LM5019 datasheet(13/25 Pages) TI1

13 / 25 page

IOUT(MAX)

CIN

8 x CSW x ûVIN

OUT

L(MIN)

REF

25mV

ûIL

COUT =

8 x Csw x ûVripple

VIN

BST

RON

RTN

VCC

VIN

VOUT

RFB1

RUV1

RON

COUT

CBST

CIN

RFB2

RUV2

UVLO

CVCC

LM5019

7.5V-100V

Shutdown

CBYP

LM5019

www.ti.com

SNVS788E – JANUARY 2012 – REVISED DECEMBER 2013

Figure 15. Reference Schematic for Selection of External Components

Output Capacitor:

The output capacitor is selected to minimize the capacitive ripple across it. The maximum ripple is observed at

maximum input voltage and is given by:

where

•

ΔVripple is the voltage ripple across the capacitor

(11)

Substituting

ΔVripple = 10mV gives COUT = 2.94 μF. A 4.7 μF standard value is selected. An X5R or X7R type

capacitor with a voltage rating 16 V or higher should be selected.

Series Ripple Resistor RC:

The series resistor should be selected to produce sufficient ripple at the feedback node. The ripple produced by

RC is proportional to the inductor current ripple, and therefore RC should be chosen for minimum inductor current

ripple which occurs at minimum input voltage. The RC is calculated by the equation:

(12)

This gives an RC of greater than or equal to 10.8 Ω. Selecting RC = 11 Ω results in ~1 V of maximum output

voltage ripple. For applications requiring lower output voltage ripple, Type II or Type III ripple injection circuits

should be used as described in the section Ripple Configuration.

VCC and Bootstrap Capacitor:

The VCC capacitor provides charge to bootstrap capacitor as well as internal circuitry and low side gate driver.

The Bootstrap capacitor provides charge to high side gate driver. A good value for CVCC is 1 μF. A good value for

CBST is 0.01 μF.

Input Capacitor:

Input capacitor should be large enough to limit the input voltage ripple:

(13)

choosing a

ΔVIN = 0.5 V gives a minimum CIN = 0.12 μF. A standard value of 1 μF is selected. The input

capacitor should be rated for the maximum input voltage under all conditions. A 100 V, X7R dielectric should be

selected for this design.

Input capacitor should be placed directly across VIN and RTN (pin 2 and 1) of the IC. If it is not possible to place

all of the input capacitor close to the IC, a 0.1

μF capacitor should be placed near the IC to provide a bypass

path for the high frequency component of the switching current. This helps limit the switching noise.

UVLO Resistors:

The UVLO resistors RFB1 and RFB2 set the UVLO threshold and hysteresis according to the following relationship:

Submit Documentation Feedback

Product Folder Links: LM5019

LM5019 Datasheet(PDF) 13 Page - Texas Instruments

LM5019 Datasheet(HTML) 13 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Datasheet Download

Link URL