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SN75ALS1177: The current consumption is different between SN75ALS1177 and SN75ALS1178

Shinichi Inoue
Guru 20536 points
Part Number: SN75ALS1177
Other Parts Discussed in Thread: SN75ALS1178, , SN65C1168E, SN75C1168, SN65C1168

Dear Specialists,

My customer is evaluating SN75ALS1177NS as a replacement for SN75ALS1178.

They have a question about current consumption.

I would be grateful if you could advise.

---

We are evaluating to use SN75ALS1177NS as a replacement for SN75ALS1178NS .
The current consumption of SN75ALS1177NS is small.

ALS1177NS　About 15mA at standby, about 35mA at 2.5Mbps operation
ALS1178NS　About 40mA at standby, about 60mA at 2.5Mbps operation

The datasheet shows no difference in current consumption between the SN75ALS1177/1178.

question)
When comparing the current consumption Icc and other AC characteristics of the SN75ALS1177 and SN75ALS1178, which one tends to be larger or faster?

Could you please let us know some possible causes?

---

I appreciate your great help in advance.

Best regards,

Shinichi

  • 0
    Guru 281410 points

    These devices have different pinouts. How exactly are you testing?

    A better replacement for the SN75ALS1178 would be the SN75C1168/SN65C1168/SN65C1168E (with a smaller common-mode range).

  • 0 in reply to Clemens Ladisch
    TI__Guru 70282 points

    Thanks for the help Clemens!

    Inoue-san,

    Let us know if you can answer Clemens questions, and I have also assigned a TI engineer to review your questions.

    Regards,

    Eric Hackett 

  • 0 in reply to Eric Hackett
    Guru 20536 points

    Hi Clemens and Eric,

    Thank you for your reply.

    The customer is currently using SN75ALS1178NS for ARCNET.

    SN75ALS1177NS is being considered as an alternative due to poor delivery times for SN75ALS1178NS.

    The customer does not know anything other than that ARCNET has strict timing requirements.

    Due to the old interface, it is difficult to confirm the details.

    They worried that changing the process could lead to big changes in timing, which was risky. 

    ---

    /RE and DE are set so that SN75ALS1177NS and SN75ALS1178NS can be used in the same.

    Therefore SN75ALS1177 4-pin L (Receiver Enable) 12-pin H (Driver Enable)

    SN75ALS1178 Receiver has no control pin and is always Enable and 4-pin and 12-pin are H (Driver Enable)

    ---

    It was confirmed that using SN75ALS1177 instead of SN75ALS1178 did not affect communication.

    However, there is a large difference in current consumption.

    Could you please advise what the difference in current consumption between the two devices.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 20536 points

    Hi Clemens and Eric,

    I forgot to mention.

    The two drivers are enabled only during transmission.

    Shinichi

  • 0 in reply to Shinichi Inoue
    Guru 281410 points

    The 1177 and 1178 use the same datasheet and have the same characteristics. (I suspect they use the same die.) They should use the same amount of power if they are configured in the same way.

    It might be possible that you got a newer die revision, but I am not aware of any PCN.

    The CMOS devices (SNx5C1168x) have a lower skew than the ALS device, so the signal quality would be improved. In my opinion, it would be worth it testing them.

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 32063 points

    Hi Shinichi,

    SN75ALS1177 and SN75ALS1178 use the same datasheet. The current consumptions should be the same for the test conditions listed in the datasheet. 

    How large is the current difference that the customer is seeing? Is there a difference in the load that each device is driving that would cause a large supply current difference? 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Guru 20536 points

    Hi Clemens and Tyler,

    Thank you for your reply.

    The customer evaluated the same board and same condition driver and receiver.

    /RE and DE are set so that SN75ALS1177NS and SN75ALS1178NS can be used in the same.

    The load is exactly the same. Both devices could communicate with no problem. 

    Therefore SN75ALS1177 4-pin L (Receiver always Enable) 12-pin H (when Driver Enable)

    SN75ALS1178 Receiver has no control pin and is always Enable and 4-pin and 12-pin are H (when Driver Enable)

    ALS1177NS　About 15mA at standby(Receiver only), about 35mA at 2.5Mbps operation(Driver and Receiver Enable)
    ALS1178NS　About 40mA at standby(Receiver only), about 60mA at 2.5Mbps operation(Driver and Receiver Enable)

    We understand the datasheet shows no difference in current consumption between the SN75ALS1177/1178.

    I think that devices are a good product each other.

    Is there such a big difference between different lots?

    The customer wants to know what caused it.

    Is there such a big difference between different lots?(I think that's just one possibility)

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Mastermind 32063 points

    Hi Shinichi,

    The ALS1177NS and ALS1178NS use two different dies, but this is mainly because of the change on pin 4. 

    Based off the datasheet, the devices are correctly represented for the driver,

    and receiver: 

    In standby, it looks like both devices technically fall within the datasheet parameters. Therefore, from a datasheet perspective we are accurately representing these devices. 

    Now on exactly why the difference tends to be so much, I couldn't exactly say. I am assuming the large difference in current consumption must be because of the change on pin 4 between the devices. 

    From a lot perspective, there shouldn't be much change in current between different lots. Each lot should adhere to the specifications listed in the datasheet. Another thing to consider would be a PCN, but I do not know of any PCN's for this device that would represent such a major change. 

    Has the customer tested the current consumption of several devices between the 1177 and 1178? Are the results consistent with the 1178 having higher current consumption in the idle and active stages? 

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Guru 20536 points

    Hi Tyler,

    Thank you for your reply.

    The difference between SN75ALS1177 and SN75ALS1178 is function of 4pin.

    Therefore there is no big difference in current value.

    There shouldn't be a large current difference even if the lot is different.

    The customer confirm only one device.

    I'll ask the customer to confirm whether the results are the same with multiple samples.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 32063 points

    Hi Shinichi,

    Shinichi Inoue said:

    The difference between SN75ALS1177 and SN75ALS1178 is function of 4pin.

    Therefore there is no big difference in current value.

    There shouldn't be a large current difference even if the lot is different.

    I would hope this is the case. The large current difference doesn't make sense if the device is simply changing only pin 4 of the device. 

    Shinichi Inoue said:

    The customer confirm only one device.

    I'll ask the customer to confirm whether the results are the same with multiple samples.

    Please confirm this. I suspect that if the current draw is only present on one device, then there may be internal damage to that device causing a high current draw through ICC.

    Regards,

    Tyler

  • 0 in reply to Tyler Townsend
    Guru 20536 points

    Hi Tyler,

    Thank you for your reply.

    When I could obtain the customer's feedback, I'll share with you. 

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • 0 in reply to Shinichi Inoue
    TI__Mastermind 32063 points

    Hi Shinichi,

    I will await your response. I am going to move the thread to "waiting for customer."

    Regards,

    Tyler