NE57811S Philipss, NE57811S Datasheet - Page 6

• Manufacturer Part Number: NE57811S
• Description: Advanced DDR memory termination power with shutdown
• Manufacturer: Philipss

Philips Semiconductors
TECHNICAL DISCUSSION
The NE57811 supplies power to the DDR memory bus termination
resistors at nominally
DIMMs. DDR memory output drivers source and sink current into
and out of their outputs. A typical DDR memory system is seen in
Figure 1 (page 2). Each input/output pin on the bus has a series
20
terminator though a 27 to 50
then require current from the V
instantaneous value of the aggregate bus state are not equal
amounts of 1s and 0s. When memory bus speeds are in the
200–300 MHz region, the period of any single bus state is extremely
small. This permits the DDR bus termination regulator to be a linear
‘power Op Amp’ that can source and sink current instantly to the
DDR bus from the V
Figure 6 models the V
equivalent circuit during operation and with terminating resistors.
2003 Apr 02
Advanced DDR memory termination power
with shutdown
resistor connected to it. The bus is terminated to the DDR
V
V
SS
DD
Figure 6. V
DD
V
1
TT
V
TT
/
SS
2
supply voltage.
loading condition of each bus line
the voltage supplied to the memory ICs or
TT
TT
resistance. The memory system will
loading conditions.
terminator bus only when the
V
V
DD
SS
V
TT
V
DD
SL01692
6
This yields the worst case current loading equation:
Where:
Hence the worst-case current loading condition, where there are
either all 1s or all 0s for an instant, and R
produces an instantaneous output current of either + or –
3.5 Amperes.
RefOut
N
lines within the DDR memory system. (typically 192)
R
R
driver.
I
O ( max )
DDR
T
S
V
V
DD
SS
is the value of the terminating resistors.
is the value of the series resistors from the active output
is the total number of terminated control, address and data
2
5
3
2( R
N
DDR
T
100 k
Figure 7. Block diagram.
V
R
DD
S
)
100 k
CURRENT
OVER
SHTDWN
4
T
TEMPERATURE
is 27
OVER
NE57811
and R
SL01693
Product data
S
is 20 ,
1
V
TT