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LMZ14202H: Maximum leakage current on EN input pin? Maximum values for ENable resistor divider network?

Jim Brinkhurst1
Mastermind 44280 points
Part Number: LMZ14202H

Hi experts

I'm working on a new design with this device, and want to minimize the current flowing through the ENable resistor divider network.

Can you provide information on the structure of the input pull-up described in datasheet section 8.2.2.1.1, and the maximum input leakage current in/out of the pin?

"The EN pin is internally pulled up to VIN and can be left floating for always-on operation. However, it is good
practice to use the enable divider and turn on the regulator when VIN is close to reaching its nominal value. This
will ensure smooth start-up and will prevent overloading the input supply."

Alternatively, what are the maximum values that can be used for RENT and RENB?

Thanks!

Jim B

  • 0
    TI__Expert 6655 points

    Hi Jim,

    Thank you for your question. The maximum input leakage current of the pin is dependent on your loading conditions. According to the datasheet, shut down quiescent current is typically 25 uA and non-switching input current is 1 mA. There is an internal pull up for EN which allows it to be left floating. Using an enable divider ensures that the device does not attempt to turn on until the desired loading conditions are met, and will give a better start-up waveform. 

    In general, larger resistances for Rent and Renb will decrease leakage current and give better efficiency. However, this comes at the cost of accuracy. It does not look like this part has a limit for Rent and Renb, but it is important to note that the voltage on EN pin should not exceed 6.5 V. 

    We do not generally share the structure of our IC's past what is on the datasheet, but I would imagine it is just a voltage divider.

    Thank you,

    Joshua Austria

  • 0 in reply to Joshua Austria
    TI__Mastermind 44280 points

    Hi Joshua

    The currents you are quoting are the total device quiescent current (on VIN to GND), not the current flowing into the EN pin. 

    We need the EN pin input impedance, input leakage current, and/or the internal pullup resistance value to be able to choose the appropriate value for RENT and RENB .

    Alternatively, you need to tell us what is the largest reasonable value for RENT and RENB that we can choose that will still give us an accurate divider voltage at the EN input.

    For example, can we make Renb 100k, 1M, 10M, 100M?

    Thanks,

    Jim B  

  • 0 in reply to Jim Brinkhurst1
    TI__Expert 6655 points

    Hi Jim, 

    You can start with 11.8 k and go from there. This is the RENB on the divider for the EVM. If the power consumption is too high, I would begin to increase the value of Renb in steps of 5-10 k until you get the leakage current you want.

    It looks like this part does have a webench and a PSPICE model so you can use these to simulate your expected efficiencies and to easily tweak values.

    Please let me know if you have any more questions,

    Joshua Austria