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MPS1474 DC DC Buck regulator design

Nilutpal66

Hi. I am designing a DC DC buck regulator using MP1474S. MP1474S | 2A, 16V, 500kHz, Synchronous, Step-Down Converter with PG | MPS (monolithicpower.com)

MPS have an online tool for designing buck regulator DC DC Designer Online - Design Tools - Design (monolithicpower.com)

These are my input specifications that I had given:

image

For which I got the following schematic circuit:

image

My query is why R4 is 0 ohm here? According to the datasheet, R4 should be nearby 16k as shown in the TYPICAL APPLICATION CIRCUIT of 5V,2A

Looking forward from hearing from you. 

Regards,

Nilotpal Baruah

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  • From what I can see, Vfb in the above is formed by the divider R1/R2, the R4 being zero just means no R4 is necessary. The ratio 47k / (301+47k) * Vout gives me Vfb = 0.810V which is about right - datasheet says typical Vfb is 0.807V.

    R4 itself is referred to as the T-type network and is recommended for low output voltages only - see datasheet Page 14:

    image

    As per the table, Rt is usually pretty close to R2, but the recommended resistor values are so much smaller than your R1/R2 values so maybe Rt is only significant in that case and the high resistances in your R1/R2 would mean that having an Rt (R4) may result in voltage errors due to the input impedance of the FB input. At least, that is my presumption.

    - Gough

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  • From what I can see, Vfb in the above is formed by the divider R1/R2, the R4 being zero just means no R4 is necessary. The ratio 47k / (301+47k) * Vout gives me Vfb = 0.810V which is about right - datasheet says typical Vfb is 0.807V.

    R4 itself is referred to as the T-type network and is recommended for low output voltages only - see datasheet Page 14:

    image

    As per the table, Rt is usually pretty close to R2, but the recommended resistor values are so much smaller than your R1/R2 values so maybe Rt is only significant in that case and the high resistances in your R1/R2 would mean that having an Rt (R4) may result in voltage errors due to the input impedance of the FB input. At least, that is my presumption.

    - Gough

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