Si5351A/B/C
Preliminary Rev. 0.95 31
Reset value = 0000 0000
Register 17. CLK1 Control
BitD7D6D5D4D3D2D1D0
Name
CLK1_PDN MS1_INT MS1_SRC CLK1_INV CLK1_SRC[1:0] CLK1_IDRV[1:0]
Type
R/W R/W R/W R/W R/W R/W
Bit Name Function
7 CLK1_PDN Clock 1 Power Down.
This bit allows powering down the CLK1 output driver to conserve power when the out-
put is unused.
0: CLK1 is powered up.
1: CLK1 is powered down.
6MS1_INTMultiSynth 1 Integer Mode.
This bit can be used to force MS1 into Integer mode to improve jitter performance. Note
that the fractional mode is necessary when a delay offset is specified for CLK1.
0: MS1 operates in fractional division mode.
1: MS1 operates in integer mode.
5 MS1_SRC MultiSynth Source Select for CLK1.
0: Select PLLA as the source for MultiSynth0.
1: Select PLLB (Si5351A/C only) or VCXO (Si5351B only) MultiSynth0.
4 CLK1_INV Output Clock 1 Invert.
0: Output Clock 1 is not inverted.
1: Output Clock 1 is inverted.
3:2 CLK1_SRC[1:0] Output Clock 1 Input Source.
These bits determine the input source for CLK1.
00: Select the XTAL as the clock source for CLK1. This option by-passes both synthesis
stages (PLL/VCXO & MultiSynth) and connects CLK1 directly to the oscillator which
generates an output frequency determined by the XTAL frequency.
01: Select CLKIN as the clock source for CLK1. This by-passes both synthesis stages
(PLL/VCXO & MultiSynth) and connects CLK1 directly to the CLKIN input. This essen-
tially creates a buffered output of the CLKIN input.
10: Reserved. Do not select this option.
11: Select MultiSynth 0 as the source for CLK1. Select this option when using the
Si5351 to generate free-running or synchronous clocks.
1:0 CLK1_IDRV[1:0] CLK1 Output Rise and Fall time / Drive Strength Control.
00: 2 mA
01: 4 mA
10: 6 mA
11: 8 mA
