Cypress CY7C1518KV18, CY7C1520KV18, CY7C1516KV18 Power Up Sequence in DDR-II SRAM, PLL Constraints

CY7C1516KV18, CY7C1527KV18 CY7C1518KV18, CY7C1520KV18

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 VDD before VDDQ.

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

❐Drive DOFF HIGH.

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 μs of stable clock to relock to the desired clock frequency.

■Provide stable DOFF (HIGH), power and clock (K, K) for 20 μs to lock the PLL.

K

K

VDD/ VDDQ

DOFF

Figure 3. Power Up Waveforms

~ ~

	~ ~
Unstable Clock	> 20Πs Stable clock	Start Normal
		Operation

Clock Start (Clock Starts after VDD/ V DDQ Stable)

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

Fix HIGH (or tie to V )

DDQ

Document Number: 001-00437 Rev. *E Page 19 of 30

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