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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LM Datasheet(PDF) – National Semiconductor (TI)
With that resistor, the current limit would be 5. The problem is that addition of this resistor modifies the current limit: If not, there are chips specifically designed to drive MOSFET gates at higher currents to force them on and off quickly.
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. Here we see the gain margin is 3. Min and max output voltage are VDC, output current is 0.
Output capacitor selection You want something big with low ESR. Adafruit has a nice boost converter calculatorassuming you’re using the simple single-inductor version. The phase margin is degrees plus the phase at which the gain is unity 0 dB.
Maybe start with this list of videos?
A boost converter design
Yes, delete it Cancel. Minimum inductance Compute the minimum inductance required. This rules out the popular MC, datasjeet has a max duty cycle of 0. Diode selection The diode has to be able to carry the maximum inductor current. And now for the complex pole.
A boost converter design | Details |
Compute the maximum current flowing through the inductor. These margins are important because the poles and zeros shift with varying load and input voltage, and without these margins your circuit could go unstable.
There is a second resistor which goes between the current sense pin of the converter and the current sense resistor. We first calculate the maximum sense resistor for current mode loop stability loop stability is always a good thing: Anyway, this is a good worked example, and very relevant! Clearly such a switch has to shut off well before 78ns.
It can handle currents up to 9A, and has an on-resistance of 0. And, a Schottky diode is recommended for high speed. Design procedure The LM datasheet provides a nice series of design procedures for various converter topologies.
Then I started reading about the compensation circuit and realized that I don’t have the means to calculate it. One of these is the resistor that goes between the switch and ground. We need to find Q, which is the damping factor. The diode has to be able to carry the maximum inductor current.
It must also be able to withstand a reverse bias of the output voltage minus the input voltage. The converter is a feedback loop, and such feedback loops need to be stable, otherwise your power supply might fail at certain frequencies.
This means raising the frequency or the inductance by at least a factor of 3. So, in fact, this converter with the components so far needs no compensation network, and we can leave the COMP pin unconnected. After the design procedure, here’s what I ended up with: And so I get a current of 4.
Again, Adafruit correctly is using the D based on the maximum input voltage, but I’m using a higher value for extra safety margin.