SN74LVC1G3157-Q1: ABS Rating at Bn pin

Part Number: SN74LVC1G3157-Q1

Hi; Team;

I have an inquiry about the rating of “Bn” pins from customer

The absolute maximum rating of them is specified as -0.3v to VCC+0.5V(max=5.5v) at parameter named VI/O.

From this specification, I guess “Bn” pins have a protection diode to VCC pin internally.

Is my understanding correct?

If it is correct, Can you tell me the rating current of the diode?

(Of course, I understand that it is not the guaranteed current.)

Best regards,

Hidekazu Someno

  • Hello Hidekazu,

    Yes you are correct, there are internal protection diodes.   The current rating for this diode is -50mA and can be found in the absolute max table shown below.

    Will this current rating be sufficient for your needs?  If not, with some more details about what you plan to use the SN74LVC1G3157 for we  can possibly recommend an alternative or a workaround .

  • In reply to Patrick Simmons:

    Patrick,

    Thanks for your reply.
    Customer's concern is about positive rating of VCC+0.5V(or 5.5V). IIOK is specified for negative rating because of VI/O<0V.
    Is there a protection diode from Bn pin to VDD? Is 50mA rating applied to protection diode to VCC?

    Regards,
    Hidekazu Someno
  • In reply to Hidekazu Someno:

    Hello Hidekazu,

    Actually this specification covers both the positive and negative rating.  The reason is that this specification is based on conventional current flow being positive when flowing into a node or in this case the device under test (SN74LVC1G3157-Q1).   So for any current flowing towards the load or source, that would actually be negative.   The following figure illustrates the point and in the following link you can find a brief note that mentions this.  Thus you can expect a diode between Bn and Vdd.

  • In reply to Patrick Simmons:

    Patrick-san,

    I understand that there is a protection diode from Bn to VDD and the rating of the diode is 50mA into Bn.

    But I can't agree that "IIOK" parameter(-50mA rating) in rating table covers the positive current, too.
    The positive current means the current which flows into the node(Bn terminal) and negative current means the current flowing out of a node.
    And furthermore, the "IIOK" parameter has been set under the condition of VIO<0V. So, " -50mA spec" is applied only for negative current flowing out of a node(Bn), I think.

    Best regards,
    Hidekazu Someno
  • In reply to Hidekazu Someno:

    Hidekazu-san,

    I now see what your issue is. I am currently trying to confirm with a design engineer whether you can expect the same rating for positive current. I may need to test this, which may take a few days as we do not have SN74LVC1G3157-Q1 readily available at my office. In the interim, if you do not necessarily need an automotive qualified part, you may consider the non-automotive SN74LVC1G3157 as its respective datasheet indicates that it is rated for +-50 mA I/O diode current.
  • In reply to Patrick Simmons:

    Patrick-san,

    Thnaks for your reply.

    I also confirmed that non-Q1 part has the current rating as +/-50mA for II/O rating current in datasheet.

    But my customer's part is Q1 part. So, They wanted to know the sink current rating for I/IO at V/I/O>VCC for Q1 part.

    If the die design is same as non-Q1 die,  Can I understand as +50mA for sink current through the protection diode to Vcc though it has not been specified in current Q1 datasheet?  (Of cource,  Though it is not psecified in current Q1 datasheet, I undetastand that +50mA sink rating curent is reference value on Vn pin configuration.)

    Best regards,

    Hidekazu Someno

  • In reply to Hidekazu Someno:

    Hidekazu-san,

    The commercial version of the device is similar to the Q1 version.  The commercial specs explicitly the current limit for the case that Vio > Vcc.  I suspect that the reason there is not a sink current rating for the case that Vio is > than Vcc because voltage on that pin will damage the device before your can sink enough current into the device to damage it. 

    Thank you,

    Adam