Starting Up under Load
The
Typical Operating Characteristics
show the Start-
Up Voltage vs. Load Current graph for bootstrapped-
mode operation. This graph depends on the type
of power switch used. The MAX770–MAX773 are
not designed to start up under full load in boot-
strapped mode with low input voltages.
Layout Considerations
Due to high current levels and fast switching wave-
forms, which radiate noise, proper PC board layout is
essential. Protect sensitive analog grounds by using a
star ground configuration. Minimize ground noise by
connecting GND, the input bypass capacitor ground
lead, and the output filter capacitor ground lead to a
single point (star ground configuration). Also, minimize
lead lengths to reduce stray capacitance, trace resis-
tance, and radiated noise. Place input bypass capaci-
tor C2 as close as possible to V+ and GND.
Excessive noise at the V+ input may falsely trigger the
timing circuitry, resulting in short pulses at EXT. If this
occurs it will have a negligible effect on circuit efficien-
cy. If desired, place a 4.7µF directly across the V+ and
GND pins (in parallel with the 0.1µF C2 bypass capaci-
tor) to reduce the noise at V+.
MAX770–MAX773
5V/12V/15V or Adjustable, High-Efficiency,
Low I
Q
, Step-Up DC-DC Controllers
______________________________________________________________________________________
19
Table 2. Component Suppliers
PRODUCTION INDUCTORS CAPACITORS TRANSISTORS
Surface Mount
Matsuo
267 series
Sprague
595D series
Through Hole
Sumida
CD54 series
CDR125 series
Coiltronics
CTX20 series
Motorola
1N5817–1N5822
MUR115 (high voltage)
Nihon
EC10 series
DIODES
Sumida
RCH855 series
RCH110 series
Renco
RL1284-18
Sanyo
OS-CON series
Nichicon
PL series
United Chemi-Con
LXF series
NPN
Zetex
ZTX694B
Coiltronics
Matsuo
USA: (714) 969-2491 (714) 960-6492
Japan: 81-6-337-6450 81-6-337-6456
Nichicon USA: (847) 843-7500 (847) 843-2798
Nihon USA: (805) 867-2555 (805) 867-2698
Renco USA: (516) 586-5566 (516) 586-5562
Sanyo
USA: (619) 661-6835 (619) 661-1055
Japan: 81-7-2070-6306 81-7-2070-1174
Sumida
USA: (847) 956-0666
Japan: 81-3-3607-5111 81-3-3607-5144
United Chemi-Con USA: (714) 255-9500 (714) 255-9400
N-FET
Siliconix
Si9410DY
Si9420DY (high voltage)
Motorola
MTP3055EL
MTD20N03HDL
USA: (561) 241-7876 (561) 241-9339
SUPPLIER PHONE FAX
Zetex
USA: (516) 543-7100 (516) 864-7630
UK: 44-61-627-4963 44-61-627-5467
