TK11830 Ver la hoja de datos (PDF) - Toko America Inc

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TK11830

POSITIVE-TO-NEGATIVE DC-DC CONVERTER

Toko America Inc  

TK11830

CIRCUIT OPERATION (CONT.)

Oscillator Frequency:

Where:

f = 1/(tON + tOFF)

And:

tON = L x [ILPK / (VIN - VSAT)]

tOFF = L x [ILPK / (|VOUT| + VF)]

Therefore:

f=

1



ILPKL ×  VIN

1

− VSAT

+

1

VOUT + VF 

The ESR of the capacitor and the effect of the input voltage

difference for the comparator function are added to VRIPPLE.

The maximum inductor current is limited by the power

transistor switch capacity: ILPK(MAX) ~ 300 mA.

Output Voltage is as follows:

VOUT = (Vref / 5) x (1 - 4 x R2 / R1)

where: Vref = 1.28 V

R3, R4: IC Internal

R4 / R3 = 1 / 4

R1, R2 : External Resistor

Vref

R3

R1

( ( ) ( ) ) =

VIN − VSAT 2 VOUT + VF

2ILOAD VIN − VSAT + VOUT + VF

2

×1

L

R4

R2

VOUT

tON / tOFF

(|VOUT| + VF) / (VIN - VSAT)

ILPK

2 x ILOAD x [(tON / tOFF) + 1]

f

( ) ( ) VIN − VSAT 2 VOUT + VF

( ) 2ILOAD VIN − VSAT + VOUT + VF

2

•1

L

COUT

(ILOAD x tON) / VRIPPLE

January 1999 TOKO, Inc.

Page 9

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