3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
N
N
MAX756
GND
V
OUT
V
IN
TRIGQ
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.
