PDF XRK7955 Data sheet ( Hoja de datos )

Número de pieza	XRK7955
Descripción	INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER
Fabricantes	Exar Corporation
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No Preview Available ! xrwww.DataSheet4U.com PRELIMINARY XRK7955 INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER MARCH 2005 GENERAL DESCRIPTION The XRK7955 is a PLL clock driver designed specifically for redundant clock tree designs. The device receives two differential LVPECL clock signals from which it generates 5 new differential LVPECL clock outputs. Two of the output pairs regenerate the input signals frequency and phase while the other three pairs generate 5x, phase aligned clock outputs. External PLL feedback is used to also provide zero delay buffer performance. The XRK7955 Intelligent Dynamic Clock Switch circuit continuously monitors both input CLK signals. Upon detection of a failure (CLK stuck HIGH or LOW for at least 1 period), the INP_BAD for that CLK will REV. P1.0.1 be latched (H). If that CLK is the primary clock, the device will switch to the good secondary clock and phase/frequency alignment will occur with minimal output phase disturbance. The typical phase bump caused by a failed clock is eliminated. FEATURES • Fully Integrated PLL • Intelligent Dynamic Clock Switch • LVPECL Clock Outputs • LVCMOS Control I/O • 3.3V Operation • 32-Lead LQFP Packaging FIGURE 1. BLOCK DIAGRAM OF THE XRK7955 CLK_Selected INP1Bad INP0Bad Man_Override Alarm_Reset Sel_CLK CLK0 CLK0 CLK1 CLK1 Ext_FB Ext_FB MR Dynamic Switch Logic OR PLL 200-400MHz ÷2 ÷10 PLL_En Qb0 Qb0 Qb1 Qb1 Qb2 Qb2 Qa0 Qa0 Qa1 Qa1 Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (510) 668-7000 • FAX (510) 668-7017 • www.exar.com 1 page XRK7955 PRELIMINARY INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER xr REV. P1.0.1 DC CHARACTERISTICS (VCC= 3.3 + 5%, TA= -40°C TO +85°C) SYMBOL CHARACTERISTICS MIN TYP MAX UNIT CONDITION LVCMOS control inputs (MR, PLL_En, Sel_CLK, Man_Override, Alarm_Reset) VIH Input voltage high 2.0 VCC+0.3 V VIL Input voltage low 0.8 V IIN Input currenta 100 -150 µΑ VIN =VCC or VIN =GND LVCMOS Control Outputs VOH Output High Voltage 2.0 V IOH=-10mA VOL Output Low Voltage 0.55 V IOL=10mA LVPECL clock inputs (CLK, CLK)b IIN Input current +100 µΑ VIN =VCC or VIN =GND LVPECL clock outputs (Qa[1:0], Qa[1:0], Qb[2:0], Qb[2:0]) VOH Output high voltage VCC-1.2 VCC-0.7 V Termination 50Ω to VTT VOL Output low voltage VCC-1.9 VCC-1.45 V Termination 50Ω to VTT Supply Current IGND Maximum ground supply current - gnd pins 180 mA GND pins ICCPLL Maximum PLL power supply - VCC_PLL pin 15 mA VCCPLL pin a. Inputs have internal pullup/pulldown resistors which affect the input current. b. Clock inputs driven by LVPECL compatible signals. 5 5 Page

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Hoja de datos destacado

Número de pieza	Descripción	Fabricantes
XRK7955	INTELLIGENT DYNAMIC CLOCK SWITCH PLL CLOCK DRIVER	Exar Corporation

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