June 2005

ASM2I2313ANZ

rev 0.4

13 Output, 3.3V SDRAM Buffer for Desktop PCs with 3 DIMMs

9 of 13

Notice: The information in this document is subject to change without notice.

Application Information

Clock traces must be terminated with either series or parallel termination, as is normally done.

Application Circuit

Summary

•

Surface mount, low-ESR, ceramic capacitors should be used for filtering. Typically, these capacitors have a value

of 0.1 µF. In some cases, smaller value capacitors may be required.

•

The value of the series terminating resistor satisfies the following equation, where Rtrace is the loaded characteristic

impedance of the trace, Rout is the output impedance of the buffer (typically 25Ω), and Rseries is the series terminating

resistor.

Rseries > Rtrace – Rout

•

Footprints must be laid out for optional EMI-reducing capacitors, which should be placed as close to the terminating

resistor as is physically possible. Typical values of these capacitors range from 4.7pF to 22pF.

•

offers greater than 50Ω impedance at the clock frequency, under loaded DC conditions.

•

If a Ferrite Bead is used, a 10µF–22µF tantalum bypass capacitor should be placed close to the Ferrite Bead. This

capacitor prevents power supply droop during current surges.

Rs

BUF_IN

SDATA

SCLK

Rs

SDRAM (0.12)

3.3V

ASM2I2313ANZ

28-Pin SOIC

CPUCLK

SDATA

SCLK

SDRAM(0.12)