LM5145 datasheet(53/69 Pages) TI

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11 Power Supply Recommendations

The LM25143 buck controller is designed to operate over a wide input voltage range of 3.5 V to 42 V. The

characteristics of the input supply must be compatible with the Absolute Maxmimum Ratings and Recommended

Operating Conditions. In addition, the input supply must be capable of delivering the required input current to the

fully-loaded regulator. Use Equation 46 to estimate the average input current.

OUT

(46)

where

• η is the efficiency.

If the regulator is connected to an input supply through long wires or PCB traces with a large impedance,

take special care to achieve stable performance. The parasitic inductance and resistance of the input cables

may have an adverse effect on regulator operation. The parasitic inductance in combination with the low-ESR

ceramic input capacitors form an underdamped resonant circuit. This circuit can cause overvoltage transients

at VIN each time the input supply is cycled ON and OFF. The parasitic resistance causes the input voltage to

dip during a load transient. The best way to solve such issues is to reduce the distance from the input supply

to the regulator and use an aluminum or tantalum input capacitor in parallel with the ceramics. The moderate

ESR of the electrolytic capacitors helps to damp the input resonant circuit and reduce any voltage overshoots.

A capacitance in the range of 10 µF to 47 µF is usually sufficient to provide parallel input damping and helps to

hold the input voltage steady during large load transients.

An EMI input filter is often used in front of the regulator that, unless carefully designed, can lead to instability as

well as some of the affects mentioned above. The Simple Success with Conducted EMI for DC-DC Converters

Application Report provides helpful suggestions when designing an input filter for any switching regulator.

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LM25143

SNVSC10 – MARCH 2022

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LM5145 Datasheet(PDF) 53 Page - Texas Instruments