SC1462A View Datasheet(PDF) - Semtech Corporation

Part Name

Description

MFG CO.

SC1462A

High Efficency Charge Pump Doubler

Semtech Corporation 

1 2 3 4 5 6 7 8 9

5+"$ )

POWER MANAGEMENT

Applications Information (Cont.)

CAPACITOR SELECTION

Capacitor selection is based on both the maximum ac-

ceptable ripple voltage and the maximum tolerable drop

at the output.

This equation can be used to calculate Cbucket for a spe-

cific Vout when Vin and Iout are known. The maximum

value for the Rsw from the Electrical Characteristics sec-

tion on page 2 should be used in order to find a worst case

number.

Ripple

LAYOUT CONSIDERATION

The peak to peak output ripple voltage is dependent on

the following factors:

1- Oscillator Frequency

2- ESR of COUT

3- Capacitance value of Cout

Item 1 is fixed and depend on the charge pump device

used. Item 2, and 3 can be optimized for best perfor-

mance and reduction of the output ripple.

Standard power board layout should be followed to ensure

proper operation. Any stray inductance should be mini-

mized, this can be achieved by using large power planes

or traces, and reducing the distances between input, out-

put and the load. All components should be placed as

close as possible to the SC1462A.

Following tables show typical capacitor characteristics, and

capacitor manufactures.

The following formula could be used for an approximation

for V . out_ripple

Vo u t_r i p p l e=

Io u t

2 x Fosc x Cout

+

2 x Iout x ESR_

Cout

Vout Drop

The voltage drop at the output is specified with the follow-

ing equation:

Component

0.1uF Ceramic 0603 Package

1.0uF Ceramic 1206 Package

10uF Ceramic 1206 Package

47uF,16V Tantalum D case

330uF,6.3V "OSCON"

330uF,16V Al. Electrolytic

820uF,4V "OSCON"

1000uF,10V Al. Electrolytic

ESR(Ω)

0.050

0.040

0.075

0.100

0.025

0.143

0.012

0.053

ESL(nH)

1.60

0.47

0.50

0.60

2.50

2.37

2.50

5.00

Vout_drop = Iout * Rout

Rout is dependent on the following factors:

1- Oscillator Frequency

2- ESR of COUT & Cbucket

3- Capacitance value of COUT & Cbucket

4- Internal switch resistance (Rsw = Total of all 4 switch

resistances).

Capacitor Manufacturers

AVX Corp.

VISHAY

Nichicon Corp.

muRata

TOKIN

Taiyo Yuden

Sanyo

Phone

(803) 448-9411

(207) 324-4140

(708) 843-7500

(800) 831-9172

(408) 432-8020

(800) 348-2496

(619) 661-6835

A good approximation for calculating the output

resistance is shown below.

R out

≅

1

Fosc x Cbucket

+ 2 × R SW + 4 × ESR_ Cbucket

+ ESR_ Cout

 2001 Semtech Corp.

6

www.semtech.com

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