19-1175; Rev 0; 12/96
High-Accuracy Step-Down Controller
with Synchronous Rectifier for CPU Power
_______________General Description
The MAX798
†
high-performance, step-down DC-DC
converter provides main CPU power in battery-powered
systems. This buck controller achieves 96% efficiency
by using synchronous rectification and Maxim’s propri-
etary Idle Mode™ control scheme to extend battery life
at full-load (up to 10A) and no-load outputs. The
MAX798’s high accuracy meets the demanding require-
ments of the latest-generation CPUs. Excellent dynamic
response corrects output transients caused by the latest
dynamic-clock CPUs within five 300kHz clock cycles.
Unique bootstrap circuitry drives inexpensive N-channel
MOSFETs, reducing system cost and eliminating the crow-
bar switching currents found in some PMOS/NMOS switch
designs.
The MAX798 has a logic-controlled and synchronizable
fixed-frequency pulse-width-modulating (PWM) operating
mode, which reduces noise and RF interference in sensi-
tive mobile-communications and pen-entry applications.
The SKIP override input allows automatic switchover to
idle-mode operation (for high-efficiency pulse skipping) at
light loads, or forces fixed-frequency mode for lowest noise
at all loads.
____________________________Features
o
96% Efficiency
o
4.5V to 30V Input Range
o
1.6V to 6V Adjustable Precision Output
o
o
o
o
o
±0.4% Max Total Load-Regulation Error
0.06%/V Max Line-Regulation Error
5V Linear-Regulator Output
Precision 2.505V Reference Output
Automatic Bootstrap Circuit
MAX798
o
150kHz/300kHz Fixed-Frequency PWM Operation
o
Programmable Soft-Start
o
1.2mA Typical Quiescent Current
(V
IN
= 12V, V
OUT
= 2.5V)
o
1µA Typical Shutdown Current
______________Ordering Information
PART
MAX798ESE
TEMP. RANGE
-40°C to +85°C
PIN-PACKAGE
16 Narrow SO
________________________Applications
Notebook and Subnotebook Computers
PDAs and Mobile Communicators
__________Typical Operating Circuit
INPUT
4.5V TO 30V
__________________Pin Configuration
TOP VIEW
V+
VL
BST
N
5V, 25mA
4.7µF
SS 1
SKIP 2
REF 3
GND 4
SYNC 5
SHDN 6
FB 7
CSH 8
16 DH
15 LX
14 BST
DH
0.1µF
R
SENSE
V
OUT
MAX798
LX
ON
SHDN
DL
PGND
CSH
CSL
N
MAX798
13 DL
12 PGND
11 VL
10 V+
9
CSL
OFF
SO
GND
FB
Idle Mode is a trademark of Maxim Integrated Products.
†
U.S. and foreign patents pending.
________________________________________________________________
Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
