JAJSFA5E September 2015 – April 2018 LMK03318
PRODUCTION DATA.
Each output can be configured as AC-LVPECL, AC-LVDS, AC-CML, HCSL or LVCMOS by programming R31, R32, R34, R35, R37, R39, R41, and R43. Each output has the option to be muted or not, in case the source from which it is derived becomes invalid, by programming R22. An invalid source could be a primary or secondary reference that is no longer present or any PLL that is unlocked. When outputs are to be muted, R20 and R21 must each be programmed to 0xFF. Outputs 0 and 1 share an output supply (VDDO_01), as well as outputs 2 and 3 (VDDO_23). Outputs 4, 5, 6, 7 have individual output supplies (VDDO_4, VDDO_5, VDDO_6, VDDO_7). Each output supply can be independently set to 1.8 V, 2.5 V or 3.3 V. When a particular output is desired to be disabled, the bits [5:0] in the corresponding output control register (R31, R32, R34, R35, R37, R39, R41 or R43) must be set to 0x00. If any of outputs 4, 5, 6, and 7 and their output dividers are disabled; their corresponding supplies can be connected to GND.
The AC-LVDS, AC-CML, and AC-LVPECL output structure is given in Figure 62 where the tail currents can be programmed to either 4 mA, 6 mA, or 8 mA to generate output voltage swings that are compatible with LVDS, CML or LVPECL, respectively. Because this output structure is GND referenced, the output supplies can be operated from 1.8 V, 2.5 V or 3.3 V and offer lower power dissipation compared to traditional LVDS, CML, or LVPECL structures without any impact on jitter performance or other AC or DC specifications. Interfacing to LVDS, CML or LVPECL receivers are done with just an external AC-coupling capacitor for each output. No source termination is needed since the on-chip termination is automatically enabled when selecting AC-LVDS, AC-CML, or AC-LVPECL for good impedance matching to 50 Ω interconnects.
The HCSL output structure is open drain and can be direct coupled or AC coupled to HCSL receivers with appropriate termination scheme. This output strcture supports either on-chip 50 Ω termination or off-chip 50 Ω termination. The on-chip 50 Ω termination is provided primarily for convenience when driving short traces. In the case of driving long traces possibly through a connector, the on-chip termination should be disabled and a 50 Ω to GND termination at the receiver should be implemented. The output supplies can be operated from 1.8 V, 2.5 V or 3.3 V without any impact on jitter performance or other AC or DC specifications.
The LVCMOS outputs on each side (P and N) can be configured individually to be complementary or in-phase or can be turned off (high output impedance). The LVCMOS outputs are always at 1.8 V logic level irrespective of the output supply. In case 3.3-V LVCMOS outputs are needed, STATUS1 and/or STATUS0 can be configured as 3.3-V LVCMOS outputs.
Figure 63 through Figure 68 show recommendations for interfacing between LMK03318’s high-speed clock outputs and LVCMOS, LVPECL, LVDS, CML, and HCSL receivers, respectively.
NOTE
If 1.8-V LVCMOS signals from the high-speed clock outputs are desired to be interfaced with a 3.3-V LVCMOS receiver, a level-shifter like LSF0101 must be used to convert the 1.8-V LVCMOS signal to a 3.3-V LVCMOS signal.