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Inconsistent PMIC output

Prasad Shetty
Prodigy 50 points
Other Parts Discussed in Thread: TPS65020

PMIC TPS65020: in some condition, voltage drop will happening in  VRTC and LOWBAT pin we are not getting 3.3V instead of that we are getting 2.99V so enabling signals are not coming from the Processor(VRTC and LOWBAT these voltages are needed for Processor to Provide SYS_EN and PWR_EN).

  • 0
    TI__Genius 16870 points
    Hi,

    What is the voltage on VSYSIN? There is a PMOS switch for powering the VRTC from the VSYSIN rail. It will have an IR drop out when VRTC is loaded. So, you should check the loading on the VRTC as well. This drop out is characterized as 250mV at 20mA of loading. Thus, if possible, cut the VRTC from the load to see if the VRTC is being loaded at the time.

    Note that if the RTC is being driven by VCC that the RTC LDO is set to 3V. This could be your situation as you are measuring 2.99V. Read the RTC section of the datasheet for more details.
  • 0 in reply to Michael Green
    Prodigy 50 points

    Hi,

    Main thing is we  are getting 2.99V in VRTC pin instead of 3.3v not all the time only in some condition and i checked VSYSIN pin also in working condition there will be 3.3v and this issue condition there is no voltage was coming in that pin, this issue only repeating in some boards not all boards and also the board which is getting this issue fails 1 out of 3 times.When it passes all voltages are coming form the PMIC.

    So Let us know is there an errata related to VRTC , VSYSIN so that board booting becomes inconsistent. 

    Thanks 

    Regards,

    Prasad

  • 0 in reply to Prasad Shetty
    TI__Genius 16870 points

    If there is no VSYSIN or VBACKUP then the RTC will be 3V driven by an LDO from VCC. You should check your BACKUP, VSYSIN, and VCC input voltages during this condition.

    "this issue condition there is no voltage was coming in that, [VSYSIN], pin" - Makes me think that the VSYSIN is < 2.65V and the LDO could be running off the 3V LDO from the VCC rail.

    In
    systems
    where
    no
    backup
    battery
    is
    used,
    the
    VBACKUP
    pin
    is
    connected
    to
    GND.
    In
    this
    case,
    a
    low
    power
    LDO
    is
    enabled,
    supplied
    from
    VCC
    and
    capable
    of
    delivering
    20
    mA
    to
    the
    3
    V
    output.
    This
    LDO
    is
    disabled
    if
    the
    voltage
    at
    the
    VSYSIN
    input
    exceeds
    2.65
    V.
    VRTC
    is
    then
    supplied
    from
    the
    external
    source
    connected
    to
    this
    pin
    as
    previously
    described.
  • 0 in reply to Michael Green
    Prodigy 50 points
    Hai,
    Actually VSYSIN is < 2.65V (in issue condition=0V), plz let me why it was happening and one more thing this issue will come only when we are giving 5V input to PMIC speed with 1sec delay by pressing switch(1 time out of 3 time pressing) at that time PMIC will not give all other voltages.
    VRTC =2.99V and inputs are proper in this condition (VCC=VINDCDC1=VINDCDC2=VINDCDC3=5V and PWRFAIL_SNS=1.6 & LOWBAT_SNS=1.3).

    Please let me how to solve this issue.

    Regards,
    Prasad
  • 0 in reply to Prasad Shetty
    Prodigy 50 points
    Hai,
    Actually VSYSIN is < 2.65V (in issue condition=0V), plz let me why it was happening and one more thing this issue will come only when we are giving 5V input to PMIC speed with 1sec delay by pressing switch(1 time out of 3 time pressing) at that time PMIC will not give all other voltages.
    VRTC =2.99V and inputs are proper in this condition (VCC=VINDCDC1=VINDCDC2=VINDCDC3=5V and PWRFAIL_SNS=1.6 & LOWBAT_SNS=1.3).

    Please let me how to solve this issue.

    Regards,
    Prasad