HD74CDC2509B

Features:

`  Meets "PC SDRAM registered DIMM design support document, Rev. 1.2"
`  Phase-lock loop clock distribution for synchronous DRAM applications
`  External feedback (FBIN) pin is used to synchronize the outputs to the clock input
`  No external RC network required
`  Support spread spectrum clock (SSC) synthesizers


Pinout




Specifications

Item	Symbol	Ratings	Unit	Conditions
Supply voltage range	VCC	-0.5 to 4.6	V
Input voltage range *1	VI	-0.5 to 4.6	V
Output voltage range *1, 2	VO	-0.5 to VCC+0.5	V	Output : H or L
		-0.5 to 4.6	V	VCC : OFF
Input clamp current	IIK	-50	mA	VI < 0
Output clamp current	IOK	±50	mA	VO < 0 or VO > VCC
Continuous output current	IO	±50	mA	VO = 0 to VCC
Continuous current through VCC or GND	ICC or IGND	±100	mA
Maximum power dissipation at Ta = 25°C (in still air) *3	PT	0.7	mW
Storage temperature	Tstg	-65 to 150	°C

Description

The HD74CDC2509B is a high-performance, low-skew, low-jitter, phase-lock loop clock driver. It uses a phase-lock loop (PLL) to precisely align, in both frequency and phase, the feedback (FBOUT) output to the clock (CLK) input signal. It is specifically designed for use with synchronous DRAMs. The HD74CDC2509B operates at 3.3 V VCC and is designed to drive up to five clock loads per output.

One bank of five outputs and one bank of four outputs provide nine low-skew, low-jitter copies of the input clock. Output signal duty cycles are adjusted to 50 percent independent of the duty cycle at the input clock. Each bank of outputs can be enabled or disabled separately via the control (1G and 2G) inputs. When the G inputs are high, the outputs switch in phase and frequency with CLK; when the G inputs are low, the outputs are disabled to the logic-low state. Unlike many products containing PLLs, the HD74CDC2509B does not require external RC networks. The loop filter for the PLL is included on-chip, minimizing component count, board space, and cost. Because it is based on PLL circuitry, HD74CDC2509B requires a stabilization time to achieve phase lock of the feedback signal to the reference signal.

This stabilization time is required, following power up and application of a fixed-frequency, fixed-phase signal at CLK, as well as following any changes to the PLL reference or feedback signals. The HD74CDC2509B PLL can be bypassed for test purposes by strapping AVCC to ground.