UR5595-S08-R datasheet(5/12 Pages) UTC

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UR5595

MOS IC

UNISONICTECHNOLOGIESCO.,LTD

5 of 12

www.unisonic.com.tw

QW-R502-062,A

PIN DESCRIPTIONS

AVIN , PVIN

Input supply pins

. AVIN and PVIN are two independent input supply pins for UR5595. AVIN is used to supply all the

internal analog circuits and PVIN is only used to supply the output stage to create the regulated VTT. Using a higher

PVIN voltages will increase the driving capability of VTT, 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 VTT is tri-stated and

VREF remains active.

For SSTL-2 applications, the AVIN and PVIN can be short together at 2.5V to eliminate the need for bypassing

capacitors for the two supply pins separately.

VDDQ

The input pin used to create the internal reference voltage from a resistor divider of two internal 50kΩ resistors for

regulating VTT and to guarantee VTT will track VDDQ/2 precisely. As a remote sense by connecting VDDQ directly to the

2.5V rail for SSTL-2 applications is an optimal implementation of VDDQ at the DIMM. This ensures that the reference

voltage tracks the DDR memory rails precisely without a large voltage drop from the power lines.

VSENSE

The sense pin supply improved remote load regulation; if remote load regulation is not used then the VSENSE pin

must still be connected to VTT. 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 VSENSE pin to the middle of the bus to provide a better distribution across

the entire termination bus can reduce the IR drop.

VREF

VREF supply the buffered output of the internal reference voltage (VDDQ/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.

VTT

VTT is a regulated output that is used to terminate the bus resistors of DDR-SDRAM. It can precisely track the

VDDQ/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.

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