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LMZ10505EXT: LMZ10505EXTTZE

pankaj gangwar
Prodigy 10 points
Part Number: LMZ10505EXT
Other Parts Discussed in Thread: LMZ10505, TPS22965-Q1

We have designed a board in which 1.5V and 3.3V is generated from SMPS LMZ10505EXTTZE/NOPB. U33 and U36 are the Load Switches. These load switches are used to protect the board. If SMPS malfunction and its Vin become Vout then board will damage (Major ICs MPC5566 and FPGA will get damage). To protect the board Load Switches are used.

In this design we are facing majorly problems from 3.3V (U36) load switch. The problems are

  1. Many times we are not able to sense the 3.3V output from vout1(pin:8) and vout2(pin:9).

  2. To make this load switch work, we removed CT capacitor(C344). But in some board without CT capacitor load switch work and in some board it didn’t work.

At some time when we probe CT via multimeter (after removing the capacitor) then load switch start giving the output. When we switch off and on the board then load switch stop working and if we again probe the CT then only it start work.

  1. If any voltage variation happens in 3.3V then this load switch stops working (got damaged)

  2. What are the failure modes of LMZ internal and external (In which Vin=Vout).


We are requesting to TI team to look the design and give us suggestion to correct the design.

  • 0
    TI__Guru*** 148090 points

    Hi,

    It's a little unclear if your problem is with the LMZ10505 or the load switch.

    1. Pin 8 and 9 are not the Vout1 and Vout2 pins on either the LMZ or load switch.

    2. The Ct cap is on the load switch.

    3. Is the load switch or LMZ damaged?

    I noticed that you use a different GND net for the GND pins and thermal pads.  Are these shorted somewhere on the PCB?  Can you post your PCB layout?

    Thanks,

    Chris

  • 0 in reply to Chris Glaser
    Prodigy 10 points

    Hi Chris,
     Thanks for reply. Let my try to clarify the issues
    1. We are facing problem with the Load Switch and not from LMZ.
    2. Its pin No8 and No7 in from Load Switch ( not pin no. 9)
    3. TGND (This is the thermal ground )and DGND are sorted.
    4. Load Switch get damaged every time not the LMZ .
    5. It is not possible to send the PCB layout however if you have specific query regarding layout, Please mail me and I will clarify.
    6. I am talking about Load switch's CT.

    Regards
    Pankaj Gangwar

  • 0 in reply to pankaj gangwar
    TI__Guru*** 148090 points

    Thanks for clarifying.  Let me loop in the apps for that device.

    Chris

  • 0 in reply to Chris Glaser
    TI__Mastermind 23380 points

    Hi Pankaj,

    1. What is the failure mode of TPS22965-Q1 when you say "damaged"? Is it permanently damaged or does it work when power is cycled?

    2. When you removed the CT capacitor, it was left floating, correct?

    3. To make sure, you said TGND and DGND are shorted, correct? Is it a low-impedance connection?

    Thanks,

    Patrick