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TCA6408A-Q1: POR question

Part Number: TCA6408A-Q1

Dear team,

In my understanding, when the device is powered on for the first time, POR is not necessary, right? If so, could you please tell me what application needs POR after the first power on?

If not, could you please tell me the sequence between POR and power-on? For example, what is the delay between POR and the first power-on? What is the minimum low level time of reset?

Thanks & Best Regards,

Sherry

  • POR also happens when the device is powered on for the first time. See footnote (2) in section 6.5 of the datasheet.

  • In my understanding, when the device is powered on for the first time, POR is not necessary, right?

    When you power on the device, the device should trigger the POR circuitry. You don't have a choice, it's part of the device design.

    If so, could you please tell me what application needs POR after the first power on?

    You should always POR after first power on, all applications should do so since it's important to reset the device's state machine and set the digital registers to a known state.

    -Bobby

  • Hi Bob,

    Thanks for your detailed reply! I still have some questions as below,

    1. It said that after the internal power-on reset, '' VCCP must be lowered to below VPORF and back up to the operating voltage for a power-reset cycle''. This action is automatically or controlled by the external VCCP power?

    2. If above action is controlled by the external VCCP power, then my customer needs to control the external power sequence, so what is the Tdelay as below for the POR after first power on? 

    3. There are two types of power-on reset are shown in datasheet Figure 36 and Figure 37. I am not clear that POR after first power-on belong to which type. I am also confused about these two types of power-on reset. When a glitch occurs, which type happens?

    Thanks & Best Regards,

    Sherry

  • This action is automatically or controlled by the external VCCP power?

    This needs to be done externally.

    2. If above action is controlled by the external VCCP power, then my customer needs to control the external power sequence, so what is the Tdelay as below for the POR after first power on? 

    The customer only needs to power up the device within the acceptable ramp rate. Is there a reason the customer is trying to power on the device to power it off and then power it back on? I think you're miss understanding something here.

    3. There are two types of power-on reset are shown in datasheet Figure 36 and Figure 37. I am not clear that POR after first power-on belong to which type. I am also confused about these two types of power-on reset. When a glitch occurs, which type happens?

    All devices with digital logic should have a power on reset circuit which automatically triggers when you power up to provide a known state for the device. You should just power up from GND to Vcc, there isn't any additional action that is required unless you're expecting a brown out event.

    Just to add one more thing, POR is the same as powering up the device then toggling the reset pin. If you're worried that the power on reset didn't occur properly due to doing something outside of the recommended conditions, then you can just toggle reset after powering up.

    -Bobby

  • Hi Bobby,

    Clear! Thanks for your help!

    Thanks & Best Regards,

    Sherry