> On Sat, 29 Jun 2013 11:18:00 -0700, Joerg <invalid@invalid.invalid>
> wrote:
>
>> Jim Thompson wrote:
>>> On Sat, 29 Jun 2013 11:08:02 -0700, Joerg <invalid@invalid.invalid>
>>> wrote:
>>>
>>>> Jim Thompson wrote:
>>>>> On Sat, 29 Jun 2013 10:22:13 -0700, Joerg <invalid@invalid.invalid>
>>>>> wrote:
>>>>>
>>>>>> Jim Thompson wrote:
>>>>>>> On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>>>>>>>
>>>>>>>> Joerg <invalid@invalid.invalid> wrote:
>>>>>>>>
>>>>>>>>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>>>>>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>>>>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>>>>>>>>> are.
>>>>>>>>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>>>>>>>>> you fretting over?
>>>>>>>>>>>>
>>>>>>>>>>> The concern are surge events that make these lines carry nasty
>>>>>>>>>>> transients, which in turn can lock up or damage the uC.
>>>>>>>>>> So you have a "dirty" 5V supply?
>>>>>>>>>>
>>>>>>>>> No, rock-stable. But clamping against it will lead to up to 7V spike
>>>>>>>>> amplitude if it's a huge transient. Those small clamper arrays can
>>>>>>>>> easily reach 2V Vf or more for a few usec.
>>>>>>>> If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>>>>>>>> around 2.5V?
>>>>>>>>
>>>>>>>> How about clamping with a 3.9V zener to ground with a small series
>>>>>>>> resistor to limit the transient current? As long as the desired signal
>>>>>>>> gets above the threshold, do you care if it goes all the way to 5V?
>>>>>>>>
>>>>>>>> For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>>>>>>>> you get above 3V, and 50mA doesn't even reach 5V:
>>>>>>>>
>>>>>>>> http://www.pridmore.com/datasheets/BZX84CA07.pdf
>>>>>>>>
>>>>>>>> Don't know what all the tolerances are, but so far nothing else seems to
>>>>>>>> have any chance of working in your application.
>>>>>>>>
>>>>>>>> JK
>>>>>>> I still haven't seen described how a "rock solid" 5V supply produces
>>>>>>> such gross transients.
>>>>>>>
>>>>>> It doesn't. It's the signal lines that do.
>>>>>>
>>>>>> [...]
>>>>> So "induced" transients? How much actual energy?
>>>>>
>>>> Hard to say how much arrives, all I know from reports is that it has
>>>> frozen the uC at times. So we had to do something about it. We should be
>>>> good with those clamps. I was just wondering how far things can go
>>>> above abs max and for how long. Of course we won't be sending in 7V for
>>>> hours. When I redesign stuff I like to make it not just good enoug to
>>>> pass a test, but ideally almost bullet-proof.
>>> The 7V limit only applies to those pins which are configurable I/O. If
>>> it's an input-only pin, it can stand a whole lot more... some
>>> processes can be as high as 50V.
>>>
>> They state a 5.8V abs max, 7V is just what one would typically see if a
>> monster pulse comes along and leans into the clamp diodes.
>>
>>
>>> But you said uC... they're probably ALL I/O :-(
>>>
>> Yup, all I/O :-(
>
> If you can get a handle on the energy involved (*), I can show you
> some simple clamps that are reliable and tight on the limits.
>
> (*) Just patch in a diode to +5V and current probe the data line.
>
I could design some clamps that are more precise but there is so little
space that just adding the teeny clamp arrays was already a challenge.
Also, it's thousands of miles away.
--
Regards, Joerg
http://www.analogconsultants.com/
Reply by Jim Thompson●June 29, 20132013-06-29
On Sat, 29 Jun 2013 11:18:00 -0700, Joerg <invalid@invalid.invalid>
wrote:
>Jim Thompson wrote:
>> On Sat, 29 Jun 2013 11:08:02 -0700, Joerg <invalid@invalid.invalid>
>> wrote:
>>
>>> Jim Thompson wrote:
>>>> On Sat, 29 Jun 2013 10:22:13 -0700, Joerg <invalid@invalid.invalid>
>>>> wrote:
>>>>
>>>>> Jim Thompson wrote:
>>>>>> On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>>>>>>
>>>>>>> Joerg <invalid@invalid.invalid> wrote:
>>>>>>>
>>>>>>>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>>>>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>>>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>>>>>>>> are.
>>>>>>>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>>>>>>>> you fretting over?
>>>>>>>>>>>
>>>>>>>>>> The concern are surge events that make these lines carry nasty
>>>>>>>>>> transients, which in turn can lock up or damage the uC.
>>>>>>>>> So you have a "dirty" 5V supply?
>>>>>>>>>
>>>>>>>> No, rock-stable. But clamping against it will lead to up to 7V spike
>>>>>>>> amplitude if it's a huge transient. Those small clamper arrays can
>>>>>>>> easily reach 2V Vf or more for a few usec.
>>>>>>> If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>>>>>>> around 2.5V?
>>>>>>>
>>>>>>> How about clamping with a 3.9V zener to ground with a small series
>>>>>>> resistor to limit the transient current? As long as the desired signal
>>>>>>> gets above the threshold, do you care if it goes all the way to 5V?
>>>>>>>
>>>>>>> For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>>>>>>> you get above 3V, and 50mA doesn't even reach 5V:
>>>>>>>
>>>>>>> http://www.pridmore.com/datasheets/BZX84CA07.pdf
>>>>>>>
>>>>>>> Don't know what all the tolerances are, but so far nothing else seems to
>>>>>>> have any chance of working in your application.
>>>>>>>
>>>>>>> JK
>>>>>> I still haven't seen described how a "rock solid" 5V supply produces
>>>>>> such gross transients.
>>>>>>
>>>>> It doesn't. It's the signal lines that do.
>>>>>
>>>>> [...]
>>>> So "induced" transients? How much actual energy?
>>>>
>>> Hard to say how much arrives, all I know from reports is that it has
>>> frozen the uC at times. So we had to do something about it. We should be
>>> good with those clamps. I was just wondering how far things can go
>>> above abs max and for how long. Of course we won't be sending in 7V for
>>> hours. When I redesign stuff I like to make it not just good enoug to
>>> pass a test, but ideally almost bullet-proof.
>>
>> The 7V limit only applies to those pins which are configurable I/O. If
>> it's an input-only pin, it can stand a whole lot more... some
>> processes can be as high as 50V.
>>
>
>They state a 5.8V abs max, 7V is just what one would typically see if a
>monster pulse comes along and leans into the clamp diodes.
>
>
>> But you said uC... they're probably ALL I/O :-(
>>
>
>Yup, all I/O :-(
If you can get a handle on the energy involved (*), I can show you
some simple clamps that are reliable and tight on the limits.
(*) Just patch in a diode to +5V and current probe the data line.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by Joerg●June 29, 20132013-06-29
Jim Thompson wrote:
> On Sat, 29 Jun 2013 11:08:02 -0700, Joerg <invalid@invalid.invalid>
> wrote:
>
>> Jim Thompson wrote:
>>> On Sat, 29 Jun 2013 10:22:13 -0700, Joerg <invalid@invalid.invalid>
>>> wrote:
>>>
>>>> Jim Thompson wrote:
>>>>> On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>>>>>
>>>>>> Joerg <invalid@invalid.invalid> wrote:
>>>>>>
>>>>>>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>>>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>>>>>>> are.
>>>>>>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>>>>>>> you fretting over?
>>>>>>>>>>
>>>>>>>>> The concern are surge events that make these lines carry nasty
>>>>>>>>> transients, which in turn can lock up or damage the uC.
>>>>>>>> So you have a "dirty" 5V supply?
>>>>>>>>
>>>>>>> No, rock-stable. But clamping against it will lead to up to 7V spike
>>>>>>> amplitude if it's a huge transient. Those small clamper arrays can
>>>>>>> easily reach 2V Vf or more for a few usec.
>>>>>> If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>>>>>> around 2.5V?
>>>>>>
>>>>>> How about clamping with a 3.9V zener to ground with a small series
>>>>>> resistor to limit the transient current? As long as the desired signal
>>>>>> gets above the threshold, do you care if it goes all the way to 5V?
>>>>>>
>>>>>> For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>>>>>> you get above 3V, and 50mA doesn't even reach 5V:
>>>>>>
>>>>>> http://www.pridmore.com/datasheets/BZX84CA07.pdf
>>>>>>
>>>>>> Don't know what all the tolerances are, but so far nothing else seems to
>>>>>> have any chance of working in your application.
>>>>>>
>>>>>> JK
>>>>> I still haven't seen described how a "rock solid" 5V supply produces
>>>>> such gross transients.
>>>>>
>>>> It doesn't. It's the signal lines that do.
>>>>
>>>> [...]
>>> So "induced" transients? How much actual energy?
>>>
>> Hard to say how much arrives, all I know from reports is that it has
>> frozen the uC at times. So we had to do something about it. We should be
>> good with those clamps. I was just wondering how far things can go
>> above abs max and for how long. Of course we won't be sending in 7V for
>> hours. When I redesign stuff I like to make it not just good enoug to
>> pass a test, but ideally almost bullet-proof.
>
> The 7V limit only applies to those pins which are configurable I/O. If
> it's an input-only pin, it can stand a whole lot more... some
> processes can be as high as 50V.
>
They state a 5.8V abs max, 7V is just what one would typically see if a
monster pulse comes along and leans into the clamp diodes.
> But you said uC... they're probably ALL I/O :-(
>
On Sat, 29 Jun 2013 11:08:02 -0700, Joerg <invalid@invalid.invalid>
wrote:
>Jim Thompson wrote:
>> On Sat, 29 Jun 2013 10:22:13 -0700, Joerg <invalid@invalid.invalid>
>> wrote:
>>
>>> Jim Thompson wrote:
>>>> On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>>>>
>>>>> Joerg <invalid@invalid.invalid> wrote:
>>>>>
>>>>>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>>>>>> are.
>>>>>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>>>>>> you fretting over?
>>>>>>>>>
>>>>>>>> The concern are surge events that make these lines carry nasty
>>>>>>>> transients, which in turn can lock up or damage the uC.
>>>>>>> So you have a "dirty" 5V supply?
>>>>>>>
>>>>>> No, rock-stable. But clamping against it will lead to up to 7V spike
>>>>>> amplitude if it's a huge transient. Those small clamper arrays can
>>>>>> easily reach 2V Vf or more for a few usec.
>>>>> If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>>>>> around 2.5V?
>>>>>
>>>>> How about clamping with a 3.9V zener to ground with a small series
>>>>> resistor to limit the transient current? As long as the desired signal
>>>>> gets above the threshold, do you care if it goes all the way to 5V?
>>>>>
>>>>> For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>>>>> you get above 3V, and 50mA doesn't even reach 5V:
>>>>>
>>>>> http://www.pridmore.com/datasheets/BZX84CA07.pdf
>>>>>
>>>>> Don't know what all the tolerances are, but so far nothing else seems to
>>>>> have any chance of working in your application.
>>>>>
>>>>> JK
>>>> I still haven't seen described how a "rock solid" 5V supply produces
>>>> such gross transients.
>>>>
>>> It doesn't. It's the signal lines that do.
>>>
>>> [...]
>>
>> So "induced" transients? How much actual energy?
>>
>
>Hard to say how much arrives, all I know from reports is that it has
>frozen the uC at times. So we had to do something about it. We should be
> good with those clamps. I was just wondering how far things can go
>above abs max and for how long. Of course we won't be sending in 7V for
>hours. When I redesign stuff I like to make it not just good enoug to
>pass a test, but ideally almost bullet-proof.
The 7V limit only applies to those pins which are configurable I/O. If
it's an input-only pin, it can stand a whole lot more... some
processes can be as high as 50V.
But you said uC... they're probably ALL I/O :-(
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by Joerg●June 29, 20132013-06-29
Jim Thompson wrote:
> On Sat, 29 Jun 2013 10:22:13 -0700, Joerg <invalid@invalid.invalid>
> wrote:
>
>> Jim Thompson wrote:
>>> On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>>>
>>>> Joerg <invalid@invalid.invalid> wrote:
>>>>
>>>>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>>>>> are.
>>>>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>>>>> you fretting over?
>>>>>>>>
>>>>>>> The concern are surge events that make these lines carry nasty
>>>>>>> transients, which in turn can lock up or damage the uC.
>>>>>> So you have a "dirty" 5V supply?
>>>>>>
>>>>> No, rock-stable. But clamping against it will lead to up to 7V spike
>>>>> amplitude if it's a huge transient. Those small clamper arrays can
>>>>> easily reach 2V Vf or more for a few usec.
>>>> If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>>>> around 2.5V?
>>>>
>>>> How about clamping with a 3.9V zener to ground with a small series
>>>> resistor to limit the transient current? As long as the desired signal
>>>> gets above the threshold, do you care if it goes all the way to 5V?
>>>>
>>>> For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>>>> you get above 3V, and 50mA doesn't even reach 5V:
>>>>
>>>> http://www.pridmore.com/datasheets/BZX84CA07.pdf
>>>>
>>>> Don't know what all the tolerances are, but so far nothing else seems to
>>>> have any chance of working in your application.
>>>>
>>>> JK
>>> I still haven't seen described how a "rock solid" 5V supply produces
>>> such gross transients.
>>>
>> It doesn't. It's the signal lines that do.
>>
>> [...]
>
> So "induced" transients? How much actual energy?
>
Hard to say how much arrives, all I know from reports is that it has
frozen the uC at times. So we had to do something about it. We should be
good with those clamps. I was just wondering how far things can go
above abs max and for how long. Of course we won't be sending in 7V for
hours. When I redesign stuff I like to make it not just good enoug to
pass a test, but ideally almost bullet-proof.
--
Regards, Joerg
http://www.analogconsultants.com/
Reply by Jim Thompson●June 29, 20132013-06-29
On Sat, 29 Jun 2013 10:22:13 -0700, Joerg <invalid@invalid.invalid>
wrote:
>Jim Thompson wrote:
>> On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>>
>>> Joerg <invalid@invalid.invalid> wrote:
>>>
>>>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>>>> are.
>>>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>>>> you fretting over?
>>>>>>>
>>>>>> The concern are surge events that make these lines carry nasty
>>>>>> transients, which in turn can lock up or damage the uC.
>>>>> So you have a "dirty" 5V supply?
>>>>>
>>>> No, rock-stable. But clamping against it will lead to up to 7V spike
>>>> amplitude if it's a huge transient. Those small clamper arrays can
>>>> easily reach 2V Vf or more for a few usec.
>>> If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>>> around 2.5V?
>>>
>>> How about clamping with a 3.9V zener to ground with a small series
>>> resistor to limit the transient current? As long as the desired signal
>>> gets above the threshold, do you care if it goes all the way to 5V?
>>>
>>> For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>>> you get above 3V, and 50mA doesn't even reach 5V:
>>>
>>> http://www.pridmore.com/datasheets/BZX84CA07.pdf
>>>
>>> Don't know what all the tolerances are, but so far nothing else seems to
>>> have any chance of working in your application.
>>>
>>> JK
>>
>> I still haven't seen described how a "rock solid" 5V supply produces
>> such gross transients.
>>
>
>It doesn't. It's the signal lines that do.
>
>[...]
So "induced" transients? How much actual energy?
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by Joerg●June 29, 20132013-06-29
Jim Thompson wrote:
> On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>
>> Joerg <invalid@invalid.invalid> wrote:
>>
>>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>>> are.
>>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>>> you fretting over?
>>>>>>
>>>>> The concern are surge events that make these lines carry nasty
>>>>> transients, which in turn can lock up or damage the uC.
>>>> So you have a "dirty" 5V supply?
>>>>
>>> No, rock-stable. But clamping against it will lead to up to 7V spike
>>> amplitude if it's a huge transient. Those small clamper arrays can
>>> easily reach 2V Vf or more for a few usec.
>> If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>> around 2.5V?
>>
>> How about clamping with a 3.9V zener to ground with a small series
>> resistor to limit the transient current? As long as the desired signal
>> gets above the threshold, do you care if it goes all the way to 5V?
>>
>> For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>> you get above 3V, and 50mA doesn't even reach 5V:
>>
>> http://www.pridmore.com/datasheets/BZX84CA07.pdf
>>
>> Don't know what all the tolerances are, but so far nothing else seems to
>> have any chance of working in your application.
>>
>> JK
>
> I still haven't seen described how a "rock solid" 5V supply produces
> such gross transients.
>
> On Sat, 29 Jun 2013 08:13:15 -0700, Joerg <invalid@invalid.invalid>
> wrote:
>
>> Jim Thompson wrote:
>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>> wrote:
>>>
>>>> Jim Thompson wrote:
>>>>> On Fri, 28 Jun 2013 17:53:15 -0700, Joerg <invalid@invalid.invalid>
>>>>> wrote:
>>>>>
>>>>>> Joerg wrote:
>>>>>>> Jasen Betts wrote:
>>>>>>>> On 2013-06-26, Joerg <invalid@invalid.invalid> wrote:
>>>>>>>>> Spehro Pefhany wrote:
>>>>>>>>>> I guess they assume you'll never exceed the absolute maximum voltage
>>>>>>>>>> limits of +5.8/-0.3, so no significant current will ever flow.
>>>>>>>>>>
>>>>>>>>> Ok, but in real life that's almost unprotectable. The way I usually do
>>>>>>>>> it, there is a diode against the 5V rail, followed by a resistor, then
>>>>>>>>> the port pin. If the pulse from hell comes along that diode can briefly
>>>>>>>>> lean in so badly that Vf goes slightly above 2V, meaning over 7V total.
>>>>>>>>> Bigger diodes aren't an option because that messes up the signal, on
>>>>>>>>> account of their large capacitance.
>>>>>>>> How about this: series resistor, shunt diode to 3.3V , port pin
>>>>>>>>
>>>>>>> That doesn't protect very well because the parasitic substrate diode
>>>>>>> will take a substantial portion of the hit. The only thing that works is:
>>>>>>>
>>>>>>> R1 -> shunt diodes -> R2 -> port pin.
>>>>>>>
>>>>>>> R2 can be small because there will only be 1-2V max across it and it
>>>>>>> only has to make sure the substrate diode gets no more than a few mA.
>>>>>>>
>>>>>>> But ... too many parts in this case.
>>>>>>>
>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work. Problem
>>>>>> is that we only have 5V in the area where the protectors are.
>>>>> If you only have 5V around driving a 5V-tolerant pin... what are you
>>>>> fretting over?
>>>>>
>>>> The concern are surge events that make these lines carry nasty
>>>> transients, which in turn can lock up or damage the uC.
>>> So you have a "dirty" 5V supply?
>>>
>> No, rock-stable. But clamping against it will lead to up to 7V spike
>> amplitude if it's a huge transient. Those small clamper arrays can
>> easily reach 2V Vf or more for a few usec.
>
> _Where_ are these "huge transients" coming from?
>
The usual, through outside cabling, induced by heavy machinery being
turned on et cetera. Unit is plastic (has to be), a decent ground
structure is difficult to impossible.
--
Regards, Joerg
http://www.analogconsultants.com/
Reply by Jim Thompson●June 29, 20132013-06-29
On Sat, 29 Jun 2013 15:49:52 GMT, John K <spam@me.not> wrote:
>Joerg <invalid@invalid.invalid> wrote:
>
>>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>
>>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>>> Problem is that we only have 5V in the area where the protectors
>>>>>> are.
>>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>>> you fretting over?
>>>>>
>>>> The concern are surge events that make these lines carry nasty
>>>> transients, which in turn can lock up or damage the uC.
>>>
>>> So you have a "dirty" 5V supply?
>>>
>>
>> No, rock-stable. But clamping against it will lead to up to 7V spike
>> amplitude if it's a huge transient. Those small clamper arrays can
>> easily reach 2V Vf or more for a few usec.
>
>If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
>around 2.5V?
>
>How about clamping with a 3.9V zener to ground with a small series
>resistor to limit the transient current? As long as the desired signal
>gets above the threshold, do you care if it goes all the way to 5V?
>
>For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
>you get above 3V, and 50mA doesn't even reach 5V:
>
>http://www.pridmore.com/datasheets/BZX84CA07.pdf
>
>Don't know what all the tolerances are, but so far nothing else seems to
>have any chance of working in your application.
>
>JK
I still haven't seen described how a "rock solid" 5V supply produces
such gross transients.
As for thresholds... a 3.3V logic block, with 5V tolerant inputs, will
threshold roughly at VDD/2, or 3.3V/2, or 1.65V.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Reply by John K●June 29, 20132013-06-29
Joerg <invalid@invalid.invalid> wrote:
>> On Sat, 29 Jun 2013 08:00:01 -0700, Joerg <invalid@invalid.invalid>
>>>>> Oops, sorry, your are right. At a 5V-tolerant pin it would work.
>>>>> Problem is that we only have 5V in the area where the protectors
>>>>> are.
>>>> If you only have 5V around driving a 5V-tolerant pin... what are
>>>> you fretting over?
>>>>
>>> The concern are surge events that make these lines carry nasty
>>> transients, which in turn can lock up or damage the uC.
>>
>> So you have a "dirty" 5V supply?
>>
>
> No, rock-stable. But clamping against it will lead to up to 7V spike
> amplitude if it's a huge transient. Those small clamper arrays can
> easily reach 2V Vf or more for a few usec.
If you are dealing with 5V logic signals, isn't the threshold VCC/2, or
around 2.5V?
How about clamping with a 3.9V zener to ground with a small series
resistor to limit the transient current? As long as the desired signal
gets above the threshold, do you care if it goes all the way to 5V?
For a BZX84C3V9, Fig. 2 on page 3 shows it doesn't start to conduct until
you get above 3V, and 50mA doesn't even reach 5V:
http://www.pridmore.com/datasheets/BZX84CA07.pdf
Don't know what all the tolerances are, but so far nothing else seems to
have any chance of working in your application.
JK