3.3V/5V or Adjustable,

Step-Up/Down DC-DC Converters

10

______________________________________________________________________________________

ing input of the low-battery comparator. Since LBI cur-

rent is less than 50nA, R3 and R4 can be large

(typically 100k

Ω to 1MΩ), minimizing input supply load-

ing. If the low-battery comparator is not used, connect

LBI+ to PS and LBI- to REF, leaving LBO unconnected.

Inductor Selection

A 22µH inductor value performs well in most

MAX710/MAX711 applications. The inductance value is

not critical, however, since the MAX710/MAX711 work

with inductors in the 18µH to 100µH range. Smaller

inductance values typically offer a smaller size for a

given series resistance, allowing the smallest overall

circuit dimensions. Circuits using larger inductance val-

ues exhibit higher output current capability and larger

physical dimensions for a given series resistance. The

inductor’s incremental saturation current rating should

be greater than the peak switch-current limit, which is

1.5A for ILIM = GND and 0.8A for ILIM = PS. However,

it is generally acceptable to bias most inductors into

saturation by as much as 20%, although this slightly

reduces efficiency. The inductor’s DC resistance signif-

icantly affects efficiency. See Tables 2 and 3 for a list of

suggested inductors and suppliers.

Capacitor Selection

A 100µF, 16V, 0.1

Ω equivalent series resistance (ESR),

surface-mount tantalum (SMT) output filter capacitor,

C2, typically exhibits 50mV output ripple when stepping

up from 2V to 5V at 100mA. Smaller capacitors (down

to 10µF with higher ESRs) are acceptable for light loads

or in applications that can tolerate higher output ripple.

The ESR of both bypass and filter capacitors affects

efficiency and output ripple. Output voltage ripple is the

product of the peak inductor current and the output

capacitor’s ESR. Use low-ESR capacitors for best per-

formance, or connect two or more filter capacitors in

parallel. Low-ESR, SMT capacitors are currently avail-

able from Sprague (595D series) and AVX (TPS series).

Sanyo OS-CON organic-semiconductor through-hole

capacitors also exhibit very low ESR and are especially

useful for operation at cold temperatures. The output

capacitor, C3, needs to be only 4.7µF to maintain linear

regulator stability. See Tables 2 and 3 for a list of sug-

gested capacitors and suppliers.

Rectifier Diode

For optimum performance, use a switching Schottky

diode. Refer to Tables 2 and 3 for the suggested diode

and supplier.

__________Applications Information

The MAX710/MAX711 high-frequency operation makes

PC layout important for minimizing ground bounce and

noise. Keep the IC’s GND pin and the ground leads of

C1 and C2 (Figure 1) less than 0.2in. (5mm) apart. Also

keep all connections to the FB and LX pins as short as

possible. To maximize output power and efficiency and

minimize output ripple voltage, use a ground plane and

solder the IC’s GND pin directly to the ground plane.

4.7µF, 16V tantalum capacitor

Sprague 595D475X0016A2T

RECTIFIERS (D1)

Schottky diode

Motorola MBRS130T3

Coilcraft DO33-08P-223

INDUCTORS (L1)

Sumida CD75-220 (1.5A),

CDRH-74-220 (1.23A), or

CD54-220

CAPACITORS

100µF, 16V low-ESR tantalum capacitor

AVX TPSE107M016R0100 or

Sprague 593D107X0016E2W

Table 2. Component Selection

Table 3. Component Suppliers

(803) 626-3123

(803) 946-0690

FAX

AVX

SUPPLIER

PHONE

(847) 639-1469

(847) 639-6400

Coilcraft

(602) 994-6430

(602) 303-5454

(603) 224-1430

(603) 224-1961

Sprague

Motorola

(847) 956-0702

(847) 956-0666

Sumida

___________________Chip Information

TRANSISTOR COUNT: 661

SUBSTRATE CONNECTED TO GND

(619) 661-1055

(619) 661-6835

Sanyo