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AM335x PORZ Delay

Vishnu Harihar1
Prodigy 245 points

Hi There,

In our design we are powering the AM335x processor from individual power supplies, and RC delay circuit with a diode is used (discharge path) for the PORZ ( pin name PWRONRSTn, B15 ZCZ package).

Will it be a problem when booting?

4 ms delay in PORZ after ramping up of last power supply rail is enough to start booting?

Are there any conventional alternative methods apart from RC circuit?

Thanks

Hari

  • 0
    TI__Guru**** 393215 points

    Hi Hari,

    4ms should be sufficient. Please ensure that the main oscillator has started and gone to full swing before reset is released. Please note that the PORZ input has hysteresis, with high-level input voltage threshold at 1.35V.

  • 0 in reply to Biser Gatchev-XID
    Prodigy 245 points

    Dear Biser,

    Thanks alot for your confirmation.

    Regards

    Hari

  • 0 in reply to Vishnu Harihar1
    TI__Guru 62975 points

    Normally this type of RC reset circuit would be powered from the same power supply connected to VDDSHV6 and this power supply should rise before the VDD_MPU and VDD_CORE power supplies. So how do you insure the VDD_MPU and VDD_CORE supplies are valid before the RC circuit releases the device from reset?

    There are a couple of other cases where the simple RC circuit may be problematic.

    If the power supply sourcing this circuit has a slow rise, the RC circuit may change at the same rate as the power supply rise so you will not be providing the expected delay after all power supplies are valid.

    The RC circuit only provides the expected delay if the system has been powered off long enough for the respective power supply decoupling capacitors and RC circuit capacitor to discharge before applying power again.  If the user performs a short power cycle on-off-on, the RC circuit may not provide the expected delay.

    The best reset solution is to use a voltage supervisor that monitors all system power supplies and holds reset low for a known time after the last supply is valid.  From the main TI web page, select Power Management, then scroll down and select Supervisor and Reset IC. This should take you to a product selector that will help you select the best option for your system. 

    http://www.ti.com/lsds/ti/power-management/supervisor-reset-ic-products.page

    Regards,
    Paul

  • 0 in reply to peaves
    Prodigy 245 points

    Dear Paul,

    Thank you very much for your valuable feedback and link.

    Regards

    Vishnu

    thank you very much for your valuable feedback