12VDC to 1VDC DC-DC converter with low EMI

[Nils227]

Hi,
What do you recommend at best for a DC-DC converter, bucking down an input voltage of 12VDC to 1VDC, noise-freely, with low EMI as possible?
I have been encountered with the ADP2303 but its working principle relies on a switching mechanism, and therefore can induce EMI.
The LM1117-n-7107 on the other hand heats up massively, despite that is possesses lower EMI than the ADP2303.

The destination is: the DC-DC converter should empower four magnetic sensors: TMR2309 effectively while inducing no EMI (in order to have the most accurate ADC readings out of it).

Do you have any suggestion? Perhaps with the relevent circuitry?

Thank you

 

[D.A.(Tony)Stewart]

What is your requirement for conducted and radiated noise? The load is ~14k per axis of ~ 1k with 3x4 axes.
What/why was load current during massive heat?

 

[Nils227]

What is your requirement for conducted and radiated noise? The load is ~14k per axis of ~ 1k with 3x4 axes.
What/why was load current during massive heat?

Hi,
I did not understand what you exactly mean by "~14k per axis of ~1k with 3x4 axes".
I did not physically implement the LM1117, but can guess that from 12VDC to 1VDC it would definitely needs a heat sink, and could have performance unstability under sudden load changes/current draws.

Bottom line: I do not want any SMPS, nor a linear (i.e., LMxx series) converter.
Other solutions, such as LT3405 are kindly asked for.
Thank you

 

[D.A.(Tony)Stewart]

The TMR2309 has 14~15 kohm per axis. What load did you see?

Define EMI tolerance and power consumption.

I imagine 4 choices:
1. SMPS
2. LDO
3. SMPS to LDO
4. Resonant sine oscillator to transformer with FWR to DC.

FWIW LT3405 is also a SMPS.

 

[Nils227]

The TMR2309 has 14~15 kohm per axis. What load did you see?

Define EMI tolerance and power consumption.

I imagine 4 choices:
1. SMPS
2. LDO
3. SMPS to LDO
4. Resonant sine oscillator to transformer with FWR to DC.

FWIW LT3405 is also a SMPS.

Hi thank you,

I did not understand what you actually mean by "axis".
The major overview of the application is as follows: I need the DC-DC converter to power the TMR2309 as well as an arduino board on which I can perform DAC of the resulting analog signals yielded by the TMR2309. I sub-counsciously keep running from the SMPS (such as ADP2303, or the LT3405 as you indicated) since I think that their inner switching mechanisms might interfere with the readings out of the TMR2309.

Do you recommend for such application the usage of the ADP2303 for example, or any similars?

 

[KlausST]

Hi,

What current?

Klaus

 

[D.A.(Tony)Stewart]

Hi thank you,

I did not understand what you actually mean by "axis".

The TMR2309 has 3-axes each with high impedance that draws very little power.

The major overview of the application is as follows: I need the DC-DC converter to power the TMR2309

No. It does not demand much power.

as well as an arduino board on which I can perform DAC of the resulting analog signals yielded by the TMR2309. I sub-counsciously keep running from the SMPS (such as ADP2303, or the LT3405 as you indicated) since I think that their inner switching mechanisms might interfere with the readings out of the TMR2309.


Do you recommend for such application the usage of the ADP2303 for example, or any similars?

All Arduinos I have seen use 5V or 3.3V LDO's not 1V..

Please confirm for power requirements. Use analog LDO's are chosen for noise sensitive analog parts with suitable voltage drop to limit wasted power. If desperate, you could use a DC-DC to reduce the voltage drop to an LDO.

 

[Nils227]

Hi,

What current?

Klaus

Hi,

Does your question refer to the "current" drawn from the LM1117?

 

[KlausST]

Hi,

For any power supply there are two key parameters: Voltage and current.
For sure there are other parameters for a power supply. But V and I are mandatory.

So asking to build a power supply but only giving the voltage makes no sense.

***
I don´t understand the reference to LM1117 at all.
Do you think that a non_LM1117 supply needs to provide more or less current?
Without additional information (from your side) the current is the same for all supplies.

Klaus

 

[Nils227]

I will reformulate the model:

I have a 12VDC battery. I intend to step-down this input voltage by means of a DC-DC converter to feed by 1VDC four magnetic sensors (TMR2309). The 1VDC is the typical voltage to feed each of the TMR2309, where the latent can withstand a feeding voltage up to 3VDC.

What is the most optimum DC-DC converter to be used in this case? The following ADP2302 provides 1.5VDC on its output:

I do not recommend the usage of the ADP2302, since it is an SMPS, where it could emit signals that might interfere with the TMR2309 readings.

1) Do you recommend the usage of the ADP2302? The analog output wires carrying the three-axis signals from each TMR2309 will be installed near the DC-DC converter. That is why I am afraid of some sorts of signals interference (such as faulty analog reading of each TMR2309 due to the interference produced by the switching mechanisms of the ADP2302)
2) What is the best alternative for a DC-DC converter with lowest noise emissions (make it a linear converter) to be used in this case? The LM1117-ADJ? Can you confirm that the usage of an LM1117-ADJ (2A output current) with a proper heat sink is the best solution for this circuitry?

Thank you

 

[Nils227]

I don´t understand the reference to LM1117 at all.
Do you think that a non_LM1117 supply needs to provide more or less current?
Without additional information (from your side) the current is the same for all supplies.

Klaus

1) I have referenced to LM1117 as an alternative for the usage of ADP2302, because the first will provoke no noise over the signal read by the TMR2309. The ADP2302, since it operates under a certain switching frequency, might induce some errors over the signals read by the TMR2309. Therefore, the LM1117 is "cleaner" to be employed in such circuitry.
2) No, not at all. My perspective has not got anything to do with the power, yet. A "non_LM1117" (i.e., SMPS) might interfere the readings procuded by the TMR2309.
3) The current is a total of four TMR2309 under operation

 

[D.A.(Tony)Stewart]

You are defining the problem of error tolerance stackup all wrong by suggesting voltage , and not specifying current. You mix up digital and analog power requirements without saying what they are instead, you suggest a part number. If you read any datasheet, your system design should also have a list of specs in exactly the style. It may change, but you need to define your expected results and tolerances for error over supply and temperature tolerances.

You expect us to look up the datasheets to find out.

To define a spec for system accuracy, you must plan an error budget and solve it for all the variables that introduce error including;

Purpose?: Weak Magnetic Field
Sensitivity, range, error tolerance for ...

Assumptions for Error Budget
1. Vcc tolerance , current range and thermal error
2. Sensor tolerance and thermal error.
3. ADC reference tolerance and thermal error.
4. EMI noise interference for egress and ingress (out and in) .
5. Power source assumptions or options.

The sum of all the errors may add up to the end result or some may cancel if you can.

But powering the TMR Linear sensor is trivial since the current is typically 0.07 mA @ 1Vdc, so for low noise , you need any LDO suitable for "no load", low error @ 1V.

Error tolerance stackup ought to be the key question, not constant rambling about part numbers. 0.07 mA per sensor is trivial ~ 1Vdc. But that is not the full range of the ADC.

If I sound harsh, sorry, I hope you focus on what you need to learn and not suggest parts without first defining your end requirements like current and error tolerance with power source and ambient range. You need to know what assumptions you made, so we can advise what you missed or understand your problem better.

 

[KlausST]

Hi,

I have a 12VDC battery.

So input voltage to the regulator is NOT 12V, but rather in the range of 10.5V ... 14.4V. (in case of a Pb battery)

What is the most optimum DC-DC converter to be used in this case?

The most optimum is that one that fits yor requirments the most.
Requirements are usually given as numbers with units. Text like "low noise" is meaningless, because one can not calculate, not validate them .. and for every designer it has a different meaning.

The following ADP2302 provides 1.5VDC on its output:

But before you asked for a 1V supply.
So I´m unsure about your true requirement. Is 1.5V sll O.K.?

I do not recommend the usage of the ADP2302, since it is an SMPS, where it could emit signals that might interfere with the TMR2309 readings.

There are three major sources of noise:
* magnetic fied through the air (may be shielded)
* electric field through the air (may be shielded)
* voltage noise of the power supply (my be filtered)

Let´s do some math:
The sensor datasheet says: Non-linearity: 0.5% FS, this is a ratio of 1:200 ... or in the digital world just a precision down to 8 bits.
The sensor says it has a hysteresis of 0.02 Oe referred to +/-8Oe saturation, so it is a ratio of 0.02 : 16 or 1:3200
or 11.5 bits. (worse if you refer to 1 Oe as given in the datasheet)

So to make it clear: You want to have 16 bits resolution, but they are not more worth than a 12 bit data (plus 4 random LSBs)

Back to the supply:
It works with 700kHz and let´s guess (that´s what we need to do unless you specify it) that the sensor frequency of interest is up to 100Hz.
Also let´s say we have a crazy high "noise" of 20% (1:5) influencing your sensor signal.

then adding a simple RC filter in front of your ADC may reduce the switching noise by a factor of 1:5000 ... resulting in negligible value, compared to the sensor errors.

If you want to improve a system, you need to reduce the biggest errors.

Klaus

 

[D.A.(Tony)Stewart]

You also need to consider the output is bipolar to be converted to unipolar with some Vref = Vdd/2 for the ADC input which may also introduce gain and offset error unless prevented but must be added to your total error budget.

 

[Nils227]

You are defining the problem of error tolerance stackup all wrong by suggesting voltage , and not specifying current. You mix up digital and analog power requirements without saying what they are instead, you suggest a part number. If you read any datasheet, your system design should also have a list of specs in exactly the style. It may change, but you need to define your expected results and tolerances for error over supply and temperature tolerances.

You expect us to look up the datasheets to find out.

To define a spec for system accuracy, you must plan an error budget and solve it for all the variables that introduce error including;

Purpose?: Weak Magnetic Field
Sensitivity, range, error tolerance for ...

Assumptions for Error Budget
1. Vcc tolerance , current range and thermal error
2. Sensor tolerance and thermal error.
3. ADC reference tolerance and thermal error.
4. EMI noise interference for egress and ingress (out and in) .
5. Power source assumptions or options.

The sum of all the errors may add up to the end result or some may cancel if you can.

But powering the TMR Linear sensor is trivial since the current is typically 0.07 mA @ 1Vdc, so for low noise , you need any LDO suitable for "no load", low error @ 1V.

Error tolerance stackup ought to be the key question, not constant rambling about part numbers. 0.07 mA per sensor is trivial ~ 1Vdc. But that is not the full range of the ADC.

If I sound harsh, sorry, I hope you focus on what you need to learn and not suggest parts without first defining your end requirements like current and error tolerance with power source and ambient range. You need to know what assumptions you made, so we can advise what you missed or understand your problem better.

Although severely harsh, but I cannot say that it isn't 100% true.
The thing is, I am no eletronics engineer. That is why I targeted directly at the technical names of some market-available DC-DC converters. I honestly do not know how to properly investigate a datasheet, as you were expecting from me.
Actually, if I already knew such methodologies, I wouldn't come here at the first instance, as the case of the majority of users here (in my point of view).
If I was at your place or KlauS's (as an expert) I would have developed a sequential approach for people who seek help, that are generally not familiar with electronics, and develop a standard to target their beginner mind sets in electronics domain. I mean this is what the forum is about right?
Nevertheless, I will try to understand your answers, then come back with my concerns, if possible.
Until now, I have only understood that one can simply turn on a TMR2309 by using a simple LDO (such as LM1117, by reading its datasheet in turn, and assigning R, C, etc.).
Thank you again my friend

--- Updated Nov 5, 2023 ---

Thank you KlauS,

Hi,


So input voltage to the regulator is NOT 12V, but rather in the range of 10.5V ... 14.4V. (in case of a Pb battery)


The most optimum is that one that fits yor requirments the most.
Requirements are usually given as numbers with units. Text like "low noise" is meaningless, because one can not calculate, not validate them .. and for every designer it has a different meaning.


But before you asked for a 1V supply.
So I´m unsure about your true requirement. Is 1.5V sll O.K.?


There are three major sources of noise:
* magnetic fied through the air (may be shielded)
* electric field through the air (may be shielded)
* voltage noise of the power supply (my be filtered)

Let´s do some math:
The sensor datasheet says: Non-linearity: 0.5% FS, this is a ratio of 1:200 ... or in the digital world just a precision down to 8 bits.
The sensor says it has a hysteresis of 0.02 Oe referred to +/-8Oe saturation, so it is a ratio of 0.02 : 16 or 1:3200
or 11.5 bits. (worse if you refer to 1 Oe as given in the datasheet)

So to make it clear: You want to have 16 bits resolution, but they are not more worth than a 12 bit data (plus 4 random LSBs)

Back to the supply:
It works with 700kHz and let´s guess (that´s what we need to do unless you specify it) that the sensor frequency of interest is up to 100Hz.
Also let´s say we have a crazy high "noise" of 20% (1:5) influencing your sensor signal.

then adding a simple RC filter in front of your ADC may reduce the switching noise by a factor of 1:5000 ... resulting in negligible value, compared to the sensor errors.

If you want to improve a system, you need to reduce the biggest errors.

Klaus

Thanks Klaus,
These represent toooo much information for me.
I will try to digest one at a time, then come back with concerns.
As a quick question, how to shield against the magnetic/electric-fields in the air? Through filtering circuits as the case of the RC that you suggested to calm down the ADP2303's noise, or some physical shields?

 

[KlausST]

Hi,

As a quick question, how to shield against the magnetic/electric-fields in the air?

Shields are physical.
GND plane does some kind of sielding, shielded cables, shielded enclosures... Just do an internet search

Klaus

 

[D.A.(Tony)Stewart]

Until now, I have only understood that one can simply turn on a TMR2309 by using a simple LDO (such as LM1117, by reading its datasheet in turn, and assigning R, C, etc.).

You might have done better to say what you expected to do with this sensor and ask how to accomplish that then state what you are able to do.

BTW LM1117 cannot regulate down to 1V, but this can. https://www.mouser.com/ProductDetai...MIC5365-1.0YC5-TR?qs=U6T8BxXiZAVfWgtQKiWN5w==

 

[Nils227]

You might have done better to say what you expected to do with this sensor and ask how to accomplish that then state what you are able to do.

BTW LM1117 cannot regulate down to 1V, but this can. https://www.mouser.com/ProductDetail/Microchip-Technology/MIC5365-1.0YC5-TR?qs=U6T8BxXiZAVfWgtQKiWN5w==

Thanks Tony,
I will read better the TMR's datasheet, then get back more appropriately.
Thank you also for the suggestion of the LDO; it however cannot be employed in my intended circuit, since its input voltage range is between 2.5VDC and 5.5VDC, where my voltage supply would be a Li-I battery of 12VDC.

Until next round,

 

[D.A.(Tony)Stewart]

Thanks Tony,
I will read better the TMR's datasheet, then get back more appropriately.
Thank you also for the suggestion of the LDO; it however cannot be employed in my intended circuit, since its input voltage range is between 2.5VDC and 5.5VDC, where my voltage supply would be a Li-I battery of 12VDC.

Until next round,

Then you better learn how to find an inexpensive way to use that part such as a 5V LDO, because your options to find a 12V in 1V out may be expensive.