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LP87565-Q1: After disabling buck 0 ... 3 - PGOOD remains High

Torsten Dr. Kilias
Intellectual 475 points
Part Number: LP87565-Q1

Hi all,

we implemented LP87565 as a companion to a PMIC in a quiet comprehensive system. PGOOD output of LP87565 is evaluated by a supervision µC in order to check the power supply state. 

We intended to check this functionality and switched off buck 0 ... 3 of LP87565 by I2C. Though buck 0 ... 3 had been disabled (voltages went to ground) the PGOOD remained High.

I think the PGOOD register are set correctly. What could be the reason for? 

===== Press 1 for LP87565 Buck0...3 off:
1
========== LP87565 Buck0...3 off: ===========
Register: 0x28 , PGOOD_CTRL1: 0xff
Register: 0x29 , PGOOD_CTRL2: 0x86
Register: 0x2a , PGOOD_FLT : 0x0
========== Buck0...3 disabled ==========
========== Done! ==========

 regards

  • 0
    TI__Genius 10885 points

    Hello,

    The PGOOD functionality is dependent on the enable status of the regulator, mentioned in section 8.3.7.1 of the datasheet:

    "When a regulator is disabled, the monitoring is automatically masked to prevent it forcing PGOOD inactive."

    With the configuration as open drain, the pull-up supply could be used to indicate the enable status of at least one regulator by connecting the pull-up resistor to either the enable signal or the output of the regulator.

    Looping in the device expert to comment.

    Best Regards,

    Rick S.

  • 0 in reply to Richard Solarski
    Intellectual 475 points

    Hello Rick,

    you are right, a disabled regulator leads to a masked PGOOD related to that regulator and PGOOD remains High. This suggests that all regulators are working properly.

    I did not find any configuration to overcome this, so that PGOOD can't be used as a common supervision indicator.

    Regards   

    Torsten

  • 0 in reply to Torsten Dr. Kilias
    TI__Expert 5590 points

    Hi Torsten,

    PGOOD functionality is described in datasheet section 8.3.7.1.

    PGOOD will stay high after enable is set low or BUCKs disabled with bit because "When a regulator is disabled, the monitoring is automatically masked to prevent it forcing PGOOD inactive. This allows connecting PGOOD signals from various devices together when open-drain outputs are used".

    Rick already suggested connecting pull-up of the BGOOD-pin to either enable signal or output voltage. That is one way. Another way it to configure unused GPIO to follow enable state and connect PGOOD and GPIO together outside the device.