Electronics > Projects, Designs, and Technical Stuff
Lack of information on datasheet
OM222O:
I plan on using the NCP718ASN500T1G for an upcoming project, datasheet available here:
https://www.onsemi.com/pub/Collateral/NCP718-D.PDF
The EN pin is active high but they don't mention if it can be directly connected to Vin to activate, or if I need a resistor. some of the LDOs require resistor and some are cmos so they don't need that. I had a look on their website and they have an evaluation board but they don't provide any schematic on that and the pictures are way too blurry to make anything out. Can anyone confirm if I can connect the EN directly to VCC and it wouldn't kill the chip?
dmills:
Second line of the 'Abs max values table' says max is Vin + 0.6V so direct connection would appear just permissible as long as there is not significant inductance between the junction and Vin....
Regards, Dan.
OM222O:
the problem is not the voltage in this case, if it's using BJTs instead of fets for the "ENABLE LOGIC" section, a resistor is mandatory to limit the current.
The "EN input current" is listed as 100nA which hints at it being a FET (just leakage level current) rather than a bjt but I want to be sure before designing the product with a fault. I contacted them directly so waiting for their answer as well.
TI always specifies these sort of things + provides "typical application" circuit diagrams. even layout guidelines for a LOT of their chips. I wish all manufacturers released detailed and comprehensive datasheets like that.
ajb:
If it needed a resistor it would give you the information you needed to calculate that resistor value (such as an input voltage characteristic plus a maximum input current rating). Also, the En pin current is given at a specified En voltage of 5.5V, so that confirms that it's not a naked BJT base like you're worried about. I'm not sure that any modern regulator out there *requires* a resistor, but pull-up/pull-down resistors are often shown anyway, because that might be what you need functionally. Also you often see dividers on the input to provide UVLO in conjunction with the input hysteresis. Obviously if you have a device with a max input voltage less than its max Vin you might see a resistor plus a zener, but that's not applicable here.
OM222O:
yes I have confirmed this device does not require a resistor, but it's not the case for all "modern" LDOs.
TI specifies a MINIMUM pullup resistor of 100k with recommended value of 300k on a few of their LDOs with modern specs :-//
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