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Small footprint single component SMD high side mosfet that can provide 6A continuously — Parallax Forums

Small footprint single component SMD high side mosfet that can provide 6A continuously

eagletalontimeagletalontim Posts: 1,399
in Propeller 1
I know I am asking a bunch, but I am hoping there is a component on DigiKey that can be connected to a Prop Pin and can provide +12V battery voltage to a coil that draws up to 6A continuously. I was looking at this this mosfet, but it requires several resistors along with an NPN transistor to drive it which make the footprint on the board too big. I am sure if I crunch some things closer together, I may could fit it, but if there is a better alternative, I am all ears :)

Comments

  • kwinnkwinn Posts: 8,697
    edited 2015-09-03 02:19
    Problem is that any p channel mosfet will require +12V on the gate to turn off, therefore the need for another transistor and resistor if you are driving it from a microcontroller. What you need is a high side switch.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2015-09-03 02:24
    Any p-channel MOSFET will require an NPN for the Prop to be able to drive it. You might scour DigiKey for an integrated high-side switch instead. Never mind that: there's nothing there that meets your requirements.

    -Phil
  • eagletalontimeagletalontim Posts: 1,399
    I was looking at this other component but me not having enough knowledge to figure the specific values of each resistor needed, I worry about designing my circuit board for a specific component and finding I did something wrong and have to change the board and reorder them.... I was also reading on the spec sheet about the current sense part of that IC and am not sure what that is or how to use it or if it is needed. Controlling higher amperage items than an LED or coils on a small relay get a little tricky for me to select the right component and properly "wire" it up.
  • kwinnkwinn Posts: 8,697
    Try Mouser. I found an 8A switch that takes about 6 x 10 mm of board space.
  • jmgjmg Posts: 15,173
    There is a class of part called High-Side Drivers, that are a large MOSFET ( P-FET, or N-FET + charge pump) and they often have current fault sense as well.
    A little more in price than a simple FET, but they do not need level shifters.
    Infineon have a series of them, down to 1.9mOhms

    or, just buy the biggest P-FET you can afford ...

    SI7145DP-T1-GE3 30V 2.6mOhms
    or about to arrive from Infineon 40V 3.1mOhms
    IPB120P04P4L03ATMA1

    PFETS can be driven from 1 x NPN(HV) and 2 resistors. Base - Vcc and drive the emitter resistor LOW to pull the FET gate to Sat @ ~2.5V (10V gate drive @ 12V)
  • eagletalontimeagletalontim Posts: 1,399
    So basically, I can find the smallest footprint PFET that can handle my amperage need and use an SOT23 2222 transistor to drive the gate like I can do with the first component I listed? All that is needed to drive a PFET is an NPN transistor and proper resistors?
  • jmgjmg Posts: 15,173
    eagletalontim wrote: »
    So basically, I can find the smallest footprint PFET that can handle my amperage need and use an SOT23 2222 transistor to drive the gate like I can do with the first component I listed? All that is needed to drive a PFET is an NPN transistor and proper resistors?

    Beware of just looking at Amps.
    Best to consider the power - at 6Amps, 10mOhms is 360mW, 3.1mOhms is 118mW.
    I'd keep sub 10mOhms for a simple load.

    Is there any in-rush to the load ? (eg light bulbs) or is it a Coil/resistor.
    A coil will need a Catch-diode.

    Simple NPN is fine for static on/off, do not expect fast PWM thru a simple driver.
    a 1.2k emitter Res to Pin, Base to Vcc and G-S-Collector resistor of 5k6 will be OFF at Reset, and drive ~ 10V on the GATE when on (check G-S with a meter before you add the load)

  • eagletalontimeagletalontim Posts: 1,399
    The coil is an automotive solenoid that may stay on for hours at a time and the coil is 3 ohms. I have seen some +/- 0.4 ohms which is a little over 5A. I do plan on adding a flyback diode for protection. The solenoid will only be on or off, never controlled with PWM so I should be good there.
  • eagletalontimeagletalontim Posts: 1,399
    So from what I gather, since I have already used this (digikey.com/product-detail/en/0/DMP3010LK3-13DICT-ND) component on another project successfully, I really could not go wrong with using it.
  • jmgjmg Posts: 15,173
    Should be just ok - give it plenty of copper for cooling, and a clamp Zener so it never gets spiked..
  • Peter JakackiPeter Jakacki Posts: 10,193
    The cooling bit is important as Ron increase with temperature which increases the dissipation which increases the temperature........
    Tip: use thermal vias, that is lots of really tiny vias to an exposed pad on the other side. By exposed I mean "no solder mask". Of course your device should have a good pad underneath it too and leave any copper that it uses exposed.

    Going straight to the graphs for the device you picked looks like it should work fine though.
  • Cluso99Cluso99 Posts: 18,069

    You can get npn transistors with inbuilt base and base/emitter resistors in sot23 and smaller sot669 ? Packages. A 1K/10K or 4K7/47K would work. Then you should use a series resistor from collector to gate and a pull-up from the gate to 12V.
  • Cluso99Cluso99 Posts: 18,069
    edited 2015-09-03 05:08
    oops... The forum is broken :(
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