
MAX756/MAX757
3.3V/5V/Adjustable-Output,
Step-Up DC-DC Converters
_______________________________________________________________________________________ 7
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.
Kommentare zu diesen Handbüchern