Philips Semiconductors

Product data

NE57810

Advanced DDR memory termination power

with external reference in

2003 Sep 12

11

Cascading the NE57810 for complex memory systems

For high-performance computer systems, sometimes memory banks

are driven 180 degrees out of phase with one another such that the

apparent access time is halved (even and odd memory addresses).

To do this, it is recommended that two NE57810s are used, one to

terminate each memory bank.

Cascading NE57810 terminators offers two advantages, it improves

the system noise performance by bringing the memory SIMMs

closer to the terminator, and distributes any heat generated by the

terminator system. By using the RefOut pin from one NE57810 to

the ExtRefIn pin for the other NE57810(s) used in the system, one

outputs should never be wired together. This is because the

terminators would ‘fight’ one another if their output were different by

only a few millivolts. This method can be used in either the normal

operating mode and the externally programmed operating mode.

This method of use can be seen in Figure 14.

SL01680

ExtRefIn

RefOut

Master

NE57810

GND

(LF)

(HF)

GND

ExtRefIn

RefOut

Slave

NE57810

(LF)

(HF)

GND

TO OTHER

NE57810s

Figure 14.

Cascading terminator systems for complex memory systems.