CY7C1663KV18 datasheet(20/31 Pages) CYPRESS

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Document Number: 001-44060 Rev. *O

Page 20 of 31

CY7C1663KV18/CY7C1665KV18

Power Up Sequence in QDR II+ SRAM

QDR 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 VDD before VDDQ.

❐ Apply VDDQ before VREF or at the same time as VREF.

❐ Drive DOFF high.

■ Provide stable DOFF (high), power and clock (K, K) for 20 s

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 tKC 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

s of stable clock to

relock to the desired clock frequency.

Figure 4. Power Up Waveforms

> 20μs Stable clock

Start Normal

Operation

DOFF

Stable (< +/- 0.1V DC per 50ns )

Fix HIGH (or tie to VDDQ)

DDQ

Clock Start (Clock Starts after

Stable)

DDQ

Unstable Clock

CY7C1663KV18 Datasheet(PDF) 20 Page - Cypress Semiconductor