MAX1561/MAX1599
input and output ripple, but at the expense of size and
higher cost. C
COMP
stabilizes the converter and con-
trols soft-start. Connect a 0.1µF capacitor from COMP
to GND. For stable operation, C
OUT
must not exceed
10 times C
COMP
.
Inductor Selection
Inductor values range from 10µH to 47µH. A 22µH
(47µH for the MAX1599) inductor optimizes the efficien-
cy for most applications while maintaining low 15mV
P-P
input ripple. With input voltages near 5V, a larger value
of inductance can be more efficient. To prevent core
saturation, ensure that the inductor-saturation current
rating exceeds the peak inductor current for the appli-
cation. Calculate the peak inductor current with the fol-
lowing formula:
Schottky Diode Selection
The MAX1561/MAX1599s’ high switching frequency
demands a high-speed rectification diode (D1) for opti-
mum efficiency. A Schottky diode is recommended due
to its fast recovery time and low forward-voltage drop.
Ensure that the diode’s average and peak current rating
exceed the average output current and peak inductor
current. In addition, the diode’s reverse breakdown volt-
age must exceed V
OUT
. The RMS diode current can be
calculated from:
Applications Information
PC Board Layout
Due to fast switching waveforms and high-current
paths, careful PC board layout is required. An evalua-
tion kit (MAX1561EVKIT) is available to speed design.
Order MAX1599 samples separately.
When laying out a board, minimize trace lengths between
the IC and R
SENSE
, the inductor, the diode, the input
capacitor, and the output capacitor. Keep traces short,
direct, and wide. Keep noisy traces, such as the LX node
trace, away from CS. The IN bypass capacitor (C
IN
)
should be placed as close to the IC as possible. PGND
and GND should be connected directly to the exposed
paddle underneath the IC. The ground connections of
C
IN
and C
OUT
should be as close together as possible.
The traces from IN to the inductor and from the Schottky
diode to the LEDs may be longer.
Chip Information
TRANSISTOR COUNT: 2895
PROCESS: BiCMOS
