LM5145 datasheet(16/60 Pages) TI2

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6.3 Feature Description

6.3.1 Input Voltage Range (VIN )

The LM25139 operational input voltage range is from 4V to 42V. The device is intended for step-down

conversions from 12V and 24V automotive supply rails. The application circuit in Figure 6-1 shows all the

necessary components to implement an LM25139 based wide-VIN step-down regulator using a single supply.

The LM25139 uses an internal LDO subregulator to provide a 5V VCC bias rail for the gate drive and control

circuits (assuming the input voltage is higher than 5V plus the necessary subregulator dropout specification).

In high input voltage applications, make sure the VIN and SW pins do not exceed the absolute maximum voltage

rating of 45V during line or load transient events. Voltage excursions that exceed the Absolute Maximum Ratings

can damage the IC. Proceed carefully during PCB board layout and use high-quality input bypass capacitors to

minimize voltage overshoot and ringing.

FPWM/SYNC

AGND

PGND

VOUT

ISNS

CBOOT

VIN

COMP

VCC

LM25139

RCOMP

CCOMP

CHF

CVCC

CBOOT

CIN

COUT

VIN = 4V...36V

VOUT = 3.3V

IOUT = 15A

SYNC

op onal

VCC

47 F

4.7nF

10 F

6.04k

100pF

1.5 H

53.6k

4.7 F

0.1 F

Figure 6-1. Typical Application Schematic

As VIN approaches VOUT, the LM25139 skips tOFF cycles to allow the controller to extend the duty cycle up to

approximately 99%. See also Figure 6-2.

Use Equation 1 to calculate when the LM25139 enters dropout mode.

• tSW is the oscillator time period

• tOFF is the minimum off time, typical 80ns

VINmin = VOUT×tSW

tSW+ tOFFmin

(1)

LM25139

SLVSJ80 – OCTOBER 2025

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