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LM25066A/register status monitoring

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: LM25066, TCA9555, LM25066A

Hi,

Could you tell me about LM25066 register status monitoring?
Customer want to read the register of LM25066 status using only I2C. 

However,PMBus support IC has the following special protocol.
And support to the following has been described as essential for "PMBus specification part1 rev1.2".

◇Group Command Protocol
◇Extend read/write
【in PMBUS Specification Part_1 rev1.2  5.Transport】
Is it possible to read the status only I2C communication?
Customer is trying to use the TCA9555.
Please tell me if you have any problems.

Best Regards,
Yusuke / Japan Disty
  • 0
    TI__Genius 12621 points
    Hi Yusuke,

    PMBus is derived from SMBus but with a set of universal commands for all PMBus devices to adhere to. For example, every PMBus device has OPERATION command 01h.

    SMBus is derived from I2C but with specific protocol and timing requirements.

    The LM25066 supports I2C/SMBus/PMBus. Basically it needs to meet the timing requirements table on page 51:
    www.ti.com/.../lm25066.pdf

    If I understand correctly, they plan to have a TCA9555 in their system. The TCA would not be communicating to the LM25066, but they are wondering if both devices can be on the same bus?

    If so, then I believe yes. They each have nearly the same timing requirements (for TCA, it's page 15):
    www.ti.com/.../tca9555.pdf

    Thanks,
    Alex
  • 0 in reply to Alex Triano
    Guru 21930 points

    Ｈｉ Alex-san,

    Thank you for your ｓｕｐｐｏｒｔ.
    I'm sorry to confuse and bother you.
    Customer wants to use LM25066A like TCA9555.
    Can you use it in defiance of PMBus layer?

    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Genius 12621 points

    Hi Tsukui,

     

    To explain it differently, the LM25066 supports I2C and SMBus. So yes, it can be used on the same bus as TCA9555, so long as the bus meets the timing spec on page 51.

     

    The LM25066 is also PMBus compliant, meaning it meets the requirements of features which PMBus devices must support.

     

    So the two concerns they had mentioned earlier:

    1. Group Command Protocol

    - The LM25066 supports group command protocol. But that does not mean that you must talk to it with group command protocol. Thus this should not be a concern for them.

    2. Extended Read/Write

    - This is a feature for PMBus devices which need to support >256 commands (and thus needs 2-bytes for commands instead of 1).

    - The LM25066 only uses 1-byte for commands (it has <256 commands), so this does not apply to it.

     

    Thanks,

    Alex