Datasheet

General Description
The MAX8550A integrates a synchronous-buck PWM
controller to generate V
DDQ
, a sourcing and sinking LDO
linear regulator to generate V
TT
, and a 10mA reference
output buffer to generate V
TTR
. The buck controller drives
two external n-channel MOSFETs to generate output volt-
ages down to 0.7V from a 2V to 28V input with output cur-
rents up to 15A. The LDO can sink or source up to 1.5A
continuous and 3A peak current. Both the LDO output
and the 10mA reference buffer output can be made to
track the REFIN voltage. These features make the
MAX8550A ideally suited for DDR memory applications in
desktops, notebooks, and graphic cards.
The PWM controller in the MAX8550A utilizes Maxim’s
proprietary Quick-PWM™ architecture with programma-
ble switching frequencies of up to 600kHz. This control
scheme handles wide input/output voltage ratios with
ease and provides 100ns response to load transients
while maintaining high efficiency and a relatively con-
stant switching frequency. The MAX8550A offers fully
programmable UVP/OVP and skip-mode options ideal in
portable applications. Skip mode allows for improved
efficiency at lighter loads.
The VTT and VTTR outputs track to within 1% of V
REFIN
/ 2.
The high bandwidth of this LDO regulator allows excel-
lent transient response without the need for bulk capac-
itors, thus reducing cost and size.
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
MOSFET. Additionally, overvoltage and undervoltage pro-
tection 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 MAX8550A allows
flexible sequencing and standby power management
using the SHDN and STBY inputs, which support all
DDRs’ operating states.
The MAX8550A is available in a small 5mm × 5mm, 28-
pin thin QFN package.
Applications
DDR I and DDR II Memory Power Supplies
Desktop Computers
Notebooks and Desknotes
Graphic Cards
Game Consoles
RAID
Networking
Features
Buck Controller
Quick-PWM with 100ns Load-Step Response
Up to 95% Efficiency
2V to 28V Input Voltage Range
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
Independent Shutdown and Standby Controls
Overvoltage/Undervoltage-Protection Option
Power-Good Window Comparator
LDO Section
Fully Integrated VTT and VTTR Capability
VTT Has ±3A Sourcing/Sinking Capability
VTT and VTTR Outputs Track V
REFIN
/ 2
All-Ceramic Output-Capacitor Designs
1.0V to 2.8V Input Voltage Range
Power-Good Window Comparator
MAX8550A
Integrated DDR Power-Supply Solution for
Desktops, Notebooks, and Graphic Cards
________________________________________________________________ Maxim Integrated Products 1
PART
TEMP RANGE
PIN-PACKAGE
MAX8550AETI
-40°C to +85°C
28 TQFN 5mm × 5mm
Ordering Information
9
8
11
12
13
14
10
27
28
25
24
23
22
26
15
16
17
18
19
20
21
7
6
5
4
3
2
1
MAX8550A
5mm x 5mm Thin QFN
TOP VIEW
OVP/UVP
TON
REF
ILIM
POK1
POK2
TPO
AV
DD
GND
PGND1
V
DD
DL
BST
LX
DH
V
IN
OUT
FB
REFIN
VTTI
VTT
PGND2
VTTR
VTTS
SS
SHDN
SKIP
STBY
Pin Configuration
19-3313; Rev 0; 5/04
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.
Typical Operating Circuit appears at end of data sheet.
EVALUATION KIT
AVAILABLE
Quick-PWM is a trademark of Maxim Integrated Products, Inc.

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