CM8563 Datasheet, PDF (5/7 Pages) List of Unclassifed Manufacturers – 1.5A LINEAR BUS TERMINATION REGULATOR

CM8563
1.5A LINEAR BUS TERMINATION REGULATOR
FUNCTIONAL DESCRIPTION
The CM8563 is a linear bus termination regulator designed to VFB
meet the JEDEC requirements of SSTL-2 and SSTL-3. The The purpose of the VFB pin is to provide improved remote load
CM8563 is capable of sinking and sourcing current at the
regulation. In most motherboard applications the termination
output VOUT, regulating the voltage to equal VDDQ/2. A
resistors will connect to VOUT in a long plane. If the output
buffered reference voltage that also tracks VDDQ/2 is
voltage was regulated only at the output of the CM8563, then
generated on the VREF pin for providing a global reference to the long trace will cause a significant IR drop, resulting in a
the DDR-SDRAM and Northbridge Chipset. VOUT is designed termination voltage lower at one end of the bus than the other.
to track the VREF voltage with a tight tolerance over the entire The VFB pin can be used to improve this performance, by
current range while preventing shoot through on the output
connecting it to the middle of the bus. This will provide a better
stage.
distribution across the entire termination bus.
The CM8563 integrates power MOSFETs that are capable of
source and sink 1.5A of current while maintaining excellent
voltage regulation. The output voltage can be regulated within
3% or less by using the external feedback. Separate voltage
supply inputs have been added to fit applications with various
power supplies for the databus and power buses.
Pin Description
VCCA & VIN
VCCA and VIN are the input supply pins for the CM8563.
VCCA is used to supply all the internal control circuitry for the
two op-amps and the output stage of VREF. VIN is used
exclusively to provide the rail voltage for the output stage on
the power operational amplifier used to the 2.5V rail for
optimal performance. This eliminates the need for bypassing
the two supply pins separately.
VREF
VREF provides the buffered output of the internal reference
voltage VDDQ/2. This output should be used to provide the
reference voltage of Northbridge chipset and memory.
VOUT
VOUT is the regulated output that is used to terminate the bus
resistors. It is capable of sinking and sourcing current while
regulating the output precisely to VDDQ/2. The CM8563 is
designed to handle peak transient currents of up to +/- 3A with a
fast transient response. The maximum continuous current is a
function of VIN. If a transient is expected to last above the
maximum continuous current rating for a significant amount of
time then the output capacitor should be sized large enough to
prevent an excessive voltage drop.
VDDQ
VDDQ is the input that is used to create the internal reference
voltage for regulating VOUT and VREF. This voltage is
generated by two internal 270kΩ resistors. This guarantees
that VOUT and VREF will track VDDQ/2 precisely.
2003/03/28
Champion Microelectronic Corporation
Page 5