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Yet Another Jellybean Opamp
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Allan Herriman
Feb 22, 2016, 4:27:53 AM2/22/16
to
Hi,
I'm looking for a single supply jellybean opamp to meet the following
requirements:
V supply = 5.0V
Vin (e.g. Vicm) 0V to 4V.
Iin +/- 100pA max. (prefer < 10pA)
Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
up to $2 for a dual, etc..
Here's the hard part: I want the Iin spec to apply over the Vin range
*even when the supply voltage is zero*.
This requires the absence of ESD protection diodes between the inputs and
the positive rail. Newer opamps almost always have these diodes.
There are plenty of cheap older opamps that can come close to meeting my
requirement, e.g. the ubiquitous LM358A and its siblings would be fine
except that Vicm only gets to Vsupply - 1.5V or so.
Microchip have some interesting parts, e.g. MCP6L02 and MCP6002 are about
US$0.25 in my quantities. They explicitly state in the datasheet that
they don't have diodes from the inputs to the positive supply rail (good)
but the absolute maximum ratings say that "Analog Inputs (V IN+, V IN–)
VSS – 1.0V to VDD + 1.0V", which isn't so good.
Does anyone have experience with those Microchip parts, and know whether
the abs max ratings can be exceeded without problem? Normally I would
never do that, but I suspect in this case that the datasheet might be
overly conservative.
Any other opamp suggestions?
If I can't find an opamp that meets these requirements I can use other
circuit topologies that aren't as elegant as the one I have in mind.
Thanks,
Allan
I'm looking for a single supply jellybean opamp to meet the following
requirements:
V supply = 5.0V
Vin (e.g. Vicm) 0V to 4V.
Iin +/- 100pA max. (prefer < 10pA)
Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
up to $2 for a dual, etc..
Here's the hard part: I want the Iin spec to apply over the Vin range
*even when the supply voltage is zero*.
This requires the absence of ESD protection diodes between the inputs and
the positive rail. Newer opamps almost always have these diodes.
There are plenty of cheap older opamps that can come close to meeting my
requirement, e.g. the ubiquitous LM358A and its siblings would be fine
except that Vicm only gets to Vsupply - 1.5V or so.
Microchip have some interesting parts, e.g. MCP6L02 and MCP6002 are about
US$0.25 in my quantities. They explicitly state in the datasheet that
they don't have diodes from the inputs to the positive supply rail (good)
but the absolute maximum ratings say that "Analog Inputs (V IN+, V IN–)
VSS – 1.0V to VDD + 1.0V", which isn't so good.
Does anyone have experience with those Microchip parts, and know whether
the abs max ratings can be exceeded without problem? Normally I would
never do that, but I suspect in this case that the datasheet might be
overly conservative.
Any other opamp suggestions?
If I can't find an opamp that meets these requirements I can use other
circuit topologies that aren't as elegant as the one I have in mind.
Thanks,
Allan
bloggs.fred...@gmail.com
Feb 22, 2016, 8:48:06 AM2/22/16
to
On Monday, February 22, 2016 at 4:27:53 AM UTC-5, Allan Herriman wrote:
> Hi,
>
> I'm looking for a single supply jellybean opamp to meet the following
> requirements:
>
> V supply = 5.0V
> Vin (e.g. Vicm) 0V to 4V.
> Iin +/- 100pA max. (prefer < 10pA)
>
> Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
> up to $2 for a dual, etc..
>
> Here's the hard part: I want the Iin spec to apply over the Vin range
> *even when the supply voltage is zero*.
> This requires the absence of ESD protection diodes between the inputs and
> the positive rail. Newer opamps almost always have these diodes.
>
> There are plenty of cheap older opamps that can come close to meeting my
> requirement, e.g. the ubiquitous LM358A and its siblings would be fine
> except that Vicm only gets to Vsupply - 1.5V or so.
>
> Microchip have some interesting parts, e.g. MCP6L02 and MCP6002 are about
> US$0.25 in my quantities. They explicitly state in the datasheet that
> they don't have diodes from the inputs to the positive supply rail (good)
> but the absolute maximum ratings say that "Analog Inputs (V IN+, V IN-)
> Hi,
>
> I'm looking for a single supply jellybean opamp to meet the following
> requirements:
>
> V supply = 5.0V
> Vin (e.g. Vicm) 0V to 4V.
> Iin +/- 100pA max. (prefer < 10pA)
>
> Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
> up to $2 for a dual, etc..
>
> Here's the hard part: I want the Iin spec to apply over the Vin range
> *even when the supply voltage is zero*.
> This requires the absence of ESD protection diodes between the inputs and
> the positive rail. Newer opamps almost always have these diodes.
>
> There are plenty of cheap older opamps that can come close to meeting my
> requirement, e.g. the ubiquitous LM358A and its siblings would be fine
> except that Vicm only gets to Vsupply - 1.5V or so.
>
> Microchip have some interesting parts, e.g. MCP6L02 and MCP6002 are about
> US$0.25 in my quantities. They explicitly state in the datasheet that
> they don't have diodes from the inputs to the positive supply rail (good)
> VSS - 1.0V to VDD + 1.0V", which isn't so good.
>
>
> Does anyone have experience with those Microchip parts, and know whether
> the abs max ratings can be exceeded without problem? Normally I would
> never do that, but I suspect in this case that the datasheet might be
> overly conservative.
>
> Any other opamp suggestions?
>
>
> If I can't find an opamp that meets these requirements I can use other
> circuit topologies that aren't as elegant as the one I have in mind.
>
> Thanks,
> Allan
Something like this is pretty compact, I'm sure you'll find a problem with it, "max" leakage spec sucks e.g.:
>
> Does anyone have experience with those Microchip parts, and know whether
> the abs max ratings can be exceeded without problem? Normally I would
> never do that, but I suspect in this case that the datasheet might be
> overly conservative.
>
> Any other opamp suggestions?
>
>
> If I can't find an opamp that meets these requirements I can use other
> circuit topologies that aren't as elegant as the one I have in mind.
>
> Thanks,
> Allan
http://datasheets.maximintegrated.com/en/ds/MAX4505.pdf
piglet
Feb 22, 2016, 9:10:55 AM2/22/16
to
what about a series mosfet to isolate the op-amp input from your source
when the circuit is unpowered - then you have a much wider choice of op-amp?
piglet
Allan Herriman
Feb 22, 2016, 4:29:37 PM2/22/16
to
though, so it doesn't meet the +5V requirement.
Regards,
Allan
Allan Herriman
Feb 22, 2016, 4:36:53 PM2/22/16
to
alluded to in my OP. I use a Diodes Inc. FET with low Vth and low cost
(can't remember the part number right now) that would be suitable in this
application.
Regards,
Allan
Hul Tytus
Feb 22, 2016, 6:04:51 PM2/22/16
to
Maybe a diode in the positive supply line.
Hul
Allan Herriman <allanh...@hotmail.com> wrote:
> Hi,
> I'm looking for a single supply jellybean opamp to meet the following
> requirements:
> V supply = 5.0V
> Vin (e.g. Vicm) 0V to 4V.
> Iin +/- 100pA max. (prefer < 10pA)
> Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
> up to $2 for a dual, etc..
> Here's the hard part: I want the Iin spec to apply over the Vin range
> *even when the supply voltage is zero*.
> This requires the absence of ESD protection diodes between the inputs and
> the positive rail. Newer opamps almost always have these diodes.
> There are plenty of cheap older opamps that can come close to meeting my
> requirement, e.g. the ubiquitous LM358A and its siblings would be fine
> except that Vicm only gets to Vsupply - 1.5V or so.
> Microchip have some interesting parts, e.g. MCP6L02 and MCP6002 are about
> US$0.25 in my quantities. They explicitly state in the datasheet that
> they don't have diodes from the inputs to the positive supply rail (good)
> but the absolute maximum ratings say that "Analog Inputs (V IN+, V IN?)
> VSS ? 1.0V to VDD + 1.0V", which isn't so good.
Hul
Allan Herriman <allanh...@hotmail.com> wrote:
> Hi,
> I'm looking for a single supply jellybean opamp to meet the following
> requirements:
> V supply = 5.0V
> Vin (e.g. Vicm) 0V to 4V.
> Iin +/- 100pA max. (prefer < 10pA)
> Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
> up to $2 for a dual, etc..
> Here's the hard part: I want the Iin spec to apply over the Vin range
> *even when the supply voltage is zero*.
> This requires the absence of ESD protection diodes between the inputs and
> the positive rail. Newer opamps almost always have these diodes.
> There are plenty of cheap older opamps that can come close to meeting my
> requirement, e.g. the ubiquitous LM358A and its siblings would be fine
> except that Vicm only gets to Vsupply - 1.5V or so.
> Microchip have some interesting parts, e.g. MCP6L02 and MCP6002 are about
> US$0.25 in my quantities. They explicitly state in the datasheet that
> they don't have diodes from the inputs to the positive supply rail (good)
> VSS ? 1.0V to VDD + 1.0V", which isn't so good.
whit3rd
Feb 22, 2016, 6:41:16 PM2/22/16
to
On Monday, February 22, 2016 at 1:27:53 AM UTC-8, Allan Herriman wrote:
> I'm looking for a single supply jellybean opamp to meet the following
> requirements:
>
> V supply = 5.0V
> Vin (e.g. Vicm) 0V to 4V.
> Iin +/- 100pA max. (prefer < 10pA)
>
> Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
> up to $2 for a dual, etc..
>
> Here's the hard part: I want the Iin spec to apply over the Vin range
> *even when the supply voltage is zero*.
What about an input relay, coil powered from your 5.0V supply? DPST-NO
> I'm looking for a single supply jellybean opamp to meet the following
> requirements:
>
> V supply = 5.0V
> Vin (e.g. Vicm) 0V to 4V.
> Iin +/- 100pA max. (prefer < 10pA)
>
> Other parameters are "normal" e.g. slow, noisy, 1mA drive, 0-70 degree C,
> up to $2 for a dual, etc..
>
> Here's the hard part: I want the Iin spec to apply over the Vin range
> *even when the supply voltage is zero*.
would lift one input from two op amps, or both inputs of a single op amp,
and some of 'em don't eat your whole budget.
<http://www.digikey.com/product-detail/en/EE2-5NU-L/399-11017-1-ND/4506469>
Allan Herriman
Feb 23, 2016, 4:56:42 AM2/23/16
to
On Mon, 22 Feb 2016 23:04:44 +0000, Hul Tytus wrote:
> Maybe a diode in the positive supply line.
>
> Hul
Whilst that would protect the opamp input, it wouldn't meet the 100pA Iin
> Maybe a diode in the positive supply line.
>
> Hul
requirement, as the input would end up powering the opamp through the ESD
protection diode.
(Assuming I've interpreted your suggestion correctly.)
Thanks,
Allan
Allan Herriman
Feb 23, 2016, 5:11:07 AM2/23/16
to
it would probably need to be driven by a brownout detector or similar.
I wouldn't use a relay for a "dry" switching application like this though.
Regards,
Allan
bloggs.fred...@gmail.com
Feb 23, 2016, 7:19:42 AM2/23/16
to
Allan Herriman
Feb 23, 2016, 9:50:19 AM2/23/16
to
They only specify the input current for voltages between the rails.
Looking at the schematic (figure 61 in the OP191 datasheet) it seems that
it actually does have clamp diodes to the positive supply and also back-
to-back diodes between the inverting and noninverting inputs. There are
5k series resistors to limit the input current.
Unfortunately this won't meet my Iin requirement.
The FET I was thinking about earlier (in my reply to Piglet's post) was
the DMG1012UW. It has a threshold voltage of 0.5 to 1V @ 250uA, meaning
I could use it to isolate the opamp input and still meet the 4V input
with 5V supply requirement.
I suspect that would work better than the Maxim parts you mentioned for
voltages close to the rail.
The leakage current is ok if I only look at the typical parameters. They
don't specify a max IDSS at anything other than 25 degree C (100nA). The
typical curve looks good though (about 7nA at 85 degree C and 4V).
I use a lot of these FETs for driving things from 1.8V logic, so they're
already on the board and only cost a few cents each.
Regards,
Allan
Hul Tytus
Feb 23, 2016, 6:20:29 PM2/23/16
to
Allan - your interpretation's correct. My suggestion shouldn't work but,
if I were in your shoes, I'd try it anyway.
if I were in your shoes, I'd try it anyway.
bill....@ieee.org
Feb 23, 2016, 9:39:54 PM2/23/16
to
--
Bill Sloman, Sydney
John Larkin
Feb 23, 2016, 10:52:46 PM2/23/16
to
On 23 Feb 2016 10:11:00 GMT, Allan Herriman
We use thousands of a tiny Fujitsu DPDT relay for low-level switching,
like thermocouple inputs, and they work fine.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
like thermocouple inputs, and they work fine.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
Allan Herriman
Feb 24, 2016, 4:18:02 AM2/24/16
to
far ...
Allan
Allan Herriman
Feb 24, 2016, 4:33:47 AM2/24/16
to
it's the choice of a relay vs a US$0.10 FET that takes no board space,
withstands any amount of vibration and will last forever in a corrosive
atmosphere. [hyperbole]
Actually, I'm still hopeful of finding an opamp that does exactly what I
want in one chip.
Contemporary 74xx series CMOS logic gates have the sort of ESD protection
I want (i.e. input voltages > Vcc without drawing a lot of current). Why
can't an opamp? Are the processes so different? Does that sort of ESD
protection have some bad effect on analog circuits (e.g. leakage current)?
Regards,
Allan
Jim Thompson
Feb 24, 2016, 10:15:41 AM2/24/16
to
On 24 Feb 2016 09:33:39 GMT, Allan Herriman
<allanh...@hotmail.com> wrote:
[snip]
do that is with specially-designed ESD, such as is found in many bus
transceivers. Off-hand I don't know of an OpAmp so constructed.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| 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.
<allanh...@hotmail.com> wrote:
[snip]
>
>Actually, I'm still hopeful of finding an opamp that does exactly what I
>want in one chip.
>Contemporary 74xx series CMOS logic gates have the sort of ESD protection
>I want (i.e. input voltages > Vcc without drawing a lot of current). Why
>can't an opamp? Are the processes so different? Does that sort of ESD
>protection have some bad effect on analog circuits (e.g. leakage current)?
>
>Regards,
>Allan
Didn't your original post say even while unpowered? The only way to
>Actually, I'm still hopeful of finding an opamp that does exactly what I
>want in one chip.
>Contemporary 74xx series CMOS logic gates have the sort of ESD protection
>I want (i.e. input voltages > Vcc without drawing a lot of current). Why
>can't an opamp? Are the processes so different? Does that sort of ESD
>protection have some bad effect on analog circuits (e.g. leakage current)?
>
>Regards,
>Allan
do that is with specially-designed ESD, such as is found in many bus
transceivers. Off-hand I don't know of an OpAmp so constructed.
...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| San Tan Valley, AZ 85142 Skype: skypeanalog | |
| 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.
Winfield Hill
Feb 24, 2016, 2:50:25 PM2/24/16
to
Allan Herriman wrote...
--
Thanks,
- Win
>
> I used to use Fujitsu relays when I worked for Fujitsu.
> Here though, it's the choice of a relay vs a US$0.10
> FET that takes no board space, withstands any amount
> of vibration and will last forever in a corrosive
> atmosphere. [hyperbole]
Keep in mind the FET has about 100pF of capacitance at 0V.
> I used to use Fujitsu relays when I worked for Fujitsu.
> Here though, it's the choice of a relay vs a US$0.10
> FET that takes no board space, withstands any amount
> of vibration and will last forever in a corrosive
> atmosphere. [hyperbole]
--
Thanks,
- Win
Allan Herriman
Feb 24, 2016, 4:51:27 PM2/24/16
to
On Wed, 24 Feb 2016 08:15:30 -0700, Jim Thompson wrote:
> On 24 Feb 2016 09:33:39 GMT, Allan Herriman <allanh...@hotmail.com>
> wrote:
>
> [snip]
>>
>>Actually, I'm still hopeful of finding an opamp that does exactly what I
>>want in one chip.
>>Contemporary 74xx series CMOS logic gates have the sort of ESD
>>protection I want (i.e. input voltages > Vcc without drawing a lot of
>>current). Why can't an opamp? Are the processes so different? Does
>>that sort of ESD protection have some bad effect on analog circuits
>>(e.g. leakage current)?
>>
>>Regards,
>>Allan
>
> Didn't your original post say even while unpowered? The only way to do
> that is with specially-designed ESD, such as is found in many bus
> transceivers. Off-hand I don't know of an OpAmp so constructed.
>
> ...Jim Thompson
Hi Jim,
> On 24 Feb 2016 09:33:39 GMT, Allan Herriman <allanh...@hotmail.com>
> wrote:
>
> [snip]
>>
>>Actually, I'm still hopeful of finding an opamp that does exactly what I
>>want in one chip.
>>Contemporary 74xx series CMOS logic gates have the sort of ESD
>>protection I want (i.e. input voltages > Vcc without drawing a lot of
>>current). Why can't an opamp? Are the processes so different? Does
>>that sort of ESD protection have some bad effect on analog circuits
>>(e.g. leakage current)?
>>
>>Regards,
>>Allan
>
> Didn't your original post say even while unpowered? The only way to do
> that is with specially-designed ESD, such as is found in many bus
> transceivers. Off-hand I don't know of an OpAmp so constructed.
>
> ...Jim Thompson
Yes, the requirement is |Iin| < 100pA under the conditions of
0 < Vin < 4
and
0 < Vsupply < 5V.
BTW, The Microchip MCP6002 family has that sort of ESD protection. Its
abs max specs mean that I can't use it (Vin max is VDD + 1V) but I'm
hoping there are others out there that I can use.
http://www.microchip.com/wwwproducts/en/MCP6002
Regards,
Allan
Allan Herriman
Feb 24, 2016, 4:59:48 PM2/24/16
to
application the voltage doesn't change very quickly and C dv/dt won't
come close to 100pA.
Nice book, BTW.
Regards,
Allan
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