Cypress CY7C1245V18 - Manual (Page 20)

CY7C1241V18, CY7C1256V18
CY7C1243V18, CY7C1245V18
Document Number: 001-06365 Rev. *D Page 20 of 28
Power Up Sequence in QDR-II+ SRAM
QDR-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
2048 cycles of stable clock.
Power Up Sequence
■ Apply power with DOFF tied HIGH (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
■ Provide stable power and clock (K, K) for 2048 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
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 2048 cycles stable clock
to relock to the clock frequency you want.
Power Up Waveforms
Figure 2. Power Up Waveforms
K
K
Fix HIGH (tie to VDDQ)
VDD/VDDQ
DOFF
Clock Start (Clock Starts after VDD/VDDQ is Stable)
Unstable Clock > 2048 Stable Clock Start Normal
Operation
~ ~
~ ~
VDD/VDDQ Stable (< + 0.1V DC per 50 ns)
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