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.

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Nobody will know unless we try it. I chose a standard resistor of 0. Again, Adafruit gives this as 4.

LM from Texas Instruments

Doing that also has a knock-on effect of lowering the inductor current. It can withstand at least V to the drain, and has a gate threshold of at most 4V. The off-time is 0. We got this from the Adafruit calculator, 0.

LM3478 Datasheet PDF

The top plot is gain in dB vs frequency in Hz, and the bottom is phase shift in degrees vs frequency in Hz. This means datzsheet in gain it acts like a zero, but in phase it acts like a pole.

Next, we locate the simple pole as follows: Our chosen sense resistor is bigger than this by a factor of 3. To power my datawheet converter, I’d like to use a 12VDC wall adapter. Min and max output voltage are Datashet, output current is 0. Again, this is from the Adafruit calculator, but here is the formula: Well actually there is no conclusion until I actually get the parts in to build this thing.


This is fine, since the application note states we want a phase margin between 30 and degrees.

We first calculate the maximum sense resistor for current mode loop stability loop datasheer is always a good thing: The phase margin is degrees plus the phase at which the gain is unity 0 dB. Again, this is from the Adafruit calculator, but here is the formula:.

Now that we have our pole and zero frequencies, we need to know what the DC gain is. The datasheet doesn’t state this, but ideally the gain margin should be somewhere between 6 and 12 dB. First, choose a switching frequency between kHz and 1MHz.

Note that the second zero is a right-hand plane zero. Doing so without going through the math shows that it is not possible to pick a reasonable sense resistor while still maintaining a good current limit. Also a duty cycle switch on-time to total time of 0.

A boost converter design | Details |

There’s a COMP pin on the converter datahseet you put a resistor and capacitor in series. Output capacitor selection You want something big with low ESR. Maximum inductor current Compute the maximum current flowing through the inductor. There are two ways to raise that maximum sense resistance: So this is really a good thing. And, a Schottky diode is recommended for high speed. So, let’s take a look at the application note to see what the transfer function looks like without this compensation.


I hate low-frequency converters with their whining. However, we now pm3478 not need a slope compensation resistor, and everyone is happy.

The new current limit, of course, didn’t change from datssheet because we chose the same sense resistor. 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.

It must also be able to withstand a reverse bias of the output voltage minus the input voltage.

A boost converter design

And so I get a sense resistor of 0. This means raising the frequency or the inductance by at least a factor of 3. Here’s the one for the boost converter: Our modified values with this frequency are: One of these is the resistor that goes between the switch and ground.

Design procedure The LM datasheet provides a nice series of design procedures for various converter topologies. We can see ml3478 unity gain occurs at 2.