• State
  • Locked Locked
  • Replies 8 replies
  • Subscribers 63 subscribers
  • Views 2272 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS51120: TPS51120 PGOOD not behaving as expected

Rushi Gajjar
Intellectual 765 points
Part Number: TPS51120

Hi,
We are using TPS51120 for our main power supply buck application to power our infotainment board.

Following is the configuration:
Mode: Current Mode operation
Output Voltage: CH1 = Fixed 5V, CH2 = Fixed 3.3V
VFB1, VFB2 Pins: Tied to V5FILT
PGOOD Pin = Pulled to V5FILT through 100K resistor.
Both Current Sense resistors are 15mOhm

In the feature description section 7.3.12 in Datasheet, PGOOD pin should go low during fault conditions (Thermal Shutdown, UVLO, UVP, OVP) and Disable; And in Table 4, it also mentions about the OCPCh1 and OCPCh2.
In our testing,
1. We are not able to see any of the PGOOD pin going low when we do Output Over Current beyond 5.5A and Output Channel ShortCircuit.
2. Even in the input Undervoltage, the PGOOD status stays high.

Is this a normal behaviour?

Can you please clarify the same?

  • 0
    TI__Mastermind 18510 points
    Hi
    Could you please upload you schematic for review?
    if there is waveform, please also upload.
  • 0 in reply to Yuchang Zhang
    Intellectual 765 points

    Yuchang Zhang said:
    Hi
    Could you please upload you schematic for review?
    if there is waveform, please also upload.

    Hi Yuchang,

    Please find attached Schematics Design for the Buck we are operating with.

    Here, NL= Not Loaded Parts on the PCB. We are checking PGOOD status on pin 11 and pin 30.  PGOOD Status on pin 30 is going to the Gate of the MOSFET, which I disconnected while testing.

    R44 has been changed to 15mR.

    I couldn't capture the waveform clearly but the observation is mentioned in the question.

  • 0 in reply to Rushi Gajjar
    TI__Mastermind 18510 points

    Hi,
    The schematic looks ok, But so far i can't get why the PGOOD keep high,
    I still need you help to catch waveform for confirm, you could just catch Vout and PGOOD pin, you could use external power to control EN (Pin12 and 29) signal to catch power on and power up waveform, and also you can catch the vout and pgood waveform when short Vout.
    you can also refer to Fig35/36/39/40 in Datasheet, which is related with GOOD function.

  • 0 in reply to Yuchang Zhang
    Intellectual 765 points

    Hi Yuchan,

    Please find attached Waveforms of the PGOOD (Pin30) we measured.

    CS Resistor is 15mR.

    CASE 1: OUTPUT SHORT CIRCUIT

    CH4(Green) = PGOOD Signal (5V) (Probing at Pin30)

    CH2(Blue) = Output Current (3.8A) (Probing before L63)

    CH3 (Purple) = Output Voltage (5V) (Probing at C61)

    CASE 2 : OUTPUT OVERCURRENT

    CH4(Green) = PGOOD Signal (5V) (Probing at Pin30)

    CH2(Blue) = Output Current (3.8A) (Probing before L63) raised to 5.8A to trigger overcurrent fault mode

    CH3 (Purple) = Output Voltage (5V) (Probing at C61)

    Note that, there us very small voltage difference at PGOOD pin when output overcurrent/short circuit happens. But the pin doesn't change it's state to low.

  • 0 in reply to Rushi Gajjar
    TI__Mastermind 18510 points
    Hi
    It's really werid from your testing, I tried EVM but can't duplicate this issue.
    I have serveral questions to confirm with you.
    1, How many borads did you test? do they have same issue?
    2, PGOOD1 and PGOOD2 are same?
    3, could you please double check whether the issue is same if you toggle EN1/2 with external power source, not use VREG5?
    Regards,
    Yuchang
  • 0 in reply to Yuchang Zhang
    Intellectual 765 points

    Hi Yuchang,

    Please find my replies inline:

    1, How many boards did you test? do they have the same issue?

    I have tested this on three different boards. The result is consistent across these boards. I have cross-verified the schematics and layout designs; consider layout design as good as your evaluation board.


    2, PGOOD1 and PGOOD2 are same?

    Yes, Both PGOOD channels show the same status by staying high in fault modes.

    3, could you please double check whether the issue is same if you toggle EN1/2 with external power source, not use VREG5?

    I can check this, but is this recommended to incorporate in the design? If yes, It might need other LDO to generate the 5V Enable voltage for EN1/2. Which I wouldn't recommend.

  • 0 in reply to Rushi Gajjar
    TI__Mastermind 18510 points
    Hi Rushi,
    EN1/2 should also can work with floating status.
    Let's discuss this question by E-mail, yuchang-zhang@ti.com.
  • 0 in reply to Yuchang Zhang
    Intellectual 765 points

    Hi Yuchang,
    We can remove the series resistors to make them float. But ideally, we have connected to VREG5 for stable operation. Separately sending this thread to email to continue there. Thanks.