PRELIMINARY
CM3121
Application Information
Other Applications
The CM3121 can be used without any external resis-
tors if a V
DDQ
voltage of 2.5V is required by connecting
the SENSE_V
DDQ
pin to GND.
Also in applications where a reference voltage (V
REF
)
is required, a PCB trace directly from the V
TT
pin can
be used. The V
TT
output pin has an error relative to
V
DDQ
/2 of up to +/-25mV, which is well within most
DDR system specs of +/-50mV. This is because the
V
TT
output internally tracks the V
DDQ
output very
closely due to the matched on-chip resistors R that tap
down from the V
DDQ
rail, and the low offset voltage of
the V
TT
regulator. It is recommended that the V
REF
trace be connected directly to the V
TT
pin, to eliminate
noise and ripple on the V
TT
line caused by current
switching
.
2.8V to 3.6V
C
CC
V
CC
V
DDQ
REGULATOR
V
DDQ
SENSE
V
DDQ
V
REF
Enable DDR
Memory #
EN_DDR
C
DDQ
DDR
MEMORY
R
R
V
TT
REGULATOR
V
TT
V
REF
=1.25V
V
TT
=1.25V
SENSE V
TT
C
TT
CURRENT LIMIT
OVERTEMP
LOW INPUT
FAULT
CPU
CORE
+ I/O
GND
Figure 4. Typical Application for the CM3121
©
2004 California Micro Devices Corp. All rights reserved.
11/12/04
430 N. McCarthy Blvd., Milpitas, CA 95035-5112
●
Tel: 408.263.3214
●
Fax: 408.263.7846
●
www.calmicro.com
9
CALMIRCO [ CALIFORNIA MICRO DEVICES CORP ]
