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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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Note that the Adafruit calculator correctly, in my opinion uses the lowest of two possible duty cycle based on the minimum input and output voltage, because this will result in the highest minimum inductance.

If Q were infinite, the thing would vibrate itself to pieces and catch fire at half the switching frequency. This gives me a required inductance of at least Lm3748 problem is, without knowing control theory, it will be difficult to select the compensation components.

It can handle currents up to 9A, and has an on-resistance of 0. Well actually there is no conclusion until I actually get the parts in to build this thing. After the design procedure, here’s what I ended up with: It can withstand at least V to the drain, and has a gate threshold of dztasheet most 4V. We need to find Q, which is the damping factor.

With my chosen frequency of kHz, I get Next, compute the duty cycle, D. That is all dwtasheet you get to the need to plot charts to solve the equations. This means raising the frequency datashewt the inductance by at least a factor of 3. Can this thing switch fast enough? And now for the complex pole. Note that the second zero is a right-hand plane zero.


A boost converter design

Now that we have our pole and zero frequencies, we need to know what the DC gain is. Frequency adjust resistor The LM uses this formula: Here we see the gain margin is 3. Let’s locate the zeros: So with a maximum input voltage of 12V, and an output current of 0.

Again, Daatasheet correctly is using the D based on the maximum input voltage, but I’m using a higher value for extra safety margin. Again, this is from the Adafruit calculator, but here is the formula:.

And, of course, this pole is located at half the switching frequency: Compute the minimum inductance required. The cause of this is the insanely low maximum sense resistance from above.

LM from Texas Instruments

The gain margin is minus the gain at which the phase is degrees. Design a boost converter that gives VDC at 0. First, choose a switching frequency between kHz and 1MHz. Note that the converter will adjust the duty cycle based on the output voltage and switch current, so this is only a value for calculation.

If not, there are chips specifically designed to drive MOSFET gates at higher currents to force them on and off quickly. I get a maximum sense resistance of 0.

Design procedure The LM datasheet provides a nice series of design procedures for various converter topologies. Here’s the one for the boost converter:. You want something big with low ESR. Duty cycle Next, compute the duty cycle, D. And indeed it is. Again, this is from the Adafruit calculator, but here is the formula: And so I get a sense resistor of 0.


So this is really a good thing. There are two ways to raise that maximum sense resistance: We must now change both the sense resistor and the slope compensation resistor so that the current limit is sane and the slope compensation datsheet is above the minimum.

The phase margin is degrees plus the phase at which the gain is unity 0 dB. They are there to add stability dataheet the converter.

LM3478 Datasheet PDF

You can see the resonance at half the switching frequency. Then I started reading about the compensation circuit and realized that I don’t have the means to calculate it.

The new current limit, of course, didn’t change from before because we chose the same sense resistor. This resistor protects the circuit against overload currents. One of these is the resistor that goes between the switch and ground.

Yes, delete it Cancel. So, let’s take a look at the application note to see what the transfer function looks like without this compensation.