CY7C1518AV18 CYPRESS [Cypress Semiconductor], CY7C1518AV18 Datasheet - Page 8

• Manufacturer Part Number: CY7C1518AV18
• Description: 72-Mbit DDR-II SRAM Two-Word Burst Architecture
• Manufacturer: CYPRESS [Cypress Semiconductor]

Programmable Impedance
An external resistor, RQ, must be connected between the ZQ pin
on the SRAM and V
driver impedance. The value of RQ must be 5 × the value of the
intended line impedance driven by the SRAM. The allowable
range of RQ to guarantee impedance matching with a tolerance
of ±15% is between 175  and 350 
output impedance is adjusted every 1024 cycles upon power-up
to account for drifts in supply voltage and temperature.
Echo Clocks
Echo clocks are provided on the DDR-II to simplify data capture
on high-speed systems. Two echo clocks are generated by the
DDR-II. CQ is referenced with respect to C and CQ is referenced
with respect to C. These are free-running clocks and are
synchronized to the output clock of the DDR-II. In single clock
mode, CQ is generated with respect to K and CQ is generated
with respect to K. The timing for the echo clocks is shown in the
Switching Characteristics on page
Application Example
Figure 1
Document Number: 001-06982 Rev. *I
Echo Clock1/Echo Clock#1
Echo Clock2/Echo Clock#2
MASTER
ASIC)
(CPU
BUS
or
shows two DDR-II used in an application.
Source CLK#
Return CLK#
Cycle Start#
Source CLK
Return CLK
Addresses
SS
R/W#
DQ
to allow the SRAM to adjust its output
R = 50ohms
22.
DQ
Vterm = 0.75V
Vterm = 0.75V
,
with V
A
LD#
DDQ
SRAM#1
R/W#
Figure 1. Application Example
= 1.5 V. The
C C#
CQ/CQ#
K
K#
ZQ
R = 250ohms
DLL
These chips use a DLL that is designed to function between
120 MHz and the specified maximum clock frequency. During
power-up, when the DOFF is tied HIGH, the DLL is locked after
1024 cycles of stable clock. The DLL can also be reset by
slowing or stopping the input clock K and K for a minimum of
30 ns. However, it is not necessary to reset the DLL to lock to the
desired frequency. The DLL automatically locks 1024 clock
cycles after a stable clock is presented. The DLL may be
disabled by applying ground to the DOFF pin. When the DLL is
turned off, the device behaves in DDR-I mode (with one cycle
latency and a longer access time). For information refer to the
application note DLL Considerations in QDRII™/DDRII.
DQ
A
LD#
SRAM#2
R/W#
CY7C1518AV18
CY7C1520AV18
C C#
CQ/CQ#
K
K#
ZQ
R = 250ohms
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