Filter
Top Products
CY7C1516KV18, CY7C1527KV18
CY7C1518KV18, CY7C1520KV18
Document Number: 001-00437 Rev. *E 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.
Power Up Sequence
■ Apply power and drive DOFF either HIGH or 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
.
❐ Drive DOFF HIGH.
■ Provide stable DOFF (HIGH), power and clock (K, K) for 20 μs
to lock the PLL.
PLL Constraints
■ PLL uses K clock as its synchronizing input. The input must
have low phase jitter, which is specified as t
KC Var
.
■ The PLL functions at frequencies down to 120 MHz.
■ If the input clock is unstable and the PLL is enabled, then the
PLL may lock onto an incorrect frequency, causing unstable
SRAM behavior. To avoid this, provide 20 μs of stable clock to
relock to the desired clock frequency.
Figure 3. Power Up Waveforms
> 20Ps Stable clock
Start Normal
Operation
DOFF
Stable (< +/- 0.1V DC per 50ns )
Fix HIGH (or tie toV
DDQ
)
K
K
DDQDD
V
V
/
DDQDD
V
V
/
Clock Start
(Clock Starts after Stable)
DDQ
DD
V
V
/
~
~
~
~
Unstable Clock
[+] Feedback