MAX1649 Maxim, MAX1649 Datasheet - Page 11

• Manufacturer Part Number: MAX1649
• Description: 5V/3.3V or Adjustable / High-Efficiency / Low-Dropout / Step-Down DC-DC Controllers
• Manufacturer: Maxim

The input bypass capacitor reduces peak currents
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.
Bypass REF with a 0.1µF or larger capacitor.
Table 2. Component Suppliers
AVX
Coiltronics
CoilCraft
Dale
International
Rectifier
IRC
Motorola
Nichicon
Nihon
Sanyo
Siliconix
Sprague
Sumida
United
Chemi-Con
COMPANY
Low-Dropout, Step-Down DC-DC Controllers
USA
USA
USA
USA
USA
USA
USA
USA
Japan
USA
Japan
USA
Japan
USA
USA
USA
Japan
USA
______________________________________________________________________________________
5V/3.3V or Adjustable, High-Efficiency,
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
81-7-5231-8461
[phone]
81-3-3494-7411
[phone]
81-7-2070-6306
[phone]
[phone]
[phone]
[phone]
81-3-3607-5111
[phone]
PHONE
or
or
or
Input Bypass Capacitor
Reference Capacitor
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
[phone]
81-7-5256-4158
[phone]
81-3-3494-7414
[phone]
81-7-2070-1174
[phone]
[phone]
[phone]
81-3-3607-5144
[phone]
FAX
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
anode of the rectifier, the input bypass capacitor
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.
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%)
and reduced current-limit sense voltage (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.
TRANSISTOR COUNT: 428
SUBSTRATE CONNECTED TO V+
___________________Chip Topography
SHDN
MAX1649/MAX1651 vs. MAX649/MAX651
REF
FB
OUT
(2.057mm)
0.081"
Layout Considerations
GND
EXT
CS
V+
(2.692mm)
0.106"
11