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| Switching frequency range of MP4569GN buck IC |
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| Axk:
Trying to figure out the switching frequency range for this: https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/MP4569/document_id/963 (I've picked this part based on high input voltage, good efficiency (need input voltage up to 56V for an ebike battery power meter) and availability from LCSC.) Cannot find the switching frequency range anywhere in the datasheet. The datasheet has an inductance value formula tied to the maximum switching frequency and a formula for the switching frequency based on the inductance value, but no switching frequency range... I wonder if I'm missing some clue in the datasheet. The only way that I see of getting an acceptable switching frequency (not the range) is to use the formula and plug the values from the reference circuits provided. |
| thm_w:
100kHz from the figure. Low end 10Hz. What number does the equation give you? |
| Axk:
thm_w, which figure are you referring to? If I assume Vin=75V, Vout=3.3V, Iout=0.A, L=33uH like in their reference circuit (Vin is actually given as a range, so I'm not sure, but I assume the inductance is given for the maximum input voltage) and plug this into their formula for the switching frequency ("Switching frequency can be estimated by below equation") it gives me 637kHz. |
| thm_w:
Page 7 - steady state 0.3A diagram. Switching time = 10us. I would try 33-47uH and see if it does what you want. |
| Axk:
I think I have it all figured out now (should be obvious to those with more knowledge I suppose). So there's no lower switching frequency limit (at least theoretically), practically this ends up determined by the size of the inductance and capacitors. The (theoretical) upper limit is determined by the minimum on time of 20ns (specified in the datasheet), which would be 50MHz. But in practice switching losses would be too big at this point. With the parameters from the reference circuits the switching frequency is around 100KHz as @thm_w noted. I suppose 200KHz should be fine also, but need to calculate based on what the switching losses are at 100KHz. I guess this can be estimated based on the specified efficiency and the inductance + high and low switch on state resistive losses. Attached is my LTSPICE model based on the functional block diagram from the datasheet (appears to work well, at least in the stead state, doesn't work to simulate the short-circuit protection) |
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