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AM3354: Problem using nRESETIN_OUT pin as output

g.f.
Guru 15520 points
Part Number: AM3354


Hi,

I have a question about AM335x nRESETIN_OUT pin .

My customer are trying to use this nRESETIN_OUT as output for reseting external device.
But after warm reset de-assertion, nRESETIN_OUT signal level is around 0.3V and never goes High level(3.3V).
so that external device never be released from reset.

In customer's board, nRESETIN_OUT pin are pulled up(10kohm) externally  to 3.3V .

In AM335x TRM(spruh73p) page.1237 "8.1.7.4.11 Warm Reset Input/Reset Output(nRESETIN_OUT)",
it said as follow:
////////////////////////////////////////////////////////////////////////////////
The nRESETIN_OUT output buffer is configured as an open-drain; consequently,
an external pull-up resistor is required.
////////////////////////////////////////////////////////////////////////////////

It said nRESETIN_OUT output buffer is open-drain, so we thought it will be High(3.3V)
by external pullup resistor after warm reset de-assertion.
What kind of factor can this problem consider?

best regards,
g.f.

  • 0
    TI__Guru**** 161600 points
    Hi,

    How did you configure the nRESETIN_OUT pin?
    See the schematic checklist:
    processors.wiki.ti.com/.../AM335x_Schematic_Checklist
    and AM3354 Errata document. Did you consider this?

    Best Regards,
    Yordan
  • 0 in reply to Yordan Kovachev
    Guru 15520 points
    Hi Yordan,

    Thank you for the reply.

    Yes, we consider about the checklist which you attached.
    As I said at above post, we are using nRESETIN_OUT terminal as an output only to reset the external device.
    So, we are not using nRESETIN_OUT as a bi-directional reset signal.

    nRESETIN_OUT terminal are pull-up to 3.3V via 10kohm resistor externally and connected to external device.
    Nothing else are connected to nRESETIN_OUT.

    By the way, do we must use external open-drain buffer as TRM(spruh73p) page.1236
    "Figure 8-21 External Buffer for nRESETIN_OUT"?

    best regards,
    g.f.
  • 0 in reply to g.f.
    TI__Genius 9655 points
    Do you have any capacitor also connected to the nRESETIN_OUT? If nRESETIN_OUT is 0.3V, can you confirm how you verified device coming out of warm reset?

    nRESETIN_OUT is a true open-drain buffer and needs an external pull-up resistor on the board.

    Regards, Siva
  • 0 in reply to sivak
    Guru 15520 points
    Hi Siva,

    Thank you for the reply.

    I asked to my customer about the questions from you.

    >Do you have any capacitor also connected to the nRESETIN_OUT?
    They are connecting push-botton for option(not using for now) and
    maybe also the capacitor are connected.
    They will check whether the capacitor are connected.

    So, I asked the customer to remove the push-button and capacitor from the line of nRESETIN_OUT
    and check whether the problem will be solved.

    >If nRESETIN_OUT is 0.3V, can you confirm how you verified device coming out of warm reset?

    They are just checking whether nRESETIN_OUT will goes to 3.3V.
    As I mention above, nRESETIN_OUT are pullup to 3.3V externally,
    so if it goes up to 3.3V, they are thinking that the warm reset are deasserted.

    best regards,
    g.f.
  • 0 in reply to g.f.
    Guru 15520 points
    Hi Siva,

    I have additional question about nRESETIN_OUT.

    In AM335x TRM(srpuh73p) page.1236 "Figure 8-20 PORz",
    it said as follow:
    ///////////////////////////////////////////////////////////////////////////////
    (1) nRESETIN_OUT is not defined (can either be driven low or pulled up high)
    until all supplies are fully ramped up.
    ///////////////////////////////////////////////////////////////////////////////
    It seem that all power need to be supplied for nRESETIN_OUT to be defined.

    In customer's board, the power are not supplied to VDDSHV3/VDDSHV4/VDDSHV5
    because they are not using the peripherals which power is supplied from VDDSHV3/VDDSHV4/VDDSHV5.
    But when they changed their board to supply the power to VDDSHV3/VDDSHV4/VDDSHV5,
    nRESETIN_OUT signal problem been solved.

    So, does all power must be supplied for nRESETIN_OUT to be defined?

    best regards,
    g.f.
  • 0 in reply to g.f.
    TI__Genius 9655 points

    You need to apply power to the rails even if the peripherals are unused. If you are leaving them floating, you are operating the device outside of the operating range of the device. The behavior the customer noted is expected - without proper supply the nRESETIN_OUT functionality will not work.

    Regards, Siva

  • 0 in reply to sivak
    Guru 15520 points
    Hi Siva,

    Thank you for the reply.
    I understood.

    best regards,
    g.f.