LM5177DCPR datasheet(48/60 Pages) TI2

48 / 60 page

9 Power Supply Recommendations

The LM5177 is designed to operate over a wide input voltage range. The characteristics of the input supply must

be compatible with the Absolute Maximum 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

48 to estimate the average input current.

II= POVI η

(48)

where

• η the efficiency.

One way to get a value for the efficiency is the data from the efficiency graphs in Section 8.2.3 in the worst case

operation mode. For most applications, the boost operation is the region of highest input current.

If the device 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 can

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

ceramic input capacitors form an under-damped 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. One 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. An EMI

input filter is often used in front of the controller power stage. Unless carefully designed, it can lead to instability

as well as some of the previously mentioned affects.

LM5177

SNVSBU4F – JUNE 2022 – REVISED JANUARY 2025

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LM5177DCPR Datasheet(PDF) 48 Page - Texas Instruments