TK65020 데이터 시트보기 (PDF) - Toko America Inc

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TK65020

STEP-UP VOLTAGE CONVERTER

Toko America Inc  

TK65020

ADVANCED INFORMATION

SINGLE-CELL APPLICATION (CONT.)

HIGHER-ORDER DESIGN EQUATION

D

( )[ ] VBB2 D 2ƒ L

D

2

1- 2ƒ L (RS + RL + RSW)

IOUT =

( ) VOUT

+

ROFIOUT(TGT)

+

D

2ƒ

L(VBBRU)

+

VF

-

VBB

D

1 - 2ƒ L (RS+ RL)

ƒCS [VBB2+ (VOUT+ VF)2 + (VOUT + VF - VBB)2 ]

-

2(VOUT + VF)

The equation above was developed as a closed form approximation. In order to allow a closed form approximation, the

design variable that required the least approximation was “IOUT,” as opposed to “L”.

The approximations made in the equation development have the primary consequence that error is introduced as

resistive losses become relatively large. As it is normally a practical design goal to ensure that resistive losses will be

relatively small, this seems acceptable. The variables used are:

IOUT

VOUT

VBB

f

RS

RSW

RU

Output current capability

Output voltage

Battery voltage, unloaded

Oscillator frequency

Source resistance (battery + filter)

Switch on-state resistance

ESR of upstream output capacitor

IOUT(TGT)

VF

D

L

RL

ROF

CS

Targeted output current capability

Diode forward voltage

Oscillating duty ratio of main switch

Inductance value

Inductor winding resistance

Output filter resistance

Snubber capacitance

Deriving a design solution with this equation is necessarily an iterative process. Use worst-case tolerances as described

for inductor selection, using different values for “L” to approximately achieve an “IOUT” equal to the targeted value. Then,

fine tune the parasitic values as needed and, if necessary, readjust “L” again and reiterate the process.

Page 10

January 1999 TOKO, Inc.

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