Hig h -Ac c u ra c y S t e p -Do w n Co n t ro lle r
w it h S yn c h ro n o u s Re c t ifie r fo r CP U P o w e r
V , 4.5V TO 30V
IN
R3
10Ω
2.2µF
4.7µF
MAX798
C1
C2
V+
REF
SKIP
VL
0.33µF
BST
DH
Q1
Q2
L1
12µH
0.1µF
ON
SHDN
15mΩ
V , +2.5V @ 4.2A
OUT
LX
OFF
C3
47pF
C4
MAX798
DL
PGND
C5
R1
R2
R4
1M
470pF
CSH
CSL
FB
0.01µF
SS
GND
SYNC
Q1, Q2 = SILICONIX Si4410DY or IRF7413
C1, C2 = 10µF/30V SANYO OS-CON (30SA10)
C4 = 470µF/4V SPRAGUE 594D SERIES (594D477X0004R2T)
L1 = SUMIDA CDRH127 120
R1 = 6.49kΩ, 1%
R2 = 11.5kΩ, 1%
f = 150kHz
Figure 1. Standard Application Circuit
mode that reduces losses due to MOSFET gate charge.
The step-down power-switching circuit consists of two
N-channel MOSFETs, a rectifier, and an LC output filter.
The output voltage is the average of the AC voltage at
the switching node, which is adjusted and regulated by
changing the duty cycle of the MOSFET switches. The
gate-drive signal to the N-channel high-side MOSFET
must exceed the battery voltage and is provided by a
flying capacitor boost circuit that uses a 100nF capaci-
tor connected between BST and LX.
_______________De t a ile d De s c rip t io n
The MAX798 is a BiCMOS, switch-mode power-supply
controller designed primarily for buck-topology regula-
tors in battery-powered applications where high accu-
racy, high efficiency, and low quiescent supply current
a re c ritic a l. The MAX798 a ls o works we ll in othe r
topologies such as boost, inverting, and CUK due to
the flexibility of its floating high-speed gate driver.
Light-load efficiency is enhanced by automatic idle-
mode operation—a variable-frequency pulse-skipping
6
_______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
