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TPS4H000-Q1: Current limit function

Kaji@PAN
Mastermind 7145 points
Part Number: TPS4H000-Q1

Hi,

I am considering using the TPS4H000-Q1 device.
I would like to ask you about the current limiting feature of this device.

Set R(CL) of CL pin to 2.4kΩ to set the current limit to 100mA.
I think that it is good to do.
From the formula (4) on page 17 of the data sheet, it can be calculated as follows, considering the Typ value.
R(CL)=[Vcl(th)×K(CL)]/Iout
=[0.8(V)×300]/0.1(A)
= 2400 (Ω)
=2.4 (kΩ)
External current limit accuracy is ±20% because it corresponds to I(limit) ≥ 100 mA.

What I would like to ask is the following description on page 7 of the datasheet.
Does this mean a 150mA overload is required to detect at 100mA current limit?
If the current slowly approaches 100mA, does that mean there is no limit at 100mA?

*Notes on page 7 of the data sheet
(2) External current limit accuracy is only applicable to overload conditions greater than 1.5 x the current limit setting

Best regards,

  • 0
    TI__Mastermind 23170 points

    Hi ,

    Yes, the 1.5x factor is something that needs to be considered for the TPS4H000. The device will only trip when the current limit exceeds 1.5x the programmed current limit. If there is a soft short event where the current exceeds your programmed current but stays below 1.5x the current limit, it will not trip. 

    The accuracy is 20% but do also consider the tolerance of the resistor to be a factor in accuracy. 

  • 0 in reply to Anthony P Pham
    TI__Mastermind 24155 points

    Please note that the "1.5x" number is only for soft short conditions. In conditions such as a short-to-ground scenario where the impedance of the output changes very quickly the current limit will engage right away. Generally this means that when the voltage drop across the switch is greater that 2.5V the it is considered a hard short and the 1.5x number does not apply.

    Say you want to set your current limit to 0.1A as the minimum current limit as you have stated. In the datasheet we specify the 100mA current range at a ±20% accuracy.

    This would give you a KCL_MIN of 240 and a KCL_MAX of 360. If you Used the KCL_MIN value to calculate your RCL value this would translate to 1920Ω which would round down to 1910Ω at a standard 1% tolerance resistor value. Taking that 1910Ω value and back calculating it KCL_MIN and KCL_MAX at 1% tolerance this would get you a current range of 100mA to 152mA. You can play around with the values to get different ranges, however please be aware of the current limit range that the accuracy of the TPS4H000 and tolerance of the resistor will provide.