LM2735XMFSLASHNOPB datasheet(15/59 Pages) TI

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( )

VIN

OUT

IN -

VOUT

VIN

D =

VOUT - IN

OUT

- D

VOUT

VIN

LM2735, LM2735-Q1

www.ti.com

SNVS485G – JUNE 2007 – REVISED AUGUST 2015

Typical Applications (continued)

8.2.1.2 Detailed Design Procedure

Table 1. Bill of Materials

PART ID

PART VALUE

MANUFACTURER

PART NUMBER

2.1-A Boost Regulator

LM2735XMF

C1, Input Capacitor

22 µF, 6.3 V, X5R

TDK

C2012X5R0J226M

C2 Output Capacitor

10 µF, 25 V, X5R

TDK

C3216X5R1E106M

C3 Comp Capacitor

330 pF

TDK

C1608X5R1H331K

D1, Catch Diode

0.4 Vf Schottky 1 A, 20 VR

STPS120M

15 µH 1.5 A

Coilcraft

MSS5131-153ML

10.2 k

Ω, 1%

Vishay

CRCW06031022F

86.6 k

Ω, 1%

Vishay

CRCW06038662F

100 k

Ω, 1%

Vishay

CRCW06031003F

8.2.1.2.1

Inductor Selection

The duty cycle (D) can be approximated quickly using the ratio of output voltage (VO) to input voltage (VIN):

(8)

Therefore:

(9)

Power losses due to the diode (D1) forward voltage drop, the voltage drop across the internal NMOS switch, the

voltage drop across the inductor resistance (RDCR), and switching losses must be included to calculate a more

accurate duty cycle (see Calculating Efficiency, and Junction Temperature for a detailed explanation). A more

accurate formula for calculating the conversion ratio is:

where

•

η equals the efficiency of the LM2735 application.

(10)

The inductor value determines the input ripple current. Lower inductor values decrease the size of the inductor,

but increase the input ripple current. An increase in the inductor value will decrease the input ripple current.

Figure 19. Inductor Current

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