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RT34063AGN

DC-to-DC Converter Control Circuits

Richtek Technology 

RT34063A

Design Formula Table

Calculation

ton/toff

(ton + toff)

toff

ton

CT

Ipk (SWITCH)

RSC

Step-up

VOUT + VF − VIN (MIN)

VIN (MIN) − VSAT

1

f

ton + toff

ton + 1

toff

(ton + toff ) − toff

4.0 × 10−5 ton

2 IOUT (MAX) ⎜⎛ ton + 1⎟⎞

⎝ toff ⎠

0.3/Ipk (SWITCH)

L (min)

( ) ⎜⎜⎝⎛

VIN(MIN) − VSAT

Ipk(SWITCH)

⎟⎟⎠⎞ton(MAX)

Step-down

VOUT + VF

VIN(MIN) − VSAT − VOUT

1

f

ton + toff

ton + 1

toff

(ton + toff ) − toff

4.0 × 10−5 ton

2 IOUT (MAX)

0.3/Ipk (SWITCH)

( ) ⎜⎜⎝⎛

VIN(MIN) − VSAT

Ipk(SWITCH)

⎟⎟⎠⎞ ton(MAX )

Voltage-Inverting

V OUT + V F

V IN − V SAT

1

f

ton + toff

ton + 1

toff

(ton + toff ) − toff

4.0 × 10−5 ton

2 IOUT(MAX) ⎜⎛ ton + 1⎟⎞

⎝ toff ⎠

0.3/Ipk (SWITCH)

( ) ⎜⎜⎝⎛

VIN(MIN) − VSAT

Ipk(SWITCH)

⎟⎟⎠⎞ ton(MAX )

CO

9 IOUT ton

Vripple (pp)

Ipk(SWITCH)(ton + toff)

8Vripple(pp)

9 IOUT ton

Vripple (pp)

VSAT

: Saturation voltage of the output switch.

VF

: Forward voltage drop of the output rectifier.

The following power supply characteristics must be chosen:

VIN

VOUT

IOUT

: Nominal input voltage.

R2

: Desired output voltage VOUT = 1.25(1+ )

R1

: Desired output current.

f

: Minimum desired output switching frequency at the selected values of Vin and IO.

Vripple(pp)

: Desired peak-to-peak output ripple voltage. In practice, the calculated capacitor value needs to be increased

due to its equivalent series resistance and board layout. The ripple voltage should be kept to a low value

since it directly affects the line and load regulation.

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8

DS34063A-13 March 2007

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