LTP5901-IPM datasheet(25/36 Pages) LINER

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LTP5901-IPM/LTP5902-IPM

59012ipmfa

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operaTion

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 Mote 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 nonvolatile 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 time slots across the network,

which is transparent to the user, Eterna’s timing manage-

mentisusedtosupporttwomechanismstosharenetwork

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 accu-

rate. The value of the timestamp is captured in hardware

relative to the rising edge of TIMEn. If an API request is

used,duetopacketprocessing,thevalueofthetimestamp

may be captured several milliseconds after receipt of

the packet due to packet processing. See the TIMEn AC

Characteristics section 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

subsystems, and all peripherals. The internal relaxation

oscillator is dynamically calibrated to 7.3728 MHz. The

internal relaxation oscillator typically starts up in a few

μs, providing an expedient, low energy method for duty

cyclingbetweenactiveandlowpowerstates.Quickstart-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.

32.768kHz Crystal

Once Eterna is powered up and the 32.768kHz crystal

source has begun oscillating, the 32.768kHz crystal re-

mains operational while in the active state, and is used as

the timing basis when in doze state. See the State Diagram

section for a description of Eterna’s operational states.

20MHz Crystal

The 20 MHz crystal source provides a frequency reference

for the radio, and is automatically enabled and disabled

by Eterna as needed.

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