TPS53355 / TPS81256 Power Down Sequence

Ryuji

Guru 20090 points

Other Parts Discussed in Thread: TPS81256, TPS53355

Hello,

The customer would like to use TPS81256 for VDD of TPS53355.

(1) Start Up time
In the TPS81256 datasheet P.5, the start up time from active EN to start switching is 70us.
Please see the attached file as start up sequence of TPS53355/TPS81256.
Could you please let me know the time of the t1 and the t3 in attached sequence ?
I think that the t1 is 70us and the t3 is 250us. Is my understanding correct?

(2) Power Up sequence
Is this power up sequence no problem?
If there is any concern, please let me know.
I believe that there is no problem.

(3) Power Down Sequence
At the power down, VIN of TPS81256/TPS53355 will be off at firstly.
And Enable of TPS81256 and TPS53355 is always ON.
Is this noproblem?
I think that there is no power sequence requirement for TPS53355 but please let me confirm.

Best Regards,
Ryuji Asaka

over 9 years ago

0 Chris Glaser over 9 years ago

TI__Guru*** 147650 points

Yes, T1 is around 70 usec. I believe the rest of the questions relate to the TPS53355.

0 Benyam over 9 years ago in reply to Chris Glaser

TI__Intellectual 970 points

HI,

1- Yes t3 is ~ 250us.

2- I don't see any issue but for TPS533555 just reminder the VDD bias voltage is from 4.5 V to25.

3- I don't think there is a problem if the EN always ON (Assuming EN not tied with Vin). Also, since the 5V-LDO is not controlled by EN, the internal circuit won't function anyways.

0 Benyam over 9 years ago in reply to Benyam

TI__Intellectual 970 points

correction on "3" 5V-LDO is controlled by EN ( i just verified that in datasheet block diagram page 14). i meant to say that since there is no VDD/Vreg presented the internal circuitry won't function.

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TPS53355 / TPS81256 Power Down Sequence