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TPS53515: Relation between VDD and VIN

Vijetha HN
Intellectual 705 points
Part Number: TPS53515
Other Parts Discussed in Thread: TPS62150, , LM3881

Hi,

We wanted to generate 3 different Power rails from 12V Input in below sequence in our design.

Power Rail 1 : 3.3V

Power Rail 2 : 1.8V and 0.9V

Current requirement on 3.3V is near to 10A and 0.9V is near to 8A and hence we selected TPS53515 for these 2 rails. For 1.8V the current requirement is very less (less than 1A) so we selected TPS62150. Initially we planned to generate 3.3V from 12V input and then 0.9V, 1.8V from 3.3V input to maintain the sequence.

With this plan we have below queries :

Query 1:

After referring datasheet we observed that TPS53515 needs voltage greater than 4.5V on VDD pin. So for the 0.9V regulator what voltage we can connect to VDD pin so that the sequence is still met?

If I connect 12V rail to VDD pin of the 0.9V regulator (TPS53515) then whether we will face any sequence violation? Because there will be a small delay for 3.3V regulation from 12V. After this delay 3.3V input will be available at the input pin of 0.9V regulator TPS53515 . But if we connect 12V to VDD pin of 0.9V regulator, before Input voltage is available 12V voltage will be available for VDD pin. Will this cause any volition of the required sequence?

Second query:

From figure 33 of datasheet of TPS53515 , the enable pin is held high only after VREG becomes high. In that case what is the expected connection to EN pin? Should we connect Input voltage or PG of previous regulator or VREG of same regulator? Please suggest.

Regards,

Vijetha 

  • 0
    TI__Guru**** 191445 points

    Vijetha,

    1.  Yes you can connect 12 V to both TPS53515.  Hold the EN pin to the 0.9 V regulator low until the 3.3 V of the first TPS53515 is available.  You can do that with the PGOOD output of the 3.3 V supply.

    2. Yes as noted above.  Connect PGOOD of the 3.3 V regulator to the EN pin of the 0.9 V regulator.

  • 0 in reply to JohnTucker
    Intellectual 705 points

    Hi,

    1. Regarding 1st question, I am not very much clear. What I understood is "you generate 3.3V from 12V using Regulator 1. Then connect the PGGOD of regulator 1 to EN of Regulator 2 (0.9V regulator) and 3.3V to Voltage Input pin of regulator 2". This will absolutely meet the sequence.

    My question was about VDD pin connection. If I connect 12V to VDD pin of Regulator 2, then Voltage will be available on VDD pin before availability of voltage on Input pin of regulator 2. So will this affect the sequencing? Do you see any concern?

    2. Understood on the EN connection for Regulator 2 (0.9V regulator).

    But What can I connect to EN pin of Regulator 1? EN is expected to held high only after VREG is available. I will be having only Input voltage of 12V in the beginning. So should I connect this 12V to EN pin? If I do so, then EN pin will be held high before VREG generation. So how to address this situation?

    Regards,

    Vijetha

  • 0 in reply to Vijetha HN
    TI__Guru**** 191445 points

    Vijetha,

    It is ok to have 12 V on VDD befor you have voltage at VIN.  Just hold EN low until VIN is ready.  For the first converter, you can use a voltage divider from VDD to EN or you can use your own logic to control it.  You may want to sequence it externally using a sequencer like LM3881.  Or you can use power good output of the previous stage.  There are multiple options.