LM65645 datasheet(32/66 Pages) TI2

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input voltage ripple and maintain the input voltage during load transients. In addition, a high frequency bypass

capacitance of 2 × 100nF ceramic capacitor must be used at the input, as close a possible to the regulator.

Place one capacitor on each side of the package and connected directly to the VIN and GND pins of the device.

This requirement provides a high frequency bypass for the control circuits internal to the device.

For this example, 2 × 4.7µF, 100V, X7R (or better) ceramic capacitors are chosen. The 100nF capacitors must

also be rated at 100V with an X7R dielectric.

Using an electrolytic capacitor on the input in parallel with the ceramics is often desirable. This statement is

especially true if long leads or traces are used to connect the input supply to the regulator, or an input EMI

filter is used. The moderate ESR of this capacitor can help damp any ringing on the input supply caused by

any inductance on the input. The use of this additional capacitor also helps with voltage dips caused by input

supplies with unusually high impedance.

Most of the input switching current passes through the ceramic input capacitor or capacitors. The approximate

RMS value of this current can be calculated from Equation 12 and must be checked against the manufacturers

maximum ratings.

(12)

8.2.2.7 CBOOT

The LM656x5 requires a bootstrap capacitor connected between the BOOT pin and the SW pin. This capacitor

stores energy that is used to supply the high-side gate driver for the power MOSFET, along with other critical

control circuits. A high-quality ceramic capacitor of 100nF and at least 16V is required.

8.2.2.8 External UVLO

In some cases, an input UVLO level different than that provided internal to the device is needed. This need can

be accomplished by using the circuit shown in Figure 8-3. The turn-on voltage is designated as VON while the

turn-off voltage is VOFF. First, a value for RENB is chosen in the range of 10kΩ to 100kΩ, then use Equation 13

and Equation 14 to calculate RENT and VOFF.

RENT

RENB

VIN

Figure 8-3. Setup for External UVLO Application

RENT =RENB× VONVEN−H −1

(13)

VOFF =VEN−L× VONVEN−H

(14)

where

• VON = VIN turn-on voltage

• VOFF = VIN turn-off voltage

8.2.2.9 Maximum Ambient Temperature

As with any power conversion device, the regulator dissipates internal power while operating. The effect of

this power dissipation is to raise the internal temperature of the converter above ambient. The internal die

LM65625, LM65635, LM65645

SNVSCH3 – JUNE 2025

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LM65645 Datasheet(PDF) 32 Page - Texas Instruments

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