Rainbow Electronics MAX1639 - Manual (Page 6)

MAX1639
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
6 _______________________________________________________________________________________
N1
N2
D1
(OPTIONAL)
R3
(OPTIONAL)
R4
(OPTIONAL)
V
CC
V
DD
PWROK
BST
DH
LX
DL
PGND
CSH
FB
AGND
R8
C8
R7
CC1
CC2
CC1
1000pF
CC2
0.056 µ F
REF
C4, 1.0 µ F
CERAMIC
RC1
1k
TO
AGND
R6
100k
C5
0.1 µ F
C6
10 µ F
R5
10 Ω
TO V DD
FREQ
C7
0.1 µ F
D2
CMPSH-3
C3
0.1
µ F
L1
R1
V IN = 4.5V
TO 5.5V
C1
C2
MAX1639
V OUT = 1.1V
TO 4.5V
CSL
Figure 1. Standard Application Circuit
_______Standard Application Circuits
The predesigned MAX1639 circuit shown in Figure 1
meets a wide range of applications with output currents
up to 35A. Use Table 1 to select components appropri-
ate for the desired output current range, and adapt the
evaluation kit PC board layout as necessary. This cir-
cuit represents a good set of trade-offs between cost,
size, and efficiency while staying within the worst-case
specification limits for stress-related parameters, such
as capacitor ripple current.
The MAX1639 circuit was designed for the specified fre-
quencies. Do not change the switching frequency with-
out first recalculating component values—particularly
the inductance, output filter capacitance, and RC1
resistance values.
___________________Detailed Description
The MAX1639 is a BiCMOS power-supply controller
designed for use in switch-mode, step-down (buck)
topology DC-DC converters. Synchronous rectification
provides high efficiency. It is intended to provide the
high precision, low noise, excellent transient response,
and high efficiency required in today’s most demand-
ing applications.