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TPS65251: About PGOOD of TPS65251-Q1

Noritomo Harukawa
Intellectual 990 points
Part Number: TPS65251

About PGOOD of TPS65251-Q1

I would like to confirm the operation of PGOOD of TPS65251-Q1.
(About the operation when only Under Voltage is detected)

Q1.
If any of the BUCK converters detects a Under Voltage exceeding 10 ms and no overcurrent is occurring, all converters are shut down for 10 ms and the startup sequence is repeated.

Is it correct?

Q2.
If the Under Voltage lasts less than 10 ms and no overcurrent is occurring, the converter ramps up and operates normally as soon as Under Voltage is removed.

Is it correct?

- Harukawa

  • 0
    TI__Genius 9550 points

    Harukawa,

    You are correct for Q1 and Q2.

    Jason Wang

  • 0 in reply to Jason Wang (BSR-MV)
    Intellectual 990 points

    Jason Wang-san,

    Thank you for your reply.

    I understood the answers to Q1 and Q2.

    I have another question.

    When an Under Voltage state lasts how much time, does PGOOD become the low output?

    (For example,100us etc..)

    - Harukawa

  • 0 in reply to Noritomo Harukawa
    TI__Genius 15135 points

    Hi, Harukawa-san

    As for Q1 & Q2,

    Why do you care about :" trigger Under Voltage and no overcurrent is occurring" ? what is the condition of this case?

    Generally, the over current will occur before Under Voltage, it means when loading become heavy, Vout drops a litte, the loop regulation will increase inductor current to provide more energy to output. it will untill trigger OC limit and the converter can not provide enough energy to the output, then Vout will drop and trigger under voltage. So i think when trigger UV for some time, IC must triggering OC, am i right?

  • 0 in reply to Zhao Ma
    Intellectual 990 points

    As for Q 2, there was an inquiry from the customer on that condition.
    However, I did not find that information in the data sheet and asked E2E.
    I am sorry but we can not explain the condition clearly.

    In addition, there are additional inquiries below from customers.

    Q.
    How long time undervoltage continuing, will PGGOD become low output?

    Again this information is not found in the data sheet.
    Would you please give me an answer to this question.

    -Harukawa

  • 0 in reply to Noritomo Harukawa
    TI__Genius 15135 points
    Hi, Harukawa

    i do a load transient on EVM, load from 1A to 5A.
    The delay time from trigger UV to PG=low is about 10.84mSec.
  • 0 in reply to Zhao Ma
    Intellectual 990 points

    Zhao Ma-san

    Thank you for your reply.

    I also performed a load transient on the EVM.

    BUCK 2 output is being monitored.(Vout=1.8V)

    I tried with loads of 4.5Ω and 0.9Ω.

    With a load of 4.5Ω, you got the same result as you.

    At 0.9Ω load, the output voltage drop was very low.

    As a result, UnderVoltage did not occur.

    From this result, it is convincing that OverCurrent will occur before UnderVoltage.

    Q1.

    "An OverCurrent does not occur and an UnderVoltage occurs."

    Customer's inquiry condition is impossible.

    Is this understanding correct?

    Q2.

    Continue, BUCK0 output is being monitored.(Vout=1.2V)

    I shorted the BUCK 0 output to GND.

    The result is an attached file.

    - BUCK0 and PGOOD-1(BUCK0 output shorted to GND).jpg

    - BUCK0 and PGOOD-2(BUCK0 output shorted to GND).jpg

    In this case, PGOOD is immediately Lo.

    What is the reason for this result?

    -Harukawa

  • 0 in reply to Noritomo Harukawa
    TI__Genius 15135 points

    Hi, Harukawa-san

    For Q1,

    Yes, it is right.

    For Q2,

    From the EVM schematic,

    http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=slvu399&fileType=pdf  

    We can see the pull up power supply for PGOOD is the output of buck1(1.2V), so when Vout1 drops, the PGOOD will drop too.

    You can change the pull up power for PGOOD to V7V, and test it again.