This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LMZM23600: UVLO setting resistors

Part Number: LMZM23600

Hi,

On page 26 in the documentation for the LMZM23600 there is a description for how to calculate the UVLO resistors. Figure 38 show a schematic with two resistors, Rent and Renb which i assume designate R-enable-top and R-enable-bottom respectively (this matches the relative positions of the resistors in figure 38)

However, in the description immediately following Figure 38, it is stated that one should select the "top resistor Renb" to be 10 to 50kOhm, which leaves me slightly puzzled. 

In short: 
Is it the top resistor (connected between Vin and EN) or the bottom resistor (between EN and GND) which should be set between 10 and 50 kohm? 

Additionally:
Are there any other guidelines for the maximum values for these two resistors? I am assuming that the bias current into the EN-pin must be accounted for, but are there other considerations that need to be taken? The EN-pin current is given only for 12V, can it be assumed to be reasonably constant for the input voltage range?

Thank you in advance for any help,

Best regards,

K

  • Hi K,

    Thanks for pointing out the discrepancy. I believe this is a simple type and should be corrected with "bottom resistor Renb". This is because Equation 3 solves for Rent given a fixed Renb value that you initially decide between 10k - 50k.

    I'd stick to the recommended value for Renb between 10k - 50k. I'd imagine that if you picked higher valued resistors the input current will be lowered at the cost of introducing thermal noise which may impact the EN pin. 

    It can be assumed that the enable pin input current is reasonable around the typical 2.7uA value.

    Regards,

    Jimmy