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The following workshop is now available for On-Demand Viewing:

 

Simon Foley from Vishay gave a presentation on microBuck Converters.  During this presentation and during the Q&A session immediately following you had a chance to win one of four Vishay Synchronous Buck Regulator EV Board (recently offered as part of our  RoadTests & Reviews program) for asking good questions.  Simon was very impressed with your questions and has done the best to answer all of them.

 

During this event, there was also a quiz to test your knowledge to help prepare you the presentation.

 

Automation is driving our world and civilizations into a completely new era of communication. As a result, the power eco system is now fundamentally being transformed into a workhorse, in order to deliver essential energy  to those critical IT infrastructures.    Vishay ICs, provide solutions to overcome the following 5 main infrastructure  power conversion challenges:

  • Global ICT power consumption to be tripled in next decade - More  efficient power conversion
  • Cooling cost skyrocketing in data centres - Superior thermal performance
  • CPU and SoC are becoming more power hungry - Fast load transient
  • Higher portability and less space in electronics devices - Ever increasing power density
  • More stringent and tougher application environment - More reliable solution

 

Q&A Session:

 

What is a buck regulator?

 

A buck regulator is a term used to describe a converter which converts an input voltage, to a lower output voltage.

 

I would like to ask about the output voltage adjustment and resistors in the feedback divider. R_fb_L should be a maximum of 10 k. This limits usage in low power application due to regulator's self consumption. Is there a way to make the regulator stable with higher value resistors (this or a future regulator family)?

 

R_FB_L should be a maximum of 10 kΩ toprevent VOUT from drifting at no load.  No plans to change this in new

 

What are minimum required pasive compoennts to use with Vishay buck convertors like SiC461? Are there any components that can be ommited in comparison to typical circuit from fiorst page of datasheet? If yes, is there any minimum upgrade to this minimal circuit which significatly improves some property of conversion?

 

The absolute minimum peripheral components, can be seen in the typical application circuit. Using the suggested schematic, in PowerCAD is always recommended 

 

How is ultrasonic mode function in this regulator and what are the benefits?

 

Ultrasonic mode improves the efficiency at light loads, over FCM.  It folds back the frequency (>20kHz) and goes into diode emulation mode, at light loads.

 

Is it possible to use it to high power high fidelity mosfet amplifiers?

 

The MOSFET drivers and error amplifier is integrated into the microBUCK/BRICK solutions

 

How accurate is PowerCad simulation vs 'actual'?

 

PowerCAD is designed to reflect real life conversion results

 

How much does the resistance of the inductor affect the overall efficiency?

 

SiC474, 24Vin to 5Vout, 3A @ 500kHz: a 10uH inductor (11.6mΩ DCR) provides an efficiency of 93.7% (95mW DCR losses).  Comparing with the same inductance value and an increased DCR of 116mΩ we see an efficiency of 93.65% (95.4mW DCR losses). The DCR power loss is proportional to the DCR

 

I don't see any heatsink, in high current operation for long periods of time is cooling needed?

 

Heatsinks and forced air cooling could be required for high switching frequency operation, if the pcb copper thickness is not thermally optimised

 

Is there an easy way to rename a project and its subsequent directories using a TCL command(s)? The reason is to reuse a certain baseline Vivado project to create variations of the same baseline SoC. By just copying and renaming a baseline project we can avoid recreating it from scratch

 

What do you see as the biggest advantage of a microBUCK to a standard regulator?.

 

More power dense, higher switching frequency (smaller and less expensive external inductor), wider output voltage range, higher efficiency, lower case temperature (less expensive and easier to cool)

 

I believe that is coming in the next episode.  Stay tuned!

 

At slide "microBUCK Key advantages" you mentioned PMBus 1.3 interface. What can be controller/moniteored using this interface?

 

Any controller with a PMBus 1.3 compatibility

 

Can this device handle 10uA to 4A in 10ms?

 

This is well within the capability of microBUCK/BRICK.  microBUCK response to load steps within uS

 

How to optimize EMI Issue in switching converter?

 

Ensure the PCB is optimised: star power ground & use multi-layer boards, keep peripheral components close to the microBUCK/BRICK, using Vishay IHLP inductors helps reduce EMI issues, shielding over the DC/DC converter will help, although not necessary

 

Is there any offer suitable for lower loads (<1A) or should be better to move to another family of Buck regulators?

 

Our lowest microBUCK is 2A.

 

Do any multi-output buck converter exists? For example buck converter that can convert one 12V input to 3.3V and 5V at once?

 

Please keep reviewing our PowerCAD tool to check pre-release solutions, in part selector/status options.  It's possible we could have something to offer 2021

 

Why didn't James Lewis didn't find a difference between the switching modes of the regulator during his roadtest?

 

Please refer to the evaluation board manual instructions, to change between FCM & PSM

 

Is there thermal performance remains same in integrated switch and external switch MOSFET buck converter

 

The integrated thermal performance of integrated solutions will differ from discrete, as the heat will be dissipated over a wider area, if designed discretely.  If the pcb is thermally suitable, there shouldn't be any issue to design with integrated solutions

 

How does the ESR value of the capacitor and DC Resistance of the coil effect the buck converter?

 

An output capacitor's ESR has an effect on the load transient response and output ripple voltage..

 

I'm really impressed with the performance of the IC. But I'm curious if the package put a higher requirement on the soldering process? Especially with the internal brackets holding the MOSFET dies down I'm imagining it having a higher thermal mass than say a discrete MOSFET.

 

microBUCK's controller & 2 x MOSFET die are bond wired and clipped, side by side internally.  The overall package has no increased stress on the solder process;  the microBUCK's thermal mass is smaller than a 6x5 PPAKSO8 MOSFET and smaller than 2 x PPAK 1212 MOSFETs (comparing against a 4x4 mm microBUCK MLP package)

 

Does switching frequency improves the EMI performance of the converter?

 

Higher switching frequencies do not give higher EMI. Adjusting the switching frequency, changes the radiated & conducted EMI fundamental & associated harmonics.  Conducted EMI is easier to filter at higher switching frequencies, as the filter values are smaller

 

Is there a comparable boost converter series?

 

Not currently

 

How does skip mode and continuous mode improve the performance of the regulator?

 

We don't use skip mode for light load performance - PSM & Ultrasonic folds back the frequency, going into diode emulation mode, at light loads, significantly improving light load efficiency. FCM offers a more stable switching frequency (± 15%).  However, FCM isn't optimised for light load efficiency.

 

How the PCB Layout degrades the performance of the buck converter?

 

The PCB layout has a big influence on noise, performance & thermal dynamics

 

Is the microbrick converter price feasible for the consumer electronics market?

 

Our pricing is competitive for the consumer market. We have been successful in this market, for quite a few years  .

 

Are heat sinks recommended?

 

Heatsinks aren't required, but forces air maybe needed, depending on the PCB specification;  the higher the case Tj to Ta, the more forced air maybe needed. A suitable PCB (optimised copper and layers, will not require forced air cooling).

 

Is there any Time based degradation  in the performance of the regulator

 

No time based degradation

 

what type of isolation in the Sic967?

 

There is no isolation with our microBUCKs/BRICKs.  There are PoL non-isolated DC/DC solutions

 

Can we make microgrid DC bus with different current an transient current required?

 

Our microBUCK & microBRICK solutions can be used to provide a DC microgrid bus voltage, assuming that the conversion spec is within specification.

 

Can we simulate this regulator in LTSpice?

 

Sorry - no, as are multi-chip solutions.

 

Are there any supply problems with SiC46x? we need to buy all the variants even for manufacturing of ca 10k per year...?

 

No supply issues with microBUCK/BRICK products

 

What is the recommended strategy to control EMI for microBuck and microBrick devices?

 

Ensure the PCB is optimised: star power ground & use multi-layer boards, keep peripheral components close to the microBUCK/BRICK, using Vishay IHLP inductors helps reduce EMI issues, shielding over the DC/DC converter will help, although not necessary

 

Does microBrick device need external heat dissipation components at its nominal current level? If yes, does the simulation tool suggest any heat dissipation solution?

 

No requirement for heat dissipation components.  PowerCAD can be used to check the MOSFET, IC & inductor temperatures. It's possible to change the speed of forced air, in the simulator.

 

Can I set input noise and ripple in PowerCad and will it give an indication of output noise and ripple based on selected periphery components?

 

It allows the user to perform line transients, but not to inject input noise

 

The SiC46x seems like a good fit for a compact, portable lab supply for field use.

 

I would suggest using a solution with PMBus.  Using  an adjustable external potentiometer would work, but it would be better to choose a solution with internal compensation, in this case

 

In power cad tool can we directly import the schematic file in my cadsoft pcb designer?

 

Sorry, this isn't possible.

 

Are all 3 modes of operation (FCM, PSM, Ultrasonic) available in any microBUCK chip?

 

Mostly yes. SiC476-9 only has FCM & PSM modes

 

I would like to know if the power cad simulation tool is  available for free or  we need pay?

 

PowerCAD is a free on-line tool

 

In terms of running the microBrick for a long  period of time, would the temperature effect the performance?

 

The temperature does effect the performance.  However, with the correct PCB thermal design, or forces air (required in high switching frequency conditions), there

 

Use of a clip at the switching node is interesting - how well does that help mitigate ringing at the SW node and propogation to output?

 

Using a clip between high side, low side and switch node, significantly reduces internal parasitic inductance (& therefore switch node ringing), compared to using only bond wires.

 

Any plans on fixed output version of the microBUCK family?

 

Not at this stage, but if there is a good business case, we would consider this.