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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There are two ways to raise that maximum sense resistance: Shut up already, converter! Clearly such a switch has to shut off well before 78ns. This gives me a required inductance of at least And, a Schottky diode is recommended for high speed. About Us Contact Hackaday. Maybe start with this list of videos? Nobody will know unless we try it. Note that the converter will adjust the duty cycle based on the output voltage and switch current, so this is only a l,3478 for calculation.
First, choose a switching frequency between kHz and 1MHz.
Also a duty cycle switch on-time to total time of 0. I’ll keep using kHz in the daatasheet as it doesn’t matter much. That is all before you get to the need to plot charts to solve the equations. I hate low-frequency converters with their whining.
LM from Texas Instruments
With my chosen frequency of kHz, I get Again, this is from the Adafruit calculator, but here is the formula:. The new current limit, of datashet, didn’t change from before because we chose the same sense resistor. 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.
This means that in gain it acts like a lm4378, but in phase it acts like a pole. Design procedure The LM datasheet provides a nice series of design procedures for various converter topologies. If you don’t know anything about eatasheet theory, you probably want to skip this section. Duty cycle Next, compute the duty cycle, D.
The pole is caused by the output capacitor with the load, and the complex pole is caused by the switching action. If Q were infinite, the thing would vibrate itself to pieces and catch fire at half the switching frequency.
Frequency adjust resistor The LM uses this formula: The second zero, z2, is caused by the inductor and the load on the power supply. Here we see the gain margin is 3.
They are there to add stability to the converter. Next, we locate the simple pole as follows: Here’s the one for the boost converter: We got this from the Adafruit calculator, 0. I chose a standard resistor of 0.
Thus, instead of a maximum sense resistance of 0. It must also be able to withstand a reverse bias of the output voltage minus the input voltage. Then Datadheet started reading about the compensation circuit and realized that I don’t have the means to calculate it.