UR5595 Datasheet, PDF (5/12 Pages) Unisonic Technologies – DDR TERMINATION REGULATOR

UR5595
MOS IC
„ PIN DESCRIPTIONS
AV_IN , PV_IN
Input supply pins. AV_IN and PV_IN are two independent input supply pins for UR5595. AV_IN is used to supply all the
internal analog circuits and PV_IN is only used to supply the output stage to create the regulated V_TT. Using a higher
PV_IN voltages will increase the driving capability of V_TT, but the internal power loss will also increase. If the junction
temperature exceeds the thermal shutdown than the UR5595 will enter a shutdown state, where V_TT is tri-stated and
V_REF remains active.
For SSTL-2 applications, the AV_IN and PV_IN can be short together at 2.5V to eliminate the need for bypassing
capacitors for the two supply pins separately.
V_DDQ
The input pin used to create the internal reference voltage from a resistor divider of two internal 50kΩ resistors for
regulating V_TT and to guarantee V_TT will track V_DDQ/2 precisely. As a remote sense by connecting V_DDQ directly to the
2.5V rail for SSTL-2 applications is an optimal implementation of V_DDQ at the DIMM. This ensures that the reference
voltage tracks the DDR memory rails precisely without a large voltage drop from the power lines.
V_SENSE
The sense pin supply improved remote load regulation; if remote load regulation is not used then the V_SENSE pin
must still be connected to V_TT. A long trace will cause a significant IR drop resulting in a termination voltage lower at
one end of the bus than the other. Connect V_SENSE pin to the middle of the bus to provide a better distribution across
the entire termination bus can reduce the IR drop.
V_REF
V_REF supply the buffered output of the internal reference voltage (V_DDQ/2). It can provide the reference voltage of
the Northbridge chipset and memory. For better performance, a bypass ceramic capacitor of 0.1μF~0.01μF, located
close to the pin, can be used to to help with noise.
V_TT
V_TT is a regulated output that is used to terminate the bus resistors of DDR-SDRAM. It can precisely track the
V_DDQ/2 voltage with the sinking and sourcing current capability. The UTC UR5595 is designed to handle peak
transient currents of up to ± 3A with a fast transient response. If a transient is expected to remain above the
maximum continuous current rating for a significant amount of time then the output capacitor size should be large
enough to prevent an excessive voltage drop.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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