switching frequency of LM can be adjusted to any value between kHz and .. mode. All the analysis in this datasheet assumes operation in continuous . Part Number: LM, Maunfacturer: National Semiconductor, Part Family: LM, File type: PDF, Document: Datasheet – semiconductor. Datasheets, LM Design Resources, LM Design with WEBENCH® Power Designer. Featured Product, Create your power design now with TI’s.

Author: Mekasa Arakree
Country: Bahamas
Language: English (Spanish)
Genre: Software
Published (Last): 28 June 2018
Pages: 432
PDF File Size: 3.10 Mb
ePub File Size: 10.85 Mb
ISBN: 938-5-24568-356-9
Downloads: 23121
Price: Free* [*Free Regsitration Required]
Uploader: Samum

The pole is caused by the output capacitor with datashet load, and the complex pole is caused by the switching action. And, of course, this pole is located at half the switching frequency: This is fine, since the application note states we want a phase margin between 30 and degrees.

Again, this is from the Adafruit calculator, but here is the formula: This resistor protects the circuit against overload currents. These margins are important satasheet the poles and zeros shift with varying load and input voltage, and without these margins your circuit could go unstable. Duty cycle Next, compute the duty cycle, D.

LM3478 Datasheet PDF

Compute the minimum inductance required. We first calculate the maximum sense resistor for current mode loop stability loop stability is always a good thing: So, let’s take a look at the application note to see what the transfer function looks like without this compensation. And now for the complex pole. Output capacitor selection You want something big with low ESR. We can see that unity gain occurs at 2. One of these is the resistor that goes between the switch and ground.


I don’t know, but suspect that the output voltage of the adapter will drop under load, so I’m just going to go ahead and specify a minimum input voltage of 8VDC. And, of course, this pole is located at half the switching frequency:.

The off-time is 0. Next, compute the duty cycle, D. Then I started reading about the compensation circuit and realized that I don’t have the means to calculate it.

We got this from the Adafruit calculator, 0. This means raising the frequency or the inductance by at least a factor of 3. Again, Adafruit correctly is using the D based on the maximum input voltage, but I’m using a higher value for extra safety margin. Minimum inductance Compute the minimum inductance required. There are two ways to raise that maximum sense resistance: Min and max output voltage are VDC, output current is 0.

Well actually there is no conclusion until I datasbeet get the parts in to build this thing. Thus, instead of a maximum sense resistance of 0. Doing that also has a knock-on effect of lowering the inductor current.

  ISO 21049 PDF

LM from Texas Instruments

Here’s the one for the boost converter: We first datasgeet the maximum sense resistor for current mode loop stability loop stability is always a good thing:. We see that there are two zeros, one pole, and one complex pole: We need to find Q, which is the damping factor. Clearly such a switch has to shut off well before 78ns. Diode selection The diode has to be able to carry the maximum inductor current. I think I will have to look at other lm478 such as the LT Next, we locate the simple pole as follows: There’s a COMP pin on the converter where you put a resistor and capacitor in series.

A boost converter design

About Us Contact Hackaday. I get a maximum sense resistance of 0. We’ll find out in the next project log. Shut up already, converter! Our chosen sense resistor is bigger than this by a factor of 3.

After the design procedure, here’s what I ended up with: