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LP8758-E0: The time when 0x23 are written by LP8758-E0

Yuto Sakai
Mastermind 6100 points
Part Number: LP8758-E0
Other Parts Discussed in Thread: LP8758

Hi,

Could you tell me the time until the device reads the current value of the core and writes the register to the address 0x22 or 0x23(I_LOAD_1/2)

after writing the register to the address 0x21(SEL_I_LOAD) to determine the core to monitor the current?

I would like to know how much time I should keep before reading address 0x22 or 0x23.

※Additional information

Since I2C frequency is 400kHz, 1 cycle is 2.5μsec.

Before reading 0x22 or 0x23, are the monitored current values stored in 0x22 and 0x23?

Best Regards,

Yuto Sakai

  • 0
    TI__Intellectual 1120 points
    Hi,

    I will assign your query to LP8758 expert and we will get back to you.

    Regards,
    Juha
  • 0 in reply to Juha Karttunen
    Mastermind 6100 points
    Hi Juha-san

    Noted with thanks.
    I look forward to your reply.

    Regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Genius 13850 points
    Hi Yuto-san,

    Typical measurement time is about 50us. I assume measurement data is latched when measurement is ready. I will check operation and get back to you.

    One way to make sure measurement data is valid is to enable interrupt on register INT_TOP.I_LOAD_READY.
    Please see section: 7.3.1.2 Buck Converter Load Current Measurement on datasheet for further details.

    Best Regards,
    Jari Niemelä
  • 0 in reply to Jari Niemela13
    Mastermind 6100 points
    Hi Jari-san

    Thank you for your reply.
    In order to read the correct current value, I understand that I have to read 0x22 or 0x23 after waiting until the measurement is completed and the data is latched, is it correct?
    Our customer is concerned about whether he can read the correct current when reading 0x22 or 0x23 immediately after writing to 0x21.
    Could you tell me when you know the data latch operation and the time from writing to 0x21 to data latch?

    Best Regards,
    Yuto Sakai
  • 0 in reply to Yuto Sakai
    TI__Genius 13850 points

    Hi  Yuto-san,

    Yes, you have to wait until data is latched.

    50us from measurement start command end should be enough to guarantee  that data is latched before read command end in 400kHz I2C speed.

    After measurement start command ends, following read command takes 26 clock cycles (stop and start, Chip ID plus write bit, register address, repeated start, Chip ID plus read bit). In 400kHz speed this means 65us which is longer than specified 50us measurement time.

    To be sure data has been latched before reading you have to setup interrupt regarding iload measurement and read interrupt if it is set or not before reading load current value. Based on the explanation above there is enough time for measurement I would not see necessary to read interrupt status.


    Best Regards,

    Jari Niemelä