how to choose a mosfet based on teh Spartan 3E output port

i have a Xilinx Spartan 3E board and i need to output pwm waveform to a mosfet. can any one tell me from which port of the board can i output tthe waveform to the mosfet and what voltage would be supply from the board to the mosfet because based on this i would choose a mosfet. if u have an idea about the mosfet that can be used please let me know
thank in advance
arshad

MOSFET and PWM suggests that you are going to be doing power control. I would suggest placing a buffer chip between the FPGA and the MOSFET. That way any inductive kick back or wiring error would tend to destroy the driver IC, not the FPGA.

Look at the Philips family of single gate ICs. Some of these accept 3V input and a 5V power source. Pick something like an AND gate and wire the two inputs together for a buffer operation .

For the MOSFET, look at International Recitifer, or Siliconix. Search for Logic Level MOSFET, then narrow the search down by the amount of current you need to switch and the package style you want to use. There are many MOSFETs that will work.

As to which Spartan 3E port, it does not really matter. If you have a bank driving by a VCCO of 3V, then this would be a good choice. If all your VCCO connections are a lower voltage, then you need to take this into account when selecting the buffer chip.

Re: how to choose a mosfet based on teh Spartan 3E output po

yes i am controlling the mosfet for power switching. can you please let me know about the chip and how can the buffer switch be added. i am using a boost converter to step up 12V to 48V and the mosfet is to be control by the spartan 3E board.should i use a drive circuit or the pwm waveform from the fpga is enough.
thanks in advance
arshad

Go to www.nxp.com and read up on their pico gate devices. This will also list some of their competitors like Fairchild. With that data, you should have an idea of what kinds of drivers are available.

For the MOSFET, look at:
**broken link removed**
This will list numerous logic level MOSFETs. If the MOSFET requires 5V logic to turn it on, then you need a pico gate driver that can interface to 5V.

In my opinion, you most definitely need a driver. On a second generation design once all the bugs are worked out, it may be possible to drive the FPGA hard enough to control a MOSFET with a very low threshold level. HOWEVER, on the initial design, you want an inexpensive buffer between the FPGA and the MOSFET. Mistakes will be made and 48V will get coupled back and burn up the driver. Without the driver in the circuit, this 48V mistake will destroy the FPGA. Xilinx FPGAs fail very badly on over-voltage. In my experience, it does not just damage one pin, it shorts out the internal power supply and the entire device is gone.

Re: how to choose a mosfet based on teh Spartan 3E output po

why don't you use some sort of protection such as zener or diodes?

You can use a zener or a diode to protect against small voltage overshoots or undershoots. However, if you try to clamp 48V with a signal diode, it will burn itself open. Once this diode is open, you are directly connected to the FPGA.
The other issue is that the most you can probably get from a Spartan3E is 3.3V I/O. Therefore, you need the driver chip to step this voltage swing up to 5V to drive the MOSFET

Hi,
I am attempting to drive a 2 level DC-3phase AC inverter from Spartan 3 FPGA (Digilent Spartan 3 starter board) and I have a similar question. What buffer chips are suitable for the interface between the converter and the FPGA? I found this:
74LVC1G07GW,125 NXP Semiconductors Tampons et circuits d
Can this do the job? Also, do I need a voltage divider chip in addition to this buffer (3.3V to 5V) or this chip can handle the voltage conversion as well? I also read somewhere that ADCs are also required in this interface circuit. Can someone please help me?

the LVC devices should be ok considering it is 74. Also look at the current drive capability.

Connect the VCC pin to 5V and drive the input with a 3.3V spartan. As mentioned be careful your current drive is ok.

I concur on the : Zener diodes as mentioned earlier would be good for undershoots and spikes, but otherwise..

Ensure your PCB has separate planes to handle the voltages with a typical GND plane in between considering it is a power converter ckt.