http://www.proto-pic.co.uk/content/datasheets/N-CHannel-MOSFET60V30ADatasheet.pdf
1. Is it capable of driving 12V/30A? I read on some posts that it requires 2 voltages, a charge pump was mentioned. Will it switch 12V if driven with a 5V TTL signal from a PIC or will it not be fully switched on? Similarly, the posts mentioned switching off being a problem. Will setting the pinto 0 on the pic cause it to fully switch off.
If you use it with the source connected to 0V and the load connected between a +12V supply and the drain, it will switch 30A at 12V. But...
(a) If the load is inductive, you must connect a diode rated for at least 30V across the load (with its cathode to the +12V rail) to suppress the back EMF from the load. Otherwise, when the MOSFET turns OFF, the back EMF (due to the load inductance) will create a high-voltage pulse on the MOSFET's drain which will exceed the 60V rating for the MOSFET and will damage it;
(b) It's never a good idea to run a component at its rated maximum (current or voltage);
(c) Running at 30A that MOSFET will dissipate up to about 42 watts and it will need a significant heatsink.
You should use a MOSFET with a higher current rating and a lower R
DS(on) specification. Here's what you need to know.
1. I would use a MOSFET that's rated for a continuous current at least 50% higher than the maximum expected current. In this case that would mean a 45A continuous drain current specification.
2. The amount of power dissipated by the MOSFET when it's conducting continuously can be calculated from the drain current and the R
DS(on) value (also called the ON-resistance) using the formula P = I
2 R, where I is the drain current in amps, and R is the R
DS(on) resistance in ohms. So for a given current, a lower R
DS(on) is better because it means less power is lost in the MOSFET and less heat needs to be dissipated.
3. Heatsinks are specified by their thermal resistance to ambient, which is measured in °C/W (degrees Celsius per watt). This figure is the number of degrees Celsius that the heatsink will rise above the ambient temperature for every watt of power dissipated. The required heatsink can be calculated from the maximum allowable temperature rise divided by the heatsink's thermal resistance to ambient. For example, for a maximum heatsink temperature of 75 °C at a maximum ambient temperature of 35 °C, the allowable temperature rise is 40 °C. If the device is dissipating 10W, your heatsink needs a thermal resistance of 40 / 10 = 4 °C/W.
4. R
DS(on) is usually specified with typical and maximum values, and often, at several V
GS voltages - often 10V and 4.5V, and sometimes lower voltages as well. At higher V
GS voltages, the MOSFET conducts more strongly, so R
DS(on) is lower. From this point of view, it's good to drive the gate with as much voltage as possible; this can be achieved using a level shifter made with transistors.
5. If you are switching the MOSFET regularly at some frequency, instead of just turning it ON and OFF periodically, you should use a MOSFET gate driver IC. These can be powered from a 12V supply (typically) to provide enough gate voltage to bias the MOSFET into heavy conduction, and a high current that charges and discharges the MOSFET's gate-source capacitance quickly and ensures that it changes quickly and cleanly between fully OFF and fully ON.
6. If you drive the MOSFET gate from a microcontroller output, you should use a MOSFET that's designed for low R
DS(on) drive; these are also called "logic level" MOSFETs. These have data sheet specifications for R
DS(on) at V
GS voltages of 4.5V and lower. MOSFETs that aren't optimised for low V
GS drive will conduct at 5V gate-source voltage, but not as heavily as they do at 10V gate-source voltage, and R
DS(on) at 4.5V gate-source voltage will be significantly higher than the value specified for 10V gate-source voltage, so the power dissipation will be higher as well.
7. N-channel MOSFETs generally have lower R
DS(on) values than P-channel MOSFETs. Most modern MOSFETs are only available in SMT (surface-mount technology) packages. Many of these can be hand-soldered, but no-lead packages (e.g. DFN, PQFN, SON - most package names that include 'N', and BGA packages) require reflow soldering and x-ray inspection. Many modern SMT MOSFETs have low V
DS limits, and low V
GS limits as well. These can easily be damaged by voltages that are quite safe for older, larger MOSFETs. Zener diodes or other clamping devices can be connected between gate and source, and between drain and source if necessary, to protect them against spikes or unexpected circuit conditions.
2. If I need to drive more amps, can these be put in paralle(gates together, sources together and drains together)?
Yes, but it's simpler and cheaper to use a more modern MOSFET. The specifications of devices you can get nowadays are really impressive. Here are a few for you to check out:
http://www.digikey.com/product-detail/en/BUK951R6-30E,127/568-9859-5-ND/3672466
http://www.digikey.com/product-detail/en/PSMN0R9-25YLC,115/568-6720-1-ND/2674297
http://www.digikey.com/product-detail/en/BUK962R5-60E,118/568-9569-1-ND/3431418
It's only a coincidence that these are all NXP devices. Other manufacturers such as STMicroelectronics, Fairchild, and especially Alpha & Omega, make some very impressive devices as well.
Sorry if these are stupid questions.
No, they're good questions.