So this is my first boost converter design and I was hoping I could get some feedback on my PCB layout and component selection. I'm using the [https://datasheet.lcsc.com/szlcsc/1812101116_Feeling-Tech-FP6291LR-G1_C18701.pdf]F96291](https://datasheet.lcsc.com/szlcsc/1812101116_Feeling-Tech-FP6291LR-G1_C18701.pdf) for the boost converter IC. I've copied the typical application circuit from the datasheet. My project is powered by a single cell lipo with a voltage range of 2.9 to 4.25 volts with a max current draw of 0.6 amps from testing. I've calculated a peak current draw of the boost converter at 1.35 amps. I've calculated a min duty cycle of 0.222 and a max of 0.462. I've calculated an output RMS current of 6.154.
For the output capacitors I'm going with 4 10uF output caps in an 0805 package in parallel. I'm using the CL21A106KAYNNNE from Samsung Electro-Mechanics. Using their dc bias curve data from http://weblib.samsungsem.com/mlcc/mlcc-ec.do I'm seeing a 50% bias at 5V so with 4 caps I'm expecting to get around 23uF. Is this acceptable or should I use cap with a higher capacitance rating that will allow me to reduce the number from 4 to 2?
For the input caps I'm using the 0805 package size and am using two 22uF caps. The site above doesn't appear to have any dc bias data on that particular model of capacitor (CL21A226MAQNNNE) however I'm assuming its the same as the 10uF capacitor and has a roughly 50% reduction at 5V.
The feedback resistors are R8 & R9 and are connected via a trace on the ground plane on the underside of the board. Is this acceptable or are they too far away from the pin of the IC?
On this board I'm using the backside of the board as a grounding plane (green) is the way I have my grounding of the IC and the various capacitor's acceptable?
Also is the way I have my Vin trace corrected to the inductor and input caps acceptable or should the trace be physically closer to the input caps than the inductor or does it matter at all?
Wawa:
Why the mosfet.
The chip has an EN pin, to turn it on/off.
Why design something tricky when you can buy the whole thing as a tiny module.
Leo..
Because the board is powered by a lipo and if you don't cut off the power going to the IC then the output pin would read what was coming to the Vin and EN pins since they have to be connected.
I'm designing it this way because its much cheaper per board than buying already made units, plus those add to the size of the case whereas making my own integrated boost converter cuts down on size and cost.
Kuusou:
...the power going to the IC then the output pin would read what was coming to the Vin and EN pins since they have to be connected.
No they don't.
If the enable pin is HIGH, connected to the LiPo voltage for example, then the converter is working.
If you ground the enable pin, then the converter turns off.
You normally use a (100k?) pull up resistor between V-in and EN, so you can use a 'switch to ground'.
That could be a real switch, or the output pin of a processor.
Switch points (with hysteresis) are 0.6volt and 0.96volt according to the datasheet.
Leo..
If the enable pin is HIGH, connected to the LiPo voltage for example, then the converter is working.
If you ground the enable pin, then the converter turns off.
Actually, he is correct. Just examine the circuit.
The design of a basic boost converter is such that there is a direct path through the inductor and diode from input to output.
With the converter disabled, the output voltage falls to the same as the input voltage (less the diode), not to zero.
I've calculated a peak current draw of the boost converter at 1.35 amps.
Could be lowered somewhat if you choose the 4.7μH inductor.
Note: I would add a 0.1μF cap at Vin and at Vout. This'll help reduce noise and EMI levels and probably improve stability. (they're shown in the datasheet)
I've calculated a min duty cycle of 0.222 and a max of 0.462. I've calculated an output RMS current of 6.154.
Curious what formulas you used to calculate these values or was it with an on-line tool? I've designed a low current 3-5V Vin, 12V Vout, 25mA, PFM Boost Converter that works really well but there's some parameters I'd like to calculate even though various testing and measurements were successful.
dlloyd:
Could be lowered somewhat if you choose the 4.7μH inductor.
Note: I would add a 0.1μF cap at Vin and at Vout. This'll help reduce noise and EMI levels and probably improve stability. (they're shown in the datasheet)
Curious what formulas you used to calculate these values or was it with an on-line tool? I've designed a low current 3-5V Vin, 12V Vout, 25mA, PFM Boost Converter that works really well but there's some parameters I'd like to calculate even though various testing and measurements were successful.
Ahh I didn't realizing going with the 4.7uH inductor would lower that, I'll have to revise my design. I've ordered 5 assembled boards from JLCPCB though so first I want to do some testing and see how this design works.
I calculated those values using various online websites explaining boost converter design, I've been spending the last several days reading all about power supplies. https://www.powerelectronicsnews.com/the-dc-dc-boost-converter-power-supply-design-tutorial-section-5-1/
was one such site
