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From: RFI-EMI-GUY on 9 Dec 2008 20:15
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.

http://media.digikey.com/PDF/Data%20Sheets/Comchip%20PDFs/TVS%20Array%20CSR%20Se\
ries.pdf

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)
| | | |
| _|_ _|_/ |
| /|\ //|\ <(5.1V) ___
(10K) | | ___ <C2
| | (GND) |
| | (GND)
(Input)>--*-----(1K)-----*------>(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

--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"�

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P
From: RFI-EMI-GUY on 9 Dec 2008 20:26
RFI-EMI-GUY wrote:
> 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.
>
> http://media.digikey.com/PDF/Data%20Sheets/Comchip%20PDFs/TVS%20Array%20CSR%20Se\
>
> ries.pdf
>
> 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)
> | | | |
> | _|_ _|_/ |
> | /|\ //|\ <(5.1V) ___
> (10K) | | ___ <C2
> | | (GND) |
> | | (GND)
> (Input)>--*-----(1K)-----*------>(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
>

Fixed link:

http://media.digikey.com/PDF/Data%20Sheets/Comchip%20PDFs/TVS%20Array%20CSR%20Series.pdf


--
Joe Leikhim K4SAT
"The RFI-EMI-GUY"�

"Treason doth never prosper: what's the reason?
For if it prosper, none dare call it treason."

"Follow The Money" ;-P
From: John Devereux on 10 Dec 2008 04:37
RFI-EMI-GUY <Rhyolite(a)NETTALLY.COM> writes:

> 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.
>
> http://media.digikey.com/PDF/Data%20Sheets/Comchip%20PDFs/TVS%20Array%20CSR%20Se\
> ries.pdf
>
> 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)
> | | | |
> | _|_ _|_/ |
> | /|\ //|\ <(5.1V) ___
> (10K) | | ___ <C2
> | | (GND) |
> | | (GND)
> (Input)>--*-----(1K)-----*------>(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).

------------------------ 3V
|
10k
|
o--------[1k]--------| I/O Port
| |
TVS ----- 10n
| -----
| |
o------------------ GROUNDPLANE


I have used this simpler structure for protection against quite large
ESD events. The idea is that the TVS limits the ESD event voltage
right at the PCB connector, before it has a chance to affect anything
else. Then the series resistance and capacitance get rid of any
remainder. (And you get some level of debouncing for free). However
unlike yours there is no protection against a *sustained* over-voltage
- the TVS will fail, probably short-circuit.

[...]


--

John Devereux
From: Jasen Betts on 10 Dec 2008 05:00
On 2008-12-10, RFI-EMI-GUY <Rhyolite(a)NETTALLY.COM> wrote:

>
> *--------------*--------*----------------(+3.1V)
> | | | |
> | _|_ _|_/ |
> | /|\ //|\ <(5.1V) ___
> (10K) | | ___ <C2
> | | (GND) |
> | | (GND)
> (Input)>--*-----(1K)-----*------>(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).

seems overkill, the chip should already have internal protection diodes.

| chip
(input)----[100k]---[
|

> 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

as you're only monitoring slow inputs like switches:
improved version.

| chip
(input)--[1M]--+--[1M]-----[
| |
=== .1uF
|
--+--


From: John Devereux on 10 Dec 2008 06:13
Jasen Betts <jasen(a)xnet.co.nz> writes:

> On 2008-12-10, RFI-EMI-GUY <Rhyolite(a)NETTALLY.COM> wrote:
>
>>
>> *--------------*--------*----------------(+3.1V)
>> | | | |
>> | _|_ _|_/ |
>> | /|\ //|\ <(5.1V) ___
>> (10K) | | ___ <C2
>> | | (GND) |
>> | | (GND)
>> (Input)>--*-----(1K)-----*------>(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).
>
> seems overkill, the chip should already have internal protection diodes.
>
> | chip
> (input)----[100k]---[
> |


He may well get away with that - but I think you could find that an
ESD spark jumps right over the 100k. Or the effective parallel
capacitance of it could allow enough current to zap the chip.

>> 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
>
> as you're only monitoring slow inputs like switches:
> improved version.
>
> as you're only monitoring slow inputs like switches:
> improved version.
>
> | chip
> (input)--[1M]--+--[1M]-----[
> | |
> === .1uF
> |
> --+--

He seems to want a pullup for the input, and 1M is a bit high for an
outdoor environment - perhaps:


|
22k
|
(input)>---1k----1k----- Chip
|
=== 1u
|
----

--

John Devereux
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