Cypress CY7C1518AV18 Manual De Usuario
CY7C1516AV18, CY7C1527AV18
CY7C1518AV18, CY7C1520AV18
CY7C1518AV18, CY7C1520AV18
Document Number: 001-06982 Rev. *D
Page 19 of 30
Power Up Sequence in DDR-II SRAM
DDR-II SRAMs must be powered up and initialized in a
predefined manner to prevent undefined operations.
predefined manner to prevent undefined operations.
Power Up Sequence
■
Apply power and drive DOFF either HIGH or LOW (All other
inputs can be HIGH or LOW).
inputs can be HIGH or LOW).
❐
Apply V
DD
before V
DDQ
.
❐
Apply V
DDQ
before V
REF
or at the same time as V
REF
.
❐
Drive DOFF HIGH.
■
Provide stable DOFF (HIGH), power and clock (K, K) for 1024
cycles to lock the DLL.
DLL Constraints
■
DLL uses K clock as its synchronizing input. The input must
have low phase jitter, which is specified as t
have low phase jitter, which is specified as t
KC Var
.
■
The DLL functions at frequencies down to 120 MHz.
■
If the input clock is unstable and the DLL is enabled, then the
DLL may lock onto an incorrect frequency, causing unstable
SRAM behavior. To avoid this, provide1024 cycles stable clock
to relock to the desired clock frequency.
DLL may lock onto an incorrect frequency, causing unstable
SRAM behavior. To avoid this, provide1024 cycles stable clock
to relock to the desired clock frequency.
Figure 3. Power Up Waveforms
> 1024 Stable clock
Start Normal
Operation
DOFF
Stable (< +/- 0.1V DC per 50ns )
Fix High (or tie to VDDQ)
K
K
DDQ
DD
V
V
/
DDQ
DD
V
V
/
Clock Start (Clock Starts after Stable)
DDQ
DD
V
V
/
~ ~
~~
Unstable Clock