what is the side effect if the power-up timing doesn't meet this spec?

Thank you.

Jim

over 6 years ago

0 Ikechukwu Anyiam over 6 years ago

TI__Mastermind 35130 points

Hi Jim,

Td1 doesn't matter as long as Td2 is met. They should ensure that both Vdd and Vcc is stable high for at least 100us before asserting OE high.

Regards,

I.K.

0 Ann_Lien over 6 years ago in reply to Ikechukwu Anyiam

TI__Genius 14580 points

Hello I.K.

Thanks for your reply! May I know why we need to define the Td1 spec if Td1 doesn't matter? Thanks a lot!

Best regards,

Ann Lien

0 Ikechukwu Anyiam over 6 years ago in reply to Ann_Lien

TI__Mastermind 35130 points

Hi Ann,

I believe it's just defined to help illustrate the power sequence. If you take a look at Table 1 in the datasheet, it shows that td1 has a minimum value of 0 us. This means that Vcc/Vdd are allowed to come up at the same time.

However, td2 has a minimum value of 100 us, which means that no matter the order that Vcc/Vdd come up, they both need to be stable for at least 100 us before OE is brought high.

Regards,

I.K.

0 Ann_Lien over 6 years ago in reply to Ikechukwu Anyiam

TI__Genius 14580 points

Hello I.K.,

Thanks for your reply :)

Best regards,

Ann Lien

0 Jim CHEN over 6 years ago in reply to Ann_Lien

TI__Expert 4795 points

Hi I.K.,

I think the requirement of Td1 is that the ramp-up time of VCC and VDD should not more than 200us.

But my customer measure Td1 on their board which sometimes is more than 200us. So this is not allowable, am I right?

Thank you.

Jim

0 David (ASIC) Liu over 6 years ago in reply to Jim CHEN

TI__Guru**** 179081 points

Jim

If OE is low, Td1 doesn't matter, you just have to meet Td2.

Thanks

David

Interface

Interface forum

SN75DP159: Violate VCC/VDD Power-Up Timing