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LM5116: EN pull-up resistor

Jim G
Intellectual 685 points
Part Number: LM5116

Tool/software:

I'm implementing LM5116 in a noisy robotics environment and would likely to minimize high impedance nets where possible to avoid susceptibility to nearby noise.

My maximum input voltage is roughly 50V.

The recommended pull-up on LM5116 is 1M to the input voltage, but this is much higher than I would prefer.

The datasheet states the input bias current on this pin to be 90uA maximum with VEN=100V. Is this the maximum input bias current the EN pin draws, or the maximum it can survive?

The datasheet later mentions in section 6.3.2 the following

The datasheet recommends 1M pull-up, but then suggests it can be reduced to 100k "at low input voltage".
It then says "The EN pin can be tied directly to VIN if this function is not needed". I initially assumed the high pull-up values were to limit the current into the EN pin, but the datasheet then suggests you can simply tie EN to VIN directly.

So is the 90uA maximum input bias current a characteristic of the EN pin, or is it a specified limit that I must control?
What is the minimum pull-up resistor value I can apply with a ~50V supply voltage on the EN pin?

  • +1
    TI__Guru 58461 points

    Hello Jim 

    You can tie EN to VIN directly without any resistor, but this also means you cannot remotely shutdown the device when VIN is applied. In other word, the EN pin can be tied directly to VIN if this function is not needed. 

    You can remotely shutdown the device using an external  open-drain / open-collector switch if you connect EN to VIN through a resistor (for example 100k), but then this 100kOhm will leak current when the device is in shutdown (For example,  50V/100k =500uA which is 500 time greater than the shutdown current of the device) 

    In order to minimize this leak current, you have to increase the resistor between VIN and EN, 1MΩ is recommended in this case. 

    This 90uA is the maximum current which the device sinks from the 100V when 100V is applied to the EN pin.  

    -EL 

  • 0 in reply to EricLee
    Intellectual 685 points

    Thanks Eric, I mainly wanted to confirm if there was a minimum pull-up resistance permitted based on some leakage current or stress on the internal EN clamping diode, which was confusing when I saw that the EN pin could be tied directly to VIN if desired.

    This gives me the info I was looking for, thank you.

  • 0 in reply to Jim G
    TI__Guru 58461 points

    Thanks for choosing TI. Please feel free to contact us if you have any question.
    -EL