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Power Supplies
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4 SNLU097A – March 2012 – Revised July 2019
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LMK00105 User’s Guide
4 Power Supplies
By default, Vdd and Vddo are supplied by two external power supplies. To modify the EVK with a different
power supply configuration, populate the resistor options as shown in
Table 5 . Then, apply the appropriate
voltage(s) to the EVK power input(s).
Decoupling capacitors and 0-ohm resistor footprints, which can accommodate ferrite beads, can be used
to isolate the EVK power input(s) from the device power pins. Do not disconnect or ground any of the
Vddo pins as they are all internally connected inside the device.
Table 5. Power Supply Configuration
DUAL EXTERNAL INPUTS(DEFAULT) SINGLE EXTERNAL INPUT 3.3 V
Vdd input Apply 3.3 V Apply 3.3 V
Vddo input Apply Voltage ≤ Vdd Not used
R26 0
Ω
DNP
R27 DNP 0
Ω
R28 0 Ω 0 Ω
5 Clock Inputs
The SMA inputs labeled CLKin & CLKin* are configured to receive a differential clock or single ended
clock. Best performance is achieved with a DC-coupled differential input clock. To configure CLKin for a
single-ended clock remove R8. Then either CLKin or CLKin* may be driven single ended.
5.1 Crystal Oscillator Interface
The LMK00105 has an integrated crystal oscillator interface (OSCin/OSCout) that supports a fundamental
mode, AT-cut crystal. If the crystal input is selected, an optional onboard crystal on either footprint Y1 or
Y2 will start-up and the oscillator clock can be measured on any enabled output.
A crystal with the HC49 footprint can be populated on the bottom side of the PCB. Alternatively, a 3.2 x
2.5 mm crystal can be populated on Y2, located on the top side. Only one crystal footprint should be used
at a time.
The values of C12 and C10 (C
EXT
) depend on the load capacitance (C
L
) specified for the crystal. The OSC
input capacitance (C
IN
) of the device is 1 pF differential, and the trace capacitance (C
TRACE
) of OSCin and
OSCout is around 1 pF. If the selected crystal is specified for C
L
of 18 pF, the C
EXT
is calculated as
follows:
C
EXT
= (C
L
–C
IN
–C
TRACE
/2) * 2 (1)
C
EXT
= (18 pF – 1 pF – 1 pF/2) * 2 (2)
C
EXT
= 33 pF (3)
5.2 Configuring OSCin for a Crystal Mode
To configure the board to use crystal mode remove C15 to disconnect the OSCin Port. Install 0 Ω resistors
on R14 and R9. Install a crystal in either footprint (Y1 or Y2) and install the proper load capacitors in C10
and C12.
6 Clock Outputs
All clock outputs are LVCMOS. In the case that not all outputs are used, any unused outputs should be
left floating.