I am designing a small telemetry board for a high altitude rocket launch. I am using a 08-M and want to protect 3 input ports from ESD, because the telemetry is also part of the recovery beacon, current consumption is a concern as I would like to have battery life extend to days or weeks on a CR123 battery. For my prototype I am using a TVS suppressor of discrete components electrically similar to a COMCHIP CSR series: (see link) Which consist of two clamping diodes (per line) and a zener which clamp the ESD event to about 5 or 6 volts. Also 2 capacitors C1 and C2 to shunt high frequency ESD that the diodes may be too slow to respond to.
The telemetry I/O ports will be wired to switches monitoring such items as chute deployement upon which the circuit will become an open circuit when the chute(s)deploy making the I/O port susceptible to ESD events from the chute or static charge of the fiberglass rocket body. The lead length will be 2 or 3 feet.
It is unclear how best to apply the TVS suppressor in circuit, my thought is that it should be wired directly to the 08-M 1/0 port with with the 10K pull up resistor and a 1K current limiting resistor wired between the external screw terminal for the external switch and the TVS device. (that way simultaneously limiting external current to the TVS and the 08-M).
(I hope this "drawing works!)
*--------------*--------*----------------(+3.1V) | | | | | _|_ _|_/ | | /|\\ //|\\ (08-M I/O port) | _|_ | /|\\ ___ | ___ < C1 GND | (GND)
Does this appear to be a viable design? Can anyone recommend value for C1 and C2? This is a low speed application (mechanical switch sense).
Is there another solution such as a transistor buffer (preferably non inverting) array in chip form that is not ESD sensitive?
Again my constraints in order are:
1) reliability
2) current consumption (a buffer will result in more current draw than passive TVS?)
3)Form factor (chip array instead of discrete components)
4)weight