Pyrotechnic firing module with high current multiplexing

Now the title might sound a little daunting, but the concept of this project is fairly simple.

I am designing a firing module. The only thing this device does is pass a high current (in relative terms - over 1A, probably up to ~3A) through a small piece of nichrome wire coated in pyrotechnic composition. This causes the nichrome wire to heat up, ignting the composition and firing the pyrotechnic effect. The igniter only requires a 100ms max. pulse and will burn out when fired, leaving an open circuit.

Due to the nature of the circuit, safety is of primary concern. There are therefore a few considerations when designing such a circuit:
1) There should be a fool-proof way of isolating any power source from the igniters (normally a physical key switch)
2) You should be able to test the connections with low current (~10mA) for continuity
3) The default state of the system should be everything off. You do not want any lines ghosting that will fire anything when you don't want it to.

With the above in mind and looking at professional systems I have started to design the attached circuit. There are a few issues with the circuit... this is where I need the ETO community's help.

The igniters are attached between the red and black dots. To test for continuity, turn on the 4 P-channel MOSFETS in turn (by taking gate low) and read the data off the continuity test port. They should be high if continuity exists. To fire, you would also turn on the corresponding N-channel MOSFET.

This is not ideal as the idle state of the circuit (with MOSFET gates low) would mean that the P-channel ones are on, supplying a small current to each igniter (hopefully limited by the resistors).

Does anyone have any suggestions for improvements to this circuit? Any advice would be appreciated!

Many thanks
Freddie

I think I would use protected switches with status. There are plenty of devices like this around. https://www.electro-tech-online.com/custompdfs/2012/06/BUK205-50Y.pdf Note the disclaimer in the datasheet.

There are some nice devices from www.linear.com that offer regulation and power protection including reverse polarity protection.

You also might consider powering it from a full wave bridge so that the DC polarity doesn't matter.

I did not look carefully at the datasheet.

So would using something like a high side switch work just as well? The only problem is that most devices are too smart and will disable their outputs when a 'short' is detected. My only worry is that due to the low resistance of the ignter (a few ohms) that the chip will think there is a short and disable the output.

Any advice on a more elegant solution than my current one (ideally one chip, but unlikely) then that would be great. You can get some high side switches with 4 outputs, but the above worry about the short protection still exists.

Many thanks

Agreed. That's why I said you'll have to look at the various devices. Protected high side and low side switches exist without status as well. They should be "safer" than a unprotected MOSFET.