Help make the Regulator design

Thread Starter

Shazam7

Joined Mar 16, 2019
7
Hello, someone can help make the design circuit to use the LM22676 regulator using:

Vin= 5V
Vout=3V3
Iout=3A

The design in datasheet have an example (attached) but could be another options to design that solution?

Thanks
 

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Papabravo

Joined Feb 24, 2006
16,829
I'm not sure exactly what you are asking for. You could be:
  1. Asking us to check this particular design for suitability. This will be difficult because you have not precisely specified the inductor, or the diode, or the capacitors. There are lots of component choices that you could make that would produce a sub-optimal result. You do not specify a target cost for the design either. So anything we tell you will be a shot in the dark. If all you are doing is copying a reference design from the datasheet then it may or may not meet your requirements.
  2. Asking us to suggest an alternative. This could involve a good deal of unpaid component engineering which is a big ask on a hobbyist forum. Again we could give you a reference design from a datasheet or an app note, but is that really what you want or need.
One more thing. Is there a reason why the enable pin has been left unconnected. It may be OK for that particular part, but for ESD reasons I always tie unused pins to some potential unless the datasheet says they are specifically a no connect.

Edit: I do not like:
  1. That you are taking the device to its maximum allowed current output of 3 Amperes.
  2. The duty cycle ratio for 5V to 3.3V conversion is larger than 50%,
  3. The efficiency in the combined condition of low input voltage and maximum current is less than about 85%
  4. Figure 14 shows an example of converting an input voltage range of 5.5 V to 42 V, to an output of 3.3 V at 3 A. This line from the datasheet does not allow for Vin=5V -- sorry.
 
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Thread Starter

Shazam7

Joined Mar 16, 2019
7
Hello thank you for your reply :)
What i was asking is a reference design from a datasheet or an app note like you refer. If someone already have experienced in the past with this regulator and could share some inputs or suggestions in the design.

Thanks
 

Papabravo

Joined Feb 24, 2006
16,829
Hello thank you for your reply :)
What i was asking is a reference design from a datasheet or an app note like you refer. If someone already have experienced in the past with this regulator and could share some inputs or suggestions in the design.

Thanks
That clears things up a bit. The thing I worry about the most with this design is going up to and/or exceeding the 3A maximum Iout limitation. The part has a current limit, things may not get damaged, but it is not likely to be happy operating so close to the edge. If you need 3 amperes of output current I recommend you use a part capable of more. I would say a minimum of 20% more. I have not used this particular part before and so I have no experience to offer.

Is this your first SMPS design?
 

Papabravo

Joined Feb 24, 2006
16,829
You have some other component that you could suggest and have experience before that i could use?

Thanks
Most of the parts that I have ever used are antiques, they have probably reached their EOL, and are no longer available. They did not come in surface mount packages and were not Pb-free. That said, I do know how to read a datasheet carefully, do the analysis, pick components, and do a layout with a high probability of success. Sorry, but I do not have a ready made solution for you.

I can recommend the use of a simulator to evaluate parts and circuit alternatives as a prelude to bench testing.

By going to the ADI website and using their parametric tool I found the following candidate part
LT1374 - 4.5A, 500kHz Step-Down Switching Regulator (analog.com)

I will se if there is a simulation model and/or a test design we can evaluate.

EDIT: There is a simulation model, and I see several examples for 12V to 5v, but none for 5V to 3.3. If you have LTspice you can at least run a simulation on it.
 
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LowQCab

Joined Nov 6, 2012
1,110
This Part looks like it could be a good fit for your application .................
https://www.digikey.com/en/products/detail/analog-devices-inc/LT1506CR-3-3-PBF/889635

I'm assuming that you are working with SMD construction,
if not .........
For Through-Hole,
you would be much better off using a higher input Voltage.
Then you would have a huge choice of TO-220-Packaged-Devices to choose from.
What is your Power-Supply-Voltage for your 5-Volt-Supply ?
.
.
.
 

Papabravo

Joined Feb 24, 2006
16,829
This Part looks like it could be a good fit for your application .................
https://www.digikey.com/en/products/detail/analog-devices-inc/LT1506CR-3-3-PBF/889635

I'm assuming that you are working with SMD construction,
if not .........
For Through-Hole,
you would be much better off using a higher input Voltage.
Then you would have a huge choice of TO-220-Packaged-Devices to choose from.
What is your Power-Supply-Voltage for your 5-Volt-Supply ?
.
.
.
It looks OK on a first pass. Since it has a simulation model you can play with ahead of time to understand it's operation.
 

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