NE57810S Philipss, NE57810S Datasheet - Page 9

• Manufacturer Part Number: NE57810S
• Description: Advanced DDR memory termination power with external reference in
• Manufacturer: Philipss

voltage is the DDR RAM supply voltage, which can range from 1.8 V
terminator’s noise performance. The two ExtRefIn bypass capacitors
Philips Semiconductors
APPLICATION INFORMATION
The NE57810 can be used in a variety of DDR memory
configurations. Its small footprint, fast transient response and
lessened need for large bulk output capacitance, makes it highly
adaptable. Some of these methods of use are given below.
Normal operating mode (V
The most common implementation of a DDR terminator regulator
using the NE57810 is shown in Figure 12. The NE57810 has an
internal resistor divider between the V
which maintains the output voltage, V
to 2.5 V. The center node of this resistor divider is brought out to
ExtRefIn (pin 4). This node acts as the reference for the V
voltage and the buffered RefOut signal (pin 5).
If the ExtRefIn pin is not connected to other voltage sources, then
two small bypass capacitors (0.01 F) should be placed between
the ExtRefIn pin and the GND and V
connected as shown in Figure 12 allow the terminator to better track
any variations in the memory V
in Figure 12.
There are two components to the memory signal load: a high
frequency component caused by the 266 MHz plus speed of the
2003 Sep 12
Advanced DDR memory termination power
with external reference in
+V
GND
DD
DD
voltage. This method can be seen
C
TT
DD
IN
TT
DD
= V
, at V
pins to improve the
(pin 2) and V
0.01 F
0.01 F
DDR
Figure 12. Normal operating method (V
DD
/2. Typically, the V
/2)
4
SS
ExtRefIn
(pin 3) pins
TT
output
NE57810
V
V
DD
DD
SS
2
3
9
RefOut
address, data, and control buses, and a low frequency component
caused by the time-average skew of all of the bus states away from
an equal number of 1s and 0s. Electrolytic and tantalum capacitor
appear inductive at the high frequencies. Therefore two types of
capacitors are needed for the output filtering.
A very good, low ESR electrolyic capacitor of no less than 470 F
should be placed next to the terminator, which should be placed as
close as possible to the memory array. One half of the high
frequency filter capacitors should be to V
V
voltage.
For different memory sizes, the values of the recommended output
filter capacitances will change. For a 256 MByte memory space, for
example, approximately 100 F of ceramic surface mount chip
capacitors should be evenly distributed across the physical memory
layout. Depending upon the PCB noise environment, this could be
10 pieces of 10 F, 20 pieces of 5 F, and so on.
It might be possible to reduce the total capacitance, provided the
performance remains stable. Examine the behavior of the V
carefully when the system is operating and verify that deviations in
the bus voltage do not exceed the DDR specification ( 40 mV).
V
SS
TT
so that the output will better track any variations in the V
1
5
TT
= V
C
(LF)
DD
OUT
V
REF
/2)
C
(HF)
OUT
SL01689
+V
GND
DD
TT
and the other half to
NE57810
Product data
TT
DD
bus