SparkFun Forums

[mrdudeman]

Does anyone know of a FET with a built-in pullup/pulldown resistor other than the LMN200? It works for my application, but I'm looking to buy 10k at a time and I was hoping there was a cheaper solution. The PNP transistor is basically unnecessary. The only thing I really need is a monolithic pullup/pulldown and N or P mosfet.

Thanks for any information you can offer.

[MichaelN]

Does it need to be a MOSFET? There are a huge number of NPN transistors with inbuilt resistors, but doesn't look like many MOSFETs. Why don't you just use a separate resistor? I can't imagine the cost or size would be an issue, even for a qty of 10K!

[mrdudeman]

It's more board space, additional vias, more time at the screening and P&P stations ($$$), another part to order as well as inventory, and various other small, but not insignificant, items.

This is a moderately low power application. The additional bias current may make a difference in the portable application, but I can deal with it if there are cheaper devices. Do you have any examples? I can't seem to find anything other than the LMN200.

[MichaelN]

The additional bias current may make a difference in the portable application, but I can deal with it if there are cheaper devices. Do you have any examples?

Look for "pre biased" or "digital" transistors. Digikey has thousands:

http://www.digikey.com/product-search/e ... transistor

[AndyC_772]

What package type gate threshold, Rds(on), current rating and gate capacitance do you need?

Surely you can find room for an 0402 resistor next to the FET?

[mrdudeman]

MichealN, thanks. I was missing the digital keyword. I found a dual NPN solution for $0.55 that will save me literally tens of thousands of dollars all things considered.

0402 is even more expensive to pick and place than 0603, so it's a no win situation. Pre-biased devices exist for a reason. Design for HVM (high volume manufacturing) has extremely different criteria than design for non-HVM.

[AndyC_772]

In my experience the cost to buy and place a resistor is as close to free as makes no difference, whether it's 0402, 0603 or 0805. CEM's often don't even bother to bill for the parts themselves, and I can't think of any reason why a good one should need to charge a different amount for an 0402 as a slightly larger package. If the process is up-to-date and reliable, the time on the machine is the same and the yield should be close to 100% for that type of component. If a CEM tells you an 0402 is difficult, it's time to look for a new CEM.

For transistors, I would have thought you'd get a better price by sticking with a component that's being shifted in higher volumes anyway; if your distributor buys 100k of a common transistor but only 10k of a part that's unique to your design, then they're bound to get a better price on the conventional part.

For what it's worth, I regularly design for volume manufacture - but nobody has ever pushed back on the cost of the standard passives and small discretes. It's all about the price of the ICs and the lead times of anything that's not on the shelf already.

[mrdudeman]

That's fine if that's your experience, but it has nothing to do with my design or application. You don't know how big or small the board is or how many extra components I'm saving. Besides, I already said there is no space for the resistor.

I'm using the biggest company in the US and there was a substantial price difference when I submitted both designs - one with resistors and one without. I've been designing products in the HVM space for many years so I don't need, nor did I ask, for any advice. Maybe you don't care about the price of small passives and discretes, but I do.

I simply needed help finding a part and I'm thankful that someone was able to help.

[MichaelN]

Dude, I think Andy was just trying to help, not criticise. Different companies probably have quite different pricing structures...