CM3109
2A Sink/Source Regulator for Front Side Bus and
DDR Memory Bus Termination
Features
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Ideal for both PC Front Side Bus and DDR memory
V
TT
applications
Sinks and sources 2A
Over current protection
Over temperature protection
Shutdown function
Integrated power MOSFETs
Excellent accuracy (0.5% of load regulation)
Minimum external components
8 pin PSOP package
Lead-free version available
Product Description
The CM3109 is a sinking and sourcing regulator specif-
ically designed for series-parallel bus termination for
high speed chip set buses as well as DDR memory
systems. It can source and sink current up to 2A with
high accuracy of 0.5 %. The V
TT
output voltage is
selectable by V
DDQ
SEL and FSBSEL pins. The
V
DDQ
SEL pin controls whether the CM3109 is in DDR
memory mode with V
TT
= V
DDQ
/2, or in FSB mode. In
FSB mode, FSBSEL controls whether V
TT
is 1.225V or
1.45V. This allows the same chip to be used in two dif-
ferent circuits on PC motherboards that support both
Northwood and Prescott processors.
The CM3109 requires no external components to use
the GMCH Enable signal in Intel chipset or correspond-
ing signals for other chip sets when powering up the
PC. For the boards which support Suspend to RAM
(STR) functionality, CM3109 provides a shutdown (SD)
pin. When SD is set low, V
TT
will be in tri-state mode,
causing the output to go high impedance. In this mode,
CM3109 power is saved by significantly reducing the
quiescent current.
The CM3109 provides over current and over tempera-
ture protection. These features protect the chip from
excessive heating due to high current and high temper-
ature. The CM3109 is housed in an 8-pin PSOP pack-
age and is available with optional lead-free finishing.
Applications
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PC Front Side Bus termination regulator
DDR Memory termination regulator
Active termination buses
Graphics card DDR memory termination
Simplified Electrical
Schematic
V
CC
V
DDQ
SEL FSBSEL
V
DDQ
50K
Output
Select
SD
Over Temp
Over Current
Reference
Driver
V
TT
50K
V
SENSE
GND
©
2004 California Micro Devices Corp. All rights reserved.
01/15/04
430 N. McCarthy Blvd., Milpitas, CA 95035-5112
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Tel: 408.263.3214
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Fax: 408.263.7846
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www.calmicro.com
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CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
