SC1462

© 2000 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

HIGH OUTPUT CURRENT

CHARGE PUMP DOUBLER

October 20, 2000

7

TEL:805-498-2111 FAX:805-498-3804 WEB:http://www.semtech.com

LAYOUT CONSIDERATION

Standard power board layout should followed to en-

sure proper operation. Any stray inductance should

be minimized, this can be achieved by using large

power planes or traces, and reducing the distances

between input, output and the load. All components

should be placed as close as possible to the SC1462.

Following tables show typical capacitor characteris-

tics, and capacitor manufactures.

CAPACITOR SELECTION

Capacitor selection is based on both the maximum

acceptable ripple voltage and the maximum tolerable

drop at the output.

Ripple

The peak to peak output ripple voltage is dependent

on the following factors:

1- Oscillator Frequency

2- ESR of C

OUT

3- Capacitance value of C

out

Item 1 is fixed and depend on the charge pump de-

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

performance and reduction of the output ripple.

The following formula could be used for an approxi-

mation for V

Vout Drop

The voltage drop at the output is specified with the

following equation:

Vout_drop = Iout * Rout

Rout is dependent on the following factors:

1- Oscillator Frequency

2- ESR of C

3- Capacitance value of C

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

switch resistances).

A good approximation for calculating the output resis-

tance is shown below.

This equation can be used to calculate Cbucket for a

specific Vout when Vin and Iout are known. The

maximum value for the Rsw from the Electrical Char-

acteristics section on page 2 should be used in order

to find a worst case number.

Component

ESR

(Ohms)

ESL

(nH)

0.1 uF Ceramic 0603 package

0.050

1.60

1.0 uF Ceramic 1206 package

0.040

0.47

10 uF Ceramic 1206 package

0.075

0.5

47 uF, 16V Tantalum D case

0.100

0.60

330 uF, 6.3V “OSCON”

0.025

2.5

330 uF, 16V Al Electrolytic

0.143

2.37

820 uF, 4.0V “OSCON”

0.012

2.5

1000 uF, 10V Al Electrolytic

0.053

5

Capacitor Manufacturers

Phone

AVX Corp.

(803)-448-9411

VISHAY

(207)-324-4140

Nichicon Corp.

(708)-843-7500

muRata

(800)-831-9172

TOKIN

(408)-432-8020

Taiyo Yuden

(800)-348-2496

Sanyo

(619)-661-6835

out

out

out

osc

out

out_ripple

C

ESR_

x

I

x

2

C

x

F

x

2

I

V

+

=

out

bucket

SW

bucket

osc

out

C

ESR_

C

ESR_

4

R

2

C

x

F

1

R

+

×

+

×

+

≅