LTP5901-IPR/LTP5902-IPR
23
59012iprf
For more information www.linear.com/LTP5901-IPR or www.linear.com/LTP5902-IPR
operaTion
POWER SUPPLY
Eterna is powered from a single pin, VSUPPLY, which
powers the I/O cells and is also used to generate internal
supplies. Eterna’s two on-chip DC/DC converters minimize
Eterna’s energy consumption while the device is awake. To
conserve power the DC/DC converters are disabled when
the device is in low power state. Eterna’s integrated power
supply conditioning architecture, including the two inte-
grated DC/DC converters and three integrated low dropout
regulators, provides excellent rejection of supply noise.
Eterna’s operating supply voltage range is high enough
to support direct connection to lithium-thionyl chloride,
Li-SOCl2, sources and wide enough to support battery
operation over a broad temperature range.
SUPPLY MONITORING AND RESET
Eterna integrates a power-on reset (PoR) circuit. As the
RESETn input pin is nominally configured with an internal
pull-up resistor, no connection is required. For a graceful
shutdown, the software and the networking layers should
be cleanly halted via API commands prior to assertion of
the RESETn pin. See the SmartMesh IP Manager API Guide
for details on the disconnect and reset commands. Eterna
includes a soft brown-out monitor that fully protects the
flash from corruption in the event that power is removed
while writing to flash. Integrated flash supervisory func-
tionality, in conjunction with a fault tolerant file system,
yields a robust non-volatile storage solution.
PRECISION TIMING
A major feature of Eterna over competing 802.15.4 prod-
uct offerings is its low power dedicated timing hardware
and timing algorithms. This functionality provides timing
precision two to three orders of magnitude better than
any other low power solution available at the time of
publication. Improved timing accuracy allows motes to
minimize the amount of radio listening time required to
ensure packet reception thereby lowering even further
the power consumed by SmartMesh networks. Eterna’s
patented timing hardware and timing algorithms provide
superior performance over rapid temperature changes,
further differentiating Eterna’s reliability when compared
with other wireless products. In addition, precise timing
enables networks to reduce spectral dead time, increasing
total network throughput.
APPLICATION TIME SYNCHRONIZATION
In addition to coordinating timeslots across the network,
which is transparent to the user, Eterna’s timing manage-
ment is used to support two mechanisms to share network
time. Having an accurate, shared, network-wide time base
enables events to be accurately time stamped or tasks to
be performed in a synchronized fashion across a network.
Eterna will send a time packet through its serial interface
when one of the following occurs:
• Eterna receives an API request to read time
• The TIMEn signal is asserted
The use of TIMEn has the advantage of being more accurate.
The value of the timestamp is captured in hardware relative
to the rising edge of TIMEn. If an API request is used, due
to packet processing, the value of the timestamp may be
captured several milliseconds after receipt of the packet due
to packet processing. See section TIMEn AC Characteristics,
for the time function’s definition and specifications.
TIME REFERENCES
Eterna includes three clock sources: an internal relaxation
oscillator, a low power oscillator designed for a 32.768kHz
crystal, and the radio reference oscillator designed for a
20MHz crystal.
Relaxation Oscillator
The relaxation oscillator is the primary clock source for
Eterna, providing the clock for the CPU, memory subsys-
tems, and all peripherals. The internal relaxation oscillator
is dynamically calibrated to 7.3728MHz. The internal re-
laxation oscillator typically starts up in a few μs, providing
an expedient, low energy method for duty cycling between
active and low power states. Quick start-up from the doze
state, defined in the State Diagram section, allows Eterna to
wake up and receive data over the UART and SPI interfaces
by simply detecting activity on the appropriate signals.