ADV
ANCEINFORMA
TION
0 V
Decision Point 2:
VDD_PLLx/VDD_INx/
VDD_DIG / VDD_XO /
VDD_
7&;2 •
2.72 V
3.135 V
Decision Point 1:
3'1 •
1.2 V
VDD_PLLx, VDD_INx,
VDD_DIG, VDD_XO,
VDD_TCXO, PDN
200 k
VDD_DIG
PDN
46
SNAS724 – FEBRUARY 2018
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Copyright © 2018, Texas Instruments Incorporated
Application Information (continued)
10.1.2 Power Down (PDN) Pin
The PDN pin (active low) can be used for device power-down and used to initialize the POR sequence. When
PDN is pulled low, the entire device is powered down and the serial interface is disabled. When PDN is pulled
high, the device POR sequence is triggered to begin the device start-up sequence and normal operation as
depicted in
Table 7. PDN Control
PDN PIN STATE
DEVICE OPERATION
0
Device is disabled
1
Normal operation
10.1.3 Power Rail Sequencing, Power Supply Ramp Rate, and Mixing Supply Domains
10.1.3.1 Mixing Supplies
The LMK05028 incorporates flexible power supply architecture. While all VDD core supplies should be powered
by the same 3.3-V rail, the individual output supplies can be powered from separate 1.8-V, 2.5-V or 3.3-V rails.
This can allow all output supplies at 1.8 V to minimize power consumption. It can also allow mixed output driver
levels simultaneously, for example, a 2.5-V LVCMOS clock from a 2.5-V rail and other differential clocks from a
1.8-V rail.
10.1.3.2 Power-On Reset (POR) Circuit
The LMK05028 integrates a built-in power-on reset (POR) circuit that holds the device in reset until all of the
following conditions have been met:
•
All VDD core supplies have ramped above 2.72 V
•
PDN pin has ramped above 1.2 V (V
IH
)
10.1.3.3 Powering Up From a Single-Supply Rail
As long as all VDD core supplies are driven by the same 3.3-V supply rail that ramp in a monotonic manner from
0 V to 3.135 V, irrespective of the ramp time, then there is no requirement to add a capacitor on the PDN pin to
externally delay the device power-up sequence. As shown in
, the PDN pin can be left floating or
otherwise driven by a host controller for meeting the clock sequencing requirements in the system.
Figure 43. Recommendation for Power Up From a Single-Supply Rail
Summary of Contents for LMK05028
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