3.3V/5V/Adjustable-Output,

Step-Up DC-DC Converters

_______________________________________________________________________________________

7

N

N

MAX756

GND

TRIG

Q

ONE-SHOT

MINIMUM

OFF-TIME

ONE-SHOT

Q

F/F

S

R

MAXIMUM

ON-TIME

ONE-SHOT

TRIG

Q

ONE-SHOT

LX

OUT

REFERENCE

REF

LBI

LBO

3/5

SHDN

Figure 2. MAX756 Block Diagram

The ESR of both bypass and filter capacitors affects

efficiency. Best performance is obtained by using spe-

cialized low-ESR capacitors, or connecting two or more

filter capacitors in parallel. The smallest low-ESR SMT

tantalum capacitors currently available are Sprague

595D series, which are about half the size of competing

products. Sanyo OS-CON organic semiconductor

through-hole capacitors also exhibit very low ESR, and

are especially useful for operation at cold tempera-

tures. Table 1 lists suggested capacitor suppliers.

Rectifier Diode

For optimum performance, a switching Schottky diode,

such as the 1N5817, is recommended. 1N5817 equiv-

alent diodes are also available in surface-mount pack-

ages from Collmer Semiconductor in Dallas, TX, phone

(214) 233-1589. The part numbers are SE014 or

SE024. For low output power applications, a pn junc-

tion switching diode, such as the 1N4148, will also

work well, although efficiency will suffer due to the

greater forward voltage drop of the pn junction diode.