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Original question:

TPS7B7702-Q1: behavior if VSENSE value is higher than 2.4V but below Ilim value

TPS7B7702-Q1: If VSENSE is 3V at current limit, will it be clamped back to 2.4V~2.6V when it is over current?

wang wan
Prodigy 140 points
Part Number: TPS7B7702-Q1

We set RLIMIT=0.82kΩ, and its corresponding current limit is 300mA; 

We set Rsense=2.2kΩ, and Vsens will be 3V at 300mA.

We know the LDO will not flag it as an error state and the ~ERR pin will stay high. I have two questions.

Q1：

When Iload is 0~300mA, Vsense is linear from 0V to 3V.

When Iload is above 300mA, it will hit current limit. Vsense wil go back to 2.4V~2.6V.  Do I understand correctly?

Q2: What does it mean when Vsense is 2.65V~2.7V and 3V~3.05V shown below?

  • 0
    TI__Mastermind 43215 points

    Hello,

    You have misunderstood how the current sense output works. The VSENSE range of 0V~2.4V is intended to be the range for 0mA ≤ ILOAD < ICL. The other VSENSE ranges (i.e. 2.4V~2.65V, 2.7V~3V, 3.05V~3.3V) are all separate fault states that do not follow a linear relationship. When one of these faults triggers, the VSENSE latches to the corresponding voltage range while the fault exists. So what you have done by setting the VSENSE max to 3V at 300mA is not using it correctly. You should size the RSENSE such that all load currents less than the current limit will result in a VSENSE that is less than 2.4V. Then, when current limit is reached, VSENSE goes straight up to the 2.4V~2.65V range. This is depicted in Figure 19. 

    The ranges 2.65V~2.7V and 3V~3.05V are kind of buffer regions that VSENSE will never take so that there is no overlap between the fault regions. 

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 140 points

    We know we don't use it  correctly. We just want to know what will happen if we set Vsense max to 3V at 300mA.

    If load current is up to 299mA at this case, will Vsense be ≈3V or go back to 2.4V ~2.65V?

    If load current is up to 301mA at this case, will Vsense be ≈3V or go back to 2.4V ~2.65V?

  • 0 in reply to wang wan
    TI__Mastermind 43215 points

    Hello,

    This is outside of the datasheet specifications so I do not know what the behavior will be. I can check with the EVM tomorrow when I'm in the office.

    Regards,

    Nick

  • +1 in reply to wang wan
    TI__Mastermind 43215 points

    Hello,

    I tested this and it does not work as you described. The VSENSE voltage stops rising at about 2.56V when the load current is around 250mA. When the load is taken up to current limit, the VSENSE voltage does not change, so there is not indication that the device has entered current limit besides the ERR pin toggling. 

    Regards,

    Nick