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Topic: Any T092 package MOSFET to replace IRLML6402 ? (Read 1 time) previous topic - next topic

MarkT

For heavens sake that's the Vds = -10V graph, irrelevant to switching.
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ReverseEMF

#16
Oct 21, 2019, 04:26 pm Last Edit: Oct 21, 2019, 07:39 pm by ReverseEMF
For pities sake that's the Vds = -10V graph, completely irrelevant.
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Well, then -- how about this:


And, yes, once again, I know this is the Typical case, but even if the VGS lines were moved down, such that 2.6V was right on the ID = 0 line, the -3.3V line would still be well above 250mA!  And the channel voltage, at VGS = -3.3V, would be well under -0.5V -- more like -0.2V or below!

And, yes, I agree, for a production run this is risky thinking -- any characteristic not clearly specified by the Datasheet is outside the manufacturer support system.  But for a one-off home project?  This is hobbyist manna, man!
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ShermanP

I'm planning to use a Microchip LP0701 to switch power from an 18650 to a Wemos D1 Mini.  It comes in a TO-92, but it has a couple ohms RDS(on).  I'm just not sure how well it will handle the high-current WiFi activity, but will be testing it when the Minis arrive.

I just wanted to confirm that the LP0701 is NOT good for switching power to a Wemos D1 Mini.  I rigged up my battery-powered scope to measure the voltage drop from source to drain when the mosfet is on, and got spikes up to about 0.4V during wifi transmission.  Using a charged 18650, the transmission still worked, but I think the battery would have to be recharged more frequently.  Just too much RDSon.

I ended up using an SSM3j328r (SOT23F), and the spikes disappeared.  I never found anything in a TO92 to match that performance.  But that "F" in SOT23F is for "flat", which is very short stubs that stick out along the bottom.  Not much area for the solder to grip.  I think the IRLML6401 has normal SOT23 legs. That's the 12V version of the 6402, with moderately improved gate threshold and RDS numbers vs the 6402, and pretty much equivalent to the SSM part.

srnet

I decided to hedge my bets a little on this, I have done a PCB that has the option of using either a SI4459ADY or a  IRLML6401 based power switch.

The SI4459ADY is the easier to solder option, I have some coming from the far East at 13p each, we shall see how good they are.
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ShermanP

I decided to hedge my bets a little on this, I have done a PCB that has the option of using either a SI4459ADY or a  IRLML6401 based power switch.

The SI4459ADY is the easier to solder option, I have some coming from the far East at 13p each, we shall see how good they are.
The SI4459ADY has a bit higher gate threshhold than I'd like, particularly for supply voltages down to about 3.5V.  But soldering would certainly be easier.  Except for the gate, you can even bridge the pins with solder.  But I do wonder about ordering this kind of thing from the far East at 13p, particularly when Digikey sells them for $1.45.  In the US I tend to resort to Digikey when it matters if it's genuine.  But in this case, I guess you can test and measure whether the RDS is right.

ReverseEMF

#20
Nov 02, 2019, 03:21 pm Last Edit: Nov 02, 2019, 03:29 pm by ReverseEMF Reason: Corrected Polarities
The SI4459ADY has a bit higher gate threshhold than I'd like, particularly for supply voltages down to about 3.5V.  
I wouldn't worry too much about that.  Worst case Gate Threshold of -2.5V and Typical RDS(on) less than 7mΩ at VGS = -4.5V and typical 14A Drain current at VGS = -3V.  I'd say this transistor will have no problem with 1/4 of an Amp, at -3.3V!

I mean, just look at this Transfer Characteristic!  With a slope that steep, it ain't gonna matter if the Gate Threshold is all the way up to -2.5V, by -3V, this transistor is going to be as ON as Flop!!  Certainly ON enough to handle "250mA, or so".

"It's a big galaxy, Mr. Scott"

Please DON'T PM me regarding what should be part of the Public Conversation -- Let it ALL hang out!!
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