ADM7151 doesn't turned off totaly. Why?


I'm using the ADM7151ACPZ-04-R2 regulators, in several places, in my board.

One of the regulators is designed to generate 5V_VCC, from 6V input.

When EN is high level (3.3V), regulator produces normal output, of about 4.9V.

When EN is low level (0V), regulator doesn't turn off output to 0V. I measure about 1V.

During the debug of this problem, I found three mistakes, in my design.

I corrected the three mistakes, but still regulator is not totally off, when EN is at low level.

See below a copy, of the relevant portion in my design. The corrected mistakes are colored Red.

I have similar problem with 3.3V regulator, which is designed using ADP125ACPZ-R7.

VOUT is 3.26V when EN is 3.3V and it reduced to 1.8V, when EN is 0V.

All other regulators seems to be okay on enabled and disabled states.

  • 0
    •  Analog Employees 
    on Sep 4, 2014 8:52 PM

      The ADM7151 is connected correctly and you say you have a similar
    issue with the ADP125.  I am thinking that there is another power source
    that is pulling up the LDO outputs via the protection diodes or some other
    leakage path in the loads.  We need to see a more complete schematic with
    the loads and any other supplies.

  • Additional investigation, which included removing ferrite beads, showed that the cause of the problem was some DC, which was forced on the line, through RF 6PST switch (P/N: RFSW6062). When the 5V_VCC was shutdown, the DC, through this RF switch, held a DC level on the 5V_VCC power signal.

    Also, on the case of the other 3.3V LDO, the problem was some DC that was exist on the line. Removing the Ferrite Beads that provided power to ADI's ADF4150 synthesizer, eliminated the problem.

    We should continue the investigation, to see why we have this kind of phenomenon, but anyway, the problems are not related to the LDOs.

    Many thanks for the prompt support.


  • Just to close this issue: Now I really understand what you, gmorita, meant, when you said "I am thinking that there is another power source  that is pulling up the LDO outputs via the protection diodes or some other leakage path in the loads".

    We found that the control signals, to the ADI's synthesizers, as well as to the RFMD RF switch, were not shutdown, when their power sources were shutdown.

    By turning off their power, we violated the Absolute Maximum Ratings restrictions, which limited the analog, digital and clock signals to VDD + 0.3V. When power was shutdown, the digital and clock signals, probably via their protection diodes, pulled up the LDOs output signals.

    Many thanks for the support.

  • 0
    •  Analog Employees 
    on Aug 2, 2018 2:45 PM
    This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin