19-3970; Rev 2; 3/07
3A, 2MHz Step-Down Regulator
with Integrated Switches
The MAX8643 high-efficiency switching regulator deliv-
ers up to 3A load current at output voltages from 0.6V
to (0.9 x VIN).The IC operates from 2.35V to 3.6V, mak-
ing it ideal for on-board point-of-load and postregula-
tion applications. Total output error is less than ±1%
over load, line, and temperature.
The MAX8643 features fixed-frequency PWM mode
operation with a switching frequency range of 500kHz
to 2MHz set by an external resistor. High-frequency
operation allows for an all-ceramic capacitor design.
The high operating frequency also allows for small-size
The low-resistance on-chip nMOS switches ensure high
efficiency at heavy loads while minimizing critical induc-
tances, making the layout a much simpler task with
respect to discrete solutions. Following a simple layout
and footprint ensures first-pass success in new designs.
The MAX8643 comes with a high-bandwidth (> 14MHz)
voltage-error amplifier. The voltage-mode control archi-
tecture and the voltage-error amplifier permit a type III
compensation scheme to be utilized to achieve maxi-
mum loop bandwidth, up to 20% of the switching fre-
quency. High loop bandwidth provides fast transient
response, resulting in less required output capacitance
and allowing for all-ceramic capacitor designs.
The MAX8643 provides two tri-state logic inputs to
select one of nine preset output voltages. The preset
output voltages allow customers to achieve ±1% out-
put-voltage accuracy without using expensive 0.1%
www.DarteasSihsetoert4sU. .Icnomaddition, the output voltage can be set to
any customer value by either using two external resis-
tors at the feedback with 0.6V internal reference or
applying an external reference voltage to the REFIN
input. The MAX8643 offers programmable soft-start
time using one capacitor to reduce input inrush current.
The MAX8643 is available in a lead-free, 24-pin, 4mm x
4mm thin QFN package.
ASIC/CPU/DSP Core and I/O Voltages
DDR Power Supplies
Base-Station Power Supplies
Telecom and Networking Power Supplies
RAID Control Power Supplies
o Internal 37mΩ RDS(ON) MOSFETs
o Continuous 3A Output Current
o ±1% Output Accuracy Over Load, Line,
o Operates from 2.35V to 3.6V Supply
o Adjustable Output from 0.6V to (0.9 x VIN)
o Soft-Start Reduces Inrush Supply Current
o 500kHz to 2MHz Adjustable Switching Frequency
o Compatible with Ceramic, Polymer, and
Electrolytic Output Capacitors
o VID-Selectable Output Voltages
0.6, 0.7, 0.8, 1.0, 1.2, 1.5, 1.8, 2.0, and 2.5V
o Fully Protected Against Overcurrent
o Lead-Free, 24-Pin, 4mm x 4mm
Thin QFN Package
+Denotes lead-free package.
*EP = Exposed pad.
24 Thin QFN-EP*
4mm x 4mm
Typical Operating Circuit
Pin Configuration appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
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.