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TCA9617B: compare NXP PCA9617A

Shu-Cheng LIN
Guru 11785 points
Part Number: TCA9617B

Hi Sirs,

Sorry to bother you.

We'll use TCA9617B to replace NXP PCA9617A, we saw NXP PCA9617A have show 

0.4VCC(A) + 0.8 V lower or equal VCC(B) for the channels to be enabled and function normally.

It's mean if VCCA is 3.3v, VCCB 2.5V, the NXP PCA9617A could meet spec.

But TI only show VCCA must lower or equal VCCB.

It's confuse us, could you help explain it?

By the way, TI TCA9617B the rise time is same as NXP PCA9617A?

  • 0
    TI__Guru 72501 points

    Hello Shu-Cheng,

    "But TI only show VCCA must lower or equal VCCB.

    It's confuse us, could you help explain it?"

    You are correct. VccA is recommended to be a maximum of VccB.

    I double checked to see if there would be any worry of back biasing through an internal diode between VccA and VccB but this doesn't seem to be the case. This device was defined and designed with the idea that VccA would be lower than VccB. One reason I could suspect for limiting this is to set specific reference voltages (ViLc) of the device. In some device's, I've seen that if VccA and VccB are widely different from each other then the ViLc can move to an unintended value.

    I have not tried to use this device outside of the recommended operating conditions so it may be possible the device can support this kind of set up however it may no longer meet datasheet specs as it was never tested outside of the intended ranges.

    "By the way, TI TCA9617B the rise time is same as NXP PCA9617A?"

    Both NXP's device and our device do not use any mechanism to to pull the signal high internal to the device. An external pull up resistor drives the signal high when the NFETs internal to the device are turned off. This means rise time is not influenced much by either device.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Guru 11785 points

    Hi Sirs,

    Thanks for your reply.

    "But TI only show VCCA must lower or equal VCCB."

    It's mean the VCCA max value is equal VCCB, right?

    But base on NXP datasheet 

    0.4VCC(A) + 0.8 V lower or equal VCC(B) for the channels to be enabled and function normally.

    If VCCA is 3.3v, VCCB is 2.5v, this spec could meet NXP datasheet, but it's over TI's, right?

     

  • 0 in reply to Shu-Cheng LIN
    TI__Guru 72501 points

    "It's mean the VCCA max value is equal VCCB, right?"

    Correct, this is the maximum recommended. It may work above this range but MAY NOT meet datasheet standards.

    "If VCCA is 3.3v, VCCB is 2.5v, this spec could meet NXP datasheet, but it's over TI's, right?"

    You would be outside of TI's recommended operating conditions.

    Thanks,

    -Bobby