RoadTest: Richtek EVB_RT7275GQW Evaluation Board
Evaluation Type: Evaluation Boards
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?:
What were the biggest problems encountered?: Had to manually add a pot to the board to adjust output voltage. Audible, high pitched whining occurs at high freq square input voltages.
Being my first review, I'm not sure how much depth to go into, or what details in specific to include, so I'll just include all the information regarding my testing, and opinions/experience with the board. To avoid just regurgitating info in the datasheet, I decided to leave it up to those interested to investigate the finer details of the board in the spec-sheets, which I found to be quite comprehensive and accurate (the board surpassed the performance outlined in the datasheet). Some info was more easily found on the spec sheet for the evaluation board than the spec sheet for the actual converter. Here I'll simply give the tests I ran, followed by my general feelings/opinions about the board.
To start, some high-def close ups:
The board came packaged nicely in a static sheilding bag, between foam in a box.
Well, I began testing this thing expecting to eventually push it beyond it's limits, and fry it. This board however, will not die. It barely got warm under the normal circumstances, and all the while providing a steady output, so long as the load was of a reasonable resistance.
To begin, I wanted to keep track of temps, so I measured the ambient temp of the room and the board out-of-the-box at 72F (infrared thermometer accurate to 1/2 a degree)
I fed it a steady 12V, and it gave me 1.04V out; pretty close to the 1.05 it was designed to output.
Lowering the voltage to below 4.5 drops the output very slightly (a couple mV) until around 3.5V, when the output drops to 0V in 0.3ms
I also measured to voltage between the PVcc pin and ground to be 5.08V, as expected.
After the the board had been running with the 12V input, and no load for about 15 minutes, the temp reached 75F
Time to sweep input voltage: I put 5Vp-p @ 1Hzto600Hz offset by +12V on the input and got a perfectly steady 1.05V out. This is to be expected, seeing as the bounds of the input (7 and 17V) are withing the boards documented operating voltages (4.5 to 18V).
I figured it was time to make the thing do some work, so I held the frequency at 600Hz and applied various resistive loads across the output terminals. I lowered resistance of the load until at just below 1.73 ohms, the output became what is shown in the first capture:
It appears that with the load this small, the board was not able to support the current when the voltage dipped, and cut itself off. (roughly .75A were trying to be pulled). Further lowering the resistance essentially lead the boar to cut off sooner and sooner:
So it can't provide lots of current without lots of voltage; I didn't expect the board to break the laws of physics. Its still pretty cool though. I next decided to give it an extreme input: 10Vp-p Square wave at 600Hz offset by +20V. Mind you, this goes 7V beyond the documented upper limit for input voltage. I'm not sure if it is by design, but even measuring the input across the terminals, there appears to be some basic low-pass filtering offered by the caps connecting the positive terminal to ground; causing the input to look like so when applied across the input terminals:
Now, even with this input, the board output a solid 1.05V open and under low resistance load!
The one peculiar thing I noticed was that the board made a loud high-pitched whine when it was given a square wave above 18KHz as input. Not great, considering the board can be expected to be run up to 700KHz, however I suspect the board was designed for sinusoidal input at worst. It has got a switching rate of 700KHz, so while it performs fine up until, and even beyond that point, it doesn't necessarily perform quietly (if you give it a square wave).
Time for the stress testing:
I fed the board 16V and repeatedly tapped a wire across the terminals to short them. The board continued to provide power, never cutting out. The board had reached 75.5F at this point.
I was able to solder a potentiometer in parallel with one of the smd resistors that controlled output voltage, and raised the output voltage to 10V. I then Connected the output terminals via a 10 ohm resistor. That resistor lasted less than a second before burning up. Wanting to push it farther, I secured some graphite from a mechanical pencil across the output terminals (around 1.5 ohms). The board supplied 5.6V with no issues, the graphite began to dimly glow, and the solder mask near the output terminals began fizzing. Allowing this to continue for several minutes allowed me to identify the hottest point on the board as the inductor, which was at 96F. Documentation states the board will intentionally shut down at 302F. I can't imagine this board would ever lead itself to reaching that temp under normal circumstances.
So to conclude, this board performed extremely well. The output was stable for all input and output ranges specified, and beyond, except when the load across the output was low (less than 2 ohms). It was able to output roughly 5A (when only rated for 3). Within the documented max/min ranges, the board performed impeccably, other than some whining with high frequency square input voltage. The protection in the board is amazing. After getting over 3A out with an input of over 18V (I was able to get up to 24V with my equipment), the board (or more specifically the inductor) didn't even get hot enough to burn. This board, and consequently the chip can be abused and still perform as expected. It would have been nice to have a pot on the board instead of an smd, so as to allow for adjusting the output voltage, however I understand that the other external components on the board are tuned to support the output of 1.05 as well, even though the board performed fine at different output voltages after adding the pot myself. I would highly recommend this converter to anyone requiring a steady, reliable voltage source for a project. A steady and adjustable converter lends itself rather well to powering any microcontroller, handheld device, really any portable electronic device, and would allow for a wide range of input voltages. The size of the external components give for a bulky design and wouldn't quite be small enough to use in a smartphone, however the chip itself is rather compact, and if a smaller inductor can be managed, the whole package would be suitable for say, a gameboy sized device. Seeing as I wasn't able to kill this one, I suspect ill be utilizing it to power my de0-nano fpga in the future. Thank you element14 for allowing me to test the richtek RT7275GQW board. It lives up to its spec sheet, and surpasses the performance I expected of it.