Step-Up/Down DC-DC Converter

in QSOP Package

_______________________________________________________________________________________

9

Capacitor Selection

The equivalent series resistance (ESR) of both bypass

and filter capacitors affects efficiency and output rip-

ple. Output voltage ripple is the product of peak induc-

tor current and filter capacitor ESR. Use low-ESR

capacitors for best performance, or connect two or

more filter capacitors in parallel.

A 100µF, 16V, input bypass capacitor (C1) with low

ESR reduces peak battery currents and reflected noise

due to inductor current ripple. Smaller ceramic capaci-

tors may also be used for light loads or in applications

that can tolerate higher input ripple.

A 100µF, 16V, surface-mount (SMT) tantalum PS filter

capacitor (C2) with 0.1

Ω ESR typically exhibits 20mV

output ripple (at OUT) when stepping up from 2V to 5V

at 100mA load. Smaller capacitors (down to 10µF with

higher ESR) are acceptable for light loads or in applica-

tions that can tolerate higher output ripple.

Only 4.7µF is needed at OUT (C4) to maintain linear

regulator stability. During boost operation, this capaci-

tor reduces output voltage spikes from the step-up con-

verter by forming an R-C lowpass filter along with the

P-channel MOSFET on-resistance. Output ripple can be

further reduced by increasing C4.

See Tables 4 and 5 for a list of suggested capacitors

and suppliers.

Diode Selection

The MAX1672’s high switching frequency demands a

high-speed rectifier. Schottky diodes, such as the

1N5817 or MBRS130T3, are recommended. Make sure

the diode’s current rating exceeds the maximum load

current. See Tables 4 and 5 for a list of suggested

diodes and suppliers.

Table 3. Suggested Inductor Values

Table 4. Suggested Components

ILIM

INDUCTOR VALUE

(µH)

0 (5V)

0 (0.5A)

10 to 22

0 (5V)

1 (0.8A)

10

3/

5

1 (3.3V)

0 (0.5A)

10

1 (3.3V)

1 (0.8A)

4.7 to 10

INDUCTORS

Sumida

CD43-100 (1.04A, 0.182

Ω)

CD54-100 (1.44A, 0.100

Ω)

CDRH73-100 (1.68A, 0.072

Ω)

L1

10µH

Coilcraft

DT1608C-103 (0.7A, 0.095

Ω)

CAPACITORS

AVX

TPSE Series

Sprague

593D or 595D Series

Tantalum

DIODES

Motorola

MBRS130LT3 (1.0A, 30V)

MBR0520LT3 (0.5A, 20V)

Schottky

1N5817 Equivalent

International Rectifier

10BQ40 (1.0A, 40V)

Table 5. Component Suppliers

PHONE

AVX

(803) 946-0690

Coilcraft

(847) 639-6400

SUPPLIER

International

Rectifier

(310) 322-3331

Motorola

(602) 303-5454

FAX

(803) 626-3123

(847) 639-1469

(310) 322-3332

(602) 994-6430

Sanyo

(619) 661-6835

(619) 661-1055

Sprague

(603) 224-1961

(603) 224-1430

Sumida

(847) 956-0666

(847) 956-0702