Comparator with Wide Common Mode Range...

[Phil Hobbs]

On 2020-07-23 02:55, Pimpom wrote:

On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).  5.5V, RRIO,
picoamp bias current, 0.3 uA supply current, 3 us, 21 cents in reels for
the single.

Nice part. I looked at various TLV types too but the OP said that he
wants one that can be used \"directly\" on 15V. RRI, low power, at least
3-15Vcc/dd *and* cheap. I wonder if such a beast exists.

Well, the 393 is good for most things on higher supplies, and with 3.3V
VDD Rick can drive a 2N7002W to higher current than the OD comparator
could handle. It\'s only an occasional extra SC70, no biggie.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-07-23 02:55, Pimpom wrote:

On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).  5.5V, RRIO,
picoamp bias current, 0.3 uA supply current, 3 us, 21 cents in reels for
the single.

Nice part. I looked at various TLV types too but the OP said that he
wants one that can be used \"directly\" on 15V. RRI, low power, at least
3-15Vcc/dd *and* cheap. I wonder if such a beast exists.

Well, the 393 is good for most things on higher supplies, and with 3.3V
VDD Rick can drive a 2N7002W to higher current than the OD comparator
could handle. It\'s only an occasional extra SC70, no biggie.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-07-20 06:04, Piotr Wyderski wrote:

Ricketty C wrote:

A buck and change is definitely pricey compared to $0.12 for a dual
LM393.

It depends. In volume it indeed is; small scale specialistic runs call
for using \"how many minutes of your work a buck is\" as a metric.
Engineers are an expensive resource. Hard to find the optimum.

Minimalist design is an art form like sonnet writing. It\'s worth
spending a bit of extra time on it, both for the fun and because it
helps keep one sharp. (My designs are prettier than my poetry by all
accounts, including mine.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-07-20 06:04, Piotr Wyderski wrote:

Ricketty C wrote:

A buck and change is definitely pricey compared to $0.12 for a dual
LM393.

It depends. In volume it indeed is; small scale specialistic runs call
for using \"how many minutes of your work a buck is\" as a metric.
Engineers are an expensive resource. Hard to find the optimum.

Minimalist design is an art form like sonnet writing. It\'s worth
spending a bit of extra time on it, both for the fun and because it
helps keep one sharp. (My designs are prettier than my poetry by all
accounts, including mine.)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-07-23 02:55, Pimpom wrote:

On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).  5.5V, RRIO,
picoamp bias current, 0.3 uA supply current, 3 us, 21 cents in reels for
the single.

Nice part. I looked at various TLV types too but the OP said that he
wants one that can be used \"directly\" on 15V. RRI, low power, at least
3-15Vcc/dd *and* cheap. I wonder if such a beast exists.

Well, the 393 is good for most things on higher supplies, and with 3.3V
VDD Rick can drive a 2N7002W to higher current than the OD comparator
could handle. It\'s only an occasional extra SC70, no biggie.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Ricketty C]

On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:

On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).  5.5V, RRIO,
picoamp bias current, 0.3 uA supply current, 3 us, 21 cents in reels for
the single.

Nice part. I looked at various TLV types too but the OP said that he
wants one that can be used \"directly\" on 15V. RRI, low power, at least
3-15Vcc/dd *and* cheap. I wonder if such a beast exists.

Well, the 393 is good for most things on higher supplies, and with 3.3V
VDD Rick can drive a 2N7002W to higher current than the OD comparator
could handle. It\'s only an occasional extra SC70, no biggie.

I think you are missing the issue. The output of the 393 is not a problem. I also don\'t want to add transistors to the outputs of the comparators. The 393 has two problems, high power consumption, nearly a mA and poor common mode input range.

In the one circuit where the TLV7042 output might possibly be exposed to a higher voltage than the rated 7 volts, adding a single resistor should protect the output in that case.

Maybe I don\'t understand your comments.

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:

On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).  5.5V, RRIO,
picoamp bias current, 0.3 uA supply current, 3 us, 21 cents in reels for
the single.

Nice part. I looked at various TLV types too but the OP said that he
wants one that can be used \"directly\" on 15V. RRI, low power, at least
3-15Vcc/dd *and* cheap. I wonder if such a beast exists.

Well, the 393 is good for most things on higher supplies, and with 3.3V
VDD Rick can drive a 2N7002W to higher current than the OD comparator
could handle. It\'s only an occasional extra SC70, no biggie.

I think you are missing the issue. The output of the 393 is not a problem. I also don\'t want to add transistors to the outputs of the comparators. The 393 has two problems, high power consumption, nearly a mA and poor common mode input range.

In the one circuit where the TLV7042 output might possibly be exposed to a higher voltage than the rated 7 volts, adding a single resistor should protect the output in that case.

Maybe I don\'t understand your comments.

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:

On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).  5.5V, RRIO,
picoamp bias current, 0.3 uA supply current, 3 us, 21 cents in reels for
the single.

Nice part. I looked at various TLV types too but the OP said that he
wants one that can be used \"directly\" on 15V. RRI, low power, at least
3-15Vcc/dd *and* cheap. I wonder if such a beast exists.

Well, the 393 is good for most things on higher supplies, and with 3.3V
VDD Rick can drive a 2N7002W to higher current than the OD comparator
could handle. It\'s only an occasional extra SC70, no biggie.

I think you are missing the issue. The output of the 393 is not a problem. I also don\'t want to add transistors to the outputs of the comparators. The 393 has two problems, high power consumption, nearly a mA and poor common mode input range.

In the one circuit where the TLV7042 output might possibly be exposed to a higher voltage than the rated 7 volts, adding a single resistor should protect the output in that case.

Maybe I don\'t understand your comments.

--

Rick C.

+-- Get 1,000 miles of free Supercharging
+-- Tesla referral code - https://ts.la/richard11209

 

[Phil Hobbs]

On 2020-07-23 16:41, Ricketty C wrote:

On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:
On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).
5.5V, RRIO, picoamp bias current, 0.3 uA supply current, 3 us,
21 cents in reels for the single.

Nice part. I looked at various TLV types too but the OP said that
he wants one that can be used \"directly\" on 15V. RRI, low power,
at least 3-15Vcc/dd *and* cheap. I wonder if such a beast
exists.

Well, the 393 is good for most things on higher supplies, and with
3.3V VDD Rick can drive a 2N7002W to higher current than the OD
comparator could handle. It\'s only an occasional extra SC70, no
biggie.

I think you are missing the issue. The output of the 393 is not a
problem. I also don\'t want to add transistors to the outputs of the
comparators. The 393 has two problems, high power consumption,
nearly a mA and poor common mode input range.

I wouldn\'t use a 393 in a battery-powered application, but at ~10 mW
dissipation it takes quite awhile to use enough line power to equal the
cost of a $1 comparator. 15 cents/kWh = $4E-8 per joule, so at 10 mW it
takes 76 years by my arithmetic. (Not counting compound interest on the
money saved.)

The CM range goes from a bit below ground to VCC-1.5V. That\'s
inconvenient in a 3.3V system but really not much of a worry when VCC >
5V or so. Certainly to save a buck one can think of ways to avoid
high-side sensing near the rail, or use an op amp.

In the one circuit where the TLV7042 output might possibly be exposed
to a higher voltage than the rated 7 volts, adding a single resistor
should protect the output in that case.

Maybe I don\'t understand your comments.

You were worrying about the drain leakage of a 2N7002 being potentially
large enough to damage the OD output of the TLV comparator, and added a
resistor for safety. A 2N7002W costs 2 cents in reels, takes 4.5 square
millimetres of board space, and solves Pimpom\'s issue entirely as well.
So getting higher-voltage capability on the OD outputs isn\'t a worry
at all.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-07-23 16:41, Ricketty C wrote:

On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:
On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).
5.5V, RRIO, picoamp bias current, 0.3 uA supply current, 3 us,
21 cents in reels for the single.

Nice part. I looked at various TLV types too but the OP said that
he wants one that can be used \"directly\" on 15V. RRI, low power,
at least 3-15Vcc/dd *and* cheap. I wonder if such a beast
exists.

Well, the 393 is good for most things on higher supplies, and with
3.3V VDD Rick can drive a 2N7002W to higher current than the OD
comparator could handle. It\'s only an occasional extra SC70, no
biggie.

I think you are missing the issue. The output of the 393 is not a
problem. I also don\'t want to add transistors to the outputs of the
comparators. The 393 has two problems, high power consumption,
nearly a mA and poor common mode input range.

I wouldn\'t use a 393 in a battery-powered application, but at ~10 mW
dissipation it takes quite awhile to use enough line power to equal the
cost of a $1 comparator. 15 cents/kWh = $4E-8 per joule, so at 10 mW it
takes 76 years by my arithmetic. (Not counting compound interest on the
money saved.)

The CM range goes from a bit below ground to VCC-1.5V. That\'s
inconvenient in a 3.3V system but really not much of a worry when VCC >
5V or so. Certainly to save a buck one can think of ways to avoid
high-side sensing near the rail, or use an op amp.

In the one circuit where the TLV7042 output might possibly be exposed
to a higher voltage than the rated 7 volts, adding a single resistor
should protect the output in that case.

Maybe I don\'t understand your comments.

You were worrying about the drain leakage of a 2N7002 being potentially
large enough to damage the OD output of the TLV comparator, and added a
resistor for safety. A 2N7002W costs 2 cents in reels, takes 4.5 square
millimetres of board space, and solves Pimpom\'s issue entirely as well.
So getting higher-voltage capability on the OD outputs isn\'t a worry
at all.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Phil Hobbs]

On 2020-07-23 16:41, Ricketty C wrote:

On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:
On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).
5.5V, RRIO, picoamp bias current, 0.3 uA supply current, 3 us,
21 cents in reels for the single.

Nice part. I looked at various TLV types too but the OP said that
he wants one that can be used \"directly\" on 15V. RRI, low power,
at least 3-15Vcc/dd *and* cheap. I wonder if such a beast
exists.

Well, the 393 is good for most things on higher supplies, and with
3.3V VDD Rick can drive a 2N7002W to higher current than the OD
comparator could handle. It\'s only an occasional extra SC70, no
biggie.

I think you are missing the issue. The output of the 393 is not a
problem. I also don\'t want to add transistors to the outputs of the
comparators. The 393 has two problems, high power consumption,
nearly a mA and poor common mode input range.

I wouldn\'t use a 393 in a battery-powered application, but at ~10 mW
dissipation it takes quite awhile to use enough line power to equal the
cost of a $1 comparator. 15 cents/kWh = $4E-8 per joule, so at 10 mW it
takes 76 years by my arithmetic. (Not counting compound interest on the
money saved.)

The CM range goes from a bit below ground to VCC-1.5V. That\'s
inconvenient in a 3.3V system but really not much of a worry when VCC >
5V or so. Certainly to save a buck one can think of ways to avoid
high-side sensing near the rail, or use an op amp.

In the one circuit where the TLV7042 output might possibly be exposed
to a higher voltage than the rated 7 volts, adding a single resistor
should protect the output in that case.

Maybe I don\'t understand your comments.

You were worrying about the drain leakage of a 2N7002 being potentially
large enough to damage the OD output of the TLV comparator, and added a
resistor for safety. A 2N7002W costs 2 cents in reels, takes 4.5 square
millimetres of board space, and solves Pimpom\'s issue entirely as well.
So getting higher-voltage capability on the OD outputs isn\'t a worry
at all.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Ricketty C]

On Friday, July 24, 2020 at 4:30:49 AM UTC-4, Phil Hobbs wrote:

On 2020-07-23 16:41, Ricketty C wrote:
On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:
On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).
5.5V, RRIO, picoamp bias current, 0.3 uA supply current, 3 us,
21 cents in reels for the single.

Nice part. I looked at various TLV types too but the OP said that
he wants one that can be used \"directly\" on 15V. RRI, low power,
at least 3-15Vcc/dd *and* cheap. I wonder if such a beast
exists.

Well, the 393 is good for most things on higher supplies, and with
3.3V VDD Rick can drive a 2N7002W to higher current than the OD
comparator could handle. It\'s only an occasional extra SC70, no
biggie.

I think you are missing the issue. The output of the 393 is not a
problem. I also don\'t want to add transistors to the outputs of the
comparators. The 393 has two problems, high power consumption,
nearly a mA and poor common mode input range.

I wouldn\'t use a 393 in a battery-powered application, but at ~10 mW
dissipation it takes quite awhile to use enough line power to equal the
cost of a $1 comparator. 15 cents/kWh = $4E-8 per joule, so at 10 mW it
takes 76 years by my arithmetic. (Not counting compound interest on the
money saved.)

It is battery powered and even with a 2 AHr SLA a single LM393 blows away the self discharge current. Run time is not the issue, as it\'s powering a 2 amp motor! Storage time is the issue. The thing has to survive storage for as long as possible. Draining the battery in a few weeks from thirsty comparators is not a good idea.

The CM range goes from a bit below ground to VCC-1.5V. That\'s
inconvenient in a 3.3V system but really not much of a worry when VCC
5V or so. Certainly to save a buck one can think of ways to avoid
high-side sensing near the rail, or use an op amp.

The device we are using is spec\'d for Vcc-2V. Even in a 5 volt system that half a volt makes a difference. 2.75v instead of 3.25v. I could live with 3.25 volt considering the signal range is up to 3.3 volts.

Not sure why you are talking a buck. We are down to less than $0.40 delta in the total board cost now and I can live with that.

I have no idea why an op amp should be added. That makes no sense to me. Yes, I could simply add more than a dozen resistors to scale the various voltage values down into the remaining ~1V range of the comparator... or I can ditch this witch and use a rail to rail part which is what I am doing.

In the one circuit where the TLV7042 output might possibly be exposed
to a higher voltage than the rated 7 volts, adding a single resistor
should protect the output in that case.

Maybe I don\'t understand your comments.

You were worrying about the drain leakage of a 2N7002 being potentially
large enough to damage the OD output of the TLV comparator, and added a
resistor for safety. A 2N7002W costs 2 cents in reels, takes 4.5 square
millimetres of board space, and solves Pimpom\'s issue entirely as well.
So getting higher-voltage capability on the OD outputs isn\'t a worry
at all.

Not sure what you are complaining about. If I can do the job with a resistor for $0.002, why use a transistor for twenty times that price? I don\'t see the 2N7002W being sold for a tuppence at any quantity, btw. Digikey does get a bit below $0.04.

My initial thoughts were to be retain the option of running a comparator from 15 volts, but that is a less likely scenario now.

Anyway, thanks for the advice.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Friday, July 24, 2020 at 4:30:49 AM UTC-4, Phil Hobbs wrote:

On 2020-07-23 16:41, Ricketty C wrote:
On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:
On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).
5.5V, RRIO, picoamp bias current, 0.3 uA supply current, 3 us,
21 cents in reels for the single.

Nice part. I looked at various TLV types too but the OP said that
he wants one that can be used \"directly\" on 15V. RRI, low power,
at least 3-15Vcc/dd *and* cheap. I wonder if such a beast
exists.

Well, the 393 is good for most things on higher supplies, and with
3.3V VDD Rick can drive a 2N7002W to higher current than the OD
comparator could handle. It\'s only an occasional extra SC70, no
biggie.

I think you are missing the issue. The output of the 393 is not a
problem. I also don\'t want to add transistors to the outputs of the
comparators. The 393 has two problems, high power consumption,
nearly a mA and poor common mode input range.

I wouldn\'t use a 393 in a battery-powered application, but at ~10 mW
dissipation it takes quite awhile to use enough line power to equal the
cost of a $1 comparator. 15 cents/kWh = $4E-8 per joule, so at 10 mW it
takes 76 years by my arithmetic. (Not counting compound interest on the
money saved.)

It is battery powered and even with a 2 AHr SLA a single LM393 blows away the self discharge current. Run time is not the issue, as it\'s powering a 2 amp motor! Storage time is the issue. The thing has to survive storage for as long as possible. Draining the battery in a few weeks from thirsty comparators is not a good idea.

The CM range goes from a bit below ground to VCC-1.5V. That\'s
inconvenient in a 3.3V system but really not much of a worry when VCC
5V or so. Certainly to save a buck one can think of ways to avoid
high-side sensing near the rail, or use an op amp.

The device we are using is spec\'d for Vcc-2V. Even in a 5 volt system that half a volt makes a difference. 2.75v instead of 3.25v. I could live with 3.25 volt considering the signal range is up to 3.3 volts.

Not sure why you are talking a buck. We are down to less than $0.40 delta in the total board cost now and I can live with that.

I have no idea why an op amp should be added. That makes no sense to me. Yes, I could simply add more than a dozen resistors to scale the various voltage values down into the remaining ~1V range of the comparator... or I can ditch this witch and use a rail to rail part which is what I am doing.

In the one circuit where the TLV7042 output might possibly be exposed
to a higher voltage than the rated 7 volts, adding a single resistor
should protect the output in that case.

Maybe I don\'t understand your comments.

You were worrying about the drain leakage of a 2N7002 being potentially
large enough to damage the OD output of the TLV comparator, and added a
resistor for safety. A 2N7002W costs 2 cents in reels, takes 4.5 square
millimetres of board space, and solves Pimpom\'s issue entirely as well.
So getting higher-voltage capability on the OD outputs isn\'t a worry
at all.

Not sure what you are complaining about. If I can do the job with a resistor for $0.002, why use a transistor for twenty times that price? I don\'t see the 2N7002W being sold for a tuppence at any quantity, btw. Digikey does get a bit below $0.04.

My initial thoughts were to be retain the option of running a comparator from 15 volts, but that is a less likely scenario now.

Anyway, thanks for the advice.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

 

[Ricketty C]

On Friday, July 24, 2020 at 4:30:49 AM UTC-4, Phil Hobbs wrote:

On 2020-07-23 16:41, Ricketty C wrote:
On Thursday, July 23, 2020 at 9:20:27 AM UTC-4, Phil Hobbs wrote:
On 2020-07-23 02:55, Pimpom wrote:
On 7/23/2020 6:55 AM, Phil Hobbs wrote:

There\'s the TLV704x (open drain) and TLV703x (totem pole).
5.5V, RRIO, picoamp bias current, 0.3 uA supply current, 3 us,
21 cents in reels for the single.

Nice part. I looked at various TLV types too but the OP said that
he wants one that can be used \"directly\" on 15V. RRI, low power,
at least 3-15Vcc/dd *and* cheap. I wonder if such a beast
exists.

Well, the 393 is good for most things on higher supplies, and with
3.3V VDD Rick can drive a 2N7002W to higher current than the OD
comparator could handle. It\'s only an occasional extra SC70, no
biggie.

I think you are missing the issue. The output of the 393 is not a
problem. I also don\'t want to add transistors to the outputs of the
comparators. The 393 has two problems, high power consumption,
nearly a mA and poor common mode input range.

I wouldn\'t use a 393 in a battery-powered application, but at ~10 mW
dissipation it takes quite awhile to use enough line power to equal the
cost of a $1 comparator. 15 cents/kWh = $4E-8 per joule, so at 10 mW it
takes 76 years by my arithmetic. (Not counting compound interest on the
money saved.)

It is battery powered and even with a 2 AHr SLA a single LM393 blows away the self discharge current. Run time is not the issue, as it\'s powering a 2 amp motor! Storage time is the issue. The thing has to survive storage for as long as possible. Draining the battery in a few weeks from thirsty comparators is not a good idea.

The CM range goes from a bit below ground to VCC-1.5V. That\'s
inconvenient in a 3.3V system but really not much of a worry when VCC
5V or so. Certainly to save a buck one can think of ways to avoid
high-side sensing near the rail, or use an op amp.

The device we are using is spec\'d for Vcc-2V. Even in a 5 volt system that half a volt makes a difference. 2.75v instead of 3.25v. I could live with 3.25 volt considering the signal range is up to 3.3 volts.

Not sure why you are talking a buck. We are down to less than $0.40 delta in the total board cost now and I can live with that.

I have no idea why an op amp should be added. That makes no sense to me. Yes, I could simply add more than a dozen resistors to scale the various voltage values down into the remaining ~1V range of the comparator... or I can ditch this witch and use a rail to rail part which is what I am doing.

In the one circuit where the TLV7042 output might possibly be exposed
to a higher voltage than the rated 7 volts, adding a single resistor
should protect the output in that case.

Maybe I don\'t understand your comments.

You were worrying about the drain leakage of a 2N7002 being potentially
large enough to damage the OD output of the TLV comparator, and added a
resistor for safety. A 2N7002W costs 2 cents in reels, takes 4.5 square
millimetres of board space, and solves Pimpom\'s issue entirely as well.
So getting higher-voltage capability on the OD outputs isn\'t a worry
at all.

Not sure what you are complaining about. If I can do the job with a resistor for $0.002, why use a transistor for twenty times that price? I don\'t see the 2N7002W being sold for a tuppence at any quantity, btw. Digikey does get a bit below $0.04.

My initial thoughts were to be retain the option of running a comparator from 15 volts, but that is a less likely scenario now.

Anyway, thanks for the advice.

--

Rick C.

+-+ Get 1,000 miles of free Supercharging
+-+ Tesla referral code - https://ts.la/richard11209

 

[server]

>Not sure what you are complaining about.

I\'m not the one doing the complaining, dude.

Cheers

Phil Hobbs

 

[server]

>Not sure what you are complaining about.

I\'m not the one doing the complaining, dude.

Cheers

Phil Hobbs

 

[Ricketty C]

On Friday, July 24, 2020 at 6:27:00 PM UTC-4, pcdh...@gmail.com wrote:

Not sure what you are complaining about.

I\'m not the one doing the complaining, dude.

What\'s going on with you? We all discussed the issues here, I thanked you for the advice. What makes you think I am complaining?

Well, it was a fruitful thread and the mission is accomplished. Thanks to everyone who contributed.

--

Rick C.

++- Get 1,000 miles of free Supercharging
++- Tesla referral code - https://ts.la/richard11209