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Ideal buck converter for high current
anishkgt:
--- Quote from: Siwastaja on August 04, 2020, 04:00:34 pm ---Using the Rds(on) sensing isn't necessarily a bad idea; it automagically turns down the current if the MOSFET is heating up!
It isn't accurate, obviously, but you don't always need accurate charging current, just ensure power dissipation below maximum ratings. And Rds(on) sensing tracks that pretty well, if you have a transistor with higher Rds(on) or higher ambient temperature, it's doing the right thing for you. Careful with current sensing layout, of course. With a separate resistor, it's easier to do Kelvin sensing, but OTOH, separate resistor increases the loop area again.
ADP1850 doesn't have 90deg phase-shifted SYNC OUT - some ADI parts do have, I remember using one some time ago - so in order to have more phases than two, you would need an external clock generator. Any circuit which provides f_sw*2 with two outputs, 90 deg phase shift to each other would work. You could use them to drive two ADP1850's. ADP1850 internally adds 180 deg phase shift, so this would result in all four phases 0, 90, 180, 270 deg apart.
I would likely end up with 4 phases doing this, but well, do the calculation, including efficiency and price. My guesstimate is that with 4 phases, you can use the most popular commercial off-the-shelf parts for a simple BOM, but with 2 phases you may have trouble finding the inductors.
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True, monitoring the current is not what i intent to achieve just close enough to keep the current within spec of the inductor.
Trying to figure how this would be practical, using just one would share the load current of 50A between each phase. So would it make sense to have two AD1850 to share 50A each totaling at 100A for the load ? I just looked at a 4 Phase one and that seems costly and moreover calculations are advanced. The one that i looked were the cheapest among the 4phase ones, the NCP81174 (https://www.onsemi.com/pub/Collateral/NCP81174-D.PDF)
anishkgt:
AD has an evaluation board (https://www.analog.com/media/en/technical-documentation/user-guides/ug-205.pdf). This seems perfect, was wondering if this can be connected in parallel to give 100A but i would be pulling just about 83A though.
Is it ok to have it done like that because i don't know a better way to achieve it.
Warhawk:
Did you look at the LM5170-Q1 i suggested before? This is exactly what you want. Dual-phase constant current controller. You have circuit diagrams for several reference design available.
1-% current regulation.
anishkgt:
--- Quote from: Warhawk on August 05, 2020, 04:31:39 pm ---Did you look at the LM5170-Q1 i suggested before? This is exactly what you want. Dual-phase constant current controller. You have circuit diagrams for several reference design available.
1-% current regulation.
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Avoided it, costly. I've been looking at the ADP1850.
Jay_Diddy_B:
Hi,
Consider that the ADP1850 demo board is designed for the following conditions:
1) Fsw 300kHz
2) Vout = 1.09V
3) The input power is around 55W, this is 4 to 5A
If you modify for 8V output
The Inductors need to be 6 to 8 times more inductance 3.3 to 4.7uH at 30A Higher values if you lower the switching frequency.
The output capacitors on the demo board 2.5V you need to change to 16V parts
At 40A x 8V = 320W
The input current at 12V is now around 27A
Regards,
Jay_Diddy_B
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