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TCA6416A: TCA6416A /RESET pin description is different from TCA6416(non A version).

Part Number: TCA6416A
Other Parts Discussed in Thread: TCA6416

Hello guys,

One of my customers is using TCA6416APWR for their current mass production.
But they want to use TCA6416PWR instead of TCA6416APWR due to long lead time.

They found that TCA6416 /RESET pin description is different from TCA6416A as the follow.

TCA6416A /RESET pin description:
"Active-low reset input. Connect to VCCI or VCCP through a pull-up resistor, if no active connection is used."

TCA6416 /RESET pin description:
"Active-low reset input. Connect to VCCP through a pullup resistor, if no active connection is used."

At this moment, they have the following questions. Could you please give me your reply for them?

Q1. Is the RESET pin internal circuit different from TCA6416A one?
Q2. In case of TCA6416, can RESET pin be pulled up to VCCI by a resistor if no active connection is used?]

Your reply would much appreciated.

Best regards,

Kazuya.

  

  • Kazuya-san,

    The internal circuitry for nRESET is different for the non-A version. The TCA6416A addresses the erratas from the TCA6416, which is why the older device is NRND.

    The older device's input high threshold for nRESET is 0.7*VCCP, instead of 0.7*VCCI for TCA6416A. Also, the new TCA6416A has back-biasing protection, which will prevent current from flowing from nRESET to VCC if the nRESET voltage is higher than VCCP.

    If your customer intends to use TCA6416 even though it is not recommended, then the nRESET pin would need to fall between 70% and 100% of VCCP (instead of VCCI). It cannot exceed VCCP (due to backbiasing) and it must be at least 70% to meet the high-level input threshold to be recognized as a high signal. You can see these thresholds in the Recommended Operating Conditions table (Section 6.3).

    Also, please note that the TCA6416 has an additional errata for the nINT output (see section 8.2.5.1 in the TCA6416 data sheet).

    Though these devices are pin-to-pin, the TCA6416 is not a drop-in backwards replacement for the TCA6416A. Your customer would need to ensure all design requirements for the older device are met.

    Does this help clarify?

    Best,

    Danny

  • Hello Danny,

    Thank you very much for your reply.

    Could I ask you an additional question?

    Q. Is /RESET pin function of each device same?

    Thank you again and best regards,

    Kazuya.

  • Kazuya-san,

    Yes, the reset function of the device is the same for each device. The difference is the electrical configuration of the nRESET pin itself.

    Best,

    Danny

  • Hello Danny,

    Thank you very much for your supports.

    Could I ask you one more question about TCA6416A /RESET pin description?

    Q.

    TCA6416A datasheet says that "Active-low reset input. Connect to VCCI or VCCP through a pull-up resistor, if no active connection is used". Also it says /RESET pin high level voltage range is 0.7xVCCI~5.5V and low level is -0.5V~0.3xVCCI.

    Why does the pin description say "Connect to VCCI or VCCP through a pull-up resistor"?
    If VCCI=5.0V and VCCP=3.3V, /RESET pin high level voltage is less than 0.7xVCCI(=3.5V) when /RESET pin is connected to VCCP.

    I think to connect /RESET pin to VCCP via a pull-up resistor in that case can not be applied. Is my thought correct?

    Thank you again and best regards,

    Kazuya.

  • Kazuya-san,

    Yes, you are correct. If the voltage is not high enough then it would not be best to connect it to the other rail.

    The difference is that the A-version has backbiasing protection that addresses the issue from the non-A device. But the electrical characteristic for the nRESET pin on the TCA6416A is correct - it would need to be held at or above 70% of VCCI in order to be recognized as a high (no reset) signal.

    Best,

    Danny