RoadTest: Become a Tester of the Vishay microBRICK® Synchronous Buck Regulator EVB
Author: Jan Cumps
Creation date:
Evaluation Type: Power Supplies
Did you receive all parts the manufacturer stated would be included in the package?: True
What other parts do you consider comparable to this product?: small footprint integrated designs: Power Integrations LinkSwitch and Texas Instruments Swift range
What were the biggest problems encountered?: none
Detailed Review:
Review of a Vishay microBRICK's SiC967 switch-mode dc converter reference design. In my road test, I put the converter on the test bench, and will look at Vishay's design support for the regulator. |
The IC is a switch mode DC converter with these specifications:
Functions:
Claims specific to the design:
1 The datasheet doesn't specify what Vishay means with internal compensation. ChatGPT gives the following answer: > what is Vishay MicroBrick internal compensation? Internal compensation refers to the module's ability to stabilize the control loop of a DC-DC converter internally, without requiring external compensation components (e.g., resistors or capacitors) that would typically be used to tune the feedback loop. |
The road test kit is an evaluation board for the SiC967. It doubles a s the reference design. These are the features that Vishay made available:
2 I asked ChatGPT what the definition and meaning of Valley Current is: > what is "valley current" in a buck converter? In a buck converter, valley current refers to the lowest point of the inductor current during each switching cycle. It is an important parameter in converters operating in continuous conduction mode (CCM) or discontinuous conduction mode (DCM). Understanding valley current is crucial for analyzing performance, designing control schemes, and ensuring stable operation. Context of Valley Current in Buck Converters:
If you are working on a specific buck converter design or application, understanding valley current dynamics is vital for optimizing performance and ensuring reliable operation. |
The schematics are available, and an image of each of the 4 PCB layers. This info, together with the PCB LAYOUT RECOMMENDATIONS section of the datasheet, will help designers to integrate the IC in a design.
Evaluation board with the core area highlighted. Image source: edited figure 1 of Vishay SiC967 datasheet
The test points have probe points that make it easy to use a DMM or oscilloscope. For a more permanent, it's easy to solder test wires directly to the PCB
The microBRICK is a hybrid IC. It contains control and power silicon, and the inductor.
image source: excerpt from Markt&Technik Stromversorgung & Power-Management 2024 www.weka-fachmedien.de - fair use
The only external components required are in- and output capacity. And a few function selector resistors. It provides its own regulator working power from input (if you want that).
The kit has been on the lab bench for a full month. I looked at efficiency, protection and behaviour.
The IC's maximum efficiency is 95% This was confirmed by a test in the optional range of the design. The exercise below checks a scenario on the lower voltage input range: 10 V, and medium load: 0.2 to 3.1 A. In continuous conduction mode.
(sample 22)
I’ve ran many more tests, with input voltages between 12 V and 48 V, in mode 2 and 4. With low to maximum load. Here are the charts for Mode 4.
note: you need to populate R14 with a 0R 0402 resistor to use the bias voltage.
(sample 34)
Check out LabView process to measure DC:DC converter efficiency for details on the bench setup, instruments used, Labview process and the additional measurements. The post includes a spreadsheet with the data.
The soft-start ramp is fixed. The datasheet specifies 6 ms.
The capture below confirms this. I used the enable signal to trigger a startup. The yellow trace is the input voltage, the blue one is the output signal during soft start.
The time between 10% and 90% is 6 ms. From 0 to 100%: 6.72 ms.
This little exersice checks the protection behaviour, and shows the Power Good signal during an error situation:
Settings:
Iout: 5.030 A
Iout: 4.390 A
The image below shows shutdown in an over-current situation. The Power Good signal follows along. The IC will auto retry, and re-soft-start.
The IC has to be configured for the minimum voltage it will operate on. dougw has elaborated on the calculations in his review. I've checked if the evaluation board behaves as configured.
note: the values of R5 and R6 on the evaluation board are different than what the board's user manual says: R5 = 10K, R6 = 43K.
Calculations indicate that the swicher should enable at 7.42V. and switch off when input drops below 6.36V. I used these test conditions: Vout = 5V, Iout = 0.317 A.
Ven measured: 7.48441 V
Vunder measured: 6.16347 V
In this section: the documentation and design tools. How does Vishay support the engineer?
This is Vishay's online application that helps you design DC converters with their products. I asked it to design a DC converter, manipulating its in-and out criteria in the hope that it would generate a SiC967 design:
This was the schematic it made:
Not surprisingly, it closely resembles the reference design's schematic. With configuration resistor values based on my requirements. There's a rich set of simulations of your design available. Here's a subset.
If you are planning to use the SiC967, this is a good application to suggest good values for the external components. And to get a feel for its operational behaviour.
The datasheet and collateral are good. They contain a good mix of raw specs and charts. And good designer information. It is a fairly enjoyable read. This snippet shows some of the charts of the datasheet. I selected these because they roughly match the measurements I did in the efficiency section of this review.
There is clear info on how to design a circuit, how to configure the protections and operating area. And good guidance to properly implement a PCB. This section, together with the evaluation kit's images of each PCB layer, will get you on track. These are the resources I used:
microBrick datasheet https://www.vishay.com/docs/76444/sic967.pdf
board user manual https://www.vishay.com/docs/77501/sic967.pdf
microBuck/Brick product sheet https://www.vishay.com/docs/48652/2309-microbuck-brick.pdf
sic976 product landing page https://www.vishay.com/en/product/76444/
sic976 infographic https://www.vishay.com/docs/48924/ig32989088-23xx-sic967.pdf
DG2034 multiplexer https://www.vishay.com/docs/73172/dg2034e.pdf
Exploded package https://passive-components.eu/wp-content/uploads/2020/08/microbrick-3D-package-integrated-power-module.jpg.webp
PowerCAD video: https://youtu.be/cNhndMu8QKw
AI use in this road test:
text in tables with light blue background is generated by ChatGPT. I provide the query and unaltered reply (except for removal of some content, indicated by [...]). |
Thank You for reading. And thank you e14 and Vishay for the road test material.