LM5143: I want to use LM5143 to design a dual-phase 24V to 12V, 20A buck circuit, can you help me to look at my problem

Hello, please send the completed quickstart calculator file for this design.

Note you can use the LM25143 here.

Regards,

Tim

The quickstart seems incorrect - it should be configured as a 2-phase single output, not a dual.

Also, do you really want 1mΩ sense resistances? This gives a 75A peak current limit on each phase, which is way too high.

No need for a resistor on HO1. That is just used to slow the gate drive if there is an EMI issue. However, we typically do not need it, given this is only a 5V gate drive and is not inherently fast.

Regards,

Tim

Just a few comments first on the quickstart file:

1. The current limit needs to be set above the full-load current, 130-150% being a typical setting. 28A is full load in this case, so the current limit should be 35-40A.
2. This means the shunt (current sense) resistor should be 3mΩ or 4mΩ for 46A or 34A current limit setpoint, respectively. A 1mΩ as entered gives a current limit of 143A, which is way too high and gives a very low current sense voltage. It needs to be a 2W rated shunt.
3. The buck inductance at 5.6uH is a little high - try 3.3uH for 33% ripple current.
4. The FETs are not chosen correctly – typically the high-side FET is higher Rdson than the low-side FET (as it has both conduction loss and switching loss).
5. Note it is important to enter the correct derated value for Cout, as this affects compensation.

Fixing the shunt in particular as well as updating the compensation for the actual derated Cout value will help stabilize your circuit and likely resolve your issues.

Regards,

Tim

Okay, thank you.