19-3173; Rev 2; 9/04
In t e g ra t e d DDR P o w e r-S u p p ly S o lu t io n s fo r
De s k t o p s , No t e b o o k s , a n d Gra p h ic Ca rd s
Ge n e ra l De s c rip t io n
The MAX8550/MAX8551 integrate a synchronous-buck
Fe a t u re s
Buck Controller
♦ Quick-PWM with 100ns Load-Step Response
♦ Up to 95% Efficiency
PWM controller to generate V
, a sourcing and sinking
DDQ
LDO linear regulator to generate V , and a 10mA refer-
TT
ence output buffer to generate V . The buck controller
TTR
♦ 2V to 28V Input Voltage Range
drives two external N-channel MOSFETs to generate out-
put voltages down to 0.7V from a 2V to 28V input with out-
put currents up to 15A. The LDO can sink or source up to
1.5A continuous and 3A peak current. Both the LDO out-
put and the 10mA reference buffer output can be made
to track the REFIN voltage. These features make the
MAX8550/MAX8551 ideally suited for DDR memory appli-
cations in desktops, notebooks, and graphic cards.
♦ 1.8V/2.5V Fixed or 0.7V to 5.5V Adjustable Output
♦ Up to 600kHz Selectable Switching Frequency
♦ Programmable Current Limit with Foldback
Capability
♦ 1.7ms Digital Soft-Start and Independent
Shutdown
♦ Overvoltage/Undervoltage-Protection Option
♦ Power-Good Window Comparator
LDO Section
The PWM controller in the MAX8550/MAX8551 utilizes
Maxim’s proprietary Quick-PWM™ architecture with pro-
grammable switching frequencies of up to 600kHz. This
control scheme handles wide input/output voltage ratios
with ease and provides 100ns response to load tran-
sients while maintaining high efficiency and a relatively
constant switching frequency. The MAX8550 offers fully
programmable UVP/OVP and skip-mode options ideal in
portable applications. Skip mode allows for improved
efficiency at lighter loads. The MAX8551, which is tar-
geted towards desktop and graphic-card applications,
does not offer the pulse-skip feature.
♦ Fully Integrated VTT and VTTR Capability
♦ VTT has 3A Sourcing/Sinking Capability
♦ VTT and VTTR Outputs Track V
/ 2
REFIN
♦ All-Ceramic Output-Capacitor Designs
♦ 1.0V to 2.8V Input Voltage Range
♦ Power-Good Window Comparator
Ord e rin g In fo rm a t io n
The VTT and VTTR outputs track to within 1% of V
/ 2.
PART
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
REFIN
The high bandwidth of this LDO regulator allows excel-
lent transient response without the need for bulk capac-
itors, thus reducing cost and size.
MAX8550ETI
MAX8550ETI+
MAX8551ETI
28 5mm × 5mm TQFN
28 5mm × 5mm TQFN
28 5mm × 5mm TQFN
The buck controller and LDO regulators are provided with
independent current limits. Adjustable lossless foldback
current limit for the buck regulator is achieved by monitor-
ing the drain-to-source voltage drop of the low-side MOS-
FET. Ad d itiona lly, ove rvolta g e a nd und e rvolta g e
protection mechanisms are built in. Once the overcurrent
condition is removed, the regulator is allowed to enter
soft-start again. This helps minimize power dissipation
during a short-circuit condition. The MAX8550/MAX8551
allow flexible sequencing and standby power manage-
ment using the SHDNA, SHDNB, and STBY inputs.
+Denotes lead-free package.
P in Co n fig u ra t io n
TOP VIEW
TON
1
2
3
4
5
6
7
21 DL
OVP/UVP
(N.C. FOR
MAX8551)
20
19
BST
LX
REF
Both the MAX8550 and MAX8551 are available in a
small 5mm × 5mm, 28-pin thin QFN package.
ILIM
18 DH
MAX8550
MAX8551
POK1
POK2
STBY
17
16
V
IN
Ap p lic a t io n s
DDR I and DDR II Memory Power Supplies
Desktop Computers
OUT
15 FB
Notebooks and Desknotes
Graphic Cards
5mm x 5mm Thin QFN
Game Consoles
RAID
Typical Operating Circuit appears at end of data sheet.
Networking
Quick-PWM is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ 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.
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