19-1239; Rev 0; 7/97
High-Voltage, Step-Down Controller with
Synchronous Rectifier for CPU Power
The MAX797H comes in a 16-pin narrow SO package.
________________________Applications
Notebook and Subnotebook Computers
____________________________Features
o 96% Efficiency
o Up to 40V Power Input
o 2.5V to 6V Adjustable Output
o
o
o
o
Preset 3.3V and 5V Outputs (at up to 10A)
5V Linear-Regulator Output
Precision 2.505V Reference Output
Automatic Bootstrap Circuit
o
o
o
o
150kHz/300kHz Fixed-Frequency PWM Operation
Programmable Soft-Start
375µA Quiescent Current (VIN = 12V, VOUT = 5V)
1µA Shutdown Current
______________Ordering Information
PART†
PIN-PACKAGE
-40°C to +85°C
16 Narrow SO
†U
__________Typical Operating Circuit
+4V TO +40V
POWER INPUT
+4.5V TO +30V
SUPPLY
INPUT
Industrial Controls
V+
__________________Pin Configuration
TEMP. RANGE
MAX797HESE
VL
SHDN
DH
MAX797H BST
TOP VIEW
SS 1
16 DH
SKIP 2
15 LX
REF 3
14 BST
+3.3V
OUTPUT
SS
GND 4
MAX797H
LX
REF
DL
13 DL
SYNC 5
SHDN 6
11 VL
FB 7
PGND
12 PGND
10 V+
SYNC
CSH 8
9
CSL
CSH
GND
CSL
SKIP
FB
SO
Idle Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800
For small orders, phone 408-737-7600 ext. 3468.
MAX797H
_______________General Description
The MAX797H high-performance, step-down DC-DC
converter provides main CPU power in battery-powered
systems. A 40V rating on the power stage’s input allows
operation with high-cell-count batteries and a wide
range of AC adaptors. This buck controller achieves
96% efficiency by using synchronous rectification and
Maxim’s proprietary Idle Mode™ control scheme to
extend battery life at full-load (up to 10A) and no-load
outputs. 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 crowbar switching currents found in
some PMOS/NMOS switch designs.
The MAX797H 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. The MAX797H is pin compatible with the popular MAX797, but has a higher input voltage range.
