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Original question:

IC VREF SHUNT ADJ - LM4041

LM4041D: Performance at low quiescent current

Will Segalla
Prodigy 50 points
Part Number: LM4041D
Other Parts Discussed in Thread: LM4041-N

I have a new design using the LM4041DIM7X-ADJ to create a ~2.5V from a 3.3V rail. My load is a very high impedance ADC input so I'm taking the load current as negligible. So selecting my Rs should just be about satisfying the quiescent current of the device which is less than 100uA. I targeted 315uA with the following values: Rs=2700, R1=R2=1000. When the boards came in the output voltage was more like 1.3V instead of 2.5V. I tried putting various resistors in parallel with Rs and only when I got to a net resistance of 533 ohms (1.6mA through Rs) did the reference achieve its target output. Did I miss something on the datasheet where these devices need a lot more quiescent current than I expected?

  • 0
    TI__Mastermind 19580 points
    Hi Will,

    I have looked at your system and I think we need to recalculate some resistor values.
    Lets look at the current values with your system.
    With your current setup. 3.3V rail into 2.5V with a Rs of 2700 has a max shunt current of 296uA. max shunt current = (3.3V - 2.5V)/2700 Ohms = 296 uA
    The 296uA needs to power both the 70uA Irmax of the LM4041 and the current through the resistors.
    If we subtract the LM4041, we get 226uA for the resistors.
    The minimum value for your resistor chain value should be R(total) = 2.5V / 226uA = 8500 Ohms.
    Your current resistor values are too low that you are not providing enough current to the LM4041-N to turn on properly.
    I am unsure on how you paralleled the resistors but I would suggest to increase the values of the resistors and give yourself some margin.
    Shoot for 5k each for R1 and R2 and try again.

    -Marcoo