Datasheet

Input Filter Capacitor
The input capacitor (C
IN
) must provide the peak current
into the inverter. This capacitor is selected the same way
as the output capacitor (C
OUT
). Under ideal conditions,
the RMS current for the input capacitor is the same as the
output capacitor. The capacitor value and ESR must be
selected to reduce noise to an acceptable value and also
handle the ripple current (I
NRMS
where:
O
2
NRMS MAX MAX
MAX
1.2 xI
I xD D
(I D )
−
−
=
Bypass Capacitor
In addition to C
IN
and C
OUT
, other ceramic bypass
capacitors are required with the MAX1846/MAX1847.
Bypass REF to GND with a 0.1µF or larger capacitor.
Bypass V
L
to GND with a 0.47µF or larger capacitor. All
bypass capacitors should be located as close to their
respective pins as possible.
PC Board Layout Guidelines
Good PC board layout and routing are required in high-
frequency-switching power supplies to achieve good
regulation, high efficiency, and stability. It is strongly
recommended that the evaluation kit PC board layouts
be followed as closely as possible. Place power components
as close together as possible, keeping their traces short,
direct, and wide. Avoid interconnecting the ground pins
of the power components using vias through an internal
ground plane. Instead, keep the power components close
together and route them in a “star” ground configuration
using component-side copper, then connect the star
ground to internal ground using multiple vias.
Main Application Circuits
The MAX1846/MAX1847 are extremely versatile devices.
Figure 2 shows a generic schematic of the MAX1846.
Table 1 lists component values for several typical appli-
cations. These component values also apply to the
MAX1847. The first two applications are featured in the
MAX1846/MAX1847 EV kit.
Figure 2. MAX1846 Main Application Circuit
COMP
C
COMP
R
COMP
R
FREQ
GND
FREQ
VL
V
IN
V
OUT
C
OUT
C
IN
1
9
8
7
5
4
2
3
P
L1
R
CS
C
FB
D1
10
22k
0.47µF
0.1µF
6
EXT
PGND
REF
IN
CS
FB
MAX1846
R2
R1
APPLICATION B
ONLY
NOTE: APPLICATIONS A & B USE POS CAPACITORS. APPLICATIONS C & D USE ALUMINUM ELECTROLYTIC CAPACITORS.
C
COMP2
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MAX1846–MAX1847 High-Efciency, Current-Mode,
Inverting PWM Controller