CM8563
1.5A LINEAR BUS TERMINATION REGULATOR
FUNCTIONAL DESCRIPTION
The CM8563 is a linear bus termination regulator designed to
meet the JEDEC requirements of SSTL-2 and SSTL-3. The
CM8563 is capable of sinking and sourcing current at the
output VOUT, regulating the voltage to equal VDDQ/2. A
buffered reference voltage that also tracks VDDQ/2 is
generated on the VREF pin for providing a global reference to
the DDR-SDRAM and Northbridge Chipset. VOUT is designed
to track the VREF voltage with a tight tolerance over the entire
current range while preventing shoot through on the output
stage.
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.
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.
VFB
The purpose of the VFB pin is to provide improved remote load
regulation. In most motherboard applications the termination
resistors will connect to VOUT in a long plane. If the output
voltage was regulated only at the output of the CM8563, then
the long trace will cause a significant IR drop, resulting in a
termination voltage lower at one end of the bus than the other.
The VFB pin can be used to improve this performance, by
connecting it to the middle of the bus. This will provide a better
distribution across the entire termination bus.
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.
2003/03/28
Champion Microelectronic Corporation
Page 5
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