19-1313; Rev 1; 8/05
KIT
ATION
EVALU
BLE
AVAILA
High-Speed Step-Down Controller with
Synchronous Rectification for CPU Power
The MAX1638 is an ultra-high-performance, step-down
DC-DC controller for CPU power in high-end computer
systems. Designed for demanding applications in which
output voltage precision and good transient response are
critical for proper operation, it delivers over 35A from 1.3V
to 3.5V with ±1% total accuracy from a +5V ±10% supply.
Excellent dynamic response corrects output transients
caused by the latest dynamically clocked CPUs. This
controller achieves over 90% efficiency by using synchronous rectification. Flying-capacitor bootstrap circuitry
drives inexpensive, external N-channel MOSFETs.
The switching frequency is pin-selectable for 300kHz,
600kHz, or 1MHz. High switching frequencies allow the
use of a small surface-mount inductor and decrease output filter capacitor requirements, reducing board area
and system cost.
The MAX1638 is available in 24-pin SSOP and QSOP
(future package) packages, and offers additional features such as a digitally programmable output;
adjustable transient response; and selectable 0.5%, 1%,
or 2% AC load regulation. Fast recovery from load transients is ensured by a GlitchCatcher™ current-boost circuit that eliminates delays caused by the buck inductor.
Output overvoltage protection is enforced by a crowbar
circuit that turns on the low-side MOSFET with 100%
duty factor when the output is 200mV above the normal
regulation point. Other features include internal digital
soft-start, a power-good output, and a 3.5V ±1% reference output.
____________________________Features
♦ Better than ±1% Output Accuracy Over
Line and Load
♦ Greater than 90% Efficiency Using N-Channel
MOSFETs
♦ Pin-Selected High Switching Frequency (300kHz,
600kHz, or 1MHz)
♦ Over 35A Output Current
♦ Digitally Programmable Output from 1.3V to 3.5V
♦ Current-Mode Control for Fast Transient
Response and Cycle-by-Cycle Current-Limit
Protection
♦ Short-Circuit Protection with Foldback Current
Limiting
♦ Glitch-Catcher Circuit for Fast Load-Transient
Response
♦ Crowbar Overvoltage Protection
♦ Power-Good (PWROK) Output
♦ Digital Soft-Start
♦ High-Current (2A) Drive Outputs
♦ Complies with Intel VRM 8.2 Specification
Typical Operating Circuit
INPUT
+5V
VCC
________________________Applications
Pentium Pro™, Pentium II™, PowerPC™, Alpha™,
and K6™ Systems
Workstations
Desktop Computers
LAN Servers
GTL Bus Termination
Ordering Information
PART
MAX1638EAG
MAX1638EAG+
TEMP RANGE
24 SSOP
BST
MAX1638 DH
LX
OUTPUT
1.3V TO 4.5V
PWROK
D0
D1
D2
D3
D4
DL
PGND
PIN-PACKAGE
-40°C to +85°C
TO VDD
VDD
AGND
-40°C to +85°C
24 QSOP
+Denotes lead-free package.
Pin Configuration appears at end of data sheet.
REF
CSH
LG
CSL
FREQ
CC1
FB
CC2
Pentium Pro and Pentium II are trademarks of Intel Corp.
PowerPC is a trademark of IBM Corp.
Alpha is a trademark of Digital Equipment Corp.
K6 is a trademark of Advanced Micro Devices.
GlitchCatcher is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
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MAX1638
General Description
