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Original question:

TIOS1013: Digital Input Clamping When Un-powered (TIOS1013/TIOS1015)

TIOS1023: Setting the current limit resistor to guarantee a minimum limit is achieved.

Martin Ford1
Prodigy 70 points
Part Number: TIOS1023

So I have designed in the new TIOS1023 part and have come to the point of setting the current limit resistor.

Figure 6-4 in the datasheet gives a graph showing current limit vs the set current limit resistor.

Question 1 : Is the current limit shown in the graph the minimum, typical or maximum current limit setting for a given current limit resistor.

Question 2 : Figure 6-4 does seem to be an inaccurate way to setting the current limit, is there a formula which could be used instead. I am assuming that a fixed current source is fed through the current limit resistor which creates a voltage dependent upon the resistor value. This voltage being used internally to compare against a current sense voltage (using an internal comparator).

I need to guarantee a minimum current limit of 50mA so need to set the resistor to ensure I achieve this.

Regards

Martin

  • +1
    TI__Mastermind 32990 points

    Hi Martin,

    I understand what you are asking for.  Unfortunately we don't have a formula and the curve is not linear.  However, I know the curve data was collected with a fine resolution sweep using a potentiometer, so it is accurate and is the typical current collected at room temperature (Ta=25C) as noted in figure 6-5.

    Temperature and silicon process variations can create a slight variance in the actual current limit as seen from the Electrical Characteristics table that shows a 110k resistor will provide a typical 50mA current limit, but could be within 35mA and 70mA across all process, voltage, and temperature conditions.

    Because there is a -15mA to +20mA variation, I would suggest you target a resistor for the 65-70mA location on the curve to cover the margin.  Perhaps a resistor in the 55-60k range for starters.  An EVM is available with a potentiometer on the ILIM_ADJ pin if you would like to make some measurements for your particular test conditions.

    Regards,

    Jonathan

  • +1 in reply to Jonathan Nerger
    Prodigy 70 points

    Hi Jonathan,

    Thanks for the quick reply and answer.

    I will use the graph to aim for a typical value of 70-75mA which will allow us to meet our minimum 50mA requirement without an excessive maximum limit.

    Thank you for your assistance.

    Regards

    Martin