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TPS7A05: Maximum EN input resistance

MattLin
Intellectual 1050 points
Part Number: TPS7A05
Other Parts Discussed in Thread: TPS7A10,

What's the maximum pull up resistance that can be put on the enable pin to minimize leakage current on this pin? Is this also the same for the TPS7A10?

  • 0
    TI__Expert 4350 points
    Hi Matt,

    Use the following in the Electrical Conditions (EC) Table to determine the max pull-up resistor from EN to IN:
    EN pin current = 10 nA (typ)
    Ven(hi) = 0.9 V (min)
    Ven(lo) = 0.4 V (max)

    Rpull-up(max) = (Vin - Ven(hi)) / EN pin current

    For example:
    Vin = 3.3 V
    Rpull-up(max) = 240 Megaohm

    The amount of current consumed is larger in the Disabled case, when EN is pulled low.
    For example:
    Vin = 3.3 V
    Rpull-up = 240 Megaohm
    Ven(lo) = 0.4 V (max). Assume Ven(lo) pulled to 0.4 V.
    I(Rpull-up when disabled) = (Vin - Ven(lo)) / Rpull-up = 12 nA

    If Rpull-up = 1 Megaohm
    I(Rpull-up when disabled) = 2.9 uA.
  • 0 in reply to Eric.Preiss
    TI__Expert 4350 points
    Hi Matt,

    I wanted to clarify that the current through the EN pull-up resistor when the LDO is disabled flows is the total of the current into the EN pin and the current through the pull-down driver circuit. 10 nA flows into EN pin and the remainder of the current flows into the switch that is pulling the EN pin low.

    In the case of Rpull-up = 1 Megaohm and I(Rpull-up when disabled) = 2.9 uA:
    10 nA flows into EN pin of TPS7A05
    2.89 uA flows into switch that is pulling EN pin low.
  • 0 in reply to Eric.Preiss
    TI__Intellectual 1050 points
    Hi Eric,

    Are you saying the minimum current that will allow the device to be enabled is 10nA? If they are using a 1.8V rail to power this, based on the calculation, it looks like 900k is the maximum resistance allowed. Is this correctly calculated? Or is it possible to go up to 1M or greater?

    Thanks,
    Matt
  • 0 in reply to MattLin
    TI__Expert 4350 points
    Hi Matt,

    The voltage on EN pin determines if the device is enabled. If the voltage is 0.9 V or higher on EN, the LDO is enabled. If voltage is 0.4 V or lower on EN, the LDO is disabled. The typical leakage current into EN is 10 nA.

    If Vin = 1.8 V, then Rpull-up(max) = 90 Megaohm.
    As 10 nA flows through the pull-up resistor, there is a voltage drop of 0.9 V from the Vin = 1.8 V. This results in 0.9 V on EN pin. If you use a larger pull-up resistor, the voltage on EN pin will be less than 0.9 V and the LDO will not be guaranteed to be enabled across temperature and all other conditions.

    If the application has a switch to pull EN low to disable the LDO, the designer needs to include the switch leakage current in the calculation for max EN pull-up resistor. The max resistor value will need to be smaller to accommodate the switch leakage.