19-1313; Rev 0; 11/97
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 synchro-
nous 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 out-
put 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 fea-
tures such as a digitally programmable output;
adjustable transient response; and selectable 0.5%, 1%,
or 2% AC load regulation. Fast recovery from load tran-
sients is ensured by a GlitchCatcher™ current-boost cir-
cuit 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% refer-
Pentium Pro™, Pentium II™, PowerPC™, Alpha™,
and K6™ Systems
GTL Bus Termination
-40°C to +85°C
-40°C to +85°C
Pin Configuration appears at end of data sheet.
*Future product—contact factory for package availability.
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.
o Better than ±1% Output Accuracy Over
Line and Load
o Greater than 90% Efficiency Using N-Channel
o Pin-Selected High Switching Frequency (300kHz,
600kHz, or 1MHz)
o Over 35A Output Current
o Digitally Programmable Output from 1.3V to 3.5V
o Current-Mode Control for Fast Transient
Response and Cycle-by-Cycle Current-Limit
o Short-Circuit Protection with Foldback Current
o Glitch-Catcher Circuit for Fast Load-Transient
o Crowbar Overvoltage Protection
o Power-Good (PWROK) Output
o Digital Soft-Start
o High-Current (2A) Drive Outputs
o Complies with Intel VRM 8.2 Specification
__________Typical Operating Circuit
TO VDD MAX1638 DH
1.3V TO 4.5V
________________________________________________________________ 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.