5 V/3 .3 V o r Ad ju s t a b le , Hig h -Effic ie n c y,
Lo w -Dro p o u t , S t e p -Do w n DC-DC Co n t ro lle rs
49/MAX651
La yo u t Co n s id e ra t io n s
Table 2. Component Suppliers
Proper PC board layout is essential because of high
current levels and fast switching waveforms that radi-
ate noise. Minimize ground noise by connecting the
a nod e of the re c tifie r, the inp ut b yp a s s c a p a c itor
ground lead, and the output filter capacitor ground
lead to a single point (“star” ground configuration). A
ground plane is recommended. Also minimize lead
lengths to reduce stray capacitance, trace resistance,
and radiated noise. In particular, the traces connected
to FB (if an external resistor divider is used) and EXT
must be short. Place the 0.1µF ceramic bypass capac-
itor as close as possible to the V+ and GND pins.
COMPANY
PHONE
FAX
(207) 282-5111
or
(800) 282-4975
AVX
USA
(207) 283-1941
Coiltronics
CoilCraft
Dale
USA
USA
USA
(407) 241-7876
(708) 639-6400
(402) 564-3131
(407) 241-9339
(708) 639-1469
(402) 563-1841
International
Rectifier
USA
USA
(310) 322-3331
(310) 322-3332
(512) 992-3377
IRC
(512) 992-7900
(602) 244-3576
or
(602) 244-5303
Motorola
USA
(602) 244-4015
MAX1 6 4 9 /MAX1 6 5 1 vs . MAX6 4 9 /MAX6 5 1
The MAX1649 and MAX1651 are pin compatible with
the MAX649 and MAX651, but have been optimized for
improved dropout performance and efficiency—partic-
ularly with low input voltages. The MAX1649/MAX1651
feature increased maximum switch duty cycle (96.5%)
a nd re d uc e d c urre nt-limit s e ns e volta g e (110mV).
Their predecessors, the MAX649/MAX651, use a high-
er two-step (210mV/110mV) current-limit sense voltage
to provide tighter current-sense accuracy and reduced
inductor peak current at light loads.
USA
Japan
(708) 843-7500
81-7-5231-8461
(708) 843-2798
81-7-5256-4158
Nichicon
Nihon
USA
Japan
(805) 867-2555
81-3-3494-7411
(805) 867-2556
81-3-3494-7414
USA
Japan
(619) 661-6835
81-7-2070-6306
(619) 661-1055
81-7-2070-1174
Sanyo
(408) 988-8000
or
(800) 554-5565
Siliconix
USA
USA
(408) 970-3950
Sprague
Sumida
(603) 224-1961
(603) 224-1430
USA
Japan
(708) 956-0666
81-3-3607-5111
(708) 956-0702
81-3-3607-5144
___________________Ch ip To p o g ra p h y
United
Chemi-Con
USA
(714) 255-9500
(714) 255-9400
GND
OUT
Input Bypass Capacitor
The inp ut b yp a s s c a p a c itor re d uc e s p e a k c urre nts
drawn from the voltage source, and also reduces the
amount of noise at the voltage source caused by the
switching action of the MAX1649/MAX1651. The input
voltage source impedance determines the size of the
capacitor required at the V+ input. As with the output fil-
ter capacitor, a low-ESR capacitor is recommended.
Bypass the IC separately with a 0.1µF ceramic capac-
itor placed close to the V+ and GND pins.
EXT
FB
0.106"
(2.692mm)
CS
SHDN
REF
Reference Capacitor
Bypass REF with a 0.1µF or larger capacitor.
V+
0. 081"
(2. 057mm)
TRANSISTOR COUNT: 428
SUBSTRATE CONNECTED TO V+
______________________________________________________________________________________ 11
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
