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Power Tip 46: Time your synchronous-buck FETs properly

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agk
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re: Power Tip 46: Time your synchronous-buck FETs properly
agk   4/14/2012 8:12:30 AM
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A brief and important analysis about the low side and high side FET when used as a switch.This is used in many applications including electronic ballasts. This analysis to be included in the R&D labs libraries.Also usable to reduce the radiations and go for EMI certification.

sharps_eng
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re: Power Tip 46: Time your synchronous-buck FETs properly
sharps_eng   4/14/2012 1:06:39 PM
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Can I add that designers do not have an easy way to time the gate drive in a reliable, low-cost circuit. No one device or circuit has appeared that fixes this problem at the right price and reliability point. I have seen many circuits loaded with hand-tweaked RC networks. If you read carefully you can spot that this article is talking about a buck converter, but using terms like hi-side and lo-side which are normally associated with H-bridges. In H-bridges, timing is a symmetric problem and turning on the lo-side is equally critical. The synchronous FET pair in this buck converter can also easily have such a symmetric mode, depending on the design parameters.

Sanjib.A
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re: Power Tip 46: Time your synchronous-buck FETs properly
Sanjib.A   4/14/2012 7:24:21 PM
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For synchronous buck topology I have used of the shelf PWM chips, which usually have built in optimization of ON/OFF timing between the hi-side and lo-side switches...not much to do with manual tuning.

Rodneyluo8
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re: Power Tip 46: Time your synchronous-buck FETs properly
Rodneyluo8   4/16/2012 11:17:10 AM
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where is the schemaic diagram

BicycleBill
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re: Power Tip 46: Time your synchronous-buck FETs properly
BicycleBill   4/16/2012 3:45:01 PM
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There is no single schematic here to show, it depends on what you are driving--the point here is to show you what you need to be aware of when doing a circuit. It's not a "cookbook" situation, unfortunately.

MrPWM
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re: Power Tip 46: Time your synchronous-buck FETs properly
MrPWM   4/17/2012 2:23:53 AM
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The timing of the upper switch turn-on is helped by a few factors. For example, as we can see in Robert's figure 1C, the gate voltage is at a low level anyhow if the upper switch turns on too early. This limits the possible amount of shoot-through. More importantly, both Spice and O-scope plots have showed me that the parasitic source inductance plays a critical role in lowering shoot-through. High di/dt across Ls in the lower switch "pushes" the gate voltage higher even though the G-S voltage is falling, and is often mistaken for a Miller plateau. The upward rise in V-gate in figure 1A is this very effect. Remember: Vgate is not the same as Vgate-source. D. Hambley, SENTEK Engineering

gayatrikumar_1
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re: Power Tip 46: Time your synchronous-buck FETs properly
gayatrikumar_1   4/26/2012 2:26:43 PM
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Some Drivers Do have Programmable Dead time to prevent shoot-through. How ever this limits the usable duty cycle range. Robert has considered 12:1 buck reg, which is one of the difficult examples. This timing problem becomes more important when we need to achive duty cycles down to 1%

kjdsfkjdshfkdshfvc
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re: Power Tip 46: Time your synchronous-buck FETs properly
kjdsfkjdshfkdshfvc   2/3/2013 8:58:53 AM
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Why is the full linked list of all tips in the series a PDF file??? I can't even use that on some of my mobile devices, but I can read the articles. The absurdity of a PDF file is clear when you see that for the next tip you have to change it, and I have to re-download it (or if I get busy and miss a few, I come back want to catch up, I need to download a PDF) Why isn't that just a link to a home page for the Power Tips Series on eetimes.com ? On that home page is the hyperlinks to other articles in the series.

kjdsfkjdshfkdshfvc
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re: Power Tip 46: Time your synchronous-buck FETs properly
kjdsfkjdshfkdshfvc   2/3/2013 9:00:56 AM
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sorry, in my annoyance at the PDF, I forgot to mention that the Series is a favorite of mine, absolutely a wealth of quality information that is hard or impossible to find or know without the experience you clearly have. I am continually learning from you, thanks, but just hate the PDF :)

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