# LM2577-12 5v to 12v help

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#### StealthRT

##### Member
Hey all i am in need of so help with a parts list for the following diagram:

Here is the parts list:
Problem i am having is that i don't know which of each to get.

- For the Caps, should i get Ceramic or Film?
- for the resistor, should i go with Carbon film or Metal film?
- For the wire coil inductor, 100uH, im not sure which to go with. A lot are listed so i was wondering what would be best for this project.

As for some background in what i will be using this 5v to 12v step-up circuit for is for a SATA hard drive to provide 12v to it.

I've talked to a digikey tech and this is the list he gave me..
LM2577T-12-NDIC REG SIMPLE SWITCHER TO-220-5
2.2KQBK-NDRES 2.2K OHM 1/4W 5% CARBON FILM
0BC1148CT-NDCAP .10UF 25V CERAMIC +80/-20%
490-3832-NDCAP CER 330000PF 50V X7R RADIAL
P10330-NDCAP 680UF 50V ELECT FC RADIAL
M8324-NDCHOKE RF HI CURRENT 100UH 1.6A
Any help would be great

David

#### Electronworks

##### New Member
Here goes one hell of a brain dump on switched mode power supply design:

Starting at the input, your 0.1uF capacitor needs to be placed close to the Vin pin to stop any noise upsetting the internal logic of the chip. A ceramic is perfect for the job.

Keep the R and C unchanged (dont try to design this bit yourself). Any resistor or cap will do. Carbon film resistors are fine and 10% tolerance is ok. You could even put 3 of the 0.1uF caps you bought for the decoupling in parallel to save you hunting around for a 0.33uF cap.

Now for the inductor. This is the worst bit of the circuit. The datasheet says the peak switch current is 3.7A, so I would pick a 4A inductor if you want 800mA on the output. Your inductor current is triangluar, whereas your output current is flat so the peak rating will be much higher. 4A seems instinctively high, but I do not have time to wade through the tons of equations in the datasheet for this voltage mode controller. Personally I would use a current mode controller where you can control the peak current (MAX1771 is much better).

Put the inductor physically close to the chip to keep interference low. Use big tracks in all the tracks going to your inductor and from it (this would be the main input rail, the ground lead of the chip - ideally this should be a ground plane- and the tracks to the output capacitor.) It is best if you build the whole circuit on a copper clad board with the components hanging in the air. Surprisingly this will give you better performance than using strip board. Use the copper clad board as the ground and build the components around this.

The 1N5821 is a Schottky diode and is very fast. Keep this component unchanged. A normal diode will be too slow. These devices are fairly easy to get hold of.

The output cap should be a 'low esr' cap, like a tantalum. You will not get a value this big in ceramic.

Again, keep the diode and output cap close together to get best performance.

Best Wishes

#### StealthRT

##### Member
Wow, Electronworks, thanks for your knowledge on what to do about the circuit! However, i am still in need to finding out what components i really do need for this project or at least let me know the list of components i have chosen will do the trick.

David

David

#### bountyhunter

##### Well-Known Member
- For the Caps, should i get Ceramic or Film?
Ceramic for the small ones, a low ESR switching electrolytic cap for the output cap. You need to use the recommended cap for the output because the ESR is involved in the loop stability. The parts list should have recommended parts for COUT.

- for the resistor, should i go with Carbon film or Metal film?
makes no difference

- For the wire coil inductor, 100uH, im not sure which to go with. A lot are listed so i was wondering what would be best for this project.
Whichever one is a toroid core. They put out the least EMI noise.

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#### bountyhunter

##### Well-Known Member

David
I recommend you go to the national Semiconductor site and use their Simple Switcher software (the LM2577 is in that product family). It will tell you what parts to use, and if you use them you will have no worries. change them and who knows.

EDIT TO ADD: the simple switcher software used to have the feature that the parts list highlighted the key specs for each part, like ESR for the output cap. If you are trying to get a different part, just match the key specs.

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#### StealthRT

##### Member
I recommend you go to the national Semiconductor site and use their Simple Switcher software (the LM2577 is in that product family). It will tell you what parts to use, and if you use them you will have no worries. change them and who knows.

EDIT TO ADD: the simple switcher software used to have the feature that the parts list highlighted the key specs for each part, like ESR for the output cap. If you are trying to get a different part, just match the key specs.
I can not seem to find anything for the LM2577-12. It says i can not design on it or its not found....

David

#### jpanhalt

##### Well-Known Member
I just visited the Webench for National. Apparently, it will not do a complete design for the LM2577. Maybe it is older, or just not included for other reasons. If you enter your design criteria, which I guessed as being 5 V in , 12 V out, and 800 mA, you will get a set of possibilities. I picked one of the cheapest, the LM2700MT-adj. For that device, National gives the complete design, including part numbers and vendors. Most important, you can buy the complete BOM from National for $4.14, excluding the PCB. A generic PCB is also available. I didn't price that out. All told, you can probably get the whole thing, including PCB, for around$25 or less. At least, that is what it cost me last year when I ordered a switching supply. It is one click ordering.

The nice thing about the LM2700 is that it operates at a higher frequency (600 KHz), uses a smaller inductor (22 uH) and is more efficient (90%) than the LM2577.

I can't link you to the order page, because you will have to establish an account to get there.

John

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#### bountyhunter

##### Well-Known Member
I can not seem to find anything for the LM2577-12. It says i can not design on it or its not found....

David
You could try to select the LM2577-adj which is the adjustable version and then specify a 12V output. That should work.

#### bountyhunter

##### Well-Known Member
I just visited the Webench for National. Apparently, it will not do a complete design for the LM2577. Maybe it is older, or just not included for other reasons.
It is the original simple switcher product, circa 1990. They may have locked it out of the software to force design traffic into the newer and more expensive product lines. They may have dropped the product for the same reason. marketing always ran the place, like letting the lunatics run the asylum but that's life.

#### StealthRT

##### Member
I just visited the Webench for National. Apparently, it will not do a complete design for the LM2577. Maybe it is older, or just not included for other reasons. If you enter your design criteria, which I guessed as being 5 V in , 12 V out, and 800 mA, you will get a set of possibilities. I picked one of the cheapest, the LM2700MT-adj. For that device, National gives the complete design, including part numbers and vendors. Most important, you can buy the complete BOM from National for $4.14, excluding the PCB. A generic PCB is also available. I didn't price that out. All told, you can probably get the whole thing, including PCB, for around$25 or less. At least, that is what it cost me last year when I ordered a switching supply. It is one click ordering.

The nice thing about the LM2700 is that it operates at a higher frequency (600 KHz), uses a smaller inductor (22 uH) and is more efficient (90%) than the LM2577.

I can't link you to the order page, because you will have to establish an account to get there.

John
Alright well i must be using something differnet. I dont even see a place to put the mA value? All i get are:

vin Min
vin Max
Vout 1
lout 1
op ambient temp

But no matter what i set it too for the LM2700MT-adj, it keeps telling me "Your soluction is not yet WEBBENCH enabled" or "design can not be created with this device"

David

#### jpanhalt

##### Well-Known Member
Now that you found where to enter your desired I out in Amperes, you need to convert 800 mA to Amperes. In order to do that, you divide by 1000. In other words, 800 mA = 0.8 amps. Enter 0.8 in the appropriate location.

John

#### bountyhunter

##### Well-Known Member
Alright well i must be using something differnet. I dont even see a place to put the mA value? All i get are:

vin Min
vin Max
Vout 1
lout 1
op ambient temp

But no matter what i set it too for the LM2700MT-adj, it keeps telling me "Your soluction is not yet WEBBENCH enabled" or "design can not be created with this device"

David
Sounds like webench is working as well as it did when I worked there. Glad I don't have to take the calls on this garbage anymore....... the idiots they had maintaining the web site were a bunch of complete morons. It was a full time job just to monitor the site on an hourly basis to see what they screwed up, and then I got to listen to my boss gripe that it was my responsibility to keep the product folder (or whatever they effed up today) in perfect order, despite the fact every person at the company had authorization to alter the site content without flagging anybody or getting clearance. It was great to have customers call and ask me about one of my app notes only to go to the site and find out it had been deleted without explanation.

Good luck. Glad it's not my job anymore.....

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