Cypress CY7C1318JV18 - Manual (Page 19)

CY7C1316JV18, CY7C1916JV18
CY7C1318JV18, CY7C1320JV18
Document Number: 001-15271 Rev. *B Page 19 of 26
Power Up Sequence in DDR-II SRAM
DDR-II SRAMs must be powered up and initialized in a
predefined manner to prevent undefined operations. During
power up, when the DOFF is tied HIGH, the DLL is locked after
1024 cycles of stable clock.
Power Up Sequence
■ Apply power and drive DOFF LOW (all other 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
■ After the power and clock (K, K) are stable take DOFF HIGH
■ The additional 1024 cycles of clocks are required for the DLL
to lock.
DLL Constraints
■ DLL uses K clock as its synchronizing input. The input must
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, provide 1024 cycles stable clock
to relock to the desired clock frequency.
Power Up Waveforms
> 1024 Stable clock Start Normal
Operation
DOFF
Stable (< +/- 0.1V DC per 50ns )
Fix High (or tied to VDDQ)
K
K
DDQ DD
V V /
DDQ DD V V /
Clock Start (Clock Starts after Stable)
DDQ DD V V /
~ ~
~~
Unstable Clock
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